Hydroxo-Bridged Complexes of Chromium (III), Cobalt (III), Rhodium (III), and Iridium (III)

Minerals as Molecules—Use of Aqueous Oxide and Hydroxide Clusters to Understand Geochemical Reactions

“…III oligomers: From work on small ions, it is clear that the first step in dissociation is protonation, which is usually much faster ( % 10 À9 -10 À4 s) than the subsequent bridging-bond ruptures, so that the relative fraction of m 2 -OH 2 and m 2 -OH is controlled by the solution pH [55,[60][61][62] (see Tables S-3 and S-4, in the Supporting Information). The second step is hydration by another incoming water molecule leading to dissociation of the bridge, sometimes via an m 2 -H 3 O 2 À moiety.…”

“…The mechanism involves bond rupture at two metal centers and the resulting surface structure is made stable by H 3 O 2 À bridges. This H 3 O 2 À bridge is known from studies of oxygen exchange in dimers [60,132] and is probably broadly relevant to surface reactions as well.…”

Synthesis of experimental models for molecular inorganic geochemistry—A review with examples

“…This type of detail exists for a considerable number of small hydrolytic molecules (see Springborg, 1988;Spiccia, 2004) so that the role that different Brønsted acidities play in controlling the reactions, both bond formation and dissociation, can be addressed immediately. Brønsted acidities of various oxygens in metal clusters have been compiled and even such things as the strengths of hydrogen-bonded structures has been estimated by careful synthesis of dimers with, and without, ligands that can accept hydrogen bonds.…”

Ab-initio structure, energy and stable Cr isotopes equilibrium fractionation of some geochemically relevant H-O-Cr-Cl complexes

“…In the dinuclear complexes two octahedrally coordinated metal ions are bound together by one, two or three Thompson and Connick, 1981). It is of interest to note that neither of the two complexes have been isolated as crystalline salts (Springborg, 1988). In addition to SBD and DBD oligomers, trinuclear and tetranuclear aqueous complexes form as well in aged Cr(III) solutions by polymerization equilibria involving the hexa-aqua-chromium(III) ion.…”

“…The minimum energy structures of gaseous SBD and DBD obtained in this study are shown in Figure 1 and some features are summarized in Table 5. The flexible hydroxo bridge in Cr(III) complexes does not impose strain and the first coordination spheres of the two metal centers are close to being undistorted octahedra (Springborg, 1988).…”