Temperature-influenced M2L and M2L2 molecular metal phosphonates and diversity of ligand conformation

Abstract

In this work, the structure diversity of three-component molecular metal phosphonates has been achieved by varying reaction temperature. Two dinuclear Co(II) phosphonate complexes, [Co2(H4tpmb)(phen)2(H2O)6]·2H2O (1·2H2O) and [Co2(H6tpmb)2(1,10-phen)2(H2O)2] (2), with M2L and M2L2 types, respectively, have been successfully synthesized from the reactions of CoCl2·6H2O, 1,2,4,5-tetrakis(phosphorylmethyl)benzene (H8tpmb), and 1,10-phenanthroline (phen) at room temperature and 60 °C, respectively. In comparison, only M2L Ni(II) phosphonate complex [Ni2(H4tpmb)(phen)2(H2O)6]·2H2O (3·2H2O), which is isostructural and isomorphous with Co(II) analogue 1·2H2O, has been obtained by using NiCl2·6H2O instead of CoCl2·6H2O under similar reaction conditions at both room temperature and 60 °C. The M(II) center in 1–3 all adopts a slight distorted octahedral geometry of {MO4N2}, made up of one phosphonate O atom, three coordination water molecules and one chelated phen ligand in 1 and 3, and three phosphonate O atoms, one coordination water molecule and one chelated phen ligand in 2. The H8tpmb ligand is partially deprotonated to be a tetracharged H4tpmb4– anion with a tctc (trans, cis, trans, cis) conformation in 1 and 3 and a dicharged H6tpmb2– anion with a ctct (cis, trans, cis, trans) conformation in 2. Complexes 1–3 are thermally stable upon heating to approximately 262–282 °C.