Reactions of guaiazulene with methyl terephthalaldehydate and 2-hydroxy- and 4-hydroxybenzaldehydes in methanol in the presence of hexafluorophosphoric acid: comparative studies on molecular structures and spectroscopic, chemical and electrochemical properties of monocarbocations stabilized by 3-guaiazulenyl and phenyl groups

Reaction of guaiazulene (1) with methyl terephthalaldehydate (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 2 h under aerobic conditions gives (3-guaiazulenyl)[4-(methoxycarbonyl)phenyl]methylium hexafluorophosphate (5) in 94% yield. Similarly, reactions of 1 with 2-hydroxybenzaldehyde (3) and 4-hydroxybenzaldehyde (4) under the same reaction conditions as 2 give (3-guaiazulenyl)(2-hydroxyphenyl)methylium hexafluorophosphate (6) and (3-guaiazulenyl)(4-hydroxyphenyl)methylium hexafluorophosphate (7) in 89 and 97% yields, respectively. Comparative studies on the molecular structures as well as the spectroscopic, chemical and electrochemical properties of the monocarbocation compounds 5-7 stabilized by 3-guaiazulenyl and 4-(methoxycarbonyl)phenyl (or 2-hydroxy- or 4-hydroxyphenyl) groups are reported.     

A facile preparation, the crystal structure, the chemical and electrochemical properties of [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate

Reaction of guaiazulene (1) with p-dimethylaminobenzaldehyde in methanol in the presence of tetrafluoroboric acid gives the title monocarbocation compound, [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate (2), in 90% yield. The title investigations of compound 2 compared with those of two other monocarbocations stabilized by a 3-guaiazulenyl group (i.e. phenyl-3-guaiazulenylmethyl and [4-(isopropyl)phenyl]-3-guaiazulenylmethyl cations) are reported.     

Synthesis, properties and crystal structures of ferrocene derivatives containing pyrazinium and quinoxalinium units

The pyrazinium salt [FcCH₂pyz][BF₄] (1) and the quinoxalinium salt [FcCH₂quin][BF₄] (2) were prepared by the reaction of [FcCH₂][BF₄] with pyrazine and quinoxaline, respectively and characterised by spectroscopic methods, cyclic voltammetry and by single-crystal X-ray diffraction, which revealed the absence of any π-π-stacking motifs in the crystal structures.     

New polynuclear compounds based on N-benzyliminodipropionic acid: solution studies,synthesis, and X-ray crystal structures

Three new polynuclear compounds based on a dicarboxylic acid ligand are reported. In particular, two Cu(II) coordination compounds, [Cu₂(H₂O)₆(Hbzlidp)₂](CF₃SO₃)₂·2H₂O (1) and [Cu(NO₃)(Hbzlidp)]_∞ (2) (bzlidp^2? = N-benzyliminodipropionate anion), and a Ni(II) dinuclear compound, [Ni₂(H₂O)₄(bzlidp)₂] (3), were synthesized and characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. Different structures were obtained depending on the reaction conditions. The structural analyses reveal that 1 was formed by dinuclear [Cu₂(H₂O)₆(Hbzlidp)₂]²⁺ units built by two copper(II) ions joined through two Hbzlidp^? ligands, while 2 was formed by pairs of Cu(II) centers bridged by four syn,syn carboxylate groups to generate “paddle wheel” units. The dinuclear copper units are arranged in a rhombus type grid, in a 2-D layer structure. In both cases, the N was protonated and not coordinated to the metal center. Compound 3 was formed by [Ni₂(H₂O)₄(bzlidp)₂] neutral dinuclear units, with octahedral Ni(II) centers. Solution studies of the ligand–M(II) systems (M(II) = Mn, Co, Ni, Cu, Zn, Cd, and Pb) were also carried out.     

Reaction of azulene with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol in a mixed solvent of methanol and acetonitrile in the presence of hydrochloric acid: a facile one-pot synthesis and properties of new triarylethylenes possessing an azulen-1-yl group

Reaction of azulene (1) with 1,2-bis[4-(dimethylamino)phenyl]-1,2-ethanediol (2) in a mixed solvent of methanol and acetonitrile in the presence of 36% hydrochloric acid at 60 °C for 3 h gives 2-(azulen-1-yl)-1,1-bis[4-(dimethylamino)phenyl]ethylene (3) (8% yield), 1-(azulen-1-yl)-(E)-1,2-bis[4-(dimethylamino)phenyl]ethylene (4) (28% yield), and 1,3-bis{2,2-bis[4-(dimethylamino)phenyl]ethenyl}azulene (5) (9% yield). Besides the above products, this reaction affords 1,1-di(azulen-1-yl)-2,2-bis[4-(dimethylamino)phenyl]ethane (6) (15% yield), a meso form (1R,2S)-1,2-di(azulen-1-yl)-1,2-bis[4-(dimethylamino)phenyl]ethane (7) (6% yield), and the two enantiomeric forms (1R,2R)- and (1S,2S)-1,2-di(azulen-1-yl)-1,2-bis[4-(dimethylamino)phenyl]ethanes (8) (6% yield). Furthermore, addition reaction of 3 with 1 under the same reaction conditions as the above provides 6, in 46% yield, which upon oxidation with DDQ (=2,3-dichloro-5,6-dicyano-1,4-benzoquinone) in dichloromethane at 25 °C for 24 h yields 1,1-di(azulen-1-yl)-2,2-bis[4-(dimethylamino)phenyl]ethylene (9) in 48% yield. Interestingly, reaction of 1,1-bis[4-(dimethylamino)phenyl]-2-(3-guaiazulenyl)ethylene (11) with 1 in a mixed solvent of methanol and acetonitrile in the presence of 36% hydrochloric acid at 60 °C for 3 h gives guaiazulene (10) and 3, owing to the replacement of a guaiazulen-3-yl group by an azulen-1-yl group, in 91 and 46% yields together with 5 (19% yield) and 6 (13% yield). Similarly, reactions of 2-(3-guaiazulenyl)-1,1-bis(4-methoxyphenyl)ethylene (12) and 1,1-bis{4-[2-(dimethylamino)ethoxy]phenyl}-2-(3-guaiazulenyl)ethylene (13) with 1 under the same reaction conditions as the above provide 10, 2-(azulen-1-yl)-1,1-bis(4-methoxyphenyl)ethylene (16), and 1,3-bis[2,2-bis(4-methoxyphenyl)ethenyl]azulene (17) (93, 34, and 19% yields) from 12 and 10 and 2-(azulen-1-yl)-1,1-bis{4-[2-(dimethylamino)ethoxy]phenyl}ethylene (18) (97 and 58% yields) from 13.     

Synthesis,spectroscopic, electrochemical and structural characterization of Cu(II) complexes with asymmetric NN′OS coordination spheres

A set of four Cu(II) complexes, [Cu(cdnapen)], [Cu(cdnappd)], [Cu(cdMenappd)] and [Cu(cdMeMeOsalpd)], derived from Schiff base ligands with an asymmetric NN′OS coordination sphere have been synthesized. The molecular and the crystal structures have been determined by X-ray diffractometry. The structural results confirm that the complexes are tetra coordinated. The copper (II) ion coordinates to two nitrogen atoms from the imine moiety of the ligand, a sulfur atom from the methyl dithiocarboxylate moiety and a phenolic oxygen atom. The complexes show an unusual tetrahedral distortion to the square-planar geometry around the metal centre in spite of the pseudomacrocyclic skeleton of the ligand. The complexes were further characterized by cyclic voltammetry and electron paramagnetic resonance spectroscopy. The degree of tetrahedral distortion of the complexes appears to be dependent on the number of carbon atoms of the aliphatic bridge and the nature of the coordinating atoms.     

Ternary Chlorides of the Trivalent Early Lanthanides. Phase diagrams,crystal structures and thermodynamic properties

A comprehensive review on phase diagrams, crystal structures and thermodynamics of ternary chlorides formed in systems ACl/LnCl₃ (A=Cs, Rb, K, Na; Ln=La−Gd) is presented. The review summarizes the author’s own studies, published since 1985, and original papers of other scientists. With the larger alkali metal ions compounds such as A₃LnCl₆, A₂LnCl₅ and ALn₂Cl₇were obtained. With sodium additional compounds NaLnCl₄ and Na₃Ln₅Cl₁₈ were obtained. The crystal structures are discussed with the concept of ionic radii, which determine the coordination numbers of Ln³⁺ and A⁺ cations against Cl⁻ anions. The formation enthalpies of the compounds from ACl and LnCl₃ were determined by solution calorimetry. Gibbs’ free energies and entropies for these reactions were obtained by e.m.f. measurements vs. temperature. The stability of a ternary chloride in a systemACl−LnCl₃ is given by the ‘free enthalpy of synproportionation’, that is, the formation of a compound from its neighbour compounds in the system. This ΔG ⁰ _syn must be negative. A surprising result is, that the highest-melting compounds in the systems, A₃LnCl₆, are formed from ACl+A₂LnCl₅ by a loss in lattice energy. They exist as high-temperature compounds due to sufficiently high gain in entropy at temperatures whereTΔS>ΔH. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reactions of pyridyl donors with halogens and interhalogens: an X-ray diffraction and FT-Raman investigation

Three different N-donors L, namely N-ethyl-N′-3-pyridyl-imidazolidine-4,5-dione-2-thione (1), N,N′-bis(3-pyridylmethyl)-imidazolidine-4,5-dione-2-thione (2), and tetra-2-pyridyl-pyrazine (3), bearing one, two and four pyridyl substituents, respectively, have been reacted with halogens X₂ (X = Br, I) or interhalogens XY (X = I; Y = Cl, Br). CT σ-adducts L · nXY, bearing linear N?XY moieties (L = 3; X = I; Y = Br, I; n = 2), and salts containing the protonated cationic donors H_nLⁿ⁺ (L = 1 − 3; n = 1, 2, 4), counterbalanced by Cl⁻, Br⁻, , , , , I₂Br⁻, , or anions, have been isolated. Among the reactions products, (H1⁺)Cl⁻, (H1⁺)Br⁻, , , and 3 · 2IBr have been characterised by single-crystal X-ray diffraction. The nature of the products has been elucidated based on elemental analysis and FT-Raman spectroscopy supported by MP2 and DFT calculations.     

Synthesis,characterization, crystal structures,enzyme inhibition,DNA binding,and electrochemical studies of zinc(II) complexes

Five zinc(II) complexes, [Zn(L¹)₂] (1), [Zn(L¹)₂(phen)H₂O]·H₂O (2), [Zn(L¹)₂(bipy)] (3), [Zn(L²)₂] (4), and [Zn(L²)₂(phen)] (5) (where L¹?=?4-nitrophenylacetate, L²?=?phenylacetate, phen?=?1,10-phenanthroline and bipy?=?2,2′-bipyridine), have been synthesized and characterized by elemental analysis, FT-IR, and multinuclear NMR. Complexes 2, 3, and 4 have been confirmed by single-crystal X-ray diffraction. In 2 and 3, zinc is bonded monodentate to two carboxylates exhibiting distorted trigonal bipyramidal and tetrahedral geometries, respectively, whereas in 4, the carboxylates are bridging bidentate in distorted tetrahedral geometry. The complexes have been screened for electro- and biological activities, including DNA interaction and enzyme inhibition studies. The effect of concentration of 1–5 on the activity of enzyme, alkaline phosphatase, showed that an increase in concentration of complex decreased the activity of the enzyme. Electrochemical behavior of HL¹, 2, and 3 was investigated by cyclic voltammetry and it was observed that ligand-centered electro-activity exhibits a proportionate change on complexation. The UV–visible spectroscopic and viscometric data indicate electrostatic and groove binding of the complexes with DNA. The binding constant and Gibb’s free energy values indicate the feasibility of the complex–DNA interaction and show potent biological activity of the complexes.     

A facile preparation, spectroscopic and chemical properties, crystal structures, and electrochemical behavior of monocarbenium ion compounds stabilized by 3-guaiazulenyl and dihydroxyphenyl (or hydroxymethoxyphenyl) groups

Reaction of guaiazulene (8) with 2,3-dihydroxybenzaldehyde (9) in methanol in the presence of hexafluorophosphoric acid (i.e., 65% aqueous solution) at 25 °C for 2 h gives (3-guaiazulenyl)(2,3-dihydroxyphenyl)methylium hexafluorophosphate (13) in 86% yield. Similarly, reaction of 8 with 2-hydroxy-3-methoxybenzaldehyde (10) [or 3,4-dihydroxybenzaldehyde (11) or 4-hydroxy-3-methoxybenzaldehyde (12)] under the same reaction conditions as for 9 affords the corresponding monocarbenium ion compound 14 (63% yield) [or 15 (43% yield) or 16 (77% yield)], respectively, each product of which is stabilized by 3-guaiazulenyl and dihydroxyphenyl (or hydroxymethoxyphenyl) groups. A facile preparation and crystal structures as well as spectroscopic, chemical, and electrochemical properties of 13-16, possessing two interesting resonance structures, respectively, i.e., a protonated o- (or p-) benzoquinonemethide form and a 3-guaiazulenylium ion form, in a solution of acetonitrile and further, in a single crystal, are reported.     

Syntheses, structures, spectroscopic, electrochemical properties and DFT calculation of Ru(II)–thioarylazoimidazole complexes

The reaction of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles (SRaaiNR) (2a/2b) with Ru(II) has synthesized [Ru(SRaaiNR)₂](ClO₄)₂ (3a/3b) in 2-methoxyethanol. The reaction in methanol, however, has synthesized [Ru(SRaaiNR)(SRaaiNR)Cl](ClO₄) (4a/4b). The solid phase reaction of SRaaiNR and RuCl₃ on silica gel surface upon microwave irradiation has synthesized [Ru(SRaaiNR)(SaaiNR)](PF₆) (5a/5b) [SRaaiNR represents tridentate N,N′,S-chelator; SRaaiNR is N,N′-bidentate chelator where S does not coordinate and SaaiNR refers N,N′,S-chelator where S refers to thiolato binding]. The structural characterization of [Ru(SEtaaiNEt)(SEtaaiNEt)Cl](ClO₄) (4b) and [Ru(SEtaaiNEt)(SaaiNEt)](PF₆) (5b) has been confirmed by single crystal X-ray diffraction study. The IR, UV–Vis, and ¹H NMR spectral data also support the stereochemistry of the complexes. The complexes show metal oxidation, Ru(III)/Ru(II), and ligand reductions (azo/azo⁻, azo⁻/azo). The molecular orbital diagram has been drawn by density functional theory (DFT) calculation. Normal mode of analysis has been performed to correlate calculated and experimental frequencies of representative complexes. The electronic movement and assignment of electronic spectra have been carried out by TDDFT calculation both in gas and acetonitrile phase.     

Chloro-diorganotin(IV) complexes of 4-methyl-1-piperidine carbodithioic acid: Synthesis, X-ray crystal structures, spectral properties and antimicrobial studies

Chloro-diorganotin(IV) complexes of 4-methyl-1-piperidine carbodithioic acid (4-MePCDTA) have been synthesized by the reaction with diorganotin dichloride in 1:1 molar ratio in anhydrous toluene. These newly synthesized complexes have been characterized by elemental, IR, multinuclear NMR (¹H and ¹³C) and mass spectrometric studies. The crystal structures of complex 1 [Me₂SnCl(4-MePCDT)] and 3 [Ph₂SnCl(4-MePCDT)] have been determined by X-ray single crystal analysis, which show trigonal bipyramid geometry. These complexes were tested for their antimicrobial activity against six different plant and human pathogens. The screening results show that the complexes exhibit higher antibacterial and antifungal activity than the free ligand.     

Crystal structures,theoretical calculations,spectroscopic and electrochemical properties of Cr(III) complexes with dipicolinic acid and 1,10-phenantroline

The crystal structures of compounds Na[Cr(dipic)₂] · 2H₂O (1) and [Cr(dipic)(phen)Cl] · 1/2H₂O (2), dipic = dipicolinate, phen = 1,10-phenantroline, were determined. In both complexes, Cr(III) is in a distorted octahedral environment. In complex (1), the metal is coordinated to two nearly perpendicular dipic anions acting as tridentate ligands through one oxygen of each carboxylate group and the pyridinic nitrogen atom. In complex (2), Cr(III) ion is similarly coordinated to a dipic anion, defining a ligand equatorial plane. The phen molecule bridges the remaining equatorial coordination site and one of the axial positions through its N-atoms. The other axial position is occupied by a chloride ion.     

New Re(I) tricarbonyl-diimine complexes with N,N′-bis(substituted benzaldehyde)-1,2-diiminoethane Schiff base ligands: Synthesis,spectroscopic and electrochemical studies and crystal structures

The syntheses, structures and spectroscopic properties of tricarbonylrhenium(I) complexes with N,N′-bis(2-bromo, 4-bromo, 4-chloro and 3-methoxybenzaldehyde)-1,2-diiminoethane Schiff base ligands have been investigated in this paper. Characterization of these complexes was carried out with FTIR, NMR, UV–Vis spectroscopy, elemental analysis and X-ray crystallography. The electrochemical behavior of the investigated complexes has been studied by cyclic voltammetry. The crystal structures of the 4-chloro, 4-bromo and 4-methoxy substituted complexes are stabilized by intermolecular C–H?Cl and C–H?O hydrogen bonds. The remarkable features of the 2-bromo, 4-bromo and 4-chloro substituted complexes are short intermolecular halogen–oxygen contacts. In the 4-bromo complex, short intermolecular Br?O and O?O contacts link neighboring molecules along the [1 0 0] direction, which are further stabilized by short intermolecular π?π interactions. In 2-bromo complex, intermolecular Br?O interactions link neighboring molecules into 1D extended chains along the [0 1 0] and [0 0 1] directions, forming a 2D network which is parallel to the bc-plane.     

Synthesis, X-ray crystal structures, spectroscopic and cyclic voltammetric studies of Cu(II) Schiff base complexes of pyridoxal

Two mononuclear Cu(II) complexes, [Cu(L¹H₂)](ClO₄)_1.25Cl_0.75·1.25H₂O (1) and [Cu(L²H₂)](ClO₄)₂ (2), of the pyridoxal Schiff base ligands N,N′-dipyridoxylethylenediimine (L¹H₂) and N,N′-dipyridoxyl-1,3-propanediimine (L²H₂) are reported. X-ray crystal structures of both complexes are also reported. In both complexes the pyridoxal nitrogen atoms remain protonated. In the solid state, the tetradentate Schiff base ligand is virtually planar in 1, while in 2 the ligand conformation is like an inverted umbrella. In cyclic voltammetry experiments it is found that in these complexes the Cu(III) and Cu(I) states are more easily accessible than in their salen type analogs. The pyridoxal Schiff base complexes are also found to be resistant to oxidative electro-polymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.     

Reactions of aroylpyruvic acids withS-methylisothiosemicarbazide hydroiodide and studies of the crystal structures of the reaction products

The reactions ofp-chlorobenzoyl- and benzoylpyruvic acids withS-methylisothiosemicarbazide hydroiodide gave 3-methylthio-6-(p-chlorophenacyl)-2,5-dihydro-1,2,4-triazin-5-one and 6-phenacyl-2,3,4,5-tetrahydro-1,2,4-triazine-3,5,-dione, respectively. The molecular and crystal structures of the compounds synthesized were studied by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 704–708, April, 1998.     

Reactions of (1R,2S)-1,2-di(2-furyl)-1,2-di(3-guaiazulenyl)ethane and (1R,2S)-1,2-di(3-guaiazulenyl)-1,2-di(2-thienyl)ethane with tetracyanoethylene (TCNE) in benzene: comparative studies on the products and their spectroscopic properties

Reactions of the title meso forms, (1R,2S)-1,2-di(2-furyl)-1,2-di(3-guaiazulenyl)ethane (1) and (1R,2S)-1,2-di(3-guaiazulenyl)-1,2-di(2-thienyl)ethane (2), with a two molar amount of TCNE in benzene at 25 °C for 5 h (for 1) and 48 h (for 2) under oxygen give new compounds, 2,2,3,3-tetracyano-4-(2-furyl)-8-isopropyl-6-methyl-1,4-dihydrocyclohepta[c,d]azulene (3) and 2,2,3,3-tetracyano-8-isopropyl-6-methyl-4-(2-thienyl)-1,4-dihydrocyclohepta[c,d]azulene (4), respectively, in 74 and 21% isolated yields. Comparative studies on the above reactions as well as the spectroscopic properties of the unique products 3 and 4, possessing interesting molecular structures, are reported and, further, a plausible reaction pathway for the formation of these products is described.