A very short Re_2~(6+) quadruple bond: first DFT calculation on a paddlewheel complex with an element of the third transition series

摘要

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. Re_2(hpp)_4Cl_2, 1, is a typical paddlewheel complex with two axial chloride ions. The Re-Re distance in 1 of 2.191 (1) A is one of the shortest known for a quadruply-bonded Re_2~(6+) complex and the Re-Cl distance of 2.794(5) A is the longest one reported for this type of complex. the second compound, Re_2(hpp)_3Cl_3, 2, has three bridging hpp ligands, two equatorial chloride ions and one axial chloride ion. The Re-Re distance is 2.189(2) A. 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.