The crystal and molecular structures of the hexarhodium carbonyl clusters R
h-6(CO)(15)L (L = P(OPh)(3), 1; P(4-XC6H4)(3), (X = CF3, 2; Cl, 3; F, 4; OM
e, 5); P(Bu-n)(3), 6; Me2SO, 7; MeCN, 8; C8H14, 9) have been determined by
single crystal X-ray crystallography. Redetermination of the structure of t
he parent Rh-6(CO)(16) cluster, 10, has also been performed and all the res
ults are compared with those for the rather disparate group of monosubstitu
ted derivatives reported earlier. The structures all relate closely to that
of the parent which has an octahedral array of Rh atoms with four opposite
faces triply bridged by CO ligands. Each Rh atom also has two terminal CO
groups attached. The substituents simply replace one of the terminal COs. A
group of ligands, comprised of the P-donors and cyclooctene, all show dist
ortions with a high degree of stereoselectivity in the vicinity of the subs
titution site, and demonstrate the significantly local character of the eff
ect. The effects on the terminal CO groups are mainly limited to the CO att
ached to the substituted Rh atom for which there is a clear decrease in the
Rh-CO distance and a smaller lengthening of the C-O distance. The triangle
of Rh atoms that contains the substituted Rh atom, with the substituent pr
ojecting above that triangle, shows a pronounced lengthening of the Rh-Rh b
onds cis to the heteroligand. There is an equally pronounced shortening of
the Rh-Rh bond across the triangle from the substituted Rh atom. A third ef
fect is the displacement of the CO groups in triply bridged Rh-3 triangles
containing the RhL moiety, so that they almost doubly bridge the two Rh-Rh
bonds cis to the substituted Rh atom. Although no clear correlations exist
within this group of substituents the localized effects can generally be as
sociated with an increase of electron density on the substituted Rh atom. T
he other monosubstituted clusters that contain quite different neutral and
anionic heteroligands do not display common trends in the structural distor
tions induced by the substituents, and this is evidently due to the very va
ried nature of the ligands within this group.