A MOSSBAUER-EFFECT AND FENSKE-HALL MOLECULAR-ORBITAL STUDY OF SOME SULFUR-CONTAINING ORGANOIRON-COBALT CLUSTERS

The electronic properties of a series of iron-cobalt clusters, H2Fe3S(CO)(9) (I), HFe2CoS(CO)(9) (II) FeCo2S(CO)(9) (III), and Fe2S2(CO)(6) (V) have been studied by the Mossbauer effect at 78K. The electronic properties of these clusters and Co-3(CO)(9)S (IV) have also been studied theoretically with Fenske-Hall molecular orbital calculations. The Mossbauer effect isomer shifts in clusters I-III and V are small and positive, ranging from 0.00 to 0.076 mm/s. The quadrupole splittings range from 0.563 to 1.109 mm/s. The s-electron density, measured by the Mossbauer effect, is similar for clusters with two iron-hydrogen groups or one iron-hydrogen group and one cobalt atom. The s-electron density is also similar for clusters with two iron-hydrogen groups or two cobalt atoms. The quadrupole splittings show a general increase with a decrease in the hydrogen content and an increase in the cobalt content. The cobalt carbonyl ligand charges and the cobalt charges are nearly constant. The sum of the iron and hydrogen charges increases as the iron carbonyl ligand charge decreases. The iron electronic configuration which begins with the 4s(0)3d(8)4p(0) atomic configuration, becomes on average, 4s(0.35)3d(6.80)4p(0.83) with a range from 4s(0.34)3d(6.80)4p(0.74) in I to 4s(0.31)3d(6.85)4p(0.89) in V. The cobalt electronic configuration which begins with the 4s(0)3d(9)4p(0) atomic configuration, becomes on average, 4s(0.43)3d(7.67)4p(1.13) With a range from 4s(0.41)3d(7.70)4p(1.08) in IV to 4s(0.44)3d(7.66)4p(1.17) in II. The isomer shift is well correlated with the sum of the iron 4s Mulliken population and the Clementi and Raimondi effective nuclear charge which they experience. The Mulliken charges and the coefficients of the molecular wave functions are used to calculate the quadrupole splittings in I-III and V.