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

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 Cr^III 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.