Co(II), Ni(II), and Zn(II) compounds of the new tridentate ligand N,N-bis(2-ethyl-5-methyl-imidazol-4-ylmethyl)aminopropane (biap).: X-ray structures of biap•H2O, [Co(biap)(NCS)(OAc)], [Ni(biap)(NCS)(OAc)], [Ni(biap)(NCS)2(MeCN)](MeCN), and [Ni(biap)2](BF4)2(EtOH)

The syntheses and characterizations are described of 18 transition metal coordination compounds with the novel tridentate ligand N,N-bis(2-ethyl-5-methyl-imidazol-4-ylmethyl)-aminopropane (biap). Compounds with formulae [M(biap)-(X)(Y)(H2O)(n)].(solvent) with X-, Y- = Cl-, Br-, NO3-, CH3COO- and NCS-, and n = 0 or 1, and [M(biap)(2)](BF4)(2).(solvent), with M = Co2+, Ni2+, and Zn2+, as well as the dinuclear complexes [Ni(biap)X-2](2) (X- = Cl-, NCS-) have been isolated. The ligand biap acts as a tridentate ligand in all compounds, either meridionally or facially, except for the cobalt compound [Co(biap)(NCS)(OAc)], where the X-ray structure indicates that the amine nitrogen is weakly bonded, almost only semi-coordinated (Co-N = 2.387(4) Angstrom). The ligand biap, synthesized in a very simple one-pot and one-step condensation reaction, crystallizes with one molecule of water, viz. biap . H2O. Its single-crystal X-ray structure reveals a three-dimensional network based on hydrogen bonds, whereby the water oxygen is tetrahedrally connected to four imidazole-nitrogens of three biap molecules. Eighteen coordination compounds have been obtained with salts of divalent cobalt, nickel, and zinc. Single-crystal X-ray structures have been obtained for four of the compounds. The nickel(II) ion is (distorted) octahedrally surrounded by biap nitrogens and/or anion or solvent nitrogens or oxygens, resulting in the chromophores NiN6, NiN3N2N, and NiN3NO2 for [Ni(biap)(2)](BF4)(2).(EtOH) (14), [Ni(biap)(NCS)(2)(MeCN)].(MeCN) (13), and [Ni(biap)(NCS)(OAc)] (12), respectively. The ligand is coordinated meridionally in 13, but facially in 14 and 12, illustrating its flexibility. The cobalt(II) ion in [Co(biap)(NCS)(OAc)] (4) is in a very distorted pseudo-octahedral environment, which can be regarded as distorted tetrahedral when considering didentate coordination of the biap and monodentate coordination of the acetate ion. This severely distorted geometry is reflected in the unusual ligand field spectrum of this cobalt complex. Spectroscopic characterization (IR, LF and NMR) of the compounds shows a remarkable variety in composition and geometry, partly determined by the solvent used for the synthesis of the complexes. The flexibility of the tridentate ligand, which can bind mer or fac, with one or two ligands coordinated to the metal ion is quite unexpected in view of the assumed steric crowding from the ethyl- and propyl-chains. (C) 2000 Elsevier Science S.A. All rights reserved.