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The synthesis of a family of iron(II) spin crossover monomers containing the bis-meridional ligands 2-(1-pyridin-2-ylmethyl-1H-pyrazol-3-yl)-pyrazine (picpzpz) and 2-(3-(2-pyridyl)pyrazol-1-ylmethyl)pyridine) (picpypz) is described.

EPR and ligand field studies are carried out on wild-type iron(III) superoxide dismutases (FeSODs) from Eschrichia coli and from Methanobacterium thermoautotrophicum and iron-substituted manganese(III) superoxide demutases (Fe(sub)(MnSODs) from E. coli and Serratia marcesnes. The same electronic structures characterize wild-type enzymes with negative zero-field splitting.

A versatile and efficient method for preparing optically active (bis)triarylphosphines bearing a ferrocene moiety is introduced. The synthetic route is tolerant toward bulky aryl substituents and exhibits excellent enantio- and diastereoselectivity. Five new phosphorus-chiral ferrocenyldiphosphines were synthesized to demonstrate the possibility and necessity of steric tuning, while their efficiency as chiral ligands was exhibited in rhodium-catalyzed asymmetric hydrogenation reactions of alpha-(acylamino)cinnamic acid derivatives.

Research was conducted to examine the structural, magnetic, and electronic properties of a pentacoordinated intermediate-spin (S = 3/2) iron(III) complex with a macrocyclic (N4)2- ligand. X-ray crystallography, EPR and Mossbauer spectroscopy, temperature-dependent magnetic susceptibility and molecular orbital measurements were used. Results illustrate a complete picture of bonding modes, intramolecular interactions and the electronic structure around the iron center.

The synthesis and characterization of Fe(super II) and Fe(super III) complexes with the pentadentate ligand N4Py were described. These complexes were found to serve as precursors of a putative Fe(super III)-OOH species, obtained by addition of H2O2. The novel spectroscopic properties of this intermediate were then examined within the context of 'activated bleomycin,' the active form of the antitumor drug.

The reaction of sulfur dioxide with heterometallic carbonyl clusters (PPN)2(MFe3(CO)14), where M = Cr, Mo, W; PPN = bistriphenylphosphonium iminium and heterometallic carbide clusters (MFe3(CO)nC)x-, where M - Mn, Cr, W, Rh, are presented. The results showed that the reaction with the heterometallic carbonyl clusters resulted in loss of the heterometal and the formation of triiron SO2- and S-containing clusters.

In situ generated high-valent iron oxo complexes of electron-rich and -deficient porphyrin ligands were employed directly in oxygen atom transfer reactions. Findings showed that the electronic characteristics of porphyrin ligands bound to iron is a significant factor in obtaining the reactivities of iron porphyrin complexes. Also, iron porphyrin complexes can be chosen to get the required reaction pathways.

The Ni-Fe heterobimetallic complex (Ni(S2fc)(PMe2Ph)) containing an Fe->Ni dative bond and a series of 1,1'-ferrocenedithiolato group 10 metal complexes without a metal-metal interactions was synthesized and its structural characterization studied. The 1,1'-ferrocenedithiolato-diphosphine complex, (Ni(S2fc)(dppe)), and the corresponding palladium and platinum complexes, acts as a potential precursor for the syntheses of heterometallic complexes with greater nuclearity. The resulting trinuclear complexes have a puckered M2S2 core with syn-axial thiolato substituents due to the distinctive cylindrical shape of the 1,1'-ferrocenedithiolato moiety.

Planar chirality is important in new oxazoline-containing ferrocenes for dialkylzinc additions to aldehydes. Results of catalyses with diastereomeric ferrocenes (S,R(sub p)) and (S,S(sub p)) show how central and planar chirality cooperate with each other. A preferential catalyst conformation proved to be relevant to diastereomeric ferrocene-based catalysts, since it led to the design of an adequate arene compound exhibiting catalytic activity similar to that of (S,R(sub p)). The compound does not have the planar chirality of the ferrocenes but leads to an identical catalytic course.

Direct structural study and 19F nuclear magnetic resonance (NMR) were used to provide proof confirming the hypothesis that the d-orbital splittings of Co(II) in porphyrin ligands should resemble those of Fe(II) in hemes. Findings showed that the beta-octafluorination of porphyrins results in reduced crystal field for chelated cobalt yielding the first examples of high-spin Co(II) porphyrins. A porphyrin containing a dilated porphyrin core was also observed in the x-ray crystal structure. NMR studies showed axial ligand-dependent downfield shifts for the beta-fluorine resonances.

The self-condensation reactions of the functionalized cluster of [FeS4(SH)4](super 2-) were evaluated to relate the results to the synthesis and characteristics of polycubane [Fe4S4]n(super 1-3) and dicubanoid [Fe4S5](sub 2)(super 4) clusters. Also, (Pr4P2)[Fe4S4(SH)4] was characterized to exhibit the relation of Fe-SH bond lengths. The terminal Fe-SH bond lengths in [Fe4S4](super2+,+) clusters were similar with the alkyl and arenethiolate ligands in the same cluster oxidation state.

The tridentate 'heteroscorpionate' mixed functionality ligand (2-thiophenyl)bis(pyrazolyl)methane (L1) was synthesized and characterized. These ligands were employed to synthesize the complexes (Fe(L1)2)(ClO4), (Co(L1)2)(BPh4) and (V(L1)2)(BPh4). X-ray crystallography was used for the latter two complexes. Resonance Raman and Jorgenson's optical electronegativity theory were utilized to assign the S -> M charge transfer transitions in all three complexes.

The bidentate phosphine ligand 1,2-diphospholanoethane (BPE5) complexes reacted with iron(II) chloride to produce cis-Fe(BPE5)2Cl2, whose structure was determined crystallographically. In solution, cis-Fe(BPE5)2Cl2 has a temperature-dependent paramagnetism caused by chloride dissociation. A chloride ligand of cis-Fe(BPE5)2Cl2 is easily substituted by small anionic or neutral ligands. The structure and chemical characteristics of cis-Fe(BPE5)2Cl2 are examined in terms of the steric bulk of the BPE5 ligands and lability of the chloride ligands.

Halide metathesis with silver nitrite can be used for either stepwise or complete substitution of all three chloride ligands in the iron(III) compound (NEt4)(HB(3,5-Me2pz)3FeCl) to produce the complexes (NEt4)(HB(3,5-Me2pz)3Fe(ONO)xCl3-x), x = 1 - 3, and (NEt4)(HB(3,5-Me2pz)3Fe(eta2-ONO)Cl). The above compounds were characterized by elemental analyses, electrochemistry and spectroscopy. The crystal structures of the ferric complexes had monodentate, O-bound nitrito ligands.

The synthesis and characterization of a new tripodal tetradentate ligand containing both imidazole and acid moieties, (bis((1-methylimidazol-2-yl)methyl)amino)acetic acid (LH), and its iron(III) complex, Fe(III)(L)Cl2 (FeL), were performed. The latter's reactivity with superoxide and dioxygen was likewise studied. The results, which indicated the formation of a stable oxygenated form of the complex of the type (Fe(III)-O2-), proved the suitability of the iron(III) complex to model mononuclear non-heme iron complexes with active sites.

Isocyanide complexes of (porphyrinato)iron(III) species, ((Porph)-Fe(t-BuNC)2)ClO4, Porph = OEP, TPP, were synthesized and characterized. Consistent with the predicted effect from the strong pi-acceptor character of the axial tert-butyl isocyanide ligands, the X-ray structure of the complex revealed that the porphyrinate ring is strongly ruffled.

(mu-Oxo)bis(mu-acetato)diiron(III) complexes, which exhibit kinetic and thermodynamic stability, are achieved first by synthesizing the novel ligand 1,2-bis(2- bis 2-pyridyl methyl -6-pyridyl)ethane. The ligand is produced upon a carbon-carbon homo-coupling of a carbanion of 2-(bis(2-pyridyl)methyl)-6-methylpyridine. The starting ligand, in turn, is formed by the reaction of a carbanion of 2,6-lutidine with 2-bromopyridine. Spectroscopic studies of the two resulting complexes reveal a strong correlation with their (mu-oxo)bis(mu-acetato)diiron(III) core structure.

The syntheses and characterization of dinuclear ion complexes of the dinucleating ligand 2,6-bis(2-hydroxybenzyl 2-pyridylmethyl aminomethyl)-4-methylphenol, are described. The complexes, which contain a biologically relevant N,O-donor ligand, were used to mimic the active site of purple acid phosphatases. Two complexes were found to be good synthetic analogues for the chromophoric site of the oxidized and reduced forms of the enzyme.

The molecular mechanism of laser-initiated 5T2-1A1 intersystem crossing in transition metal complexes are investigated in spin-crossover complexes (Fe tpen)(ClO4)2, (Fe tppn)(ClO4)2, (Fe tpn)(ClO4)2, (Fe t-tpchxn)(ClO4)2 and (Fe dpa 2)(ClO4)2. Excited-state relaxation data at different temperatures are calculated by nanosecond laser flash photolysis. An experimental agreement is found between activation parameters and ligand structural rearrangements which determines the harmonious action for spin-state interconversion reaction.

The (mu-oxo)diiron complexes of borlyated dimethylglyoximes (Fe DMG BPh2 2)2O bind one or two axial ligands trans to the oxo bridge. The axial phenyl substituents therefore effect a cyclophane-like binding domain which influences the ligation characteristics of the BPh2 and BF2 complexes. The ligand binding of both systems is greater by at least 6 orders of magnitude than that of heme or Fe(salen) mu-oxo systems but weaker compared to FeII(DMG BR2)2 complexes. The contact shifts of DMG methyl, pyridine, and imidazole derivatives 1H resonances vary for the different ligated forms.

Tridentate ligands H2PhL, H2ToL, and H2NpL react with iron(III) chloride to yield iron(III) salts Et4N(Fe ArL 2). Azo oxime chelation affords spin-pairing while the coordination of the carboxylate effects a stabilized trivalent state. Distinct rhombic spectra are achieved in frozen dimethylformamide-toluene glass, which are in agreement with the cis-FeN4O2 metal coordination geometry. This configuration is generated from meridional binding of the two ligands to the metal through oximato N, azo N, and carboxyl O atom pairs.

The properties and reactions of trans-tricarbonylbis(phosphine)iron(O) complexes trans-Fe(CO)3L2 (L = PPh2Me, PPh3) are investigated relative to the role of the phosphine ligand. The crystal structure of trans-Fe(CO)3(PPh2Me)2 shows a twisted trigonal bipyramid bearing unlike phosphines whereas the Fe(CO)3 portion diverges from trigonal plane. The phosphines are in staggered conformation in relation to the carbonyls while the P1 and P2 methyl groups are gauche to each other. This conformation is effected by the overall intermolecular arene-arene interactions.

The kinetics of dissociation of the mono, bis, and tris complexes of 1,2-dihydroxy-3,5-benzenedisulfonate (Tiron) have been examined as a function of (H+) and temperature. The rate constants and activations parameters for the forward and reverse reactions were obtained and indicated the presence of monoprotonated Tiron complexes. A mechanism has been proposed which involves the substitution of Fe(L)2 and Fe(L)3 complexes by dissociative activation, promoted by catecholate ligands.

The meso-tetraaryl iron porphyrins with an OH- axial ligand and halogen substituents in the pyrrole beta-positions were irradiated at 365 nanometer without dioxygen to produce Fe(super II) and OH radicals. The reduction of Fe(III) involved the transfer of the electron from the ligand to the metal center. The photoreduction quantum yields were affected by the OH- axial ligand and the various substituents in the beta-positions. The photoexcitation method can also oxidize cyclohexane to cyclohexanone by O2 with the formation of OH radicals.

A dinuclear micro-phenolate bis(mu-acetate) diiron(III) complex, Fe2 (BIOMP)(mu-O2CCH32)(ClO4)*H2O, may be synthesized from a septadentate ligand (H3BIOMP). This compound may provide a model of of the active site of purple acid phosphatase. The crystal structure is in the space group P2(sub 1)/n. The two central, weakly ferromagnetic Fe cations are bridged by a phenolate oxygen and two acetate ions, and the facial sites are connected by amine and imidazole pendants. A large cathodic shift is detected for the complex ion system. Two Mossbauer spectra are seen at 295 and 125 K.

The synthesis and characterization of the ferric complexes FEIII(3,6-DBSQ)3 and Fe(3,6-DBSQ)2(mu-OMe) (sub)2, are presented. The monomeric complex was prepared by the reaction of Fe(CO)5 and 3,6-di-tert-butyl-1,2-benzoquinone (3,6-DBSQ). Solvolysis in methanol of the monomeric ferric complex affords the dimeric Fe(3,6-DBSQ)2(mu-OMe) (sub 2). The structural and electrochemical characterization of these complexes are discussed.

Photochemical or chemical oxidation of Fe(III)-hexadentate macrocyclic ligand complexes, FeLp or FeLo, involves the elimination of an electron from a phenolate ligand, leading to the formation of cationic complexes. FeLo and FeLp can be used as biocatalysts for the reaction of metal ions and radicals. These radicals show a homology to the protonated parent compounds, as revealed by Mossbauer, UV/vis and resonance Raman spectroscopies.

Electrochemical, spectrophotochemical and spectroscopic techniques are capable of characterizing the reactivity of superoxide with iron II complexes. The complexes have pentadentate ligands and hexadentate ligands. Electrically conductive polymers on the electrode surface at negative potentials exist and is indicated by the repetitive cyclic voltammograms of the two complexes. The polymers are formed under aerobic conditions which are induced by hypervalent iron species.

Dimetallic species are generated when oxime-hydrazone ligands are used to prepare a sequence of iron clathrochelate complexes that are topped with ferrocenylboronic acid. 1, 1'-ferrocenediyldiboronic acid is employed as a capping or bridging factor between two clathrochelate complexes in metal complexes for the first time. A new trimetallic species is produced by this usage. Cyclic voltammetry and controlled-potential electrolysis are used to study the redox chemistry of the multiple metal systems.

The reactions of iron(II) tetramesitylporphyrin and iron(II) tetraphenylporphyrin with ligands in the sixth positions are elucidated. The binding kinetics and equilibria of isonitriles, 1-methylimidazole, 1, 2-dimethylimidazole and carbon dioxides to the iron porphyrins show the fifth and sixth ligand combinations which result in steric repulsion with the porphyrin group. The results also show a larger binding constant and lower dissociation rates for the tetramesitylporphyrins than the tetraphenylporphyrins.

The effect of pressure on the complex formation reactions of Fe(CN)5H2O(super 3-) with neutral and negatively charged ligands is investigated. The reactions are pseudo-first-order for three half-lives of the reaction, with the rate law formulated as k(sub obs) = k(L(super n-)). The reactions are not greatly influenced by pH and k decreases considerably with increasing pressure. Finally, an analysis of the dissociative interchange and ion-pair dissociative mechanisms proposed for the substitution reaction allows for the conclusion that the reaction proceeds via the latter pathway.

The single-crystal X-ray diffraction structure of Fe(btz)2(NCS)2 and Fe(phen)2(NCS)2 at 273 and 130 degrees K and their variable temperature magnetic behavior were investigated. Results revealed that both compounds belong to the space group Pcbn and have similar molecular packings which remain the same in both low- and high-spin isomers. Moreover, the mean metal-ligand bond length and the unit cell volumes vary closely for the compounds. Similarity is also found in the volume changes occurring from lattice thermal expansion.

The barrier to rotation of the complexes (MH(eta2-H2)PP3)1+, where M = Fe or Ru and which are crystallized as BPh4 salts, is investigated to derive evidence for the intensity of the back-bonding interaction. Results show that Ru's binding strength for the dihydrogen ligand is not consistent with its expected order in the periodic table. This is the result of the better back-donation properties of the Fe center as compared to Ru.

A small amount of the bis(phosphino enolate) complex cis-Fe(Ph2PCH___...C(___...O)Ph)2(CO)2 was generated from the reaction of Fe3(CO)12 with P-O in Me3NO in THF, together with Fe3(CO)11(P-O). An octahedral coordination exists about the Fe(II) center of the cluster, with the carbonyl ligands in the cis position and the phosphorus donor atoms trans to each other. The molecule possesses no symmetry element and the unit cell contains the two enantiomers.

The compound (NEt4)2(Fe(Z-cys-Pro-Leu-cys-Gly-Val-OMe)2) was synthesized to afford a basis for the investigation of the function of NH---S hydrogen bonds around the active site of rubredoxin. Isotropic shifts ofthe amide N2H signal as measured by 2H NMR spectroscopy provided evidence for NH---S hydrogen bonding. Moreover, solvent-independent contact-shifted N2H signals in (FeII(Z-cys-Pro-Leu-cys-OMe)2)2- showed that the NH---S hydrogen bonds are shielded from the solvent.

The electrochemical analysis of iron(2) complexes of 2,2'-bipyridine, 2,2'-bipyrimidine, 1,10-phenanthroline and 2, 2':6',2''-terpyridine showed that all the complexes undergo a three-step one-electron reversible reduction except for terpyridine complexes which involve a two-step one-electron reduction. Moreover, all the four complexes featured a single one-electron reversible oxidation with electrochemical potentials ranging from +0.785 to +1.036. In addition, the application of ultraviolet-vis-near-infrared spectroscopy in the examination of the products provided reliable results.

The synthesis, structural and magnetic properties of new cyanide-bearing molecular precursor, mer-[Fe(pzcq)[(CN).sub.3]] and zigzag chain, [Fe(pzcq)[(CN).sub.3]][Mn(salen)].4[H.sub.2]O (where pzcq = 8-(pyrazine-2-carboxamido)quinoline anion, and salen = N',N'-ethylenebis-(salicyclideneiminato) dianion are described.

The catalytic performance for solvent-free aerobic oxidation of a long-chain n-alkane by iron(III)-substituted polyoxotungstates immobilized on 3-aminopropyl)triethoxysilane-modified mesoporous (SBA)-15 is described.

Bis-macrocyclic FeII/FeII complex is electrochemically oxidized to form a mixed valence FeII/FeII compound. Electronic interaction is facilitated by a delocalized Pi-system of binucleating ligand. Mossbauer spectrum of the mixed valence complex consists of a single, quadrupole-split doublet, showing the equivalence of two iron atoms.

The study conducted indicates that the nature of axial ligand allows it to alter the distribution of electrons between the metal and the porphyrin in complexes where there is an oxygen atom replacing one of the meso protons.

High-oxidation state iron complexes that features metal-to-ligand multiple bonds are proposed as key intermediates in numerous biocatalytic transformations. The maiden observation of the terminal iron (IV) nitride, [PhBP(sub 3)(super iPr)]Fe(super IV) triple bond N ([PhBP(sub 3)(super iPr)]= [PhB(Ch2P(super i)Pr2)(sub 3)](super -)), is described.

A detailed experiment and theoretical study of the series [Fe (NO) (cyclam-ac)] (super 2+/+/0) is described. The findings provide strong evidence for ligand-centered reduction steps with consequences for the reactivity of the bound NO ligand.

A successful approach to the synthesis of biomimetic dirron(II) complexes is to apply terphenyl-based carboxylates as ligands to assemble the desired dinuclear complexes and to mimic the protective pocket at the protein active sites. The present experiment results expanded the palette of substrates that can be oxygenated with O2 under ambient conditions with carboxylate-rich dirron centers in synthetic models of MMOH and ToMOH.

A few mononuclear iron (III) complexes of tetradentate tripodal and linear bis(phenolate) ligands with N2O2 donor sets are isolated and studied as functional models for catechol 1,2- dioxygenases. The complexes [Fe(L1)Cl], [Fe(L2)(H2O)Cl] , [Fe(L3)Cl] and [Fe(L4)(H2O)Cl] are characterized using absorption spectral and electrochemical techniques.

A study on the application of unique macromolecular ligands Ln(sub 3)TACN, where n=number of aromatic layers=1-4, to investigate the bioinorganic chemistry of non-heme iron proteins is presented. Structural-reactivity relationships and some mechanistic aspects of the oxygenation of iron(II) complexes capped with Ln(sub 3)TACN, together with dendrimer effects on chemical and electrochemical properties of the resulting iron(III) complexes are discussed.

The N-donor effects on carboxylate binding in mononuclear iron(II) complexes of a sterically hindered 2,6-dimesitybenzoate ligand Mes2ArCO2 are described. Results suggest that a subtle conformational change in a protein could result in the necessary lengthening or shortening of a metal-nitrogen bond, thus altering the preferred carboxylate binding mode during catalysis.

The first Rapid-freeze-quench magnetic circular dichroism (RFQ-MCD) data on transient, high-valent iron-oxo intermediate X. Fe(super IV) ligand field (LF) transitions are presented. The analysis favors the mono-mu-oxo model for X, where the reductive cleavage of the O-O bond generates an oxo bridge and H2O.

Two mechanistic characteristics are observed in the mono and binuclear non-heme iron dependent monooxygenase paths. They include the heterolytic O-O bonding of iron coordinated peroxide ligand and the subsequent tightly coupled transfer of one oxygen atom to substrate for each equivalent of dioxygen/peroxide consumed.

Research is presented concerning the use of photodissociation to investigate the structure and dynamics of ferrous hemoprotein and ligand binding. The photodissociation which occurs in a low-spin ferric complex is discussed.