Coordination polymers based on Rh-Ag carbide clusters

Coordination polymers are nowadays intensively studied, for their potential application in nanoelectronics, and catalysis. They are typically composed by stereochemically rigid metallic ions (the linkers) and bifunctional ligands (the spacers). Organometallic linkers are very uncommon, probably because the soft transition metals in their low oxidation state do not bind stabily with the hard N- or O- donors. Howevwer, several organometallic clusters are known, which contain metal ions of the 11-12 groups. One example of this sort is [Rh6C(CO)15]2-, which has two nucleophilicic triangular faces which can be capped by [M-L] electrophilic groups (such as Ag-PPh3, Au-PPh3, Cu-NCMe). When both faces are capped, the neutral molecule [{L-M}2Rh6C(CO)15] are formed, which are stable and can be isolated in the solid state, and characterized by X-ray analysis. Moreover, it has been shown that bwo cluster unit can bind a single metal ion, as in the structurally caracterized [{Rh6C(CO)15}2Ag]-. Therefore, we tested the possibility to construct linear polymers, alternating cluster units, metal ions and, possibly, organic bifunctional spacers. As a matter of facts, the reaction between [Rh6C(CO)15]2- and [Cu(NCMe)4]PF6, or AgBF4 (in the presence of CH3CN) affords the known [{CH3CNM}2Rh6C(CO)15] (M = Cu, Ag), which were not isolated, but allowed to diffuse into a diluted solution of bifunctional heteroaromatic ligands (such as pyrazine or 4,4’ bipyridyl), obtaining cluster-containing insoluble materials. In the case of pyrazine, we also obtain single crystals suitable for X-ray analysis, and determined the solid state structure of the organometallic polymer of formula [N2C4H4-(C4H8O)Ag-Rh6C(CO)15-Ag(C4H8O)]. Suprisingly, the polymer is not linear, because the silver ions are trigonal planar, with the third coordination site occupied by a THF molecule. As an extension of this work, we aim to obtain analogous species with other metal ions, other spacers, or without solvent molecules.