Five 3D metal-organic frameworks constructed from V-shaped polycarboxylate acids and flexible imidazole-based ligands

Five new metal-organic frameworks, namely, Cd₂(SA)(obix) (1), Zn₂(SA)(bimb) (2), Cd(SDBA)(timb)·3H₂O (3), Co(SDBA)(bimb) (4), and Co(SDBA)(obix) (5) (H₄SA = 3,3′,4,4′-diphenylsulfonetetracarboxylate acid, H₂SDBA = 4,4′-dicarboxybiphenyl-sulfone, obix = 1,2-bis(imidazol-1-ylmethyl) benzene, timb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene and bimb = 4,4′-bis(imidazol-1-ylmethyl)biphenyl), have been synthesized under hydrothermal conditions by employing mixed ligands of various imidazole-based ligands with H₄SA or H₂SDBA. The networks exhibit a variety of topologies and coordination modes at the metal centers. Complex 1 features a novel (5,7)-connected seh net consisting of one-dimensional inorganic chains which are bridged by carboxylate groups of SA^4- ligands, whereas complex 2 possesses a unique 4-connected 3D framework with (6 ²·8²·10²)(6²· 8³·10)(6²·8³·9) topology. Complex 3 exhibits a rare (3,5)-connected 3D framework with gra topology. Complex 4 shows 4-connected MOFs with (6⁵·8) CdSO ₄-type topology, while in 5, the SDBA and obix ligands linked the Co(ii) atoms into a deeply corrugated 2D sheet. The corrugated 2D sheets polycatenate each other in a parallel manner yielding a rare 2D → 3D parallel polycatenation net. The photoluminescence properties of 1-3 were studied in the solid state at room temperature. Moreover, the second-harmonic-generation (SHG) activity of 2-5 have also been investigated.