Metal cluster chemistry: Structure and stereochemistry in the polynuclear rhodium hydrides HnRhn[P(OR)3]2n

Crystallographic analyses of x-ray and neutron diffraction data have provided a definitive structural representation of {HRh[P(O- i -C 3 H 7 ) 3 ] 2 } 2 and {HRh[P(OCH 3 ) 3 ] 2 } 3 . These polynuclear hydrides are generated from square planar H 2 Rh[P(OR) 3 ] 2 units by edge (hydrogen atom) sharing and by vertex (hydrogen atom) sharing to form the dimeric and trimeric structures, respectively. The square-planar units are held together through four-center and three-center two-electron Rh—H—Rh bonds in the dimer and trimer, respectively. The dimer and trimer molecules each add one molecule of hydrogen to form H[( i -C 3 H 7 O) 3 P] 2 RhH 3 Rh [P(O- i -C 3 H 7 ) 3 ] 2 and H 5 Rh 3 [P(OCH 3 ) 3 ] 6 , respectively. NMR spectral information has served to define the stereochemical features of these polyhydrides. The significance of this chemistry in the metal cluster-metal surface analogy is described. metal cluster-metal surface analogy neutron and x-ray crystallographic studies