Inorganica Chimica Acta 324 (2001) 194 – 202 www.elsevier.com/locate/ica Complexation of Cu(II)M(II) (M = Cd, Co, Ni, Zn) heterodinuclear compounds of an octacoordinate hexaazamacrocyclic ligand Jide Wang 1 , Deyuan Kong, Arthur E. Martell *, Ramunas J. Motekatis, Joseph H. Reibenspies Department of Chemistry, Texas A&M Uniersity, College Station, TX 77842 -3012, USA Received 11 June 2001; accepted 6 August 2001 Abstract In this paper the investigation of the formation of HDTHCu heterodinuclear complexes of Zn(II), Cd(II),Co(II) and Ni(II) and HDTHCo heterodinuclear complexes with Ni(II) and Pb(II) in aqueous solution by control of the stoichiometry of metal ions and HDTH as well as p[H] of the solution (HDTH is a dinucleating 28-membered hexaazadiphenol macrocyclic ligand 3,7,11,19,23,27-hexaaza-33,34-dihydroxy-15,31-dimethyl-tricyclo-tetratriaconta-1(32),13,15,17(34),29(33),30-hexaene). The pH po- tentiometric method has been utilized successfully to determine formation constants while in turn determine the distribution of species present in the solution as a function of p[H]. Spectrophotometry was used to investigate the formation process of the heterodinuclear complexes. The X-ray crystal structures of two homodinuclear complexes of Cu(II) and Zn(II) are also reported. These results show that the two moieties of the ligand react with Cu(II) ions separately, functioning like two independent binding groups. These studies suggested that the Cu(II) complexes of the macrocyclic ligand can form the basis for discrete and stable heterodinuclear complexes and can be used to investigate the complexation in solution by taking Cu(II) as one moiety of the heterodinuclear complex. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Stability constants; Azamacrocycle heterodinuclear complexes; Macrocyclic dinucleating ligand; Crystal structures; Transition metal complexes 1. Introduction Bimetallic enzymes catalyze diverse reactions ranging from alkane oxidation to biopolymer degradation [1]. The discoveries of the heterodinuclear centers in some metalloproteins, such as purple acid phosphatase and human calcineurin [FeZn] [2], human protein phos- phatase 1 [FeMn] [3] and Cu  -heme centers [CuFe] [4], have stimulated interest in the investigation of models containing heterodinuclear complexes [5]. However, so- lution studies of heterodinuclear complexes can be made difficult by metal dissociation and metal scram- bling. To overcome this difficulty, Okawa et al. [6,7] have proposed and even developed some dinucleating compartmental ligands whose two metal-binding sites are not equivalent with respect to the cavity size, the coordination number or the nature of the donor atoms, in order to provide discrete and stable heterodinuclear complexes. Dinucleating macrocyclic ligands capable of binding two metal ions in close proximity have received particu- lar attention. A series of studies has been reported from this lab on the design and synthesis of polyaza macro- cyclic ligands, and the stabilities of corresponding metal complexes. Some of them are HDTH [8], BDBPH [9], [24]RBPyBC [10] and OBISDIEN [11] (Chart 1). From the results of these studies it was found that Cu(II) and Fe(III) display much stronger binding with the macro- cyclic ligands than do other divalent transition metal ions, especially in the case of HDTH and BDBPH, * Corresponding author. Tel.: +1-979-845 5055; fax: +1-979-845 4719. E-mail address: martell@mail.chem.tamu.edu (A.E. Martell). 1 Current address: Department of Chemistry, Xinjiang University, Urumqi 830046, China. 0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0020-1693(01)00590-4