Vibronic dynamics and electron spin relaxation of Cu(formate) 4 (H 2 O) 2 complexes in dibarium zinc formate tetrahydrate, Ba 2 Zn(HCOO) 6 ·4H 2 O single crystals.

Continuous wave and pulsed X-band electron paramagnetic resonance experiments have been performed for Cu 2+ ions substituting Zn(II) in Ba 2 Zn(HCOO) 6 ·4H 2 O single crystals in the temperature range 4.2-300 K. Spin-Hamiltonian parameters of octahedral Cu(HCOO) 2 (H 2 O) 2 complexes at the rigid lattice limit (below 77 K) are the following: g z = 2.405, g y = 2.095, g x = 2.065, A z = 130, A y = 4, and A x = 11 × 10 -4 cm -1 . The parameters along the y and z -axes display vibronic averaging effects on heating which allows evaluation of the energy difference δ 12 = 347 cm -1 between the two lowest energy Jahn-Teller distorted configurations. The electron spin-lattice relaxation is governed by Raman processes and the Debye temperature has been determined as Θ D = 204 K. The electron spin echo amplitude decay is determined by instantaneous diffusion below 10 K and then the dephasing rate weakly increases on heating because of libration motions of Cu 2+ complexes and/or excitations to the first excited vibronic level of energy Δ = 63 cm -1 . [ABSTRACT FROM AUTHOR]