5-COORDINATE COMPLEXES [TRIPODM-(ORTHO-(X )(Y)C6H4)](N) (X, Y=O, S) WITH D(5)-, D(6)- AND D(7)-SYSTEMS - SYNTHESIS, STRUCTURE, ELECTROCHEMISTRY AND ESR-SPECTRA

The d(6)-Co(III)-species [tripodCo-(ortho-(X)(Y)C6H4)](+) (X, Y = O, S , tripod = CH3C(CH(2)PPh(2))(3)) 1 are reversibly reduced to the neutr al d(7)-Co(II)-compounds [tripodCo-(ortho-(X)(Y)C6H4)] (X, Y = O, S) 2 . Both species show fivefold coordination of cobalt with coordination polyhedra in between the limits of the square pyramid and the trigonal bipyramid respectively. The low-spin d(7)-species 2 give clearly reso lved ESR-spectra revealing the coexistence of two geometric isomers ab ove -80 degrees C, with only one isomer persistent at temperatures aro und 100 K. As an analogous d(5)-system [benzyltripodFe-(ortho-(S)(S)C6 H4)](+) 3 (benzyltripod = C6H5CH2C(CH(2)PPh(2))(3)) h as been obtained from [benzyltripodFe(NCCH3)(3)](2+) and C6H6S2. Alternatively complex es of this type, e. g. [tripodFe-(ortho-(S)(S)C6H4)](+) 4, may be prep ared from Fe(H2O)6 (BF4)(2)/tripod/C6H6S2 when the reaction mixture is activated by acidification with HBF4. The geometry of the d(5)-specie s 3 and 4 is close to a trigonal bipyramid.