F. Albert Cotton, Jiande Gu, Carlos A. Murillo and Daren J. Timmons
The first complexes containing third row transition elements with bridging hpp (the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) are presented. Re2(hpp)4Cl2, 1, is a typical paddlewheel complex with two axial chloride ions. The Re–Re distance in 1 of 2.191(1) Å is one of the shortest known for a quadruply-bonded Re26+ complex and the Re–Cl distance of 2.749(5) Å is the longest one reported for this type of complex. The second compound, Re2(hpp)3Cl3, 2, has three bridging hpp ligands, two equatorial chloride ions and one axial chloride ion. The Re–Re distance is 2.189(2) Å. The electronic structure of 1 has been determined by DFT calculations, the first time this has been done on a paddlewheel complex containing a third row transition element.