Siddiqui, Zahir Uddin (1974) Syntheses and studies of carbonylchromium complexes of some metal chelates. Doctoral (PhD) thesis, Memorial University of Newfoundland.
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Complexes obtained by displacement of two and three carbonyl groups from hexacarbonylchromium by transition metal Schiff bases have been prepared and identified. Two carbonyl groups are replaced by a metal Schiff base forming a σ-bonded tetracarbonylchromium complex. Tricarbonylchromium π-complexes of metal Schiff bases are formed by displacement of three carbonyl groups from hexacarbonylchromium. The stereochemistry about the acceptor metal in the tetracarbonylchromium complex approximates to C₂v symmetry; under these conditions, four i.r. active carbonyl bands are expected and observed. Considering the local symmetry of the carbonyl groups, the tricarbonylchromium complexes belong to the C₃v point group, and so display two i.r. active carbonyl bands. -- Carbonyl stretching vibrations are used to see if electronic effects are transmitted from the central metal to the tricarbonylchromium moiety. The i.r. data for the C0 stretching region indicate a very small shift (∿ 10 cm⁻¹ higher in d¹⁰ than d⁴ systems) of νC₀ using different transition metals at the centre. The observed trend of C0 frequency is opposite to that expected in M(R-N-sal)n Cr(C0)₃ (n = 2 or 3) complexes (M, the central metal = Cr(II), Co(III), Co(II), Ni(II), Cu(II) and Zn(II) and R = CH₃, C₆H₅ and –CH₂-). This reverse increase of order of C0 stretching frequencies from that expected suggests that electron density of the ligand is decreasing as the number of d electrons increases in the central transition metals. This can be explained if π-bonding between M(II) and (R-N-sal)₂ is considered negligible compared to σ-bonding. -- β, the ratio of B in complex/B of free ion determined for a few complexes with the help of electronic spectra, was high (0.75-0.85). The high values of β suggest that the bonding is mostly ionic and a very small amount of covalency exists between the central metal and the ligand. -- These complexes are fairly stable toward oxidation by air and, in some cases, are even stable in solution for more than a day. – The overall spectroscopic study (i.r., U.V./visible and near i.r.) of tricarbonylchromium complexes of metal Schiff bases provides the following information: -- 1. The addition of a Cr(C0)₃ group to a metal Schiff base has no significant effect on stereochemistry of metal Schiff bases. -- 2. The electronic distribution of the Iigand (Schiff base) does not change very much by varying the central metal. – 3. There is very little covalent bonding between the central metal and the ligand (Schiff base). -- The reaction between metal phthalocyanine (metal = Cr(II), Cu(II) and Zn (11)) and hexacarbonylchromium yielded tricarbonylchromium complexes, but the purification of the complexes was not achieved.
|Item Type:||Thesis (Doctoral (PhD))|
|Additional Information:||Bibliography: leaves 177-183.|
|Department(s):||Science, Faculty of > Chemistry|
|Library of Congress Subject Heading:||Carbonyl compounds; Chelates|
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