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Equatorial Positions (equatorial + position)

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Synthesis and Characterization of Copper Complexes Containing the Tripodal N7 Ligand Tris{2-[(pyridin-2-ylmethyl)amino]ethyl}amine (=N,-(Pyridin-2-ylmethyl)- N,N -bis{2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine): Equilibrium, Spectroscopic Data, and Crystal Structures of Mono- and Trinuclear Copper(II) Complexes

HELVETICA CHIMICA ACTA, Issue 9 2005
Christian Gérard
The stability constants of the CuII chelates with the tripodal heptadentate ligand tris{2-[(2-pyridylmethyl)amino]ethyl}amine (=N,-(pyridin-2-ylmethyl)- N,N -bis{2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine; tpaa), determined by potentiometry and UV spectrometry, show the formation of [Cu(tpaaH)]3+ and [Cu(tpaa)]2+ species. In the solid state, two mononuclear CuII compounds, [Cu(tpaa)](PF6)2 (1) and [Cu(tpaaH)](ClO4)3,H2O (2), and one trinuclear [Cu3(tpaa)2(ClO4)2](ClO4)4,2,H2O (3) complex were isolated and characterized by IR, UV/VIS, and EPR spectroscopy. An X-ray structure of the mononuclear protonated complex 2 shows that the Cu2+ ion has a distorted square-pyramidal geometry (,=0.21). and the proton is bound to the secondary-amine function of one uncoordinated arm of the tripod ligand (Fig.,4). The crystal lattice for 2 is stabilized by the H-bonds between the N-atom of the free pyridinyl group with the proton of the free secondary-amine function of the neighboring molecule. The linear trinuclear complex 3 consists of two entities of the pyramidal mononuclear complex 1 bound to the third central Cu2+ ion by the free unprotonated arms of the ligands in equatorial position (Fig.,5). The octahedral geometry of the third CuII atom is achieved by two perchlorate anions in the axial positions. The redox properties of 1,3 compounds was examined by cyclic voltammetry. [source]

Effect of Through-Bond Interaction on Conformation and Structure in Rod-Shaped Donor,Acceptor Systems.

HELVETICA CHIMICA ACTA, Issue 3 2003
Part
The crystal structures of five N -arylpiperidin-4-one derivatives 2P2, 3P2, 5P2, 1P3, and 2P3 are presented (Fig.,2 and Tables,1,5) and discussed together with the derivatives 1P2 and 4P2 published previously. In all but one structure, 1P2, the aryl group is in an equatorial position. The piperidine ring adopts a normal chair conformation. In 1P2, the piperidine ring central CC bonds are significantly elongated, which is consistent with the idea that through-bond interaction is more pronounced in the axial conformation. Through-bond interaction also influences the pyramidalization at the piperidine C(4)-atom in such a way that a strong interaction is directing the ethylene C-atom C(9) into the axial direction. [source]

Low-temperature 1H and 13C NMR spectra of N -substituted 1,2,3,4-tetrahydropyrazino[1,2- a]indoles

MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2005
Alan R. Katritzky
Abstract The temperature-dependent 1H and 13C NMR spectra of 2-(2-butynyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2- a]indole (4) (as a representative example of 1,9) in CFCl3 + CD2Cl2 solution are described and discussed. Below 183 K, the hexahydropyrazine ring inversions become slow on the NMR time-scale and 4 exists in principle as two conformational diastereomers. In fact, only one was observed with the N-2 substituent in an equatorial position as shown by a low-temperature NOESY experiment. The energy barrier for conformational interchange was calculated from NMR data to be 8.3 kcal mol,1 (1 kcal = 4.184 kJ), in agreement with quantum chemical calculations. Unambiguous assignments for all proton and carbon resonances of 1,9 were made using 1D (APT, DEPT, NOE difference) and 2D (COSY, NOESY, gHMQC, gHMBC) NMR techniques. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Two isomeric cucurbitane derivatives

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009
Maciej Kubicki
Two isomeric cucurbitane derivatives, 3,,7,,11,-triacetoxycucurbit-5(10)-ene, (I), and 3,,7,,11,-triacetoxy-5,-cucurbit-1(10)-ene, (II), both C36H58O6, have their single endocyclic C=C double bonds in different positions. This results in differences in the conformation of the four-ring system, which is close to a half-chair/half-chair/chair/half-chair arrangement in (I) and to a half-chair/twist-boat/boat/half-chair arrangement in (II). The orientation of some of the substituents is also different; the 3,-acetoxy group is in an equatorial position in (I) but in an axial position in (II), while the 11,-acetoxy group occupies an axial position in (I) and an equatorial position in (II). The asymmetric unit of (I) contains two symmetry-independent molecules which do not differ significantly, being related by a pseudo-twofold axis of symmetry. In both structures, the aliphatic chain fragments are disordered and the disorder persists at lower temperatures. [source]

3,5-Bis{3-[4-(dimethylamino)phenyl]prop-2-enylidene}-1-methyl-4-piperidone and 3,5-bis[3-(4-methoxyphenyl)prop-2-enylidene]-1-methyl-4-piperidone: potential biophotonic materials

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2008
Vladimir N. Nesterov
The structures of the title compounds, C28H33N3O, (I), and C26H27NO3, (II), together with their two-photon absorption properties and fluorescence activities are reported. Molecules of (II) reside on crystallographic mirror planes containing the piperidone C=O group and N -methyl H atoms. Because of the conjugation between the donor and acceptor parts, the central heterocycle in both (I) and (II) exhibits a flattened boat conformation, with deviations of the N atom and the opposite C atom from the planar fragment. The dihedral angles between the coplanar heterocyclic atoms and terminal C6 rings are less than 20° in both (I) and (II). In (I), the N -methyl group of the ring occupies an equatorial position, but in (II) it is positioned in an axial site. In the crystal structure of (I), weak intermolecular C,H...,(arene) and C,H...O steric contacts link the molecules along the a axis. In the crystal structure of (II), molecules form stacks along the b axis. [source]

Unexpected Conformational Properties of 1-Trifluoromethyl-1-Silacyclohexane, C5H10SiHCF3: Gas Electron Diffraction, Low-Temperature NMR Spectropic Studies, and Quantum Chemical Calculations,

CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2007
Georgiy
Abstract The molecular structure of axial and equatorial conformers of 1-trifluoromethyl-1-silacyclohexane, (C5H10SiHCF3), as well as the thermodynamic equilibrium between these species was investigated by means of gas electron diffraction (GED), dynamic nuclear magnetic resonance (DNMR) spectroscopy, and quantum chemical calculations (B3LYP, MP2, and CBS-QB3). According to GED, the compound exists as a mixture of two Cs symmetry conformers possessing the chair conformation of the six-membered ring and differing in the axial or equatorial position of the CF3 group (axial=58(12) mol,%/equatorial=42(12) mol,%) at T=293,K. This result is in a good agreement with the theoretical prediction. This is, however, in sharp contrast to the conformational properties of the cyclohexane analogue. The main structural feature for both conformers is the unusually long exocyclic bond length SiC 1.934(10),Å. A low-temperature 19F,NMR experiment results in an axial/equatorial ratio of 17(2) mol,%:83(2) mol,% at 113,K and a ,G,, of 5.5(2),kcal,mol,1. CBS-QB3 calculations in the gas-phase and solvation effect calculations using the PCM(B3LYP/6-311G*) and IPCM(B3LYP/6-311G*) models were applied to estimate the axial/equatorial ratio in the 100,300,K temperature range, which showed excellent agreement with the experimental results. The minimum energy pathways for the chair-to-chair inversion of trifluoromethylsilacyclohexane and methylsilacyclohexane were also calculated using the STQN(Path) method. [source]

Conformational Landscapes and Free-Jet Rotational Spectrum of Indan-1-ol

CHEMPHYSCHEM, Issue 3 2006
Biagio Velino Dr.
Nonbonding interactions: The most stable configuration of indanole as determined by rotational spectroscopy in supersonic expansions results in the hydroxyl group in the equatorial position, with the hydroxyl hydrogen pointing towards the cyclopentenyl ring (see figure). Five other rotamers, generated by the hydroxyl group rotation and by the five-membered ring puckering, relax to this one upon supersonic expansion. [source]

First (Peroxo)vanadium(V) Complex with Heteroligand Formed in Reaction System , Synthesis, Structure and Reactivity of K[VO(O2)(omeida)]·H2O {omeida = N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetato(2,)}

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003
Michal Sivák
Abstract The crystalline peroxo complex of vanadium(V), K[VO(O2)(omeida)]·H2O, where omeida is a ,-lactone derivative, N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetate(2,), has been obtained by reaction of vanadate with H2O2 and N -(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) in acidic aqueous solution at pH = 3 and 278 K. X-ray analysis revealed a distorted pentagonal-bipyramidal coordination around the vanadium atom, with a typical cis arrangement of oxo and peroxo ligands in apical and equatorial positions, respectively. Two amino nitrogen atoms of the tetradentate omeida(2,)-N1,N2,O1,O2 ligand occupy the neighbouring equatorial positions of the pentagonal plane, and two oxygen atoms of carboxymethyl groups bound to the same N1 nitrogen atom are in equatorial and apical positions. The six-membered lactone ring in omeida was formed in the reaction solution from carboxy and hydroxy groups not involved in coordination with the vanadium atom. The 51V NMR spectra of K[VO(O2)(omeida)]·H2O, and of peroxovanadate/HEDTA/H2O and vanadate/HEDTA/H2O solutions, as well as the 1H NMR spectrum of HEDTA, proved that lactone ring closure proceeds only in peroxovanadate but not vanadate solutions. Spectroscopic investigation of the oxygen transfer reaction from the peroxo ligand in [VO(O2)(omeida)], to the thiolato sulfur atom in [Co(en)2{S(CH2)2NH2}]2+ or [Co(en)2(cyst)]+, and of the oxidation of N -acetyl- L -cysteine by K[VO(O2)(omeida)]·H2O, revealed much more complicated reaction mechanisms than those of other (amino-polycarboxylato)monoperoxo complexes of vanadium(V). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Structures and Thermodynamics of the Sulfuranes SF3CN and SF2(CN)2 as well as of the Persulfurane SF4(CN)2 , An ab initio MO Study by the G3(MP2) Method

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003
Yana Steudel
Abstract At the G3(MP2) level of theory the trans isomer 1a of the hypothetical molecule SF4(CN)2 is more stable than the cis isomer 1b by 8 kJ·mol,1. The isomerization of 1a to 1b requires an activation enthalpy of 319 kJ·mol,1 at 298 K. The decomposition of trans -SF4(CN)2 to SF2(CN)2 and F2 is endothermic (,Ho298 = 395 kJ·mol,1) but the elimination of FCN from trans -SF4(CN)2 is exothermic by ,7 kJ·mol,1. The elimination of (CN)2 from cis -SF4(CN)2 is exothermic by ,137 kJ·mol,1. The activation enthalpies for the latter two reactions were calculated as 251 and 311 kJ·mol,1, respectively. Thus, SF4(CN)2 should be a thermally stable compound. In the sulfuranes SF3CN and SF2(CN)2 the CN ligands prefer the equatorial positions; mutual exchange of an axial F atom by an equatorial CN group requires a reaction enthalpy of 51 kJ·mol,1 [SF3CN] or 58 kJ·mol,1 [SF2(CN)2]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Exchange Interactions at the Supramolecular Level , Synthesis, Crystal Structure, Magnetic Properties, and EPR Spectra of [Mn(MAC)(TCNQ)2] (MAC = Pentaaza Macrocyclic Ligand; TCNQ·, = Radical Anion of 7,7,8,8-Tetracyano- p -quinodimethane)

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2003
Augustin M. Madalan
Abstract The reaction between [Mn(MAC)(H2O)2]Cl2·4H2O and LiTCNQ (MAC = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene) affords a complex with the formula [Mn(MAC)(TCNQ)2] (1), whose crystal structure has been determined. Its structure consists of neutral mononuclear entities. The manganese(II) ion is heptacoordinated, with a pentagonal bipyramidal geometry. The apical positions are occupied by the TCNQ·, radicals, while the macrocyclic ligand is coordinated at the equatorial positions. The seven Mn,N distances range from 2.273(3) to 2.301(6) Å. The strong intermolecular ,,, stacking interactions between the TCNQ radicals (3.2 Å) leads to weave-like infinite chains, which propagate along the crystallographic c axis. The cryomagnetic investigation of 1 revealed a weak intermolecular antiferromagnetic coupling of the Mn2+ ions (J = ,0.18 cm,1), which is mediated by the diamagnetic (TCNQ)22, pairs resulting from the stacking interactions in the crystal. The intermolecular exchange interaction between the Mn2+ ions was further confirmed by variable temperature EPR spectroscopic measurements [|J| = 0.15(5) cm,1], which have been carried out in both the X and Q bands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Spatial substituent effects of various fluorinated groups on the 13C chemical shifts in cyclohexanes

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2007
Yvan Carcenac
Abstract The effect of introduction of fluorinated groups (CH2F, CHF2, CF3, C2F5, OCF3, SCF3) on the 13C NMR chemical shifts in cyclohexanes is examined. The two main effects are caused by location at the , and , carbon positions. Comparison of the various data allowed the calculation of increments corresponding to the introduction of fluorinated groups at axial or equatorial positions on the cyclohexane ring. The introduction of fluorine atoms in methoxy and thiomethoxy groups has only a slight effect through the heteroatom on the 13C chemical shifts. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Peracetylated ,- d -glucopyranosyl fluoride and peracetylated ,-maltosyl fluoride

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010
Simone Dedola
The X-ray analyses of 2,3,4,6-tetra- O -acetyl-,- d -glucopyranosyl fluoride, C14H19FO9, (I), and the corresponding maltose derivative 2,3,4,6-tetra- O -acetyl-,- d -glucopyranosyl-(1,4)-2,3,6-tri- O -acetyl-,- d -glucopyranosyl fluoride, C26H35FO17, (II), are reported. These add to the series of published ,-glycosyl halide structures; those of the peracetylated ,-glucosyl chloride [James & Hall (1969). Acta Cryst. A25, S196] and bromide [Takai, Watanabe, Hayashi & Watanabe (1976). Bull. Fac. Eng. Hokkaido Univ.79, 101,109] have been reported already. In our structures, which have been determined at 140,K, the glycopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents, except for the anomeric fluoride (which adopts an axial orientation), in equatorial positions. The observed bond lengths are consistent with a strong anomeric effect, viz. the C1,O5 (carbohydrate numbering) bond lengths are 1.381,(2) and 1.381,(3),Å in (I) and (II), respectively, both significantly shorter than the C5,O5 bond lengths, viz. 1.448,(2),Å in (I) and 1.444,(3),Å in (II). [source]

2,3,4,6-Tetra- O -acetyl-,- d -glucopyranosyl azide

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2008
Simone Dedola
The CuI -catalysed 1,3-dipolar cycloaddition of an azide and a terminal alkyne is becoming an increasingly popular tool for synthetic chemists. This is the most representative of the so-called `click reactions' and it is used to generate 1,4-disubstituted triazoles in high yield. During studies on such cycloaddition reactions, a reduced reactivity of an ,-glucosyl azide with respect to the corresponding ,-anomer was observed. With the aim of understanding this phenomenon, the structure of the title compound, C14H19N3O9, has been determined at 140,K. The glucopyranosyl ring appears in a regular 4C1 chair conformation with all the substituents in equatorial positions, except for the anomeric azide group, which adopts an axial orientation. The observed bond lengths are consistent with a strong anomeric effect, which is reflected in a change in dipolar character and hence reduced reactivity of the ,-glucosyl azide. [source]

Organotin(IV) tryptophanylglycinates: potential non-steroidal antiinflammatory agents; crystal structure of dibutyltin(IV) tryptophanylglycinate

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2009
Mala Nath
Abstract Diorganotin(IV) derivatives of tryptophanylglycine (H2Trp,Gly) with general formula R2Sn(Trp,Gly), where R = Me, n -Bu, Ph and n -Oct, and triorganotin(IV) derivatives R,3 Sn(HTrp,Gly) where R, = Me, n -Bu and Ph, have been synthesized and structurally characterized in the ,solid state as well as in solution on the basis of various spectroscopic techniques, viz. FT-IR, multinuclear 1H, 13C and 119Sn NMR, 119Sn Mössbauer and single crystal X-ray diffraction. These investigations suggest that tryptophanylglycine in R2Sn(Trp,Gly) acts as dianionic tridentate coordinating through carboxylate oxygen [C(O)O,], amino nitrogen (NH2) and N,peptide, while in the case of R,3 Sn(HTrp,Gly), the ligand acts as monoanionic bidentate coordinating through C(O)O, and NH2. This is further confirmed by the single-crystal X-ray structure of n -Bu2Sn(Trp,Gly) which shows that two butyl groups and peptide nitrogen (N,peptide) are in the equatorial positions, while the two axial positions are occupied by the carboxylic oxygen [C(O)O,] and the amino nitrogen (NH2) atom from the same ligand molecule in the distorted trigonal,bipyramidal geometry around tin. The anti-inflammatory (using the carrageenan-induced paw edema bioassay in rats), cardiovascular activities and acute toxicity (LD50) of some of these compounds have been examined. All of the studied R2Sn(Trp,Gly) and Ph3Sn(HTrp,Gly) exhibit very high anti-inflammatory activities comparable to that of phenylbutazone along with high safety margin (LD50 > 400 mg kg,1) with no side effects on the cardiovascular system. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Tetraaqua-1,4O -bis(,-caprolactam-1,O)-,-cyano-1:2,2N:C -pentacyano-2,5C -iron(III)yttrium(III), a novel cyano-bridged dinuclear complex

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2002
Yi He
Using caprolactam as a ligand, the novel title cyano-bridged yttrium(III),ferricyanide complex, [Y(caprolactam)2(H2O)4Fe(CN)6] or [FeY(CN)6(C6H11NO)2(H2O)4], has been synthesized and structurally characterized. The Y atom is seven-coordinate and has approximately pentagonal,bipyramidal stereochemistry, with water molecules occupying apical positions. Of the five ligands in equatorial positions, one is the N -bound bridging cyano group, and flanking this are two O -bound caprolactam moieties, which are markedly inclined towards the bridged ferricyanide moiety such that they partially envelop it. Water molecules occupy the remaining two equatorial positions. The Y,N,C,Fe,C,N sequence of atoms lies on a crystallographic twofold axis and is therefore perfectly linear, which has not been observed previously in cyano-bridged bimetallic complexes. [source]

catena -Poly[[trans -dichlorocopper(II)]-,-1,4,7,10,13,16-hexathiacyclooctadecane- S1:S10]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2001
Alexander J. Blake
In the title complex, [CuCl2(C12H24S6)]n, the CuCl2 unit and the ligand lie on and about inversion centres, respectively. The coordination geometry at CuII is a tetragonally elongated octahedron with the equatorial positions occupied by two chlorides, Cu,Cl 2.2786,(12),Å, and two S donors, Cu,S 2.3710,(13),Å. The apical positions of the octahedron are defined by two S donors at distances of 2.8261,(14),Å from the metal. The macrocyclic ligand adopts a very puckered and distorted conformation. Eight of the 18 torsion angles are less than 90° and all S-donors are oriented exo to the ring. [source]

Head-to-Head Right-Handed Cross-Links of the Antitumor-Active Bis(,- N,N,-di- p -tolylformamidinato)dirhodium(II,II) Unit with the Dinucleotides d(GpA) and d(ApG)

CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2008
Helen
Abstract Reactions of cis -[Rh2(DTolF)2(NCCH3)6](BF4)2 with the dinucleotides d(GpA) and d(ApG) proceed to form [Rh2(DTolF)2{d(GpA)}] and [Rh2(DTolF)2{d(ApG)}], respectively, with bridging purine bases spanning the Rh,Rh unit in the equatorial positions. Both dirhodium adducts exhibit head-to-head (HH) arrangement of the bases, as indicated by the presence of H8/H8 NOE cross-peaks in the 2D ROESY NMR spectra. The guanine bases bind to the dirhodium core at positions N7 and O6, a conclusion that is supported by the absence of N7 protonation at low pH,values and the notable increase in the acidity of the guanine N1H sites (pKa,7.4 in 4:1 CD3CN/D2O), inferred from the pH-dependence titrations of the guanine H8 proton resonances. In both dirhodium adducts, the adenine bases coordinate to the metal atoms through N6 and N7, which induces stabilization of the rare imino tautomer of the bases with a concomitant substantial decrease in the basicity of the N1H adenine sites (pKa,7.0,7.1 in 4:1 CD3CN/D2O), as compared to the imino form of free adenosine. The presence of the adenine bases in the rare imino form is further corroborated by the observation of DQF-COSY H2/N1H and ROE N1H/N6H cross-peaks in the 2D NMR spectra of [Rh2(DTolF)2{d(GpA)}] and [Rh2(DTolF)2{d(ApG)}] in CD3CN at ,38,°C. The 2D NMR spectroscopic data and the molecular modeling results suggest the presence of right-handed variants, HH1R, in solution for both adducts (HH1R refers to the relative base canting and the direction of propagation of the phosphodiester backbone with respect to the 5, base). Complete characterization of [Rh2(DTolF)2{d(GpA)}] and [Rh2(DTolF)2{d(ApG)}] by 2D,NMR spectroscopy and molecular modeling supports anti- orientation of the sugar residues for both adducts about the glycosyl bonds as well as N- and S-type conformations for the 5,- and 3,-deoxyribose residues, respectively. [source]

Structures of N - (2,3,4,6-Tetra- O -acetyl-,- D -glycosyl) thiocarbamic Benzoyl Hydrazine

CHINESE JOURNAL OF CHEMISTRY, Issue 2 2002
Shu-Sheng Zhang
Abstract The crystal structure of N - (2,3,4,6-Tetra- O -acetyl-,- D -glycosyl)-thiocarbamic benzoyl hydrazine (C22H27N3O9S) was determined by X-ray diffraction method. The hexopyranosyl ring adopts a chair conformation. All the ring substituents are in the equatorial positions. The acetoxyl-methyl group is in synclinal conformation. The S atom is in synperiplanar conformation while the benzoyl hydrazine moiety is anti -periplanar. The thiocarbamic moiety is almost coplanar with the benzoyl hydrazine group. There are two intramolecular hydrogen bonds and one intermolecular hydrogen bond for each molecule in the crystal structure. The molecules form a network structure through intermolecular hydrogen bonds. [source]