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This report contains recent results which help clarify previous ambiguities about some aspects of Mn(III) coordination chemistry.1 These results clearly demonstrate the expected formation of distorted octahedral complexes of high-spin Mn(III)-a result contrary to some published structural work.2 This distortion, which frequently manifests itself in the form of a tetragonal elongation, is probably responsible for the ready incorporation of Mn(III) into porphyrins.34 The results reported herein also tend to contradict to some extent those which report high-spin octahedral manganese(III) porphyrins containing a very tightly cotí) See, for instance, F. A. Cotton and G. Wilkinson, "Advanced

The crystal structure of thiocyanatobis(acetylacetonato)manganese(III), Mn(0zC5H7)z(NCS), has been determined by single-crystal X-ray diffraction techniques and refined anisotropically for all nonhydrogen atoms by full-matrix least-squares techniques to R I = 0.057 and Rz = 0.061 by using 1917 independent diffractometer-recorded reflections (Nb-filtered Mo K, radiation and 8-28 scans) having 28MoK& < 55" and I > 2a(I). The compound crystallizes in the uniquely determined centrosymmetric orthorhombic space group Pbca with eight molecules in a unit cell of dimensions a = 13.422 (2) A, b = 14.519 (3) A, and c = 13.763 (3) 8, (pcalcd = 1.541 g/cm3, &,bad = 1.540 g/cm3). Each thiocyanato ligand bridges two adjacent quasi-planar Mn(acac)z* groups in the three-dimensional lattice by using the glide operator perpendicular to the c'axis of the unit cell to generate infinite chains of octahedral Mn(II1) subunits along the 2 axis. The octahedral coordination polyhedron is tetragonally elongated and approximates idealized C , symmetry with the trans-coordinated thiocyanato nitrogen and sulfur atoms on the pseudo-fourfold axis. The four "short" Mn-0 bonds have average lengths of 1.912 (4) 8, while the two long trans Mn-N and Mn-S' bonds to the ends of bridging thiocyanato ligands have lengths of 2.189 (5) and 2.880(2) A, respectively. The dissimilarity of the two ends of the thiocyanato ligand has a pronounced effect on the Mn coordination geometry in this complex. The Mn atom is displaced by 0.12 8, from the mean plane of the quasi-square of four coordinated oxygen atoms toward the coordinated thiocyanato nitrogen atom.

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