A new copper( ii ) complex ( I ) was obtained by the reaction of a sterically crowded 2,4-di-( tert -butyl)-9-chloro-benzo5,61,4oxazine2,3- b phenoxazine bridging ligand with Cu( ii ) hexafluoroacetylacetonate. Compound I is a quasi-one-dimensional complex in which the Cu(hfac) 2 moieties are co-crystallized with the triphenodioxazine molecules through only weak Cu N short intermolecular interactions (the Cu N distances are 2.732 and 2.752 Å). The magnetic AC susceptibility data show that in spite of the absence of zero-field splitting in the Cu( ii ) ion with S = 1/2, the compound demonstrates a slow magnetic relaxation behaviour at a weak applied magnetic field ( H DC = 500 Oe). The EPR spectra and DC magnetic measurements show the strong axial anisotropy of the g-tensor. The temperature dependence of the relaxation time is well described by the combination of one-phonon direct and two-phonon Raman processes. A new copper( ii ) complex ( I ) was obtained by the reaction of a sterically crowded 2,4-di-( tert -butyl)-9-chloro-benzo5,61,4oxazine2,3- b phenoxazine bridging ligand with Cu( ii ) hexafluoroacetylacetonate.