Structural diversity and modification in Ni(ii) coordination polymers: a peculiar phenomenon of reversible structural transformation between a 1D ladder and 2D layer

Abstract

Reactions of metal(II) salts (M = Cd, Ni and Zn) with 5-tert-butylbenzene-1,3-dicarboxylic acid (5-tert-H₂IPA) and N,N′-bis(3-pyridyl)terephthalamide (L¹) or N,N′-bis(4-pyridyl)terephthalamide (L²) afforded {[Cd(L¹)(5-tert-IPA)(H₂O)]·2H₂O}_n, 1, {[Ni(L¹)_1.5(5-tert-IPA)(H₂O)₂]·2.5H₂O}_n, 2, {[Ni(L¹)(5-tert-IPA)(CH₃OH)]·2CH₃OH}_n, 3, [Zn(L¹)_0.5(5-tert-IPA)]_n, 4, and {[Ni(L²)(5-tert-IPA)(H₂O)]·2H₂O}_n, 5, which have been structurally determined by using single-crystal X-ray diffraction. Complexes 1 and 2 are 1D ladders with the {4·8⁴·12}{4}{8}-2,2,4C1 and {8²·12}₂{8}₃-2,2,3C4 topologies, and 3 and 5 are 2D layers showing {8⁴·12²}{8}₂-2,4L2 and {4⁴·6²}-sql topologies, respectively, while complex 4 exhibits a 3-fold interpenetrated 3D net with the {4²·6·10²·12}{4²·6}-coe-3,4-C2/c topology, which can be further simplified as the {6⁵·8}-cds topology, indicating that solvents and metal identity play important roles in determining the structural diversity. Moreover, complexes 2 and 3 display a reversible structural transformation upon coordination as well as co-crystallized solvent exchange between H₂O and CH₃OH, which can be ascribed to the alternations of the bonding modes of the 5-tert-IPA²⁻ ligand upon solvent attack, together with the conformation changes of the L¹ ligand. Their thermal decomposition and the luminescence properties of 1 and 4 are also discussed.