Antiferromagnetic complexes with a metal-metal bond

Abstract The reaction of (CH 3 C 5 H 4 CrSCMe 3 ) 2 S (Ia) with Cp 2 Mn in boiling toluene (containing some THF) has been used to prepare a pentanuclear cluster, [(CH 3 C 5 H 4 ) 2 Cr 2 (SCMe 3 )(μ 3 -S) 2 ]Mn (II), which is antiferromagnetic and crystallizes into the monoclinic crystal system: space group Cc , a 26.540(10), b 9.208(3), c 21.595(9) A; β 135.30(2)°, V = 3712.1 A 3 , Z = 4. According to X-ray analysis, cluster II contains a metallospirane core, Cr 4 Mn, which appears to be strongly distorted, compared to its earlier studied cyclopentadienyl analogue [Cp 2 Cr 2 SCMe 3 (μ 3 -S) 2 ] 2 Mn, due to the short intramolecular contacts CH 3 …S (2.9–3.1 A). The angle between the metal triangle planes of Cr 2 Mn is 109.60°. Here, the two long CrMn bonds (3.019(3) and 3.104(4) A) are combined with the shorter Cr Cr bond (2.651(6) A) in one triangle and, vice versa, the less extended CrMn bonds (2.839(4) and 2.967(3) A) are combined with a longer CrCr bond (2.726(6) A) in the other triangle of Cr 2 Mn. By the reaction of Ia with [CpFe(CO) 2 ] 2 (taken in the ratio of 2 1 ) in boiling toluene, the antiferromagnetic cluster [(CH 3 C 5 H 4 ) 2 Cr 2 (SCMe 3 )(μ 3 -S) 2 ] 2 Fe (III) has been synthesized in which the same distortions as in cluster II are present, as revealed by X-ray analysis. In the metallospirane core of the molecule of III, the Cr 2 Fe triangles make an angle of 113.84° with each other. In this cluster, the CrCr distances in the peripheral binuclear fragments (CH 3 C 5 H 4 ) 2 Cr 2 (μ-SCMe 3 )(μ 3 -S) 2 are practically equal (2.688(3) and 2.661(3) A), whereas the FeCr bond lengths are markedly different (2.749(2) and 2.827(2) A in on triangle and 2.910(2) and 2.969(2) A in the other). The dependence of the geometries of clusters II and III on the steric effects of the methyl substituents in the cyclopentadienyl ligands and on the electronic effect of the central metal atom (Mn II or Fe II ) is discussed.