Data coordination geometry

On the basis of infrared and Raman data 102), the structure is believed to have bridging halogen atoms between the metal atoms, the coordination geometry around each... 

Bis(bipyridyl)nickel(0) has been prepared by metal-vapor methods and electrochemical data were obtained for it. In these low-valence states, a significant proportion of the electron density lies on the bipy ligand.2469 Also, the crystal and molecular structure of 4,6-dimethyl-2,2 -dipyr-idyldicarbonylnickel(O) (1021) has been determined. The coordination geometry about Ni is tetrahedral.2470... 

Zn and N K-edge XANES have been used to distinguish the coordination geometries in (1,2-ethanediylidene)-bis(5 -methylhydrazonecarbodithionate) zinc complexes (109). The technique distinguished between tetrahedral species, square pyramidal dimers, and square pyramidal monomers, formed when pyridine was present. These studies were in conjunction with spectroscopic characterization and X-ray single-crystal data where possible.53 The results demonstrated the value of this technique when single crystals could not be obtained. 

Comparison of the experimental data with the trends predicted from quantum chemistry ab initio simulations demonstrated that the multiple conductance values of Au-alkanedithiol-Au junctions could be attributed to different Au-sulfur coordination geometries and to different conformations of the alkyl chain. In particular, the medium conductance corresponds to an all-trans conformation of the alkyl chain, with each sulfur atom coordinated in atop position to a single... 

EPR. The EPR of the Cu complex 62c has been reported as a 1% powder sample at 77 K and is given in Table XI (Section IV.A), which compares the EPR data for 62c to Cu[pz(SMe)8] (48) (Scheme 9), Cu(TPP) and Cu(pc). The spectrum is typical of a monomeric square-planar copper with axial symmetry. The EPR spectrum for 62c closely matches that of 48 implying that although the peripheral tridentate coordination geometry has an effect on the ir-clcctronic structure of the pz ring it does not effect the electronic properties of the central Cu2+ ion, whose unpaired electron density is in a a orbital. 

Structural Characterization. The crystal structure of 83 (Fig. 15) surprisingly revealed eight Ag+ ions coordinated to the periphery of the porphyrazine—four bound in an endocyclic fashion by the crown moieties, consistent with the optical data, and four coordinated to the meso pockets in a (S-N-S) tridentate coordination geometry. The lack of evidence for meso coordination in solution suggests a preference for the ligation of Ag+ by the crown moieties (25). 

The d-d spectra of copper(II) compounds have provided a fruitful field for practitioners of the AOM. A wealth of structural data is available, and a rich variety of coordination geometries has been revealed. If we can make allowance for the dependence of the AOM parameters on the intemuclear distance, we are provided with excellent opportunities to test the validity of AOM parameters over a range of related systems. However, the progress of such studies over the years has illustrated the fact that a simple model may be very successful in explaining a limited amount of dubious experimental data as more crystal structures appear and as better spectroscopic data become available, the simple model may require considerable refurbishment, perhaps to the extent that it loses some of its appeal and utility. 

X-ray structural data for [Ru(bpy)3] " " and a wide range of other polypyridyl derivatives of Ru have been used to develop molecular mechanics parameters for these types of complex with the MM3 force field. Correlations between coordination geometry and emission properties of the Ru complexes have been examined. 

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