Influence of OH⋯N and NH⋯O inter- and intramolecular hydrogen bonds in the conformational equilibrium of some 1,3-disubstituted cyclohexanes through NMR spectroscopy and theoretical calculations

The analysis of concentration effects in the (1)H NMR data of cis-3-aminocyclohexanol (ACOL) showed that its diequatorial conformer changes from 60% at 0.01 mol L(-1) to 70% at 0.40 mol L(-1) in acetone-d(6). A similar increase was also observed for the diequatorial conformer of cis-3-N-methylaminocyclohexanol (MCOL), from 32% (CDCl(3) 0.01 mol L(-1)) to 55% (CDCl(3) 0.40 mol L(-1)). The increase in solvent basicity leads to a large stabilization effect for the diequatorial conformer of both compounds too. For ACOL, it changes from 47% (ΔG(eqeq-axax)=0.06 kcal mol(-1)) in CCl(4) to 93% (ΔG(eqeq-axax)=-1.53 kcal mol(-1)) in DMSO, while for MCOL it goes from 7% (ΔG(eqeq-axax)=1.54 kcal mol(-1)) in CCl(4) to 82% (ΔG(eqeq-axax)=-0.88 kcal mol(-1)) in pyridine-d(6). These results indicate that the intramolecular hydrogen bonds (IAHB) OH?N and NH?O stabilize the diaxial conformers of these compounds in a non-polar solvent. For cis-3-amino-1-methoxycyclohexane (ACNE) and cis-3-N-methylamino-1-methoxy-cyclohexane (MCNE) no changes were observed in equilibrium with the variation of solvent polarity. These results indicate for the first time that the IAHB NH?O is not strong enough to stabilize the diaxial conformer of these compounds and that the conformation equilibria of the cis isomers of compounds ACOL and MCOL are influenced only by the IAHB OH?N. Moreover, the presence of a secondary amino group (93% of diaxial conformer in CCl(4)) leads to an IAHB OH?N stronger than in primary and tertiary amino-derivatives (53 and 54% of diaxial conformer, respectively) for 1,3-disubstituted cyclohexanes. Values obtained from the theoretical data through the B3LYP functional are in agreement with the experimental results and indicate that the IAHB strength that influences the conformational equilibrium of these compounds is the IAHB OH?N. Thus, the IAHB NH?O do not stabilize the diaxial conformer of the cis isomer of compounds ACNE and MCNE showing that the diequatorial conformer will always be more stable than the diaxial conformer, independent of concentration or solvent.     

Synthesis,characterization and reactions of the transition metal halogenoalkyl carbocation complexes [Cp(CO)2M{η2-CH2CH(CH2)nX}]PF6 (n = 1–8, 10, M = Fe; n = 3, 4 M = Ru; X = Br,I)

The halogenoalkyl complexes [Cp(CO)₂M{(CH₂)_nX}] (n = 3–10, 12, M = Fe; n = 5, 6, M = Ru, X = Br, I) react with Ph₃CPF₆ in dry CH₂Cl₂ to give the corresponding carbocation complexes [Cp(CO)₂M{η²-(CH₂CH(CH₂)_n?2X}]PF₆ in high yields. NMR evidence indicates that the metals form metallacyclopropane type structures with the carbocation ligand. The reactions of some of the cationic complexes with NaI, PPh₃, Na[Cp(CO)₂Fe] and Et₃N are discussed. NaI and Na[Cp(CO)₂Fe] displace the halogeno-olefin, while PPh₃ adds at the β-CH^δ+ giving the unstable phosphonium adducts [Cp(CO)₂Fe{CH₂CH(PPh₃)(CH₂)_n?2X}]PF₆ which decompose to the halogeno-olefins and the cationic PPh₃ complex [Cp(CO)₂Fe(PPh₃)]⁺. Et₃N causes allylic deprotonation forming internal olefin complexes of the type [Cp(CO)₂Fe{CH₂CHCH(CH₂)_n?3X}]PF₆.     

Strength of Si–H ⋯ B charge-inverted hydrogen bonds in 1-silacyclopent-2-enes and 1-silacyclohex-2-enes

It is shown that the H ? B contacts in 1-silacyclohex-2-enes are clearly stabilizing and strong, whereas those in 1-silacyclopent-2-enes are much weaker. This result is supported by analysis of QTAIM-based parameters and appropriate structural changes taking place upon the open form → closed form transformation and is in full agreement with previous NMR spectroscopic data [Wrackmeyer et al. (2006) Appl Organometal Chem 20:99–105]. Also, the influence of electronic and steric effects originating from the presence of specific substituents on the strength of the H ? B contacts is discussed in detail. Some problems and ideas associated with the use of the so-called open-closed method utilized in assessing values of interaction energies are discussed in detail. Particular attention is paid to the correct choice of reference open systems. It is shown that their partial geometry optimization leads to reliable values of interaction energies.     

Thermodynamic study of (alkyl esters + α,ω-alkyl dihalides) III. HmEandVmE for 20 binary mixtures {xCu − 1H2u − 1CO2C4H9 + (1 − x)α,ω-ClCH2(CH2)v − 2CH2Cl}, where u = 1 to 4, α = 1 and v = ω = 2 to 6

In this article, the experimental data of excess molar enthalpies $H_{\mathrm{m}}^{\mathrm{E}}$ and excess molar volumes $V_{\mathrm{m}}^{\mathrm{E}}$ are presented for a set of 20 binary mixtures comprised of the first four butyl alkanoates (methanoate to butanoate) and five α,ω-dichloroalkanes (1,2-dichloroethane to 1,6-dichlorohexane), obtained at atmospheric pressure and at a temperature of 298.15 K. The results indicate the existence of specific interactions between both kinds of compounds resulting in exothermic processes for most mixtures, except for those containing butyl methanoate which give rise to net endo/exothermic effects. The $V_{\mathrm{m}}^{\mathrm{E}}$ are positive for mixtures of (butyl esters + 1,2-dichloroethane or 1,3-dichloropropane) and negative for the remaining ones. The change in $H_{\mathrm{m}}^{\mathrm{E}}$ with the dichloroethane chain length for a same ester is regular although the $V_{\mathrm{m}}^{\mathrm{E}}$ presents an irregular variation. It can, therefore, be deuced from this that the mixing process involves both effects, exothermic/endothermic and expansion/contraction, simultaneously. The behaviour of the mixtures is interpreted on the basis of the results observed and attributed to different effects taking place among the molecules studied.To improve application of the UNIFAC model using the version of Dang and Tassios, average values were recalculated again for parameters of the ester/chloride interaction, distinguishing, during its application, the functional group of the acid part of the ester. In spite of this, the model does not adequately reproduce the systems’ behaviour.     

Thermodynamics of formation of double salts M2SO4 · M′SO4 · 6H2O and M2SeO4 · M′SeO4 · 6H2O where M denotes Rb,or Cs and M′ denote Co,Ni, or Zn

This paper describes a chemical model that calculates (solid + liquid) equilibria in the (m₁Rb₂SO₄ + m₂CoSO₄)(aq), (m₁Rb₂SeO₄ + m₂CoSeO₄)(aq), (m₁Rb₂SO₄ + m₂NiSO₄)(aq), (m₁Rb₂SO₄ + m₂ZnSO₄)(aq), (m₁Rb₂SeO₄ + m₂ZnSeO₄)(aq), (m₁Cs₂SO₄ + m₂CoSO₄)(aq), (m₁Cs₂SeO₄ + m₂CoSeO₄)(aq), (m₁Cs₂SO₄ + m₂NiSO₄)(aq), (m₁Cs₂SeO₄ + m₂NiSeO₄)(aq), (m₁Cs₂SO₄ + m₂ZnSO₄)(aq), and (m₁Cs₂SeO₄ + m₂ZnSeO₄)(aq) systems, where m denotes molality at the temperature T=298.15 K. The Pitzer ion-interaction model has been used for thermodynamic analysis of the experimental osmotic and solubility data presented in the literature. The thermodynamic functions needed (binary and ternary parameters of ionic interaction, thermodynamic solubility products) have been calculated and the theoretical solubility isotherm has been plotted. The mixing parameters {θ(MN) and ψ(MNX)} have been chosen on the basis of the compositions of saturated ternary solutions and data on the binary solubility of the sulfate M₂SO₄. M^′SO₄ · 6H₂O double salts in water. To validate the mixing solutions model two different approaches have been used in evaluation of the ternary parameters: (I) preserving the same value of the binary mixing θ(MN) for the corresponding chloride, bromide, sulfate, and selenate systems with the same cations, and (II) with constant θ(MN) value (set equal to −0.05) for the all 11 sulfate and selenate systems. Very good agreement between experimentally determined and model predicted solubilities has been found. Important thermodynamic characteristics (thermodynamic solubility products, standard molar Gibbs free energy of formation) of the solid phases (simple salts, six sulfate – M₂SO₄ · M^′SO₄ · 6H₂O, and five selenate – M₂SeO₄ · M^′SeO₄ · 6H₂O – double salts) crystallizing in the systems under consideration are determined.     

Synthesis and structural characterisation of new ettringite and thaumasite type phases: Ca6[Ga(OH)6·12H2O]2(SO4)3·2H2O and Ca6[M(OH)6·12H2O]2(SO4)2(CO3)2, M = Mn,Sn

Investigations into the formation of new ettringite-type phases with a range of trivalent and tetravalent cations were carried out to further study the potential this structure type has to incorporate cations covering a range of ionic radii (0.53–0.69 Å). We report the synthesis and structural characterisation of a new ettringite-type phase, Ca₆[Ga(OH)₆·12H₂O]₂(SO₄)₃·2H₂O, which was indexed in space group P31c with the unit cell parameters a = 11.202(2) Å, c = 21.797(3) Å and two new thaumasite-type phases Ca₆[M(OH)₆·12H₂O]₂(SO₄)₂(CO₃)₂, M = Mn, Sn which were indexed in space group P6₃ with the unit cell parameters a = 11.071(5) Å, c = 21.156(8) Å and a = 11.066(1) Å, c = 22.420(1) Å respectively. These new phases show the versatility of the ettringite family of structures to tolerate a large range of cation sizes on the octahedral M site and highlights the preference of tetravalent cations to crystallise with the thaumasite structure over the ettringite structure.     

Study on the cesium Tutton compounds,Cs2M(XO4)2∙6H2O (M = Mg,Co, Zn; X = S,Se): Preparation,X-ray powder diffraction and infrared spectra

The crystallization processes in the three-component systems Cs₂SO₄–MSO₄–H₂O (M = Mg, Co, Zn) have been studied at 25 °C. It has been established that cesium Tutton compounds, Cs₂M(SO₄)₂·6H₂O (M = Mg, Co, Zn; X = S, Se), crystallize from the ternary solutions within large concentration ranges. The double salts were identified by means of X-ray powder diffraction and infrared spectroscopy. Infrared spectra of the cesium compounds are presented and discussed with respect to both the normal modes of the tetrahedral ions and the water molecules. The water librations are also discussed. The strength of the hydrogen bonds formed in the cesium salts as deduced from the frequencies of ν_OH is commented. The analysis of the spectra reveals that stronger hydrogen bonds are formed in the cesium selenates as compared to those in the respective sulfates due to the stronger proton acceptor ability of the selenate ions.     

Theoretical and Experimental Studies on the Metal Complex of Diethylenetriamino-trioxo-molybdenum(Ⅵ)[MoO3(NH2C2H4NHC2H4NH2)]

For diethylenetriamino-trioxo-molybdenum(VI), density functional theory (DFT) method calculations of the structure, atomic charge distributions, electronic spectra, natural po- pulation analyses and thermodynamic properties at different temperatures have been performed by B3LYP method using LANL2DZ, CEP-121G and CEP-31G basis sets, respectively. The calculated results show that B3LYP/LANL2DZ method can best reproduce the molecular structure. The atomic charge distribution analyses indicate that during forming the complex, the ligand of diethyl- enetriamine donates negative charges to MoO3 and these charges are accepted by molybdenum(VI) atom as well as three oxygen atoms. The electronic spectra calculations indicate that B3LYP/ LANL2DZ results are nearest to experimental data among the three methods and electronic tran- sitions are mainly derived from the contribution of bands π→π*. The calculation of the second order optical nonlinearity was carried out, and the molecular hyperpolarizability was 0.7881*10-30 esu.     

Double beryllium iodate dihydrates,M2Be(IO3)4·2H2O (M = K,NH4+, Rb): Preparation,X-ray powder diffraction and vibrational spectra

The solubilities in the three-component systems MIO₃–Be(IO₃)₂–H₂O (M = K, NH₄⁺, Rb, Cs) were studied at 25 °C by the method of isothermal decrease of supersaturation. It has been established that double salts, K₂Be(IO₃)₄·2H₂O, (NH₄)₂Be(IO₃)₄·2H₂O, and Rb₂Be(IO₃)₄·2H₂O, crystallize from the ternary solutions within wide concentration ranges. Both the X-ray powder diffraction and the spectroscopic studies (infrared and Raman) reveal that the title compounds are isostructural. They crystallize in the monoclinic space group P2/m with lattice parameters: K₂Be(IO₃)₄·2H₂O – a = 14.218(5) Å, b = 6.747(2) Å, c = 5.765(2) Å, β = 98.74(4)°, V = 546.6(2) Å³; (NH₄)₂Be(IO₃)₄·2H₂O – a = 14.414(4) Å, b = 6.838(2) Å, c = 5.947(2) Å, β = 99.52(4)°, V = 578.0(2) Å³; Rb₂Be(IO₃)₄·2H₂O – a = 14.423(4) Å, b = 6.867(2) Å, c = 5.743(3) Å, β = 98.15(3)°, V = 562.9(3) Å³.Infrared spectroscopic experiments show that comparatively strong hydrogen bonds are formed in the potassium and rubidium salts as deduced from the wavenumbers of ν_OD of matrix-isolated HDO molecules (isotopically dilute samples) owing to the strong Be–OH₂ interactions (synergetic effect). However, the IO₃⁻ ions in the ammonium compound are involved in hydrogen bonds with NH₄⁺ ions additionally to those with water molecules and as a result of these intermolecular interactions the proton acceptor strength of the iodate ions decreases (anti-cooperative effect), thus leading to the formation of weaker hydrogen bonds in this compound (bonds of moderate strength) as compared to those formed in the potassium and rubidium ones. The normal vibrations of other entities (IO₃⁻ ions and BeO₄ tetrahedra (skeleton vibrations)) are also discussed.     

The Synthesis and Characterization of [4-CH3OC6H4CH2NH3]4P2O7·6H2O

Inorganic–organic hybrid compounds exhibit interesting properties in several application areas. In this regard, chemical preparation and characterization by X-ray diffraction, thermal analysis, and IR spectroscopy are given for a new organic cation diphosphate [4-CH₃OC₆H₄CH₂NH₃]₄P₂O₇·6H₂O. This later crystallizes in a C2/c unit cell with a = 38.238(6)Å, b = 6.453(1)Å, c = 16.942(7)Å; β = 97.60(4)°; Z = 4; and V = 4144(2)ų and D_x = 1.377 g·cm^?3. Its crystal structure has been determinated and refined to R = 0.044, using 7978 independent reflections. This atomic arrangement consists of inorganic layers built up from P₂O₇ ^4? anions and water molecules. On these layers, which are parallel to the (b, c) planes, the (4-CH₃OC₆H₄CH₂NH₃)⁺ cations are anchored through multiple hydrogen bonds.     

Bonding situation and stability of η1- and η6-bonded heteroarene complexes M(η1-EC5H5)6 and M(η6-EC5H5)2 (M = Cr,Mo, W; E = N,P, As,Sb, Bi)

Density functional calculations at the BP86/TZ2P level are reported for the pseudo-octahedral heteroarene complexes M(η¹-EC₅H₅)₆ and for the sandwich complexes M(η⁶-EC₅H₅)₂ (M = Cr, Mo, W; E = N, P, As, Sb, Bi). The complexes M(CO)₆ and M(η⁶-C₆H₆)₂ have been calculated for comparison. The nature of the metal–ligand interactions was analyzed with the EDA (energy decomposition analysis) method. The calculated bond dissociation energies (BDE) of M(η¹-EC₅H₅)₆ have the order for E = P > As > N > Sb ? Bi and for M = Cr < Mo < W. All hexaheteroarenes bind more weakly than CO in M(CO)₆. Except for pyridine, which is the weakest η⁶-bonded ligand, the trend in the BDE of the M(η⁶-EC₅H₅)₂ complexes is opposite to the trend of the M(η¹-EC₅H₅)₆ complexes NC₅H₅ < PC₅H₅ < AsC₅H₅ < SbC₅H₅ < BiC₅H₅. The opposite trend is explained with the different binding modes in M(η⁶-EC₅H₅)₂ and M(η¹-EC₅H₅)₆. The bonding in the former complexes mainly takes place through the π electrons of the ligand which are delocalized over the ring atoms while the bonding in the latter takes place through the lone-pair electrons of the heteroatoms E. The Lewis basicity of the group-15 heterobenzenes EC₅H₅ becomes weaker for the heavier elements E. The occupied π orbitals of the heterobenzene ring become gradually more polarized toward the five carbon atoms in the heavier arenes EC₅H₅ which induces stronger metal-carbon bonds in M(η⁶-EC₅H₅)₂ and weaker metal-E bonds. The EDA calculations show that the nature of the M-EC₅H₅ bonding in M(η¹-EC₅H₅)₆ is similar to the M–CO bonding in M(CO)₆. Both types of bonds have a slightly more covalent than electrostatic character. The π orbital interactions in the chromium and molybdenum complexes of CO and heterobenzene are more important than the σ interactions. This holds true also for the tungsten complexes of CO and the lighter heteroarenes while the σ- and π-bonding in the heavier W(η¹-EC₅H₅)₆ species have similar strength. The EDA results also show that the nature of the bonding in the sandwich complexes M(η⁶-EC₅H₅)₂ is very similar to the bonding in the bisbenzene complexes M(η⁶-C₆H₆)₂. The orbital interactions contribute for all metals and all arene ligands about 60% of the attractive interactions while the electrostatic attraction contributes about 40%. The largest contribution to the orbital term comes always from the δ orbitals. The calculations predict that the relative stability of the sandwich complexes M(η⁶-EC₅H₅)₂ over the octahedral species M(η¹-EC₅H₅)₆ increases when E becomes heavier and it increases from W to Mo to Cr when E = N, P, As.     

Structural and Physicochemical Studies of [4-ClC6H4CH2NH3]4Li2P6O18·4H2O

The crystal structure of a new organic cation cyclohexaphosphate, [4-ClC ₆ H ₄ CH ₂ NH ₃ ] ₄ Li ₂ P ₆ O ₁₈ .4H ₂ O, is reported. It crystallizes in the triclinic system (space group P-1) with the following unit-cell parameters: a = 9.628(8), b = 12.801(9), c = 19.528(6) Å, α = 78.60(4)°, β = 83.00(5)°, β = 89.98(4)°, Z = 2, and V = 2341(3)Å ³ . The structure has been solved using direct methods and refined by least-squares analysis [R ₁ = 0.043, wR ₂ = 0.108]. The structure can be described as infinite anionic layers with composition of [Li ₂ (P ₆ O ₁₈ )(H ₂ O) ₄ ] ^{4 ?} and parallel to the ac plane. The organic groups are located in the accessible voids. The molecules are stabilized by O─H…O and N─H…O types of intermolecular hydrogen bonds in the unit cell in addition to Van der Waals forces.     

Reactions of the 6,6-dimethylcyclohexadienyl anion with MCl4(PMe3)2 complexes (M = Hf,Nb) – Isolation of complex intramolecular coupling products

Reactions of NbCl₄(PMe₃)₂ and HfCl₄(PMe₃)₂ with four equivalents of the 6,6-dimethylcyclohexadienyl anion lead to Nb(6,6-dmch)[η^2,4-(dmch)₂](PMe₃) and Hf(6,6-dmch)[η^3,4-(dmch)₃](PMe₃). Each complex has been crystallographically characterized, and found to contain one η⁵-bound 6,6-dmch ligand, with the other dmch units coupled together to yield olefin, allyl, and diene coordinations, resulting in 18 electron configurations for these compounds.     

Effects of substituents and charge on the RCHO⋯X–Y {X = Cl,Br, I; Y = –CF3, –CF2H, –CFH2, –CN, –CCH, –CCCN; R = –OH, –OCH3, –NH2, –O−} halogen-bonded complexes

Structural Chemistry - Noncovalent interactions involving halogen bonding interactions, one of the emerging interactions due to its directionality, have been a subject of interest for various...     

Solubilities,densities and refractive indices for the ternary systems ethylene glycol + MCl + H2O (M = Na,K, Rb,Cs) at (15 and 35) °C

The solubilities, densities and refractive indices data for the four ternary systems ethylene glycol + MCl + H₂O (M = Na, K, Rb, Cs) at different temperatures were measured, with mass fractions of ethylene glycol in the range of 0 to 1.0. In all cases, the presence of ethylene glycol significantly reduces the solubility of the salts in aqueous solution. The experimental data of density, refractive index and solubility of saturated solutions for these systems were correlated using polynomial equations as a function of the mass fraction of ethylene glycol. On the other hand, the refractive index and density of unsaturated solutions was also determined for the four ternary systems with varied unsaturated salt concentrations. Values for both the properties were correlated with the salt concentrations and proportions of ethylene glycol in the solutions.