The single-crystal X-ray structures of [Cu2(4,ll-diene-N4)2CN](C104)3, where 4,ll-diene-N4 is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene, and [Cu2(tren)2(CN)2](BPh4)2, where tren = 2,2′,2′′-triaminotriethylamine, have been determined and preliminary results communicated. The copper atom environments are trigonal bipyramidal in both of these Cu(II) dimers; in the former complex there is Cu-CN-Cu bridging while in the latter system bridging is via the coordinated cyanide on each copper atom hydrogen bonding through its N atom to a primary amine of the tren ligand coordinated to the second Cu atom, Cu-CN· · σ- HN-Cu. The electronic structures of the two Cu(II) dimers have been characterized by electronic absorption, ir, esr, and variable-temperature (4.2-283 °K) magnetic susceptibility measurements. Low-intensity γ(CN) bands are shown to be indicative of CN bridging for these two Cu(II) dimers. Antiferromagnetic exchange is present in both cyanide- bridged dimers, where J = —4.8 cm-1 for the Cu-CN-Cu system and J = —1.8 cm-1 for the Cu-CN…HNCu system. The observed exchange in the hydrogen-bonded tren system is of special interest, because it provides a lucid illustration of magnetic exchange through a bridging moiety possessing only -electron density. The observed electronic effects are discussed with regard to the coordination geometry and bridge bonding in each molecule, and a comparison is made between the two cyanide-bridged systems and the five-coordinate chloride-bridged compound [Cu2(tet-b)2Cl](C104)3, where (tet-b) = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The magnetism (J = ′144 cm-1) for this system is reported in this paper.