SLOW PARAMAGNETIC RELAXATION OF HIGH-SPIN IRON III IN A TRIGONAL BIPYRAMIDAL ENVIRONMENT A STUDY OF THE PENTA-AZIDO FERRATE ION, FE(N3)52-

The temperature dependence of the zero field Mossbauer spectrum of [ϕ 4 As] 2 [Fe(N 3 ) 5 ] il has been determined over the range 300 K to 1.60 K and exhibits the effects of paramagnetic relaxation broadening and magnetic hyperfine splitting (H n ~ 486 kG a 4,2 K) at low temperatures corresponding to a negative zero field splitting, D ~ -1 cm -l . These results are consistent with the isolated trigonal bipyramidal Fe(N 3 ) 5 2- anion known to be present in this compound and slow spin-spin relaxation between highly separated (11 A or greater) metal centers. D || > µ ⊥ with [Formula: see PDF file] at ~5 K. The X and Q band ESR spectra of the system over the range 300 to 3.6 K indicate a typical axial Fe 3+ compound but with slight rhombicity of the local FeN 5 coordination environment.