text: In addition to M–M single bonds, metal pairs can be linked by double, triple, quadruple, and in a few cases, quintuple bonds. Isolable complexes with multiple bonds are most common among the transition metals in the middle of the d-block, such as rhenium, tungsten, technetium, molybdenum and chromium. Typical the coligands are π-donors, not π-acceptors.  Well studied examples are the tetraacetates, such as dimolybdenum tetraacetate (quadruple bond) and dirhodium tetraacetate (single bond).  Mixed-valence druthenium tetraacetates have fractional M–M bond orders, i.e., 2.5 for [Ru(OAc)(HO)].
  The complexes NbX(SR) adopt a face-sharing bioctahedral structures (X = Cl, Br; SR = thioether). As dimers of Nb(III), they feature double metal–metal bonds, the maximum possible for a pair of metals with d configuration. 
  Hexa(tert-butoxy)ditungsten(III) is a well studied example of a complex with a metal–metal triple bond.