THE NATURE OF METAL-AZIDE INTERACTIONS IN A HIGH-VALENT TETRAAZIDO-MANGANESE(IV) COMPLEX. ISOLATION, STRUCTURE AND PROPERTIES, INCLUDING UV-VIS, EPR AND RESONANCE RAMAN SPECTROSCOPY OF [Mn(bpy)(N3)4] (bpy = 2,2′-bipyridine)

Abstract

Abstract A mononuclear high-valent tetraazidomanganese(IV) complex, [Mn(bpy)(N3)4] (bpy = 2,2′-bipyridine), which possesses two pairs of distinct metal-azide interactions, has been isolated from an in situ reaction between [Mn2O(O2CCH3)2(bpy)2(H2O2]2+ [S. Menage, J.-J Girerd and A. Gleizes, J. Chem. Commun. 1988, 431] and sodium azide. The complex has been structurally characterized by single crystal X-ray crystallography and UV-vis, EPR and resonance Raman (RR) spectroscopic methods. The crystals are monoclinic, space group C2/c, with a = 16.570(3) Å, b = 13.946(3) Å, c = 7.019(1) Å, β = 111.17(3)°, and Z = 4. The two azides trans to the nitrogens of the bpy ligand show stronger Mn-N bonds compared to those cis to bpy. The difference in Mn-azide interactions is reflected in splittings of the v(Mn-N3) (373, 362 cm−1), v s(N3) (1354, 1335 cm−1) and v as(N3) (2055, 2038 cm−1) stretching vibrational frequencies of the coordinated N3 − as identified by RR spectroscopy. These modes are enhanced in resonance with the visible absorption band of [Mn(bpy)(N3)4] centered at 442 nm, indicating that the 442 nm electronic transition must have N3 − → Mn(IV) charge-transfer character. A very rare example of a d 3 system with an isotropic g = 2 signal observed for the title complex indicates a nearly perfect octahedral ligand field around the Mn(IV) ion.