Synthesis, structures and characterization of the dinuclear nickel(II) complexes containing N,N,N ',N '-tetrakis[(1-ethyl-2-benzimidzolyl)methyl]-2-hydroxy-1,3-diaminopropane and their urea complexes relevant to the urease active site

New dinuclear nickel(II) complexes ([Ni-2(L-Et)(CH2ClCOO)(H2O)(2)](ClO4)(2) .H2O (3), [Ni-2(L-Et)(CCl3COO)-(H2O)(2)](ClO4)(2).H2O (4), [Ni-2(L-Et)(CF3C OO)(H2O)(2)](ClO4)(2). 3H(2)O (5)) and their urea complexes ([Ni-2(L-Et)(RC OO)-(ur)(H2O]ClO4)(2) (R = CH3 (6), C2H5 (7), CH2Cl (8), CCl3 (9), CF3 (10) ) (HL-Et = N,N,N'N'-tetrakis[(1-ethyl-2-benzimidazolyl)methyl]-2-hydroxy-1, 3-diaminopropane and ur = urea) have been prepared in order to model the ac tive site urease. These complexes were characterized by IR and UV-vis spect ra, and by magnetic susceptibilities. The crystal structures of the complex es [Ni-2(L-Et)(CH2ClCOO)(CH3OH)(2)](ClO4)(2)] (3') and [Ni-2(L-Et)(OAc)(ur) (H2O)](ClO4)(2). (CH3)(2)CO (OAc = acetate) (6') were determined by X-ray c rystallography. In the cation of 6', the two nickel(II) ions are bridged by an alkoxo of L-Et- and an acetato, and a monodentate urea molecule is atta ched to a nickel(II) through its oxygen atom. Variable temperature magnetic susceptibility measurements of the urea complexes 6, 8, and 10 show an ant iferromagnetic exchange coupling (2J = - 15.8, - 8.0, and - 13.3 cm(-1) for 6, 8, and 10, respectively, Hamiltonian H = -2JS(1).S-2 with S-1 = S-2 = 1 ) between two nickel(II) ions.