The new octadentate ligand (R)-(+)-N,NЈ-dimethyl-N,NЈ-bis{-2-[bis(1-methyl-2-benzimidazolylmethyl)]-2-methyl- at low temperatures. In the case of [Cu 2 L] 4+ , a weak dipolar interaction between the two spin centres was found. A similar weak spin interaction occurred in the trinuclear copper cluster, which could be treated likewise as a weakly coupled three-spin system. The analysis was substantiated by studying the complex EPR temperature behaviour, where population of the quartet state occurred only at high temperature (77 K), whereas at cryogenic temperatures (4 K) the system adopted a doublet state as a ground-state spin configuration. Titration with sodium azide of [Cu 2 L] 4+ was consistent with terminal binding of one N 3 -molecule to each copper ion.