Synthesis, structures, surface photovoltage and luminescence properties of two new nickel(ii) carboxyphosphonates with a 3D framework structure

Abstract

By introduction of 4,4′-bipyridine (4,4′-bipy) as a second organic ligand, two new nickel(II) carboxyphosphonates with a 3D framework structure, namely, [Ni₃(H₂L)₂(4,4′-bipy)(H₂O)₄] (1) and [Ni₃(H₂L′)₂(4,4′-bipy)₂(H₂O)₂]·4H₂O (2) (H₅L = 4-{[bis(phosphonomethyl)amino]methyl}benzoic acid; H₅L′ = N,N-bis(phosphonomethyl)aminoacetic acid) have been synthesized under hydrothermal conditions. Compounds 1 and 2 both feature three-dimensional (3D) framework structures with two-dimensional (2D) layers pillared by 4,4′-bipy. For compound 1, {Ni(1)O₄N₂}, {Ni(2)O₆} and {CPO₃} polyhedra form a 2D inorganic layer in the bc-plane via corner-sharing. Then adjacent layers are further pillared by 4,4′-bipy ligands into a 3D pillar-layered structure. In compound 2, {Ni(1)O₄N₂}, {Ni(2)O₄N₂} and {CPO₃} polyhedra are interconnected by carboxyphosphonate ligands to a 2D layer in the ab-plane. Neighboring layers are further cross-linked via 4,4′-bipy ligands, generating a 3D framework structure. Whereas the carboxylate oxygen atoms of carboxyphosphonate ligands are coordinated to Ni(II) atoms in compound 2 but not in compound 1. The surface photovoltage and luminescence properties of compounds 1 and 2 have been investigated at the same time.