A Mössbauer Effect and Fenske-Hall Molecular Orbital Study of the Bonding in a Series of Organoiron-copper Clusters


The electronic properties of a series of organoiron-copper clusters, Na2[Cu6Fe4(CO)16] (I), Na3[Cu5Fe4(CO)16] (II), Na3[Cu3-Fe3(CO)12] (III), [Cu(P(CH3)3)4]2[Fe3(CO)12Cu4(P(CH3)3)2] (IV), [((C6H11)3PCu)2Fe(CO)4] (V), [((Ph3P)2Cu)2Fe(CO)4] (VI), [(Ph3P)2CuFe(CO)3(NO)] (VII), and [((NH3)2Cu)2Fe(CO)4] (VIII), have been investigated experimentally by the Mössbauer effect and theoretically by Fenske- Hall molecular orbital calculations. The Mössbauer effect hyperfine parameters are sensitive to the variety of bonding situations found in these clusters. The Mössbauer effect isomer shifts observed for these clusters range from -0. 141 to -0.037 mm/s at 78 K. The expected increase in the isomer shift with a decrease in the iron 4s Mulliken atomic orbital population, and a decrease in the Clementi effective nuclear charge experienced by the iron 4s electrons is observed. The electric field gradients at the iron sites have been calculated and compared with the experimental quadrupole splittings which range from 0.191 to 2.497 mm/s at 78K. The valence contribution was found to be the major component of the electric field gradient and is directly related to the symmetry of the iron electronic environment. The calculated values of the electric field gradients are also used to confirm the Mössbauer effect spectral assignments in II. The calculated metal-metal bond energy decreases as the cluster metal-metal bond length increases. The major bonding in these clusters is the iron-copper bond in which the iron 3d atomic orbitals overlap the copper 4s and 4p atomic orbitals. © 1993.



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© 1993 Elsevier, All rights reserved.