Substituted derivatives of [Fe2(CO)9] and [Ru2(CO)9] and their susceptibility to electrophilic attack: X-ray crystal structure of [Fe2(μ-Br)(CO)4{μ-(C6H5O)2PN(C2H5)P(OC6H5)2}2]PF6

Bis- and, in particular, tetra-substituted ditertiary phosphine and diphosphazane derivatives of [Fe2(CO)9] and [Ru2(CO)9], readily synthesised by reaction of the appropriate bidentate ligand with [Fe2(CO)9] and [Ru3(CO)12], respectively, are very susceptible to electrophilic attack by reagents such as halogens and protons; the solid state structure of one of the products [Fe2(μ-Br)(CO)4 {μ-(PhO)2PN(Et)P(OPh)2}2]PF6 has been determined by X-ray crystallography.