IFLP   13074
INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Crystallographic and Theoretical Studies on a Coupled Chain of Binuclear Cu(II)-Fluoraspirinate Complexes
Autor/es:
C. A. LAMAS; O. E. PIRO; E. E. CASTELLANO; E. M. RUSTOY; O. V. QUINZANI
Lugar:
Bahía Blanca, Argentina
Reunión:
Congreso; IV Reunión de la Asociación Argentina de Cristalografía (AACr); 2008
Institución organizadora:
Asociación Argentina de Cristalografía (AACr)
Resumen:
Abstract. Numerous studies have been carried out on the pharmacological properties of copper carboxylates. In particular, copper aspirinates have been found to act as anti-inflammatory, analgesic, anti-carcinogenic, anticonvulsant, antithrombotic, catecholase mimetic and potential neuron-protective agents [1,2]. These pharmacological studies often contain copper-aspirinate systems either involving simple mononuclear complexes or paddle-wheel dinuclear tetrakis-aspirinate complexes. In contrast with the large number of experimental and theoretical studies about aspirin [2,3], less is know about its 5-halogenated derivatives. We present here the low temperature (116K) crystal and molecular structure of poly-[m-pyrazine{tetrakis-fluoraspirinate-dicopper(II)}]diacetonitrile, for short [Cu(Fasp)4Cu(pyz)]n, and discuss the theoretically expected magnetic and thermodynamic behavior of this interesting system for molecular magnetism.The complex crystallizes in the triclinic space group P-1 with a=9.8900(2), b=11.0850(3), c=11.7900(3) Å, a=78.818(1), b=65.294(1), g=73.048(1)º, and one molecule per unit cell. The structure was solved from 3987 X-ray reflections with I>2s(I) by direct methods and refined to an agreement R-factor of 0.0375. The Cu(Fasp)4Cu [d(Cu…Cu)=2.6417(5) Å] dimeric group is sited on a crystallographic inversion center and shows a lantern-like conformation where the Cu(II) ions are equatorially bridged by four Fasp groups acting as bidentate ligands through their carboxylic oxygen atoms [Cu-O bond lengths from 1.964(2) to 1.974(2) Å]. Neighboring Cu(Fasp)4Cu groups in the lattice are axially linked by pyrazine (pyz) N(C4H4)N groups (also on a inversion center) through their N-atoms [d(Cu-N)=2.233(2) Å] giving rise to a ...Cu(Fasp)4Cu…N(C4H4)N…Cu(Fasp)4Cu...N(C4H4)N.. polymeric structure that extends along the crystal a-axis. We also present numerical results on the magnetic behavior of the chain as a function of the inter-dimer super-exchange coupling constant, obtained by the Lanczos’ technique. In this framework we calculated the low-laying energy levels and magnetic and thermodynamics properties as magnetic susceptibility and specific heat as a function of temperature and compare them with the results corresponding to non interacting AF dimers. [1]   J. E.Weder et al., Coord. Chem. Rev. 232 (2002) 95. [2]  J. R. Vane, R. M. Bottling (Eds.), “Aspirin and Other Salicylates”, Chapman and Hall, London, 1992. [3]   X. Wang, Medical Hypotheses 50 (1998) 239.
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