Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone and its bis(aza-18-crown-6)-containing analogue in acetonitrile

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone (CH1) and its bis(aza-18-crown-6) derivative (CH2) in acetonitrile at ambient temperature and 77 K have been studied. The absorption, fluorescence, and phosphorescence spectra of CH1 and CH2 are similar. The probability of the formation of the triplet state is higher for CH2 molecules (λ_T-T^max = 660 nm, lifetime τ_T ~ 20 μs). The lifetime of the CH1 molecule in the triplet state is estimated at τ_T ~ 2–3 μs. Photoisomers of CH1 and CH2 are formed along with the triplet state. According to DFT calculation results, the formation of trans–cis photoisomers of CH1 and CH2 is the most energetically favorable.     

The photolysis of bis(acetonitrile)tetrachlorotungsten in acetonitrile

When WCl₆ is dissolved in CH₃CN it is reduced to WCl₄(CH₃CN)₂ in a first-order process with a half-life of 52 s. Irradiation of the WCl₄(CH₃CN)₂ solution at 365 nm yields WO₂Cl₂(CH₃CN)₂. Further irradiation of this solution with access to air yields a blue, partially reduced form of WO₃ · 2H₂O, which eventually precipitates.     

Preparation and characterization of bis(acetonitrile)bis(acetylacetonato)technetium(III)

A new chemical species of bis(acetonitrile)bis(acetylacetonato)technetium(III), [Tc(acac)₂(CH₃CN)₂]⁺, has been prepared by the reaction of tris(acetylacetonato)technetium(III) with acetonitrile in the presence of a strong acid, perchloric or hydrochloric acid. The reaction kinetics were followed by observing spectral change of Tc(acac)₃ in the UV-visible region. The complex has been characterized by combination of elemental analyses, IR and UV-visible spectrophotometry, ion-exchange chromatography, and paper electrophoresis. Applicability of this substance to synthesize mixed-ligand technetium(III) complexes was discussed based on the solubility of this complex and the ease of substitution of the acetonitrile ligand.     

Preparation and x-ray crystal structure of racemic bis(ethylfumarate)bis(acetonitrile)cobalt(0)

The preparation and properties of some new tetracoordinated cobalt(0) complexes containing nitrile and fumaric ester ligands are described. One of them, Co(C₂H₅OOCCHCHCOOC₂H₅)₂(CH₃CN)₂, (la), reacts with 1,10-phenanthroline to give new pentacoordinated and hexacoordinated cobalt(0) complexes.The structure of Ia has been determined from X-ray diffractometer data. The structure was solved by Patterson and Fourier methods and refined by least square techniques to R  0.060 for 2215 independent reflections. Crystals are triclinic, space group P$\text{1}$, with Z  2 in a unit cell of dimensions: a 14.794(18), b 9.448(11), c 10.125(12) Å, α 108.55(9), β 111.42(11), γ 84.95(18)°. The metal is linked to the four carbon atoms of the CHCH groups of the ethyl fumarate residues and to the nitrogen atoms of the two acetonitrile ligands. The coordination of the four ligands around the cobalt atom corresponds to a distorted trigonal pyramid. The four asymmetric carbon atoms of a molecule have the same absolute configuration. RRRR and SSSS molecules are present in the unit cell.     

Molecular and electronic structure of the square planar bis(o-amidobenzenethiolato)iron(III) anion and its bis(o-quinoxalinedithiolato)iron(III) analogue

Crystalline purple [PPh4][FeIIIL2] (1), where L2- represents the closed-shell dianion of 4,6-di-tert-butyl-2-[(pentafluorophenyl)amino]benzenethiol, has been synthesized from the reaction of H2L and FeBr2 (2:1) in acetonitrile with excess NEt3, careful, brief exposure of the solution to air, and addition of [PPh4]Br. The monoanion has been shown by X-ray crystallography to be square planar. The oxidation of 1 with 1 equiv of iodine produces the neutral species [FeI(L*)2]0 (2) where (L*)1- represents the one-electron oxidized pi radical anion of L2-. The reaction of H2Land PtCl2 (2:1) and NEt3 in CH3CN in the presence of air produced green, crystalline [PtII(L*)2] (3). From temperature dependent(2-300 K) magnetic susceptibility measurements, it was established that 1 possesses a central intermediate spin ferric ion (SFe ) 3/2), whereas neutral 2 has a doublet ground state (St ) 1/2) comprising an intermediate spin ferric ion coupled antiferromagnetically to two ligand pi radicals (L*)1- (Srad ) 1/2). Complex 3 is diamagnetic. Almeida et al.'s complexes in ref 1, [N(n-Bu)4][FeIII(qdt)2] (A), and [PPh4]2[FeIII2(qdt)4] (B), have been revisited. It is shown here that the square planar anion in mononuclear [FeIII(qdt)2]- also possesses an SFe ) 3/2 ground state. The zero-field M?ssbauer spectra of 1, 2, A, and B have been recorded and the molecular and electronic structures of all mononuclear iron species have been calculated by density functional theoretical methods.It is shown that the S ) 3/2 ground state in 1 and A is lower in energy by 8.5 and 16.6 kcal mol(-1), respectively,than the S ) 1/2 state.     

Synthesis and characterization of technetiumtetrakis(acetonitrile)bis(triphenylphosphine) cationic complexes

A new route to low-valent technetium complexes containing multiple acetonitrile ligands has been developed. The reduction of TcCl(4)(PPh(3))(2) with zinc metal dust in acetonitrile results in the formation of [Tc(CH(3)CN)(4)(PPh(3))(2)][Zn(2)Cl(6)](1/2). The hexafluorophosphate salt of the analogous Tc(II) cation can be prepared via chemical oxidation of the Tc(I) species, and the Tc(I) cation can be regenerated via chemical reduction. The compounds have been characterized in the solid state via single-crystal X-ray crystallography, and in solution via a combination of spectroscopic techniques and cyclic voltammetry. The structural parameters found in the two complexes are similar to each other; however, the difference in oxidation state is reflected, as expected, in the spectroscopic results. The electrochemical data, obtained from cyclic voltammograms of Tc(CH(3)CN)(4)(PPh(3))(2)](PF(6))(n)() (n = 1,2), mirror the synthetic results in that both compounds possess a reversible redox couple at -0.55 V versus ferrocene, which has been assigned to the Tc(II)/Tc(I) couple.     

Synthesis of novel bis(chromenes) and bis(chromeno[3,4-C]pyridine) incorporating piperazine moiety

Novel bis(2-oxo-2H-chromene) as well as bis(2-imino-2H-chromene) derivatives incorporating piperazine moiety were prepared by the cyclocondensation reaction of bis(2-hydroxybenzaldehyde) with two equivalents of each of the appropriate β-ketoesters or acetonitrile derivatives. The bis(2-imino-2H-chromene-3-carbothioamide) derivative was used as a key synthon for construction of novel bis(3-(4-substituted thiazol-2-yl)-2H-chromen-2-one) derivatives via its cyclocondensation with a series of the appropriate α-halocarbonyl derivatives. Moreover, the bis(2-hydroxybenzaldehyde) reacted with four equivalents of the appropriate acetonitrile derivatives to afford the corresponding bis(3H-chromeno[3,4-c]pyridine) derivatives. Elucidation of the structure of the novel bis(chromenes) bearing piperazine nucleus was established by the spectral data and elemental analyses.     

X-ray crystal structure of racemic bis(ethyl fumarate) (acetonitrile)nickel(0)

The crystal and molecular structure of racemic bis(ethyl fumarate)(acetonitrile) nickel(0) was determined from X-ray diffractometer data. The structure was solved by Patterson and Fourier methods, and refined by least-squares techniques to R = 0.045 for 3034 independent reflections.Crystals are triclinic, space group P$\text{1}$, with Z = 2, in a unit cell of dimensions: a 9.219 (6), b 13.257 (3), c 10.521 (9) », α 92.57 (9)°, β 109.25 (10)°, γ 110.0 (9)°.The coordination around the nickel(0) atom (the four carbon atoms of the HCCH groups, and the N atom of the acetonitrile residue), may be described as planar, with a slightly distorted trigonal symmetry. The conformations of the two ehtyl fumarate residues agree, more or less closely, with the principle of staggered bonds. The torsion angles around the HCCH groups are significantly different from 180°, as observed in other similar complexes. The four asymmetric carbon atoms of a molecule have the same absolute configuration. SSSS and RRRR molecules are present in the unit cell.     

Preparation of a cyclodextrin dimer linked with a bis(picolinyl)cystine moiety and its intra- and intermolecular inclusion behavior

A novel cyclodextrin (CD) dimer linked with a bis(picolinyl)cystine (Cys) moiety was prepared by the coupling of Boc-protected Cys with amino-modified CDs, followed by deprotection of the Boc groups and bispicolinylation. The dimer showed less affinity to an organic guest molecule compared to that of a native CD monomer. It was attributed to an intramolecular inclusion of the pyridine moiety into CD cavity. The dimer caused significant increase of its organic guest affinity by an addition of a copper ion. The included pyridine group may come out of a CD cavity to bind the copper ion and the two CDs included cooperatively and intermolecularly a guest molecule with high affinity.     

Transition-state variation in the nucleophilic substitution reactions of aryl bis(4-methoxyphenyl) phosphates with pyridines in acetonitrile

The kinetics and mechanism of the reactions of Z-aryl bis(4-methoxyphenyl) phosphates, (4-MeOC(6)H(4)O)(2)P(=O)OC(6)H(4)Z, with pyridines (XC(5)H(4)N) are investigated in acetonitrile at 55.0 degrees C. In the case of more basic phenolate leaving groups (Z = 4-Cl, 3-CN), the magnitudes of beta(X) (beta(nuc)) and beta(Z) (beta(lg)) indicate that mechanism changes from a concerted process (beta(X) = 0.22-0.36, beta(Z) = -0.42 to -0.56) for the weakly basic pyridines (X = 3-Cl, 4-CN) to a stepwise process with rate-limiting formation of a trigonal bipyramidal pentacoordinate (TBP-5C) intermediate (beta(X) = 0.09-0.14, beta(Z) = -0.08 to -0.28) for the more basic pyridines (X = 4-NH(2), 3-CH(3)). This proposal is supported by a large negative cross-interaction constant (rho(XZ) = -1.98) for the former and a positive rho(XZ) (+0.97) for the latter processes. In the case of less basic phenolate leaving groups (Z = 3-CN, 4-NO(2)), the unusually small magnitude of beta(Z) values is indicative of a direct backside attack TBP-5C TS in which the two apical sites are occupied by the nucleophile and leaving group, ap(NX)-ap(LZ). The instability of the putative TBP-5C intermediate leading to a concerted displacement is considered to result from relatively strong proximate charge transfer interactions between the pi-lone pairs on the directly bonded equatorial oxygen atoms and the apical bond (n(O)(eq) - sigma(ap)). These are supported by the results of natural bond orbital (NBO) analyses at the NBO-HF/6-311+G//B3LYP/6-311+G level of theory.     

The synthesis and structure of bis(acetonitrile)nitrosyl tris(3,5-dimethylpyrazolyl)borato molybdenum hexafluorophosphate

Summary Treatment of [Mo{HB(3,5-Me₂C₃HN₂)₃}(NO)I₂] with one or two moles of AgPF₆ in acetonitrile afforded the paramagnetic (one unpaired electron) complex [Mo{HB(3,5-Me₂C₃NH₂)₃}(NO)(NCMe)₂][PF₆]. The structure of this complex was determined crystallographically, and the six-coordinate geometry of the complex cation confirmed.     

Cationic and alkynyl complexes of the trans(mesityl)bis(phenyldimethylphosphine)nickel(II) moiety

A cationic complex, trans-[(mesityl)Ni(PPhMe₂)₂(NCMe)]ClO₄ (IIa), has been prepared rom trans-(mesityl)Ni(PPhMe₂)₂Br and silver perchlorate in acetone/acetonitrile. IIa reacts with several neutral ligands to give trans-[(mesityl)Ni(PPhMe₂)₂L]ClO₄ (L = 2-pic, 3-pic, 3,4-lut, 2,5-lut, methyl isonicotinate, N-ethyl imidazole, PPhMe₂, P(Ome)₃), with halide anions to give trans-(mesityl)Ni(PPhMe₂)₂X (X = Cl, NNN), and with terminal alkynes in the presence of triethylamine to give trans-(mesityl)Ni(PPhMe₂)₂CCR (R = H, Me, CH₂CH₂Oh, Ph, C₆H₄OMe-p). Some related alkynyl complexes trans-CCl₂CClNi(PPhMe₂)₂CCR (R = H, Me, Ph, C₆H₄OMe-p) and trans-{(o-MeO)₂C₆H₃}Ni(PPhMe₂)₂CCr (R = H, Ph) also have been prepared from the corresponding trans-R′Ni(PPhMe₂)₂Cl, silver perchlorate and HCCR in acetonitrile-triethylamine. trans-(Mesityl)Ni(PPhMe₂)₂CCH reacts with methanol in the presence of perchloric acid to give a cationic carbne complex, trans-[(mesityl)Ni(PPhMe₂)₂{C(OMe)Me}]ClO₄.     

Bis(acetonitrile)bis(acetylacetonato)ruthenium(III) mediated chemical transformations of coordinated 2-methylthioanilide

Chemical reaction of [Ru(III)(acac)(2)(CH(3)CN)(2)]ClO(4) (1) with 2-methylthioaniline, HL(1) in ethanol under basic conditions yielded three new complexes Ru(II)(acac)(2)(L(1b)) (1b), (L(1b) = 4-imino-3-(methylsulfanyl)cyclohexa-2,5-dien-1-one), Ru(III)(acac)(2)(L(1c)) (1c), (HL(1c) = N-(2-methylthiophenyl)formamide) and (acac)(2)Ru(II)(μ-L(1d))Ru(II)(acac)(2) (1d), (L(1d) = 1,4-bis(2-methylthioaniline)-1,4-diazabutadiene) via the intermediate Ru(III)(acac)(2)(L(1a)) (1a, L(1a) = (L(1))(-) = 2-methylthioanilide). The reaction proceeded through temperature induced valence tautomerisation between the Ru(III) center and its 2-methylthioanilide counterpart in 1a with concomitant reduction of ruthenium from +III to +II oxidation state and oxidation of ligand L(1a), resulting in aromatic ring hydroxylation, N-formylation and C-C bond formation reactions. All the complexes have been characterised by their single-crystal X-ray structure determination and various spectroscopic and electrochemical techniques. The identity of complex 1a has been confirmed by X-ray crystal structure determination of complex 2, a phenyl analogue of complex 1a. The complexes (1a-d) showed intense charge transfer (MLCT/LMCT) transition in the long wavelength region. The paramagnetic compounds, 1a and 1c, along with the diamagnetic compound 1b showed two one-electron responses in the ranges, -0.4 to -1.0 V and 0.3 to 1.1 V. The diamagnetic complex 1d displayed two successive one-electron reversible reductions (-1.31 and -1.55 V) and two one-electron reversible oxidation processes (-0.036 and 0.51 V). The redox processes are characterized by EPR spectroscopy and spectroelectrochemistry. The compound 1c has been found to exhibit solvatochromism and concentration dependent aggregation in solution.     

Novel seven coordination geometry of Sn(IV): crystal structures of phthalocyaninato bis(undecylcarboxylato)Sn(IV), its Si(IV) analogue, and phthalocyaninato bis(chloro)silicon(IV). The electrochemistry of the Si(IV) analogue and related compounds

Three newly elucidated crystal structures of group IV phthalocyaninato complexes are reported, along with data for two further SiPc carboxylate complexes. In one of these crystal structures, bis(undecylcarboxylate)Sn(IV) phthalocyanine, the tin ion is seven coordinate, which is a unique finding for this atom in phthalocyanine ring coordination. Comparison of these structures with other group IV phthalocyaninato and related structures reveals differences, illustrating features significant in the chemistries of Si(IV) and Sn(IV) ions. These differences are thought to originate from their differing sizes and polarizabilities. The structures show that the Sn(IV) ion can only occupy an in-plane location in the phthalocyaninato ring where it elongates toward the two axial ligands. When the axial ligands do not facilitate this elongation cis coordination is preferred and the Sn(IV) ion sits above the phthalocyaninato ring plane. In contrast, the Si(IV) structures, with smaller, harder (i.e., less polarizable) Si(IV) ions, are six coordinate with the Si(IV) ion in the phthalocyaninato ring plane in a distorted octahedral symmetry. The electronic spectra and cyclic voltammetry of some of the Si compounds indicate that on the electrode the oxidized/reduced species behave as though they are in a solid film, rather than a soluble freely diffusing species.     

A novel bis(imino)amine ligand as a result of acetonitrile coupling with the diiodides of Dy(II) and Tm(II)

Complexes of Dy(III) and Tm(III) with novel 1,1'-bis(iminoethyl)ethylamine ligands, [{(HN=CMe)2MeCNH2}Ln(MeCN)6]I3, were obtained by the reactions of LnI2 (Ln = Dy(II), Tm(II)) with acetonitrile.     

双冠醚配位作用的热力学性质V. 双(苯并-15-冠-5)与稀土(III)硝酸盐在无水乙腈溶液中分子内夹心配位作用

本文用分光光度滴定法测定了双(苯并-15-冠-5)(1)与轻稀土(III)硝酸盐在无水乙腈溶液中, 20.0-35.0℃时分子内夹心配位作用的稳定常数, 进而计算了配位焓和配位熵, 并与母体苯并15-冠-5(2)的实验结果作了比较。化学计量法表明, 所有稀土硝酸盐均与双(苯并-15-冠-5)形成了1 : 1的配合物。从热力学的观点, 讨论了双冠醚分子结构、尺寸效应和空间构型等配位稳定性的影响。研究结果发现, 双冠醚(1)对于Eu^3^+具有较强的配位能力和配位选择性, Nd^3^+次之。配合物的稳定性主要来自于熵的贡献。