Two new hexacoordinated coordination polymers of cadmium(II) containing bridging units only: Syntheses, structures and molecular properties

The syntheses, characterizations and structures of a neutral 2D coordination polymer [Cd(bnzd)(NCS) 2 ] n ( 1 ) and a polycationic 3D coordination polymer isolated as perchlorate salt [Cd(bnzd) 3 ] n (ClO 4 ) 2n ( 2 ) (bnzd = benzidine) are described. X-ray structural analyses reveal that each hexacoordinated cadmium(II) center in 1 adopts a distorted octahedral geometry with a CdN 4 S 2 chromophore bound by two N atoms of two different bnzd units and two N and two S atoms of symmetric doubly bridged end-to-end NCS − units extended in a 2D sheet. Six N atoms of six different bridged bnzd units are bonded to each cadmium(II) in 2 in a non-ended fashion affording a 3D network structure. In the crystalline state, each 2D sheet structure in 1 is further stabilized by π ⋯ π interaction which in turn affords a 3D network structure through multiple intermolecular N-H ⋯S hydrogen bonds. On the other hand, the 3D network structure in 2 is stabilized by weak intermolecular N-H ⋯O hydrogen bonds and C-H ⋯ π interactions. Bnzd, 1 and 2 display intraligand 1 ( π - π *) fluorescence in DMF solution at room temperature. Graphical Abstract Two cadmium(II) coordination polymers of benzidine with or without thiocyanate afford varied metal-organic frameworks (MOFs) through multiple weak non-covalent forces and are good luminous materials.