Vibronic spectra and normal coordinate analysis of substituted anilines—I. 2,3-, 2,4-, and 2,5-dimethylanilines

Vibronic spectra of 2,3-, 2,4-, and 2,5-dimethylanilines (DMA) have been recorded in the vapor phase and analysed primarily for ascertaining the frequencies of certain low lying fundamentals (< 1000 cm⁻¹) which were observed earlier in infrared and Raman spectra with rather poor intensities. In most cases, the investigation of vibronic spectra has supported the data observed in infrared and Raman spectra. However, a new frequency has been observed at ∼120 cm⁻¹ in each molecule and has been assigned to the CNH₂ out-of-plane wag. A detailed analysis of the vibronic spectra of these three molecules revealed that an interaction-induced blue-shift of nearly 1700 cm⁻¹ is caused in the (0, 0) band of all the three DMAs due to an electrostatic interaction between the NH₂ and CH₃ groups.The normal coordinate analyses (NCA) of the above three molecules have been carried out using a general valence force field (GVFF) with 21 principal and 30 interaction force constants, assuming an averaged structure, a planar geometry, and a C_s symmetry in each case. The fundamental frequencies were mostly taken from an earlier work reported from this laboratory. Some frequencies were also picked up from the investigation of the vibronic spectra reported herein. The force field calculations were carried out using the least-squares iterative technique. During final calculations, all the 51 force constants were allowed to iterate simultaneously, which reproduced the 52 experimentally observed fundamentals out of the 54 (35a′+ 19a″) expected ones within an average error of ± 1.0% with a reasonable potential energy distribution (PED) among the various normal modes.     

Intramolecular force field for the Ni(NH3)62+ 25 atom system in the octahedral point molecular group

On the basis of new and recent experimental data, a complete full normal coordinate analysis has been undertaken for the 25 atom system Ni(NH₃)²⁺₆ in the salt Ni(NH₃)₆Cl₂, assuming a perfect octahedral environment and freely rotating NH₃ groups about the NiN axis. The calculation has been carried out for two main reasons: Firstly, there is no strong experimental evidence to support a descent of symmetry from O_h to D_3d, and secondly, previous intensity calculations in centro-symmetric coordination compound of the transition metal ions (R. Acevedo, in Vibronic Processes in Inorganic Chemistry (edited by C. D. Flint), NATO ASI Series C, 288, 139 (1988) [1] and Refs therein), have shown the sensitivity of the calculated vibronic intensity on the details of the intermolecular force field.Two different modified general valence force fields are put forward to describe the dynamics of this polyatomic system and both of them give strong support to the spectral assignments given in the present work. Finally, and for the sake of completeness, values for the mean amplitudes of vibration are reported at different temperatures.     

Microwave spectrum,conformational preference,barrier to internal rotation,and centrifugal distortion of 1-amino-2-propanol

The microwave spectrum of CH₃CH(OH)CH₂NH₂ has been investigated in the 26.5–39.7 GHz region. One rotamer with an intramolecular hydrogen bond formed between hydroxyl and ammo groups was assigned. This conformation is also characterized by having the methyl group anti to the amino group. Other forms, if they exist, must be at least 1 kcal mole^?1 less stable. Four vibrationally excited states belonging to three different normal modes were assigned and the barrier to internal rotation of the methyl group was found to be 3173 ± 100 cal mole^?1.     

Infrared spectra of the ammonium ion in ammonium metavanadate NH4VO3

The ND stretching modes of isotopically dilute NH₃D⁺ ions in NH₄VO₃ are in agreement with the predicted splitting into C_s, C_s and C₁(2) components under C_s site symmetry for the NH⁺₄ ion. The three bands observed represent the three NH bonding distances in the crystal, and the position, shape and low temperature behaviour of each band confirms the existence of two types of hydrogen bonding in NH₄VO₃. The low temperature infrared modes of NH⁺₄ and ND⁺₄ in NH₄VO₃ and ND₄VO₃, respectively, can be assigned under space group Pbcm. Temperature dependence of these modes also reflects the presence of both normal and bifurcated hydrogen bonds in NH₄VO₃.     

The rotational barrier in dimethyl acetylene and related molecules

The rotational barriers in dimethyl acetylene (CH₃CCCH₃), diamino acetylene (H₂NCCNH₂), dihydroxy acetylene (HOCCOH), methyl trifluoro methyl acetylene (CF₃CCCH₃), silyl methyl acetylene (SiH₃CCH₃), propene, cis and trans 2-butene and ethane were studied by ab initio molecular orbital methods using various basis sets. The eclipsed structure for dimethyl acetylene and its CF₃ and SiH₃ analogs was found to be the most stable, as has been inferred from experimental work, and the barrier height for these compounds has been predicted. The barriers in the OH and NH₂ substituted acetylenes, propene, butene and ethane were studied in order to more clearly understand the important influences in determining the barrier mechanism; specifically, the delocalized molecular orbital and Pauling VB model have been compared.     

Conformational studies of some 2-phenylpropyl derivatives by NMR spectroscopy and use of lanthanide shift reagents

The conformational distribution of CH₃CH(Ph)CH₂X (X = OH, OCH₃, NH₂ Cl) has been studied by NMR and IR spectroscopy. The results are interpreted in favour of the conformers with methoxy- or chloro-groups anti to the phenyl group, but the amino group anti to the methyl group. For the alcohol both forms are about equally populated. It is suggested that intra-molecular hydrogen bonding might be affecting the conformational equilibria when X = OH, NH₂.     

Synthesis and crystal structure of nitrosoruthenium aquadiammine complex, [Ru(NO)(NH3)2Cl2(H2O)]Cl·H2O

The reaction between [RuNO(NH₃)₂(NO₂)₂OH] and an excess of 3 M HCl leads to denitration of the starting complex and precipitation of [Ru(NO)(NH₃)₂Cl₃]. Crystals of the tittle complex have been obtained by evaporation of the mother liquor at ambient temperature. The crystal structure of the product has been determined. The linear nitroso group and a water molecule are coordinated in the trans positions, three nitrogen atoms from NO and NH₃ ligands occupy the coordination octahedron face.     

Vibrational spectra and normal coordinate analysis of plant growth regulator 1-naphthalene acetamide

FT Raman and IR spectra of the biologically active molecule, 1-naphthalene acetamide (NA) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers of NA have been calculated with the help of B3LYP density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The downshifting of NH₂ stretching wavenumber indicates the formation of intermolecular N–H?O hydrogen bonding. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.     

Unusual NH Activation of 2‐Aminopyrimidine: Supramolecular Assembly into an AgI Metal–Organic Framework

A rare example of coordination at the amino group of NH₂pym (2‐aminopyrimidine) relevant to N? H activation is described that leads to a novel Ag^I–imide 3D metal–organic framework (MOF). The coordination of Ag^I to NH₂pym produced an electron‐withdrawing effect and thus increased its acidity, which facilitated the N? H activation and the subsequent formation of the Ag–imide bond. A cooperative metalation/deprotonation process for the N? H activation of NH₂pym is suggested. Interestingly, photoluminescence of 1 is switched on at the low temperature of 77 K.     

Hydrolysis of coordinated aminoacetonitrile in a platinum(IV) complex. Crystal structure of [PtPy(NH<Subscript>2</Subscript>CH<Subscript>2</Subscript>COO)Cl<Subscript>3</Subscript>]

Heating of a hydrochloric acid solution of trans-PtPy(NH₂CH₂CN)Cl₄ results in the hydrolysis of coordinated aminoacetonitrile to aminoacetic acid with the formation of a five-membered chelate ring attached to platinum through the nitrogen atom of the amino group and the oxygen atom of the carboxy group. X-ray diffraction analysis of [PtPy(NH₂CH₂COO)Cl₃] is carried out. The crystals are monoclinic: space group C2/c, a = 21.704(2), b = 8.7027(7), c = 15.576(1) Å, β = 126.606(1)^o, V = 2361.8(3) ų, Z = 8; R _hkl = 0.057, wR = 0.141. In the neutral complex, the Pt atom has a distorted octahedral coordination. The equatorial plane is formed by a Cl atom (Pt-Cl, 2.284(3) Å), the N atom of the Py molecule (Pt-N, 2.062(8) Å), and the N and O atoms of the bidentate-chelating ligand (Pt-N, 2.039(8); Pt-O, 2.026(7) Å); two Cl atoms are arranged in the apical positions (Pt-Cl, 2.301(3) and 2.312(3) Å). The five-membered chelate ring has a flattened gauche conformation with an NCCO torsion angle of 19(1)°.     

Separation of 97Ru from niobium target using PEG based aqueous biphasic systems

Separation of no-carrier-added (NCA) ⁹⁷Ru from bulk niobium target has been carried out for the first time using green analytical technique, aqueous biphasic system. 50 % (w/v) polyethylene glycol (PEG)-4000, against 2 M solutions of various salts such as Na-citrate, Na-tartarate, Na-malonate, Na₂CO₃, NaHSO₃, Na₂SO₄, Na₂S₂O₃ K₂HPO₄, K₃PO₄, K₂CO₃ and 4 M KOH were employed at room temperature for the extraction of NCA ⁹⁷Ru from bulk niobium. Influence of molecular weight of PEG rich phase as well as pH of some salt rich phase (e.g., Na-tartarate) on the extraction behaviour of NCA ⁹⁷Ru into PEG rich phase was also observed. In the presence of sodium-tartarate salt solution, when volume of PEG-4000: Na-tartarate was 3:1, 91 % of NCA ⁹⁷Ru was extracted into the PEG rich phase without any contamination of niobium target. Dialysis of PEG rich phase containing NCA ⁹⁷Ru was carried out against deionised water to obtained pure NCA ⁹⁷Ru.     

Synthesis,spectroscopic analysis and structure deduction of gold(III), palladium(II) and platinum(II) complexes with the tripeptide glycyl-<Emphasis Type="SmallCaps">l</Emphasis>-phenylalanyl-glycine

The coordination behaviour of the tripeptide glycyl-l-phenylalanyl-glycine (H-Gly-Phe-Gly-OH) with Au(III), Pd(II), and Pt(II) in both solution and in the solid state has been investigated experimentally. In addition, quantum chemical calculations have been carried out with a view to obtain the structures and spectroscopic properties of the ligand and its complexes. Both in solution and in the solid state the tripeptide interacts in a tetradentate manner with the Au(III) and Pd(II) ions through the NH₂, two deprotonated amide N atoms and the COO⁻group, forming [Au(H-Gly-Phe-Gly-OH)H₋₂)] × H₂O and [Pd(H-Gly-l-Phe-Gly-OH)H₋₂)]Na × H₂O complexes. The MN₃O chromophores are calculated to be near planar. Interaction with cisplatin leads to the formation of a mononuclear complex with tridentate coordination of the ligand by NH₂ and two N- atoms from the deprotonated amide groups ([Pt(H-Gly-l-Phe-Gly-OH)H₋₂)NH₃] × 2H₂O). The fourth coordination position of the Pt(II) is occupied by an NH₃ ligand. The PtN₄ chromophore is flat with a deviation from planarity of 0.3°. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural diversity of homobinuclear transition metal complexes of the phenazine ligand: theoretical investigation

DFT/BP86 calculations have been carried out on a series of hypothetical binuclear compounds of general formula (L₃M)₂(C₁₂N₂H₈) (M?=?Sc–Ni, L₃?=?(CO)₃, (PH₃)₃ and Cp^?, and C₁₂N₂H₈?=?phenazine ligand-denoted Phn). The various structures with syn and anti configurations have been investigated, in order to determine the phenazine’s coordination to first-row transition metals of various spin states with syn and anti conformations. The lowest energy structures depend on the nature of the metal, the spin state, and the molecular symmetry. This study has shown that the electronic communication between the metal centers depends on their oxidation state and the attached ligands. The tricarbonyl and the triphosphine ligands gave rise to comparable results in terms of stability order of isomers, metal-metal bond distances, and the coordination modes. Metal-metal multiple bonding has been evidenced for Sc, Ti, and V complexes to compensate the electronic deficiency. The Cr, Mn, Fe, Co, and Ni-rich metals prefer the anti conformation due to the enhancement of the metal valence electron count. The spin density values calculated for the triplet and quintet spin structures point out that the unpaired electrons are localized generally on the metal centers. The Wiberg bond indices are used to evaluate the metal-metal bonding. Furthermore, calculations using the BP86-D functional which take into account the attractive part of the van der Waals type interaction potential between atoms and molecules that are not directly connected to each other gave comparable results to those obtained by BP86 functional in terms of coordination modes, HOMO-LUMO gaps, metal-metal bond orders, and the stability order between isomers, but with slight deviation of M–C, M–N, and M–M bond distances not exceeding 3%.     

Comparative study on the nonadditivity of methyl group in lithium bonding and hydrogen bonding

Quantum chemical calculations at the second‐order Moeller–Plesset (MP2) level with 6‐311++G(d,p) basis set have been performed on the lithium‐bonded and hydrogen‐bonded systems. The interaction energy, binding distance, bond length, and stretch frequency in these systems have been analyzed to study the nonadditivity of methyl group in the lithium bonding and hydrogen bonding. In the complexes involving with NH₃, the introduction of one methyl group into NH₃ molecule results in an increase of the strength of lithium bonding and hydrogen bonding. The insertion of two methyl groups into NH₃ molecule also leads to an increase of the hydrogen bonding strength but a decrease of the lithium bonding strength relative to that of the first methyl group. The addition of three methyl groups into NH₃ molecule causes the strongest hydrogen bonding and the weakest lithium bonding. Although the presence of methyl group has a different influence on the lithium bonding and hydrogen bonding, a negative nonadditivity of methyl group is found in both interactions. The effect of methyl group on the lithium bonding and hydrogen bonding has also been investigated with the natural bond orbital and atoms in molecule analyses. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

One-pot synthesis of ortho-hydroxycinnamate esters

Phenols are converted to salicylaldehydes with paraformaldehyde, MgCl₂-Et₃N in THF, and subsequent treatment with methyl (triphenylphosphoranylidene)acetate gave the corresponding methyl ortho-hydroxycinnamate derivatives. The sequence is conveniently carried out as a one-pot procedure.     

Infrared spectra of the ammonium ion in ammonium hexavanadate (NH4)2V6O16

The infrared bands of the NH⁺₄ and ND⁺₄ groups in (NH₄)₂V₆O₁₆ and its deuterated analogue can be assigned with a fair amount of certainty at 90 K under the space group P2₁/m(C²_2h). The ND stretching modes of isotopically dilute NH₃D⁺ ions in the crystal are in agreement with the predicted splitting into C_s, C_s and C₁(2) components. The frequencies, shapes and temperature dependence of these modes suggest that both normal and bifurcated hydrogen bonds are formed. The latter closely resembles corresponding bonds in NH₄VO₃, but the normal hydrogen bonds are not as strong as the similar bonds in NH₄VO₃. This can be expected as NH⁺₄ ions are dynamic in character in (NH₄)₂V₆O₁₆ and remain so down to temperatures of 90 K.     

A Theoretical Study of Amine Bonding in Titanium Alkoxide Adducts

Summary. DFT calculations were carried out on Ti₂(OCH₃)₈ (NH₂CH₃)₂ and Ti₂(OCH₃)₈(NH₃)₂, which are model compounds for the previously isolated amine adducts Ti₂(OR)₈(NH₂ R′)₂. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on Ti t_2g-like orbitals.     

Synthesis,Characterization, and Energetic Properties of Nitroso Compounds

Sodium and potassium methyl(nitroso)amide (M[CH₃N₂O], M = Na ( 1 ), K ( 2 )) were prepared by the reaction of monomethylhydrazine with iso‐pentyl nitrite or n‐butyl nitrite and a suitable metal ethoxide (M[CH₃CH₂O], M = Na, K) in an ethanol‐ether mixture. The reaction of monomethylhydrazine with a small excess of iso‐pentyl nitrite or n‐butyl nitrite and in the absence of a metal ethoxide led to the formation of N‐nitroso‐N‐methylhydrazine (CH₃(NO)N–NH₂, ( 3 )). Alternatively, compound 3 was prepared by the amination reaction of 1 or 2 using the sodium salt of HOSA in ethanol solution. Compounds 1–3 were characterized using elemental analysis, differential scanning calorimetry, mass spectrometry, vibrational (infrared and Raman) and UV spectroscopy and multinuclear (¹H, ¹³C and ¹⁵N) NMR spectroscopy. For compounds 1–3 , several physical and chemical properties of interest and sensitivity data were measured and for compound 3 thermodynamic and explosive properties are also given. Additionally, the solid‐state structure of compound 3 was determined by single‐crystal X‐ray analysis and the structures of the cis‐ and trans‐[CH₃N₂O]^– anions and that of 3 were optimized using DFT calculations and used to calculate the NBO charges.     

Organo-imido alkoxides of tungsten(VI). The crystal and molecular structures of [W(NPh)(μ-OMe)(OMe)3]2 and [W(NPh)(OCMe3)3Cl(NH2CMe3)]

Reaction of phenylimido tungsten tetrachloride with MeOH and t-butylamine gave the dimeric complexes [W(NPh)(μ-OMe)(OMe)₃]₂ and [W(NPh)(μ-OMe)(OMe)₂Cl]₂. With ethanol [W(NPh)(μ-OEt)(OEt)₂Cl]₂ was formed whereas isopropyl and neopentyl alcohols gave the monomeric complexes [W(NPh)(OR)₄(NH₂CMe₃)](R = CHMe₂, CH₂CMe₃); t-butanol gave [W(NPh)(OCMe₃)3Cl(NH₂CMe₃)] which could not be converted to [W(NPh) (OCMe₃)₄]. Further reaction of [W(NPh)(μ-OMe)(OMe)₃]₂ with o-HOC₆H₄CH = NC₆H₃Me₂(salim-H) gave the salicylaldimine complex [W(NPh)(OMC)₃(salim)]. The products were characterised by analytical data, IR, ¹H NMR, ¹³C NMR and mass spectroscopy. The crystal and molecular structures of the title complexes have been determined from single crystal X-ray diffractometer data. Crystals of [W(NPh)(μ-OMe)(OMe)₃]₂are triclinic with a = 8.473(7), b = 10.776(5), c = 7.683(Å, α = 102.26(3), β = 102.68(4), γ = 71.13(6)°, space group P$\text{1}$ Crystals of 3) [W(NPh)(OCMe₃)₃Cl(NH₂CMe₃) are monoclinic with a = 9.341(2), b = 29.608(7), c = 10.257(2) Å, β = 106.28(2)°, space group, P2₁/c. Both structures were solved by Patterson and Fourier methods and refined to R = 0.075 for the 1022 observed data of [W(NPh) (μ-OMe)(OMe)₃]₂ and to R = 0.074. For the 2033 observed data of [W(NPh)(OCMe₃)₃Cl(NH₂CMe₃). The former molecule is shown to be a dimer, the two halves of the molecule being related by a centre of symmetry. Both W atoms adopt a distorted octahedral coordination geometry and they are linked by two methoxy bridges. Trans to one of the bridging donors is the phenyl imido group with a WN bond length of 1.61(4) Å; the remaining coordination sites are filled with methoxy groups. The structure of W(NPh)(OCMe₃)₃ Cl(NH₂CMe₃) is monomeric with the phenylimido group trans to the NH₂CMe₃ ligand in a distorted octahedral coordination geometry. Remaining sites are filled with the chloride and 3 OCMe₃ ligands. The WN (imido) bond length is 1.71(2) Å, whilst WN(amine) is 2.40(2) Å