Influence of Anion on the Coordination Mode of a Flexible Neutral Ligand in Zn(II) Complexes: From Discrete Zero-Dimensional to Infinite 1D Helical Chains, 2D Nanoporous Bilayer Networks, and 3D Interpenetrated Metal−Organic Frameworks

Abstract

A series of Zn(II) complexes with a flexible ligand have been synthesized in the presence of different anions [Cl− (1) and (4), CH3COO− (2), CF3COO− (3), Br− (5), I− (6), HCO2− (7), SO4− (8) and (9), and NO3− (10)]. Employment of different anions have resulted in different architectures, ranging from discrete zero-dimensional to infinite one-, two-, and three-dimensional (1D, 2D, and 3D) coordination polymers. Complexes 1, 2, and 3 exhibit binuclear metallocyclic zero-dimensional structures, while 4−7 form 1D helical networks. Among the halides, Cl− and Br− form interesting helical networks with the coexistence of both left-handed and right-handed helical chains, while the introduction of I− ion results in a water mediated right-handed helical network. Complex 7, on the other hand, represents an unique example of an alternative array of a left-handed and right-handed helical network, which can also be described as a hydrogen bonded 2D (4,4) network. Complexes 8 and 9 exhibit bilayer structures containing a distinct nanoporous void and channels within the networks. Furthermore, complexes 8 and 9 can be described as resulting from the structural transformation of 1 and 2, respectively, by replacing the terminally coordinated anions with bridging sulfate ions, whereas complex 10 exhibits a 2-fold interpenetrated diamondoid network assisted by the molecular recognition of the nitrate ions. Throughout the series, hydrogen bonds, anion−π interactions, and other intermolecular interactions involving the anions play some crucial role in stabilizing the resulting networks. Different conformations adopted by the flexible ligand further facilitate to achieve a suitable coordination environment around the metal center.