Completion of the Series of M₂(hpp)₄Cl₂ Compounds from W to Pt: The W, Os, and Pt Compounds

The series of M2(hpp)4Cl2 complexes (hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) from M = W to M = Pt has been completed by the preparation and characterization of those with M = W, Os, and Pt. W2(hpp)4Cl2 (1) has a W−W distance of 2.250(2) Å, is diamagnetic, and can be assigned a W−W triple bond based on a σ2π4 electron configuration. Os2(hpp)4Cl2 (2) has an Os−Os distance of 2.379(2) Å and displays a temperature-independent paramagnetism. It can be assigned a σ2π4δ2δ*2 configuration. Pt2(hpp)4Cl2 has a Pt−Pt distance of 2.440(1) Å and is diamagnetic. A bond order of 1, based on a configuration in which only the σ* orbital is empty, is consistent with these data.