Self-assembled metallacycles with pyrazine edges: a new example in which the unexpected molecular triangle prevails over the expected molecular square.

The combination of cis-protected metal fragments with linear linkers is expected to yield molecular squares. We found instead that treatment of the 90° angular precursor trans -[RuCl 2 (dmso−S) 4 ] (1) with an equivalent amount of the linear and rigid pyrazine (pyz) linker unexpectedly yields, in a number of different experimental conditions, the molecular triangle [{ trans,cis -RuCl 2 (dmso−S) 2 (í-pyz)} 3 ] (3), together with polymeric material. Very similar results were also obtained from the reaction between 1 and the preformed corner fragment trans,cis,cis -[RuCl 2 (dmso− S) 2 (pyz) 2 ] (6). In both cases, the expected molecular square [{ trans,cis -RuCl 2 (dmso−S) 2 (í-pyz)} 4 ] (4) was observed only as a transient species.