Antiferromagnetic complexes with a metal—metal bond

The triangular cluster (MeC 5 H 4 ) 2 Cr 2 (μ-SCMe 3 )(μ 3 -S) 2 Co(CO) 2 V was obtained by reaction of the binuclear complex (MeC 5 H 4 ) 2 Cr 2 (μ-SCMe 3 ) 2 (μ 3 -S) (IV) with Co 2 (CO) 8 in heptane. The structure of V was solved by an X-ray structural study. Crystals of V are monoclinic, space group P2 1 , a 9.437(1), b 15.9460(8), c 7.2540(8) Å, β 109.399(9), V 1029.6 Å 3 , Z = 4, R = 0.047, R w = 0.052. The main geometric parameters of V are close to those of its previously described cyclopentadienyl analogue (C 5 H 5 ) 2 Cr 2 (μ-SCMe 3 )(μ 3 -S) 2 Co(CO) 2 (III), however, the CrCr bonds in V are somewhat shorter (by 0.02–0.04 Å) and the methylcyclopentadienyl rings are in a staggered conformation in contrast to the eclipsed conformation of the C 5 H 5 ligands in III. A photochemical reaction of (C 5 H 5 ) 2 Cr 2 (μ-SCMe 3 ) 2 (μ 3 -S) (I) with Mn 2 (CO) 10 with a reagent ratio of 2 1 in boiling benzene (3 h) yielded the heteronuclear cluster (C 5 H 5 ) 2 Cr 2 (μ-SCMe 3 )(μ 3 -S) 2 Mn(CO) 3 (VI), characterized by an X-ray study (space group C 2, a 18.709(7), b 9.883(4), c 11.470(5) Å, β 109.65(2)°, V 1997.3 Å 3 Z = 4). VI has a triangular metal frame Cr 2 Mn (CrCr 2.646(2), CrMn 2.828(2) and 2.716(2) Å). The electronic and steric factors governing the formation of III, V and VI are discussed. I, III–VI exhibit antiferromagnetic properties with the exchange parameter (−2 J ) increasing on introduction of a methyl group into the cyclopentadienyl ligand, as well as with the formation of metal cycle Cr 2 M (−2 J (CrCr) 430, 530, 478, 556, 654 cm −1 , respectively).