A new type of heterogeneous alkylalumoxane olefin polymerization catalyst, n-MAO, has been synthesized using carboxylate-alumoxane nanoparticles as the support material. This new catalyst has a comparable activity for ethylene polymerization to those of traditional heterogeneous catalysts with similar Al:Zr ratios, but shows a better catalytic activity per unit mass of catalyst. In an effort to develop alternative routes for the formation of methylalumoxane, MAO, the reaction of trimethylaluminum with tertiary group 14 hydroxides (Ph 3EOH) has been investigated. Two distinct mechanisms are observed depending on the relative basicity of the hydroxide. In the case of the basic hydroxides, Ph3SnOH and Ph3PbOH, a hydroxide/alkyl exchange reaction results in the formation of MAO. In contrast, reaction of AlMe3 with acidic hydroxides, Ph3EOH (E = C, Si, Ge), results in alkane elimination and the formation of [Me2Al(mu-OEPh3)] 2. The thermal decomposition of [Me2Al(mu-OCPh3)] 2 to yield MAO is found to be catalyzed by the addition of a Lewis acid, AlClxMe3-x (x = 0--3), however, the MAO product is also an efficient catalyst for the reaction. The overall rate of MAO formation is dependent on the concentration of the Lewis acid and the product (MAO), as well as the nature of the tertiary alcohol. In contrast to the reaction of [Me2Al(mu-OCPh3)]2 with a Lewis acid, the reaction of [Me2Al(mu-OCPh3)]2 with a Lewis base, THF, results in ligand disproportionation to yield MeAl(mu-OCPh 3)2(THF). A new hydrogen bond stabilized gallium alkoxide complex, [Ga2(tBu)4(neol-H)2] (Neol-H2 = 2,2-dimethyl-1,3-propanediol) has been synthesized. This complex has been shown to act as a flexible, strong ligand field, bifunctional (two OH) tetradentate (4O) ligand to first row transition metals in square planar environments.

Reaction of HgCl2 with two equivalents of MCl3 in an aromatic solvent yields Hg(arene)2(MCl4) 2 where arene = C6H5Me, C6H5Et, o-C6H4Me2, C6H3 -1,2,3-Me3, M = Al, Ga. Reaction of HgCl2 with MCl3 in benzene, m-xylene, and p-xylene results in the formation of liquid clathrates whose spectroscopic characterization is reported. In the solid state, all compounds, with the exception of o-xylene complexes, exist as neutral complexes in which two arenes are bound to the mercury and the MCl3 groups are bound through bridging chlorides to the mercury. o-xylene complex exists as a cation anion pair [Hg(o-C6H4Me 2)2(AlCl4)][AlCl4]. However, in solution all mercury-arene compounds exist as neutral complexes. The structures of Hg(arene)2(AlCl4)2 and [Hg(arene)2(AlCl 4)]+ have been optimized by DFT calculations to facilitate the assignment of the 13C CPMAS NMR spectra, and are in good agreement with the X-ray diffraction structures. Dissolution of Hg(arene)2(MCl4)2 in C6D6 results in a rapid H/D exchange and the formation of the appropriate dn-arene and C6D5H. H/D exchange between excess arene and C6D6 is also found to be catalyzed by Hg(arene)2(MCl4)2 including those with a different arene ligand. Based on DTF calculations the inter- and intra-molecular mechanism of the exchange is proposed. Mercury-arene complexes are found to be very active catalysts for the alkylation of arenes by olefins. Ethylene, propylene, and cyclohexene reacts with benzene or toluene to form mono- and polyalkylated products, the distribution being dependent on the nature of olefin. Based on the deuterium labeling experiments two different mechanisms of arene alkylation are discussed. Reaction of K[CpFe(CO)2] with a large excess of GaCl 3 yields [{CpFe(CO)2}Ga(Cl·GaCl3)(mu-Cl)] 2, while reactions with 1 and 0.5 equivalents yields [{CpFe(CO) 2}GaCl2]n, and [{CpFe(CO)2}2Ga(mu-Cl)] infinity, respectively. [{CpFe(CO)2}GaCl2] n reacts with MeCN to yield [CpFe(CO)2]GaCl2(MeCN). Reduction of [{CpFe(CO)2}2Ga(mu-Cl)]infinity with potassium in Et2O yields the previously reported [CpFe(CO) 2]3Ga and gallium metal. Reaction of K[CpFe(CO)2] with GaI3 yields [CpFe(CO)2]GaI2, which upon hydrolysis gives the unusual galloxane, [CpFe(CO)2]6Ga 6(mu3-O)4(mu-OH)2I2. Reaction of K[CpFe(CO)2] with InCl in toluene results in the formation of previously reported [CpFe(CO)2]3In and indium metal. Reaction of CpMo(CO)3H with Ga(tBu)3 yields [CpMo(CO)3]Ga(tBu)2 which forms a Lewis acid-base complex with MeCN: [CpMo(CO)3]Ga(tBu) 2(MeCN). The structure of [CpMo(CO)3]Ga(tBu) 2 shows evidence of unusual intra- and inter-molecular carbonyl &cdots; gallium interactions.

The reaction of M(tBu)3 (M = Al, Ga) and hydroquinone in a non-coordinating solvent yields the metal aryloxide polymer, [{( tBu)2M}2(mu-OC6H4O)] n. The gallium aryloxide polymer reacts with pyridines, via both a solution and a solid/vapor reaction, to yield the yellow compound [(tBu) 2Ga(L)]2(mu-OC6H4O) [L = pyridine, 4-Mepy, and 3,5-Me2py] via cleavage of the Ga2O 2 dimeric core. The thermolysis in the solid state results in the loss of the Lewis base and the formation of [{(tBu)2Ga} 2(mu-OC6H4O)]n. The DeltaH‡ and DeltaS‡ for the solid/vapor reactions have been determined. The inter-conversion of polymer to the pyridine complexes, and the reverse reactions, have been followed by 13C CPMAS NMR spectroscopy, TG/DTA, SEM, EDX, and powder XRD. Insight into the solid state mechanism of this polycondensation polymerization reaction may be gained from the single crystal X-ray crystallographic packing diagrams of the pyridine complexes. The aluminum aryloxide polymer reacts with Lewis bases to yield the compound [(tBu)2Al)L)]2([mu-OC6H 4O) [L = py, 3,5-Me2py, and THF] via cleavage of the Al 2O2 dimeric core. Unlike their gallium-pyridine analogs, these compounds do not undergo a clean dissociation to [{(tBu) 2Al}2(mu-OC6H4O)]n in the solid state. But they react by a solid/vapor reaction with solid Lewis bases to form colorful polymers of [{(tBu)2Al} 2(mu-OC6H4O)(mu-L)]n, where L = pyrazine, 4,4-bipyridine, and 1,4-benzoquinone. The formation of these compounds has been comfirmed by 13C CPMAS, 27Al MAS, and solution 1H NMR. The reaction between [(tBu)2Al(mu-OPh)] 2 and 4,4-bipyridine in toluene or CH2Cl2 yields [(tBu)2Al(OPh)]2(mu-4,4-bipy). In CDCl 3, [(tBu)2Al(OPh)]2(mu-4,4-bipy) dissociates forming [(tBu)2Al(OPh)(mu-4,4-bipy)], [(tBu)2Al(mu-OPh)]2, and uncoordinated 4,4-bipyridine. Based on equilibrium data, we have found that for [( tBu)2Al(OPh)]2(mu-4,4-bipy) one aluminum center electronically "communicates" to the second aluminum center by deactivating the nitrogen nine bonds away from the first aluminum center making one Al-N bond stronger than the other. The reaction of [Ga2(tBu)4(neol-H) 2] (neol-H2 = 2,2-dimethylpropane-1,3-diol) with TiCl 4, ZrCl4, or VCl4 in the presence of proton sponge [C10H6(NMe2)2] yields [( tBu)GaCl3][C10H6(NMe 2)2H]. The reaction of [Ga2(tBu) 4(neol-H)2] with M(NMe2)4 (M = Ti, Zr) yields [(tBu)2Ga(mu-NMe2)] 2 along with multiple transition metal containing products. The reaction of CpTi(NMe2)3 with [(tBu)2Ga(neol-H)] 2 yields [(tBu)2Ga(neol)2TiCp] and [(tBu)2Ga(mu-NMe2)]2.

Various solid-solid, solid-gas, and gas-gas reactions were explored for preparation of new refractory metal-nitrogen-fluorine compounds. The gas-gas reactions represent a new method for preparing this type of compound. The reaction of metal fluoride vapors with ammonia yielded two new nitride-fluorides, Y(,2)NF(,3) and TiNF, as confirmed by electron microprobe analysis and x-ray powder diffraction. Using computer methods in indexing x-ray powder patterns, crystal systems were found for both. Y(,2)NF(,3) crystallizes with nearly the same hexagonal unit cell as TcNF giving lattice constants of a(,0) = 5.93 (ANGSTROM) and c(,0) = 4.79 (ANGSTROM). TiNF was indexed with a low-symmetry triclinic unit cell, a(,0) = 9.76 (ANGSTROM), b(,0) = 5.88 (ANGSTROM), c(,0) = 5.47 (ANGSTROM), (alpha)(,0) = 77.52(DEGREES), (beta)(,0) = 136.24(DEGREES), (gamma)(,0) = 112.27(DEGREES). Evidence for the formation of Sc(,2)NF(,3) and Al(,2)NF(,3) is also presented. These compounds are amorphous but give elemental analyses consistent with theoretical percentages. Calculations of estimated heats of formation for nitride-fluorides have been made, assuming ionic crystals and using the Kapustinsky approximation, the third electron affinity of nitrogen, and other physical and thermodynamic data for the components in Born-Haber cycle relationships. These results confirm the refractory nature of the nitride-fluorides and their resistance to attack by HF and F(,2) at high temperatures. An estimation of the third electron affinity of nitrogen was made using thermodynamic data for the nitrides and crystal energy approximations in Born-Haber cycle calculations. The estimated value is 600 (+OR-) 50 kcal/mole. The gas-phase reaction apparatus was also used to investigate the high-temperature carbon-silicon dioxide reaction which is used to form SiC whiskers. By using a quartz-crystal microbalance to measure condensable species from pyrolized samples, it was found that the amount of elemental silicon vaporized during pyrolysis increased with decreasing carbon content of the samples, so for the desired formation of silicon carbide crystals, high carbon samples were favored.

This work involves the infrared matrix isolation study of metal atom reactions with water molecules in an argon matrix at 15(DEGREES)K. The metals studied include Mg, Ca, Sr and Ba from Group IIa; the first row transition metals, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn; the Group IIIa metals, Al, Ga, In and Tl; and the Group IVa metals, Si, Ge, Sn and Pb. Iron metal atom reactions with the isoelectronic species, CH(,4), NH(,3), and HF are also included in this study. In most cases, a metal atom-water molecule adduct is formed on co-condensation. Adduct formation is detected in these experiments by a red shift in the (nu)(,2) water bending mode frequency at 1593 cm('-1), over a range of 5 - 35 cm('-1). Photolysis of the adduct with (lamda) (TURNEQ) 300 - 600 nm light results in an oxidative insertion of the metal atom into the O-H bond of water to produce the metal hydroxy hydride molecule, HMOH. The Zn, Tl and Pb adducts do not react under normal experimental conditions. Sc, Ti, V and Al metal atoms spontaneously insert into the water molecule to form the HMOH molecule on co-condensation. Preliminary studies on nickel indicate that the metal atom does not form an adduct with water and does not undergo an insertion reaction. The HMOH molecule in some cases undergoes photolytic cleavage of one or two hydrogen bonds to form the metal monohydroxide, MOH, or metal monoxide, MO. The metal dimer-water molecule adduct was also observed for Mg, Cr, Mn, Fe, Co, Cu, Zn, Ga, In, Ge, Sn, and Pb. Photolysis of this adduct resulted in an insertion of the metal dimer into water to give a HM(,2)OH molecule. A di-insertion reaction to form the HMOMH molecule was observed for Mg, Ca, Mn and Fe. This product is believed to form by a sequential insertion of a metal atom into an already formed HMOH molecule on photolysis. Reaction products resulting from the insertion of one metal atom into water molecules were observed for Ca, Sc, Ti, V, Cr, Fe, Al, Ga, In, Si and Ge, and the ultimate product depended on the valent state of the metals. The M(OH)(,2), HM(OH)(,2) and H(,2)M(OH)(,2) species were observed for divalent, trivalent, and tetravalent metal atoms, respectively. A water monohydrated HMOH species was observed for Al, Ga, In, Si and Ge. Iron metal atoms reacted with NH(,3) and HF to form an adduct on co-condensation. It is thought that the metal atom bonds through the nitrogen and fluorine atoms, respectively. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI

The {bis-2,6-{1-(2-imidazol-4-ylethylimino)ethyl}pyridine}copper(I) cation, {Cu(I)(imidH)(,2)DAP}('+), has previously been reported to react reversibly with O(,2) in a 2:1 stoichiometry under ambient conditions in solution, thus providing a copper(I) complex to model the active site function of hemocyanin {J. Chem. Soc. (Dalton), 1827 (1980)}. The reactivity of O(,2) with other closely related derivatives of this complex has been previously studied, with those derivatives found to be either less reversible in their reactivity with O(,2) or to be unreactive toward O(,2). In the present work, a new, closely related series of copper(I) derivatives, {Cu(I)(imidH)(,2)PDA}('+), {Cu(I)(imidR)(,2)PDA}('+), and {Cu(I)(py)(,2)PDA}('+), have been synthesized, characterized, and their reaction with O(,2) studied in order to better understand what determines the degree of reversible O(,2) reactivity. These new complexes were found to be either unreactive with O(,2) or their reactivity to be less reversible than that of the previously studied parent complexes. It was found possible to relate the O(,2) reactivity and degree of reversibility to the E(, 1/2) of the copper center for a series of closely related complexes. The zinc(II) and copper(II) complexes were also synthesized and characterized for comparison. In a continuing study of O(,2) reactivity with transition metal complexes, the ligand systems {(imidH)(,2)DAP} and {(py)(,2)DAP} were studied with iron(II) to investigate the possibility that these complexes might also serve as model compounds for the active site function of hemerythrin. Whereas {Fe(II)(py)(,2)DAP}(BF(,4))(,2) was found to be unreactive with O(,2), {Fe(II)(imidH)(,2)DAP}(BF(,4))(,2) was found to react slowly and irreversibly under ambient conditions in a ratio of one O(,2) molecule per iron center. As there are now many known cobalt(II) O(,2)-carriers, these same ligands were also studied with cobalt as the metal center. The {Co(II)(py)(,2)DAP}(BF(,4))(,2) complex was found to be unreactive toward O(,2), whereas both {Co(I)(py)(,2)DAP}(BF(,4)) and {Co(II)(imidH)(,2)DAP}(BF(,4))(,2) reacted slowly and irreversibly with O(,2) in a ratio of one O(,2) molecule per cobalt center. In addition, {Co(II)(imidH)(,2)DAP}(BF(,4))(,2) yielded an isolatable and characterizable monomeric cobalt-O(,2) complex. In summary, a total of fifteen new complexes of zinc(II), copper(II), copper(I), iron(II), cobalt(II) and cobalt(I) were synthesized, characterized, and studied for reversible reactivity with O(,2), with some insight gained into the mechanism responsible for irreversible oxidation of the O(,2) reactive complexes.

Several new and unique (mu)-imidazolato and (mu)-oxo binuclear complexes of iron and copper have been synthesized and characterized as models for the active site of cytochrome c oxidase. Characterization of these novel complexes included physical measurements utilizing magnetic susceptibility, ('57)Fe Mossbauer, nmr, epr, mcd, uv-visible, resonance Raman, and infra-red spectroscopy, electrochemistry, and ESCA. (mu)-Imidazolato complexes based on the UroTPP('2-) ligand where UroTPP('2-) is the dianion of urocanic acid have been synthesized via the general route {Fe('III)(UroTPP)Cl} + {M('II)(acac)(,2)} (--->) {Fe('III)(UroTPP)M('II)(acac)(,2)} where M=Cu,Zn and acac=acetylacetonate. The Fe('III)/Cu('II) complex exhibits properties suggestive of two magnetically and electronically isolated high-spin Fe('III) (S=5/2) and Cu('II) (S=1/2) centers. In addition, various solution-dependent measurements indicate that the binuclear complexes retain their integrity in solution. The reduced species {Fe('II)(UroTPP)}, its CO adduct, and its reaction product upon exposure to air (presumably {Fe('III)(UroTPP)}(,2)O)have also been synthesized and characterized as the basis for future modeling studies. For example, future species of the type {Fe('II)(UroTpp)M('II)(acac)(,2)}('-) or {(UroTPP)Fe('III)-O-Cu('II)(imidH)(,2)DAP}('+) should exhibit interesting properties and serve as further models for the active structure. Finally, the first reported oxo-bridged heterobimetallic of copper(II) and an iron(III) porphyrin complex has also been prepared and thoroughly and systematically characterized. Its low temperature synthesis (-78(DEGREES)C) is novel and proceeds via reaction between a ferryl intermediate, (TPP)Fe('IV)=O, and {Cu('I)(imidH)(,2)DAP}('+) to give {(TPP)Fe('III)-O-Cu('II)(imidH)(,2)DAP}('+), which has been isolated as its BF(,4)('-) salt. The magnetochemistry and epr results for this compound indicate the presence of strong antiferromagnetic coupling between the Fe('III) (S=3/2) center and the Cu('II) (S=1/2) center to give a resultant S=1 ground state. This oxo-bridged complex has also been studied by a wide range of solution-dependent techniques which verify its binuclear nature in solution and S=1 magnetic behavior. Results from oxo-bridge lability studies on this complex, the first of its kind, have also been performed and are intepreted in light of similar experiments involving actual resting Cytochrome c Ocidase. Each of the (mu)-imidazolato and (mu)-oxo binuclear complexes described above have been discussed as they pertain to structural models for deciphering the active site structure of Cytochrome c Oxidase.

In the presence of a Lewis base solvent (THF) the Group IIB tetracarbonyl ferrates, {MFe(CO)(,4)}(,x) (M = Zn, Cd, and Hg) undergo stepwise reduction to give the mixed-metal dianion clusters, M(Fe(CO)(,4))(,2)('2-), first, and subsequently Fe(,2)(CO)(,8)('2-). The mechanism for the base reduction is considered in terms of competing base reactions. The solid state structures of {Na(THF)(,2)('+)}(,2){M(Fe(CO)(,4))(,2)('2-)} (M = Zn and Hg) have been determined and are directly related to their solution state infrared and NMR spectra with structural distortions retained in both the solution and solid states. The results of the structural determination on {Na(THF)(,2)('+)}(,2) {Zn(Fe(CO)(,4))(,2)('2-)} showed the zinc to crystallize in the space group 12/m with approximate C(,2h) site symmetry. The cell dimensions are a = 10.654(3) (ANGSTROM), b = 9.848(3) (ANGSTROM), c = 15.333(3) (ANGSTROM), (beta) = 100.79(2)(DEGREES), and V = 1580 (ANGSTROM)('3). The geometry about the iron atoms is that of a Fe(CO)(,4) tetrahedron with the zinc atom approximately bridging an edge. Crystals of the mercury analogue form in the space group C 2/m with D(,3d) symmetry site symmetry. The cell dimensions for the mercury complex are a = 12.39(3) (ANGSTROM), b = 8.54(1) (ANGSTROM), c = 16.01(1) (ANGSTROM), (beta) = 105.5(2) , and V = 1636 (ANGSTROM)('3). The mercury is capping one face of the Fe(CO)(,4) tetrahedron. Bonds between carbonyl oxygen atoms of the dianions and the Na(THF)(,2)('+) cations results in an extended structure in the solid state. ('57)Fe Mossbauer recorded on the zinc and cadmium dianion complexes gave the following parameters: Zn: (delta) = 0.156 mm s('-1) and (DELTA) = 0.910 mm s('-1); Cd: (delta) = 0.232 mm s('-1) and (DELTA) = 1.112 mm s('-1) (relative to iron foil). The dimeric dialkyltin tetracarbonyl ferrates, {Sn(R)(,2)Fe(CO)(,4)}(,2), establish an equilibrium in Lewis base solvents forming a monomer base adduct, Sn(R)(,2){B}Fe(CO)(,4). For B = THF or C(,5)H(,4)N, the monomer adduct undergoes reduction to form a radical anion, Sn(R)(,2)Fe(CO)(,4)('-), where the reduction process is seen as populating a nonbonding sp('3) orbital on tin with possible (pi) back-bonding to the iron. The ('57)Fe Mossbauer spectrum exhibits a doublet ((delta) = 0.06 mm s('-1) and (DELTA) = 1.50 mm s('-1)) in the region of Fe(CO)(,4)('2-). The ('119)Sn Mossbauer spectrum exhibits a doublet ((delta) = 1.54 mm s('-1) and (DELTA) = 1.19 mm s('-1)) in the region normally associated with tin (IV).

In the last decade metal vapor synthesis has become an important method for producing organometallic species that have been unattainable or difficult to make by other routes. However, many important reactions lie just outside the reach of the procedure because the energy of activation for the process is too high. Matrix isolation experiments indicate that direct photolysis of a metal-organic cocondensate is an excellent method for introducing energy into a metal vapor reaction system so that new chemical processes can be accessed. A metal vapor reactor was built in which one could irradiate with U.V.-visible light the deposition surface during co-deposition of the reactants. The reactor was designed so that the reaction surface was a rotating drum placed between the furnace and the photolysis well. This design minimized the accumulation of a metal coating on the photolysis lamp but introduced a time lag between deposition and photolysis. The reactions of transition metal vapors with acetone produced both pinacol by a metal atom process and aldol condensation products formed by a metal particle catalyzed process. Photolysis of the co-deposited layers of some transition metals with acetone produced an increase in the amount of pinacol formed (from 1.0 to 6% for iron, 0.8 to 3.7% for cobalt and 0.0 to 1.1% for nickel). No such reductive coupling products were observed for the reaction of iron and nickel with cyclohexanone under photochemical conditions. Nickel was the only transition metal (of Cr, Mn, Fe and Ni) that reacted with ethyl acetate without photolysis. This reaction produced products which were apparently formed from the decomposition of oxidative insertion products of nickel and ethyl acetate: Et-O-Ni-Ac and Et-Ni-O-Ac. Chromium and manganese reacted via a photolytically induced oxidative insertion to produce acetaldehyde and other products which were derived from a similar R-O-M-Ac complex. The yield of acetaldehyde in this reaction was dependent on the R-group in the ester and the deposition ratio of the metal and organic.

Part I. Magnetochemical Studies of Bovine Cytochrome c Oxidase. The variable-temperature (20-200 K) magnetic susceptibility properties of bovine cytochrome c oxidase in its fully-oxidized or resting state (Hartzell-Beinert and Yonetani preparations), its fully-reduced state (Hartzell-Beinert) and its resting(.)CN('-) state (Hartzell-Beinert and Yonetani) have been examined. In general, the magnetochemical results for the Hartzell-Beinert (g(,12) and g(,12)-less) and Yonetani resting enzyme forms are nearly Curie in nature and identical to those of Tweedle. All three sets of data are consistent with a strong antiferromagnetic exchange-coupled pair at the active site with -J (GREATERTHEQ) 200cm('-1) to give a epr inactive S = 2 ground state. The Hartzell-Beinert reduced enzyme displays magnetochemical behavior like that previously reported by Tweedle, where only cyt.a(,3)('2+) (S = 2) is a paramagnetic center. Finally, the magnetochemistry of the Hartzell-Beinert and Yonetani resting(.)CN('-) derivatives were also found to be nearly identical to that of Tweedle, in that the data are non-Curie in nature and can be interpreted in terms of a weak antiferromagnetic exchange-coupled pair at the active site. Part II. A Synthetic Model Compound Approach to the Active Site Structure of Cytochrome c Oxidase. Twelve new (mu)-imidazolato heterobinuclear metal complexes have been synthesized to model the proposed imidazolate-bridged cyt.a(,3)('3+)(imid)Cu(,U)('2+) active site structure of resting cytochrome c oxidase where -J(,(Fe('III)-Cu('II))) (GREATERTHEQ) 200 cm('-1) may be the case. The model compounds have been derived from LFe('III)(TPP) (TPP('2-) = tetraphenylporphyrinato and L = OSO(,2)CF(,3)('-)) and M'('II)(2-meimidH)(,2)DAP ('2+) or M'('II)(imidH)(,2)DAP ('2+) (M'('II) = Zn and Cu) to yield 12 species. The variable-temperature (ca. 20-200 K) magnetochemical and epr (10 K) data obtained indicate that the Fe(III) and Cu(II) centers in compound 2 and Co(II) and Cu(II) centers in compounds 6 and 8 are electronically isolated from one another with -J (TURN) 0 cm('-1). Compound 4 exhibits magnetochemcial and epr spectral properties consistent with strong antiferromagnetic coupling between Fe(III) (S = 5/2, 1/2) and Cu(II) (S = 1/2) where -J(,(Fe('III)-Cu('II))) (GREATERTHEQ) 200 cm('-1). Compounds 10 and 12 also display variable-temperature magnetochemical and epr spectral behavior consistent with a strong antiferromagnetic exchange-coupled Mn('II)(S = 5/2)(imid)Cu('II)(S = 1/2) ('+) pair with -J (GREATERTHEQ) 200 cm('-1) to give a resultant epr inactive S = 2 ground state. As such, these model compounds may be considered to be good spin mimics of the cyt.a(,3)('3+)(S = 5/2)- Cu(,U)('2+)(S = 1/2) active site of cytochrome c oxidase in its resting state. (Abstract shortened with permission of author.)