Abstract
The structures of [(py)2CdFe(CO)4]3 and {(THF)5[CdFe(CO)4]3} have been determined (py = pyridine; THF = tetrahydrofuran). Each is composed of a six-membered ring having alternating cadmium and iron centers. The presence of the more strongly basic amine ligands in the former led to a greater contribution of an ionic resonance form, which resulted in overall longer Cd–Fe bonds and a greater contribution of a bicapped tetrahedral coordination geometry about iron. Thus, the Cd–Fe distances range from 2.5679(4) to 2.6501(1) Å for the THF complex versus 2.6445(8) to 2.6833(7) Å for the py complex. Similarly, the Fe–Cd–Fe and Cd–Fe–Cd angles for the THF complex fell in respective ranges of 139.03(2)–157.27(2)° and 84.41(1)–99.79(1)°, as compared to 135.31(3)–139.51(4)° and 102.52(3)–104.62(4)° for the py complex. The space group for the former compound is Pbcn, with a = 12.2678(2), b = 22.4601(5), and c = 17.0039(4) Å, while for the THF complex, the space group is P21/c, with a = 10.7297(2), b = 20.4961(2), c = 18.7464(3) Å, and β = 94.2715(6)°.
Highlights
The complex HgFe(CO)4 was first reported in 1929, and due to its insolubility, it was proposed to be a polymeric species [1]
The respective metal coordination geometries were shown to be linear and cis-disubstituted octahedral, and powder pattern data demonstrated that the mercury compound was isomorphous [3]
The crystallization of the cadmium compound was made possible by the fact that some ether, ketone, and amine ligands readily coordinate, while that does not happen for the mercury compound, and in at least some of these cases, the coordination is readily reversible
Summary
The complex HgFe(CO) was first reported in 1929, and due to its insolubility, it was proposed to be a polymeric species [1]. The base-coordinated cadmium compounds typically exist as [L2CdFe(CO)4]n species (L = an ether, ketone, or amine; L2 = a bidentate amine) [2,3,4], and they would generally be expected to be dimeric or trimeric (i.e., n = 2 or 3, Figure 1) though at least one [LCdFe(CO)]n species (L = 4-phenylpyridine) is known, as well as monomeric LxCdFe(CO) complexes, in which Lx represents a combination of at least three donor sites [3, 5] The isolations of such species appear to have been promoted by the use of chelating ligands, or via the use of coordinating solvents for crystallization. In order to attempt to gain a better understanding of the factors that control the extent of oligomerization in these complexes, we have determined the structures of [LxCdFe(CO)4]n complexes in which the coordinated ligands are pyridine or THF
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