Syntheses, crystal structures and properties of transition metal coordination polymers based on isophthalic acid and flexible bis(pyridyl) ligand with unsymmetrical spacer: influence of metal cations, ligand conformations and coordination modes

Abstract

Eight new transition metal coordination complexes, namely [Mn₂(ip)₂(L1)₂(H₂O)₃]_n·nH₂O (1), [Co(ip)L1(H₂O)]_n (2), [Zn(ip)L1]_n (3), [Cd₂(ip)₂L1]_n (4), [Mn(ip)L2(H₂O)]_n·nCH₃OH (5), [M(ip)L2(H₂O)]_n·nH₂O [M = Co (6) and Ni (7)], and [Zn₃(ip)₂(OH)₂(L2)₂]_n (8) (H₂ip = isophthalic acid, L1 = N-(pyridin-3-ylmethyl)pyridin-2-amine, L2 = N-(pyridin-3-ylmethyl)pyridin-3-amine), have been synthesized and characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. Complex 1 exhibits a 1D ‘ladder’ chain structure, which is extended by the hydrogen-bonding interactions to form a 3D supramolecular network. Complexes 2, 3 and 5 display 2D (4,4) layer networks and are extended by the hydrogen-bonding, π⋯π stacking and C–H⋯π interactions to generate 3D supramolecular networks. Complex 4 is a 3D pillared layered framework by linking a 2D Cd(II)-ip double layer with L1 molecules. Complex 6 and 7 are isomorphous and exhibit a 3D tcb net with the Schläfli symbol of 8⁶, while complex 8 is a 3D network and presents a new topology with the Schläfli symbol of (5⁵·6⁹·7). The structural diversities indicate that the versatile coordination modes of the ip dianions, conformations of L1 and L2, as well as the nature of the metal cations play crucial roles in modulating structures and topologies of the coordination complexes. Moreover, solid-state luminescent properties demonstrate that complexes 3, 4 and 8 exhibit strong blue emission at room temperature.