Part I. Previously the {bis-2,6{1-(2-imidazol-4-ylethylimino)-^ethyl}pyridine}copper(I) cation, {Cu('I)(imidH)(,2)DAP}('+), was found to reversibly bind dioxygen, whereas the {bis-2,6-{1-(2-pyridin-2-ylethylimino)ethyl}pyridine}copper(I) cation, {Cu('I)(py)(,2)DAP}('+), was unreactive toward O(,2). Magnetochemical and resonance Raman experiments were conducted to characterize the {Cu('I)(imidH)(,2)DAP}('+)-dioxygen interaction. {Cu('I)(imidR)(py)DAP}('+), {Cu('I)(imidH)(py)DAP}('+), {Cu('I)(imidR)(,2)DAP}('+), and {Cu('I)(imidR)(imidH)DAP}('+) where R = -CH(,2)(C(,6)H(,4))CH(,3), were synthesized to examine the role of the acidic imidazole proton of {Cu('I)(imidH)(,2)DAP}('+) in the reversible oxygenation process. While {Cu('I)(imidR)(py)DAP}('+) was dioxygen-inactive, {Cu('I)(imidH)(py)DAP}('+) reacted irreversibly with dioxygen. {Cu('I)(imidR)(,2)DAP}('+) and {Cu('I)(imidR)(imidH)DAP}('+) reacted reversibly with dioxygen (1 mole O(,2):2 moles Cu), paralleling the dioxygen reactivity for {Cu('I)(imidH)(,2)DAP}('+). Correlation between the redox potential of the Cu(II) (DBLHARR) Cu(I) couple and the reaction of the Cu(I) center toward O(,2) was proposed. Analogous Cu(II) and Zn(II) complexes of all the Cu(I) species were characterized. The relevance of these copper(I) compounds as the first synthetic copper(I) dioxygen carriers to model the active site function of hemocyanin was discussed. Part II. (mu)-Imidazolato mixed-metal complexes were synthesized^to model the proposed imidazolate-bridged {Cyt.a(,3)('3+)(imid)Cu('2+)}^active site structure of cytochrome oxidase where -J(,(Fe)III(,-Cu)II(,)(, ))>(, )200 cm('-1). The compounds were derived from {Fe('III)(TPP)X} (TPP('2-) = tetraphenylporphyrinato and X = Cl('-) or OSO(,2)CF(,3)('-)) and {M('II)(imidH)(,2)DAP}('2+) or {M('II)(imidH)(py)DAP}('2+) (M = Zn or Cu) to yield species containing the following (mu)-imidazolato cationic cores: {ClFe('III)(imid)Zn('II)}('+) {compound (1)}, {ClFe('III)(imid)Cu('II)}('+) {compound (2)}, {(OSO(,2)CF(,3))Fe('III)(imid)Zn('II)}('+) {compound (3)}, {(OSO(,2)CF(,3))Fe('III)(imid)Cu('II)}('+) {compound (4)}, {ClFe('III)(imid)Zn('II)(py)}('+) {compound (5)}, and {ClFe('III)(imid)Cu('II)(py)}('+) {compound (6)}. The variable-temperature magnetochemical and EPR data obtained on the solid state samples indicated that the iron(III) and copper(II) centers of the (2) and (6) complexes are electronically isolated with -J(,(Fe)III(,-Cu)II(,)) (, )200 cm('-1). Compound (4) is the first synthetic (mu)-imidazolato iron(II)-copper(II) metalloporphyrin complex where strong antiferromagnetic exchange interaction between metal centers has been observed. Reinvestigation of the magnetic properties of the "2Co('II)2Cu('II)" superoxide dismutase derivative confirmed that strong antiferromagnetic coupling {-J(,(Co)II(,-CU)II(,)(, ))>(, )300 cm('-1)}, mediated by a bridging imidazolate moiety, exists between the Co(II) and Cu(II) centers. These results provided evidence supporting the possibility of an imidazolate bridge at the active site of cytochrome oxidase.