The first crystallographic data for a-bonded alkylcobalt(III) phthalocyanine complexes are reported. A single-crystal X-ray structure of (CH3CH2COPC)-P-III (PC = dianion of phthalocyanine) reveals that the solid consists of centrosymmetric face-to-face dimers in which the (CH3CH2COPc)-Pc-III 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 (CH3CH2COPC)-P-III (2.031(5) angstrom) is the longest found in five-coordinate RCoIII(chel) complexes (R = simple primary alkyl group). Another X-ray study demonstrates that (CH3COPc)-Pc-III(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 fivecoordinate RCoIII(chel) complexes: electron-rich equatorial systems seem to make the Co-C axial bond shorter. Kinetic data for the homolysis of (RCoPc)-Pc-III 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 CH3COPc(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.