Sensitised near-infrared emission from lanthanides using an iridium complex as a ligand in heteronuclear Ir2Ln arrays

Fang-Fang Chen a, Zu-Qiang Bian *a, Bin Lou a, En Ma b, Zhi-Wei Liu a, Dao-Bo Nie a, Zhu-Qi Chen a, Jiang Bian a, Zhong-Ning Chen b and Chun-Hui Huang *a
aBeijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China. E-mail: chhuang@pku.edu.cn; bianzq@pku.edu.cn; Tel: +86-10-6275-7156
bState Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China

Received 13th June 2008 , Accepted 11th July 2008

First published on 9th September 2008


Abstract

The iridium(III) complex Ir(ppy)2(phen5f) [ppy = 2-phenylpyridinato-N,C2′, and phen5f = 4,4,5,5,5-pentafluoro-1-(1′,10′-phenanthrolin-2′-yl)-pentane-1,3-dionate] has been synthesised and used as “complex ligands” to make heteronuclear d–f complexes by the attachment of Ln(NO3)3·xH2O at the vacant coordination sites in the bridging ligand phen5f. The microanalyses and crystal structure characteristics confirmed the formation of the heteronuclear Ir2Ln arrays. The measurement of the lowest triplet state energy level of Ir(ppy)2(phen5f) indicates that it is suitable for the NIR (near-infrared) lanthanide ions, NdIII, YbIIIand ErIII. Upon irradiation of the MLCT (metal-to-ligand charge transfer) absorption of Ir(ppy)2(phen5f) at an excitation wavelength from 380–490 nm, the characteristic emission spectra of the three Ir2Ln arrays (Ln = Nd, Yb, Er) in both the solid state and in CH3CN solution were measured. According to the results, more IrIII complexes will be designed for lanthanide NIR emission by the proper combination between the cyclometalated ligand and the tetradentate ancillary ligand.


Introduction

Lanthanide ions, such as NdIII, YbIII and ErIII, are well-known near-infrared (NIR) emitters with excellent luminescence properties due to the characteristics of their f–f transitions, including lifetimes in the microsecond time domain and narrow bandwidth emissions in the 900–1600 nm region. They have become a hot topic of research because of their potential applications in many areas such as optical communication,1 medical imaging and biological labelling.2 To obtain a highly efficient NIR luminescence, many organic chromophores, as high absorbing sensitisers, were introduced to LnIII complexes due to the low extinction coefficients of their f–f absorptions.3 On the other hand, the use of strongly absorbing d-block chromophores as sensitisers for the NIR emissions from lanthanides have attracted more and more attention since van Veggel and co-workers reported the first example of NdIII and YbIII luminescence sensitised by the transition metal complexes Ru(bpy)32+ and ferrocene in 2000.4 Subsequently, many d-block chromophores, based on related transition metals, such as PtII,5,6RuII,7ReI,8OsII,9PdII,10ZnII,11CrIII12 and CoIII13 sensitising NIR lanthanides (NdIII, YbIII and ErIII) were extensively studied. Because most of the energy levels of these d-block chromophores are around 13[thin space (1/6-em)]000–18[thin space (1/6-em)]000 cm−1, energy transfers from the transition metals to the lanthanide ion centers are most efficient and the characteristic emission from these NIR lanthanides were successfully obtained.

However, the IrIII ion, as a very important member of the transition metals, has not been used much for NIR lanthanide luminescence, though the energy transfer from the IrIII moiety to the EuIII complex has been studied,14,15 and the only example, regarding the NIR emission of an IrIII–YbIII complex has recently been reported by De Cola and co-workers.16 In fact, as important phosphorescent materials, many IrIII complexes with different energies of the lowest excited states have been extensively investigated by modifying cyclometalated ligands,17,18 which give us a good strategy to seek more suitable IrIII complexes to sensitise NIR lanthanide ions.

Recently, we reported an IrIII complex Ir(dfppy)2(phen5f) as a complex ligand, which can efficiently sensitise EuIII.15 In this work, we have changed the cyclometalated ligand from dfppy [2-(4′,6′-difluorophenyl)-pyridinato-N,C2′] to ppy (2-phenylpyridinato-N,C2′) in order to decrease the triplet energy level of the whole d-block complex ligand and make it more suitable for the NIR LnIII (Ln = Nd, Yb, Er) ions.19 As shown in Scheme 1, the d-block “complex ligand” used is Ir(ppy)2(phen5f), in which phen5f = 4,4,5,5,5-pentafluoro-1-(1′,10′-phenanthrolin-2′-yl)-pentane-1,3-dionate.15 The hetero-trinuclear Ir2Ln arrays (Ln = Nd, Yb, Er, Gd, Eu) have been obtained by the reaction of Ir(ppy)2(phen5f) and Ln(NO3)3·xH2O. We will describe the structural and photophysical properties of Ir(ppy)2(phen5f) and the Ir2Ln arrays in this paper.


Synthetic route of the Ir2Ln arrays.
Scheme 1 Synthetic route of the Ir2Ln arrays.

Results and discussion

Syntheses and structures

The complex Ir(ppy)2(phen5f) was prepared from a reaction of the chloride-bridged IrIII dimer (ppy)2Ir(μ-Cl)2Ir(ppy)2 and the ligand Hphen5f under similar conditions to those for the synthesis of Ir(C⁁N)2(O⁁O),18 which was also very similar to the synthesis of Ir(dfppy)2(phen5f).15

The crystals of Ir(ppy)2(phen5f) were obtained from a slowly evaporating solution of acetone (Fig. 1a). The central ion IrIII is six coordinated by two carbon atoms and four nitrogen atoms, very similar to the complex Ir(dfppy)2(phen5f).15 Herein, the C⁁N sites arise from two cyclometalated ppy ligands and the N⁁N sites are contributed by the ancillary ligand phen5f. The Ir–C and Ir–N bonds in Ir(ppy)2(phen5f) (Table 1) are also similar to those in Ir(dfppy)2(phen5f). Furthermore, the Ir–N bond lengths between the IrIII ion and the ancillary ligand phen5f is longer than those between the IrIII ion and the cyclometalated ligand ppy, which showed that the combination of the IrIII ion and the C⁁N ligand anion was tighter than that of the IrIII ion and the N⁁N ancillary ligand.

Table 1 Selected bond lengths and angles for Ir(ppy)2(phen5f)
Selected bond lengths/Å Selected angles/°
Ir(1)–C(22) 1.998(11) C(22)–Ir(1)–N(2) 80.8(4)
Ir(1)–N(2) 2.052(7)  
Ir(1)–C(11) 2.028(8) C(11)–Ir(1)–N(1) 80.6(3)
Ir(1)–N(1) 2.063(7)  
Ir(1)–N(3) 2.166(7) N(3)–Ir(1)–N(4) 76.1(3)
Ir(1)–N(4) 2.239(7)  



ORTEP diagrams of Ir(ppy)2(phen5f) (a) and [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3 (b). The hydrogen atoms and solvent molecules are omitted for clarity.
Fig. 1 ORTEP diagrams of Ir(ppy)2(phen5f) (a) and [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3 (b). The hydrogen atoms and solvent molecules are omitted for clarity.

The bimetallic complexes [(ppy)2Ir(μ-phen5f)]2Ln(NO3)3 (Ln = Nd, Yb, Er, Gd, Eu) were simply obtained by mixing a 2 : 1 molar ratio of Ir(ppy)2(phen5f) and Ln(NO3)3·xH2O in a MeOH solution and allowing the MeCN–MeOH solution by slow diffusion of Et2O. X-Ray quality crystals were obtained for Ln = Nd. The structure and metric parameters of [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3 are shown in Fig. 1b and Table 2. The NdIII ion is ten coordinated by ten oxygen atoms, in which four oxygen atoms come from two β-diketate fragments in Ir(ppy)2(phen5f) while the other six oxygen atoms come from the three nitrates. The IrIII complex ligands in [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3 are similar to the individual IrIII complex according to the comparison between the corresponding bond lengths and angles (Table 1 and Table 2). It is important that the configuration of the two carbonyl groups in the β-diketate has been changed from the trans form to the cis form upon coordination. The non-bonding distances for Nd⋯Ir are 6.170 and 6.216 Å, which may efficiently improve the d→f energy transfer in the hetero-bimetallic complex.20

Table 2 Selected bond lengths and angles for [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3
Selected bond lengths/Å Selected angles/°
Nd(1)–O(1) 2.436(7) O(1)–Nd(1)–O(2) 69.1(3)
Nd(1)–O(2) 2.458(8)  
Nd(1)–O(3) 2.447(8) O(3)–Nd(1)–O(4) 69.4(3)
Nd(1)–O(4) 2.479(7)  
Nd(1)–O(6) 2.556(8) O(6)–Nd(1)–O(5) 49.8(2)
Nd(1)–O(5) 2.576(8)  
Nd(1)–O(9) 2.589(9) O(9)–Nd(1)–O(8) 49.6(3)
Nd(1)–O(8) 2.603(9)  
Nd(1)–O(12) 2.522(9) O(12)–Nd(1)–O(11) 49.9(3)
Nd(1)–O(11) 2.575(9)  
Ir(1)–C(35) 1.996(11) C(35)–Ir(1)–N(4) 80.8(4)
Ir(1)–N(4) 2.054(9)  
Ir(1)–C(24) 2.024(12) C(24)–Ir(1)–N(3) 79.7(4)
Ir(1)–N(3) 2.065(9)  
Ir(1)–N(1) 2.168(10) N(1)–Ir(1)–N(2) 76.6(4)
Ir(1)–N(2) 2.204(11)  
Ir(2)–C(63) 2.004(14) C(63)–Ir(2)–N(7) 80.0(5)
Ir(2)–N(7) 2.058(10)  
Ir(2)–C(74) 2.016(11) C(74)–Ir(2)–N(8) 79.4(4)
Ir(2)–N(8) 2.060(9)  
Ir(2)–N(5) 2.127(9) N(5)–Ir(2)–N(6) 77.8(4)
Ir(2)–N(6) 2.195(10)  


The ESI-MS spectra of the Ir2Ln complexes also support the formula of a relative heterometallic molecule (Table 3). For the Ir2Nd complex, the ESI-MS spectrum exhibits a peak at m/z 970.00, corresponding to the major species {[(ppy)2Ir(μ-phen5f)]2Nd(NO3)}2+, indicating that this discrete molecule exists in solution. Similarly, the peaks at m/z 985.08, 982.05 and 978.00 in the ESI-MS spectra, also suggest the formation of {[(ppy)2Ir(μ-phen5f)]2Ln(NO3)}2+ (Ln = Yb, Er, Gd) in solution, respectively.

Table 3 Molecular peaks of the Ir2Ln arrays in DMSO
Ir2Ln Cation m/z
Ir2Nd {[(ppy)2Ir(μ-phen5f)]2Nd(NO3)}2+ 970.00
Ir2Yb {[(ppy)2Ir(μ-phen5f)]2Yb(NO3)}2+ 985.08
Ir2Er {[(ppy)2Ir(μ-phen5f)]2Er(NO3)}2+ 982.05
Ir2Gd {[(ppy)2Ir(μ-phen5f)]2Gd(NO3)}2+ 978.00


Photophysical properties

When compared with the bimetallic complex {[(dfppy)2Ir(μ-phen5f)]3EuCl}Cl2,15 which exhibited highly efficient red emission, the complex [(ppy)2Ir(μ-phen5f)]2Eu(NO3)3 showed hardly any observable emission from EuIII (Fig. 2). It is implied that the ligand change from dfppy to ppy should decrease the lowest triplet energy level of the whole IrIII complex to a great extent. Therefore, we recorded the low temperature emission of [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 in an EtOH rigid-matrix under the same experimental conditions as for the measurement of {[(dfppy)2Ir(μ-phen5f)]3GdCl}Cl2.15 From the phosphorescence spectra of [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 in solution at 77 K (Fig. 2), the triplet energy level of Ir(ppy)2(phen5f) was obtained as 2.19 eV (1.76 × 104 cm−1),21 which was much lower than the triplet energy level of Ir(dfppy)2(phen5f) (2.64 eV, 2.12 × 104 cm−1). It was obvious that Ir(ppy)2(phen5f) should be more suitable for sensitising the NIR lanthanide ions NdIII, YbIII and ErIII instead of EuIII.

            Emission spectra of {[(dfppy)2Ir(μ-phen5f)]3GdCl}Cl2 (red dash), and [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 (black dash) in an EtOH rigid-matrix (1 × 10−5 M) at 77 K, and {[(dfppy)2Ir(μ-phen5f)]3EuCl}Cl2 (red solid), and [(ppy)2Ir(μ-phen5f)]2Eu(NO3)3 (black solid) in CH3CN (1 × 10−5 M) at room temperature.
Fig. 2 Emission spectra of {[(dfppy)2Ir(μ-phen5f)]3GdCl}Cl2 (red dash), and [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 (black dash) in an EtOH rigid-matrix (1 × 10−5 M) at 77 K, and {[(dfppy)2Ir(μ-phen5f)]3EuCl}Cl2 (red solid), and [(ppy)2Ir(μ-phen5f)]2Eu(NO3)3 (black solid) in CH3CN (1 × 10−5 M) at room temperature.


            UV-vis absorption spectra of Ir(ppy)2(phen5f) (black line) and heteronuclear Ir2Ln arrays (Ln = Gd (red), Nd (blue), Yb (green) and Er (orange)) in CH3CN (1 × 10−5 M).
Fig. 3 UV-vis absorption spectra of Ir(ppy)2(phen5f) (black line) and heteronuclear Ir2Ln arrays (Ln = Gd (red), Nd (blue), Yb (green) and Er (orange)) in CH3CN (1 × 10−5 M).

The UV-vis absorption spectrum of Ir(ppy)2(phen5f) in CH3CN (Fig. 3) shows a high energy band (π–π*) from 220–300 nm, which may originate from the cyclometalated ligand ppy and the ancillary ligand phen5f, while the weaker absorption tail from 440–480 nm (centered at ca. 466 nm) should be assigned to the 3MLCT transition in the Ir(ppy)2+ moiety22 and Ir to phen5f (N⁁N) ligand.15 Moreover, the absorption spectra of the bimetallic complexes Ir2Ln (Ln = Nd, Yb, Er, Gd) are obviously similar in shape but different in absorbance to that of Ir(ppy)2(phen5f) at room temperature due to the weak absorption from Ln(NO3)3. The extinction coefficients of the bimetallic complexes Ir2Ln are about two times higher than those of Ir(ppy)2(phen5f), as expected (Table 4), which also shows the adduct formation of Ir(ppy)2(phen5f) and Ln(NO3)3 in a ratio of 2 : 1.

Table 4 The absorbance peaks and extinction coefficients for the Ir complex and bimetallic complexes
Complex Absorbance λ/nm (logε)
Ir 229 (4.7), 266 (4.8), 377 (3.8), 415 (3.5), 464 (2.9)
Ir2Nd 228 (5.0), 252 (5.0), 267 (5.0), 380 (4.2), 416 (3.8), 467 (3.2)
Ir2Yb 230 (5.0), 252 (5.0), 268 (5.0), 379 (4.2), 417 (3.8), 465 (3.2)
Ir2Er 228 (5.0), 251 (5.0), 268 (5.0), 380 (4.2), 418 (3.8), 467 (3.2)
Ir2Gd 229 (5.0), 253 (5.0), 268 (5.0), 378 (4.2), 415 (3.8), 465 (3.2)


All the complexes, Ir(ppy)2(phen5f) and Ir2Ln (Ln = Nd, Yb, Er, Gd) in CH3CN, showed hardly any observable emission in the visible region at room temperature. However, they exhibited quite different solid state luminescence behaviour (Fig. 4). Under excitation at 450 nm, the powdered Ir(ppy)2(phen5f) luminesced yellow-green with a maximum at ca. 553 nm, which might originate from face-to-face π–π interactions between the aromatic molecules in the solid state and be ascribed to an excimer formation.22 The crystal packing for Ir(ppy)2(phen5f) is shown in Fig. 5. The crystal packing (a) shows that the π–π spacing between the phen5f ligands of adjacent molecules is ca. 3.55 Å, and the crystal packing (b) shows that the middle parts of the two phenanthroline rings are almost face-to-face with some extent of π–π overlap. Moreover, the angle between the two phenanthroline rings is about 1.6° (Table 5), which confirms that the two planes are near parallel. The solid state luminescence of the Ir2Gd complex undergoing excitation with an absorption range from 400–490 nm exhibited a broad and structureless emission at 638 nm, which should also arise from the intermolecular interactions including not only the π–π interactions between the phen5f ligands but also the π–π interactions between the ppy ligands (Fig. 6 and Table 5). Because the crystal structure of [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 has not been obtained, we will take [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3 as a reference to discuss the packing of this class of complex in the solid state. The crystal packing (a) shows that the π–π spacing between the phen5f ligands of adjacent molecules is ca. 3.58 Å with an angle between them of 1.4°, and the crystal packing (b) shows that the π–π spacing between the parallel ppy ligands of adjacent molecules is ca. 3.45 Å. The latter caused the red shift in the emission maximum for the bimetallic Ir2Gd arrays compared with that for the monomeric Ir(ppy)2(phen5f). Moreover, the emission spectra of Ir(ppy)2(phen5f) and Ir2Gd complexes in solution at 77 K are fairly overlapping (Fig. 7), which also supports the hypothesis that their solid state luminescence originates from the π–π interactions and the formation of the excimer.

Table 5 Crystal packing data for Ir(ppy)2(phen5f) and [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3
Complex λ em/nm π–π spacing Distance/Å Anglea
a It presents the angle between two phen5f planes or two ppy planes.
Ir 553 phen5f 3.55 1.6
Ir2Nd 638 phen5f 3.58 1.4
ppy 3.45 0.0



Solid state emission spectra (powdered samples) in the visible region of Ir(ppy)2(phen5f) (black) under excitation at 450 nm and heteronuclear Ir2Ln arrays (Ln = Gd (red), Nd (blue), Yb (green) and Er (orange)) at room temperature under excitation at 490 nm.
Fig. 4 Solid state emission spectra (powdered samples) in the visible region of Ir(ppy)2(phen5f) (black) under excitation at 450 nm and heteronuclear Ir2Ln arrays (Ln = Gd (red), Nd (blue), Yb (green) and Er (orange)) at room temperature under excitation at 490 nm.

Crystal packing for Ir(ppy)2(phen5f).
Fig. 5 Crystal packing for Ir(ppy)2(phen5f).

Crystal packing for [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3.
Fig. 6 Crystal packing for [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3.


            Emission spectra of Ir(ppy)2(phen5f) (black) and [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 (red) in an EtOH rigid-matrix (1 × 10−5 M) at 77 K.
Fig. 7 Emission spectra of Ir(ppy)2(phen5f) (black) and [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 (red) in an EtOH rigid-matrix (1 × 10−5 M) at 77 K.

As the LnIII ion was changed from GdIII to other LnIII (Ln = Nd, Yb, Er), the emission intensity largely diminished in the Ir2Ln arrays under the same experimental conditions (Fig. 4). It is apparent that an efficient energy transfer occurs from the IrIII moieties to the LnIII (Ln = Nd, Yb, Er) centers. The weighted-average lifetimes of the IrIII-based luminescence decay at 638 nm are 129 ns (Ln = Gd) and <2 ns (Ln = Nd, Yb, Er, almost undetectable). Using the emission lifetimes, we can estimate the IrIII→LnIII energy transfer rates kET from the equation6kET = 1/τq − 1/τu, where τq is the residual lifetime of the IrIII-based emission undergoing quenching by a lanthanide ion, and τu is the “unquenched” lifetime in the reference complex Ir2Gd array, so the IrIII→LnIII energy transfer rates for Nd, Yb, and Er may all be estimated to be above 4 × 108 s−1, which could well imply that all of the Nd, Yb, and Er ions are good quenchers of the IrIII centered emission.

Upon irradiation of the MLCT absorption of the Ir complex at λex from 380–490 nm, the emission spectra of the three Ir2Ln arrays (Ln = Nd, Yb, Er) were measured in both the solid state and the CH3CN solution (Fig. 8, the emission of the solution is not shown due to the analogue of solid). As expected, three strong emission bands were observed at ca. 872 nm, 1057 nm and 1330 nm, corresponding to the 4F3/24I9/2, 4I11/2 and 4I13/2 transitions of NdIII, respectively. For the YbIII complex, there is only one emission band around 978 nm and it is affected by crystal-field splitting, which is assigned to the 2F5/22F7/2 transition. An observed emission band around 1530 nm is attributed to the 4I13/24I15/2 transition for the ErIII complex. Moreover, the quantum yield of the Ir2Yb complex was determined by the equation ΦLn = τobs/τ0, in which τobs is the observed emission lifetime and τ0 is the radiative or ‘natural’ lifetime, 2 ms for YbIII. The luminescence decay of YbIII was measured at 1012 nm in the solid state and at 980 nm in solution, and the lifetimes were 17.9 μs and 22.1 μs, respectively and the corresponding quantum yields were about 1 × 10−2.


Solid state NIR emission spectra (powdered samples) of Ir2Nd (red), Ir2Yb (black) and Ir2Er (blue) arrays.
Fig. 8 Solid state NIR emission spectra (powdered samples) of Ir2Nd (red), Ir2Yb (black) and Ir2Er (blue) arrays.

Conclusions

The proper combination between the cyclometalated ligand (ppy) and the tetradentate ancillary ligand (phen5f) sufficiently decreased the triplet energy level of the whole IrIII complex as a ligand for lanthanide ions. The heteronuclear [(ppy)2Ir(μ-phen5f)]2Ln(NO3)3 (Ln = Nd, Yb, Er) arrays exhibited good quenching properties when compared with the analogous [(ppy)2Ir(μ-phen5f)]2Gd(NO3)3 array. Furthermore, the bridging ligand, phen5f, played an important role in linking the IrIII center to the LnIII center, which made the space separation very close and the energy transfer efficient. The near-infrared emission upon photoexcitation of the IrIII centered antenna chromophore was successfully obtained. According to the results, more IrIII complexes will be designed for lanthanide NIR emission by proper combination between cyclometalated ligands and tetradentate ancillary ligands.

Experimental

Physical measurements

The 1H NMR spectra were recorded using an ARX-400 NMR spectrometer. The chemical shift data for each signal were reported in ppm units with tetramethylsilane (TMS) as the internal reference. Elemental analyses (C, H, N) were performed on a VARIO EL instrument. Mass spectra were recorded on an Ultraflex tandem TOF mass spectrometer and an HPLC-Q-TOF micro mass spectrometer. IR spectra were recorded using a Bio-Rad FTS-65A/896 FTIR system. UV-vis absorption spectra were recorded on a Shimadzu UV-3100 spectrometer. The photoluminescence (PL) spectra were recorded on an Edinburgh Analytical Instruments FLS920 spectrometer.

The steady state near-infrared (NIR) emission spectra were measured on an Edinburgh FLS920 fluorescence spectrometer equipped with a Hamamatsu R5509–72 supercooled photomultiplier tube at 193 K and a TM300 emission monochromator with NIR grating blazed at 1000 nm. The corrected spectra were obtained via a calibration curve supplied with the instrument. The emission lifetimes above 10 μs were obtained by using an Edinburgh Xe900 450 W pulse xenon lamp as the excitation light source. Because the emission lifetimes of the Ir2Nd and Ir2Er arrays are both below 10 μs, accurate lifetime values could not be obtained under the experimental conditions.

Syntheses

[Ir(ppy)2(phen5f)] . (ppy)4Ir2Cl2 (0.5 mmol),23 Hphen5f (1.1 mmol) and anhydrous sodium carbonate (5 mmol) were refluxed in 2-ethoxyethanol under a N2 atmosphere for 12 h. After cooling to room temperature, the mixture was poured into water. The crude product was obtained by filtration and then dissolved in CHCl3. The solution was dried in anhydrous sodium sulfate overnight. After evaporation of the solvent, the residue was purified viachromatography, using an acetone–petroleum ether mixture as the eluent. The pure product was obtained as a yellow powder. Yield: 45%. 1H NMR (400 MHz, DMSO-d6): δ/ppm 8.84–8.70 (m, 2H), 8.53–8.18 (m, 3H), 8.16–8.14 (m, 1H), 8.08–7.73 (m, 6H), 7.68–7.66 (m, 1H), 7.56–7.38 (m, 2H), 7.08–6.96 (m, 1H), 6.88–6.84 (m, 2H), 6.84–6.73 (m, 2H), 6.64–6.44 (m, 1H), 6.13–5.92 (m, 2H), 4.27–4.11 (m, 1H). Anal. calcd for C39H24F5IrN4O2·H2O: C 52.88, H 2.96, N 6.32. Found: C 52.74, H 3.14, N 6.07. MALDI-TOF-MS: m/z 869 [M + H]+. FT-IR: ν/cm−1 3600–3400 (w), 3100–3000 (w), 1609 (m), 1535 (vs), 1481 (s), 1441 (m), 1424 (m), 1323 (m).
[(ppy)2Ir(μ-phen5f)]2Ln(NO3)3 (Ln = Nd, Yb, Er, Gd, Eu). Ir(ppy)2(phen5f) and 0.5 equiv. of Ln(NO3)3·xH2O were stirred in methanol for 6 h to give an orange-red solution. Crystallization from a MeCN–MeOH solution by slow diffusion of Et2O led to microcrystalline [(ppy)2Ir(μ-phen5f)]2Ln(NO3)3.

Anal. calcd for C78H48F10Ir2N11NdO13·H2O: C 44.95, H 2.42, N 7.39. Found: C 45.18, H 2.77, N 7.10. FT-IR: ν/cm−1 3600–3500 (w), 3100–3000 (w), 1622 (s), 1610 (s), 1525 (m), 1480 (vs), 1443 (vs), 1321 (s).

Anal. calcd for C78H48F10Ir2N11O13Yb·H2O: C 44.34, H 2.39, N 7.29. Found: C 44.34, H 2.48, N 7.24. FT-IR: ν/cm−1 3600–3500 (w), 3100–3000 (w), 1610 (s), 1527 (s), 1481 (vs), 1443 (s), 1322 (s).

Anal. calcd for C78H48ErF10Ir2N11O13·3H2O: C 43.72, H 2.54, N 7.19. Found: C 43.43, H 2.66, N 7.23. FT-IR: ν/cm−1 3600–3500 (w), 3100–3000 (w), 1622 (s), 1610 (s), 1480 (vs), 1443 (s), 1322 (s).

Anal. calcd for C78H48F10Ir2N11O13Gd·2H2O: C 44.30, H 2.48, N 7.28. Found: C 44.07, H 2.87, N 7.15. FT-IR: ν/cm−1 3600–3500 (w), 3100–3000 (w), 1610 (s), 1526 (m), 1480 (vs), 1444 (s), 1321 (s).

Anal. calcd for C78H48EuF10Ir2N11O13·H2O: C 44.79, H 2.41, N 7.37. Found: C 44.62, H 2.67, N 7.64. FT-IR: ν/cm−1 3600–3500 (w), 3100–3000 (w), 1610 (s), 1526 (m), 1480 (vs), 1443 (s), 1321 (s).

X-Ray crystallography

The X-ray diffraction data were collected on a Rigaku MicroMax-007 CCD diffractometer by the ω scan technique using graphite-monochromated Mo/Kα radiation. An absorption correction by multi-scan was applied to the intensity data. The structures were solved by direct methods and the heavy atoms were located from E-map. The remaining non-hydrogen atoms were determined from the successive difference Fourier syntheses. The non-hydrogen atoms were refined anisotropically, whereas the hydrogen atoms were generated geometrically with isotropic thermal parameters. The structures were refined on F2 by full-matrix least-squares methods using the SHELXTL-97 program.24 Because the crystal structure of [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3 contained some solvent molecules that were highly disordered, PLATON/SQUEEZE25 was used to correct the data for the presence of the disordered solvent. A summary of the refinement details and resulting factors are given in Table 6.
Table 6 Crystallographic data for the crystal structures
Complex Ir(ppy)2(phen5f) [(ppy)2Ir(μ-phen5f)]2Nd(NO3)3·2.5CH3CN·CH3CH2OCH2CH3
Empirical formula C39H24F5IrN4O2 C87H65.5F10Ir2N13.5NdO14
Formula weight/g mol−1 867.82 2242.67
Temperature/K 293(2) 113(2)
λ 0.71073 0.71070
Crystal system Monoclinic Monoclinic
Space group P21/c P21/c
a 12.612(2) 15.4979(18)
b 17.190(3) 17.028(2)
c 18.641(3) 34.616(4)
β 98.554(3) 90.743(7)
V3 3996.4(13) 9134.3(19)
Z 4 4
D calcd /g cm−3 1.442 1.631
Absorption coefficient/mm−1 3.400 3.555
F(000) 1696 4392
Crystal size/mm 0.14 × 0.10 × 0.06 0.22 × 0.18 × 0.16
Theta range for data collection/° 2.02–25.02 1.68–25.00
Reflections collected/unique 19[thin space (1/6-em)]499/7008 [Rint = 0.0790] 65[thin space (1/6-em)]277/15[thin space (1/6-em)]938 [Rint = 0.0856]
Data/restraints/parameters 7008/313/523 15[thin space (1/6-em)]938/114/1231
Goodness-of-fit on F2 1.098 1.107
Final R indices [I>2σ (I)] R1 = 0.0515, wR2 = 0.1064 R1 = 0.0761, wR2 = 0.1865
R indices (all data) R1 = 0.1168, wR2 = 0.1343 R1 = 0.0925, wR2 = 0.1974


Acknowledgements

The authors are grateful to the National Basic Research Program (2006CB601103) and the NNSFC (20471004, 20221101, 20423005, 20671006) for financial support. The authors also thank Prof. Chun-Ying Duan and Dr Cheng He at Dalian University of Technology for their kind help with the EIS-MS measurements.

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Footnote

CCDC reference numbers 631669 and 648231. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b810016k

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