HETERONUCLEAR METAL CLUSTER COMPLEXES WITH A NEW COORDINATION MODE OFTHE FE2S2(CO)(6) UNIT - SYNTHESIS, STRUCTURE AND POSSIBLE REACTION PATHWAY OF THE FIRST FE-CU-S CLUSTER COMPOUND, [FE6CU5S6(CO)(18)(PPH(3))(2)](-)

The first iron-copper-sulfur cluster compound [Et(4)N][Fe6CU5(mu(4)-S) (6)(CO)(18)(PPh(3))(2)] (1) is Prepared by the reaction of [Et(4)N][Cu Cl(2)PPh(3)] with Li-2[Fe2S2(CO)(6)] in mixed solvents of MeCN-CH3OH. 1.MeCN crystallizes in the monoclinic, space group Pn with a = 12.426( 3), b = 15.572(4), c =20.709(4) Angstrom; beta = 90.14(2)degrees; V = 4007.2 Angstrom(3); Z = 2, D-c = 1.80 g cm(-3), and R(1) = 0.032, R(2) = 0.037 for 3319 independent reflections (I> 3 sigma(I)). The anion of 1 contains an undeca-nuclear Fe-Cu-S core with Fe-I and Cu-I, [Fe6Cu5 (mu(4)-S)(6)](-), which consists of a central trigonal bipyramid compo sed of five copper atoms in the center and three 'butterfly' type Fe2S 2 units chelating to the copper atoms of the central Cu-5 trigonal bip yramid along the pseudo-D-3 axis resulting in pseudo-D-3 symmetry. All the sulfur atoms in 1 are mu(4)-S, linking to two iron and two copper atoms. Around the core, twelve terminal carbonyls, six bridging CO gr oups and two PPh(3) ligands meet the requirement of four-coordination of the copper atoms and five-coordination of the iron atoms. Fe-S and Cu-S distances are 2.28-2.36 and 2.24-2.51 Angstrom, respectively. The re are fifteen M-M bonds in 1, including three Fe-Fe of 2.5 Angstrom, six Cu-Fe of 2.7 Angstrom and six Cu-Cu of 2.6 Angstrom. The Fe2S2(CO) (6) units in 1 take a new coordination mode in that each unit coordina tes to four metal atoms by its two sulfur atoms in a mu(4)-type fashio n. A possible reaction pathway for 1 via the formation of two reactive fragments is proposed and discussed.