Barium(II)–Chromium(III) Coordination Polymers Based on Dimethylmalonate Anions: Synthesis, Crystal Structure, Magnetic Properties, and EPR Spectra

Abstract

A new 1D coordination polymer {[Ba2Cr2(OH)2(Me2mal)4(H2O)6]·2H2O}n (1) containing binuclear structural units [Cr2(OH)2(Me2mal)4]4– was synthesized by the reaction of an inorganic chromium(III) salt with a barium salt of dimethylmalonic acid (H2Me2mal). Depending on the nature of the counterion of the starting chromium salt, the addition of an excess of H2Me2mal to the reaction mixture resulted in the formation of a new 2D polymer {[Ba2Cr(Me2mal)2(HMe2mal)2(NO3)(H2O)5]·3.55H2O}n (2) containing mononuclear units [Cr(Me2mal)2(HMe2mal)2]3– or a new 3D polymer {[BaCr(Me2mal)2(HMe2mal)(H2O)2]·H2O}n (3) composed of two types of mononuclear units, [Cr(Me2mal)2(HMe2mal)2]3– and [Cr(Me2mal)2(H2O)2]–. Magnetic measurements, EPR spectroscopy studies, and quantum chemical calculations demonstrated that compound 1 exhibits ferromagnetic exchange interactions between CrIII ions in the binuclear unit (2J = 6.77 cm–1) and displays slow relaxation of the magnetization in external dc‐magnetic field. Compound 3 has porous structure, with channels occupied by solvent water molecules. However, the dehydration of 3 is accompanied by a structural rearrangement and the collapse of the porous structure.