Crystallographic and Theoretical Studies on a Coupled Chain of Binuclear Cu(II)-Fluoraspirinate Complexes

C. A. LAMAS; O. E. PIRO; E. E. CASTELLANO; E. M. RUSTOY; O. V. QUINZANI

Bahía Blanca, Argentina

Congreso; IV Reunión de la Asociación Argentina de Cristalografía (AACr); 2008

Asociación Argentina de Cristalografía (AACr)

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.