Self-Assembly of 1-D Platinum Carbonyl Cluster Polymers

Recent improvements in the synthesis of [Pt3n(CO)6n]2- (n ~ 10), via carbonylation of M2PtCl6 (M = Na, K) in water, [1] and characterization of [NBu4]2[Pt24(CO)48] [2] prompted structural re-investigations of miscellaneous salts of the [Pt3n(CO)6n]2- (n = 4-10) oligomers and measurements of their conductivity in the solid state. Indeed, the [Pt24(CO)48]2- dianion in its [NBu4]+ salt self-assembles upon crystallization in a 1-D polymer morphologically resembling a CO-sheathed tri-platinum wire. [2] It was of interest to understand the factors triggering self-assembly and experimentally verify whether or not the above morphological resemblance was indicative of functional behaviour. Therefore, we have synthesized, structurally characterized and measured the resistivity of a series of [Pt3n(CO)6n]2- (n = 4-10) oligomers with miscellaneous counterions. Thus far, it can be concluded that decreasing Coulombic repulsion, consequent to spreading of the constant -2 charge over an increased number of Pt3(CO)6 units, is more relevant than cation size in leading to self-assembly of 1-D stacks. Moreover, whereas salts featuring structures with separated ions are insulators, those displaying 1-D stacks of Pt3(CO)6 units are semiconductors which begin to approach the lowest limit of metal conductivity.