The trinuclear complex [Bu4N2[Cu-3(mu(3)-Cl)(2)(mu-pz)(3)Cl-3] (pz = pyrazolato anion) (1) exhibits ferromagnetic interactions resulting in an S = 3/2 ground state which is characterized by a small zero field splitting tensor [17]. Herein, the S = 3/2 state is further characterized using High-Frequency and -Field Electron Paramagnetic Resonance spectroscopy. The spin relaxation properties of 1 are studied with alternating current susceptometry in the presence of external magnetic fields. In the 4.5-8.0 K temperature range, the system relaxes via an Orbach mechanism involving transitions between the S = 3/2 and the excited S = 1/2 spin manifolds. (C) 2010 Elsevier B. V. All rights reserved.