The use of high magnetic field and high frequency in an unconventional spectrometer has provided very informative EPR spectra of a manganese(III) octahedral complex for the first time. The parameters of the spin Hamiltonian operator are in fair agreement with those calculated with ligand‐field theory. High‐frequency EPR is thus a powerful tool for the structural investigation of complexes that contain metal ions with integer spins.

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Four highly crystalline, cobalt-containing microporous aluminophosphates have been investigated by using liquid He X-and/or Q-band electron spin resonance (ESR) spectroscopy in order to investigate the coordination of high-spin cobalt before and after calcination. The ESR spectra of the four zeolite structures are characterized by an axial signal with an effective g ⊥ ≈ 5.80-5.44 and g || ≈ 2.00. Quantitative temperature dependence measurements of this axial signal in the temperature range 4-30 K reveal a Curie-Weiss behavior for both as-synthesized and calcined samples confirming (a) the m s ) ( 1/2 ground state of magnetically isolated high-spin cobalt and (b) a zero field splitting ∆ > 0 cm -1 . Quantitation of the ESR signals indicated that most of the Co 2+ is ESR active and that only about 30% of this Co 2+ can be oxidized to the ESR-inactive Co 3+ after calcination. The spin Hamiltonian parameters of as-synthesized and calcined CoAPO-5 material, as determined by spectrum simulation and the microwave power saturation technique, support the presence of framework Co 2+ in a flattened or elongated tetrahedron (D 2d ).