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Apr 26, 2017 - Tungsten(VI)−Copper(I)−Sulfur Cluster-Supported Metal−Organic. Frameworks Bridged by in Situ Click-Formed Tetrazolate Ligands. Qiu-Fang...
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Tungsten(VI)−Copper(I)−Sulfur Cluster-Supported Metal−Organic Frameworks Bridged by in Situ Click-Formed Tetrazolate Ligands Qiu-Fang Chen,†,‡ Xin Zhao,† Quan Liu,† Ji-Dong Jia,§ Xiao-Ting Qiu,† Ying-Lin Song,§ David James Young,⊥ Wen-Hua Zhang,*,† and Jian-Ping Lang*,†,‡ †

State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, People’s Republic of China ‡ State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China § School of Physical Science and Technology, Soochow University, Suzhou 215006, Jiangsu, People’s Republic of China ⊥ Faculty of Science, Health, Education and Engineering, University of the Sunshine Coast, Maroochydore, Queensland 4558, Australia S Supporting Information *

ABSTRACT: Six analogous two-dimensional (2D) [Tp*WS3Cu3]-based (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate) networks, namely, {[(Tp*WS3Cu3)2L3](μ3N3)}n (2: L = 5-methyltetrazolate (Mtta); 3a: L = 5ethyltetrazolate (Etta)) and {[(Tp*WS3Cu3)2L3]BF4}n (3b: L = Etta; 4: L = 5-propyltetrazolate (Ptta); 5: L = 5butyltetrazolate (Btta); 6: L = 5-pentyltetrazolate (Petta)) were synthesized by reactions of [Et4N][Tp*WS3] (1), [Cu(CH3CN)4]BF4, NaN3, and NH4BF4 in different nitrile solvents (CH3(CH2)nCN, n = 0, 1, 2, 3, and 4) under solvothermal conditions. In the structures of 2−6, each alkyl tetrazolate L as a bridging ligand was generated in situ from the “click” reaction between azide and nitrile. These 2D (6,3) networks support two types of voids wherein the pendant alkyl groups are accommodated. A tetrahedron cage-like cluster [Tp*W(μ3-S)3(μ3-S′)Cu3]4 (7) was also formed in some of the above reactions and can be readily separated by solvent extraction. The proportion of 7 increased with the elongation of the alkyl chains and finally became the exclusive product when heptylnitrile was employed. Further use of CuCN as a surrogate for [Cu(CH3CN)4]BF4 with the aim of introducing additional CN bridges into the network led us to isolate a tetrazolate-free compound, {[Et4N]{(Tp*WS3Cu3)[Cu2(CN)4.5]}2·2PhCH2CN}n (8·2PhCH2CN), a unique 2D network that features {(Tp*WS3Cu3)[Cu2(CN)5]}22−, {(Tp*WS3Cu3)3[Cu3(CN)7]2[Cu(CN)3]}4−, and {(Tp*WS3Cu3)[Cu4(CN)9]}26− ring subunits. Compounds 5−8 are soluble in DMF and exhibit a reverse saturable absorption and self-focusing third-order nonlinear optical (NLO) effect at 532 nm with hyperpolarizability γ values in the range of 4.43 × 10−30 to 5.40 × 10−30 esu, which are 400− 500 times larger than that of their precursor 1. The results provide an interesting insight into the synergetic synthetic strategy related to the assembly of the [Tp*WS3Cu3]2+ cluster core, the “click” formation of the tetrazolate ligands, and the construction of the [Tp*WS3Cu3]2+ cluster-based 2D networks.

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INTRODUCTION The “click” reaction is ubiquitous in biological and materials chemistry, and while a number of reactions qualify for this epithet, the label is generally reserved for the Cu(I)-catalyzed azide−alkyne cycloaddition (CuAAC).1−11 The popularity of this reaction arises from the reaction tolerance of both the azide and alkyne reactants to these mild conditions as well as the reliably high yields of single regioisomer triazole products.12−20 Sharpless et al. also reported the analogous preparation of 5substituted 1H-tetrazoles from nitriles and azides in water.21−24 This “click” formation of 1H-tetrazoles has intriguing applications in the field of metal−organic frameworks (MOFs) because of the rich coordination modes of this kind of ligands, which may ultimately lead to structural diversity of the MOFs.25−34 The charge of a tetrazolate resembles that of a © 2017 American Chemical Society

carboxylate, but the multiple nitrogen donors provide increased stability to the frameworks.35,36 Tetrazolate-ligated MOFs are made by heating a mixture of the metal source, an azide, and a polynitrile, or by direct metal assembly with a presynthesized tetrazole ligand. This protocol permits a variety of different metal ions to be used, generating an array of structures and facilitated by the reasonably high temperatures used for this chemistry. The metal sources are mainly the d10 metal ions such as Zn(II), Cd(II), Cu(I), and Ag(I).34,37−43 Divalent Cu(II) coupled with a reducing reagent such as ascorbic acid has also been used to prepare Cu(I)-based MOFs.44 Received: January 31, 2017 Published: April 26, 2017 5669

DOI: 10.1021/acs.inorgchem.7b00261 Inorg. Chem. 2017, 56, 5669−5679

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Inorganic Chemistry

reactions, isolation, structural characterization, and NLO properties.

One of our ongoing interests is to incorporate Cu(I) into the skeleton of (organo)thiometallates, such as [MOxS4−x]2− (M = Mo, W; x = 0, 1, and 2),45−49 [Cp*MS3]− (Cp* = 1,2,3,4,5pentamethylcyclopentadiene; M = Mo, W),50−53 [TpMoS(S4)]− (Tp = hydridotris(pyrazol-1-yl)borate),54 [Tp*MoS(S4)]−,55 and [Tp*WS3]− (Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate)56−70 to form a set of heterobimetallic polynuclear Mo(W)−Cu−S clusters, as well as the subsequent use of selected clusters as secondary building units (SUBs) in the construction of unique cluster-supported MOFs. These molecular networks can be formed via a one-pot assembly of (organo)thiometalates, Cu(I) sources, and bridging ligands or via a precursor approach from the preformed clusters with defined geometry and connectivity, mixed with the bridging ligands. We have also recently demonstrated the in situ generation of S2− as a single-atom ligand by adding S8 during the reaction to obtain structurally intriguing products that are otherwise inaccessible.57 On the other hand, the third-order nonlinear optical (NLO) properties of those Mo(W)−Cu−S clusters are of particular interest to us.48,56−60,63 This is because NLO materials are relevant to several important sectors relevant to data processing, such as ultrafast optical communication, data storage, optical limiting, logic devices, optical switching, image transmission, and optical computing.71,72 The majority of Mo(W)−Cu−S cluster-based MOFs possess an extensive dπ−pπ delocalized system and dπ−dπ conjugated system and exhibit cubic effects such as third-harmonic generation (THG) or four-wave mixing (FWM), and are promising NLO materials.58 To expand the scope of the in situ ligand formation strategy toward atom economy and inspired by the very recent discovery that the CuAAC reaction proceeds through a synergistic Cu2 cluster process as well as the stability of tetrazolate-ligated MOFs that may result in increased NLO performances,73 we conducted our preliminary study on the formation of the W−Cu−S cluster-based MOFs via a one-pot assembly using [Et4N][Tp*WS3] (1), [Cu(CH3CN)4]BF4, NaN3, and NH4BF4 in different nitriles (CH3(CH2)nCN, n = 0, 1, 2, 3, and 4) under solvothermal conditions. A family of six analogous two-dimensional (2D) [Tp*WS3Cu3]-based networks including {[(Tp*WS3Cu3)2L3](μ3-N3)}n (2: L = 5methyltetrazolate (Mtta); 3a: L = 5-ethyltetrazolate (Etta)) and {[(Tp*WS 3 Cu 3 ) 2 L 3 ]BF 4 } n (3b: L = Etta; 4: L = 5propyltetrazolate (Ptta); 5: L = 5-butyltetrazolate (Btta); 6: L = 5-pentyltetrazolate (Petta)) were obtained. From some of these reactions, a tetrahedral cage-like cluster, [Tp*W(μ3S)3(μ3-S′)Cu3]4 (7), was also separated. We discovered that the presence of Cu(I) in the [Tp*WS3Cu3]2+ cluster core is also effective in promoting “click” reactions between nitrile and azide. The tetrazolates formed in situ could in turn bridge these cluster cores into 2D (6,3) networks. These networks feature two types of voids wherein the pendant alkyl chains are accommodated. We further demonstrated that a similar reaction using CuCN as a replacement for [Cu(CH3CN)4]BF4 in PhCH2CN solution yielded a unique 2D tetrazolate-free network of {[Et 4 N]{(Tp*WS 3 Cu 3 )[Cu 2 (CN) 4 . 5 ]} 2 · 2PhCH2CN}n (8·2PhCH2CN) exhibiting {(Tp*WS3Cu3)[Cu2(CN)5]}22−, {(Tp*WS3Cu3)3[Cu3(CN)7]2[Cu(CN)3]}4−, and {(Tp*WS3Cu3)[Cu4(CN)9]}26− ring subunits. Compounds 5−8 have been investigated as NLO materials and exhibit much higher hyperpolarizability γ values than that of the starting material 1. Described below are their assembly

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EXPERIMENTAL SECTION

General Procedures. [Et4N][Tp*WS3] (1).74 This was prepared by the published procedure and stored under an N2 atmosphere. Anhydrous solvents were purchased and stored over activated 4 Å molecular sieves. Other chemicals were commercially available and used without further purification. A PANalytical X’Pert PRO MPD system (PW3040/60) was used to investigate the powder X-ray diffraction (PXRD) patterns, and other analytical instruments employed were as described in our prior reports.57,59 {[(Tp*WS3Cu3)2(Mtta)3](μ3-N3)}n (2). Method 1: A mixture of 1 (75 mg, 0.1 mmol), [Cu(CH3CN)4]BF4 (188 mg, 0.6 mmol), NaN3 (20 mg, 0.3 mmol), and NH4BF4 (10 mg, 0.1 mmol) in 5 mL of CH3CN was sealed in a Pyrex glass tube. The tube was heated in an oven at 100 °C for 48 h and then cooled to ambient temperature at a rate of 5 °C· h−1 to form black crystals of 2, which were collected by filtration, washed with CH2Cl2, and dried in vacuo. Yield: 66 mg (72% based on W). Anal. Calcd (%) for C36H53B2Cu6N27S6W2: C 23.67, H 2.92, N 20.70. Found: C 23.97, H 3.12, N 20.21. IR (KBr disc): 2991 (w), 2962 (w), 2930 (w), 2853 (w), 2571 (w), 2026 (m), 1547 (s), 1440 (s), 1416 (s), 1350 (s), 1222 (s), 1139 (m), 1073 (m), 1036 (m), 868 (m), 826 (m), 788 (m), 695 (m), 651 (m), 480 (w), 416 (m) cm−1. Method 2: A similar procedure without the presence of NH4BF4 also afforded black crystals of 2, but accompanied by the formation of 7. Compound 7, due to its highly soluble nature in CH2Cl2, can be readily separated from 2 through CH2Cl2 extraction and DMF/Et2O recrystallization to form black crystals. Yield for 2: 9 mg (10% based on W). Yield for 7: 45 mg (56% based on W). Characterization data for 7 are listed as follows. Anal. Calcd (%) for C60H88B4Cu12N24S16W4: C 22.52, H 2.77, N 10.51. Found: C 22.01, H 3.065, N 10.77. UV−vis (DMF, λmax (nm (ε M−1 cm−1))): 336 (25600), 419 (31900). IR (KBr disc): 2968 (w), 2919 (w), 2857 (w), 2561 (m), 2078 (m), 1546 (s), 1439 (m), 1414 (s), 1348 (s), 1218 (s), 1071 (m), 1036 (m), 859 (m), 821 (m), 788 (m), 692 (w), 650 (w), 480 (w), 407 (w) cm−1. {[(Tp*WS3Cu3)2(Etta)3](μ3-N3)}n (3a) and {[(Tp*WS3Cu3)2(Etta)3]BF4}n (3b). A mixture of 1 (75 mg, 0.1 mmol), [Cu(CH3CN)4]BF4 (94 mg, 0.3 mmol), NaN3 (33 mg, 0.5 mmol), and NH4BF4 (10 mg, 0.1 mmol) in 5 mL of CH3CH2CN was sealed in a Pyrex glass tube. The tube was heated in an oven at 100 °C for 48 h and then cooled to ambient temperature at a rate of 5 °C·h−1 to form black crystals of 3a, accompanied by 3b. A small amount of pure 3a was accumulated with a single-crystal X-ray diffractometer by examining the cell parameters of each hand-picked specimen. These crystals were then washed with hexane to remove the grease and subjected to IR testing. IR (KBr disc): 2974 (w), 2917 (w), 2859 (w), 2570 (w), 2026 (m), 1636 (m), 1547 (m), 1438 (s), 1414 (s), 1384 (s), 1348 (m), 1217 (m), 1138 (m), 1072 (m), 1035 (m), 861 (w), 820 (m), 796 (m), 695 (w), 618 (m), 528 (m), 419 (w) cm−1. Pure compound 3b was obtained by the same method described for the preparation of 2 (method 1), but using CH3CH2CN instead of CH3CN. Yield: 70 mg (75% based on W). Anal. Calcd (%) for C39H59B3Cu6F4N24S6W2: C 24.48, H 3.11, N 17.57. Found: C 24.11, H 3.38, N 17.59. IR (KBr disc): 2978 (w), 2920 (w), 2863 (w), 2572 (w), 1548 (s), 1438 (s), 1415 (s), 1346 (s), 1220 (s), 1073 (s), 1034 (s), 861 (m), 820 (m), 691 (w), 652 (w), 445 (w), 419 (m) cm−1. {[(Tp*WS3Cu3)2(Ptta)3]BF4}n (4). A method similar to that (method 1) of 2 except that CH3CN was replaced with CH3(CH2)2CN produced black crystals mixed with 4 and 7, which were filtered and then dissolved in CH2Cl2. Crystals of 4 were collected by filtration, washed with CH2Cl2, and dried in vacuo. Yield for 4: 58 mg (59% based on W). Anal. Calcd (%) for C42H65B3Cu6F4N24S6W2: C 25.79, H 3.35, N 17.19. Found: C 25.74, H 3.59, N 16.99. IR (KBr disc): 2964 (m), 2924 (w), 2873 (w), 2565 (w), 1548 (s), 1439 (s), 1415 (s), 1346 (s), 1220 (s), 1084 (vs), 1033 (s), 861 (m), 820 (m), 695 (w), 650 (w), 483 (w), 416 (m) cm−1. The above filtrate was concentrated to dryness and recrystallized from DMF/Et2O to give black crystals of 7. Yield for 7: 7 mg (9% based on W). 5670

DOI: 10.1021/acs.inorgchem.7b00261 Inorg. Chem. 2017, 56, 5669−5679

Article

Inorganic Chemistry Table 1. Crystal Data and Structure Refinement Parameters for 2−7 and 8·2PhCH2CN formula fw cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Dc/(g cm−3) Z μ (Mo Kα)/mm−1 F(000) total reflns unique reflns no. of observns no. of params Rint R1a wR2b GOFc formula fw cryst syst space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Dc/(g cm−3) Z μ (Mo Kα)/mm−1 F(000) total reflns unique reflns no. of observns no. of params Rint R1a wR2b GOFc

2

3a

3b

4

C36H53B2Cu6N27S6W2 1826.97 trigonal R3̅c 12.5054(6) 12.5054(6) 71.307(5) 90 90 120 9657.4(12) 1.885 6 5.745 5316 85 027 3064 2619 125 0.0427 0.0328 0.0878 1.120 5

C39H59B2Cu6N27S6W2 1869.05 trigonal R3̅ 12.0896(7) 12.0896(7) 81.755(7) 90 90 120 10348.2(15) 1.800 6 5.363 5460 18 442 4370 2861 248 0.1091 0.0991 0.2286 1.117 6

C39H59B3Cu6F4N24S6W2 1913.83 trigonal R3̅c 11.4912(3) 11.4912(3) 93.945(6) 90 90 120 10743.2(9) 1.775 6 5.175 5580 41 259 2980 2363 138 0.0679 0.0304 0.0744 1.003 7

C42H65B3Cu6F4N24S6W2 1955.91 trigonal R3̅c 11.5194(10) 11.5194(10) 94.135(12) 90 90 120 10818(2) 1.801 6 5.141 5724 109 518 3020 2705 155 0.0719 0.0427 0.1187 1.304 8·2PhCH2CN

C15H23.67BCu2F1.33N8S2W0.67 665.99 trigonal R3̅c 11.5288(10) 11.5288(10) 93.891(9) 90 90 120 10807(2) 1.842 18 5.148 5868 112 112 3854 3207 157 0.0614 0.0429 0.1120 1.179

C16H25.67BCu2F1.33N8S2W0.67 680.57 trigonal R3̅c 11.6295(6) 11.6295(6) 93.185(8) 90 90 120 10914.4(14) 1.830 18 5.099 5802 96 444 3040 2715 159 0.0584 0.0423 0.1059 1.162

C60H88B4Cu12N24S16W4 3199.62 tetragonal I41/acd 25.994(17) 25.994(17) 33.868(17) 90 90 90 22884(32) 1.857 8 6.513 12 288 421 140 7115 5339 280 0.1302 0.0353 0.0739 1.219

C63H78B2Cu10N24S6W2 2388.57 triclinic P1̅ 10.255(2) 15.408(3) 15.654(3) 71.90(3) 70.88(3) 70.56(3) 2146.6(10) 1.848 1 5.285 1168 83 465 8746 6247 497 0.1787 0.0826 0.0961 1.100

a R1 = ∑∥Fo| − |Fc∥/∑|Fo|. bwR2 = {∑w(Fo2 − Fc2)2/∑w(Fo2)2}1/2. cGOF = {∑w((Fo2 − Fc2)2)]/(n − p)}1/2, where n = number of reflections and p = total number of parameters refined.

{[(Tp*WS3Cu3)2(Btta)3]BF4}n (5). Compound 5 was prepared as dark crystals in an approach analogous to that described for the preparation of 4 except that CH3(CH2)3CN was used instead of CH3(CH2)2CN. Yield for 5: 30 mg (30% based on W). Anal. Calcd (%) for C15H23.67BCu2F1.33N8S2W0.67: C 27.03, H 3.58, N 16.81. Found: C 26.64, H 3.83, N 16.51. UV−vis (DMF, λmax (nm (ε M−1cm−1))): 315 (31900). IR (KBr disc): 3138 (m), 2962 (m), 2930 (m), 2873 (m), 2565 (m), 1549 (s), 1451 (s), 1415 (s), 1345 (s), 1218 (s), 1083 (vs), 1053 (s), 1031 (s), 868 (m), 819 (m), 691 (m), 650 (m), 480 (w), 413 (m) cm−1. Yield for 7: 16 mg (20% based on W).

{[(Tp*WS3Cu3)2(Petta)3]BF4}n (6). Compound 6 was synthesized in a manner similar to that described for 4, but with CH3(CH2)4CN as a replacement for CH3(CH2)2CN. Yield for 6: 5 mg (5% based on W). Anal. Calcd (%) for C16H25.67BCu2F1.33N8S2W0.67: C 28.24, H 3.80, N 16.47. Found: C 27.98, H 3.891, N 16.70. UV−vis (DMF, λmax (nm (ε M−1 cm−1))): 315 (34400). IR (KBr disc): 2957 (w), 2925 (w), 2867 (w), 2562 (w), 1636 (s), 1550 (s), 1413 (s), 1384 (s), 1343 (s), 1217 (s), 1124 (s), 1084 (vs), 1054 (s), 1031 (s), 861 (w), 812 (m), 695 (w), 624 (w), 520 (w), 480 (w), 412 (w) cm−1. Yield for 7: 40 mg (50% based on W). 5671

DOI: 10.1021/acs.inorgchem.7b00261 Inorg. Chem. 2017, 56, 5669−5679

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Inorganic Chemistry

Scheme 1. Reactions of [Et4N][Tp*WS3] (1) with [Cu(CH3CN)4]BF4 and NaN3 in Various Nitrile Solvents with or without NH4BF4

[Tp*W(μ3-S)3(μ3-S′)Cu3]4 (7). Compound 7 was prepared using a method similar to that of 4 but with CH3(CH2)5CN as a replacement for CH3(CH2)2CN. Yield: 48 mg (60% based on W). {[Et4N]{(Tp*WS3Cu3)[Cu2(CN)4.5]}2·2PhCH2CN}n (8·2PhCH2CN). A mixture of 1 (75 mg, 0.1 mmol), CuCN (54 mg, 0.6 mmol), and NaN3 (20 mg, 0.3 mmol) in 5 mL of PhCH2CN was sealed in a Pyrex glass tube. The tube was heated in an oven at 100 °C for 48 h and then cooled to ambient temperature at a rate of 5 °C·h−1 to form red crystals of 8·2PhCH2CN. The crystals were separated by filtration, washed with CH3CH2OH, and dried in vacuo. Yield: 96 mg (80% based on W). Anal. Calcd (%) for C63H78B2Cu10N24S6W2: C 31.68, H 3.29, N 14.07. Found: C 31.76, H 3.52, N 14.38. UV−vis (DMF, λmax (nm (ε M−1 cm−1))): 316 (44100). IR (KBr disc): 2979 (w), 2912 (w), 2565 (m), 2248 (w), 2122 (vs), 1636 (s), 1547 (s), 1454 (s), 1439 (s), 1413 (s), 1385 (s), 1348 (s), 1225 (m), 1139 (m), 1072 (m), 1034 (m), 1002 (w), 861 (m), 787 (m), 750 (m), 719 (w), 700 (m), 616 (m), 522 (w), 478 (w), 416 (m) cm−1. Single-Crystal X-ray Structure Determination. Measurements were made on a Bruker D8-Quest (2, 3b, 4, 5, 6, 7, and 8· 2PhCH2CN) or an Agilent Xcalibur (3a) CCD X-ray diffractometer by using graphite-monochromated Mo Kα (λ = 0.710 73 Å) radiation. Each single crystal was obtained directly from the above preparations and mounted at the top of a glass fiber in a stream of nitrogen. The programs Bruker SAINT and CrysAlisPro (Agilent Technologies, Ver. 1.171.35.21, 2012) were used for the refinement of cell parameters and the reduction of collected data of 2−7 and 8·2PhCH2CN, respectively, while absorption corrections (multiscan) were applied.75 All the crystal structures were solved by direct methods and refined on F2 using the full-matrix least-squares method in the SHELXTL-2013 programs.76 The H atom on B(1) of 2 was located from the difference Fourier map, and the B−H distance restrained to 1.15 Å with the thermal parameter constrained to Uiso(H) = 1.5Ueq(B). The occupancy factor for the encapsulated N3− was fixed to 0.1667 to obtain a reasonable thermal factor and correct overall charge. For 3a, the H atom on B(1) was added by HFIX 13, and the H atom on B(2) was found from the difference Fourier map. Their B−H distances were restrained to 1.15 Å with thermal parameters constrained to Uiso(H) = 1.5Ueq(B). In 3b, the H atom on B(1) was located from the difference Fourier map and the B−H distance restrained to 1.15 Å with the thermal parameter constrained to Uiso(H) = 1.5Ueq(B). The ethyl group and the BF4− anion lie in a special position of higher symmetry than the molecule can possess. They were treated as a spatial disorder but applying PART −1 and PART 0 in the .ins file with the site occupation factors changed to 0.50 for the atoms. The H atoms on B(1) of 4−6 were located from the difference Fourier map and the B−H distances restrained to 1.15 Å with thermal parameters constrained to Uiso(H) = 1.5Ueq(B). The propyl (4), butyl (5), and pentyl (6) groups displayed a positional disorder with an occupancy factor fixed at 0.25 for each part. The BF4−

anions lie in a special position of higher symmetry than the molecule can possess. They were treated as spatially disordered ones by applying PART −1 and PART 0 in the .ins file with the site occupation factors changed to 0.16667. The H atom on B(1) of 7 was located from the difference Fourier map with its B−H distance restrained to 1.15 Å and thermal parameter constrained to Uiso(H) = 1.5Ueq(B). The H atom on B(1) of 8·2PhCH2CN was added by HFIX 13 first, the B−H distance restrained to 1.15 Å, and thermal parameter constrained to Uiso(H) = 1.5Ueq(B). The [Et4N]+ cation lies on a special position of higher symmetry than the molecule can possess. It was treated as a spatial disorder but applying PART −1 and PART 0 in the .ins file with the site occupation factors changed to 0.50 for the atoms. One CN (C2 and N2) occupied one atom site, and the occupancy factors for both were fixed at 0.50, followed by EXYZ and EADP to constrain their thermal parameters and coordinates. The phenyl ring of the PhCH2CN solvate was constrained to be rigid by AFIX 66. In addition, some spatially delocalized electron densities in the lattice of 2, 3a, 3b, or 7 were found, but acceptable refinement results could not be obtained for them. The solvent contribution was then modeled using SQUEEZE in the Platon program suite.77 Crystallographic data have been deposited with the Cambridge Crystallographic Data Center (CCDC) as supplementary publication numbers 1527250−1527257. These data can be obtained free of charge either from the CCDC via www.ccdc.cam.ac.uk/data_request/cif or from the Supporting Information. A summary of pertinent crystal data and structure refinement parameters of 2−7 and 8·2PhCH2CN are given in Table 1. Third-Order Nonlinear Optical (NLO) Measurements. Compounds 5−7 and 8·2PhCH2CN were stable in air and laser light under experimental conditions. Solutions of these compounds in dimethylformamide (DMF) (5.0 × 10−5 M) were placed in a 2 mm quartz cuvette, and the third-order NLO properties measured using the picosecond Z-scan technique. A frequency-doubled, mode-locked, Qswitched Nd:YAG laser that delivers a 21 ps at 532 nm single pulse was employed. Other experimental conditions for these NLO measurements were the same as described in our previous articles.57,59

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RESULTS AND DISCUSSION Synthesis and Characterization. Solvothermal reaction of 1 with [Cu(CH3CN)4]BF4, NaN3, and NH4BF4 (molar ratio = 1:6:3:1) in CH3CN (5 mL) at 100 °C produced black crystals of 2 in 72% yield (Scheme 1). The Mtta ligands in 2 were in situ generated by a “click” reaction between CH3CN and NaN3 and functioned as μ-bridging ligands. However, if we did not introduce NH4BF4 in the system, the similar reaction produced mixed crystals containing 2 and 7. As compound 7 was highly soluble in CH2Cl2, the above mixed crystals were dissolved in CH2Cl2 and filtered. The remaining crystals were confirmed to 5672

DOI: 10.1021/acs.inorgchem.7b00261 Inorg. Chem. 2017, 56, 5669−5679

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Inorganic Chemistry be pure 2 with ca. 10% yield. The filtrate was further dried under reduced pressure and recrystallized from DMF/Et2O to form pure crystals of 7 (56% yield). The extra S2− anion in 7 was assumed as from the partial degradation of 1 under solvothermal conditions. The ammonium cation of NH4BF4 was reported to facilitate the nucleophilic attack of azide on the carbon of nitriles and thus explains the increased yield for 2.24,78 Substituting other nitriles CH3(CH2)nCN (n = 1, 2, 3, and 4) for CH3CN resulted in the formation of 3b (75% yield), 4 (59% yield), 5 (30% yield), and 6 (5% yield). Notably, mixing 1 with 3 equiv of [Cu(CH3CN)4]BF4, 5 equiv of NaN3, and 1 equiv of NH4BF4 in CH3CH2CN under the same conditions resulted in a change of counteranion from BF4− to N3−, generating 3a as the major product, accompanied by 3b. We were not able to separate the bulk sample of 3a from the mixture since 3a and 3b possess similar shape, color, and solubility. When we changed the reaction stoichiometry, temperature, and time, the percentage of 3a accordingly changed but still with the presence of 3b. We also performed additional experiments with the presence of terephthalic acid or triethylamine as the acid or base modulator. For the use of terephthalic acid, we still obtained a mixture of 3a and 3b, while for the use of trimethylamine, we only obtained some uncharacterizable products. Three assembly routes existed in the above tetrazolateformation reactions. The first is that 1 equiv of 1 combines 3 equiv of [Cu(CH3CN)4]BF4 to form a [Tp*WS3Cu3]2+ cluster core. The second is that the remaining 2−3 equiv of [Cu(CH3CN)4]BF4 is believed to initiate the “click” reaction between the azide and nitrile to afford a tetrazolate. The presence of Cu(I) in the [Tp*WS3Cu3]2+ core may also be useful in promoting a “click” reaction between the nitrile and azide. The third is that the in situ click-formed tetrazolates could in turn connect these cluster cores into 2D (6,3) networks. Intriguingly, in the synthesis of 4−6, these reactions were accompanied by the generation of 7 with the increased yields of 9%, 20%, and 50%, respectively. When employing CH 3(CH 2) 5CN as a reactant, no expected compound {[(Tp*WS3 Cu 3) 2(Htta)3](μ3-N 3)}n or {[(Tp*WS3 Cu 3) 2(Htta)3]BF4}n (Htta = 5-hexyltetrazolate) but 7 was isolated as the sole product in 60% yield. These results suggested that besides the three assembly reactions, the formation of 7 is a fourth competitive reaction. As described later in this article, the 2D networks of 2−6 possess two types of voids where the pendant alkyl chains are housed. The longer alkyl chains such as hexyl groups may not fit with the two types of voids, which would go against the formation of the 2D networks but promote the assembly of 7. In addition, we found that using CuCN or CuX (X = I, Br, Cl) instead of [Cu(CH3CN)4]BF4 gave neither 7 nor the desired “click” products, but some uncharacterizable amorphous precipitates. Only in one case, when 1 was mixed with an excess amount of CuCN in PhCH2CN, a CuCN-rich compound, {[Et 4 N]{(Tp*WS 3 Cu 3 )[Cu 2 (CN) 4 . 5 ]} 2 · 2PhCH2CN}n (8·2PhCH2CN), was isolated, in 80% yield. In this case, the click reaction did not happen, which may be due to the strong tendency of cyanide to be a bridging ligand to link Cu(I) ions. In addition, compound 8 was also attempted to react NaN3 but failed to isolate any tetrazolate derivatives. Compounds 2−8 were isolated as air- and moisture-stable fine crystals. Compounds 2−6 and 8 were insoluble in CH3OH, CH2Cl2, and CH3CN, while 7 was readily soluble in CH2Cl2. With the increase of alkyl chain size, 2−6 accordingly exhibited

increased solubilities in DMF. While 2 and 3 were virtually insoluble in DMF, 4 was slightly soluble, and 5 and 6 exhibited considerable solubility in DMF. In addition, the two tetrazolatefree compounds 7 and 8 were also soluble in DMF. The elemental analyses of these complexes were congruent with their chemical formulas, and PXRD patterns coincided well with those simulated from single-crystal X-ray diffraction data, except in the case of 3a (Figure S1). Differences in intensity of the 2θ signals for these complexes may be due to the preferred orientation of the crystalline powder samples. IR spectra revealed the vibrations of B−H and W−S bonds at 2571 and 416 cm−1 for 2, 2570 and 419 cm−1 for 3a, 2572 and 419 cm−1 for 3b, 2565 and 416 cm−1 for 4, 2565 and 413 cm−1 for 5, 2562 and 412 cm−1 for 6, 2561 and 407 cm−1 for 7, 2565 and 416 cm−1 for 8, respectively. The characteristic stretching vibration for N3− was observed at around 2026 cm−1 in the spectra of 2 and 3a. The strong vibration of the CN bonds in 8 was observed at 2122 cm−1. In their UV−vis spectra, bands at 315 nm (5 and 6), 336 nm (7), and 316 nm (8) were assigned to the S → W(VI) charge-transfer transitions of the [Tp*WS3]− moiety and were blue-shifted with respect to the corresponding band in 1 (385 nm) (Figure 1).70 The band at

Figure 1. Electronic spectra of 5−8 (1.0 × 10−5 M) in DMF solution.

419 nm (7) is tentatively assigned to the S → Cu(I) chargetransfer transition.79 The ESI-MS spectra of 5−8 (Figures S2− S5) suggested that neither the coordination polymers (5, 6, 8) nor discrete cluster (7) remains intact under ionization conditions. Nontheless, the tetrazolate or CN ligated-cluster aggregates still exist under such a harsh condition. This observation contributes to our understanding of the enhanced third-order NLO performances of 5−8 in solution, as discussed below. Crystal Structures of 2−6. Compounds 2−6 are structural analogues, and only the structure of 2 is discussed in detail here. Compound 2 crystallizes in the trigonal space group R3c̅ , and its asymmetric unit is composed of one-sixth of a {[(Tp*WS3Cu3)2(Mtta)3](μ3-N3)} molecule. The nest-shaped [Tp*WS3Cu3]2+ cluster core in 2 interacts weakly with a N3− anion via three Cu−μ3-N associations with the same contact of 2.698 Å (Figure 2a). The N3− anion plays an important role in this structure, not only balancing the charge but also filling the void space of the nest-shaped cluster core to yield a cuboidal core. Each Cu(I) on the cluster core is tetrahedrally coordinated by two μ3-S atoms and two N atoms (one from the N3− anion and the other from the Mtta ligand). The mean W···Cu distances (2.6384(5) Å) and Cu−S distances 5673

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Figure 2. (a) Structure of the nest-shaped [Tp*WS3Cu3]2+ cluster core associated by the μ3-N3− anion in 2. (b) 2D network of 2 extended within the ab plane. The Tp* groups (for b) and all hydrogen atoms are omitted for clarity. Color codes: W (red), Cu (cyan), S (yellow), N (blue), C (black), B (orange).

(2.2087(11) Å) (Table S1) are slightly shorter than those found in the tetrahedrally coordinated W−Cu−S cluster [Tp*WS3Cu3(α-MePy)3(μ3-Br)](PF6)·0.5CH2Cl2 (2.697(2) Å/2.252(3) Å).66 The mean Cu−N contacts (1.919(3) Å) are also slightly shorter than those found in the N donor ligand bridged W−Cu−S clusters {[(WS4Cu4)I2(dptz)3]·DMF}n (2.062(6) Å, dptz = 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine),80 {[(WS4Cu3)2(L)6](CuCl3)(H2O)8} (L = 1-(3-(1H-imidazol-1yl)phenyl)-1H-imidazole, 2.014(5) Å),81 and [Et4N][Tp*W(μ3-S)(μ-S)2Cu2(py)3](PF6)2 (2.040(4) Å).62 In 2, six [Tp*WS3Cu3(μ3-N3)0.5]1.5+ cores are linked together via six in situ-generated Mtta ligands to form a cyclohexaneshaped {[Tp*WS3Cu3]6(Mtta)6(μ3-N3)3}3+ unit in a chair conformation (Figure S6a). These cyclohexane-shaped units are interconnected via sharing six Mtta ligands to yield a 2D (6,3)-type network in the ab plane (Figure 2b). Further analysis of the packing diagram of 2 reveals that there are two types of confined spaces within the unit cell (Figure S6b and c). The first type of space is generated between a pair of {[Tp*WS3Cu3]4(Mtta)3}5+ units in two consecutive layers. These two {[Tp*WS3Cu3]4(Mtta)3}5+ units are packed in a mutually staggered and face-to-face arrangement. We denote this as a “type I” space (Figure 3a and b). The second type of space requires consideration of three consecutive layers with the space at the center of the cyclohexane-shaped {[Tp*WS3Cu3]6(Mtta)6}6+ group and blocked in the c direction by a pair of [Tp*WS3Cu3]2+ units arranged in a back-to-back fashion. We designate this as a “type II” space (Figure 3c and d). It is clear from Figure 4 that the small pendant tetrazolate alkyl chains prefer “type II” spaces (−CH3 in 2: Figure 4a; −CH2CH3 in 3: Figure 4b and c; and −(CH2)2CH3 in 4: Figure 4d), while on elongation of the carbon chains, these alkyl groups start to diffuse into “type I” spaces (−(CH2)3CH3 in 5: Figure 4e; −(CH2)4CH3 in 6: Figure 4f) to minimize steric repulsion. The size of the pendant groups also affects the anion selection for charge balance. When the chain is small (−CH3 in 2), N3− is the exclusive anion, forming a cuboidal cluster unit with the three Cu(I) centers. However, when the pendant alkyl chains are larger (−(CH2)2CH3, −(CH2)3CH3, and −(CH2)4CH3 in 4, 5, and 6), BF4− anions are found to balance the charge. Interestingly, anion selection for 3 depends on the ratio of N3− to BF4−. When the ratio of N3−:BF4− = 5:4, we are able to isolate 3a as the major product, accompanied by 3b (PXRD analysis). A N3−:BF4− = 3:5 ratio yields 3b exclusively, while a N3−:BF4− ratio between 5:4 and 3:5 gives a mixture of 3a and 3b, with the latter predominating.

Figure 3. (a and b) Two simplified representations of “type I” space, viewed along the horizontal plane and the c axis. (c and d) Two simplified representations of “type II” space, viewed along the horizontal plane and the c axis. Some Tp* groups, methyl groups, and all hydrogen atoms are omitted for clarity. See Figure 2 for the atom color codes.

Not surprisingly, the size of the pendant groups and counterions impacts the size of the voids. The latter is determined by the dihedral angle between the tetrazolate skeleton (N4C) and the plane defined by the three Cu centers in the 2D layer. This dihedral angle, in turn, dictates the extension direction of the pendant chain and subsequently the separation between the two 2D layers. Using “type I” space as an example (Table S2), we denote the dihedral angle between the tetrazolate skeleton with the plane defined by three Cu atoms as α, the W···W separation of the two W atoms overlapped along the c direction (polar axis) as L, and the radius of the circle defined by six [Tp*WS3Cu3]2+ units at the periphery positions as R (equatorial plane). The dihedral angles α in 2−6 are 134.3°, 130.4°, 124.0°, 123.8°, 125.1°, and 126.6°; the distances L are 20.107, 20.594 or 23.737, 24.493, 24.542, 24.472, and 24.336 Å; the radius R are 7.220, 6.980, 6.634, 6.650, 6.656, and 6.715 Å. Similar trends are also observed for “type II” spaces (Table S3). Thus, it can be concluded that in order to accommodate the growing size of the alkyl groups from 2 to 3b, the structures are primarily reducing the horizontal radius and concomitantly enlarging the longitudinal distance. However, the horizontal and longitudinal spaces are both extended in 4. Because the longitudinal expansion is limited by packing forces, in 5 and 6, the alkyl chains cause the expansion of the horizontal radius and reduce the longitudinal distance (Figure S7). 5674

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Compound 8·2PhCH2CN crystallizes in the triclinic space group P1.̅ Its asymmetric unit comprises half a {(Tp*WS3Cu3)[Cu2(CN)4.5]}2− anion, half a [Et4N]+ cation, and one PhCH2CN solvent molecule. In 8, each Cu(I) in the [Tp*WS3Cu3]2+ cluster core is bonded to a CuCN unit, and the two nest-shaped [Tp*WS3Cu3]2+ cores along the c axis are connected by a pair of [Cu2(CN)5]3− fragments to form a cyclohexane-shaped {(Tp*WS3Cu3)[Cu2(CN)5]}22− unit with a chair conformation (Figure 6a). The {(Tp*WS3Cu3)-

Figure 4. Spectator behavior of alkyl groups of 2−6 in two confined spaces. (a) Methyl group (2); (b) ethyl group (3a); (c) ethyl group (3b); (d) propyl group (4); (e) butyl group (5); (f) pentyl group (6). The spaces constructed with blue and silver lines represent “type I” spaces, and those constructed with dark green and silver lines represent “type II” spaces. See Figure 2 for the atom color codes.

Figure 6. Crystal structure of 8. (a) Cyclohexane-shaped {(Tp*WS3Cu3)[Cu2(CN)5]}22− unit with a chair conformation. (b) 2D network extending in the ab plane. (c) Boat-shaped {(Tp*WS3Cu3)3[Cu3(CN)7]2[Cu(CN)3]}4− macrocyclic unit. (d) {(Tp*WS3Cu3)[Cu4(CN)9]}26− macrocyclic unit. The Tp* groups (for b and c), lattice solvates, and all hydrogen atoms are omitted for clarity. See Figure 2 for the atom color codes.

Crystal Structures of 7 and 8·2PhCH2CN. Compound 7 crystallizes in the tetragonal space group I41/acd, and its local structure consists of a quarter of one [Tp*W(μ3-S)3(μ3S′)Cu3]4 molecule. Four nest-shaped [Tp*WS3Cu3]2+ cores are located at the four vertices of a tetrahedron. Each of the four faces of the tetrahedron is capped by a μ3-S′ atom, which is, in turn, linked to three Cu centers (Figure 5). The tetrahedral

[Cu2(CN)5]}22− unit propagates along the b direction through the CN linkage (Figure S8). Adjacent cluster units along the a direction are anchored by Cu(I) atoms to give a pair of 1D chains. The overall structure is therefore a 2D network extending in the ab plane (Figure 6b). Notably, two additional and large macrocyclic units also exist in 8. One is the {(Tp*WS3Cu3)3[Cu3(CN)7]2[Cu(CN)3]}4− fragment containing three [Tp*WS3Cu3]2+ cluster cores and seven CuCN moeties to give a boat-shaped unit (Figure 6c). In the other, larger {(Tp*WS3Cu3)[Cu4(CN)9]}26− unit, a pair of [Tp*WS3Cu3]2+ clusters and eight CuCN pairs are found, which, to the best of our knowledge, is unprecedented (Figure 6d). From a topological point of view, both the [Tp*WS3Cu3]2+ cluster core and the naked Cu ion are 3conneting nodes, and the overall topology of 8 is (62·9)cluster(6· 92)Cu topology (Figure 6b). In contrast to those compounds with CuCN linkers previously reported, including {Tp*WS3Cu3(μ3-DMF)[Cu(CN)3]}2n,63 {[Et4N][(Tp*WS3Cu2)2{Cu(CN)2.5}2(bpee)]· 3MeCN} n (bpee = 1,2-bis(4-pyridyl)ethylene), 62 and {[Tp*WS3Cu3(μ3-DMF)(CN)3Cu]·2(DMF)0.5}n60 where the nest-shaped [Tp*WS3Cu3]2+ cores are bridged by [Cu(CN)3]2− anionic motifs and the formed units can be viewed as 4-connecting “square-planar” nodes, the nest-shaped [Tp*WS3Cu3]2+ cores in 8 are bridged by [Cu2(CN)5]3− metal anions and the formed units can be seen as 6-connecting “chair-like-cyclohexane” nodes. Moreover, as mentioned above for the {(Tp*WS3Cu3)[Cu4(CN)9]}26− unit, [Tp*WS3Cu3]2+ cores are linked by [Cu4(CN)9]5− clusters, which are similar to

Figure 5. Molecular structure of 7 with one Tp* ligand projecting the backside and all hydrogen atoms omitted for clarity. See Figure 2 for the atom color codes.

structure of 7 resembles the Mo analogue [Tp*Mo(μ3-S)3(μ3S′)Cu3]4.55 The average W···Cu (2.6693(17) Å), Cu−μ3-S (2.222(2) Å), and Cu−μ3-S′ (2.187(2) Å) contacts (Table S1) are, not unexpectedly, slight longer than those found in [Tp*Mo(μ 3 -S) 3 (μ 3 -S′)Cu 3 ] 4 (Mo···Cu (2.6444(17) Å), Cu−μ3-S (2.201(2) Å), and Cu−μ3-S′ (2.180(2) Å)). 5675

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Figure 7. Z-scan data for 5 (5 × 10−5 M) in DMF solution investigated at 532 nm. (a) Normalized Z-scan data obtained using an open-aperture configuration showing the nonlinear absorption; (b) collected by dividing the normalized Z-scan data under closed-aperture configuration by that in (a) to show the nonlinear refraction. The black solid spheres are experimental data, and the red solid curves are the theoretical fits.

Table 2. Third-Order NLO Parameters of Compounds 5−8 compound

T0

α2 (10−13 m·W−1)

n2 (10−19 m2·W−1)

−13 χ(3) esu) R (10

−13 χ(3) esu) I (10

χ(3) (10−13 esu)

γ (10−30 esu)

5 6 7 8

71% 67% 80% 64%

2 3 10 6

2.0 2.0 1.8 2.2

4.88 4.88 4.39 5.37

6.58 9.87 3.29 1.97

4.88 4.88 4.41 5.37

4.91 4.91 4.43 5.40

those found in K[Tp*W(μ3-S)3Cu3(μ3-DMF){Cu2(CN)4.5}]2n.63 Third-Order Nonlinear Optical Properties of 5−8. Compounds 5−8 are soluble in DMF with negligible linear absorption at 532 nm (Figure 1), and thus the third-order NLO properties of these complexes in this solvent were investigated using the picosecond Z-scan technique at this wavelength. Both the open- and closed-aperture configurations were employed to deduce the nonlinear absorption and nonlinear refraction data, respectively. All complexes displayed a reverse saturable absorption and self-focusing effect (Figure 7 for 5 and Figures S9−S11 for 6−8).71 The values of α2 (nonlinear absorptive index), n2 (third-order NLO refractive index), χ(3) (third-order susceptibility), and γ (hyperpolarizability) were calculated from eqs 1−7,82 which were listed in Table 2. α0 T (Z ) = × π βIi(Z)(1 − e−α0L) ∞ ⎡ 1 − e−α0L −τ 2⎤ ln⎢1 + βIi(Z) e ⎥d τ −∞ ⎣ α0 ⎦ (1)

2

γ = χ (3) /[N ((n0 +2)/3)4 ]

It should be noted that the γ value reflects the intrinsic nature of a neat material and so is concentration-independent and can thus be utilized to characterize the performance of a material. The γ values of 5−8 are 4.91 × 10−30, 4.91 × 10−30, 4.43 × 10−30, and 5.40 × 10−30 esu, respectively. These γ values are comparable to those of the Mo(W)−Cu−S clusters derived from [MS4]2−, [MOS3]2−, [Cp*MS3]− (M = Mo, W), and [Tp*WS3]− (Table S4).49,53,57,59,67,68,83−87 It should be noted that γ values measured by picosecond and nanosecond laser pulses are approximately 2−3 orders of magnitude higher than those investigated by femtosecond experiments. The γ values of 5−8 are 2 orders of magnitude larger than that of 1 (1.07 × 10−32 esu).70 This enhanced NLO performance can be attributed to the increase of heavy atoms and the skeletal expansion of 1, as well as the existence of stable cationic or anionic aggregates in the solution under experimental conditions (cf. ESI-MS results). Moreover, these values are higher than those reported for C60 (7.50 × 10−34 esu) and C70 (1.30 × 10−33 esu).88

∫

ΔZ V − P = 1.72πω02 /λ

(2)

αL n eff 2 = λα0ΔTV − P /[0.812πI (1 − e )]

(3)

χI(3) = 9 × 108ε0n0 2c 2β /(4ωπ )

(4)

χR(3) = cn0 2n2 /(80π )

(5)

χ (3) = [(χI(3) )2 + (χR(3) )2 ]1/2

(6)

(7)

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CONCLUSIONS A family of Tp*−W−Cu−S cluster-based MOFs (2−6) were prepared by using in situ “click”-formed tetrazolate bridging ligands. These compounds are structural analogues of 2D (6,3) networks in the solid state with profoundly adjustable void spaces to accommodate tetrazolate pendant alkyl arms of increasing size. Such a structural behavior is reminiscent of Aristotle’s maxim that “Nature abhors a vacuum”. The formation of the tetrazolate products was associated with the generation of the tetrahedral cage compound 7, whose yield increased with the elongation of the pendant size. The results 5676

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(2) Meng, X. T.; Edgar, K. J. “Click” Reactions in Polysaccharide Modification. Prog. Polym. Sci. 2016, 53, 52−85. (3) Haldón, E.; Nicasio, M. C.; Pérez, P. J. Copper-Catalysed Azide− Alkyne Cycloadditions (CuAAC): An Update. Org. Biomol. Chem. 2015, 13, 9528−9550. (4) Thirumurugan, P.; Matosiuk, D.; Jozwiak, K. Click Chemistry for Drug Development and Diverse Chemical−Biology Applications. Chem. Rev. 2013, 113, 4905−4979. (5) Le Droumaguet, C.; Wang, C.; Wang, Q. Fluorogenic Click Reaction. Chem. Soc. Rev. 2010, 39, 1233−1239. (6) Hein, J. E.; Fokin, V. V. Copper-Catalyzed Azide−Alkyne Cycloaddition (CuAAC) and Beyond: New Reactivity of Copper(I) Acetylides. Chem. Soc. Rev. 2010, 39, 1302−1315. (7) Golas, P. L.; Matyjaszewski, K. Marrying Click Chemistry with Polymerization: Expanding the Scope of Polymeric Materials. Chem. Soc. Rev. 2010, 39, 1338−1354. (8) El-Sagheer, A. H.; Brown, T. Click Chemistry with DNA. Chem. Soc. Rev. 2010, 39, 1388−1405. (9) Decréau, R. A.; Collman, J. P.; Hosseini, A. Electrochemical Applications. How Click Chemistry Brought Biomimetic Models to the Next Level: Electrocatalysis under Controlled Rate of Electron Transfer. Chem. Soc. Rev. 2010, 39, 1291−1301. (10) Amblard, F.; Cho, J. H.; Schinazi, R. F. Cu(I)-Catalyzed Huisgen Azide-Alkyne 1,3-Dipolar Cycloaddition Reaction in Nucleoside, Nucleotide, and Oligonucleotide Chemistry. Chem. Rev. 2009, 109, 4207−4220. (11) Meldal, M.; Tornøe, C. W. Cu-Catalyzed Azide-Alkyne Cycloaddition. Chem. Rev. 2008, 108, 2952−3015. (12) Sun, Y.; Hong, S. Y.; Ma, X. W.; Cheng, K.; Wang, J.; Zhang, Z.; Yang, M.; Jiang, Y. X.; Hong, X. C.; Cheng, Z. Recyclable Cu(I)/ Melanin Dots for Cycloaddition, Bioconjugation and Cell Labelling. Chem. Sci. 2016, 7, 5888−5892. (13) Oakdale, J. S.; Kwisnek, L.; Fokin, V. V. Selective and Orthogonal Post-Polymerization Modification using Sulfur(VI) Fluoride Exchange (SuFEx) and Copper-Catalyzed Azide−Alkyne Cycloaddition (CuAAC) Reactions. Macromolecules 2016, 49, 4473− 4479. (14) Ladomenou, K.; Nikolaou, V.; Charalambidis, G.; Coutsolelos, A. G. “Click”-Reaction: An Alternative Tool for New Architectures of Porphyrin Based Derivatives. Coord. Chem. Rev. 2016, 306, 1−42. (15) Xu, Z. H.; Han, L. L.; Zhuang, G. L.; Bai, J.; Sun, D. In Situ Construction of Three Anion-Dependent Cu(I) Coordination Networks as Promising Heterogeneous Catalysts for Azide−Alkyne “Click” Reactions. Inorg. Chem. 2015, 54, 4737−4743. (16) Arunrungvichian, K.; Fokin, V. V.; Vajragupta, O.; Taylor, P. Selectivity Optimization of Substituted 1,2,3-Triazoles as α7 Nicotinic Acetylcholine Receptor Agonists. ACS Chem. Neurosci. 2015, 6, 1317− 1330. (17) Worrell, B. T.; Ellery, S. P.; Fokin, V. V. Copper(I)-Catalyzed Cycloaddition of Bismuth(III) Acetylides with Organic Azides: Synthesis of Stable Triazole Anion Equivalents. Angew. Chem., Int. Ed. 2013, 52, 13037−13041. (18) Kappe, C. O.; Van der Eycken, E. Click Chemistry under Nonclassical Reaction Conditions. Chem. Soc. Rev. 2010, 39, 1280−1290. (19) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation” of Azides and Terminal Alkynes. Angew. Chem., Int. Ed. 2002, 41, 2596−2599. (20) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chem., Int. Ed. 2001, 40, 2004−2021. (21) Roh, J.; Vávrová, K.; Hrabálek, A. Synthesis and Functionalization of 5-Substituted Tetrazoles. Eur. J. Org. Chem. 2012, 2012, 6101− 6118. (22) Himo, F.; Demko, Z. P.; Noodleman, L.; Sharpless, K. B. Why Is Tetrazole Formation by Addition of Azide to Organic Nitriles Catalyzed by Zinc(II) Salts? J. Am. Chem. Soc. 2003, 125, 9983−9987. (23) Demko, Z. P.; Sharpless, K. B. Preparation of 5-Substituted 1HTetrazoles from Nitriles in Water. J. Org. Chem. 2002, 66, 7945−7950.

demonstrated that besides the competitive formation of 7, three more assembly routes existed in the formation of 2−6: the assembly of the [Tp*WS3Cu3]2+ core, the “click” formation of the tetrazolate ligands, and the construction of the [Tp*WS3Cu3]2+ cluster-based 2D networks, which made up a unique synergetic synthetic strategy for cluster-based MOFs. A variation of the Cu(I) source from [Cu(CH3CN)4]BF4 to CuCN also led us to isolate a unique 2D network of 8· 2PhCH2CN that features three CuCN-rich ring subunits. The ESI-MS data suggest that tetrazolate or CN ligated-cluster aggregates exist even under relatively harsh ionization conditions, and we believe that the presence of these cationic or anionic fragments is an essential contributor to the enhanced NLO performances of 5−8, relative to that of starting material 1. Future work in our laboratory will employ the same strategy to prepare cluster-based MOFs with polydentate tetrazolate ligands to tailor voids for specific hosts.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00261. Additional information regarding PXRD, ESI-MS, cell packing diagrams, selected bond distances, variation data of “type I” and “type II” spaces, regular variations diagram of “type I” spaces, 1D chain of 8, third-order NLO measurements, hyperpolarizability values of some Mo(W)−Cu−S clusters and known NLO active materials (PDF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Fax: +86-512-65880328. Tel: +86-512-65882865. ORCID

Wen-Hua Zhang: 0000-0001-9047-8881 Jian-Ping Lang: 0000-0003-2942-7385 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 21373142, 21401134, 21531006, and 21671143), Science and Technology Department of Jiangsu Province (BK20140307), Department of Education of Jiangsu Province (14KJB150023), and the State Key Laboratory of Organometallic Chemistry of Shanghai Institute of Organic Chemistry (2015kf-07). J.P.L. is grateful for funding from the Priority Academic Program Development of Jiangsu Higher Education Institutions, the State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, and the “Soochow Scholar” Program of Soochow University. The authors are grateful to the useful comments from the editor and the reviewers.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b00261 Inorg. Chem. 2017, 56, 5669−5679

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