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Magnetic coupling in trinuclear partial cubane copper(II) complexes with a hydroxo bridging core and peripheral phenoxo bridges from NNO donor Schiff base ligands |
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| Authors: | Chaitali Biswas Michael GB Drew Silvia Gómez-Coca Vassilis Tangoulis |
| Institution: | a Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India b Sarojini Naidu College for Women, 30, Jessore Road, Kolkata 700 028, India c School of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6 6AD, UK d Nanobiotechnology Facility, Fondazione Istituto Italiano di Tecnologia, IIT, via Morego 30, 16163 Genoa, Italy e Departament de Química Inorgànica, Institut de Química Teòrica i Computacional, Av. Diagonal 647, 08028 Barcelona, Spain f Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece |
| Abstract: | Three new trinuclear copper(II) complexes, (CuL1)3(μ3-OH)](ClO4)2·3.75H2O (1), (CuL2)3(μ3-OH)](ClO4)2(2) and (CuL3)3(μ3-OH)](BF4)2·0.5CH3CN (3) have been synthesized from three tridentate Schiff bases HL1, HL2, and HL3 (HL1 = 2-(2-amino-ethylimino)-methyl]-phenol, HL2 = 2-(2-methylamino-ethylimino)-methyl]-phenol and HL3 = 2-1-(2-dimethylamino-ethylimino)-ethyl]-phenol). The complexes are characterized by single-crystal X-ray diffraction analyses, IR, UV-vis and EPR spectroscopy, and variable-temperature magnetic measurements. All the compounds contain a partial cubane Cu3O4] core consisting of the trinuclear unit (CuL)3(μ3-OH)]2+ together with perchlorate or fluoroborate anions. In each of the complexes, the three copper atoms are five-coordinated with a distorted square-pyramidal geometry except in complex 1, in which one of the CuII ions of the trinuclear unit is six-coordinate being in addition weakly coordinated to one of the perchlorate anions. Variable-temperature magnetic measurements and EPR spectra indicate an antiferromagnetic exchange coupling between the CuII ions of complexes 1 and 2, while this turned out to be ferromagnetic for complex 3. Experimental values have been fitted according to an isotropic exchange Hamiltonian. Calculations based on Density Functional Theory have also been performed in order to estimate the exchange coupling constants in these three complexes. Both sets of values indicate similar trends and specially calculated J values establish a magneto-structural correlation between them and the Cu-O-Cu bond angle, in that the coupling is more ferromagnetic for smaller bond angle values. |
| Keywords: | CuII Schiff base Trinuclear Crystal structure Magnetic study DFT calculations |
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