Coligand Modulated Six-, Eight-, and Ten-Connected Zn/Cd-1,2,4-Triazolate Frameworks Based on Mono-, Bi-, Tri-, Penta-, and Heptanuclear Cluster Units

Using nonsubstituted 1,2,4-triazole and the second bridging ligands as coligands, a series of three-dimensional metal–organic frameworks based on different secondary building units (SBUs), namely, Zn 2 (trz) 3 (SCN) ( 1 ), Zn 2 (trz) 2 (ox) ( 2 ), Cd 3 (trz) 2 (suc)Cl 2 ( 3 ), [Cd 5 (trz) 6 (OAc) 2 Cl 2 (H 2 O) 2 ]·2H 2 O ( 4 ), and [Zn 7 (trz) 6 (1,2,4,5-BTC) 2 (H 2 O) 6 ]·8H 2 O ( 5 ) (trz = 1,2,4-triazole, ox = oxalate, suc = succinic acid, 1,2,4,5-BTC = 1,2,4,5-benzenetetracarboxylate), have been synthesized and structurally characterized with the aid of single-crystal X-ray diffraction. The SBUs in 1 – 5 vary from mononuclear, binuclear, linear trinuclear, linear pentanuclear to heptanuclear d 10 -1,2,4-triazolate polynuclear clusters. Compound 1 presents a complicated 3,6-connected topology based on three nonequivalent nodes. Compound 2 adopts a 6-connected 3D network of distorted α-Po topology that is built from dizinc units. The structure of 3 consists of two intersecting (4,4) grids which generate a novel self-penetrating 4,8-connected net with (4 5 6)(4 12 6 16 ) topology when the tricadmium cores and succinic acid ligands are regarded as eight-connected and four-connected nodes, respectively. Compound 4 can be described as an 8-connected CsCl-type net utilizing unprecedented linear pentacadmium cores as eight-connected nodes and trz ligands as linkers. The microporous structure of 5 exhibits a novel 4,10-connected net constructed from ten-connected heptanuclear [Zn 7 (trz) 6 ] 8+ cluster and four-connected 1,2,4,5-BTC ligand. Detailed structural comparison of these complexes indicated that the increase in the length of the second bridging ligands induces the progressive increase in the metal nuclearity and the increase in the connectivities of the ultimate nets: that is, the length of the second bridging ligand plays a significant role in tuning the nuclearity of metal-1,2,4-triazolate clusters and the connectivity of a specific network. All the complexes exhibit high thermal stability and strong fluorescence properties.