Steric effect on the formation of columnar phases in β-diketonate copper(II) complexes

A systematic study of the mesomorphic properties of three series of copper(II) complexes based on β-diketonate ligands containing branched side chains is reported. These disc-like compounds have four, six and eight flexible alkoxy side chains appended to the central core, in which two or four side chains were substituted by bulkier secondary alkoxy groups: 1-methylbutyloxy R ' = C₅(2°) or 1-methylheptyloxy R ' = C₈(2°). The mesomorphic results indicated that at least eight side chains are required to form stable columnar mesophases; other compounds with four or six side chains are not mesogenic regardless of the combination of the carbon length on the alkoxy or secondary alkoxy groups of the side chains. The compounds 3 with shorter R ' = C₅(2°) side chains were all non-mesogenic regardless of the carbon length of three alkoxy side chains (R = C₈, C₁₀, C₁₂) used. However, when the longer 1-methylheptyloxy side chain R ' = C₈(2°) was substituted, the compounds 3b-3e with various alkoxy groups (R = C₆, C₇, C₈, C₁₀, C₁₂) exhibited columnar phases. The mesophases were characterized and identified as columnar hexagonal phases (Col_h), as expected, by thermal analysis and optical polarized microscopy. The presence of the introduced secondary alkoxy groups apparently appeared to influence the formation of columnar phases. The clearing points were relatively lower than other similar copper(II) compounds not substituted by secondary alkoxy side chains.     

NMR and luminescence spectroscopy study of the formation of mixed europium β-diketonate complexes with trifluoroacetic acid in nonaqueous solutions

The ligand substitution in Eu(AA)₃ · Phen-CDCl₃-TFA systems, where AA is acetylacetone, Phen is 1,10-phenanthroline, and TFA is trifluoroacetic acid was studied at various molar ratios (m) of competing ligands (m = TFA/AA) using NMR (¹H, ¹⁹F) and luminescence spectroscopy. The formation of mixed Eu(AA)₂(TFA) · Phen and Eu(AA)(TFA)₂ · Phen complexes in the resultant solutions was attested. The luminescence spectra were studied. The competitive capacity of TFA was ascertained to be higher than that of AA. Depending on the m value, the substitution of acido ligands was shown to occur successively according equations Eu(AA)₃ · Phen + (TFA) _n = Eu(AA)_{3 − n} (TFA) _n · Phen + (AA) _n (n = 1, 2, 3).     

Volatility and thermal stability of vanadyl β-diketonate complexes

Thermal behavior and thermodynamic characteristics of vanadyl β-diketonates—acetylacetonate VO(acac)₂, dipivaloylmethanate VO(thd)₂, and tris-hexafluoroacetylacetonate VO(hfa)₂ (Hacac, 2,4-pentanedione; Hthd, 2,2,6,6-tetramethyl-3,5-heptanedione; Hhfa, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione)—have been studied by thermal analysis and the Knudsen effusion mass spectrometry study of gas phase composition. The compounds have been shown to undergo congruent sublimation. Saturated vapor over the complexes has been shown to comprise monomeric VOL₂ molecules. Absolute values of partial pressures and sublimation enthalpies of these compounds have been determined.     

Kinetics of the formation of copper β-octaphenylporphyrin complexes in pyridine and acetic acid

The formation kinetics of copper β-octaphenylporphyrin complexes in pyridine and acetic acid is reported and is compared with that of copper β-octamethylporphyrin and dodecaphenylporphyrin complexes. The introduction of electron-donating or electron-withdrawing substituents in the β-positions of the porphyrin macrocycle change the rate of the complexation reaction by at most one order of magnitude. On passing from the planar porphyrin macrocycle to the heavily distorted one, the rate of the reaction in pyridine (electron donor solvent) and acetic acid (electron acceptor solvent) increases and decreases, respectively, by several orders of magnitude.     

Static sterochemistry of the β-diketonate complexes of group II metals

The static sterochemistry in solution of the β-diketonate complexes of Be, Mg, Ca, Ba and Zn was investigated using ¹H-NMR techniques. It was ascertained that the bis-acetylacetonate complexes of Mg, Ca and Ba are polymeric in solution, in contrast to the dipivaloylmethanate complexes of Mg and Zn which are monomeric in solution. The benzoylacetonate chelates of all the metals studied were found also to be monomeric in solution. Chemical shift values and other arguments led us to favor a pseudo-tetrahedral D_2d idealized structure for all the complexes investigated.     

Synthesis and photophysical properties of europium pentafluorinated β-diketonate complexes

Research on Chemical Intermediates - Two pentafluorinated β-diketone ligands, 4,4,5,5,5-pentafluoro-1-(4-methoxyphenyl)pentane-1,3-dione (PFMP) and 4,4,5,5,5-pentafluoro-1-(4-dimethyl...     

Synthesis and crystal structures of dichlorocyclopentadienyl β-diketonate titanium complexes

Complexes of acetylacetonatodichlorocyclopentadienyltitanium(IV) (1) and dichlorocyclopentadienyl(2,2,6,6-tetramethyl-3,5-heptanedionato)titanium(IV) (2) have been prepared and their crystal structures determined by X-ray diffraction methods. Complex 1 crystallizes in space group P2₁/m with a?=?7.1893(10), b?=?11.7680(17), c?=?7.6129(11) Å, β?=?109.901(12)°; complex 2 crystallizes in space group P2₁/n with a?=?10.065(2), b?=?16.322(3), c?=?12.219(2) Å, β?=?110.99(3)°. The molecular structures of 1 and 2 can be described as square-based pyramidal, with the centroid of the C₅H₅ ring occupying the apical site and the bidentate β-diketonate and two chloride ligands occupying the basal positions. The average distances between titanium and oxygen atoms are 1.991(2) and 1.967(3) Å in compounds 1 and 2, respectively.     

Photoelectron spectroscopy and electronic structures of β-diketonate complexes of rare-earth elements

The electronic structures of lanthanide tris(β-diketonate) complexes and their adducts, being of interest as luminophores, were studied by UV photoelectron spectroscopy of vapors and X-ray photoelectron spectroscopy. The spectral regularities identified by the density functional theory revealed the influence of the substitution of the Me groups in the ligands by Bu^t, CF₃, and neutral ligand in the adducts on the electronic structure of the complexing agent from Pr to Lu.     

Mixed ligand complexes of trivalent lanthanide ions with β-diketones and heterocyclic amines and their use as possible shift reagents

Sixty new complexes of the trivalent lanthanides (except Pm and Lu) and Yttrium of the general formulae, Ln(TFAA)₃o-phen, Ln(TFAA)₃dipy·2H₂O, Ln(dpm)₃im, Ln(dpm)₃pz, and Ln(fod)₃o-phen where TFAA = trifluoroacetyl-acetone-H, dpm = 2,2,6,6-tetramethyl 3,5-heptane dione-H, fod = 1,1,1,2,2,3,3-heptafluoro, 7,7-dimethyl 4,6-octane dione-H, o-phen = 1,10-phenathroline, dipy = 2,2′dipyridyl, im = imidazole and pz = pyrazole, have been synthesised and characterised by elemental analyses, melting points, molar conductance, magnetic susceptibility, thermogravimetric analysis, and IR spectral studies. The trivalent lanthanide ions have a coordination number of ten in the series Ln(TFAA)₃dipy·2H₂O. Their avidity to enhance their coordination number is so great that een in the presence of three such bulky ligands as heptafluorooctane dione the Ln(fod)₃ still coordinates with o-phen. Hexacoordinated trivalent lanthanides act as LIS reagents but it has been observed that even the eight coordinated and very bulky Pr(fod)₃o-phen produces dipolar shifts in the proton resonances of organic moities.     

Molybdenum(VI) dioxo and oxo-imido complexes of fluorinated β-ketiminato ligands and their use in OAT reactions

Substitution of a methyl by a trifluoromethyl moiety in well-known β-ketimines afforded the ligands (Ar)NC(Me)CH(2)CO(CF(3)) (HL(H), Ar = C(6)H(5); HL(Me), A r= 2,6-Me(2)C(6)H(3); HL(iPr), Ar = 2,6-(i)Pr(2)C(6)H(3)). Subsequent complexation to the [MoO(2)](2+) core leads to the formation of novel complexes of general formula [MoO(2)(L(R))(2)] (R = H, 1; R = Me, 2; R = iPr, 3). For reasons of comparison the oxo-imido complex [MoO(N(t)Bu)(L(Me))(2)] (4) has also been synthesized. Complexes 1-4 were investigated in oxygen atom transfer (OAT) reactions using the substrate trimethylphosphine. The respective products after OAT, the reduced Mo(IV) complexes [MoO(PMe(3))(L(R))(2)] (R = H, 5; R = Me, 6; R = iPr, 7) and [Mo(N(t)Bu)(PMe(3))(L(Me))(2)] (8), were isolated. All complexes have been characterized by NMR spectroscopy, and 1-4 also by cyclic voltammetry. A positive shift of the Mo(VI)-Mo(V) reduction wave upon fluorination was observed. Furthermore, molecular structures of complexes 2, 4, 5, and 8 have been determined via single crystal X-ray diffraction analysis. Complex 8 represents a rare example of a Mo(IV) phosphino-imido complex. Kinetic measurements by UV-vis spectroscopy of the OAT reactions from complexes 1-4 to PMe(3) showed them to be more efficient than previously reported nonfluorinated ones, with ligand L' = (Ar)NC(Me)CH(2)CO(CH(3)) [MoO(2)(L')(2)] (9) and [MoO(N(t)Bu)(L')(2)] (10), respectively. Thermodynamic activation parameters ΔH(?) and ΔS(?) of the OAT reactions for complexes 2 and 4 have been determined. The activation enthalpy for the reaction employing 2 is significantly smaller (12.3 kJ/mol) compared to the reaction with the nonfluorinated complex 9 (60.8 kJ/mol). The change of the entropic term ΔS(?) is small. The reaction of the oxo-imido complex 4 to 8 revealed a significant electron-donating contribution of the imido substituent.     

Solvent-dependent structures of lanthanide–TCNQ coordination networks and their magnetic properties

Abstract

Lanthanide complexes were prepared with 2,6-diacetylpyridinebis(benzoylhydrazone) (DAPBH₂) and 7,7,8,8-tetracyano-p-quinodimethanide (TCNQ^??). The complexes adopted one of two structure types depending on the reaction solvent. The complexes were categorized as Type I (i.e. bis{[2,6-diacetylpyridinebis(benzoylhydrazone)] methanollanthanide(III)}bis(µ₂- 7,7,8,8-tetracyanoquinodimethanide(1?))bis(7,7,8,8-tetracyanoquinodimethanide(1?))bis(7,7,8,8-tetracyanoquinodimethanide(1?)) methanol disolvate, [Ln₂(DAPBH₂)₂ (µ₂-TCNQ^??)₂(TCNQ^??)₂(MeOH)₂](TCNQ^??)₂·2MeOH (Ln?=?Gd, Tb, or Dy) or Type-II (i.e. [Ln₂(DAPBH₂)₂(µ₂-TCNQ^??)₂(TCNQ^??)₂(EtOH)₂] (TCNQ^??)₂·solvent (Ln?=?Tb and Dy, solvent =4EtOH for the Tb and 2EtOH·2CH₂Cl₂ for the Dy complexes). These two complexes exhibit dramatically different molecular structures and packings. In all complexes, the strong intra- and intermolecular stacking interactions of the TCNQ^?? radicals lead to the formation of 1D TCNQ chains. Magnetic susceptibility measurements for Type I and Type II complexes reveal that they exhibit paramagnetic behavior and that their magnetic properties originate from the lanthanide ions alone, owing to the diamagnetic nature of the TCNQ^?? stacks.     

Structural investigations of copper(II) complexes containing unsymmetrical β-diketonate and monothio-β-diketonate ligands

The crystal structures of the complexes Cu(txhd)₂ and Cu(S-tmhd)₂ (where txhd is the anion of 2,2,6-trimethylheptane-3,5-dione and S-tmhd is the anion of 5-mercapto-2,2,6,6-tetramethyl-4-hepten-3-one) were determined. In the solid state, both complexes are square planar. In each case, only one geometrical isomer (trans or cis) was observed in the crystals; arguments are presented that both isomers are present in bulk samples of Cu(txhd)₂, while from electronic considerations, the monothio-β-diketonate ligands probably have cis geometry in Cu(S-tmhd)₂. Calculations of molecular volumes for structurally similar Cu[t-BuC(O)CHC(O)R]₂ complexes showed that there is a slight decrease in packing efficiency as the steric bulk of R increases. More importantly, strong ring-stacking interactions, such as those found for Cu(acac)₂ are not observed, or are greatly attenuated, in complexes with bulkier peripheral substituents. [Cu(txhd)(μ₃-OEt)]₄, an impurity that co-sublimed with Cu(txhd)₂, was isolated in low yield. The tetrameric structure, which is isomorphous with known [Cu(tmhd)(μ₃-OEt)]₄ (where tmhd is the anion of 2,2,6,6-tetramethylheptane-3,5-dione), has a cubane-like core.     

Phenyl bismuth β-diketonate complexes: Synthesis and structural characterization

The first examples of arylbismuth diketonate complexes are reported. Phenylbismuth(III) bis(hexafluoroacetylacetonate), BiPh(hfac)₂ (1) and its adducts [BiPh(hfac)₂(L)] (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; L = H₂O (1a), Me₂CO (1b), THF (1c), DMA (N,N-dimethylacetamide) (1d), DMSO (1e), PhCN (1f), as well as a mixed hexafluoroacetylacetonate-trifluoroacetate complex, [BiPh(hfac)(O₂CCF₃)]₂ (2), have been synthesized and characterized. Compound 1 is isolated from the reaction of BiPh₃ with 2 equiv. of Hhfac in dry hexanes. Compound 2 can be synthesized using two different routes: one utilizes the reaction between stoichiometric amounts of 1 and CF₃CO₂H, while the second method involves the interaction of the previously described BiPh₂(O₂CCF₃) (3) with Hhfac. Crystallographic analysis of the [BiPh(hfac)₂(L)] adducts reveals a pentagonal pyramidal geometry around the metal center; similarly, the dinuclear [BiPh(hfac)(O₂CCF₃)]₂ complex is composed of two distorted pentagonal pyramids connected into dimers by the bridging carboxylate groups. The effect of replacing the Lewis base in the coordination sphere of Bi(III) on the coordination polyhedron and crystal packing is discussed. The ¹H and ¹⁹F NMR spectra of the title complexes at room temperature indicate single environments for the hfac group and suggest that they are fluxional in solutions on the NMR time scale. Compounds 1 and 2 are promising starting materials in the chemistry of bismuth(III) and as building blocks for the construction of heterometallic species.     

Synthesis of platinum complexes containing (+)-bornyl- and (−)-menthylammonium in the outer coordination sphere and their catalytic activity in hydrosilylation reactions

Optically active (+)-bornyl- and (−)-menthylammonium platinates were synthesized starting from H₂[PtCl₆] · 4H₂O and hydrochlorides of the corresponding amines. Catalytic activity of the complexes in the hydrosilylation reactions of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 1,1,3,3-tetramethyldisiloxane and acetophenone with diphenylsilane was studied. The addition of the siloxanes leads to a predominant formation of β-adduct. Activity of the catalysts, evaluated on the 50% conversion of the substrate, decreases in the following sequence: (−)-(menthylNH₃)₂[PtCl₆] > (Et₃NH)₂[PtCl₆] > (+)-(bornylNH₃)₂[PtCl₄] > (+)-(bornylNH₃)₂[PtCl₆]. Asymmetric induction is observed in the hydrosilylation of aceto-phenone in the presence of (+)-(bornylNH₃)₂[PtCl _n ] (n = 4, 6); (+)-(bornylNH₃)₂[PtCl₆] showed the highest catalytic activity and selectivity. The hydrosilylation of acetophenone gave 1-phenylethoxy(diphenyl)silane, 1-phenylvinyloxy(diphenyl)silane, and 2-phenylethyl-2-diphenylsiloxy(diphenyl)silane as the products. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 341–349, February, 2008.     

Thermodynamic characteristics of the formation of α- and β-cyclodextrin complexes with lumichrome, lumazine, and uracil in aqueous solution

Interactions of α- and β-cyclodextrins with lumichrome and its structural fragments, lumazine and uracil, were studied by means of solubility and 1H NMR spectroscopy. α-Cyclodextrin was found to have a weak complexing ability toward the studied compounds. It was established that β-cyclodextrin forms stable complexes with lumichrome and does not complex with lumazine and uracil. It was shown that only the benzene ring of lumichrome penetrates the β-cyclodextrin cavity, leading to a substantial increase in the solubility of lumichrome in water. We concluded that β-cyclodextrin complexation with lumichrome is highly exothermic due to the van der Waals interactions and hydrogen bonding between polar groups of the reagents.     

Two-step synthesis of β-alkyl chalcones and their use in the synthesis of 3,5-diaryl-5-alkyl-4,5-dihydropyrazoles

We report a simple and efficient two-step synthesis of variously substituted β-alkyl chalcones (7) from the corresponding Weinreb amide and a terminal alkyne, and that these chalcones are useful intermediates for the synthesis of medicinally interesting 3,5-diaryl-5-alkyl-4,5-dihydropyrazoles (6). The current methodology allows for the incorporation of many substitution patterns not available from the few previously reported approaches to compounds in this class.     

X-ray structural study of fluorinated β-diketonate complexes of zirconium(IV)

Three novel complexes of zirconium(IV) are prepared and characterized by single crystal X-ray diffraction: zirconium(IV) pivaloyltrifluoroacetonate Zr(ptac)₄, zirconium(IV) trifluoroacetylacetonate Zr(tfac)₄, and zirconium(IV) hexafluoroacetylacetonate Zr(hfac)₄. Crystal data for C₃₂H₄₀F₁₂ZrO₈: a = 19.9842(6) Å, b = 11.8417(3) Å, c = 16.4831(5) Å; β = 95.2880(10)°, monoclinic, space group Cc, Z = 4, d _calc = 1.491 g/cm³, R = 0.061. Crystal data for C₂₀H₁₆F₁₂ZrO₈: a = 21.5063(15) Å, b = 7.9511(5) Å, c = 16.0510(10) Å; β = 113.736(4)°, monoclinic, space group C2/c, Z = 4, d _calc = 1.860 g/cm³, R = 0.047. Crystal data for C₂₀H₄F₂₄ZrO₈: a = 15.3533(13) Å, b = 20.2613(15) Å, c = 19.6984(17) Å; β = 95.828(2)°, monoclinic, space group P2₁/c, Z = 2, d _calc = 2.004 g/cm³, R = 0.078. All the structures are molecular and include isolated mononuclear Zr(β-dik)₄ complex molecules. Coordination environment of zirconium atom is made by eight oxygen atoms of four β-diketonates; the coordination polyhedron is an almost regular square antiprism. The Zr-O distances fall within 2.14–2.23 Å. Complexes in the structures are joined by van der Waals interactions. Using the structural data, the van der Waals energies of crystal lattices of the studied compounds are calculated by the atom-atom potential method.     

X-ray photoelectron study of electron density distribution in palladium(II) β-diketonate complexes

This work is devoted to experimental (X-ray photoelectron) and theoretical investigations of electron density distribution in Pd(II) β-diketonate complexes. Data about the electronic structure (effective charges, core level energies) of the compounds are compared with their thermodynamic parameters (thermal stability, vaporization enthalpy). In molecular crystals of Pd(II) β-diketonates, the volatility of the complexes and vaporization enthalpy ΔH _T ⁰ depend not only on van der Waals interactions, but also on electrostatic interactions of molecules in crystal.