VARIABLE-STRUCTURE OF THE CU2S2 CORE IN DOUBLY THIOLATE-BRIDGED DICOPPER(I) COMPLEXES - AN X-RAY CRYSTALLOGRAPHIC, ELECTROCHEMICAL AND EPR STUDY OF (DMP)(2)(O-CH3C6H4S)(2)CU-2, DMP=2,9-DIMETHYL-1,1O-PHENANTHROLINE, AND A COMMENT ON THE NATURE OF PHENANTHROLINE-CONTAINING CU(O) COMPLEXES
Af. Stange et al., VARIABLE-STRUCTURE OF THE CU2S2 CORE IN DOUBLY THIOLATE-BRIDGED DICOPPER(I) COMPLEXES - AN X-RAY CRYSTALLOGRAPHIC, ELECTROCHEMICAL AND EPR STUDY OF (DMP)(2)(O-CH3C6H4S)(2)CU-2, DMP=2,9-DIMETHYL-1,1O-PHENANTHROLINE, AND A COMMENT ON THE NATURE OF PHENANTHROLINE-CONTAINING CU(O) COMPLEXES, Zeitschrift fur Naturforschung. B, A journal of chemical sciences, 50(1), 1995, pp. 115-122
The molecular and crystal structure of the dicopper(I) complex (dmp)(2
)(mu-o-CH3C6H4S)(2)Cu-2 (1), dmp = 2,9-dimethyl-1,10-phenanthroline, h
as been determined. With Cu/S/Cu and S/Cu/S bond angles between 80 and
100 degrees, the planar structure of the central CuSCuS four-membered
ring is much more symmetric for 1 as compared to the analogous comple
x 2 of unsubstituted 1,10-phenanthroline which has a folded Cu2S2 core
with bond angles between 67 and 108 degrees. This result illustrates
a considerable structural flexibility of the LCu(mu-SR)(2)CuL entity w
hich is being discussed as a possible model for Cu, centers of cytochr
ome c oxidase or nitrous oxide reductase. Oxidation of both complexes
1 and 2 remains irreversible even at cyclovoltammetric scan rates of 1
V/s. However. the methyl substitution in complex 1 causes increased r
eversibility of the electronically coupled dmp-based reduction process
es. Accordingly, the EPR spectrum of 1(-.) is characterized by hyperfi
ne splitting from dmp(-.) and a relatively small Cu-63.65 coupling of
0.53 mT. The stabilization of 2,9-disubstituted 1,10-phenanthroline ra
dical anions by coordination to Cu(I) is also demonstrated by detectio
n of a single broad EPR line at g 2.0028 for the formal ''Cu(O)'' comp
lex Cu(dpp)(2) = Cu-I(dpp(-.))(dpp), dpp = 2,9-diphenyl-1,10-phenanthr
oline. While the EPR signal of Cu(dpp)(2) loses intensity on cooling,
possibly due to dimerization and spin-pairing, the distorted tetrahedr
al configuration with essential orthogonal arrangement of dpp pi syste
ms seems to disfavour an intramolecular electron hopping.