A very short Re26+ quadruple bond: first DFT calculations on a paddlewheel complex with an element of the third transition series

Abstract

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.