Syntheses, crystal structures, thermal stability, magnetism and luminescence of four new metal phosphonates

Abstract

Hydrothermal reactions of Cd²⁺, Mn²⁺, Co²⁺ and Ni²⁺ ions with 4-pyridyl-CH₂N(CH₂COOH)(CH₂PO₃H₂) (H₃L) afforded four new metal phosphonates, namely, (H₃O)₄[Cd₇(L)₆]·16H₂O (1), (H₃O)₄[Mn₇(L)₆]·17H₂O (2), [Co(HL)(H₂O)]·2H₂O (3) and [Ni(HL)(H₂O)]·2H₂O (4). Compounds 1 and 3 are isomorphous with compounds 2 and 4, respectively. Solid 1 is a 3D open-framework consisting of heptanuclear cadmium clusters. The framework of solid 1 is thermally stable up to 250 °C under an air atmosphere. In 3, HL²⁻ anions exhibit pentadentate modes to combine Co²⁺ ions into a 2D hybrid layer. It is interesting that solid 1 displays bright blue luminescence, which can be enhanced upon cooling to 10 K. Furthermore, after heat-treatment at 250 °C under an air atmosphere, solid 1-250 also gives off blue emission. And the magnetic properties of 2–4 have also been studied.