A Crystalline Phase Transition And Optical Properties In A Co Iicuii Oxamato-bridged Ferrimagnetic Chain

The compound [CoCu(opba)(DMSO)3] (1) [opba = orthophenylenebis(oxamato)] has been synthesized and characterized. Its crystal structure has been analyzed by X-ray diffraction techniques at 100 and 298 K. A structural phase-transition has been detected at around 150 K. An orthorhombic crystalline system is found at both temperatures, with very similar unit-cell dimensions. At room temperature 1 crystallizes in the Pnam space group (α-1 phase), with a = 7.6712(2), b = 14.8003(3), c = 21.0028(5) Å, and Z = 4, whereas at low temperature it crystallizes in the Pna21 space group (β-1 phase), with a = 7.3530(2), b = 14.5928(4), c = 21.0510(7) Å, and Z = 4. Both crystalline phases consist of linearly ordered bimetallic chains with the [Cu(opba)]2- units tied by CoII ions to form a one-dimensional system. The DMSO molecules in α-1, which are coordinated to either CuII or CoII, are disordered. At low temperature, a small reorganization of the CuII and Co II environments is observed. 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