A structural study of the hydrated and the dimethylsulfoxide, N,N′-dimethylpropyleneurea, acetonitrile, pyridine and N,N-dimethylthioformamide solvated nickel(II) ion in solution and solid state

The structure of the solvated nickel(II) ion has been studied in solution by EXAFS in a series of solvents with different coordinating properties. The solvents studied are water, dimethylsulfoxide, N,N'-dimethylpropyleneurea (oxygen donors), acetonitrile, pyridine (nitrogen donors) and N,N-dimethylthioformamide (sulfur donor). A number of solid solvate structures has been determined crystallographically, hexakis(dimethylsulfoxide)nickel(II) perchlorate, [Ni(OS(CH3)(2))(6)](ClO4)(2), tetrakis(dimethylsulfoxide)bis(N,N'-dimethylpropyleneurea)nickel(II)perchlorate, [Ni(OS(CH3)(2))(4)(OCN2(CH3)(2)(CH2)(3))(2)](ClO4)(2), tetrakis(pyridine)bis(trifluoromethanesulfonato)nickel(II), [Ni(NC5H5)(4)(O3SCF3)(2)], bisaquatetrakis(pyridine)nickel(II) perchlorate pyridine solvate, Ni(NC5H5)(4)(OH2)(2)(ClO4)(2).C5H5N, and hexakis(N,N-dimethylthioformamide)nickel(II) perchlorate, [Ni(SCHN(CH3)(2))(6)](ClO4)(2), in order to be used as model compounds in the EXAFS studies of the solutions. The hydrated and the dimethylsulfoxide, acetonitrile and N,N-dimethylthioformamide solvated nickel(II) ions are all octahedral in solution with Ni-solvent bond distances of 2.055(2), 2.064(2), 2.062(2) and 2.454(2) Angstrom, respectively. Pyridine has too low permittivity to allow dissociation of nickel(II) salts. The nickel(II) trifluoromethanesulfonate complex is solvated by four pyridines in the equatorial plane with two oxygen atoms from the trifluoromethanesulfonate anions in the axial positions completing the octahedron, and the perchlorate salt takes up water very easily, forming a bisaqua(tetrakispyridine)nickel(II) solvate in both solid state and pyridine solution. The Ni-N and Ni-O bond distances are approximately 2.10 Angstrom in these complexes. The nickel(11) ion is five-coordinated, probably in square-pyramidal fashion, in N,N'-dimethylpropyleneurea with a mean Ni-O bond distance of 2.000(2) Angstrom. The reason for this lower coordination number is certainly sterical due to the bulkiness of the N,N'-dimethylpropyleneurea molecule. The octahedral complexes with oxygen and sulfur donor solvents are green, while with nitrogen donor solvents they are blue due to different ligand field splitting ability versus the nickel(II) ion. The five-coordinated N,N'-dimethylpropyleneurea solvated nickel(II) ion has a deep red color. (C) 2002 Elsevier Science B.V. All rights reserved.