Near-Infrared Emitters: Stepwise Assembly of Two Heteropolynuclear

Apr 25, 2016 - Two 3d–4d heteropolynuclear clusters with Ag–Zn ratios of 9:2 and 9:4 were stepwise constructed from a robust nonanuclear silver cl...
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Near-Infrared Emitters: Stepwise Assembly of Two Heteropolynuclear Clusters with Tunable AgI:ZnII Ratio Zhi Wang,†,⊥ Gui-Lin Zhuang,‡,⊥ Yong-Kai Deng,† Zhen-Yu Feng,† Zhao-Zhen Cao,† Mohamedally Kurmoo,§ Chen-Ho Tung,† and Di Sun*,† †

Key Lab of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, People’s Republic of China ‡ College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou, 310032, People’s Republic of China § Institut de Chimie de Strasbourg, Université de Strasbourg, CNRS-UMR 7177, 4 Rue Blaise Pascal, 67008 Strasbourg Cedex, France S Supporting Information *

ABSTRACT: Two 3d−4d heteropolynuclear clusters with Ag−Zn ratios of 9:2 and 9:4 were stepwise constructed from a robust nonanuclear silver cluster. Their crystal structures consist of a common bucket-shaped [Ag9(mba)9]9− (H2mba = 2-mercaptobenzoic acid) core with different numbers of ZnII connected by different exo-oriented carboxylates. Most fascinating is the observation of emission (∼703 nm) in the near-infrared (NIR) region at 300 K that may be compared to the related Ag9Zn3 cluster with aliphatic polyamine as auxiliary ligand that emits from the visible (∼580 nm). The shift is associated with the change of ligand field of the 2,2′-bipyridine. The emission intensity and lifetime were dramatically enhanced along with the slight bathochromic shift upon cooling from 300 K to 80 K. The results raise two significant issues: (a) the structural and electronic effects of the secondary metal binding to the metalloligand and the factors influencing the heteropolynuclear cluster assembly and (b) the use of NIR fluorescence, introduced by integrating two luminophores into one heteropolynuclear entity, in detecting free-moving zinc in biological systems both in vivo and in vitro.

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and also found their tunable light emission behaviors.13 In order to further explore heterometallic compounds from larger Ag(I) metalloligands, we innovatively synthesized a nonanuclear [Ag9(mba)9]9− and obtained one Ag−Cu coordination chain and three Ag−Zn clusters.14 Although a series of heteropolynuclear structures have been established based on hexa- and nonanuclear silver metalloligands, in-depth insights into this field are still needed to address several questions including where and how many secondary metal atoms can be immobilized on such metalloligands with up to nine possible binding sites as well as the factors influencing their structural and electronic properties. On the other hand, compared to visible light, NIR light could reduce scattering, enhance the penetration, and lower light absorption and autofluorescence in their use as biosensors and -markers.15 Due to the above advantages, everlasting attention has been devoted to the development of NIR emitters for various applications in the biological imaging and telecommunications areas.16 Organic dyes and lanthanide coordination compounds are the most common materials for NIR emission;17 however, the instability of organic dyes upon light

INTRODUCTION The research field involving rational design and tactical assembly of heteropolynuclear clusters is becoming attractive for their fascinating structures and potential properties, especially those derived from synergetic interactions between the different metal atoms.1 Compared to the serendipitous onepot self-assembly, structure-predictable and -controllable stepwise assembling of extended clusters using directeddesigned metalloligands has witnessed great success.2 Hitherto, metalloligands are mainly metal-pyridinedicarboxylate,3 -Schiff bases,4 -bis(oxamato),5 -tris(triazolyl)borates,6 -α,β-unsubstituted dipyrrin,7 -pyridyl or -carboxyl-decorated porphyrins,8 -pyridyl-decorated β-diketonate,9 and -thiolate,10 which have one to four empty coordination sites for further binding to the secondary metal cations. However, polymetallic clusters as a metalloligand,11 especially those made of AgI, are sporadically investigated and are ripe for further development. First, inspired by [Na6Ag6(mna)6] (H2mna = 2-mercaptonicotinic acid),12 we were attracted by its outstanding structural features: (a) molecular aesthetics; (b) six dangling carboxylates on the periphery capable of coordination to a secondary metal, and (c) excellent water solubility and stability. With regard to the latter two features, we recently used [Ag6(mna)6]6− as a metalloligand to construct two heterometallic coordination networks © XXXX American Chemical Society

Received: January 7, 2016

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DOI: 10.1021/acs.inorgchem.6b00044 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Scheme 1. Schematic Representation of Stepwise Assembly of the Two Heteropolynuclear Clusters Based on a [Ag9(mba)9]9− Metalloligand

radiation and the fixed emission characteristics of lanthanide18 strongly limit their applications. Therefore, stable and tunable NIR materials are urgently needed, and the d6, d8, and d10 metal coordination compounds with extraordinary photophysical properties recently appear to be promising substitutes for those luminophores.19 However, reports of Ag(I) coordination compounds with NIR emission characteristics remain relatively rare until now, and most of the examples are Ag−Ln heterometallic compounds.20 In these respects, we assemble a robust [Ag9(mba)9]9− metalloligand and study its reaction with Zn-2,2′-bipy (2,2′bipyridine) in the presence of different amounts of 4,4′-bipy (4,4′-bipyridine) by the liquid−liquid diffusion method. We isolated two heteropolynuclear clusters with Ag−Zn ratios of 9:2 and 9:4, namely, (NH4)3[Zn(2,2′-bipy)3][Zn2Ag9(mba)9(2,2′-bipy)(H2O)3]·46H2O (1) and [Zn(2,2′bipy)3][Zn4Ag9(mba)9(2,2′-bipy)5(OH)(H2O)2]·2(2,2′-bipy)· 52H2O (2). The bucket-shaped core of the [Ag9(mba)9]9− cluster is maintained in both structures, although the Ag−Zn ratio is dependent on the amount of 4,4′-bipy. Compared to the previously reported {(NH4)2(H2en)0.5[Zn3Ag9(mba)9(en)6]·7H2O (3, en = ethanediamine),14 the conjugated 2,2′-bipy ligand in 1 and 2 effectively shifts the emission band maximum from the visible (∼580 nm) into the NIR (∼710 nm) region. These results not only illustrate the strategy to tune the ratio of metals in the two closely related heteropolynuclear clusters but also provide an avenue to achieve the NIR emission materials.

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gauge were used to realize the variable-temperature measurement in the range 80−300 K. Spectra were collected at different temperatures after a 5 min homeothermy. Time-resolved photoluminescence lifetime measurements were measured on the same instrument using a time-correlated single-photon counting technique after excitation at 460 nm with a diode laser excitation. Synthesis of 1. To 3 mL of an aqueous solution of AgNO3 (85 mg, 0.5 mmol) was added H2mba (77 mg, 0.5 mmol) in a beaker. The precipitate was dissolved by dropwise addition of aqueous NH3 (25%) until a clear yellow solution (solution A) was formed. Then, 4 mL of a water/ethanol (v/v = 1:1) solution of mixed Zn(NO3)2·6H2O (149 mg, 0.5 mmol), 2,2′-bipy (78 mg 0.5 mmol), and 4,4′-bipyridine·2H2O (288 mg 1.5 mmol) in a breaker was subjected to ultrasonic treatment (200 W, 40 kHz) for 20 min at room temperature to give a clear colorless solution (solution B). Fifteen milliliter test tubes (⦶ = 1 cm) were carefully set up for diffusion of the yellow solution A at the bottom with a 1 mL water buffer and the colorless solution B at the top. After leaving the tubes undisturbed at room temperature for 1 week pale yellow rod crystals of 1 were obtained (yield: 68%, based on AgNO3). Anal. Calcd (%) for 1 (C103H205Ag9N11O67S9Zn3): C 29.99, H 5.01, N 3.73, Zn 4.76, Ag 23.53. Found: C 30.15, H 4.86, N 3.89, Zn 4.96, Ag 23.56. Selected IR peaks (cm−1): 3669 (s), 2970 (s), 2880 (m), 1563 (s), 1437 (m), 1365 (s), 1338 (m), 1257 (w), 1016 (m), 747 (m), 711 (m), 648 (m), 478 (m). Synthesis of 2. The procedure for the synthesis of 2 is the same as that for 1, but with 1 mmol of 4,4′-bipyridine·2H2O used. The block yellow crystals were isolated in a yield of 59% based on AgNO3. Anal. Calcd (%) for 2 (C163H252Ag9N20O73S9Zn5): C 37.32, H 4.84, N 5.34, Zn 6.23, Ag 18.50. Found: C 37.41, H 4.50, N 5.55, Zn 6.98, Ag 17.78. Selected IR peaks (cm−1): 3676 (w), 2997 (s), 2893 (m), 1580 (w), 1388 (m), 1240 (w), 1049 (s), 885(w), 753 (m), 620 (w), 473 (w). X-ray Single-Crystal Crystallography. The crystals of 1 and 2 quickly lose the solvents from their lattice once removed from their mother liquors. So intensity data were collected on a Bruker APEX II CCD diffractometer with a graphite-monochromated Cu Kα radiation source (λ = 1.541 78 Å) at 173(2) K, using ω scans to generate 27 sets for 1 and 22 sets for 2 of frames at different ϕ angles with a frame width of 2°. Cell refinement, data reduction, and absorption correction were carried out using the Bruker SAINT software package.21 The intensities were extracted by the program XPREP. The structures were solved by direct methods using SHELXS, and least-squares refinement was done against Fobs2 using routines from the SHELXTL software.22 In order to limit the disorder of the guest molecules in the structures of the 2, SIMU restraints have been applied in the refinement. For 1 and 2, the unit cells contain a large region of disordered solvent water molecules, which could not be modeled as discrete atomic sites; thus we employed PLATON/SQUEEZE23 to produce a set of solvent-free diffraction intensities, which was used for further refinements. Crystal data for both compounds are given in Table 1.

EXPERIMENTAL SECTION

Materials and General Methods. All solvents and reagents were commercially available and are not further purified as received unless otherwise noted. Silver salt was purchased from Nanjing Luxury Catalytic Materials Co., Ltd. IR spectra were recorded on a Nicolet AVATAT FT-IR360 spectrometer as KBr pellets in the frequency range of 400−4000 cm−1. Elemental analyses for C, N, and H were performed on a PerkinElmer 2400 CHN elemental analyzer and, for Ag and Zn, were determined with a PLASMASPEC (I) ICP atomic emission spectrometer. Powder X-ray diffraction (PXRD) data were collected on a Philips X’Pert Pro MPD X-ray diffractometer with Mo Kα radiation equipped with an X’Celerator detector. Thermogravimetric analyses (TGA) were performed on a Netzsch STA 449C thermal analyzer from room temperature to 800 °C under a nitrogen atmosphere at a heating rate of 10 °C/min. UV−vis spectra (diffusereflectance mode) were recorded on a Hitachi U-4100 UV−vis−NIR spectrophotometer at 298 K. Temperature-dependent photoluminescence measurements were carried out in an Edinburgh spectrofluorimeter (F920S) coupled with an Optistat DN cryostat (Oxford Instruments), and the ITC temperature controller and a pressure B

DOI: 10.1021/acs.inorgchem.6b00044 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

bipy) 3 ][Zn 4 Ag 9 (mba) 9 (2,2′-bipy) 5 (OH)(H 2 O) 2 ]·2(2,2′bipy)·52H2O (2). As indicated by X-ray single-crystal diffractions, both clusters 1 and 2 crystallize in the triclinic P1̅ space group, and each unit cell contains two complete molecules related by an inversion center. The bucket-shaped [Ag9(mba)9]9− cores in 1 and 2 are very similar, and the nine mba2− ligands anchored around the core are equally distributed on the upper edge, equatorial position, and lower edge. The mercapto groups of the mba2− ligand on the upper and lower edges exhibit a μ3 coordination mode, whereas those in equatorial position exhibit a μ2-mode. The average Ag−S bond distances are 2.529(2) and 2.543(4) Å for 1 and 2, respectively. Five of the nine carboxylate groups participate in bonding to silver atoms in a unified monodentate mode for 1 and 2 (Ag− O: 2.459(9)−2.541(9) Å for 1 and 2.489(8)−2.547(11) Å for 2). The nonanuclear silver core is constructed by three cornershared tetrahedra, which create a triangle in the center (Figure 1a and b). The Ag···Ag distances are in the range 2.9133(10)−

Table 1. Crystal Data for 1 and 2 empirical formula fw temp/K cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg volume/Å3 Z ρcalc/mg/mm3 μ/mm−1 F(000) reflns collected indep reflns data/params final R indexes [I ≥ 2σ(I)] final R indexes [all data]

C103H205Ag9N11O67S9Zn3 4125.34 173(2) triclinic P1̅ 19.2601(5) 19.7648(6) 21.6077(6) 78.141(2) 82.001(2) 79.392(2) 7868.3(4) 2 1.365 10.797 3166.0 92 301 25 708 [Rint = 0.1178] 25 708/1390 R1 = 0.0798, wR2 = 0.1980

C163H252Ag9N20O73S9Zn5 5246.19 173(2) triclinic P1̅ 20.2213(9) 20.2213(9) 26.3995(12) 107.385(4) 104.141(3) 105.049(4) 9465.5(9) 2 1.502 9.393 4248.0 83 805 30 270 [Rint = 0.1521] 30 270/1950 R1 = 0.0941, wR2 = 0.2185

R1 = 0.1100, wR2 = 0.2169

R1 = 0.1815, wR2 = 0.2578

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RESULTS AND DISCUSSION Synthetic Aspects and General Characterizations. 2Mercaptobenzoic acid, a very simple, inexpensiveness, and commercially available ligand, is a typical model compound for the HSAB (hard and soft acids and bases) principle.24 In H2mba, the S group of high polarizability has a strong tendency to coordinate with the sof t AgI, while the carboxylate group prefers the hard 3d transition metals. We have recently documented the efficacy of similar ligands such as 2mercaptonicotinic acid (H2mna) and 2-mercaptobenzoic acid (H2mba) to assemble [Ag6(mna)6]6− and [Ag9(mba)9]9− metalloligands followed by reaction with 3d transition metals such as CuII and ZnII to give a series of heterometallic coordination networks or clusters.13,14 Motivated by these advances, we were interested in checking the universality of [Ag9(mba)9]9− in assisting such heterometallic ensemblies and investigated more examples to get deeper information on the assembly. Both heteropolynuclear clusters have been synthesized in a stepwise manner without the isolation of the nonanuclear silver cluster and mononuclear ZnII compounds. Upon directly mixing [Ag9(mba)9]9− metalloligands with the Zn-2,2′-bipy component, a white precipitate is immediately formed; thus the solution diffusion method was selected in the stepwise assembly. Regarding the effect of the amount of 4,4′bipy on the assembly, we also performed several comparative experiments by changing the amount of 4,4′-bipy from 0 to 1.75 mmol. The results showed that the best yields, highest purity, and largest crystals were obtained using 1.5 and 1 mmol of 4,4′-bipy for 1 and 2, respectively. The detailed results are summarized in Table S2. Comparison of the PXRD patterns (Figure S1) of polycrystalline samples suggests both 1 and 2 are pure phases. Due to the large amount of crystallization water molecules, 1 and 2 showed quick dehydration even at room temperature. Their TGA curves (Figure S2) show similar weight lost, especially for the dehydration process from 30 to 200 °C. Crystal Structures of (NH 4 ) 3 [Zn(2,2′-bipy) 3 ][Zn2Ag9(mba)9(2,2′-bipy)(H2O)3]·46H2O (1) and [Zn(2,2′-

Figure 1. Structure representations of the clusters in 1 and 2. The bucket-shaped Ag9 core for 1 (a) and 2 (b). The Ag9Zn2 (c) and Ag9Zn4 (d) heteropolynuclear clusters (color code: purple = Ag, green = Zn, yellow = S, red = O, blue = N, gray = C).

3.3370(12) Å and 2.9101(16)−3.2959(17) Å for 1 and 2, respectively, suggesting the important role of argentophilicity in building the clusters.25 There are several differences in the structural features of 1 and 2. The anionic heteropolynuclear clusters are charge-balanced by NH4+ and [Zn(2,2′-bipy)3]2+ for 1 and [Zn(2,2′-bipy)3]2+ for 2. One coordinated water ligand is found in the Ag9 core of 1 but not in 2. The important differences between 1 and 2 are the binding modes and the numbers of coordinated ZnII ions by carboxylate. As shown in Figure 1c, two ZnII ions are captured at adjacent sites by four carboxylates of one [Ag9(mba)9]9− core to form the Ag9Zn2 cluster in 1. The Zn1 with a trigonal-bipyramid geometry (τ5 = 0.61)26 is coordinated by two N atoms from one 2,2′-bipy, two O atoms from two carboxylate groups, and one terminal water, C

DOI: 10.1021/acs.inorgchem.6b00044 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. Luminescence of 1 (a) and 2 (c) as a function of temperature from 80 to 300 K in the solid state under the excitation of 460 nm (insets are photographs of 1 and 2 without irradiation (left) and when irradiated with 365 nm UV light (right) at room temperature). (b and d) Temperature dependence of emission intensity (the red solid lines are linear fitting in the range 80−220 K).

τ2), giving lifetime values of τ1 = 1.72 and τ2 = 11.88 μs for 1 and τ1 = 1.10 and τ2 = 13.00 μs for 2. The microsecond-scale emissive lifetime indicates their phosphorescent nature, possibly associated with a spin-forbidden triplet parentage.29 The absolute luminescent quantum yields were determined by using an integrating sphere to be 2.76% and 1.87% for 1 and 2, respectively, at 298 K. When cooled to 80 K, the maxima emission peaks shift from 703 to 714 nm and 702 to 711 nm, respectively, whereas the lifetime values upon cooling to 80 K increase to τ1 = 44.91, τ2 = 117.63 μs and τ1 = 42.69, τ2 = 108.23 μs for 1 and 2, respectively, suggesting a reduction in the nonradiative decay rate.30 The slightly red-shifted phosphorescent bands suggest that the shrinkage of Ag···Ag contacts upon cooling can lead to a decrease in the energy gap of metal-centered phosphorescence to a certain extent. The unstructured NIR emission bands of 1 and 2 are energetically impossible from π−π* excited states of 2,2′-bipy or mba2−. The contribution of the [Zn(2,2′-bipy)3]2+ cation to the NIR emissions should also be ruled out because its excited state also has a high energy as seen in [Zn(2,2′-bipy)3]SO4 or [Zn(2,2′bipy)3](ClO4)2.31 Thus, the NIR emissions at 703 nm are believed to mainly originate from the 2,2′-bipy → Ag9 ligandto-metal charge-transfer (LMCT) triplet transition mixed with a metal-centered (MC) (d−s/d−p) state modified by argentophilicity.32 When comparing with the emission behavior of 3 ({(NH4)2(H2en)0.5[Zn3(en)6][Ag9(mba)9]·7H2O}, en = ethanediamine),14 we found that when π-delocalized 2,2′-bipy was ligated to ZnII, then anchored on the Ag9 cluster, it could effectively effect the emission change from orange-yellow (579

whereas Zn2 is four-coordinated by two O atoms from two carboxylate and two terminal water molecules to form a tetrahedron (τ4 = 0.9).27 However in 2, two pairs of ZnII ions are captured at the upper and lower edges, respectively; that is, in total four ZnII ions are involved in the formation of the Ag9Zn4 cluster (Figure 1d). The Zn1 adopts an octahedral geometry completed by four N atoms from two 2,2′-bipy and two O atoms from one carboxylate, whereas the remaining three ZnII ions are trigonal bipyramids with a τ5 of 0.66, 0.57, and 0.73 for Zn2−Zn4, respectively. The Zn−N and Zn−O bond lengths are in the ranges 2.105(10)−2.215(9) and 1.952(7)−2.043(7) Å and 2.015(19)−2.201(14) and 2.005(12)−2.341(13) Å for 1 and 2, respectively, which are comparable to related compounds.28 The π···π interaction between 2,2′-bipy and mba2− and hydrogen bonding contribute to the stabilities of the resultant crystal packing of 1 and 2. Regarding the assembly process of 1 and 2, only different amounts of 4,4′-bipy, 1.5 and 1.0 mmol, were added, which may influence the alkaline environments of the upper solution during the diffusion. Although 4,4′-bipy does not appear in the final products, its side-influence on the coordination abilities of carboxylate is clear. As a consequence, the number of captured ZnII are different in 1 and 2, while the metalloligands are kept intact, so the bimetallic ratio is successfully tuned in this system. Luminescent Properties. 1 and 2 exhibit very similar NIR emission at room temperature in the solid state with the λem maxima at ∼703 nm under the excitation of 460 nm (Figure 2). The decay measurements (Figure S4) at 300 K fit the biexponential function I = I0 + A1 exp(−t/τ1) + A2 exp(−t/ D

DOI: 10.1021/acs.inorgchem.6b00044 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry nm) to NIR (703 nm), which indicates the 2,2′-bipy plays a crucial role in inducing the NIR emission. With respect to en, 2,2′-bipy has a larger π-conjugated system, which may promote the charge transfer from 2,2′-bipy to Ag9 at a lower energy level. This effective strategy to realize NIR emission was also observed in some other phosphorescent coordination by expanding the degree of π-conjugation in the ligand.33 From a structural viewpoint, the external ZnII ions bind with the [Ag9(mba)9]9− core through O-bridges of mba, which also provide a suitable route for remote charge transfer between bipy and Ag cluster entities. Although the temperaturedependent photoluminescent shifts were only ca. 10 nm between 80 and 300 K, notably, the maximum emission intensities for 1 and 2 at ∼700 nm display more than 60- and 37-fold enhancement, respectively. Moreover, there are good linear relationships between the maximum emission intensity and temperature for 1 and 2 in the range 220−80 K. The linear relationship can be fitted as a function of T = 927846.5− 3802.9Imax with a correlation coefficient 0.996 for 1 and T = 77318.8−304.6Imax with a correlation coefficient 0.994 for 2. The Imax vs T profile in Figure 2b and d provides their calibration curves as molecular luminescent thermometers in the low-temperature range. In order to identify the emission mechanism, especially the unique effect of 2,2′-bipy in the NIR emission, density function theory calculations were performed (for details see the SI). The initial structures were derived from the results of X-ray singlecrystal diffractions, where the guest molecules and counter cations were removed. Geometrical optimizations were divided into two steps: all hydrogen atoms were relaxed by constraints of other atoms; subsequently, the obtained configurations were fully optimized without any constraints. The final structures were in good agreement with those obtained by X-ray analyses. Furthermore, frontier orbitals were plotted as shown Figure 3. For 1, the HOMO concentrates on the localized p-type dangling orbitals of S atoms and carboxylate of ligands and four d orbitals of Ag, while the LUMO is derived from π-type antibonding orbitals of 2,2′-bipy and localized 3d orbitals of Zn. In 2, both the HOMO and LUMO show similar components to those of 1, respectively. For 3 the HOMO also shows similar components to those of 1 and 2; however, the LUMO involves 4d orbitals of Ag and 3p orbitals of S atoms. Comparing the different populations of frontier orbitals, we can conclude that [Zn(2,2′-bipy)] serves as an antenna to achieve the NIR emission. Accordingly, the transition of 1 and 2 can be attributed to [2,2′-bipy → Ag9] 3LMCT, whereas (mba2− → Ag9) LMCT mixed with some MC transition state is mostly possible for 3. From the view of Kohn−Sham orbital energy, the HOMO−LUMO gaps are 0.88 eV for 1, 0.63 eV for 2, and 1.28 eV for 3. It is observed that the existence of the Zn(2,2′bipy) moiety can effectively reduce the HOMO−LUMO gaps, which may be the important reasons that emission peaks of 1 and 2 more red-shifted than that of 3.

Figure 3. HOMO (a) and LUMO (b) of 1, HOMO (c) and LUMO (d) of 2, and HOMO (e) and LUMO (f) of 3.

energy level induced by the conjugated 2,2′-bipy ligand. The variable-temperature luminescence shows the enhanced emission intensity and elongated lifetime along with the bathochromic shift upon cooling. Our work not only answered how the secondary metal ions bind to a specific multisite metalloligand and the factors influencing the above results in the heteropolynuclear cluster assembly but also provided a combinational strategy to realize NIR emission in one heteropolynuclear entity.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00044. Selected bond lengths and angles of 1 and 2, powder Xray diffraction pattern, TGA curves, IR spectra, solidstate UV−vis absorption spectra, and luminescent lifetimes of 1 and 2, and computational details (PDF) X-ray crystallographic data for 1 and 2 (CIF)

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CONCLUSIONS We have sequentially constructed a couple of 3d−4d heteropolynuclear clusters with metal ratios of 9:2 and 9:4 based on a robust [Ag9(mba)9]9− cluster as metalloligand. The presence of different amounts of 4,4′-bipy during the assembly is responsible for the different metal ratios, although it is not incorporated into the final structures. Compared to previously reported 3, the emission maxima of 1 and 2 shift to the NIR region, which should be ascribed to the decreased LMCT

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. E

DOI: 10.1021/acs.inorgchem.6b00044 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Author Contributions

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Z. Wang and G.-L. Zhuang contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the NSFC (Grant Nos. 21201110 and 21571115), Young Scholars Program of Shandong University (2015WLJH24), and The Fundamental Research Funds of Shandong University (104.205.2.5 and 2015JC045). M.K. is funded by the CNRS-France.

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DOI: 10.1021/acs.inorgchem.6b00044 Inorg. Chem. XXXX, XXX, XXX−XXX