Solution coordination structural considerations

Copper and nickel complexes of the tridentate l-(2-carboxyphenyl)-3,5-diphenyl- (169 X = C02 R = R = Ph) and 1-(2-hydroxyphenyl)-3,5-diphenyl-(169 X = 0 R = R = Ph) formazans were prepared118 by the interaction of the formazan and the appropriate metal acetate in alcohol and were assigned the three-coordinate structures (170 X = O, C02 R = R = Ph M = Ni, Cu) since the diamagnetic nickel complexes were found to be unimolecular in benzene solution. Treatment of the nickel complex (170 X = O, R = R = Ph M = Ni) with pyridine gave a violet crystalline adduct which was assigned the four-coordinate structure (171 X = O R = R = Ph M = Ni). A product similar to the latter could not be obtained from the nickel complex of l-(2-carboxyphenyl)-3,5-diphenylformazan but nickel complexes of this type were obtained from both l-(2-hydroxyphenyl)- (169 X = O, R = CN R = Ph) and l-(2-carboxyphenyl)- (169 X = C02 R = CN R = Ph) 3-cyano-5-phenylformazans. In all three cases a considerable shade change occurred on going from the three-coordinate complex to the pyridine adduct. 

Only the most electropositive metals, the alkali metals and alkaline-earths, form hydrosulphides. LiSH is particularly unstable, being very sensitive to hydrolysis and oxidation, and decomposes at temperatures above about 50°C. It may be prepared in a pure state by the action of HjS on lithium n-pentyl oxide in ether solution. Its structure is of the zinc-blende type and similar to that of UNH2, but there is considerable distortion of the tetrahedral coordination groups ... 

Figure 3 depicts a schematic of how one can arrive at different meso-ciystal structures. Consideration of the coordination environment of the metal ions is crucial for predicting the nature of the resulting meso-ciystal. For example, a nanocomposite mesociystal may be obtained of phase-separated CuO and ZnO (Fig. 3b). This is due to the differing coordination environments of the copper ions (Cu in Jahn-Teller distorted octahedra in CuO) and the zinc ions (Zn in a tetrahedral environment in ZnO). On the other hand, a solid solution of Zno 2Nio sO is formed when zinc and nickel nitrates are employed as precursors, since the coordination environments are similar. One strength of this synthetic approach is the effective charge transfer which can occur in...

COORDINATION OF THE URANYL ION THROUGH REACTION WITH AQUEOUS SOLUTIONS CONTAINING POLYACRYLIC ACID AND POLYSODIUM ACRYLATE-STRUCTURAL CONSIDERATIONS... 

The elucidation of actinide chemistry in solution is important for understanding actinide separation and for predicting actinide transport in the environment, particularly with respect to the safety of nuclear waste disposal.72,73 The uranyl CO + ion, for example, has received considerable interest because of its importance for environmental issues and its role as a computational benchmark system for higher actinides. Direct structural information on the coordination of uranyl in aqueous solution has been obtained mainly by extended X-ray absorption fine structure (EXAFS) measurements,74-76 whereas X-ray scattering studies of uranium and actinide solutions are more rare.77 Various ab initio studies of uranyl and related molecules, with a polarizable continuum model to mimic the solvent environment and/or a number of explicit water molecules, have been performed.78-82 We have performed a structural investigation of the carbonate system of dioxouranyl (VI) and (V), [U02(C03)3]4- and [U02(C03)3]5- in water.83 This study showed that only minor geometrical rearrangements occur upon the one-electron reduction of [U02(C03)3]4- to [U02(C03)3]5-, which supports the reversibility of this reduction. 

It is especially important to investigate the molecular structure of coordination compounds in the vapor phase because the relatively weak coordination interactions may be considerably influenced by intermolecular interactions in solutions and especially in crystals. It has been shown that the geometrical variations can be correlated with other properties of the molecular complexes ). In particular the structural changes in the F3B N(CH3)3 and CI3B N(CH3)3 molecules ) relative to the respective monomeric species unambiguously indicated boron trichloride to be a stronger acceptor than boron trifluoride. Data on the geometry and force field have also been correlated ). 

The coordination of the dinitrogen ligand is maintained when traTO-[Re(N2)Cl(dppe)2] is exposed to NaX salts (X = NCS, NCO , Ns ) in THF/MeOH solutions. The isothiocyanato and azido complexes of type (276) have been studied by X-ray structural analysis.A Re— N2 bond length of 1.951 A is observed for the NCS compound which is somewhat shorter than that in the starting material and indicates a considerable degree of double bond character. 

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