Abstract A straightforward route to Ru (pyz) 2 (Hpyz) 4 (Hpyz= pyrazole) has been developed. This has been found to react readily with a modified Co (pyrazolylborate) Cl complex in the presence of triethylamine as an HCl acceptor to yield a bimetallic cobalt– ruthenium complex, in which the two metals are each six-coordinate, and bridged by three pyrazolyl anions. Both species have been characterized structurally, as has a modified Co ...