COORDINATION BEHAVIOR OF 2-GUANIDINOBENZIMIDAZOLE TOWARDS COBALT(II),NICKEL(II), COPPER(II) AND ZINC(II) - AN EXPERIMENTAL AND THEORETICAL-STUDY

The following coordination compounds derived from 2-guanidinobenzimida zole (2GB) (1); [Ni(2GB)(2)]Cl-2 . H2O, (2); [Ni(2GB)(2)]Br-2 . 3H(2)O , (3); [Ni(2GB)(2)](NO3)(2), (4); [Ni(2GB)(2)](OAc)(2), (5); [Cu(2GB)C l-2], (6); [Cu(2GB)Br-2], (7); [Cu(2GB)(2)]Br-2 . 2H(2)O, (8); [Cu(2GB )(2)](NO3)(2) . H2O, (9); [Cu(2GB)(2)](OAc)(2) . H2O, (10); [Zn(2GB)Cl -2]. H2O, (11); [Zn(2GB)Br-2]. H2O, (12); [Co(2GB)Cl-2(H2O)(2)]. H2O, (13), [Co(2GB)(2)Cl-2]. 3H(2)O, (14); [Co(2GB)(2)(H2O)(2)](NO3)(2) . 4 H(2)O, (15); and [Co(2GB)(2)(H2O)(2)] (OAc)(2), (16) have been synthes ized and characterized by i.r. and electronic spectroscopy. In additio n (6)-(10) were analysed by e.p.r. The X-ray diffraction structure of compound (4) was obtained. It crystallizes in the monoclinic system, C 2/c (a = 22.511(7), b = 6.735(6) and c = 15.345(5) Angstrom, beta = 11 5.31(3)degrees, Z = 4, final R = 0.0360 and R(w) = 0.0388 for 1167 obs erved independent reflections). The nickel(II) atom coordinates two li gands in a square-planar geometry through the imidazolic N(3) and the guanidino N(12). The probable ligand isomers involved in the coordinat ion were determined by theoretical calculations, and the possible stru ctures of the coordination compounds were investigated in order to ver ify that the experimentally proposed structures were stable. Two diffe rent types of coordination compounds were found. One, where the ligand is chelating through the imidazolic N(3) and the guanidino N(12), whi ch is the case for most of the complexes [(2)-(13)]. With only one lig and in the coordination sphere, the structure was either tetrahedral ( copper and zinc chloride and bromide complexes) or octahedral (cobalt) . With two chelating 2GB units a square-planar geometry was stabilized [(2)-(5) and (8)-(10)]. The second type of coordination behaviour was observed in the cobalt compounds [(14)-(16)]. Here the ligand coordin ates monodentate through the imidazolic N(3); the structure is tetrahe dral.