THE NATURE OF METAL-AZIDE INTERACTIONS IN A HIGH-VALENT TETRAAZIDOMANGANESE(IV) COMPLEX - ISOLATION, STRUCTURE AND PROPERTIES, INCLUDING UV-VIS, EPR AND RESONANCE RAMAN-SPECTROSCOPY OF [MN(BPY)(N-3)(4)] (BPY=2,2'-BIPYRIDINE)

A mononuclear high-valent tetraazidomanganese(IV) complex, [Mn(bpy)(N-3)(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)(H2O)(2)](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 W-vis, EPR and resonance Raman (RR) spectroscopic methods. The crystals are monoclinic, space group C2/c, with a = 16.570(3) Angstrom b = 13.946(3) Angstrom, c = 7.019(1) Angstrom, beta = 111.17(3)degrees, 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 nu(Mn-N-3) (373, 362 cm(-1)), nu(s)(N-3) (1354, 1335 cm(-1)) and nu(as)(N-3) (2055, 2038 cm(-1)) stretching vibrational frequencies of the coordinated N-3(-) as identified by RR spectroscopy. These modes are enhanced in resonance with the visible absorption band of [Mn(bpy)(N-3)(4)] centered at 442 nm, indicating that the 442 nm electronic transition must have N-3(-) --> 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.