Investigation of Flexible Organic Ligands in the Molybdate System: Delicate Influence of a Peripheral Cluster Environment on the Isopolymolybdate Frameworks

By introducing the flexible 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene (L1) and 1,4-bis(imidazole-1-ylmethyl)benzene (L2) ligands into the molybdate system under hydrothermal conditions, 12 novel isopolymolybdate frameworks were obtained: [CuL1(H2O)][Mo3O10] (1), [ML1(H2O)2][Mo3O10] [M = Cu (2), Zn (3), and Co (4)], [Cu2(L1)4][θ-Mo8O26] (5), [Cu4(L1)4][β-Mo8O26]0.5[γ-Mo8O26]0.5·H2O (6), [Ag4(L1)2][β-Mo8O26] (7), [M2(L1)3(H2O)4][β-Mo8O26]·2H2O [M = Zn (8), Co (9), and Ni (10)], and [M4(L2)4][δ-Mo8O26] [M = Cu (11) and Ag (12)]. Compound 1 and isostructural compounds 2−4 exhibit similar three-dimensional (3D) pillar-layered structures. Compound 5 shows a novel pillar-layered framework constructed from two sorts of [CuL1]n left- and right-handed helical chains and the θ-[Mo8O26]4− polyoxoanion. Compound 6 contains two sorts of isomers of β-[Mo8O26]4− and γ-[Mo8O26]4− coexisting in one structure, which induce the formation of two sorts of ladderlike building blocks and finally the polythread structure. The cationic and anionic fragments in compound 7, the dinuclear molecular loop of [Ag2(L1)2]2+ and β-[Mo8O26]4−, are both linked up by single Ag ions, forming two kinds of infinite chains of [Ag3(L1)2]n3n+ and [Ag-β-Mo8O26]n3n−, respectively. Compounds 8−10 are isostructural and exhibit the parallel two-fold (2D→2D) interpenetrated networks based on the β-[Mo8O26]4− cluster. Isostructural compounds 11 and 12 have 3D polythread penetrated frameworks based on the δ-[Mo8O26]4− polyoxoanion. The luminescent properties of the ligands and complexes 3, 6−8, and 11−12 are investigated in the solid state.