Dinuclear nickel(II) complexes of phenol-based "end-off" compartmental ligands and their urea adducts relevant to the urease active site

Two phenol-based compartmental ligands of the "end-off" type, 2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenol (HL1) and 2-{N-[2-(dimethylamino)ethyl]iminomethyl}-6-{N-methyl-N-[2-(dimethylamino)ethyl]aminomethyl}-4-bromophenol (HL2), have been used to form [Ni-2(L-1)(AcO)(NCS)(2)(MeOH)] (1), [Nh(L-1)(AcO)(2)-(MeOH)]BPh4 (2), [Ni-2(L-2)(AcO)(NCS)(2)(MeOH)] (3), [Ni-2(L-2)(AcO)(2)]BPh4 (4), and [Ni-2(L-2)(NCS)(3)(MeOH)] (5). X-ray crystallographic studies were done for 2-5. 2: triclinic, space group P (1) over bar, a 13.613(3) Angstrom, b = 16.475(4) Angstrom, c = 11.307(4) Angstrom, alpha = 99.90(2)degrees, beta = 104.16(2)degrees, gamma = 109.01(2)degrees, V = 2253(1) Angstrom(3), Z = 2. The complex cation has a dinuclear core triply bridged by the phenolic oxygen of (L-1)- and two acetate groups in the syn-syn mode. One Ni has a six-coordinate geometry together with a methanol oxygen. 3: triclinic, space group P (1) over bar, a = 10.167(1) Angstrom, b = 16.119(2) Angstrom, c = 9.472(3) Angstrom, alpha = 103.53(2)degrees, beta = 100.91(1)degrees, gamma = 85.62(1)degrees, V = 1481(1) Angstrom(3), Z = 2. A pair of Ni ions are bridged by the phenolic oxygen of (L-2)(-), an isothiocyanate nitrogen, and an acetate group. The sixth position of one Ni is occupied by a methanol oxygen and that of the other Ni by isothiocyanate nitrogen. 4: monoclinic, space group P2(1)/n, a = 15.146(2) Angstrom, b = 9.442(3) a, c = 30.844(2) Angstrom, beta = 93.427(9)degrees, V = 4402(1) Angstrom(3), Z = 4. TWO Ni ions are bridged by the phenolic oxygen of (L-2)(-) and an acetate group. The Ni bound to the iminic pendant arm is nearly planar whereas the Ni bound to the aminic pendant arm is of six-coordination together with a bidentate acetate group. 5: monoclinic, space group C2/c, a = 26.744(5), b = 10.323(4) Angstrom, c = 21.785(6) Angstrom, beta = 94.73(2)degrees, V = 5993(3) Angstrom(3), Z = 8. TWO Ni ions are bridged by the phenolic oxygen of (L-2)(-) and an isothiocyanate nitrogen. The Ni bound to the iminic pendant arm is of five-coordination along with an isothiocyanate nitrogen. The Ni bound to the aminic pendant arm has a six-coordinate geometry together with a methanol oxygen and an isothiocyanate nitrogen. 1-5 were examined regarding their ability to bind urea, and 4 and 5 were shown to form [Ni-2(L-2)(AcO)(2)(urea)]BPh4 (4') and [Ni-2(L-2)(NCS)(3)(urea)] (5'), respectively. 5' crystallizes in the monoclinic system, space group P2(1)/n, with a = 11.709(5), b = 15.100(4), c = 17.548(5) Angstrom, beta = 95.58(3)degrees, V = 3087(1) Angstrom(3), and Z = 4. Its dinuclear core is very similar to that of 5 except that the methanol of 5 is replaced by a urea molecule.