Coordination behaviour of 2-guanidinobenzimidazole towards cobalt(II), nickel(II), copper(II) and zinc(II). An experimental and theoretical study |
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| Authors: | Norah Barba-Behrens America Vázquez-Olmos Silvia E Castillo-Blum Germund Höjer Sara Meza-Höjer Rosa María Hernández María de Jesús Rosales-Hoz Ramón Vicente Albert Escuer |
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| Institution: | (1) División de Estudios de Posgrado, Facultad de Química, UNAM, 04510 México DF, Mexico;(2) Departamento de Química, Centro de Investigatión y de Estudios Avanzados del IPN, Apartado Postal 14-740, 07000 México DF, Mexico;(3) Departament de Química Inorgánica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain |
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| Abstract: | Summary The following coordination compounds derived from 2-guanidinobenzimidazole (2GB) (1); Ni(2GB)2]Cl2· H2O, (2); Ni(2GB)2]Br2·3H2O, (3); Ni(2GB)2-(NO3)2, (4); Ni(2GB)2](OAc)2, (5); Cu(2GB)Cl2], (6); Cu(2GB)Br2], (7); Cu(2GB)2]Br2·2H2O, (8); Cu(2GB)2](NO3)2·H2O, (9); Cu(2GB)2](OAc)2· H2O, (10); Zn(2GB)Cl2]·H2O, (11); Zn(2GB)Br2]·H2O, (12); Co(2GB)Cl2(H2O)2]·5H2O, (13); Co-(2GB)2Cl2]·3H2O, (14); Co(2GB)2(H2O)2](NO3)2· 4H2O, (15); and Co(2GB)2(H2O)2](OAc)2, (16) have been synthesized and characterized by i.r. and electronic spectroscopy. In addition (6)–(10) were analysed by e.p.r. The X-ray diffraction structure of compound (4) was obtained. It crystallizes in the monoclinic system, C2/c (a = 22.511(7), b = 6.735(6) and c= 15.345(5)Å,  =115.31(3)°, Z = 4, final R = 0.0360 and R
w = 0.0388 for 1167 observed independent reflections). The nickel(II) atom coordinates two ligands in a square-planar geometry through the imidazolic N(3) and the guanidino N(12).The probable ligand isomers involved in the coordination were determined by theoretical calculations, and the possible structures of the coordination compounds were investigated in order to verify that the experimentally proposed structures were stable. Two different types of coordination compounds were found. One, where the ligand is chelating through the imidazolic N(3) and the guanidino N(12), which is the case for most of the complexes (2)–(13)]. With only one ligand 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 coordinates monodentate through the imidazolic N(3); the structure is tetrahedral. |
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