Synergistic electronic coupling/cross-talk between the isolated metal halide units of zero dimensional heterometallic (Sb, Mn) halide hybrid with enhanced emission

Abstract

Heterometallic 0D metal halide hybrids, consisting of more than one kind of metal halide units, are anticipated to manifest synergistic effects on the photo-physical properties of the constituent metal halide units. Such architectures hold great promise for design and development of function-targeted materials. However, heterometallic 0D hybrids, featuring isolated metal halide units, typically do not show any synergistic effects due to large inter-unit spatial separations that inhibit interactions/coupling between the constituent metal halide units. It remains challenging to design synthetic strategies that would support structural modifications to allow synergistic electronic coupling between the metal halide units in heterometallic 0D hybrids. Here, we report synthesis and characterization of heterometallic (Sb, Mn) 0D hybrid, namely Tris SbMnCl, with isolated MnCl₅ units, (Sb/Mn)Cl₆ units, dispersed in the organic ligand matrix and layer of dynamic and networked water molecules. Steady state and time resolved emission spectra (TRES) analysis suggests strong synergistic interaction between the isolated metal halide units. Efficient energy transfer from the strongly absorbing Sb centres to emissive Mn centres results in the observed enhanced emission. Proton conductivity measurements together with first-principles calculations suggest the unique role of the networked water molecules in mediating the electronic coupling/energy transfer between the separated metal halide units in Tris SbMnCl hybrid. This report highlights the role of structure/composition of the synthesized heterometallic 0D hybrid in attaining electronic dimensionality higher than 0D through synergistic electronic interaction between the isolated metal halide units.

---

Introduction

Organic–inorganic metal halide hybrids are a new class of multifunctional materials that is currently drawing huge research interest due to their enabling properties appropriate for myriads of optoelectronic applications such as solar cells, optically pumped lasers, and light emitting diodes.^1–6 Current research efforts have demonstrated synthetic control on dimensionality in these materials at the molecular level.^7–11 Appropriate choice of metal halides, organic ligands, and reaction conditions allow control of dimensionality from three dimensionally networked AMX₃ structures (3D), to networked two dimensional layered structures A₂MX₄ (flat and contorted) (2D), to one dimensionally networked chain structures (1D), to non-networked zero dimensional structures (0D).^12–18 Herein, the networking is with respect to the connectivity (through bridged halides) of the constituent semiconducting metal halide units that controls electronic dimensionality (and not physical dimensionality). In bulk self-assembled 0D hybrids, anionic semiconducting metal halides (or their clusters) are completely isolated/disconnected from each other and are periodically dispersed in the cationic dielectric organic ligand moieties. This site isolation (quantum and dielectric confinement) enables 0D hybrids to manifest intrinsic properties of the constituent metal halide units with minimal electronic interaction/coupling between the metal halide units displaying strongly bound excitons and enhanced environmental stability.¹⁷ The large separation between the metal halide units and wide band gap nature of the interspersed organic molecules minimize ‘cross-talk’ between the metal halide units.¹⁷ Such 0D materials are excellent solid state luminophores owing to their interesting photo-physical properties (highly efficient, broadband, tunable, self-trapped excitonic emission).¹⁷ Research efforts have been recently dedicated for exploiting their fantastic emissive properties for solid state lighting applications, particularly for Sb(III) based metal chloride hybrids owing to their ns² electronic configuration and oxidative/environmental stability.^17,19–24 Sb(III) based metal halide hybrids typically show strong, highly Stokes shifted, broadband, long lived (∼2–5 μs) emission with characteristic high energy (<400 nm) absorption and photoluminescence excitation (PLE) features that show steep onset ∼ 400 nm.^17,24 Along similar lines, bulk 0D Mn(II) halide hybrids (octahedral/tetrahedral geometry) have also been explored as material for lighting applications that show emission in the red/green region with long lifetimes (∼10 ms) and characteristic molecular absorption/PLE features across 300–550 nm region.^18,25 Such 0D materials have shown success in variety of applications in lighting, thermometry, and scintillation.^17,26–29

Naturally, 0D hybrids provide a strong vantage point for the further development of multi-functional crystalline materials wherein multiple metal halide centres can be integrated to synthesize single phase material.^17,30,31 However, lack of design rules and formation of phase separated single component 0D metal halide hybrids render the synthesis of single crystalline organic metal halide 0D hybrids containing multiple metal halide units non-trivial. Encouragingly, rational choice of organic ligands, combination of apt metal halides, and synthetic strategy has recently allowed the synthesis of heterometallic 0D hybrids that show interesting applications as function-directed materials in catalysis, small molecule activation, molecular magnetism, and photoluminescence.^32–36 Indeed, there have been reports on the synthesis and photophysical properties of bimetallic and trimetallic 0D organic–inorganic hybrids.^17,37–45 Importantly, such multicomponent heterometallic single phase 0D materials manifest properties of the constituent isolated metal halide units and rarely show any synergistic effects due to strong interactions/coupling between the constituent metal halide units.^17,38,43,45 This absence of any synergistic electronic coupling interactions between the metal halide units in heterometallic 0D hybrids is not surprising due to the organic ligand molecule induced dielectric confinement that causes site isolation of the metal halide units. Hence, it remains urgent but extremely challenging to design and exploit synthetic strategies that support structural modifications to allow synergistic electronic coupling between the metal halide units in heterometallic/multicomponent crystalline 0D halide hybrids.

Reported herein is an unprecedented example of bulk assembly of zero dimensional heterometallic halide hybrid that highlights strong synergistic electronic interaction between the constituent isolated metal halide units. Here, the reported 0D heterometallic halide hybrid (Tris SbMnCl) shows enhanced emission due to synergistic energy transfer between the comprising metal halide units (Sb → Mn). Weakly emitting Tris MnCl hybrid,¹⁸ with constituent MnCl₅ (trigonal bipyramidal) and MnCl₆ (octahedral) units, is exploited as a host to incorporate Antimony (Sb) atoms to generate a unique Tris SbMnCl hybrid with isolated MnCl₅ (trigonal bipyramidal) and isolated (Sb/Mn)Cl₆ (octahedral) units surrounded by organic ligands and networked water molecules. Excitingly, Tris SbMnCl hybrid shows enhanced Mn emission with strong Sb based absorption. These optical signatures along with the observed time resolved emission spectral evolution suggest strong electronic interaction between the SbCl₆ and MnCl₆ units in 0D Tris SbMnCl hybrid. The interaction between the isolated metal halide units is likely mediated by the water channel present in close proximity to the (Sb/Mn)Cl₆ octahedral units as supported by the single crystal structure. Such water layer mediated electronic interaction between the isolated SbCl₆ and MnCl₆ units in ‘0D’ Tris SbMnCl hybrid is further substantiated by the experimentally measured high proton conductivity and first-principles band structure calculations performed herein. This report highlights the first example of strong and synergistic electronic interaction between the isolated metal halide units in a heterometallic 0D hybrid wherein the structure and composition of the hybrid allows attaining electronic dimensionality higher than 0D facilitating coupling of constituent isolated metal halide units.

Experimental

Materials

Antimony(III) oxide (99%), Hydrochloric acid (37%), manganese(II) chloride (≥99%), zinc(II) chloride (≥98%) and acetone were purchased from Sigma Aldrich. Tris(2-aminoethyl)amine was purchased from TCI Chemicals. Diethyl ether was purchased for HiMedia. All chemicals were used as purchased without further purification.

Synthesis

Synthesis of single crystals of tris MnCl. To prepare tris Mn crystal, 0.2 mmol (25 mg) of manganese(II) chloride were dissolved in 5 mL of hydrochloric acid. To this, 0.2 mmol (29.2 mg) tris(2-aminoethyl) amine was added. The solution turns turbid white after some time. The resulting precipitate was preheated oil bath at 70 °C till dissolution. The solution is slowly cooled to obtain crystals. The crystals were filtered and washed with diethyl ether repeatedly and dried in a vacuum for further characterization.

Synthesis of powdered Tris SbMnCl. To prepare tris SbMn powder sample, 0.1 mmol (29.1 mg) of antimony(III) oxide and 0.1 mmol (12.5 mg) of manganese(II) chloride were dissolved in 5 mL of hydrochloric acid. To this, 0.2 mmol (29.2 mg) tris(2-aminoethyl) amine was added. The solution turns turbid white after some time. The resulting precipitate is filtered and washed with diethyl ether repeatedly and dried in a vacuum for further characterization.

Synthesis of single crystals of Tris SbMnCl. To obtain single crystals of tris SbMn, the same reaction procedure was followed with the following details: 0.1 mmol (29.1 mg) of antimony(III) oxide and 0.1 mmol (12.5 mg) of manganese(II) chloride were dissolved in 5 mL of hydrochloric acid. To this, 0.2 mmol (29.2 mg) Tris(2-aminoethyl) amine was added. The resultant mixture was heated in a preheated oil bath at 70 °C till dissolution. The solution is slowly cooled to obtain white crystals. Crystallization led to colorless crystals, which appear bright red under UV (365 nm) light. The crystals were filtered using a vacuum pump and washed repeatedly with acetone and diethyl ether for further characterization.

Synthesis of powdered tris SbZnCl. To prepare tris SbZn powder sample, 0.1 mmol (29.1 mg) of antimony(III) oxide and 0.1 mmol (13.6 mg) of zinc(II) chloride were dissolved in 5 mL of hydrochloric acid. To this, 2 mmol (29.2 mg) tris(2-aminoethyl) amine was added. The solution turns turbid white after some time. The precipitate appears bright yellow under UV (365 nm) light.

Characterization methods

UV-Vis Absorbance was performed in a Shimadzu UV-VIS-NIR3600Plus spectrometer. Steady State PL and lifetime was measured using an Edinburgh Instruments FS5 spectrofluorometer. TGA measurements were performed using a TAG system (Mettler-Toledo, Model TGA/SDTA851e) and samples were heated in the range of 25–800 °C at a heating rate of 5 °C min⁻¹ under nitrogen atmosphere. ¹H NMR spectra were recorded on Bruker A-400 MHz system using DMSO-d₆ as the solvent at room temperature. Powder X-ray diffraction (XRD) patterns were recorded using a PANalytical X’Pert Pro equipped with Cu Kα radiation (λ = 1.5406 A). Absolute quantum yield measurements were carried out in a Horiba JOBIN YVON Fluoromax-4 spectrometer with a calibrated integrating sphere attachment. Scanning Electron Microscopy (SEM) imaging and mapping were performed by Zeiss™ Ultra Plus field-emission scanning electron microscope. X-ray photoelectron spectroscopy (XPS) characterization was performed with ESCALab spectrometer having Al Kα X-ray source (hυ = 1486.6 eV) operating at 150 W using a Physical Electronics 04-548 dual Mg/Al anode and in a UHV system with base pressure of ≤5 × 10⁻⁹ torr. Low temperature PL of the crystals was performed using an Edinburgh FLS1000 photoluminescence spectrometer, attached with Optistat DN cryostat and the temperature was controlled using Mercury iTC temperature controller (Oxford instruments). The sample was excited using a xenon lamp and emission was collected from 320 nm to 800 nm. Single crystals X-ray intensity data measurements of compounds were carried out on a Bruker D8 VENTURE Kappa Duo PHOTON II CPAD diffractometer. Raman spectroscopic measurements were recorded at room temperature on an HR 800 Raman spectrophotometer (Jobin Yvon, Horiba, France) using monochromatic radiation (achromatic Czerny–Turner type monochromator with silver treated mirrors) emitted by a He–Ne laser (633 nm). Proton conductivity study was carried out using two probe AC impedance analyses under humidified conditions. Between two stainless steel electrodes, a pellet (13 mm diameter) was placed, and the set up was kept inside a temperature-controlled humidity chamber (SH-241, ESPEC Co. Ltd, Japan), which was also connected to a BioLogic electrochemical work station (VMP-3). The sample was left to equilibrate for at least 1 hour or until a steady state was reached at a particular temperature. The electrochemical impedance experiments were carried out in the frequency range of 1 MHz–0.1 Hz using an input voltage amplitude of 10 mV. Comparison of the proton conductivity using H₂O and D₂O were conducted in a home-built smaller demonstration chamber using 30 mL of H₂O and D₂O, under 98% RH for reliable results. Both proton and deuteron conductivities were measured after saturating the pellets in H₂O and D₂O, respectively, for 12 hours. More details on proton conductivity measurements are provided in ESI.†

Computational details

We adopt ab initio level of calculations based on density functional theory (DFT) as implemented in Quantum Espresso package,⁴⁶ with a generalized gradient approximation (GGA)⁴⁷ without any spin-polarization. We use ultra-soft pseudopotentials⁴⁸ with the following valence electron configurations: Mn – 3s² 3p⁶ 3d⁵ 4s², Cl – 3s² 3p⁵, O – 2s² 2p⁴, and H – s¹. For electronic integration, we use a k-point mesh of 5 × 5 × 1. The wave functions and the charge density are expanded using an 80 and a 640 Ry energy cutoff, respectively. We consider a single MnCl₆ octahedron along with six water molecules in the unit cell that is periodic in two-dimension with a vacuum of 40 Å in the perpendicular direction, ensuring an isolated slab structure. Note that, we consider the atomic positions in the rhombus unit cell with lattice constants of 9.594 Å, as obtained from the experimental structure elucidation to mimic the experimental scenario and to avoid any unwanted position relaxation in absence of the surrounding environment in the slab structure. As we know, the positions of the lightweight elements like hydrogen and oxygen cannot be derived precisely within X-ray crystallography. Therefore for computational analyses, we consider the positions of the water molecules as per their highly probable locations in X-ray crystallographic data. Note that, the Mn is in 2+ charged state with 5 electrons in its 3d-orbital and surrounded by six Cl⁻ ligands in an octahedral fashion. This gives rise to an overall 4-charge per unit cell in the slab structure. The delocalized charges in the charged supercells give rise to some fictitious dispersive bands.⁴⁹ We further analyze the projected density of states arising from orbitals of each element to identify those fictitious bands and remove them from our calculations.

Results & discussion

Tris MnCl hybrid, that acts as the host material, is synthesized utilizing HX method following a prior report.¹⁸ Briefly, MnCl₂ and Tris(2-aminoethyl)amine is dissolved (molar ratio = 1 : 2 respectively) in hot HCl, followed by slow cooling to harvest light-green colored sheet shaped crystals. Tris SbMnCl hybrid sample is synthesized utilizing the same procedure but with the inclusion of Sb₂O₃ as the additional component. Harvested Tris SbMnCl crystals are colorless under ambient light. Importantly, the crystals of both Tris MnCl and Tris SbMnCl hybrids appear orange-red under UV (365 nm) light illumination. However, the emission intensity of Tris SbMnCl hybrid is stronger than Tris MnCl hybrid. The presence of Antimony in Tris SbMnCl hybrid is confirmed by XPS analysis (Fig. S1, ESI†) and SEM-EDS analysis (Fig. S2, ESI†), while ¹H NMR analysis confirms the presence of cationic organic ligand moiety (Fig. S3, ESI†) in the product. Detailed optical characterization and comparison of the host Tris MnCl hybrid and the Antimony incorporated Tris SbMnCl hybrid was performed as shown in Fig. 1. Host Tris MnCl hybrid shows weak absorption bands at ∼325 nm and ∼440 nm (Fig. 1a) attributable to the ⁶A₁ → 4E(D) and ⁶A₁ → ⁴T₂(D) terms respectively pertaining to Mn²⁺ absorption features.¹⁸ Room temperature steady state photoluminescence (PL) characterization of the Tris MnCl crystals (Fig. 1a) shows a weak emission band peaked at ∼630 nm when excited at 340 nm with PLQY ∼18%. Photoluminescence excitation (PLE) spectrum of the host Tris MnCl crystals (λ_emi = 630 nm) shows features in 300–550 nm range that highlights the characteristic d–d transition of Mn²⁺ ions.¹⁸ The observed PLE features match well with the absorption spectra in accord with the previous report.¹⁸

Fig. 1 Optical characterization of (a) Tris MnCl and (b) Tris SbMnCl hybrid showing the normalized plots of absorbance, PL (excited at 340 nm), and PLE (collected at 630 nm) spectra; (c) comparison of PL and PLE; (d) absorbance spectra of the two hybrids.

Fig. 1b shows the optical characterizations of Sb-incorporated Tris SbMnCl hybrid. Here, the absorption spectrum shows strong peaks at ∼440 nm and ∼330 nm with a sharp onset of absorption at ∼ 400 nm. PL spectra reveals a strong emission band peaked at ∼630 nm when excited at 340 nm with PLQY ∼ 37%. PLE spectrum (λ_emi = 630 nm) shows features in 300–500 nm range that match very well with the absorption spectra. The ∼440 nm PLE feature in Tris MnCl and Tris SbMnCl hybrid arises due to direct Mn²⁺ absorption.¹⁸ However, the high energy PLE features of Tris SbMnCl hybrid appears strikingly different than the high energy PLE features of Tris MnCl hybrid. Noteworthy, the sharp onset of PLE spectra for Tris SbMnCl hybrid is convincingly different than the PLE features of Tris MnCl hybrid. The observed absorption/PLE profile and its sharp onset for Tris SbMnCl hybrid are reminiscent of the absorption/PLE profiles of pure Sb based 0D metal halide hybrids prevalent in the literature.^{17,19,20,23,24,39} Such differences in the PLE features of the two hybrids suggest different absorbing species in action. Fig. 1c compares and contrasts the PL/PLE spectra of the two hybrids highlighting the following: (i) both the hybrids show emission peaked at ∼630 nm likely due to one type of emissive species albeit the strength of the emission is stronger for Tris SbMnCl hybrid; (ii) PL emission is weak and comparable for both the hybrids when Mn²⁺ centres are excited exclusively at ∼440 nm; (iii) when excited at ∼340 nm the PL emission is stronger for Tris SbMnCl than Tris MnCl hybrid suggesting the role played by Sb atoms in absorption process; (iv) the observed difference in the high energy PLE features further suggest the key role played by incorporated Sb atoms in the absorption. Fig. 1d clearly shows the difference in the absorption profile for the two hybrids highlighting the molecular absorption features of Mn centres for Tris MnCl while the absorption bands are observable for both Mn and Sb centres for Tris SbMnCl hybrid.

The above steady state optical characterizations clearly indicate that the emission is from Mn centres while absorption is preferentially (not exclusively) through Sb centre for Tris SbMnCl hybrid. To note, PLE collected across the emission band and excitation dependent PL for Tris MnCl and Tris SbMnCl hybrid, as shown in Fig. S4 (ESI†), are consistent with unique emissive species (Mn centres) and both the Sb and Mn centres participating in the absorption process for Tris SbMnCl hybrid. Cumulatively, this suggests strong electronic interaction between Sb and Mn centres of Tris SbMnCl hybrid. Here, Sb centres act as antennae, harvesting energy through high energy absorption and transferring energy to the luminescent Mn centres that act as acceptors. This synergy between the electronically coupled/interacting Mn and Sb centres allow efficient energy transfer resulting in enhanced Mn emission for Tris SbMnCl hybrid.

Temperature dependent PL spectra were collected for both TrisSbMnCl and Tris MnCl hybrid as presented in Fig. S5, ESI.† Photoluminescence (λ_exc = 440 nm) collected for the host Tris MnCl hybrid shows a gradual increase in intensity as the temperature is lowered from 290 K to 95 K with a concomitant band narrowing. Similar trend is observed for the luminescence peak for Tris SbMnCl hybrid when excited at 440 and 340 nm clearly suggesting Mn centres to be the emissive species. Low temperature lifetime decay profile analysis was performed for TrisSbMnCl hybrid as shown in Fig. 2. Analysis of the decay profiles of Tris SbMnCl hybrid collected over millisecond timescales for 340 nm excitation over the temperature range investigated allows extraction of lifetime value ∼10 ms (Fig. 2a, and Table S1, ESI†). Further, temperature dependent lifetime decay profiles of Tris SbMnCl and Tris MnCl hybrids were collected over millisecond timescales when excited at 440 nm and are presented in Fig. S6 and Table S2, ESI.† Clearly, the observed lifetimes are ∼10 ms for both the host TrisMnCl and Tris SbMnCl hybrid. This comparison allows confirmation of the emissive species to be the Mn centres in Tris SbMnCl hybrid. Noteworthy here, the lifetime decay profiles across the Mn emission band remains almost unchanged for Tris SbMnCl and Tris MnCl hybrid (Fig. S7, Tables S3–S5; ESI†). The long lifetime (∼10 ms) of the emissive Mn centres are well-known to be due to the spin forbidden emissive transition.^17,18,25

Fig. 2 Temperature dependent lifetime PL decay profiles excited at 340 nm of Tris SbMnCl collected over (a) millisecond and (b) microsecond timescales.

Interestingly, analysis of the lifetime decay profile of Tris SbMnCl hybrid when excited at 340 nm and collected over microsecond timescales within the investigated temperature range reveals a fast component as presented in Fig. 2b. The extracted lifetimes for this fast emitting component is ∼3 μs (Table S6, ESI†). Note that this fast emitting channel decays sharply within the first ∼ 20 μs but does not show complete decay as can be inferred from the constancy of the decay profile within the 50 μs timeframe (Fig. 2b). This decay is complete only when the decay is followed into the millisecond timescales (Fig. 2a). In order to gain further insight to the origin of this fast (μs) emissive component, evolution of the time resolved emission spectra (TRES) of Tris SbMnCl hybrid over the microsecond to millisecond timescales was monitored when excited at 340 nm. The contour plots of the evolution of the emission profile over different timescales (μs to ms) is presented in Fig. S8, (ESI†) for Tris SbMnCl hybrid. The various ‘time-slices’ showing the spectral evolution over millisecond to microsecond timescales and their direct comparison is presented in Fig. 3.

Fig. 3 Time resolved emission spectra (TRES) of Tris SbMnCl hybrid excited at 340 nm collected over (a) millisecond and (b) microsecond timescales; (c) normalized TRES profiles over various timescales, and (d) PL intensity comparison over various timescales.

The PL profile collected at 340 nm excitation and over millisecond timescales (0.04–22.04 ms), as presented in Fig. 3a, shows the emission profile closely matching with the steady state emission profile of Fig. 1b. Further, the PL emission intensity decreases monotonously over the investigated millisecond timescales suggestive of the long lifetime (∼ms) Mn emission channel. Interestingly, the TRES data collected over microsecond timescales (0.35–9.35 μs) shows a broad emissive PL profile spanning 450–850 nm region as shown in Fig. 3b. Further, this PL intensity decreases over the microsecond timescales. Such broadband emission with lifetime component in the microsecond timescales is similar to heavily studied broadband emission from Sb based 0D metal halide hybrids.^{17,19–24,39} This allows us to tentatively associate the fast μs lifetime component with the emissive Sb centres in the Tris SbMnCl hybrid. Fig. 3c presents the normalized TRES data that directly compares the integrated emission profile over ns, μs, ms timescales that clearly shows the evolution of the spectral profile demonstrating the Sb emission channel (ns–μs) switching over to Mn emission channel (ms). Further, Fig. 3d compares the relative PL intensities of the Sb and Mn emission channel over the timescales investigated. Clearly, the Mn based emission channel integrated over ms timescales is strongest with very weakly emitting Sb based channel integrated in μs timescales (inset Fig. 3d). This order of magnitude difference in the emission strength leads to the steady state emission profile being dominated by the Mn emission channel exclusively. In order to further justify that Sb centres are operative in the absorption process with fast emission in the microsecond timescales, Tris SbZnCl hybrid powder samples were synthesized wherein the Zn centres are introduced and Mn centres are eliminated. The elemental composition characterization of Tris SbZnCl hybrid through SEM EDS, XPS, NMR is presented in Fig. S9, ESI.† Optical characterization of such Tris SbZnCl hybrid, as presented in Fig. S10a, ESI,† shows strong and broadband PL centred at 590 nm spanning 450–800 nm attributable to Sb based emission. The PLE spectra shows high energy features with sharp onset at ∼390 nm highlighting Sb based absorption. These PL/PLE features are characteristic of 0D Sb based metal halide hybrids and matches well with the PLE feature of Tris SbMnCl hybrid (Fig. 1b) and the TRES profile collected in the microsecond timescales (Fig. 3b–d). Further, temperature dependent lifetime decay analysis of Tris SbZnCl hybrid, as shown in Fig. S10b, ESI,† extracts lifetimes in ∼3 μs. Such microsecond lifetimes are common for 0D Sb based metal halide hybrids and is in agreement with the fast decaying μs component of Tris SbMnCl hybrid. Evolution of the low temperature PL intensity and bandwidth profile for Tris SbZnCl hybrid is shown in Fig. S10c and d, ESI.† Here, the PL intensity becomes weaker as temperature is lowered in sharp contrast to the temperature dependence of the PL intensity of Tris SbMnCl hybrid. Such differences in the temperature dependence of the PL intensity for the two hybrids suggest two different emissive centres-Sb for Tris SbZnCl and Mn for Tris SbMnCl hybrid. Altogether, these evidences suggest that for Tris SbMnCl hybrid the fast and weak μs emission component is due to Sb emission channel that presents the broad emission profile in the microsecond timescale TRES data.

Succinctly, the above optical characterization suggests the following:

(i) Tris SbMnCl hybrid shows stronger emission than Tris MnCl hybrid due to the incorporation of Sb centres;

(ii) the emissive species in both the hybrids is Mn centres;

(iii) PLE features of Tris SbMnCl hybrid suggests that both Mn and Sb centres participate in the absorption process;

(iv) stronger emission in Tris SbMnCl hybrid is due to preferential absorption by Sb centres;

(v) Sb centres act as strongly absorbing antennae while luminescent Mn centres act as acceptors that shows enhanced emission.

These optical characteristics suggest the presence of strong electronic coupling between the Sb and Mn centres in Tris SbMnCl hybrid that allows efficient energy transfer from the Sb to Mn centres. The nature/mechanism of this ‘cross-talk’/coupling between the metal halide centres (Sb, Mn) needs further probing/analysis. Admittedly, upon high energy absorption, Sb centres emit broadband light in Tris SbMnCl hybrid (Fig. 3b). However, this emission is weak and has minimal overlap with the absorption features of Mn centres. This likely precludes absorption (by Mn centres) of emitted radiation (by Sb centres) as the determining factor in enhancing the Mn emission in Tris SbMnCl hybrid (Note – direct excitation of Mn centres of Tris SbMnCl hybrid at 450 nm does not show enhanced Mn emission; Fig. 1c). Energy transfer interaction between the Sb and Mn centres in Tris SbMnCl hybrid likely populates the excited state(s) of Mn centres thereby enhancing the Mn emission. Such a forethought is likely supported by the long (μs) lifetime of the excited Sb centres that would allow facile exchange interactions between the Sb and Mn centres. This would further bolster the fact that the Sb centres emit weakly in Tris SbMnCl hybrids. However, such Dexter type energy transfer, mediated through exchange interactions, need close proximity of the interacting metal centres. In order to gain further physical understanding on the nature of this energy transfer based ‘cross-talk’/electronic coupling between the Sb and Mn centres, single crystal X-ray diffraction (SCXRD) structure of the Tris MnCl and Tris SbMnCl hybrid were examined.

SCXRD structure of as synthesized Tris MnCl hybrid (CCDC 2105558) herein matches with the reported structure.¹⁸ Briefly, Tris MnCl hybrid, C₁₂H₄₇Cl₁₃Mn₂N₈O₄, crystallizes in R3̄c space group. The asymmetric unit (Fig. S11, ESI†) contains an one sixth Mn–Cl octahedral unit, an one sixth Mn–Cl trigonal bipyramidal (tbp) unit, with one third of organic ligand, one third of chloride, one sixth of hydronium ions, and a half solvated water molecule. The octahedral unit is regular with six Mn–Cl bond lengths of 2.563 Å, while the tbp unit has shorter equatorial Mn–Cl bond lengths (2.371 Å) and longer axial bond lengths (2.695 Å). The packing diagram (Fig. S12a and b, ESI†) shows that the octahedral and tbp units are packed alternately within the holes created by the organic ligands. The octahedral and tbp units are disconnected and isolated thereby leading to 0D structure of the Tris MnCl hybrid. The in-plane octahedral units are separated by 9.612 Å which is same as the distance between the in-plane tbp units. However, the octahedral and tbp units across plane is separated by 8.203 Å. Noteworthy, water molecules are localized in the plane containing the octahedral units while the plane containing the tbp units lack water molecules (Fig. S12a–b, ESI†). Experimental and simulated PXRD pattern, as presented in Fig. S13 (ESI†), show good match indicating sample purity. The details of the bond angles, bond lengths, and structure data for Tris MnCl hybrid are provided in ESI† (Tables S7–S11).

SCXRD structure analysis of Tris SbMnCl hybrid (CCDC 2105557) reveal that Tris SbMnCl and Tris MnCl hybrid have very similar 0D structure wherein the Sb atoms have now been partially incorporated into the Mn–Cl octahedral units. Notably, Tris SbMnCl hybrid, C₁₂H₄₄Cl₁₃Mn_1.73N₈O₆Sb_0.27, crystallizes in R3̄c space with isolated Mn–Cl trigonal bipyramidal (tbp) units and isolated Sb incorporated octahedral units. Again here, the octahedral unit is regular with six metal–halide bond lengths of 2.585 Å, while the tbp unit has shorter equatorial Mn–Cl bond lengths (2.383 Å) and longer axial bond lengths (2.638 Å). The packing diagram (Fig. 4a and b) shows that the (Sb/Mn)–halide octahedral units and (Mn)–halide tbp units are packed alternately within the cavities created by the organic ligands. The in-plane octahedral units are separated by 9.594 Å which is same as the distance between the in-plane tbp units. However, the octahedral and tbp units across plane is separated by 8.201 Å. Noteworthy, water molecules are localized in the plane containing the octahedral units while the plane containing the tbp units lack water molecules (Fig. 4a and b). These observations suggest a strong similarity of the structure of Tris SbMnCl and Tris MnCl hybrid with very similar metal–halide bond lengths and importantly similar distances between the in-plane and out of plane polyhedral units. One of the striking difference, however, is the water content in these systems: Tris SbMnCl hybrid, with more number of water molecules than the Tris MnCl hybrid, shows dynamic and highly networked water ‘layer’ present in the plane containing the octahedral units. The presence of the water molecules in Tris SbMnCl hybrid is also confirmed by thermogravimetric analysis showing a broad weight loss peak at ∼100 °C as presented in Fig. S14 a, ESI.† Experimental and simulated PXRD pattern, as presented in Fig. S14bESI,† show good match indicating sample purity. The details of the bond angles, bond lengths, and structure data for Tris SbMnCl hybrid are provided in ESI† (Tables S12–S16).

Fig. 4 SCXRD structure of Tris SbMnCl highlighting (a) 0D metal halide units (isolated MnCl₅, isolated Sb doped MnCl₆ units) surrounded by organic ligands and (b) isolated Sb doped MnCl₆ units dispersed in the plane of the water channel with networked structure.

As presented above, Tris SbMnCl hybrid has a bulk self-assembled 0D structure wherein the metal halide units (MnCl₅, SbCl₆, MnCl₆) are completely isolated/disconnected and dispersed in the matrix of the organic ligand and solvent water molecules. Isolated MnCl₅ trigonal bipyramidal units and (Sb/Mn)Cl₆ octahedral units are separated by the layers of organic ligand molecule. This dielectric separation allows minimal electronic coupling between the MnCl₅ and (Sb/Mn)Cl₆ units across the layers. In-plane coupling between the isolated MnCl₅ units is also unlikely due to the large separations (∼0.96 nm) between the units. Importantly, isolated (Sb/Mn)Cl₆ octahedral units are dispersed within the water ‘layer’ albeit with large separations (∼0.96 nm). However, the network of the water molecules bind the (Sb/Mn)Cl₆ units in the plane that could potentially lead to coupling between the isolated MnCl₆ and SbCl₆ units mediated by the water ‘layer’. The experimentally observed absorption by Sb centres, enhanced emission by Mn centres with plausible energy and/or charge transfer is likely due to this water ‘layer’ mediated in-plane coupling between the Sb and Mn octahedral centres. Such in-plane coupling would endow Tris SbMnCl hybrid with electronic dimensionality higher than 0D. In order to identify the role played by the water ‘layer’ in allowing ‘cross-talk’ between the (Sb/Mn)Cl₆ units, we attempted to synthesize the Tris SbMnCl hybrid using the antisolvent diffusion method wherein water molecules can be avoided. Unfortunately, such synthesis did not yield any crystal. Hence, we annealed the Tris SbMnCl hybrid (synthesized using HX method) at different temperatures and the collected PL/PLE spectra are shown in Fig. S15, ESI.† Clearly, PL intensity is observed to drop as the annealing temperatures are raised with a complete loss of the PL when the samples are annealed at temperatures higher than 100 °C. This suggests key role played by the water ‘layer’ in allowing in-plane coupling between the metal halide units leading to enhanced luminescence in Tris SbMnCl hybrid. It is indeed very challenging to decipher the nature (energy transfer, charge transfer/exciton diffusion) of this water ‘layer’ mediated electronic coupling in between the metal halide units. In order to address this and to further support the idea of water layer mediated ‘cross-talk’ between the metal halide units, proton conductivity measurements of the pelletized hybrids were performed (Fig. 5).

Fig. 5 Proton Conductivity measurement at 50 °C and 80% relative humidity (RH) showing (a) EIS spectra of Tris SbMnCl and Tris MnCl hybrid and (b) Comparison of the Nyquist plots of Tris SbMnCl hybrid measured using H₂O and D₂O vapors.

Proton conductivity of Tris SbMnCl hybrid is found to depend strongly on temperature and relative humidity (RH) as presented in Fig. S16(a–d), ESI.† Proton conductivity is observed to increase as the temperature is raised (30–50 °C). Further, a clear rise of conductivity is also observed with the gradual rise of RH suggesting strong inter-connections (plausibly through hydrogen bonds) forming between the inherent water layer of the hybrid and the water molecules of the humidified environment. Such enhanced hydrogen bonding network can provide effective proton conduction pathways as commonly observed in water facilitated proton conductors.^50,51 Under optimized conditions of 50 °C and 80% RH, Tris SbMnCl hybrid records the highest proton conductivity value of 5.6 × 10⁻² S cm⁻¹ (Fig. 5a). Mechanistic insight into proton conduction is gained by the analysis of the temperature dependent conductivities. Activation energy for proton transfer in the temperature range of 30–50 °C is calculated to be 0.4 eV (Fig. S16 d, ESI†). This indicates that the leading proton hopping mechanism is likely through the Grotthuss mechanism⁵⁰ that strongly relies on the participation of the inherent water layer of the Tris SbMnCl hybrid in providing proton conduction pathways. Further, proton conductivity measurements of Tris MnCl hybrid control sample shows lower value (4.32 × 10⁻² S cm⁻¹) than TrisSbMnCl hybrid (Fig. 5a). This highlights the role of strongly networked and dynamic water layer present in Tris SbMnCl hybrid in providing efficient conduction pathways. This is further confirmed by comparing the conductance of Tris SbMnCl hybrid when exposed to H₂O and D₂O vapors (Fig. 5b). The proton conductivity value dropped as H₂O vapors were replaced with D₂O vapors. Such drop in conductivity may result because the D₂O vapour molecules connect loosely with the inherent networked water layer of Tris SbMnCl hybrid. This suggests that the dynamic and strongly interconnected layered water molecules of Tris SbMnCl hybrid is primarily responsible for the observed proton conductivity. Interestingly, the proton conductivity value recorded by Tris SbMnCl hybrid is comparable to the best values reported for proton-conducting porous materials to date (Table S17, ESI†), and is the first effort that demonstrates high proton conductivity for 0D metal halide hybrids.

Noteworthy, Tris SbMnCl hybrid with water ‘layer’ shows high proton conductivity with a Grotthuss mechanism of conduction with internal water molecules playing a key role in proton transfer mechanism. These evidences from the conductivity measurements suggest plausible charge transfer/exciton diffusion mechanism to be operative that allows electronic coupling between the isolated in-plane metal halide units leading to the observed energy transfer. However, this by no means, is definitive and needs further probing.

In order to pursue this further, we performed DFT based calculations, considering an isolated slab of MnCl₆ octahedra along with the water molecules. Such choice of ‘reduced’ sample structure essentially mimics the structure of the antimony incorporated host structure with (Mn/Sb)Cl₆ octahedral plane including the networked water layer. It helps to reduce the computational expense of considering the full unit cell, however providing the essential insight about the role of water molecules in regulating the relative electronic properties of the total system as compared to its counterpart without water molecules. In Fig. 6a and b, we show the band structure in the irreducible Brillouin zone (inset of Fig. 6a) and density of states of the MnCl₆ slab, respectively without any water molecules. The completely dispersion-less degenerate bands with diverging spikes in the density of states indicate that each MnCl₆ octahedron is isolated without any interaction in between them in the two-dimensional slab. The inclusion of water molecules in between the MnCl₆ octahedra in the slab structure introduces asymmetric electrostatic perturbation that lifts the degeneracy and makes the bands dispersive, as can be seen in Fig. 6c. The dispersive bands have contributions from Mn, Cl and water molecules, as evident from their projected density of states in Fig. 6d. Such band dispersions indicate the water molecule mediated interactions and consequent “cross-talk” among metal halide octahedral units in two-dimensional plane.

Fig. 6 (a) The band structures and (b) density of states (DOS) along with the projected density of states (pDOS) in arbitrary units for the slab structure with MnCl₆ octahedra in absence of water molecules. (d) and (e) show the same for the system in presence of water molecules. The inset in (a) shows the hexagonal Brillouin zone with high-symmetric points. The vertical dashed lines in band structures show the location of high-symmetric points. The charge densities calculated at Γ point for the top of the valence bands of the systems (e) without and (f) with the water molecules in the slab structures. (g) and (h) show one isolated MnCl₆ octahedra in these structures, respectively.

To gain further insights, we analyze and compare the wave functions and present the corresponding charge densities of the systems without and with water molecules in Fig. 6e and 6f, respectively. These are calculated for the top of the valence bands at Γ point. As can be seen, the MnCl₆ octahedra are completely isolated in absence of the water molecules, with symmetric charge distribution on surrounding Cl⁻ ligands (see Fig. 6g) in each octahedron. However, the delocalized charge densities on the interceding water molecules clearly indicate the interaction among the MnCl₆ octahedra. In Fig. 6h, we present the charge density distribution on a MnCl₆ octahedron in the water environment. It shows asymmetric charge densities on Cl⁻ ligands, which can be attributed to the asymmetric electrostatic field exerted by the surrounding water molecules. The consequent perturbation lifts the band degeneracies and results in band dispersions. Such band dispersions lead to observable effects of cross-talk between the metal halide octahedral units (MnCl₆ and SbCl₆) incorporating the networked water layer leading to energy transfer (Sb → Mn) between the isolated metal halide centres.

Conclusions

The presented work reports synthesis and characterization of heterometallic (Sb, Mn) 0D chloride hybrid, namely Tris SbMnCl, that clearly shows strong synergistic coupling between the constituent isolated metal halide units leading to enhanced Mn emission. Herein, the structurally 0D material, containing isolated metal halide units (MnCl₆ – octahedral, SbCl₆ – octahedral, MnCl₅ – trigonal bipyramidal) dispersed in organic ligand matrix of Tris(2-aminoethyl)amine, highlights highly connected and dynamic water layer containing the in-plane (Sb/Mn)Cl₆ units. Detailed optical (steady state PL; TRES analysis; lifetime analysis; absorbance), SCXRD structural characterization, proton conductivity measurements, and DFT based band structure calculations on Tris SbMnCl hybrid suggest strong in-plane electronic coupling of the (Sb/Mn)Cl₆ units that causes strong Mn centre based emission. Sb centres of Tris SbMnCl hybrid, showing strong absorption, transfers energy to the Mn sites leading to synergistic enhancement of Mn emission. This energy transfer between the in-plane isolated metal halide units is likely mediated by the dynamic and networked water layer as substantiated by high proton conductivity of Tris SbMnCl hybrid. Enhancement of the band dispersions, as observed within first principles calculations support the unique role of the networked water layer in mediating the electronic coupling between the separated metal halide units. This report highlights the first example of strong and synergistic electronic interaction between the isolated metal halide units in a heterometallic 0D hybrid wherein the structure and composition of the hybrid allows attaining electronic dimensionality higher than 0D facilitating coupling of constituent isolated metal halide units that leads to enhanced emissive properties. Undoubtedly, the nature of the physical mechanism of the observed energy transfer in this 0D material needs further probing. This first effort on heterometallic 0D metal halide hybrids successfully demonstrating synergistic effects on the photo-physical properties of the constituent metal halide units is expected to fuel further research in rational synthesis and design of function-directed, multi-metallic, low dimensional “perovskite-type” materials.

Author contributions

A. B., R. B., D. K. D. synthesized samples and performed experiments; B. P. M.; R. G. G. performed SCXRD studies; C. B., S. S. K. R. performed low TPL studies; N. M. S. K. performed conductivity measurements; J. S., S. D. performed theoretical calculations; S. T. performed TRES studies; J. K. conceived the idea, designed experiments, and analysed data. All authors contributed to manuscript writing.

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

The authors acknowledge Milan K Bisai (NCL Pune), Dr J. Nithyanandhan (NCL Pune), Dr Partha Hazra (IISER Pune) for insightful discussion. This work was financially supported by DST Grant No. CRG/2019/000252. A. B. and R. B. acknowledges CSIR for Senior Research Fellowship. J. S. and S. D. acknowledge National Supercomputing Mission (NSM) for providing computing resources of ‘PARAM Brahma’ at IISER Pune, which is implemented by C-DAC and supported by the Ministry of Electronics and Information Technology (MeitY) and Department of Science and Technology (DST), Government of India.

References

1. B.-B. Cui, Y. Han, B. Huang, Y. Zhao, X. Wu, L. Liu, G. Cao, Q. Du, N. Liu, W. Zou, M. Sun, L. Wang, X. Liu, J. Wang, H. Zhou and Q. Chen, Nat. Commun., 2019, 10, 1–8.
2. R. Gautier, F. Massuyeau, G. Galnon and M. Paris, Adv. Mater., 2019, 31, 1807383.
3. H. Lin, C. Zhou, Y. Tian, T. Siegrist and B. Ma, ACS Energy Lett., 2017, 3, 54–62.
4. M. I. Saidaminov, O. F. Mohammed and O. M. Bakr, ACS Energy Lett., 2017, 2, 889–896.
5. H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos, R. Asadpour, B. Harutyunyan, A. J. Neukirch, R. Verduzco, J. J. Crochet, S. Tretiak, L. Pedesseau, J. Even, M. A. Alam, G. Gupta, J. Lou, P. M. Ajayan, M. J. Bedzyk, M. G. Kanatzidis and A. D. Mohite, Nature, 2016, 536, 312–316.
6. C. Zhou, H. Lin, S. Lee, M. Chaaban and B. Ma, Mater. Res. Lett., 2018, 6, 552–569.
7. R. Quintero-Bermudez, A. Gold-Parker, A. H. Proppe, R. Munir, Z. Yang, S. O. Kelley, A. Amassian, M. F. Toney and E. H. Sargent, Nat. Mater., 2018, 17, 900–907.
8. M. P. Haris, R. Bakthavatsalam, S. Shaikh, B. P. Kore, D. Moghe, R. G. Gonnade, D. Sarma, D. Kabra and J. Kundu, Inorg. Chem., 2018, 57, 13443–13452.
9. R. Bakthavatsalam, M. P. Haris, S. R. Shaikh, A. Lohar, A. Mohanty, D. Moghe, S. Sharma, C. Biswas, S. S. K. Raavi, R. G. Gonnade and J. Kundu, J. Phys. Chem. C, 2020, 124, 1888–1897.
10. C. Zhou, Y. Tian, M. Wang, A. Rose, T. Besara, N. K. Doyle, Z. Yuan, J. C. Wang, R. Clark, Y. Hu, T. Siegrist, S. Lin and B. Ma, Angew. Chem., Int. Ed., 2017, 56, 9018–9022.
11. L. J. Xu, H. R. Lin, S. Lee, C. K. Zhou, M. Worku, M. Chaaban, Q. Q. He, A. Plaviak, X. S. Lin, B. H. Chen, M. H. Du and B. Ma, Chem. Mater., 2020, 32, 4692–4698.
12. L. Dou, A. B. Wong, Y. Yu, M. Lai, N. Kornienko, S. W. Eaton, A. Fu, C. G. Bischak, J. Ma, T. Ding, N. S. Ginsberg, L.-W. Wang, A. P. Alivisatos and P. Yang, Science, 2015, 349, 1518–1521.
13. M. D. Smith and H. Karunadasa, Acc. Chem. Res., 2018, 51, 619–627.
14. Z. Yuan, C. Zhou, Y. Tian, Y. Shu, J. Messier, J. C. Wang, L. J. Van De Burgt, K. Kountouriotis, Y. Xin, E. Holt, K. Schanze, R. Clark, T. Siegrist and B. Ma, Nat. Commun., 2017, 8, 1–7.
15. C. Zhou, H. Lin, Y. Tian, Z. Yuan, R. Clark, B. Chen, L. J. van de Burgt, J. C. Wang, Y. Zhou, K. Hanson, Q. J. Meisner, J. Neu, T. Besara, T. Siegrist, E. Lambers, P. Djurovich and B. Ma, Chem. Sci., 2018, 9, 586–593.
16. C. Zhou, H. Lin, Q. He, L. Xu, M. Worku, M. Chaaban, S. Lee, X. Shi, M.-H. Du and B. Ma, Mater. Sci. Eng., R, 2019, 137, 38–65.
17. M. Li and Z. Xia, Chem. Soc. Rev., 2021, 50, 2626–2662.
18. Y. Mei, H. Yu, Z. Wei, G. Mei and H. Cai, Polyhedron, 2017, 127, 458–463.
19. Z. Li, Y. Li, P. Liang, T. Zhou, L. Wang and R.-J. Xie, Chem. Mater., 2019, 31, 9363–9371.
20. C. Zhou, M. Worku, J. Neu, H. Lin, Y. Tian, S. Lee, Y. Zhou, D. Han, S. Chen, A. Hao, P. I. Djurovich, T. Siegrist, M.-H. Du and B. Ma, Chem. Mater., 2018, 30, 2374–2378.
21. C. Zhou, H. Lin, Y. Tian, Z. Yuan, R. Clark, B. Chen, L. J. van de Burgt, J. C. Wang, Y. Zhou, K. Hanson, Q. J. Meisner, J. Neu, T. Besara, T. Siegrist, E. Lambers, P. Djurovich and B. Ma, Chem. Sci., 2018, 9, 586–593.
22. Z.-P. Wang, J.-Y. Wang, J.-R. Li, M.-L. Feng, G.-D. Zou and X.-Y. Huang, Chem. Commun., 2015, 51, 3094–3097.
23. A. Biswas, R. Bakthavatsalam, B. P. Mali, V. Bahadur, C. Biswas, S. S. K. Raavi, R. G. Gonnade and J. Kundu, J. Mater. Chem. C, 2021, 9, 348–358.
24. K. M. McCall, V. Morad, B. M. Benin and M. V. Kovalenko, ACS Mater. Lett., 2020, 2, 1218–1232.
25. V. Morad, I. Cherniukh, L. Pöttschacher, Y. Shynkarenko, S. Yakunin and M. V. Kovalenko, Chem. Mater., 2019, 31, 10161–10169.
26. S. S. Yakunin, B. M. Benin, Y. Shynkarenko, O. Nazarenko, M. I. Bodnarchuk, D. N. Dirin, C. Hofer, S. Cattaneo and M. V. Kovalenko, Nat. Mater., 2019, 18, 846–852.
27. V. Morad, Y. Shynkarenko, S. Yakunin, A. Brumberg, R. D. Schaller and M. V. Kovalenko, J. Am. Chem. Soc., 2019, 141, 9764–9768.
28. L.-J. Xu, X. Lin, Q. He, M. Worku and B. Ma, Nat. Commun., 2020, 11, 4329.
29. V. Morad, S. Yakunin, B. M. Benin, Y. Shynkarenko, M. Grotevent, I. Shorubalko, S. C. Boehme and M. V. Kovalenko, Adv. Mater., 2021, 33, 2007355.
30. G. Xiong, L. Yuan, Y. Jin, H. Wu, Z. Li, B. Qu, G. Ju, L. Chen, S. Yang and Y. Hu, Adv. Opt. Mater., 2020, 8, 2000779.
31. G. Xiong, L. Yuan, Y. Jin, H. Wu, B. Qu, Z. Li, G. Ju, L. Chen, S. Yang and Y. Hu, J. Mater. Chem. C, 2021, 9, 13474–13483.
32. R. Chen, Z. H. Yan, X. J. Kong, L. S. Long and L. S. Zheng, Angew. Chem., Int. Ed., 2018, 57, 16796–16800.
33. C. Chen, Y. Chen, R. Yao, Y. Li and C. Zhang, Angew. Chem., Int. Ed., 2019, 58, 3939–3942.
34. M. Andruh, Chem. Commun., 2018, 54, 3559–3577.
35. M. Pan, W.-M. Liao, S.-Y. Yin, S.-S. Sun and C.-Y. Su, Chem. Rev., 2018, 118, 8889–8935.
36. J. R. Berenguer, E. Lalinde and M. T. Moreno, Coord. Chem. Rev., 2018, 366, 69–90.
37. L.-J. Xu, S. Lee, X. Lin, L. Ledbetter, M. Worku, H. Lin, C. Zhou, H. Liu, A. Plaviak and B. Ma, Angew. Chem., Int. Ed., 2020, 59, 14120–14123.
38. Y. Peng, L. Li, C. Ji, Z. Wu, S. Wang, X. Liu, Y. Yao and J. Luo, J. Am. Chem. Soc., 2019, 141, 12197–12201.
39. C. Zhou, S. Lee, H. Lin, J. Neu, M. Chaaban, L.-J. Xu, A. Arcidiacono, Q. He, M. Worku, L. Ledbetter, X. Lin, J. A. Schlueter, T. Siegrist and B. Ma, ACS Mater. Lett., 2020, 2, 376–380.
40. S. Sujin Lee, C. Zhou, J. Neu, D. Beery, A. Arcidiacono, M. Chaaban, H. Lin, A. Gaiser, B. Chen, T. E. Albrecht-Schmitt, T. Siegrist and B. Ma, Chem. Mater., 2020, 32, 374–380.
41. C. Zhou, H. Lin, J. Neu, Y. Zhou, M. Chaaban, S. Lee, M. Worku, B. Chen, R. Clark, W. Cheng, J. Guan, P. Djurovich, D. Zhang, X. Lü, J. Bullock, C. Pak, M. Shatruk, M.-H. Du, T. Siegrist and B. Ma, ACS Energy Lett., 2019, 4, 1579–1583.
42. C. Zhou, H. Lin, M. Worku, J. Neu, Y. Zhou, Y. Tian, S. Lee, P. I. Djurovich, T. Siegrist and B. J. A. C. S. Ma, J. Am. Chem. Soc., 2018, 140, 13181–13184.
43. M. Li, J. Zhou, G. Zhou, M. S. Molokeev, J. Zhao, V. Morad, M. V. Kovalenko and Z. Xia, Angew. Chem., Int. Ed., 2019, 58, 18670–18675.
44. M. Li, M. S. Molokeev, J. Zhao and Z. Xia, Adv. Opt. Mater., 2020, 8, 1902114.
45. J. Zhou, M. Li, M. S. Molokeev, J. Sun, D. Xu and Z. Xia, J. Mater. Chem. C, 2020, 8, 5058–5063.
46. S. Baroni, S. D. Gironcoli, A. D. Corso and P. Giannozzi, Rev. Mod. Phys., 2001, 73, 515–562.
47. J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77, 3865–3868.
48. D. Vanderbilt, Phys. Rev. B: Condens. Matter Mater. Phys., 1990, 41, 7892–7895.
49. E. H. Lieb and B. Simon, Adv. Math., 1977, 23, 22–116.
50. W. J. Phang, H. Jo, W. R. Lee, J. H. Song, K. Yoo, B. Kim and C. S. Hong, Angew. Chem., Int. Ed., 2015, 54, 5142–5146.
51. N. T. T. Nguyen, H. Furukawa, F. Gándara, C. A. Trickett, H. M. Jeong, K. E. Cordova and O. M. Yaghi, J. Am. Chem. Soc., 2015, 137, 15394–15397.

---

Footnote

† Electronic supplementary information (ESI) available: XPS, SEM-EDS, NMR analysis of Tris SbMnCl, Tris SbZnCl, Tris MnCl hybrids; optical characterization (absorption, PL, PLE, temperature dependent lifetimes) of Tris SbMnCl, Tris SbZnCl, Tris MnCl hybrids; TRES contour plots of Tris SbMnCl hybrid; SCXRD structure data (.cif) with tables of bond lengths, bond angles for Tris SbMnCl (CCDC 2105557), and Tris MnCl (CCDC 2105558) hybrids; proton conductivity measurement details and its optimization data; TGA plots. CCDC 2105557 and 2105558. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/d1tc04704c

---