Oxalate, squarate and croconate complexes with bis(2-pyrimidylcarbonyl)amidatecopper(II): synthesis, crystal structures and magnetic properties |
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Authors: | Danielle Cangussu Humberto O Stumpf Jim A Thomas Miguel Julve |
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Institution: | a Departamento de Química, ICEX, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, Belo Horizonte-MG, 31270-901, Brazil b Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, United Kingdom c Departament de Química Inorgànica/Instituto de Ciencia Molecular, Facultat de Química de la Universitat de València, Dr. Moliner 50, 46100-Burjassot (València), Spain |
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Abstract: | The preparation and magnetic properties of three copper(II) compounds of formulae Cu2(bpcam)2(H2O)2(C2O4)] (1), Cu2(bpcam)2(H2O)4(C4O4)] · 10 H2O (2) and Cu2(bpcam)2(C5O5)(H2O)3 (3) bpcam = bis(2-pyrimidyl)amidate, and are reported. The structures of two of them (1 and 2) have been solved by single crystal X-ray diffraction and consists of centrosymmetric discrete copper(II) dinuclear units bridged by bis-bidentate oxalate (1) and bis-monodentate squarate (2), with the bpcam group acting as a terminal tridentate ligand. Each copper atom in 1 exhibits a distorted elongated octahedral coordination geometry. Three bpcam nitrogen atoms and one oxalate oxygen define the basal plane while the other oxalate oxygen and a water molecule take up the axial positions. Each copper atom in 2 is in an elongated octahedral surrounding with three bpcam nitrogen atoms and one squarate oxygen in the equatorial plane and two water molecules in the axial positions. The intramolecular copper-copper separations are 5.677(1) (1) and 7.819(53) Å (2). Magnetic susceptibility measurements for 1-3 in the temperature range 1.9-290 K show the occurrence of weak ferromagnetic interactions through oxalato (J = +0.75 cm−1) and squarato (J = +1.26 cm−1), the Hamiltonian being defined by . These values are analyzed and discussed in the light of the available magneto-structural data for analogous systems. The quasi-Curie law observed in 3 (θ = −1.15 K) contrasts with the significant antiferromagnetic interaction through bis-chelating croconate in other structurally characterized croconate-bridged copper(II) complexes and rules out the presence of bridging croconate in this compound. |
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Keywords: | Copper(II) complexes Crystal structures Magnetic properties Oxalate complexes Squarate complexes Croconate complexes |
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