Β-diketonato Complexes Research Articles

Synthesis and Characterization of Fe(II) β-Diketonato Complexes with Relevance to Acetylacetone Dioxygenase: Insights into the Electronic Properties of the 3-Histidine Facial Triad

A series of high-spin iron(II) β-diketonato complexes have been prepared and characterized with the intent of modeling the substrate-bound form of the enzyme acetylacetone dioxygenase (Dke1). The Dke1 active site features an Fe(II) center coordinated by three histidine residues in a facial geometry--a departure from the standard 2-histidine-1-carboxylate (2H1C) facial triad dominant among nonheme monoiron enzymes. The deprotonated β-diketone substrate binds to the Fe center in a bidentate fashion. To better understand the implications of subtle changes in coordination environment for the electronic structures of nonheme Fe active sites, synthetic models were prepared with three different supporting ligands (L(N3)): the anionic (Me2)Tp and (Ph2)Tp ligands ((R2)Tp = hydrotris(pyrazol-1-yl)borate substituted with R-groups at the 3- and 5-pyrazole positions) and the neutral (Ph)TIP ligand ((Ph)TIP = tris(2-phenylimidazol-4-yl)phosphine). The resulting [(L(N3))Fe(acac(X))](0/+) complexes (acac(X) = substituted β-diketonates) were analyzed with a combination of experimental and computational methods, namely, X-ray crystallography, cyclic voltammetry, spectroscopic techniques (UV-vis absorption and (1)H NMR), and density functional theory (DFT). X-ray diffraction results for complexes with the (Me2)Tp ligand revealed six-coordinate Fe(II) centers with a bound MeCN molecule, while structures of the (Ph2)Tp and (Ph)TIP complexes generally exhibited five-coordinate geometries. Each [(L(N3))Fe(acac(X))](0/+) complex displays two broad absorption features in the visible region that arise from Fe(II)→acac(X) charge transfer and acac(X)-based transitions, consistent with UV-vis data reported for Dke1. These absorption bands, along with the Fe redox potentials, are highly sensitive to the identity of L(N3) and substitution of the β-diketonates. By interpreting the experimental results in conjunction with DFT calculations, detailed electronic-structure descriptions of the complexes have been obtained, with implications for our understanding of the Dke1 active site.

Structure Formation in Metal Complex/Polymer Hybrid Nanomaterials Prepared by Miniemulsion

Polymer/complex hybrid nanostructures were prepared using a variety of hydrophobic metal β-diketonato complexes. The mechanism of structure formation was investigated by electron paramagnetic resonance (EPR) spectroscopy and small-angle X-ray scattering (SAXS) in the liquid phase. Structure formation is attributed to an interaction between free coordination sites of metal β-diketonato complexes and coordinating anionic surfactants. Lamellar structures are already present in the miniemulsion. By subsequent polymerization the lamellae can be embedded in a great variety of different polymeric matrices. The morphology of the lamellar structures, as elucidated by transmission electron microscopy (TEM), can be controlled by the choice of anionic surfactant. Using sodium alkylsulfates and sodium dodecylphosphate, "nano-onions" are formed, while sodium carboxylates lead to "kebab-like" structures. The composition of the hybrid nanostructures can be described as bilayer lamellae, embedded in a polymeric matrix. The metal complexes are separated by surfactant molecules which are arranged tail-to-tail; by increasing the carbon chain length of the surfactant the layer distance of the structured nanomaterial can be adjusted between 2 and 5 nm.

Iodomethane oxidative addition to β-diketonatobis(triphenylphosphite)rhodium(I) complexes: A synthetic, kinetic and computational study

New rhodium(I)- and rhodium(III)-β-diketonato complexes of the type [Rh(FcCOCHCOR)(P(OPh) 3) 2] and [Rh(FcCOCHCOR)(P(OPh) 3) 2(CH 3)(I)], with Fc = ferrocenyl and R = Fc, CH 3 and CF 3, have been synthesized. The reactivity of complexes of the type [Rh(β-diketonato)(P(OPh) 3) 2] increase in the order: β-diketonato = (CF 3COCHCOCF 3) − < (CF 3COCHCOPh) − < (CF 3COCHCOCH 3) − < (PhCOCHCOPh) − < (CF 3COCHCOFc) − < (CH 3COCHCOPh) − < (CH 3COCHCOCH 3) − < (CH 3COCHCOFc) − < (FcCOCHCOFc) −, giving linear relationships between the kinetic parameter ln k 2 and the parameters that are related to the electron density on the rhodium centre; the sum of the group electronegativities of the β-diketonato side groups ( χ R + χ R′) and the p K a of the uncoordinated β-diketone RCOCH 2COR′. The large negative values of the volume and entropy of activation indicated a mechanism which occurs via a polar transition state. A density functional theory study, at the PW91/TZP level of theory, indicates that oxidative addition of iodo methane to [Rh(FcCOCHCOCF 3)(P(OCH 3) 3) 2] occurs via a two-step mechanism. This mechanism involves a nucleophilic attack by the metal on the methyl carbon to displace iodide to form a metal-carbon bond and the coordination of iodide to the five-coordinated intermediate to give a six-coordinated trans alkyl product.

ChemInform Abstract: Catalysis Using β‐Diketonato Metal Complexes

AbstractReview: 297 refs.

Methyl iodide oxidative addition to [Rh(acac)(CO)(PPh3)]: an experimental and theoretical study of the stereochemistry of the products and the reaction mechanism

Density functional theory was used to investigate the oxidative addition and subsequent carbonyl insertion and deinsertion steps of the reaction of methyl iodide to a rhodium(I) acetylacetonato complex of the formula [Rh(acac)(CO)(PPh(3))] (Hacac = acetylacetone). This process has been studied experimentally for many rhodium β-diketonato complexes, but, to the best of our knowledge, this is the first systematic computational study of the complete reaction sequence. Experimental (1)H techniques complement the theoretical results on the stereochemistry of the reaction intermediates and products. (1)H NMR also revealed the existence of a second rhodium(III)-acyl product, which has not been previously observed in this reaction. The calculated Gibbs free energy of activation of the oxidative addition reaction is 71 kJ mol(-1), which is in agreement with the experimental value of 82(1) kJ mol(-1). The DFT-calculated oxidative addition corresponds to an associative S(N)2 nucleophilic attack by the rhodium metal centre on the methyl iodide, which is in agreement with calculated and experimental (in brackets) activation parameters of the reaction, 27 (38.8) kJ mol(-1) for ΔH((≠)) and -147 (-146) J K(-1) mol(-1) for ΔS((≠)).

Substitution and Isomerization of Asymmetric β-Diketonato Rhodium(I) Complexes: A Crystallographic and Computational Study

Ligand substitution of PPh3 for CO in the asymmetric square-planar β-diketonato complex [Rh(PhCOCHCOCH2CH3)(CO)2] leads to formation of the monosubstituted [Rh(PhCOCHCOCH2CH3)(CO)(PPh3)] product. Two geometrical product isomers are possible, which unexpectedly crystallize in the same crystal lattice. DFT calculations of the substitution reaction support a two-step mechanism, involving temporary dissociation of a β-diketonato ligand and formation of a square-planar intermediate. Analysis of the mechanisms involved in product isomerization suggests several noncatalyzed and solvent-assisted interconversion pathways.

Synthesis, Substitution Kinetics, and Electrochemistry of the First Tetrathiafulvalene-Containing β-Diketonato Complexes of Rhodium(I)

The synthesis of the first rhodium(I) cyclooctadiene complexes containing tetrathiafulvalene (TTF) groups substituted on a beta-diketonato ligand in either the methine position (3 position), [Rh(cod)(H(3)CCOC{S-TTF-(MeS)(3)}COCH(3))] (3), or terminal position (1 position), [Rh(cod){(Me(3)-TTF)COCHCOCH(3)}] (4), is reported. The effect of the beta-diketonato substitution position on the kinetics of substitution of the TTF-containing beta-diketonato ligand with 1,10-phenanthroline from 3 and 4 to give [Rh(cod)(phen)](+), as well as on the electrochemical properties of 3 and 4, was investigated. Second-order substitution rate constants, k(2), in methanol were found to be almost independent of the substitution position, with 4 (k(2) = 2.09 x 10(3) dm(3) mol(-1) s(-1)) reacting only about twice as fast as 3. An appreciable solvent pathway in the substitution mechanism was only observed for 4 with k(s) = 42 s(-1). A complete mechanism for both substitution reactions is proposed. The electrochemistry of 3 and 4 in CH(2)Cl(2)/0.10 mol dm(-3) [N((n)Bu)(4)][B(C(6)F(5))(4)] showed three redox processes. Two of these were electrochemically reversible and are associated with the redox-active TTF group. For 3, TTF-based formal reduction potentials, E degrees', were observed at 0.082 and 0.659 V vs Fc/Fc(+), respectively; 4 exhibited them at -0.172 and 0.703 V vs Fc/Fc(+) at a scan rate of 100 mV s(-1). A Rh(II)/Rh(I) redox couple was observed at E degrees' = 0.89 V for 3, after both TTF oxidations were completed, and at 0.51 V for 4; this is between the two TTF redox processes. The more difficult oxidation of the Rh(I) center of 3 indicates more effective electron-withdrawing from the Rh(I) center to the first-oxidized TTF(+) group at the methine position of the beta-diketonato ligand of 3(+) than to the terminal-substituted TTF(+) group in 4(+).

Prediction of the retention of β-diketonato complexes in TLC systems on silica gel by quantitative structure-retention relationships

Quantitative structure-retention relationships for a series of 30 mixed β-diketonato complexes of cobalt(III), chromium(III) and ruthenium(III) were derived by multiple linear regression analyses using molecular descriptors obtained by quantum chemical calculations. The retention parameters were obtained by thin layer chromatography on silica gel using mono and two-component solvent systems. The molecular descriptors included in the multiple linear regression analysis were molecular weight, molecular volume, surface area, hydrophilic-lipophilic balance, percent hydrophilic surface area, dipole moment, polarizability, refractivity, energy of the highest occupied molecular orbital and energy of the lowest unoccupied molecular orbital. High agreement between the experimental and predicted retention parameters was obtained when polarizability and the hydrophilic-lipophilic balance were used as the molecular descriptors. Comparison of the models with those established on polyacrylonitrile showed that the structure of the sorbent is responsible for the chromatographic behaviour of the same compounds. The presented models can be used for the prediction of the retention of new solutes in screening chromatographic systems.

Prediction of the retention of β-diketonato complexes in TLC systems on silica gel by quantitative structure-retention relationships

Quantitative structure-retention relationships for a series of 30 mixed ?-diketonato complexes of cobalt(III), chromium(III) and ruthenium(III) were derived by multiple linear regression analyses using molecular descriptors obtained by quantum chemical calculations. The retention parameters were obtained by thin layer chromatography on silica gel using mono and two-component solvent systems. The molecular descriptors included in the multiple linear regression analysis were molecular weight, molecular volume, surface area, hydrophilic-lipophilic balance, percent hydrophilic surface area, dipole moment, polarizability, refractivity, energy of the highest occupied molecular orbital and energy of the lowest unoccupied molecular orbital. High agreement between the experimental and predicted retention parameters was obtained when polarizability and the hydrophilic-lipophilic balance were used as the molecular descriptors. Comparison of the models with those established on polyacrylonitrile showed that the structure of the sorbent is responsible for the chromatographic behaviour of the same compounds. The presented models can be used for the prediction of the retention of new solutes in screening chromatographic systems.

Density Functional Theory Study of Substitution at the Square-Planar Acetylacetonato-dicarbonyl-rhodium(I) Complex

Density functional theory results show that the ligand substitution of PPh3 for CO in the square-planar β-diketonato complex [Rh(acac)(CO)2] to give the monosubstituted [Rh(acac)(CO)(PPh3)] occurs in two reaction steps. Nucleophilic attack by PPh3 results in temporary dissociation of an acetylacetonato oxygen and formation of a square-planar intermediate, while carbonyl dissociation first occurs in the second step. The unexpected course of the reaction is rationalized by the order of the trans influence of the involved ligands: PPh3 > CO > Oacac.

Photoelectrochemical studies of ionic liquid-containing solar cells sensitized with different polypyridyl–ruthenium complexes

The efficiency of dye-sensitized nanocrystalline solar cells containing ionic liquids, composed of organic sulfonium or imidazolium iodides, or a standard organic-liquid-based electrolyte was studied, while using sensitizers based on different polypyridyl–ruthenium complexes. The dyes N-719, [ cis-Ru(II)(H 2dcbpy) 2(NCS) 2(TBA) 2] and Z-907, [ cis-Ru(II)(H 2dcbpy)(dnbpy)(NCS) 2, Z-907 having a more hydrophobic character, as well as a bidentate β-diketonato complex, [(dcbpy) 2Ru(acetylacetonate)]Cl −, was studied. Solar cells sensitized with the dye N-719 were more efficient than the Z-907 cells, for all electrolytes studied. Adding a co-adsorbent, the amphiphilic hexadecylmalonic acid (HDMA), to Z-907 solar cells containing an organic-liquid electrolyte resulted in increased overall light-to-electricity conversion efficiencies, from 3.7% to 4.0%, (100 W m −2, AM 1.5). Possibly, this is caused by an insulating hydrophobic barrier formed to suppress unwanted electron losses. By applying TiO 2 (P25) nanoparticles, assumed to support electron transfer reactions, to the organic-liquid electrolyte, the conversion efficiency was increased from 4.1% to 4.6% (100 W m −2, AM 1.5). In 1000 W m −2 illumination, the highest overall short-circuit current density, 9.3 mA cm −2, was achieved with the N-719 sensitized cells, with the TiO 2 nanocomposite-containing organic-liquid-based electrolyte. For solar cells sensitized with N-719, Z-907 or the β-diketonato complex, and containing imidazolium or sulfonium iodide ionic liquids, no improvements of the overall conversion efficiency could be noticed at addition of HDMA to the dye or nanoparticles to the electrolyte.

Quantitative Structure-Retention Relationships of Mixed Tris-β-Diketonato Complexes on Polyacrylonitrile Sorbent

Quantitative structure-retention relationships models have been developed for thin-layer chromatographic parameters of 30 mixed β-diketonato complexes. In order to obtain predictive and interpretative models, we chromatographed a series of β-diketonato complexes of cobalt(III), chromium(III) and ruthenium(III) on thin-layer polyacrylonitrile sorbent. Chemical descriptors: volume, surface area, energy of the highest occupied molecular orbital, energy of the lowest unoccupied molecular orbital, dipole moment, refractivity and polarizability were calculated from the structure and related to their chromatographic retention parameters by multiple linear regression analysis. The obtained models were used for interpretation of the retention behaviour of the investigated β-diketonato complexes.

Kinetic study of the oxidative addition reaction between methyl iodide and [Rh(FcCOCHCOCF 3)(CO)(PPh 3)]: Structure of [Rh(FcCOCHCOCF 3)(CO)(PPh 3)(CH 3)(I)

The kinetics of oxidative addition of CH 3I to [Rh(FcCOCHCOCF 3)(CO)(PPh 3)], where Fc = ferrocenyl and (FcCOCHCOCF 3) − = fctfa = ferrocenoylacetonato, have been studied utilizing UV/Vis, IR, 1H and 31P NMR techniques. Three definite sets of reactions involving isomers of at least two distinctly different classes of Rh III-alkyl and two different classes of Rh III-acyl species were observed. Rate constants for this reaction in CHCl 3 at 25 °C, applicable to the reaction sequence below, were determined as k 1 = 0.00611(1) dm 3 mol −1 s −1, k −1 = 0.0005(1) s −1, k 3 = 0.00017(2) s −1 and k 4 = 0.0000044(1) s −1 while k −3 ≪ k 3 and k −4 ≪ k 4 but both ≠0. The indeterminable equilibrium K 2 was fast enough to be maintained during Rh I depletion in the first set of reactions and during the Rh IIIalkyl2 formation in the second set of reactions. From a 1H and 31P NMR study in CDCl 3, K c1 was found to be 0.68, K c2 = 2.57, K c3 = 1.00, K c4 = 4.56 and K c5 = 1.65. [Display omitted] The above reaction sequence represents a completely general reaction sequence for the oxidative addition of iodomethane to any β-diketonato complex of the type [Rh(β-diketonato)(CO)(PPh 3)], although the equilibrium K 2 may not necessarily always be fast. A temperature dependence study in chloroform led to the activation enthalpies, Δ H #, and activation entropies, Δ S #, for both the first and second sets of reactions. A solvent dependence study utilizing five different solvents showed the rate of the first set of reactions are directly proportional to the dielectric constant of the solvent. The molecular formula of all the Rh III-alkyl and Rh III-acyl species are [Rh(FcCOCHCOCF 3)(CH 3)(CO)(PPh 3)(I)] and [Rh(FcCOCHCOCF 3)(COCH 3)(PPh 3)(I)], respectively (Fc = ferrocenyl), but the geometries of the two Rh III isomers and the initial Rh I species all differ due to different coordination spheres. A crystal structure determination ( Z = 4, monoclinic, P2 1/c) of [Rh(FcCOCHCOCF 3)(CO)(PPh 3)(CH 3)(I)], an isomer of the Rh III-alkyl2 species, is also reported.

Synthesis of benzene ruthenium triazolato complexes by [3+2] cycloaddition reactions of activated alkynes and fumaronitrile to benzene ruthenium azido complexes

The dinuclear complex [(η 6-C 6H 6)Ru(μ-N 3)Cl] 2 ( 1) is obtained by the reaction of [(η 6-C 6H 6)RuCl 2] 2 with sodium azide in ethanol. The benzene ruthenium β-diketonato complexes of the general formula [(η 6-C 6H 6)Ru(L∩L)Cl] {L∩L = O, O′-acac ( 2); O, O′-bzac ( 3); O, O′-dbzm ( 4)} are obtained in methanol by the reaction of [(η 6-C 6H 6)RuCl 2] 2 with the corresponding β-diketonates. These complexes further react with sodium azide in ethanol to yield complexes of the type [(η 6-C 6H 6)Ru(L∩L)N 3] [L∩L = O, O′-acac ( 5); L∩L = O, O′-bzac ( 6); L∩L = O, O′-dbzm ( 7)]. The complexes 5– 7 are obtained as well by treating 1 with sodium salts of β-diketonates. These neutral benzene ruthenium azido complexes undergo [3+2] dipolar cycloaddition reaction with activated alkynes (MeO 2CC CCO 2Me, EtO 2CC CCO 2Et) or fumaronitrile (NCHC CHCN) to yield the corresponding benzene ruthenium triazolato complexes; [(η 6-C 6H 6)Ru( O, O′-acac){N 3C 2(CO 2Me) 2}] ( 8), [(η 6-C 6H 6)Ru( O, O′-acac){N 3C 2(CO 2Et) 2}] ( 9), [(η 6-C 6H 6)Ru( O, O′-acac){N 3C 2HCN}] ( 10), [(η 6-C 6H 6)Ru( O, O′-bzac){N 3C 2HCN}] ( 11) and [(η 6-C 6H 6)Ru( O, O′-dbzm){N 3C 2HCN}] ( 12). These complexes are fully characterized on the basis of microanalyses, FT-IR and FT-NMR spectroscopy. The molecular structure of [(η 6-C 6H 6)Ru( O, O′- acac){N 3C 2(CO 2C 2H 5) 2}] ( 9) is confirmed by single crystal X-ray diffraction study.

Chlorido-, aqua-, 9-ethylguanine- and 9-ethyladenine-adducts of cytotoxic ruthenium arene complexes containing O,O-chelating ligands

The synthesis and X-ray structures of a half-sandwich RuIIp-cymene β-diketonato complex as chlorido-, aqua-, 9-ethylguanine- and 9-ethyladenine-adducts are reported. Structural features which contribute to stabilisation of adducts through non-covalent, weak interactions are discussed. The X-ray crystal structure of the cytotoxic complex [(η6-p-cym)Ru(Ph2acac)Cl] (1), where Ph2acac=1,3-diphenyl-1,3-propanedionate and p-cym=para-cymene, shows that the phenyl rings of the acac-type ligand form a hydrophobic face, conferring lipophilic character on the complex. The structure of the aqua adduct [(η6-p-cym)Ru(Ph2acac)H2O]CF3SO3·H2O·Et2O (4·H2O·Et2O), a possible activated species, possesses a comparatively short Ru–OH2 bond. In the structure of [(η6-p-cym)Ru(Ph2acac)9EtG-N7]CF3SO3·2tol (5·2tol), where tol=toluene and 9EtG=9-ethylguanine, a comparatively long Ru–N7 bond is observed in addition to weak G CH8⋯O (Ph2acac) H-bonds. The crystal structure of [(η6-p-cym)Ru(acac)9EtA-N7]PF6 (6), where acac=acetylacetonate and 9EtA=9-ethyladenine, a rare example of a ruthenium complex containing monodentate adenine, shows a strong H-bonding interaction between N6H⋯O(acac), which may contribute to the selectivity of {(η6-p-cym)Ru(acac)}+ towards adenine bases.

Photoelectron spectroscopy of metal β-diketonato complexes

The electronic structures of yttrium(III), gadolinium(III) and ytterbium(III) tris-2,2,6,6-tetramethyl-3,5-heptanedione (tmhd) complexes have been investigated by HeI and HeII photoelectron spectroscopy (UPS), UDFT and OVGF calculations. We discuss metal–ligand bonding in the series of metal β-diketonato complexes on the basis of empirical arguments. The photoionization cross-sections and orbital energies of metal atoms must both be taken into account in order to rationalize changes in relative band intensities of the HeI/HeII spectra.

Half-sandwich β-diketonato complexes of zirconium and their application as catalysts to ethylene polymerization

The bis(β-diketonato) Zr complexes CpZr(acac)2Cl (acac = acetylacetonato) (1) and Cp*Zr(acac)2Cl (2) can be synthesized by the reaction of Cp′ZrCl3(Cp′ = Cp or Cp*) with 2 equiv of lithium acetylacetonate. CpZr(acac)2Cl (1) can be quantitatively prepared by treatment of Cp2ZrCl2 with excess acetylacetone. The tris(β-diketonato) Zr complex CpZr(tfac)3 (tfac = trisfluoroacetylacetonato) (3) has been prepared by treatment of CpZrCl3 with sodium trisfluoroacetylacetonate. The replacement of both chlorine atoms and one Cp group from zirconocene dichloride by nonfluorinated diketone, acetylacetone, readily occurs at room temperature in triethylamine medium, offering the tris(β-diketonato) Zr complex CpZr(acac)3 (4). The complexes were characterized by 1H NMR spectroscopic methods. In addition, the molecular structures of complexes 3 and 4 have been determined by X-ray diffraction methods. When activated by excess methylaluminoxane (MAO), these complexes were active for ethylene polymerization, offering polyethylenes with high molecular weights and narrow molecular weight distributions. Complex 4 showed a very high ethylene polymerization activity of up to 7100 kg PE/mol Zr·h at 5 atm. Complexes 1 and 2 were also active for ethylene/1-hexene copolymerization.

Raman spectral shifts of CO 2 as measure of CO 2-philicity of solutes in supercritical carbon dioxide

We have examined the solute–solvent interactions by measuring Raman spectra of CO 2 in neat supercritical CO 2 (sc-CO 2), and sc-CO 2 containing β-diketones (acetylacetone, trifluoroacetylacetone, and hexafluoroacetylacetone) and uranyl β-diketonato complex [UO 2(hfacac) 2DMSO] (hfacac: hexafluoroacetylacetone, DMSO: dimethyl sulfoxide). As a result, it was found that the Raman bands of sc-CO 2 containing β-diketones are shifted to lower wavenumber compared with those of neat sc-CO 2 and that such a red-shift is not observed in sc-CO 2 containing UO 2(hfacac) 2DMSO. From these results, it was suggested that the Lewis acid–Lewis base (LA–LB) interactions between carbonyl oxygens of β-diketones and CO 2 carbon, and the hydrogen bondings between OH of β-diketones and CO 2 oxygen are formed in sc-CO 2 containing β-diketones, and that the shifts in Raman bonds of sc-CO 2 can be used as the measure of CO 2-philicity of solutes in sc-CO 2. On the basis of such results, we measured Raman spectra of CO 2 in sc-CO 2 containing compounds with different donicity. As a result, we found out that the wavenumbers ( ν l ) of Raman bands of CO 2 correlate with the donor number (DN) of compounds, i.e., ν l = 1281.24–0.0109 DN at 25.0 MPa and 40 °C.

Estimation of the hydrophobicity of tris-β-diketonato complexes from reversed-phase thin-layer chromatographic data

Experimental R M values for two series of β-diketonato complexes, M(acac) 3- n (phacphac) n and M(acac) 3- n (phSacphSac) n , where M represents cobalt(III) or chromium(III), have been determined by reversed-phase thin-layer chromatography on RP-18 silica with binary tetrahydrofuran-water, acetonitrile-water, and acetone-water mobile phases. R M 0 values were determined for the different mobile phase mixtures by linear extrapolation to 0% ( v/v ) organic modifier. Lipophilicity C 0 was calculated as the ratio of the intercept and slope values. Chromatographically obtained lipophilicity was correlated with calculated C log P values.

Synthesis and characterization of oxo-bridged, trinuclear, six-coordinate mixed-carboxylato complexes of chromium (III)

Mixed-carboxylato β-diketonato complexes of chromium (III) (R=C13H27, C15H31 or C17H35 and L=CH3OH) [Cr3O(OOCR)3(dike)3L3]+ have been synthesized by enforced substitution reactions of [Cr3O(OOCCH3)7(H2O)] first with straight chain fatty acids (myristic, palmitic or stearic acid) and then with β-diketones (Hβ-dike) like acetylacetone(Hacac) or benzoylacetone(Hbzac) in toluene under reflux. These are new type of oxo-bridged chromium(III) complexes in which one ligand is a fatty acid while the other one is a β-diketone. The complexes were characterized by elemental analyses, spectral (infrared, electronic, FAB mass and powder XRD) studies, molar conductance and magnetic susceptibility measurements. Bridging coordination modes for both carboxylate and β-diketonate anions were indicated by presence of νasym(Cr3O) vibrations in the infrared spectra. Trinuclear nature of the complexes and their structural features have been discussed on the basis of physicochemical studies.