X-ray Structures and Homolysis of Some Alkylcobalt(III) Phthalocyanine Complexes

Autor:	Maciej Kubicki, Wlodzimierz Galezowski
Rok vydání:	2005
Předmět:	Chemistry Ligand Stereochemistry Bond-dissociation energy Square pyramidal molecular geometry Homolysis Inorganic Chemistry Bond length Crystallography chemistry.chemical_compound Octahedral molecular geometry Pyridine Phthalocyanine Physical and Theoretical Chemistry
Zdroj:	Inorganic Chemistry. 44:9902-9913
ISSN:	1520-510X 0020-1669
DOI:	10.1021/ic051078p
Popis:	The first crystallographic data for o-bonded alkylcobalt(lll) phthalocyanine complexes are reported. A single-crystal X-ray structure of CH 3 CH 2 Co I I I Pc (Pc = dianion of phthalocyanine) reveals that the solid consists of centrosymmetric face-to-face dimers in which the CH 3 CH 2 Co I I I Pc units retain their square pyramidal geometry. The structure appears to be the first one reported for a five-coordinate RCo(III)(chelate) complex with an electron-deficient equatorial system. The Co-C bond in CH 3 CH 2 Co I I I Pc (2.031(5) A) is the longest found in five-coordinate RCo"'(chel) complexes (R = simple primary alkyl group). Another X-ray study demonstrates that CH 3 Co I I I Pc(py) has a distorted octahedral geometry with axial bonds of very similar length to those in methylcobalamin. The axial bonds are shorter than those in its octaethylporphyrin analogue, in accordance with a weaker trans axial influence in six-coordinate complexes containing an electron-deficient phthalocyanine equatorial ligand. A different trend has been observed for five-coordinate RCo I I I (chel) complexes: electron-rich equatorial systems seem to make the Co-C axial bond shorter. Kinetic data for the homolysis of RCo I I I Pc complexes (R = Me, Et) in dimethylacetamide are also reported. Homolysis of ethyl derivatives is faster. The Co-C bond dissociation energies (BDEs) for the pyridine adducts of the methyl and the ethyl derivative are 30 ′ 1 and 29 ′ 1 kcal/mol, respectively. The BDE for CH 3 CoPc(py) is considerably lower than that for MeCbl despite the very similar lengths of the axial bonds in the two complexes. The results of this work do not support any correlation between the Co-C bond length and the bond strength as defined by BDE.
Databáze:	OpenAIRE
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