Rf. See et al., METAL-LIGAND BOND DISTANCES IN FIRST-ROW TRANSITION-METAL COORDINATION-COMPOUNDS - COORDINATION-NUMBER, OXIDATION-STATE, AND SPECIFIC LIGAND EFFECTS, Inorganic chemistry, 37(20), 1998, pp. 5369-5375
Mean metal-ligand bond distances for the coordination ligands isothioc
yanate, pyridine, imidazole, water, and chloride, bound to the transit
ion metals Mn, Fe, Co, Ni, Cu, and Zn in their 2+ oxidation states, we
re collected from searches the Cambridge Structure Database. The metal
-ligand bond distances were converted to bond orders through the bond
distance-bond order technique, as suggested by Pauling. The mean bond
order sums at the 2+ metal centers were found to be independent of coo
rdination number or geometry and to be strongly ligand-dependent; the
values (by ligand) are as follows: isothiocyanate = 2.56 +/- 0.13; imi
dazole = 2.13 +/- 0.04; chloride = 2.12 +/- 0.07; pyridine 1.95 +/- 0.
10; water = 1.88 +/- 0.10. The bond order sum for Fe(III) bound to chl
oride was found to be 3.09, approximately one bond order unit larger t
han for the 2+ metal centers bound to chloride. Division of the ligand
-specific bond order sums by coordination number allows prediction of
the M-L bond distance to within 0.017 Angstrom, regardless of the spec
ific coordination geometry. The physical basis for the ligand-specific
variation in bond order sum is also discussed.