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Crystallography, the most powerful method for obtaining structural data, can benefit from help from other techniques. In this work, 119Sn Mössbauer spectroscopy was used to assist crystallography, for finding the tin(II) positions in the unit-cell and determine a tin(II) coordination in agreement with both the diffraction data and the tin electronic structure. Even high quality single crystal data do not guarantee that the right solution will be obtained. A first attempt at the structure of α–SnF2 yielded the tin positions with very reasonable R and Rw residuals, 0.23-0.25. However, the fluorine positions could not be found (Bergerhoff, 1962). After many other attempts, the full crystal structure was finally solved 14 years later (R.C. McDonald et al. 1976). The difference in the tin position with the initial solution (1962) was that, in the latter, half of the tin atoms were on special sites, however, the tin sublattice was identical. Because the tin sites in the initial solution gave very reasonable residuals, 14 years of hopeless efforts were wasted. The presentation will show that this could have been avoided using 119Sn Mössbauer spectroscopy. This was possible since the spectrum had already been recorded (A.J.F. Boyle et al., 1962). Mössbauer spectroscopy can also help determine the tin coordination, when combined with powder diffraction data, in case of disordered structures. The presence of tin(II), disordered with a metal ion in cubic coordination, when diffraction shows there is no lattice distortion and no superstructure, suggests that tin has also a cubic coordination. This would require the tin lone pair to be non-stereoactive; however Mössbauer spectroscopy shows it is stereoactive.
abstracts
Carboxylate groups may interact as bridging ligands with divalent transition metals present in biological environments, thereby altering the bioavailability of drugs. Moreover, it is well known that many complexes of divalent transition metals are capable of catalyzing the hydrolysis of RNA (Stem et al., 1990; Kimura, 1994). The coordination chemistry of Cu2+ complexes bridged by phenylacetate has been reported. We have found only two reports of a dinuclear Co2+ complexes, namely tetrakis (phenylacetato)bis[(quinoline-N)-cobalt(II)](Cui et al.,1999),μ-aqua-κ2O:O-di-μ-phenylacetato-κ4O:O′-bis[(1,10-phenanthroline-κ2N,N′) (phenyl acetato-κO)cobalt(II)](Kong et al., 2005) and dinuclear Cu2+ complex, namely tetrakis (phenylacetato)bis-[(N,N-dimethylformamide)copper(II)], in which all phenylacetate groups are in bidendate bridging modes. In this presentation, the crystal structure of a new dimeric complex obtained by reaction of phenylacetic acid with copper(II) acetate is described. Each Cu(II) atom is six-coordinated by five O atoms from carboxylate groups of the phenylacetate and DMSO ligands and is completed by a Cu-Cu bond in a strongly distorted octahedral coordination, in which an inversion center is located at the mid-point of the Cu-Cu bond with a Cu...Cu distance of 2.6321(4) Å. This is longer than the 2.251(2)Å distance found in the polymeric complex [Cu2(C8H7O2)4]n. However, it is similar to the 2.6414(8) Å and 2.6261(8)Å distances found in the complex [Cu2(C8H7O2)4(C3H7NO)2] (Kong et al., 2005). The Cu-O phenylacetate bond length lies in the range 1.9644(14) to 1.9734 (14) Å and the Cu-ODMSO bond length is 2.1319(13) Å.
