High-field EPR investigation of a series of mononuclear Mn(II) complexes doped into Zn(II) hosts

The five-coordinate mono-halide mononuclear Zn(II) complexes Zn(tpa)X]⁺ (tpa = tris(2-pyridylmethyl)amine; X = I (Zn(tpa)I]I; 1a), Br (Zn(tpa)Br](ZnBr₄)_0.5; 2a) and Cl (Zn(tpa)Cl](ZnCl₄)_0.5; 3a)) and the six-coordinate mononuclear complex Zn(tpa)(NCS)₂] (4a) have been synthesized and characterized by X-ray crystallography. The Zn(tpa)X]⁺ complexes doped with the corresponding Mn(tpa)X₂] complexes (X = I (1b), Br (2b) and Cl (3b)) have been synthesized and their electronic properties investigated by multifrequency high field EPR (HF-EPR) (95–285 GHz). The magnetically diluted conditions allow the determination of the hyperfine coupling constant A (A = 68.10⁻⁴ cm⁻¹ for 1b–3b). The zero-field splitting parameters (D and E) found for 1b–3b are comparable to those found for neat samples of the Mn(tpa)X₂] complexes (1b: D = 0.635 cm⁻¹, E/D = 0.189; 2b: D = 0.360 cm⁻¹, E/D = 0.192; 3b: D = 0.115 cm⁻¹, E/D = 0.200). The efficacy of using multifrequency EPR under dilute conditions to precisely determine spin Hamiltonian parameters is discussed.