Polymeric templates and solvent effects: syntheses and properties of polymeric iodoargentates containing solvated [Mn(4,4′-bpy)]²⁺ cations

Abstract

Four new polymeric iodoargentates were prepared by the reactions of AgI and KI templated by solvated [Mn(4,4′-bpy)]²⁺ complex cation in different mixed solvents. The reaction in DMF/H₂O, DMSO/H₂O, and DMF/DMSO/H₂O (DMF = N,N’-dimethylformamide; DMSO = dimethylsulfoxide) produced [Mn(4,4′-bpy)(DMF)₃(H₂O)]Ag₅I₇·4,4′-bpy (1), [Mn(4,4′-bpy)(DMSO)₄]₂Ag₁₁I₁₅ (2), [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]Ag₁₀I₁₂·2DMSO·2H₂O (3), and [Mn₂(4,4′-bpy)₂(DMF)₅(DMSO)₂(H₂O)]Ag₁₀I₁₄·2DMF (4) (4,4′-bpy = bipyridine), respectively. In 1, four AgI₄ units are joined by sharing common edges forming a Ag₄I₉ fragment. The Ag₄I₉ fragments are connected into a 1-D [Ag₅I₇²⁻]_n polymeric anion by a AgI₄ unit. In 2, six AgI₄ units share common edges to form [Ag₆I₁₂]_n chain-like subunits. Two [Ag₆I₁₂]_n subunits are joined by μ-I bridges, forming a novel ladder-shaped [Ag₁₁I₁₅⁴⁻]_n polymeric anion. The [Ag₁₀I₁₂²⁻]_n in 3 is composed of a circular Ag₅I₁₂ subunit via sharing five terminal iodine atoms. Two Ag₄I₉ and one Ag₂I₄ fragments are interjoined via sharing a common face to form the 1-D [Ag₁₀I₁₄⁴⁻]_n anion in 4. Compounds 1, 2 and 4 are the first examples of iodoargentates containing polymeric counter cations. The stronger Ag⋯Ag interactions in the [Ag₁₁I₁₅⁴⁻]_n and [Ag₁₀I₁₄⁴⁻]_n anions cause red-shift in the luminescent spectra of compounds 2 and 4, compared with those of 1 and 3.

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Introduction

Interest in organic–inorganic hybrid halometallates of heavy metals originates not only from their wide range of intriguing structural topologies but also from the opportunity to combine useful properties of both components, and the possibility to tune the physical properties using the organic components to form functional materials.^1,2 The chemistry of silver(I) iodide organic–inorganic hybrid complexes have received special attention for their tunable structural owing to the strong affinity of Ag(I) for the iodine anion and interesting physical properties. The high tendency for self-assembly of the AgI₄ units via corner-, edge-, or face-sharing lead to different compositions and structures ranging from isolated anions to extended arrays dependent on the templates or counter cations used in the synthesis. Much effort in exploratory templating synthesis has led to a large number of iodoargentate anions with different dimensional structures using a variety of organic cations as structure directing agents.³ Transition metal complex cationic templates [Cu(en)₂]²⁺ and [TM(en)₃]²⁺ (TM = Ni, Zn; en = ethylenediamine) have led to compounds [Cu(en)₂][Ag₂I₄] and [TM(en)₃][Ag₂I₄] in N,N’-dimethylformamide, which contain one-dimensional (1-D) [Ag₂I₄²⁻]_n chain and three-dimensional (3-D) [Ag₂I₄²⁻]_n network, respectively.^4,5 Recently, a 1-D [Ag₁₀I₁₂²⁻]_n anion has been obtained in the presence of [Ni(2,2′-bpy)(THF)₂(H₂O)₂]²⁺ complex cation.⁶ A third class of iodoargentates is based on lanthanide (Ln) complex counter ions, an area dominated by the work of Mishra and co-workers.⁷ A number of iodoargentates containing solvated Ln(III) cations were isolated from DMF or DMSO solvents. In the syntheses of the metal-containing iodoargentates, the TM or Ln complexes formed in situ act as space fillers and/or charge compensating ions in the final iodoargentates. Compared with the extensively investigated iodoargentates with organic cations, the iodoargentate with metal–organic cations remains less explored. Furthermore, all above iodoargentates were prepared templated by discrete cations. As far as we know, the synthesis of iodoargentates using polymeric cations as templates has not been reported before.

It has been documented that the compositions, structures and dimensionalities of halometallates are sensitive to specific reaction conditions, such as reaction temperature, reactant concentrations, solvents and crystallization conditions, and to the nature and size of the templates or counter ions used for crystallization.⁸ The high tendency for self-assembly of the AgI₄ tetrahedron provides a wide selection of reaction conditions and counter ions in design and preparation of new iodoargentates. In this manuscript, we chose the [Mn(4,4′-bpy)]²⁺ complex cation modified by small ligands via solvating in different polar solvents, to fine-tune the assembling of AgI₄ unit. The reactions of AgI, KI, MnCl₂·4H₂O and 4,4′-bipyridine (4,4′-bpy) in different mixed solvents afforded a series of polymeric iodoargentates [Mn(4,4′-bpy)(DMF)₃(H₂O)]Ag₅I₇·4,4′-bpy (1), [Mn(4,4′-bpy)(DMSO)₄]₂Ag₁₁I₁₅ (2), [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]Ag₁₀I₁₂·2DMSO·2H₂O (3), and [Mn₂(4,4′-bpy)₂(DMF)₅(DMSO)₂(H₂O)]Ag₁₀I₁₄·2DMF (4). In the syntheses, all Mn²⁺ ions are coordinated by 4,4′-bpy and solvated by solvent moleclues to form mixed-coordinated polymeric cations in 1, 2 and 4, or mononuclear complex cation in 3. Compounds 1, 2 and 4 are the first examples of iodoargentates containing polymeric cations. Herein, we report the syntheses, crystal structures, and solid-state optical absorption, luminescent and thermal properties of compounds 1–4.

Experimental

Materials and general methods

All starting materials were of analytical grade and were used as received. Elemental analyses were performed using an EA1110-CHNS-O elemental analyzer. Fourier-transform infrared (FT-IR) spectra were recorded with a Nicolet Magna-IR 550 spectrometer, using dry KBr discs, in the range of 4000–400 cm⁻¹. Powder X-ray diffraction (PXRD) patterns were collected on a D/MAX-3C diffractometer using graphite monochromatized CuKα radiation (λ = 1.5406 Å). Room-temperature optical diffuse reflectance spectra of the powdered samples were obtained using a Shimadzu UV-3150 spectrometer. The absorption (α/S) data were calculated from the reflectance using the Kubelka–Munk function α/S = (1 – R)²/2R,⁹ where R is the reflectance at a given energy, α is the absorption, and S is the scattering coefficient. Photoluminescence spectra of the crystalline samples were recorded on a F-2500 FL spectrophotometer with wavelength increment 1.0 nm at room temperature using a xenon arc lamp as the excitation source. Thermal gravimetric analyses (TGA) were conducted on an SDT 2960 microanalyzer; the samples were heated at a rate of 5 °C min⁻¹ under a nitrogen stream of 100 mL min⁻¹.

Syntheses of 1–4

[Mn(4,4′-bpy)(DMF)₃(H₂O)]Ag₅I₇·4,4′-bpy (1). MnCl₂·4H₂O (0.099 g, 0.5 mmol), and 4,4′-bpy·2H₂O (0.096 g, 0.5 mmol) were dissolved in 3 mL of DMF/H₂O (volume ration 2 : 1) mixed solvent by stirring and a yellowish solution was obtained. 5 mL of DMF solution containing AgI (0.235 g, 1.0 mmol) and KI (0.249 g, 1.5 mmol) was added drop wise to the above solution. After stirring for 2 h, the mixture was filtered. The filtrate was kept at room temperature for about one week, and prismatic crystals of 1 were obtained. The crystals were filtered off, washed with ethanol and stored under a vacuum (75% yield based on AgI). Elem. anal. calcd for C₂₉H₃₉N₇O₄MnI₇Ag₅ (1): C, 17.14; H, 1.93; N, 4.82; found: C, 17.01; H, 1.84; N, 4.68%. IR data (KBr, cm⁻¹): 3068(w), 2286(w), 1660(s), 1598(s), 1569(w), 1470(m), 1436(s), 1384(w), 1308(m), 1247(w), 1160(m), 1096(w), 1017(m), 903(w), 764(s), 733(m), 651(w), 578(w), 511(w), 410(w).

[Mn(4,4′-bpy)(DMSO)₄]₂Ag₁₁I₁₅ (2). MnCl₂·4H₂O (0.099 g, 0.5 mmol), and 4,4′-bpy·2H₂O (0.096 g, 0.5 mmol) were dissolved in 3 mL of DMSO/H₂O (volume ration 2 : 1) by stirring and a light yellow solution was obtained. 3 mL of DMSO solution containing AgI (0.235 g, 1.0 mmol) and KI (0.249 g, 1.5 mmol) was added drop wise to the above solution. After stirring for 2 h, the mixture was filtered. The filtrate was kept at room temperature for about one week, and block crystals of 2 were obtained. The crystals were filtered off, washed with ethanol and stored under a vacuum (57% yield based on AgI). Elem. anal. calcd for C₃₆H₆₄O₈S₈Mn₂I₁₅Ag₁₁ (2): C, 10.45; H, 1.56; N, 1.35; found: C, 10.38; H, 1.48; N, 1.21%. IR data (KBr, cm⁻¹): 3072(w), 2346(w), 1980(w), 1594(m), 1466(w), 1436(s), 1304(m), 1251(w), 1157(m), 1104(w), 1010(s), 899(w), 817(w), 764(s), 733(s), 651(m), 521(w), 439(w), 412(w).

[Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]Ag₁₀I₁₂·2DMSO·2H₂O (3). MnCl₂·4H₂O (0.099 g, 0.5 mmol), and 4,4′-bpy·2H₂O (0.096 g, 0.5 mmol) were dissolved in 3 mL of DMSO/H₂O (volume ration 1 : 1) mixed solvent by stirring and a yellowish solution was obtained. 3 mL of DMSO solution containing AgI (0.235 g, 1.0 mmol) and KI (0.249 g, 1.5 mmol) was added drop wise to the above solution. After stirring for 2 h, the mixture was filtered. The filtrate was kept at room temperature for about one week, and prismatic crystals of 3 were obtained. The crystals were filtered off, washed with ethanol and stored under a vacuum (64% yield based on AgI). Elem. Anal. Calcd for C₂₉H₃₉N₇O₄MnI₁₂Ag₁₀ (3): C, 10.03; H, 1.44; N, 1.67; found: C, 9.89; H, 1.32; N, 1.58%. IR data (KBr, cm⁻¹): 3068(w), 2362(w), 2335(w), 1663(w), 1602(m), 1564(w), 1466(m), 1440(s), 1311(m), 1270(w), 1239(m), 1157(m), 1119(w), 1036(w), 884(w), 802(w), 760(s), 729(m), 651(w), 563(w), 420(w).

[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]Ag₁₀I₁₄·2DMF (4). MnCl₂·4H₂O (0.099 g, 0.5 mmol), and 4,4′-bpy·2H₂O (0.096 g, 0.5 mmol) were dissolved in 3 mL of DMSO/DMF/H₂O (volume ration 1 : 1 : 1) mixed solvent by stirring and a yellowish solution was obtained. 4 mL of DMSO/DMF (volume ration 1 : 1) solution containing AgI (0.235 g, 1.0 mmol) and KI (0.249 g, 1.5 mmol) was added drop wise to the above solution. After stirring for 2 h, the mixture was filtered. The filtrate was kept at room temperature for about one week, and block crystals of 4 were obtained. The crystals were filtered off, washed with ethanol and stored under a vacuum (68% yield based on AgI). Elem. Anal. Calcd for C₄₅H₇₉N₁₁O₁₀S₂Mn₂I₁₄Ag₁₀ (4): C, 13.64; H, 2.01; N, 3.89; found: C, 13.48; H, 1.95; N, 3.81%. IR data (KBr, cm⁻¹): 3060(w), 2925(w), 2849(w), 1745(w), 1663(s), 1594(m), 1519(w), 1466(m), 1436(s), 1304(w), 1247(w), 1157(w), 1096(w), 1054(w), 1013(m), 964(w), 874(w), 771(s), 737(m), 691(w), 647(w), 597(w), 552(w), 507(w), 458(w), 412(m).

X-ray crystal structure determinations

All data were collected on a Rigaku Saturn (1, 3, 4) or a Rigaku Mercury (2) CCD diffractometer using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) in ω-scanning mode, to a maximum 2θ of 50.70°. An empirical absorption correction was applied to the data. The structures were solved using SHELXS-97,^10a and refinement was performed against F² using SHELXL-97.^10b All the non-hydrogen atoms were refined anisotropically. The hydrogen atoms were added geometrically and refined using a riding model. The S(3) and S(4) atoms in 2 are disordered. The occupancies of the disordered atoms are refined as 73% and 27% for S(3), and 54% and 46% for S(4). The occupancies of the disordered atoms C(20), C(31)–C(33) and C(38)–C(39) in 4 are refined as 55% and 45%, 58% and 42%,and 52% and 48%, respectively. Crystallographic, experimental, and analytical data for the title compounds are listed in Table 1.

Table 1 Crystallographic and refinement of 1–4

	1	2	3	4
Empirical formula	C29H39N7O4MnAg5I7	C36H64N4O8S8Mn2Ag11I15	C28H48N4O8S4MnAg10I12	C45H79N11O10S2Mn2Ag10I14
Formula weight	2032.26	4137.34	3353.38	3963.49
Crystal system	Monoclinic	Monoclinic	Monoclinic	Triclinic
Space group	P21 (no. 4)	P21/n (no. 14)	P21/c (no. 14)	P1̄
a/Å	11.7091(18)	8.2323(12)	16.3520(11)	13.0276(18)
b/Å	15.066(2)	34.488(5)	7.8920(5)	16.091(2)
c/Å	13.811(2)	15.856(2)	27.221(2)	22.994(5)
β/°	96.441(4)	94.218(4)	100.299(2)	86.076(14)
V/Å^3	2421.1(7)	4489.6(11)	3456.3(4)	4608.8(13)
Z	2	2	2	2
T/K	223(2) K	293(2)	223(2)	223(2) K
Measured reflections	12 364	36 858	27 056	36 645
Independent reflections	8000	8164	6323	16 758
Rint	0.0318	0.0740	0.0476	0.0601
Parameters	456	402	309	699
R1 [I > 2σ(I)]	0.036	0.0411	0.0474	0.0584
wR2 (all data)	0.0700	0.1350	0.0869	0.1418
Goodness of fit	0.977	1.013	1.193	1.127

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Results and discussion

Syntheses and IR spectra

Title compounds were prepared by the reaction of AgI, KI, MnCl₂·4H₂O and 4,4′-bpy in different mixed polar solvents at ambient temperature (Scheme 1). Reactions of AgI, KI, MnCl₂·4H₂O and 4,4′-bpy in mixed solvents DMF/H₂O and DMSO/H₂O (volume ration 2 : 1) produced compounds [Mn(4,4′-bpy)(DMF)₃(H₂O)]Ag₅I₇·4,4′-bpy (1) and [Mn(4,4′-bpy)(DMSO)₄]₂Ag₁₁I₁₅ (2), respectively. The increase of H₂O in preparation of 2 gave a new compound [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]Ag₁₀I₁₂·2DMSO·2H₂O (3), in which H₂O solvent molecules besides DMSO are integrated in the Mn²⁺ complex as the H₂O molecules occur in 1. The reaction in triple DMF/DMSO/H₂O mixed solvent produced compound [Mn₂(4,4′-bpy)₂(DMF)₅(DMSO)₂(H₂O)]Ag₁₀I₁₄·2DMF (4), simultaneously containing DMF, DMSO and H₂O three coordinated solvent ligands. Summarily, the [Mn(4,4′-bpy)]²⁺ units are solvated by DMF, DMSO and/or H₂O solvent molecules to form mixed coordinated complexes in 1–4. The purity of bulk phases of compounds 1–4 are investigated using powder X-ray diffraction (PXRD). The PXRD patterns of the bulk phases of 1–4 are consistent with the simulated PXRD patterns based on single-crystal XRD data (Fig. S1–S4†), respectively.

Scheme 1 Syntheses of compounds 1–4.

The FT-IR spectra show characteristic absorptions from the DMF, DMSO, and 4,4′-bpy ligands on the Mn²⁺ ions (Fig. S5–S8†). Compounds 1 and 4 show an intense C=O vibration in the frequency range 1655–1663 cm⁻¹. The C–N stretching vibrations are at about 1096 cm⁻¹. The intense absorptions in the frequency range 1010–1013 cm⁻¹ in compounds 2, 3 and 4 are attributed to the S=O vibrations. The vibrations of pyridine ring in compounds 1–4 occur between 1579 cm⁻¹ and 1598 cm⁻¹.

Crystal structures of 1–4

Compound 1 crystallizes in the monoclinic space group P2₁ with two formula units in the unit cell. It consists of a 1-D polymeric iodoargentate anion [Ag₅I₇²⁻]_n, and 1-D polymeric [Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺ counter cation, as well as a free 4,4′-bpy molecule. The Mn²⁺ ion binds three DMF and one H₂O molecules, forming a [Mn(DMF)₃(H₂O)]²⁺ fragment. The [Mn(DMF)₃(H₂O)]²⁺ fragments are bridged by a 4,4′-bpy ligand, generating the linear coordination polymer {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺}_n (Fig. 1). The Mn²⁺ ion is in a slightly distorted octahedral geometry with axial angles in the range of 175.1(3)–177.7(3)° (Table S1†). The Mn–N bond lengths are 2.303(7) and 2.314(7) Å, while the Mn–O bond lengths are in 2.138(7)–2.184(8) Å (Table S1†). The Mn–N and Mn–O bond lengths are in accordance with those of Mn-complexes containing bpy and DMF ligands, respectively.¹¹

Fig. 1 Crystal structure of the coordination polymer {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺}_n in 1 with labeling scheme. Hydrogen atoms are omitted for clarity.

The [Ag₅I₇²⁻]_n polymeric anion contains five crystallographically independent Ag⁺ ions, and seven iodine anions (Fig. 2). All Ag(I) ions are coordinated to four iodine anions at distances in the range of 2.7461(11)–3.1878(12) Å, forming distorted tetrahedral AgI₄ units with I–Ag–I angles in the range of 95.43(3)–127.25(3)° (Table S1†). The bond lengths and bond angles of the AgI₄ tetrahedra are in agreement with those of reported iodoargentates.^3–7 As shown in Fig. 2, four AgI₄ (containing Ag2, Ag3, Ag4, Ag5) units are connected by sharing common edges to form a circular Ag₄I₉ fragment, in which I1 shares the four Ag⁺ ions. The Ag₄I₉ fragments are joined by the fifth Ag(1)I₄ unit via sharing I1, I2, I3, and I4 atoms, to form the 1-D [Ag₅I₇²⁻]_n polymeric anion. There are no terminal iodide anions in the [Ag₅I₇²⁻]_n anion. The iodide anions adopt μ₅-I (I1), μ₃-I (I2, I3, I4) and μ-I (I5, I6, I7) bridging coordination modes to the Ag(I) ions. Correspondingly, the Ag–I bond lengths decrease in the order Ag–μ₅-I [av.: 3.0177(10) Å] > Ag–μ₃-I [av.: 2.8737(10) Å] > Ag–μ-I [av.: 2.7738(11) Å]. Short Ag⋯Ag distances of 3.1181(14) and 3.1986(14) Å, which are shorter than the sum of the van der Waals radii of 3.44 Å,¹² are observed in the [Ag₅I₇²⁻]_n chain (Table S1†), indicating metal–metal interactions.

Fig. 2 Crystal structure of the [Ag₅I₇²⁻]_n chain in 1 with the labeling scheme.

In 1, the free 4,4′-bpy molecules run along the {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺}_n chain. The pyridine planes of the coordinated and free 4,4′-bpy molecules are parallel to each other, with interplane distance of 3.361 Å, indicating weak π–π stacking interaction (Fig. S9†). The free 4,4′-bpy molecules are connected end to end by the H₂O molecules of {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺}_n via N–H⋯O [N⋯O: 2.742(10), 2.777(12) Å] (Table S5†) interactions. As a result, a cationic chain {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺·4,4′-bpy}_n is formed (Fig. S9†). The cationic {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺·4,4′-bpy}_n and anionic [Ag₅I₇²⁻]_n chains run perpendicular to each other, forming a penetrating crystal lattice work (Fig. 3 and S10†).

Fig. 3 View of 1 along the b axis. The AgI₄ units are shown as blue tetrahedra. Hydrogen atoms are omitted for clarity.

Compound 2 crystallizes in the monoclinic space group P2₁/n (Table 1). It is composed of polymeric {[Mn(4,4′-bpy)(DMSO)₄]²⁺}_n cation, and [Ag₁₁I₁₅⁴⁻]_n anion. Four DMSO molecules coordinate to the Mn²⁺ ion via O-donor atom, forming a [Mn(DMSO)₄]²⁺ unit. The [Mn(DMSO)₄]²⁺ units are joined by 4,4′-bpy ligands, generating a novel zigzag coordination polymer {[Mn(4,4′-bpy)(DMSO)₄]²⁺}_n (Fig. 4). The Mn²⁺ ion forms a slightly distorted octahedron MnN₂O₄ with axial angle in the range of 171.1(5)–79.2(6)° (Table S2†). Unlike the 4,4′-bpy ligand in 1 which connects the [Mn(DMF)₃(H₂O)]²⁺ fragments into a linear coordination polymer {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺}_n (Fig. 1), the 4,4′-bpy ligand leads to a zigzag coordination polymer {[Mn(4,4′-bpy)(DMSO)₄]²⁺}_n (Fig. 4) in which two N atoms are at the cis position of the MnN₂O₄ octahedron. The Mn–N and Mn–O bond lengths are similar to the corresponding bond lengths in 1 (Table S1 and S2†). Compound 2 contains five and a half crystallographically independent Ag⁺ ions, and seven and a half iodine anions (Fig. 5). All Ag⁺ ions are tetrahedrally coordinated to four iodine anions at distances in the range of 2.800(3)–3.052(3) Å. Five AgI₄ (containing Ag1, Ag2, Ag3, Ag4, Ag5) units are connected by sharing common edges to form an Ag₅I₁₀ fragment, in which I1 shares four Ag⁺ ions. The Ag₅I₁₀ fragments are joined by the Ag(6)I₄ units via sharing I3, I4, I6 (concerning Ag2, Ag3, Ag5), and I3, I6, I7 (concerning Ag1, Ag4, Ag5) atoms, to form the 1-D [Ag₆I₁₂]_n chain. Two [Ag₆I₁₂]_n chains are joined by sharing μ-I8, forming a novel ladder-shaped [Ag₁₁I₁₅⁴⁻]_n polymeric anion (Fig. 5). The [Ag₁₁I₁₅⁴⁻]_n polymeric anion contains 12-membered Ag₆I₆ rings. Iodine anions adopt μ-I (I2, I8), μ₃-I (I3, I5, I6) or μ₄-I (I1, I4, I7) bridging coordination modes in the [Ag₁₁I₁₅⁴⁻]_n chain (Fig. 6).

Fig. 4 Crystal structure of the zigzag polymer of {[Mn(4,4′-bpy)(DMSO)₄]²⁺}_n in 2 with labeling scheme. Hydrogen atoms are omitted for clarity.

Fig. 5 Crystal structure of the [Ag₁₁I₁₅⁴⁻]_n chain in 2 with the labeling scheme.

Fig. 6 View of 2 along the a axis. The AgI₄ units are shown as blue tetrahedra. Hydrogen atoms are omitted for clarity.

Compound 3 crystallizes in the monoclinic space group P2₁/c (Table 1). It consists of a mononuclear [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]²⁺ cation, and [Ag₁₀I₁₂²⁻]_n polymeric anion, as well as two DMSO and H₂O molecules. The Mn²⁺ ion is coordinated by two 4,4′-bpy, two DMSO, and two H₂O molecules, forming an octahedral [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]²⁺ cation (Fig. 7). Unlike the 4,4′-bpy in 1 and 2, which coordinates to Mn²⁺ ion as a bidentate bridging ligand, the 4,4′-bpy in 3 binds the Mn²⁺ ion with a monodentate coordination mode. As a result, The Mn²⁺ ion forms a mononuclear complex cation. The Mn–N and Mn–O bond lengths are consistent with corresponding bond lengths observed in compounds 1 and 2 (Table S1–S3†). Compound 3 contains five crystallographically independent Ag⁺ ions, and six iodine anions (Fig. 8a). Five AgI₄ units are connected end to end by sharing common edges to form a circular Ag₅I₁₂ asymmetrical unit containing a pentagram shaped ring, in which I1 shares the five Ag⁺ ions. The Ag₅I₁₂ units are interjoined by sharing I2, I3, I4, I5, and I6 atoms, to form the 1-D [Ag₁₀I₁₂²⁻]_n polymeric anion (Fig. 8b). All I1 anions in the [Ag₁₀I₁₂²⁻]_n chain are in the same line, and the pentagrams stack along the line. In the [Ag₁₀I₁₂²⁻]_n chain, the iodine anions adopt μ₃-I (I2–I6) or μ₅-I (I1) bridging coordination modes. The [Ag₁₀I₁₂²⁻]_n chain is isostructural with the iodoargentate anion observed in {[Ni(2,2′-bpy)(THF)₂(H₂O)₂](Ag₁₀I₁₂)·2DMF}_n, which contains a solvated [Ni(2,2′-bpy)]²⁺ unit.⁶

Fig. 7 Crystal structure of the [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]²⁺ cation in 3 with labeling scheme. Hydrogen atoms are omitted for clarity.

Fig. 8 (a) Crystal structure of Ag₅I₁₂ asymmetrical unit with the labeling scheme in 3. (b) Crystal structure of the [Ag₁₀I₁₂²⁻]_n chain in 3.

In 3, [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]²⁺, DMSO and H₂O are connected into a cationic layer perpendicular to the a axis via O–H⋯O [O⋯O: 2.699(9)–2.964(9) Å] and O–H⋯N [O⋯N: 2.811(11) Å] (Table S5†) intermolecular interactions (Fig. S11†). All the [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]²⁺ cations in the same layer run parallel to the c axis (Fig. 9). The [Ag₁₀I₁₂²⁻]_n anionic chains run along the b axis, and are located between the [Mn(4,4′-bpy)₂(DMSO)₂(H₂O)₂]²⁺/DMSO/H₂O cationic layer (Fig. 9).

Fig. 9 (a) View of 3 along the b axis. The AgI₄ units are shown as blue tetrahedra. Hydrogen atoms are omitted for clarity. (b) The [Ag₁₀I₁₂²⁻]_n chain viewed along the b axis.

Compound 4 crystallizes in the triclinic space group P1̄ (Table 1). It consist of a 1-D {[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]⁴⁺}_n polymeric cation, a 1-D [Ag₁₀I₁₄⁴⁻]_n polymeric anion, and two DMF lattice molecules. There are two crystallographically independent Mn²⁺ ions, ten Ag⁺ ions, and fourteen iodine anions in 4. Mn(1)²⁺ is coordinated by two DMF and two DMSO molecules, forming a [Mn(DMF)₂(DMSO)₂]²⁺ unit, while Mn(2)²⁺ is coordinated by three DMF and one H₂O molecules, forming a [Mn(DMF)₃(H₂O)]²⁺ unit. Acting as a bidentate bridging ligand, the 4,4′-bpy molecule interjoins [Mn(DMF)₂(DMSO)₂]²⁺ and [Mn(DMF)₃(H₂O)]²⁺ units to form a zigzag coordination polymer {[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]⁴⁺}_n, in which Mn(1)²⁺ and Mn(2)²⁺ appear alternately (Fig. 10). Both Mn(1)²⁺ and Mn(2)²⁺ are in octahedral geometry with axial angle in the range of 170.8(10)–179.0(10)° and 173.5(12)–176.2(17)°, respectively (Table S4†). Ten AgI₄ units are connected via sharing common edges to form an Ag₁₀I₁₇ asymmetrical unit. The asymmetrical units are interjoined by sharing I3, I4, and I12 atoms, to form the novel 1-D [Ag₁₀I₁₄⁴⁻]_n polymeric anion (Fig. 11). In the [Ag₁₀I₁₄⁴⁻]_n chain, bridging coordination modes of μ-I (I2, I4, I5, I7, I10, I11, I14), μ₃-I (I6, I8) and μ₄-I (I1, I3, I9, I12, I13) are observed. The Ag⋯Ag separates in the [Ag₁₀I₁₄⁴⁻]_n chain are in the range of 2.834(6)–3.195(6) Å, indicating Ag⋯Ag interactions.

Fig. 10 Crystal structure of the zigzag polymer {[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]⁴⁺}_n in 4 with labeling scheme. Hydrogen atoms are omitted for clarity.

Fig. 11 Crystal structure of the [Ag₁₀I₁₄⁴⁻]_n chain in 4.

The zigzag {[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]⁴⁺}_n chains run parallel to the b axis (Fig. 12a), and stack a cationic layer perpendicular to the a axis. The free DMF molecules are located between the chains. Although the Mn²⁺ ions form similar zigzag coordination polymers in 2 and 4, the two compounds show different crystal packing. In 2, the [Ag₁₁I₁₅⁴⁻]_n and {[Mn(4,4′-bpy)(DMSO)₄]²⁺}_n chains are crossed. The [Ag₁₁I₁₅⁴⁻]_n anionic chains are enclosed in the channels between the zigzag {[Mn(4,4′-bpy)(DMSO)₄]²⁺}_n cationic chains, forming a penetrating crystal packing (Fig. 8). Differently, the [Ag₁₀I₁₄⁴⁻]_n anionic chains in 4 are sandwiched between the cationic layers (Fig. 12a) because that the channels between the zigzag {[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]⁴⁺}_n chains are occupied by free DMF molecules, forming a sandwiched structure (Fig. 12b).

Fig. 12 (a) Layered stacking of zigzag {[Mn₂(4,4′-bpy)₂(DMSO)₂(DMF)₅(H₂O)]⁴⁺}_n chains and the free DMF molecules between the chains in 4. (b) View of 4 along the c axis. The AgI₄ units are shown as blue tetrahedra. Hydrogen atoms are omitted for clarity.

A series of binary iodoargentate aggregates have been prepared by using organic cations, TM-complex cations, and Ln-complex cations as counter ions. The structures of these binary iodoargentates range from polyneclear discreted clusters [Ag₂I₅]³⁻,^7a,b [Ag₂I₆]⁴⁻,^3a [Ag₃I₆]³⁻,^7a [Ag₄I₈]⁴⁻,^3b,c,7a 1-D chains [Ag₂I₃⁻]_n,^3c,d [Ag₂I₄²⁻]_n,^3e,f,4 [Ag₄I₆²⁻]_n,^3g [Ag₅I₇²⁻]_n,^3g–i,6 [Ag₆I₉³⁻]_n,^7a,b [Ag₁₀I₁₂²⁻]_n⁶ and [Ag₁₂I₁₆⁴⁻]_n,^3h 2-D layers [Ag₅I₆⁻]_n,^3j [Ag₅I₈³⁻]_n,^7b to 3-D framework [Ag₂I₄²⁻]_n,⁵ depending on the counter ions or crystallization conditions in the syntheses. Now 1-D polymeric iodoargentates [Ag₅I₇²⁻]_n, [Ag₁₁I₁₅⁴⁻]_n, [Ag₁₀I₁₂²⁻]_n, and [Ag₁₀I₁₄⁴⁻]_n were prepared using large Mn(II) complex cations. [Ag₁₁I₁₅⁴⁻]_n and [Ag₁₀I₁₄⁴⁻]_n represent new members of the binary iodoargentate aggregates. Compound 1, 2 and 4 are the first examples of TM-iodoargentates containing both polymeric iodoargentate anoins and polymeric cations. The polymeric anoins and cations in 1 and 2 are penetrated in the crystal packing, which have never been observed in iodoargentates. It is noteworthy that the [Ag₅I₇²⁻]_n anions can be isolated using several discrete counter ions. Now, the 1-D [Ag₅I₇²⁻]_n were obtained with polymeric {[Mn(4,4′-bpy)(DMF)₃(H₂O)]²⁺}_n cation as template in compound 1.

Optical absorption and photoluminescent properties

Solid-state optical absorption spectra of compounds 1–4 were recorded from powder samples at room temperature. The absorption data calculated the reflectance spectra using the Kubelka–Munk function⁹ demonstrate that compounds 1–4 show well-defined abrupt absorption edges from which the band gaps can be estimated as 3.12, 3.07, 3.21, and 3.02 eV for 1–4, respectively (Fig. 13). The band gaps are bigger than those of Ni- and Cu-containing iodoargentates.^7b

Fig. 13 Optical absorption spectra of compounds 1–4.

The luminescent properties of 1–4 were measured on crystalline samples at room temperature (Fig. 14). When excited at 270 nm, 1 and 3 exhibit a strong photoluminescent emission band at 458, and 449 nm, respectively. Compounds 2 and 4 give an emission band at 487 and 475 nm respectively, on excited at 280 nm. According to the results for similar hybrid iodoargentates,^3g,6,13 the emission bands can be assigned to the mixture of metal-to-metal transfer (Ag 5s or 5p-to-Ag 4d) and iodide-to-metal charge transfer (I 5p-to-Ag 4d) and affected by the metal–metal interactions. The emission bands shift to the red from 3 to 1, and to 2 and 4. The red shift was attributed to stronger silver–silver interactions in the [Ag₁₁I₁₅⁴⁻]_n and [Ag₁₀I₁₄⁴⁻]_n chains, manifested by the shorter Ag⋯Ag separates. This situation is similar to the observed red shift from chair (Ph₃P)₄Ag₄I₄ to the cube (Ph₃P)₄Ag₄I₄ with more silver–silver interactions.^13a

Fig. 14 Solid state emission spectra of compounds 1–4 at room temperature. The photoluminescent spectra were excited by 270 nm (1, 3), and 280 nm (2, 4) lights.

Thermal properties

Thermal gravimetric analyses of compounds 1–4 were investigated under a nitrogen atmosphere in the temperature range of 25–500 °C, and the TAG curves are shown in Fig. S12.† Compound 1 decomposes in multi-steps. It loses free 4,4′-bpy molecule (weight loss: theoretical 7.7%, observed 7.5%) between 120 and 215 °C. In the subsequent steps, it loses three DMF and one H₂O ligands in 225–290 °C, and 4,4′-bpy ligand in 300–380 °C. Compound 2 decomposes in two steps. The observed total mass losses of 24.3% corresponds to the losses of eight DMSO (15.1%) and two 4,4′-bpy (7.6%) ligands. Compound 3 starts losing free H₂O molecule at about 100 °C and loses two H₂O and two DMSO molecules before 220 °C. In the subsequent steps, it gradually loses two H₂O and two DMSO ligands, followed by loss of two 4,4′-bpy ligands. The observed total mass losses of 20.7% matches with the theoretical value for complete removal of all the ligands and solvent molecules. Like compound 3, 4 also exhibits a multi-step decomposition process. The total mass losses of 26.7% are in accordance with the removal of two free DMF (3.7%) molecules in the first step, DMF, DMSO and H₂O ligands (13.6%) in the second and third step, and two 4,4′-bpy ligands (7.9%) in the fourth step.

Conclusions

In summary, solvent effects on the system AgI/KI/Mn²⁺/4,4′-bpy were observed. Polymeric iodoargentates 1, 2, 3 and 4 were obtained by the reaction of AgI and KI in different mixed polar solvents and crystallization with large Mn(II) complex cations, indicating the influence of solvated [Mn(4,4′-bpy)]²⁺ cation on the self-assembly of iodoargentates. The [Mn(4,4′-bpy)]²⁺ cations solvatetd with different solvent molecules led to 1-D polymeric iodoargentate anions [Ag₅I₇²⁻]_n, [Ag₁₁I₁₅⁴⁻]_n, [Ag₁₀I₁₂²⁻]_n, and [Ag₁₀I₁₄⁴⁻]_n, among which [Ag₁₁I₁₅⁴⁻]_n and [Ag₁₀I₁₄⁴⁻]_n represent new members of binary iodoargentate aggregates. These results illustrate the potential of using TM complex cations modified by small solvent ligands to tune the structure and compositions of iodometallate anions.

Acknowledgements

This work was supported by the National Natural Science Foundation of P. R. China (nos 21171123), and the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: Selected bond lengths and angles for 1–4, IR spectra, PXRD patterns, structural figures, and TG curves. CCDC 995786–995789. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4ra08121h

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