The structures of solvated complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and In(III) ions in 1,1,3,3-tetramethylurea (TMU) have been determined by means of EXAFS (extended X-ray absorption fine structure) and electronic spectroscopy. The solvation structures in TMU are square pyramidal for the Mn(II) and Ni(II) ions, distorted tetrahedral for the Co(II) and Cu(II) ions, tetrahedral for the Zn(II) ion, and octahedral for the Cd(II) and In(III) ions, while in water all these metal ions are six-coordinated octahedrons. The solvation structure of Fe(II) ion is square pyramidal or trigonal bipyramidal. In the bulky TMU solvent, the coordination number should be reduced for relaxation of the sterically repulsive interaction around the solvated metal ions. The metal-oxygen (M-O) bond lengths of solvated metal ions in TMU are
Solvation structures of the Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Ga(III) ions in methanol (MeOH), ethanol (EtOH), dimethyl sulfoxide (DMSO), and trimethyl phosphate (TMP) have been determined using extended X-ray absorption fine structure (EXAFS) spectroscopy. In MeOH, EtOH, and DMSO, the solvation structures of all metal(II,III) ions are 6-coordinate octahedral as in water, and the M-O bond lengths are similar to those in water. In the bulky solvent TMP, the 5-coordinate solvation structure is observed for the Zn(II) ion without ligand-field stabilization. The Ga(III) ion has the 6-coordinate solvation structure in TMP despite its smaller ionic radius than the Zn(II) ion because of the higher charge density on the Ga(III) ion. In the cases of the Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) ions, the electronic absorption spectra have been measured in MeOH, EtOH, and DMSO. All solutions for each metal(II) ion show a spectral pattern similar to that in water, which is consistent with the results of the EXAFS measurements.
Structure parameters of solvated silver(I) ions in
eight neat solvents were determined by extended X-ray
absorption fine structure spectroscopy. The coordination geometry
of the solvated silver(I) ion is
four-coordinate tetrahedral at the Ag−O bond distances of 239 pm in
trimethylphosphate, 239 pm in N,N-dimethylformamide, 238 pm in 1,1,3,3-tetramethylurea, and 238 pm in
dimethyl sulfoxide as oxygen-donating
solvents, and at the Ag−N bond distances of 229 pm in acetonitrile,
230 pm in 2-methylpyridine, 229 pm in
n-propylamine, and 231 pm in ethylenediamine as
nitrogen-donating solvents. According to our present
ab
initio molecular orbital calculations concerning the structure of
the silver(I) ion bound by n molecules of
hydrogen cyanide (n = 1−6) and acetonitrile
(n = 1−5) in the gas phase, the maximal stabilization
for the
solvation is observed at n = 4. The results of the
theoretical calculations in the gas phase are consistent
with
the experimental observations in solution.
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