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Abstract
From the Cu(II)-NCO−-3,4,5-trimethylpyrazole (tmpz) system three isomeric compounds of the composition Cu(NCO)2.2tmpz and one compound of the composition Cu(NCO)2.tmpz were isolated. According to the infrared data two of the 1 : 1 compounds consist of Cu(tmpz.NCO)2 complexes, comprising 3,4,5-trimethyl-1-carbamoylpyrazolate anions as chelate ligands, while the third represents the cyanato complex Cu(NCO)2(tmpz)2. This type of isomerism might be designated as coligand isomersm. The 1 : 1 compound exhibits terminally bonded as well as bridging NCO ligands. The ligand field spectra indicate that one of the compounds Cu(tmpz.NCO)2 shows a square-planar configuration while the second differs by axial interactions between the basic structure units. Cu(NCO)2(tmpz)2 shows a molecular pseudotetrahedral structure and Cu(NCO)2(tmpz) has also a pseudotetrahedral but polymeric structure. The g values from the ESR spectra strongly support the above structure conclusions.