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)(Me(2)mal)(4)(H2O)(6)]center dot 2H(2)O}(n) (1) containing binuclear structural units [Cr-2(OH)(2)(Me(2)mal)(4)](4-) was synthesized by the reaction of an inorganic chromium(III) salt with a barium salt of dimethylmalonic acid (H(2)Me(2)mal). Depending on the nature of the counterion of the starting chromium salt, the addition of an excess of H(2)Me(2)mal to the reaction mixture resulted in the formation of a new 2D polymer {[Ba2Cr(Me(2)mal)(2)(HMe(2)mal)(2)(NO3)(H2O)(5)]center dot 3.55H(2)O}(n) (2) containing mononuclear units [Cr(Me(2)mal)(2)(HMe(2)mal)(2)](3-) or a new 3D polymer {[BaCr(Me(2)mal)(2)(HMe(2)mal)(H2O)(2)]center dot H2O}(n) (3) composed of two types of mononuclear units, [Cr(Me(2)mal)(2)(HMe(2)mal)(2)](3-) and [Cr(Me(2)mal)(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.