Binuclear copper(II) complexes of the tetradentate ligand 1,4-di(2′-pyridyl)aminophthalazine: some novel five-coordinate derivatives

Abstract

Reaction of the title ligand (L) with copper salts leads to the formation of three principal series of compounds, LCu2X3(OH)•H2O (X = Cl, Br), LCu2(RCO2)3, and LCu2(RCO2)4, where RCO2 represents various aliphatic and aromatic carboxylate species. Magnetic data, electronic spectroscopic data both at room temperature and at −196 °C, infrared spectra, and microanalytical data are correlated to reveal that these complexes contain a binuclear copper-copper system in which the copper atoms are 5-coordinate and square pyramidal. Brief details are presented of an X-ray structural analysis of the chloride complex confirming the structure proposed.The ligand forms complexes both in its neutral form and in an anionic deprotonated form. The ultraviolet spectra of the complexes distinguish these modes of bonding. The electronic spectra are discussed in terms of the 5-coordinate square pyramidal copper chromophore deemed to be present. In the complex L2Cu, the copper atom has a trigonally distorted 6-coordinate environment with tridentate anionic ligand.

Copper complexes of polyfunctional phthalazines. Mononuclear and polynuclear derivatives

“…Neutral ligand derivatives are confirmed for all the carboxylate complexes in the solid state, with the possible exception of VII, by the presence of at least one charge transfer band at 27000 cm-I or higher (13). Although compound VII has a solid state charge transfer band at 27500 cm-I, analytical and other data suggest an anionic derivative.…”

“…Previous studies have shown that the presence of an infrared band above 1000 cm-I, associated with the ring breathing mode of the pyridine ring in PAP, indicates the coordination of this group to the metal centres (13). Absorptions in the range 1017-1025 cm-I (Table 2) for compounds V-IX indicate the involvement of the pyridine rings in coordination and suggest that PAP behaves as a tetradentate ligand.…”

“…Polyfunctional ligands derived from hydrazine (1 -3), pyrazole (4)(5)(6)(7)(8), pyridazine (4, 9-1 I), and phthalazine (4,9,11,(12)(13)(14)(15)(16)(17)(18)(19) form transition metal complexes in which the metals are brought into close proximity because of the presence of the N,, diazine, fragments in these systems. Antiferromagnetic exchange between the adjacent metal centres has been demonstrated in some of these complexes (4,11,13,15,16,18) and catecholase activity has been shown with binuclear copper complexes of the binucleating ligand 1,4-di(2'-pyridyl) aminophthal- 'To whom all correspondence should be addressed. azine (PAP) (Fig.…”

“…PAP has been shown to bind preferentially to two metal centres forming binuclear complexes with copper, cobalt, nickel, and zinc salts ( 13,15,16,18,19). Antiferromagnetic exchange exists between the metal centres in cobalt, nickel, and copper complexes of PAP (13,15,16,18).…”

“…Antiferromagnetic exchange exists between the metal centres in cobalt, nickel, and copper complexes of PAP (13,15,16,18). PAP appears to be quite sensitive to protonation, even in mildly acidic solution, and as a result of the inherent acidity of aqueous and alcoholic solutions of certain commercially available metal salts, protonated FIG.…”