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

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),1(-) (6), HCO2- (7), SO4- (8) and (9), and NO3- (10)]. Employment of different anions have resulted in different architectures, ranging from dicrete 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 1(-) 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 (,an 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-pi 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.