Single crystal EPR of Cu(II) doped [Co(tbz) 2 (NO 3 )(H 2 O)]NO 3 : probe into copper /thiabendazole interaction K.K. Mothilal a , Chandran Karunakaran b , P. Sambasiva Rao c , Ramachandran Murugesan d, * a Department of Chemistry, Saraswathi Narayanan College, Madurai, Tamil Nadu, India b Department of Chemistry, VHNSN College, Virudhunagar 626 001, Tamil Nadu, India c Department of Chemistry, Pondicherry University, Pondicherry, India d School of Chemistry, Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India Received 2 December 2002; received in revised form 21 March 2003; accepted 21 March 2003 Abstract EPR of Cu(II) doped, low symmetry Co(II) /thiabendazole complex [Co(tbz) 2 (NO 3 )(H 2 O)](NO 3 ) is investigated at 300 K. The spin Hamiltonian parameters are found to be orthorhombic with g 33 /2.305, g 22 /2.1351, g 11 /2.0626 and A 33 /147.0 /10 4 , A 22 /33.5 /10 4 and A 11 /23.1 /10 4 cm 1 . Computer simulation of isofrequency plots reveal that the Cu(II) ions is substitutionally incorporated in the host lattice. Angular variation of the spectra shows the presence of two magnetic sites in the lattice. The low magnitude of A 33 of the complex is rationalized in terms of admixture of d x 2 y 2/ d z 2 ground state and delocalization of unpaired spin density onto the ligands. # 2003 Elsevier B.V. All rights reserved. Keywords: Single crystal EPR; Low symmetry Cu(II) complex; Cu(II) EPR; Metal /thiabendazole interaction; Admixed ground state 1. Introduction During the last decade metal complexes of drugs have been developed as pharmaceuticals, owing largely to their biomimetic and enhanced drug action efficiency [1 /8]. In this context, coordina- tion compounds offer a great variety of geometry and reactivity for use in drug design and metal- drug interaction [3 /8]. Thiabendazole, tbz belongs to the benzimadazole group, and is of interest because of its importance as fungicide and anthel- mintic agent [9 /12]. Without loosing the medicinal properties of tbz, several metal complexes of tbz have been isolated and characterized [13 /16]. Many other physical parameters (aqueous solubi- lity, stability, etc.) are increasingly being studied in the context of modeling of metal /tbz interaction and also to study the dissolution ability of com- plexes in water [17,18]. A number of crystals structure determinations of metal /tbz complexes by three-dimensional X-ray methods have been carried out. These metal /tbz complexes have been revealed to adopt widely different symmetry * Corresponding author. Fax: /91-452-859105. E-mail address: rammurugesan@yahoo.com (R. Murugesan). Spectrochimica Acta Part A 59 (2003) 3337 /3345 www.elsevier.com/locate/saa 1386-1425/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S1386-1425(03)00153-7