Spectral and XRD studies on perchlorate salts of several Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes from 1-methyllumazine and 1,6,7-trimethyllumazine Esther R. Acun ˜ a-Cueva a , Rene ´ Faure b , Nuria A. Illa ´n-Cabeza a , Sonia B. Jime ´nez-Pulido a , Miguel N. Moreno-Carretero a, * a Dep. Quı ´mica Inorga ´nica y Orga ´nica, Universidad de Jae ´n, E-23071 Jae ´n, Spain b Dep. Chimie Analitique 2, Universite ´ ‘Claude Bernard’, Lyon I, France Received 8 April 2002; accepted 7 May 2002 Abstract A number of complexes with general formula ML 2 (ClO 4 ) 2 × /n H 2 O × /m CH 3 CN [M/Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)] have been synthesized by reaction of 1-methyllumazine (MLM) and 1,6,7-trimethyllumazine (MLMD) and perchlorate salts in acetonitrile. The complexes have been characterized by elemental analysis, TG and DSC, as well as by IR, UV /Vis, EPR spectroscopies and magnetic measurements. The crystal structures of [Cu(MLM) 2 (H 2 O) 2 ](ClO 4 ) 2 , [Zn(MLM) 2 (H 2 O) 2 ](ClO 4 ) 2 and [Cu(MLM)(MLMD)(H 2 O)(CH 3 CN)](ClO 4 ) 2 have been determined by X-ray diffraction methods. In the complexes Cu/MLM and Zn/MLM, the metal ions involve an octahedral geometry with two water molecules and two lumazine ligands coordinated through O4 and N5 atoms. The compound Cu/MLM/MLMD consists of monomeric units in which the Cu(II) atom is linked by two different lumazine derivatives (MLM and MLMD), a water and an acetonitrile molecules bonding directly to the metal ion. The environment around metal ion exhibits a geometry between a square-based pyramidal and an elongated tetragonal octahedral due to the different distances Cu /O4 in the apical positions. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Crystal structures; Copper complexes; Lumazine complexes; Zinc complexes 1. Introduction Much of the selectivity and efficiency of chemical transformations, which involve metalloproteins are due to a modulation of the properties of the metal ions by the protein to which they are bound. Geometric and electronic distortions, enforced by the protein backbone, and specific electrostatic fields and solvation patterns may lead to a destabilization of the catalytically active site (metal center(s) and/or enzyme-substrate com- plex(es)) and, therefore, to an activation of certain reaction channels. It is important to elucidate the relationship between the physical structure of the site, electronic structure of the metal, and protein function in order to discern those characteristics of the metal site that serve to perform a biological role [1  /3]. Pterin and pteridine derivatives should occur in conjugated or unconjugated form in a wide range of biological systems. Therefore, these compounds act as cofactors in oxygen activating reactions of physiological importance and, it is well known, their use as model to mimic the environment and reactivity of the metal site of the related enzymes [4  /9]. Previously, spectroscopic and magnetic properties, as well as some structures of coordination compounds with pteridine related ligands as lumazine (2,4-(1H ,3H )- pteridinedione) [10,11] and 1,3-dimethyllumazines have been reported [12  /19]. In an earlier study, several nitrate [12,14], perchlorate [13,17] and halide [15,18,19] complexes of 1,3-dimethyllumazine (DLM) and 1,3,6,7- tetramethyllumazine (DLMD) were synthesized and characterized. With the only exception of cis- * Corresponding author. Tel.:  /34-9-53-002738; fax:  /34-9-53- 012141 E-mail address: mmoreno@ujaen.es (M.N. Moreno-Carretero). Polyhedron 21 (2002) 1961  /1968 www.elsevier.com/locate/poly 0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0277-5387(02)01085-9