Anion-Controlled Synthesis of Enantiomeric Twofold Interpenetrated 3D Zinc(II) Coordination Polymer with Ligand Substitution-Induced Single-Crystal-to-Single-Crystal Transformation and Photocatalysis

Abstract

An anion-controlled synthesis of a new three-dimensional (3D) “racemate”, an enantiomorphic twofold interpenetrated 3D zinc(II) coordination polymer containing bridging glutarate (glu) and 4,4′-bipyridine (4,4′-bipy) ligands, {[Zn4(H2O)2(4,4′-bipy)4(glu)3](NO3)2}n, 1 (P21/c), with ligand substitution-induced single-crystal-to-single-crystal (SCSC) transformation and photocatalysis for dye degradation was studied. The influence of a counteranion in zinc(II) starting materials and synthetic techniques upon the phase formation were explored. The complex 1 was successfully synthesized from zinc(II) nitrate salt via microwave-assisted techniques as well as the conventional hydrothermal technique, whereas the employment of zinc(II) acetate or sulfate salt yielded a two-dimensional coordination polymer, [Zn(4,4′-bipy)(glu)]n, 2 (P1̅), and the use of zinc(II) chloride led to a one-dimensional (1D) zigzag chain, [Zn(4,4′-bipy)Cl2]n 3 (C2/c). The synthetic-method-dependent formation was illustrated as the microwave-assisted techniques and conventional hydrothermal technique enabled the formation of crystalline-phase pure 1, while the sonochemical synthesis provided mixed crystalline-phases of 1 and 2. In the structure of 1, the 4,4′-bipy ligand links dinuclear Zn(II) building units into 1D chains along the [1̅01] direction. The glu2– ligand acts as tethering linkers expanding the structure into a cationic 3D coordination polymer that interpenetrates with its enantiomer to give a 3D solid-state “racemate”. Powder X-ray diffraction revealed that the ligand substitution-induced SCSC transformation of the twofold interpenetrated 3D framework, 1 (P21/c), which was triggered by chloride, led to a 1D zigzag chain, 3 (C2/c), whereas the bromide-triggered reaction led to a mixed crystalline phase between the isostructural 1D zigzag chain, [Zn(4,4′-bipy)Br2]n, 4 (C2/c), and its polymorph, [Zn(4,4′-bipy)Br2]n, 5 (P212121). The photocatalysis for the methyl orange degradation of 1 was studied.