Rotamer stability in cis-[Pt(diA)G2] complexes (diA = diamine derivative and G = guanine derivative) mediated by carrier-ligand amine stereochemistry as revealed by circular dichroism spectroscopy

Extensive investigations of cis-[Pt(diA)G2] complexes (in which G = a guanine ligand; diA = a single diamine ligand) revealed the types of interactions between the two G ligands and between the G and the cis-amine substituents when diA is a diamine ligand with substituents on each nitrogen atom being a small hydrogen atom and a bulky group able to slow the rotation about the Pt-G bond. All these interactions are shown to apply also when diA = dach (1,2-diaminocyclohexane), even though this chiral primary diamine has only small N-H atoms on each side of the coordination plane. However, a slight difference in the stereochemistry of the two protons (one N-H has "quasi axial" and the other "quasi equatorial" character) is sufficient to induce a significant change in the relative stabilities of the [Pt(dach)G2] deltaHT and lambdaHT rotamers (HT = head-to-tail). The new results show that at acidic and neutral pH the induction of asymmetry from the dach ligand to the HT rotamers is governed by the G-to-G dipole-dipole interaction, which is greater for the six-membered ring of each guanine leaning towards the cis-G. Such a "six-in" canting of the two guanine ligands can be hampered by the steric interaction between the H8 of each guanine and the substituent on the cis-amine that is on the same side of the coordination plane. Such a repulsion is greater for a "quasi equatorial" N-H than for a "quasi axial" N-H. Under basic pH conditions, deprotonation of the guanine N1-H renders the O6 atom a much better hydrogen-bond acceptor; therefore, the stability of the HT rotamers is governed by the hydrogen-bond interaction of guanine O6 and the cis-amine N-H group. Such a guanine O6/N-H cis-amine interaction is stronger for a "quasi axial" than for a "quasi equatorial" N-H group. In the head-to-head (HH) rotamer, in which the electrostatic repulsion between electron-rich O6 atoms, both on the same side of the platinum coordination plane, tends to place the six-membered rings of each guanine further from the cis-guanine and closer to the cis-amine, we can expect better N-H...O6 hydrogen bonding for the "quasi equatorial" N-H groups.     

High-performance liquid chromatographic assay of N(G)-monomethyl-L-arginine, N(G),N(G)-dimethyl-L-arginine, and N(G),N(G)'-dimethyl-L-arginine using 4-fluoro-7-nitro-2, 1,3-benzoxadiazole as a fluorescent reagent

N(G)-Monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (ADMA), and N(G),N(G)'-dimethyl-L-arginine (SDMA) are emerging cardiovascular risk factors. A high-performance liquid chromatographic method with fluorescence detection for the simultaneous determination of L-NMMA, ADMA and SDMA is described. The assay employed 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as a fluorescent derivatization reagent. After solid phase extraction with cation-exchange column, the methylated arginines were converted to fluorescent derivatives with NBD-F, and the derivatives were separated within 32 min on a reversed-phase column. Nomega-Propyl-L-arginine was Used as an internal standard. Extrapolated detection limits were 12 nM (12 fmol per injection) for L-NMMA and 20 nM (20 fmol per injection) for ADMA and SDMA, respectively, with a signal-to-noise ratio of 3. The calibration curves for L-NMMA, ADMA and SDMA were linear within the range of 50-5000 fmol. The method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in 200 microl of rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.03, 0.80 +/- 0.25 and 0.40 +/- 0.21 microM, respectively (n = 5).     

Electronic effects of (N2S2)M(NO) complexes (M = Fe, Co) as metallodithiolate ligands

Heterobimetallic complexes comprised of W(CO)4 adducts of (N2S2)M(NO) have been isolated and characterized by nu(CO) and nu(NO)IR spectroscopies and X-ray diffraction. The molecular structures of (N2S2)M(NO) compounds (bme-dach)Co(NO), [(bme-dach)Co(NO)]W(CO)4, and [(bme-dach)Fe(NO)]W(CO)4 [bme-dach = N, N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane)] find the square-pyramidal (bme-dach)M(NO) unit to serve as a bidentate ligand via the cis-dithiolato sulfurs, with a hinge angle of the butterfly bimetallic structures of ca. 130 degrees . The W(CO)4 moiety is used as a probe of the electron-donor ability of the nitrosyl complexes through CO stretching frequencies that display a minor increase as compared to analogous [(N2S2)Ni]W(CO)4 complexes. These findings are consistent with the electron-withdrawing influence of the {Co(NO)}(8) and {Fe(NO)}(7) units on the bridging thiolate sulfurs relative to Ni(2+). Also sensitive to derivatization by W(CO)4 is the NO stretch, which blue shifts by ca. 30 and 50 cm(-1) for the Co and Fe complexes, respectively. Cyclic voltammetry studies find similar reduction potentials (-1.08 V vs NHE in N, N-dimethylformamide solvent) of the (bme-dach)Co(NO) and (bme-dach)Fe(NO) free metalloligands, which are positively shifted by ca. 0.61 and 0.48 V, respectively, upon complexation to W(CO)4.     

Cisplatin--DNA cross-link models with an unusual type of chirality-neutral chelate amine carrier ligand, N,N dimethylpiperazine (Me2ppz): Me2ppzPt(guanosine monophosphate)2 adducts that exhibit novel properties

Most simple cis-PtA2G2 complexes that model the G-G cross-link DNA lesions caused by the clinically used anticancer drug cis-PtCl2(NH3)2 undergo large fluxional motions at a rapid rate (A2 = two amines or a diamine; G = guanine derivative). The carrier amine ligands in active compounds have NH groups, but the fundamental role of the NH groups has been obscured by the dynamic motion. To assess carrier ligand effects, we examine retro models, cis-PtA2G2 complexes, in which dynamic motion has been reduced by the incorporation of steric bulk into the carrier ligands. In this study we introduce a new approach employing the chirality-neutral chelate (CNC) ligand, Me2ppz (N,N'-dimethylpiperazine). Because they lie in the Pt coordination plane, the methyl groups of Me2ppz do not clash with the 06 of the base of G ligands in the ground state, but such clashes sterically hinder dynamic motion. NMR spectroscopy provided conclusive evidence that Me2ppzPt(GMP)2 complexes (GMP = 5'- and 3'-GMP) exist as a slowly interconverting mixture of two dominant head-to-tail (HT) conformers and a head-to-head (HH) conformer. Since the absence of carrier ligand chirality precluded using NMR methods to determine the absolute conformation of the two HT conformers, we used our recently developed CD pH jump method to establish chirality. The most abundant HT Me2ppzPt(5'-GMP)2 form had A chirality. Previously this chirality was shown to be favored by phosphate-cis G NIH hydrogen-bonding interligand interactions; such interactions also favor the HT conformers over the HH conformer. For typical carrier ligands, G O6 and phosphate interactions with the carrier ligand NH groups also favor the HT forms. These latter interactions are absent in Me2ppzPt(GMP)2 complexes, but the HT forms are still dominant. Nevertheless, we do find the first evidence for an HH form of a simple cis-PtA2G2 model with A2 lacking any NH groups. In previous studies, the absence of the HH conformer in cis-PtA2G2 complexes lacking carrier NH groups may be due to the presence of out-of-plane carrier ligand bulk. Such bulk forces both G O6-G O6 and G O6-carrier ligand clashes, thereby disfavoring the HH form. The major DNA cross-link adduct has the HH conformation. Thus, for anticancer activity, the small bulk of the NH group may be more important than the H-bonding interaction.     

Synthesis and structural characterisation of primary amine adducts of gallane, RH2N.GaH3, and of their decomposition products, [RHNGaH2]n(R = Me, n= 3; R =tBu, n= 2)

Primary amine-gallane adducts, RH(2)N.GaH(3)[R = Me (1) and (t)Bu (2)], have been isolated for the first time from the reaction of [RNH(3)]Cl with LiGaH(4) in Et(2)O solution at ca. 273 K and characterised by their vibrational and (1)H NMR spectra. The structures of single crystals, grown at low temperatures and determined by X-ray diffraction, reveal pseudo-polymeric arrays of RH(2)N.GaH(3) molecules with Ga-N distances of 2.0424(18) and 2.058(5)A for 1 and 2, respectively. The adducts decompose at or near ambient temperatures with the elimination of H(2) and formation of the corresponding monoalkylamido derivative [RHNGaH(2)](n). The crystal structures of these at 150 K consist of either [MeHNGaH(2)](3) molecules with a "skew-boat" conformation for the cyclic Ga(3)N(3) skeleton (3) or [(t)BuHNGaH(2)](2) molecules with a four-membered Ga(2)N(2) core (4), with Ga-N distances averaging 1.986(8) and 1.991(3)A for 3 and 4, respectively. The crystalline solids 1, 3 and 4 feature intermolecular N-H...H-Ga interactions with H...H distances estimated to fall in the range 2.1-2.3 A. The significance of these is discussed.     

Factors influencing the reductive cleavage of C-x multiple bonds in their reactions with meal-meal multiple bonds (X = C, N, O, S)

Though metal-metal multiple bonds of the transition elements are redox active, their reactivity towards C-X multiple bonds (X = C, N, O, S) vary greatly depending principally on: 1. The coordination geometry of the metal. 2. The oxidation state of the metal and the electronic configuration of the M-M bond. 3. The nature of the attendant ligands. Specific examples of C-X multiple bond activation at dimolybdenum and ditungsten centers are presented that illustrate the importance of these factors. Evidence is presented to support the view that reductive cleavage of a C-X multiple bond can be considered to be equivalent to an intramolecular redox reaction within a [M2CX] "cluster complex," for which the frontier orbital energies of the C-X and M-M multiple bonds are of paramount importance. Some applications of these C-X reductive cleavage reactions toward organic synthesis are described.     

First paramagnetic 4d transition-metal complex with a redox-active tetrathiafulvalene derivative, [Ru(salen)(PPh3)(TTF-CH=CH-Py)]BF4 [salen(2-) = N,N'-ethan-1,2-diylbis(salicylidenamine), PPh3 = triphenylphosphine, TTF-CH=CH-Py = 4-(2-tetrathiafulvalenylethenyl)pyridine

The first paramagnetic 4d transition-metal complex with a redox-active tetrathiafulvalene ligand has been synthesized. The preparation, X-ray structure, electrochemistry, and electron paramagnetic resonance measurements of [Ru(salen)(PPh3)(TTF-CH=CH-Py)](BF4) [1(BF4)] are reported. The crystal structure reveals that the paramagnetic Ru(III) (s = 1/2) center is in a tetragonally elongated octahedral geometry and the TTF-CH=CH-Py ligand is coordinated to the axial position of the Ru(III) ion through the nitrogen atom of the pyridine group. Thus, 1(BF4) is an attractive precursor to study future pi-4d interactions in dual-property conducting and magnetic materials.     

Synthesis, molecular and electronic structure, and TDDFT and TDDFT-PCM study of the solvatochromic properties of (Me2Pipdt)Mo(CO)4 complex (Me2Pipdt = N,N'-dimethylpiperazine-2,3-dithione)

The synthesis, spectroscopic, and structural characterization of the (Me2Pipdt)Mo(CO)4 complex (Me2Pipdt = N,N'-piperazine-2,3-dithione) are presented in this paper. The title complex crystallizes in the P2(1)/n space group with a = 25.541(3) A, b = 10.3936(14) A, c = 10.9012(12) A, beta = 92.261(9) degrees , V = 2891.6(6) A(3), and Z = 8. Gas- and solution-phase structural and electronic features of (Me2Pipdt)Mo(CO)4 and Me2Pipdt have been investigated using density functional theory. The molecular structure underscores the flexibility of the NC(S)C(S)N fragment in both the free ligand and the metal complex. On the basis of structural, spectroscopic, and theoretical results, the bidentate ligand in (Me2Pipdt)Mo(CO)4 is considered to be in the dithione, not dithiolate, form. Time-dependent density functional theory has been used for the investigation of the excited states and solvatochromic properties of (Me2Pipdt)Mo(CO)4. The calculated vertical excitation energies in solution are consistent with the experimental data, showing that the metal-to-ligand charge-transfer transitions, in both the visible and UV regions, dominate over the ligand-based pi-pi transitions.     

A New Diiminopyridyl Cobalt Complex [CoCl2L] (L = 2,6-Bis(N,N'-bis(2,6-diisopropyl-4-(2,3-dimethyoxylbenzoylamide)phenylimino))pyridine)

The reaction of CoCl2·6H2O with 2,6-bis(N,N'-bis(2,6-diisopropyl-4-(2,3-dimethy-oxyl-benzoylamide)phenylimino))pyridine (L) afforded the complex [CoCl2L], which was fully characterized by elemental analysis, UV-vis, IR spectroscopy, fluorescence, and X-ray diffraction analysis. The compound is oftriclinie system, space group P1- with a = 13.058(3), b = 13.798(3), c =16.695(3) (A), α = 98.191(3),β = 102.792(3), γ = 101.820(3)°,V= 2815.0(9) (A)3, Z= 2, F(000) = 1122,μ = 0.45 mm-1, R = 0.061 and wR= 0.1349 for 9842 observed reflections (1 2σ(Ⅰ)). The Co(Ⅱ center adopts a distorted square-pyramidal coordination geometry. The extended structure shows a one-dimensional zigzag double chain linked by hydrogen bonds and π-π stacking interactions.     

Spectroscopic detection and theoretical confirmation of the role of Cr2(CO)5(C5R5)2 and .Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by .Cr(CO)3(C5R5) (R = H, CH3)

Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes .Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr[triple bond]Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)]2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, .Cr(CO)2(ketene)(C5R5) and Cr2(CO)5(C5R5)2 have been detected spectroscopically. The complex .Cr(13CO)2(O=13C=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)2(C5H5)]2 and CO addition to 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show DeltaH approximately equal 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr[triple bond]Cr bond strength in [Cr(CO)2(C5H5)]2 as 72 kcal mol(-1). The complex [Cr(CO)2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50 degrees C implying that 3Cr2(CO)5(C5H5)2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.     

Small molecule fixation by a dithiadiazolyl radical: X-ray crystal structures of (CF3C6H3FCNSSN)2 and (CF3C6H3FCNSSN)2 x G (G = N2, Ar, CO2 and SO2)

The title dithiadiazolyl radical, F3CC6H3FCNSSN (1) forms inclusion structures with small molecules (such as N2, CO2, Ar and SO2) when sublimed under partial atmospheres of the guest.     

Probing the electronic structures of [Cu2(mu-XR2)]n+ diamond cores as a function of the bridging X atom (X = N or P) and charge (n = 0, 1, 2)

A series of dicopper diamond core complexes that can be isolated in three different oxidation states ([Cu2(mu-XR2)]n+, where n = 0, 1, 2 and X = N or P) is described. Of particular interest is the relative degree of oxidation of the respective copper centers and the bridging XR2 units, upon successive oxidations. These dicopper complexes feature terminal phosphine and either bridging amido or phosphido donors, and as such their metal-ligand bonds are highly covalent. Cu K-edge, Cu L-edge, and P K-edge spectroscopies, in combination with solid-state X-ray structures and DFT calculations, provides a complementary electronic structure picture for the entire set of complexes that tracks the involvement of a majority of ligand-based redox chemistry. The electronic structure picture that emerges for these inorganic dicopper diamond cores shares similarities with the Cu2(mu-SR)2 CuA sites of cytochrome c oxidases and nitrous oxide reductases.     

Two new one-dimensional compounds with end-to-end dicyanamide as a bridging ligand: syntheses and structural characterization of trans-[Mn(4-bzpy)2(N(CN)2)2]n and cis-[Mn(Bpy)(N(CN)2)2]n, (4-bzpy = 4-benzoylpyridine; bpy = 2,2'-bipyridyl)

Two new one-dimensional compounds, trans-[Mn(4-bzpy)2(N(CN)2)2]n (1) and cis-[Mn(bpy)(N(CN)2)2]n (2), have been synthesized and studied from a magnetic point of view (4-bzpy = 4-benzoylpyridine; bpy = 2,2'-bipyridyl). The crystal structures of 1 and 2 have been solved. Compound 1 crystallizes in the monoclinic system, P2(1)/n group, a = 6.374(2) A, b = 7.584(2) A, c = 26.766(5) A, beta = 91.87 degrees, and Z = 2, whereas compound 2 crystallizes in the monoclinic system, C2/c group, a = 6.707(2) A, b = 17.188(5) A, c = 13.096(5) A, beta = 90.54 degrees, and Z = 4. The two compounds consist of chains with double mu 1,5-dicyanamide bridges between neighboring manganese(II) atoms. The weak antiferromagnetic coupling found for the two compounds (J = -0.3 cm-1 for 1 and -0.4 cm-1 for 2) has been studied by MO analysis, and the superexchange pathway through the mu 1,5-(NCNCN-) bridge has been compared with the shorter mu 1,3-(NNN-).     

Synthesis of alkaline earth diazenides M(AE)N2 (M(AE) = Ca, Sr, Ba) by controlled thermal decomposition of azides under high pressure

The alkaline earth diazenides M(AE)N(2) with M(AE) = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at high-pressure/high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) ?, c = 5.9844(9) ?, Z = 2, wR(p) = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN(2) and BaN(2). Accordingly, CaN(2) is isotypic with SrN(2) (space group I4/mmm (no. 139), a = 3.8054(2) ?, c = 6.8961(4) ?, Z = 2, wR(p) = 0.057) and the corresponding alkaline earth acetylenides (M(AE)C(2)) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN(2) adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) ?, b = 4.3776(3) ?, c = 7.2188(4) ?, β = 104.9679(33)°, Z = 4 and wR(p) = 0.049). The N-N bond lengths of 1.202(4) ? in CaN(2) (SrN(2) 1.239(4) ?, BaN(2) 1.23(2) ?) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N(2)](2-). Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides M(AE(2))N (M(AE) = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm(-1) assigned to the N-N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides.     

A kinetically controlled trans bifunctionalized organoimido derivative of the Lindqvist-type hexamolybdate: synthesis, spectroscopic characterization, and crystal structure of (n-Bu4N)2{trans-[Mo6O17(NAr)2]} (Ar = 2,6-dimethylphenyl)

A kinetically controlled trans bifunctionalized organoimido derivative of hexamolybdate, (n-Bu(4)N)(2){trans-[Mo(6)O(17)(NAr)(2)]} (Ar = 2,6-dimethylphenyl) 1, in which the two 2,6-dimethylphenylimido groups are bonded to hexamolybdate at the trans positions, has been successfully synthesized in ca. 60% yield under mild reaction conditions. Its trans structure has been confirmed by a single-crystal X-ray diffraction study. In the crystals, cluster anions of 1 self-assemble into a 3D netlike structure via two different kinds of C-H...O hydrogen bondings, in which 1D supramolecular rectangular channels containing tetrabutylammonium cations form along the a axis. Compound 1 has also been characterized by (1)H NMR, IR, and UV-vis spectroscopic studies. UV-vis-near-IR reflectance spectroscopy measurements reveal the compound's nature of semiconductivity with an optical energy gap of 2.55 eV.     

One- or two-dimensional 2,3-naphtho crown ether complexes [Na(N15C5)]2[M(SCN)4] and [K(N18C6)]2[M(SCN)4] (M = Pd, Pt) constructed by pi-pi stacking interactions

Four novel 2,3-naphtho-15-crown-5 (N15C5) and 2,3-naphtho-18-crown-6 (N18C6) complexes [Na(N15C5)]2[Pd(SCN)4] (1), [Na(N15C5)]2[Pt(SCN)4] (2), [K(N18C6)]2[Pd(SCN)4] (3) and [K(N18C6)]2[Pt(SCN)4] (4) were synthesized and characterized by elemental analysis, FT-IR spectra and single-crystal X-ray diffraction. The structure analyses reveal that both 1 and 2 are assembled into zigzag chains by the strong intermolecular pi-pi stacking interactions between adjacent 2,3-naphthylene groups of N15C5. The molecules of complexes 3 and 4 are linked into 1D chains by the bridging K-O(ether) interactions between the adjacent [K(N18C6)]+ units and the resulting chains are constructed into a novel 2D network by inter-chain pi-pi stacking interactions between the neighboring 2,3-naphthylene moieties of N18C6. According to the supramolecular self-assemblies of complexes 1-4, two types of stacking model of naphthylene groups are given and discussed.     

Tl(I), Fe(II), and Co(II) complexes supported by a monoanionic N,N,N'-heteroscorpionate ligand bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr (Ar = 2,6-iPr2C6H3)

The lithium salt (L)Li(THF) (L- = bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr, Ar = 2,6-iPr2C6H3) can be readily prepared from lithium bis(3,5-di-tertbutylpyrazol-1-yl)methide and the N-methyleneaniline H2C=NAr. This N,N,N'-heteroscorpionate lithium reagent can be transmetalated with Tl(OTf), FeCl2(THF)(1.5), and CoCl2 to yield the (L)Tl, (L)FeCl, and (L)CoCl complexes, respectively. Single crystal structural data for compounds (L)Li(THF), (L)Tl, (L)FeCl, and (L)CoCl reveal in each case the hapticity of the sterically demanding, monoanionic L- ligand to be kappa3-N3.     

Characterization of three members of the electron-transfer series [Fe(pda)2]n (n=2-, 1-, 0) by spectroscopy and density functional theoretical calculations [pda=redox non-innocent derivatives of N,N'-bis(pentafluorophenyl)-o-phenylenediamide(2-, 1.-, 0)

The four-coordinate iron complexes, [Fe(III)(pda(2-))(pda(.-))] (1) and [AsPh(4)](2)[Fe(II)(pda(2-))(2)] (2) were synthesized and fully characterized; pda(2-) is the closed-shell ligand N,N'-bis(pentafluorophenyl)-o-phenylenediamido(2-), and pda(.-) represents its one-electron-oxidized pi-radical anion. Single-crystal X-ray diffraction studies of 1 and 2 performed at 100(2) K reveal a distorted tetrahedral coordination environment at the iron centers, as a result of the intramolecular pi-pi interactions between C(6)F(5) rings. The electronic structures of 1 and 2 were unambiguously determined by a combination of (57)Fe M?ssbauer and electronic spectroscopy, magnetic susceptibility measurements, X-ray crystallography, and DFT calculations. Compound 1 contains an intermediate-spin Fe(III) ion (S(Fe)=3/2) strongly antiferromagnetically coupled to a pi-ligand radical (S(R)=1/2) yielding an S(t)=1 ground state. Complex 2 possesses a high-spin Fe(II) center (S(Fe)=2) with two closed-shell dianionic ligands. Complexes 1 and 2 are members of the redox series [Fe(pda)(2)](n) with n=0 for 1 and n=2- for 2. The anion n=1- has been reported previously in the coordination salt [Fe(dad)(3)][Fe(pda)(2)] (3; dad=N,N'-bis(phenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene). A complicated temperature-dependent electronic structure has been observed for this salt. Here, DFT calculations performed on 3 confirm the previous assignments of spin- and oxidation-states. Thus, [Fe(pda)(2)](n) (n=0, 1-, 2-) constitutes an electron-transfer series, which has also been established by cyclic voltammetry; the mono- and dications (n=1+ and 2+) are also accessible in solution, but have not been further investigated. The (57)Fe M?ssbauer spectra of [Fe(pda)(2)](n) species in 1 and 3 show extremely large quadrupole splitting constants due to addition of the valence and covalence contributions that have been confirmed by DFT calculations.