Novel structurally characterized Co(II) metal-organic framework and Cd(II) coordination polymer self-assembled from a pyridine-terminal salamo-like ligand bearing various coordination modes

Abstract

Two novel structurally characterized Co(II) metal-organic framework (Co(II) MOF) and Cd(II) coordination polymer (Cd(II) CP), [{Co(L)}2]n·nCH3COCH3 and [Cd(H2L)(CH3COO)2]n were self-assembled from a newly designed salamo-like ligand H2L bearing double terminal pyridine groups and Co(II) and Cd(II) ions, respectively. In the Co(II) MOF, the Co1 and Co2 ions are six-coordinated octahedron geometries, have similar coordination environments, and are located in the N2O2 cavities of the ligand (L)2− units, forming "Co1-L" and "Co2-L" parts, respectively. The terminal pyridine N atoms of the "Co1-L" (or "Co2-L") part are connected with "Co1-L" and "Co2-L" parts respectively, forming a metal-organic framework with double helix structure in thea-direction and regular channels in the c-direction. In the Cd(II) CP, Cd(II) ion is seven-coordinated single cap triangular prism geometry, did not participate in the coordination of the N2O2 cavity, but coordinated with free acetate in the solution. Two bidentate acetate anions chelate to Cd1 ion, and two Cd1 ions are bridged by O atom of one of the acetate anions to form Cd2(OAc)2 unit which was used as the junction point to connect with the terminal pyridine N atoms of H2L. Finally, the coordination polymer with large pore channels was formed. Spectroscopic analyses of H2L and its Co(II) MOF and Cd(II) CP are performed using IR, UV–Vis and fluorescence spectroscopy. TGA analyses show that the Co(II) MOF and Cd(II) CP have good stabilities. Various short-range interactions in the Co(II) MOF and Cd(II) CP are investigated through Hirshfeld surfaces analyses.