Antiferromagnetic complexes with the metalmetal bond

Abstract Interaction of (MeC 5 H 4 ) 2 Cr with oxygen or selenium results in formation of 60-electron clusters (MeC 5 H 4 ) 4 Cr 4 (μ 3 -O) 4 (I) and (MeC 5 H 4 ) 4 Cr 4 (μ 3 -Se) 4 (III). Their structures were determined by X-ray diffraction study (I: space group I 4, a = b = 13.0857(7), c = 7.0538(4) A, V = 1207.9 A 3 , Z = 2, R 1 = 0.058, R w = 0.066; III: space group Pbca, a = 18.456(2), b = 17.164(1), c = 16.227(2) A, V = 5140.4 A 3 , Z = 8, R 1 = 0.054, R w = 0.047). In contrast to the relatively symmetrical structure of sulfide (MeC 5 H 4 ) 4 Cr 4 (μ 3 -S) 4 (II) (CrCr 2 × 2.848 and 4 × 2.822 A) and selenide III, in I a pronounced tetrahedral distortion of the metal core is observed (CrCr 2 × 2.896(3) and 4 × 2.759(3) A). All the CrCr bonds in III are elongated, compared with those in II (up to ∼ 3.00–3.04 A). The oxide cluster I is antiferromagnetic whereas the analogous sulfide and selenide clusters are diamagnetic.