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Physical studies of the imidazolate-bridged dicopper(II) ion coordinated to the ligands l, 4,7,13,16,19-hexaaza-10,22-dioxacyclotetracosane (A) and 1,4,7,13,16,19-hexaazacyclotetracosane (A') were carried out to explore the influence of these binucleating macrocycles on the stability of the Cu2(im)3+ core (imH = imidazole). Temperature-dependent magnetic susceptibility studies of solid [Cu2(im)(imH)2CA](C104)3 and [Cu2(im)CA'](C104)3-H20 revealed antiferromagnetic behavior with J = -27.60 (7) and -29.40 (3) cm"1, respectively. These values demonstrate that the magnetic interaction between copper(II) centers in the Cu2(im)3+ ion is unaltered by its coordination to these macrocyclic ligands. The solution properties differed markedly, however. From pH-dependent electron spin resonance and potentiometric titration data it was determined that the imidazolate bridge in [Cu2(im)CA']3+ is much more stable than ih related complexes such as [Cu2(TMDT)2(im)]3+, where TMDT = 1,1,7,7-tetramethyldiethylenetriamine. Equilibrium constants as well as AH and AS values for the bridge-splitting reactions were determined. Cyclic voltammograms of [Cu2(im)CA']3+ in acetonitrile under various conditions showed only irreversible behavior, ascribed to the instability of the cuprous derivatives of the binucleating macrocycle.

The synthesis and spectroscopic characterization of discrete, water soluble, imidazolate-bridged copper(I1) complexes are reported. Binuclear imidazolate-bridged complexes were crystallized from basic aqueous or methanolic solutions of Cu(pip)2+, pip = 24 (2-(2-pyridyl)ethylimino)methyl]pyridine, or CU(PMDT)~+, PMDT = 1,1,4,7,7-pentamethyldiethylenetriamine, and various substituted imidazoles. The condensation of imidazole-4,5-dicarboxaldehyde with (2-(2-aminoethyl)-pyridine)copper(II) afforded the Cu2bpim3+ cation, where bpim is 4,5-bis[(2-(2-pyridyl)ethylimino)methyl]imidazolate. Addition of imidazole and sodium hydroxide to aqueous solutions of this cation yielded the tetranuclear complex [C~~bpim(im)]~(N0~)~4H~O (im = imidazolate). Potentiometric titrations and solution electron spin resonance spectroscopic studies showed that the integrity of the imidazolate bridge in the Cu2bpim3+ cation is maintained in the range 3.5 < pH < 11.5. Similar studies of the [Cu(pip)12im3+ complex revealed that the bridge is broken both by protonation of the imidazolate group at low pH and by competition with hydroxide ions at high pH. Four protons are reversibly titrated in solutions of [Cu2bpim(im)]:+ corresponding to protonation of the imidazolate rings that link the two Cu2bpim3+ units in this complex to form 2 equiv of imidazolium ion. IntroductionThe imidazolate (im) anion, the deprotonated form of im-

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