Structure diversity and anion exchange property of zinc(II) coordination polymers with flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene

Flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene (L) was used to react with various zinc(II) salts ZnX [X = (BF4)2, SO4, Cl2, Br2, I2] to afford a series of coordination polymers with different structures. {[Zn(L)2](BF4)2}n (1) has an infinite 2D cationic double layered structure, while {[Zn4(L)3(SO4)4] · 9H2O}n (2) possesses a 3D framework structure with two different kinds of channels. The structure of [Zn3(L)2Cl6]n (3) is 2D network and the one of {[Zn3(L)2Br6] · CH3OH}n (4) is an infinite 1D zigzag chain in a plywood-like stacking fashion. {[Zn(L)I]I}n (5) has 2D network structure which is further linked by hydrogen bonds to give rise to a fascinating 3D interlocked framework with twofold interpenetration. The results demonstrated that the counteranions have drastic effects on the structure of the coordination polymers. On the other hand, the flexible ligand L acts as a three-connecting node to connect three zinc(II) centers with different conformations. In 1 and 5, L has cis, cis, cis-conformation, while in 2, it adopts cis, trans, trans-conformation. It is interesting that two different conformations (cis, cis, cis and cis, trans, trans) of L coexist in 3 and in the case of 4, the ligand L adopts a special trans-conformation. The results attest that the flexible ligand L can adopt different conformations to form complexes with varied structures. In addition, the uncoordinated tetrafluoroborate anions in 1 can be exchanged by nitrate or nitrite anions, which mean that 1 has anion exchange property.