Completion of the series of M-2(hpp)(4)Cl-2 compounds from W to Pt: The W,Os, and Pt compounds

The series of M-2(hpp)(4)Cl-2 complexes (hpp is the anion of 1,3,4,6,7,8-he xahydro-2H-pyrimido[1,2-a]pyrimidine) from M = W to M = Pt has been complet ed by the preparation and characterization of those with M = W, Os, and Pt. W-2(hpp)(4)Cl-2 (1) has a W-W distance of 2.250(2) Angstrom, is diamagneti c, and can be assigned a W-W triple bond based on a sigma(2)pi(4) electron configuration. Os-2(hpp)(4)Cl-2 (2) has an Os-Os distance of 2.379(2) Angst rom and displays a temperature-independent paramagnetism. It can be assigne d a sigma(2)pi(4)delta(2)delta(*2)configuration. Pt-2(hpp)(4)Cl-2 has a Pt- Pt distance of 2.440(1) Angstrom and is diamagnetic. A bond order of 1, bas ed on a configuration in which only the sigma* orbital is empty, is consist ent with these data.