pH-dependent monomer <-> oligomer interconversion of copper(II) complexes with N-(2-R-imidazol-4-ylmethylidene)-2-aminoethylpyridine (R = methyl, phenyl)

The monomer <-> oligomer interconversion of the reported metal complexes is generated by proton abstraction/supply as a common external information in put. The mononuclear copper(II) complexes 1 and 2 with [CuCl2(HLn)] chemica l formula have been prepared (HL1 = N-(2-methylimidazol-4-ylmethylidene)-2- aminoethylpyridine; HL2 = N-(2-phenylimidazol-4-ylmethylidene)-2-aminoethyl pyridine). The crystal structures were determined. 1 . H2O, C12H16N4OCl2Cu: a = 13.773(2) Angstrom, b = 8.245(2) Angstrom, c = 13.861(2) Angstrom, bet a = 110.10(1)degrees, monoclinic, P2(1)/n, and Z = 4. 2, C17H16N4Cl2Cu: a = 7.6659(7) Angstrom, b = 16.287(1) Angstrom, c = 14.103(1) Angstrom, beta = 95.058(7)degrees, monoclinic, P2(1)/c, and Z = 4. Complexes 1 . H2O and 2 assume a pentacoordinated square pyramidal geometry with a N3Cl2 donor set consisting of the nitrogen atoms of the protonated tridentate ligand and tw o chloride ions in the solid state, while in aqueous solution the Cu(II) io n is tetracoordinated (N(3)Ow donor set). When 1 and 2 are treated with an equimolar amount of sodium hydroxide or triethylamine, the deprotonation of the imidazole moiety promotes a self-assembly process, arising from coordi nation of the imidazolate nitrogen atom to a Cu(II) ion of an adjacent unit , to yield compounds 1'. 4H(2)O as the perchlorate salt, and 2'a . 6H(2)O a s the perchlorate salt and 2'b as the hexafluorophosphate salt, respectivel y. 1'. 4H(2)O, C12H15N4O5ClCu: a = b = 13.966(2) Angstrom, c = 33.689(3) An gstrom, tetragonal, I4(1)/a, and Z = 16. 2'a . 6H(2)O, C51H51N12O15Cl3Cu3: a = 15.177(3) Angstrom, b = 15.747(3) Angstrom, c = 14.128(3) Angstrom, alp ha = 100.06(2)degrees, beta = 110.37(2)degrees, gamma = 63.54(1)degrees, tr iclinic, P (1) over bar, and Z = 2. 2'b, C17H15N9F6PCu: a = b = 29.812(5) A ngstrom, c = 11.484(3) Angstrom, trigonal, R (3) over bar, and Z = 18. The nuclearity of the self-assembled molecules and their detailed structure wer e confirmed to be cyclic imidazolate-bridged tetranuclear for 1'. 4H(2)O an d hexanuclear for 2'a . 6H(2)O and 2'b, respectively, through single-crysta l X-ray analyses and FAB-MS spectra. Variable-temperature experimental magn etic susceptibility data were well reproduced by using the Heisenberg model based on a cyclic tetranuclear structure for 1' and a cyclic hexanuclear s tructure for 2'a and 2'b. The reversible interconversion between the proton ated monomeric and deprotonated oligomeric species were confirmed by pH-dep endent potentiometric and electronic spectral titrations in aqueous solutio n, whereas the Pd(II) complex did not show a perfect disassembly process.