Synthesis of Water-Soluble Planar Cobalt(II), Nickel(II), and Copper(II) Hydroxo Clusters Using a (1,4,7-Triazacyclononane)cobalt(III) Complex as a Hydrolysis-Terminating Group

Abstract

We report on a group of planar cobalt(II), nickel(II), and copper(II) hydroxo clusters that have a definite composition and are water-soluble: [{Co(tacn)- 6), where tacn is 1,4,7triazacyclononane. The peripheral of each metal hydroxo cluster plane is chemically protected by the coordination of {Co III (tacn)(OH) 2 } + groups to prevent further hydrolysis. These clusters were synthesized by the reaction of an equimolar amount of [Co(tacn)(OH 2 ) 3 ] 3+ and cobalt, nickel, or copper salt at pH values in the range of 6.0−12.0. The structure of the cation in compounds 1, 2a or 2b, 4, and 5 is relevant to the surface structure of the cobalt phosphate and nickel borate oxygen-evolution catalysts; in particular, the Co 7 (OH) 12 core in 1. Moreover, the arrangement of M 7 (OH) 12 in 1 and 2a or 2b and Cu 4 (OH) 6 in 6 represents the solid-state structures of the (111) face of the cubic CoO or NiO and the (002) plane of Cu(OH) 2 , respectively. Extended X-ray absorption fine structure spectra of an aqueous solution of 1, 2a, 4, and 5 exhibit well-resolved peaks at the first and second coordination spheres due to the M−O and M••• M distances, respectively; the solution-state bond distances were estimated, and they agreed well with the bond distances in the solid-state structures.

Reactivity of Organoiridium Tungsten Oxide Clusters with Transition Metal Aquo Cations

“…For example, Isobe and co-workers reported that the {Cp*Rh} 2+ units (Cp* is C 5 Me 5 – ) of [{Cp*Rh} 4 V 6 O 19 ] dissociate in an acidic solution, and the addition of [Cp*Ir­(OH 2 ) 3 ] 2+ into the solution produces a series of [{Cp*Rh} 4– x {Cp*Ir} x V 6 O 19 ] clusters where x can take values of 1, 2, 3, or 4 . In other words, the organometallic cations of organo–POMs function as a protecting , or placeholder group by temporarily blocking the reactive sites of a POM anion, and they are exchangeable to other incoming metal cations (Scheme ). We were thus motivated to exploit this substitution reaction to functionalize organo–POMs with simple transition metal–aquo complexes that can provide association sites for various incoming ligands.…”