CDCl3 Solution Research Articles

High-frequency hydrogen-bond stretching vibrations as indicators of the character of molecular aggregation in solutions

A complementary analysis of the theoretically predicted structure, stability, and vibrational spectra of the H-bonded clusters with an emphasis on the high-frequency IR range typical of proton vibrations makes it possible to judge the probable character of molecular aggregation in solutions if it is driven by H-bonding. This is illustrated by an example of pentamethylene diaziridine (PMDA) solutions in CDCl3, the spectra of which involve two characteristic bands with peaks at 3213 and 3265 cm−1, the relative intensity of which depends on the PMDA concentration. The analysis showed that the basic building blocks of the crystal structure are scarcely present in the solutions. Actual aggregates are probably stabilized by bi- and trimolecular joints. At the PMDA–chloroform interface, anti single H-bridges between molecules should prevail. At the low concentrations, syn (twisted) double H-bond bridges between the neighboring molecules screened from the solvent can be formed. Anti (nearly planar) double H-bridges should appear at a concentration no lower than 0.5 M, while adjacent syn and anti joints (arranged successively) can probably be found in the inner parts of the aggregates above a content of 0.8 M. The larger H-bonded rings seem to be formed at still higher concentrations. The ring-like joints are expected to be arranged successively with no fused H-bonded rings, which form the basis of the crystal structure. The increase in the experimental IR absorption within the lower-frequency band with an increase in the concentration of PMDA solutions reflects the better structuring inside PMDA aggregates predetermined by the alternation of anti, equatorial, and syn arrangement of the neighboring hydrophobic pentamethylene fragments. This variant becomes possible in large clusters if they have a helical staircase organization.

Solution and solid state structures of lanthanides(III) and uranyl(II) complexes of tripodal tris(2-pyridyl)-containing ligand on Ph3P(O) platform

Reaction of tris[2-(2′-pyridylmethoxy)phenyl]phosphine oxide (L) with f-element nitrates resulted in 1:1 complexes. The isolated complexes of ligand L with La(III), Eu(III), Tb(III), and U(VI) nitrates, and with La(III) chloride were studied in the solid state and solution by IR, Raman, and NMR spectroscopy, X-ray analysis, and also DFT calculations. Composition and structure of the complexes vary with lanthanide cation radius. According to the data of elemental analysis, vibrational spectroscopy, and X-ray diffraction, the ligand is coordinated in tridentate mode in crystalline La(III) and solid Eu(III) complexes: [Ln(OPO,N,Oeth-L)(H2O)(O,O-NO3)3], and in monodentate mode in crystalline complex [Tb(OPO-L)(H2O)2(O,O-NO3)3]. Nitrogen atoms of pyridine fragments of the ligand not involved in coordination produce intra- and intermolecular H-bonds with coordinated water molecules in the second coordination sphere of Ln(III). According to IR, NMR spectrometry, and DFT calculations, the structure of coordination polyhedron of the main species of Ln(III) complexes in acetonitrile solutions is retained including coordination of one of pyridine fragments in the second coordination sphere: [Ln{OPO,N,(N*),Oeth-L}(H2O)(O,O-NO3)3] and [Tb{OPO,(N*)-L}(H2O)2(O,O-NO3)3], where Ln = La, Eu, and N* is the nitrogen atom of pyridine fragment producing intramolecular H-bond with coordinated water molecule. According IR and Raman spectroscopy, ligand L is coordinated in bidentate mode in solid complex [UO2(OPO,N-L)(O,O-NO3)], and uncoordinated nitrogen atoms remain free. Solution structure of uranyl complex is labile and depends on solvent nature. Equilibria of complex species with variable coordination of nitrate ions, ligand L, and with probable involvement of water take place in CD3CN and CDCl3 solutions. Photophysical properties of the prepared Eu(III) and Tb(III) complexes were studied. The preliminary assessment of extraction properties of compound L was made. Stability of studied compounds in acetonitrile solutions was examined, and the structure of one of protolysis product of Eu(III) complex, [Eu(LH)(H2O)(NO3)4], was established by micro-IR and X-ray analysis.

Coordination chemistry of 4-aminopyrazole: Structure and physicochemical properties of cobalt(II) chlorido complexes, and amino group reactivity towards a ketone to yield an imine bond

An outline of the in situ construction of a coordination polymer by reacting a mononuclear cobalt(II) complex, functionalised with an amine substituent, with acetone is given. The methodology involved 4-amino-3,5-diisopropyl-1-pyrazole (denoted as L1pzHNH2) as the precursor, putative linker molecule. Reaction of the ligand with anhydrous cobalt(II) chloride, yielded a four-coordinated cobalt(II) chlorido complex, [CoCl2(L1pzHNH2)2]. When the complex was reacted with acetone, a four-coordinated cobalt(II) chlorido coordination polymer, [CoCl2{L1pzHN=C(CH3)2}]n, with an imine bond, was obtained. The complexes were characterised by various spectroscopic techniques. X-ray crystallography shows [CoCl2(L1pzHNH2)2]·2(thf) to comprise a tetrahedrally coordinated cobalt(II) centre with the donors being two chlorido and two pyrazolyl-N atoms. Similarly, [CoCl2{L1pzHN=C(CH3)2}]n features a Cl2N2 donor set defining an approximately tetrahedral geometry with the imine-N donors being derived from a pyrazolyl ring and a symmetry related exocyclic imine-N atom with the result that a one-dimensional coordination polymer with a helical topology is formed. When the uncoordinated precursor molecule, L1pzHNH2, was reacted with acetone, the formation of the imine was confirmed by 1H NMR measured in (CD3)2CO solution. However, from the 1H NMR measured for the imine in CDCl3 solution, a 70:30 equilibrium between the imine and amine was established. It is concluded that the nucleophilicity of the amine group is enhanced by the binding of cobalt(II) to the pyrazole nitrogen in [CoCl2(L1pzHNH2)2]·2(thf), thereby favouring irreversible imine formation. The facile formation of [CoCl2{L1pzHN=C(CH3)2}]n in the solid-state also correlates with the reduced solubility of the coordination polymer structure in organic solvents.

Investigation of the molecular structure of CHBP, biological activities and SARS-CoV-2 protein binding interaction by molecular and biomolecular spectroscopy approaches

The objective of this investigation is to learn more about the structural, electrical, spectroscopic, and physiochemical characteristics of biologically active cyano-4′-hydroxybiphenyl (CHBP). The title molecule’s optimized conformational analysis was computed using the DFT/B3LYP/6–311++G (d, p) level of theory. The observed wavenumbers were compared with theoretical FT-IR and FT-Raman spectra. 1H and 13C NMR experimental spectra in CDCl3 solution (solvent phase) were recorded and the chemical shift was calculated. NBO analysis was used to examine the transfer of charge as well as the intermolecular and intramolecular bonding of orbitals. The TD-DFT (time-dependent DFT) approach was used to estimate theoretical values for both the gas and solvent (ethanol) in the corresponding transitional research, which was conducted using UV–Vis’s spectra. Energy gap (Eg = 0.26764 eV) implies that the strong potential for charge transfer, and the stability of the CHBP compound. CHBP compound’s has bioactive nature, its drug-likeness and biological properties were evaluated. The predicted topological polar surface area of 44.02 \\AA2 for the molecule falls within the permissible range of < 140 \\AA2. Based on the docking results, the most stable docking score value is −6.84 kcal/mol. In that interaction, MET 165 affects both phenyl rings in a pi-sulphur fashion and a single bond hydrogen with protein moieties GLN 192. This suggests that the pi-alkyl in PRO 168 is a hydroxyl substitutional ring. Our findings demonstrate the CHBP compound is a good inhibitor against the SAR COVID-19 viral protein.

Investigation on molecular and biomolecular spectroscopy of the novel 2BCA molecule to analyse its biological activities and binding interaction with nipah viral protein

The molecule of 2-Biphenyl Carboxylic Acid (2BCA), which contains peculiar features, was explored making use of density functional theory (DFT) and experimental approaches in the area of quantum computational research. The optimised structure, atomic charges, vibrational frequencies, electrical properties, electrostatic potential surface (ESP), natural bond orbital analysis and potential energy surface (PES) were obtained applying the B3LYP approach with the 6–311++ G (d,p) basis set.. The 2BCA molecule was examined for possible conformers using a PES scan. The methods applied for spectral analyses included FT-IR, FT-RAMAN, NMR, and UV–Vis results. Vibrational frequencies for all typical modes of vibration were found using the Potential Energy Distribution (PED) data. The UV–Vis spectrum was simulated using the TD-DFT technique, which is also seen empirically. The Gauge-Invariant Atomic Orbital (GIAO) approach was employed to model and study the 13C and 1H NMR spectra of the 2BCA molecule in a CDCL3 solution. The spectra were then exploited experimentally to establish their chemical shifts. To predict the donor and acceptor interaction, the NBO analysis was used. The electrostatic potential surface was employed to anticipate the locations of nucleophilic and electrophilic sites. Hirshfeld surfaces and their related fingerprint plots are exploited for the investigation of intermolecular interactions. Reduced Density Gradient (RDG) helps to measure and illustrate electron correlation effects, offering precise insights into chemical bonding, reactivity, and the electronic structure of 2BCA. According to Lipinski and Veber’s drug similarity criteria, 2BCA exhibits the typical physicochemical and pharmacokinetic properties that make it a potential oral pharmaceutical candidate. According to the findings of a molecular docking study, the 2BCA molecule has promise as a treatment agent for the Nipah virus (PDB ID: 6 EB9), which causes severe respiratory and neurological symptoms in humans.

An Air and Moisture Stable Boat Shaped Hydroxo‐Bridged Ruthenium(II) Binuclear Complex for the Catalytic Hydrogenation of CO2

AbstractA new hydroxo‐bridged ruthenium (II) complex [{Ru(η6‐p‐cymene)(iPr2P−O)}2(μ‐OH)]Cl (2) has fortuitously been isolated from the reaction between the known ruthenium(II) complex [RuCl2(η6‐p‐cymene)(iPr2P‐OH)] (1) in either CDCl3 or CHCl3 solutions in the presence of excess DBU (1,8‐diazabicyclo(5.4.0)undec‐7‐ene) at room temperature. Complex 2 is only formed under specific conditions as an orange‐colored air and moisture stable binuclear complex. It is formed via the deprotonation of the P−OH unit in [RuCl2(η6‐p‐cymene)(iPr2P‐OH)]. Complex 2 has been fully characterized by spectroscopic and analytical methods. Its structure was determined by single crystal X‐ray diffraction which reveals a boat‐shaped motif containing a bridging hydroxide unit which undergoes hydrogen bonding with a chloride counterion. Complex 2 was utilized as a catalyst for the hydrogenation of CO2 to formic acid salt using molecular hydrogen. The catalytic reactions were performed at 100 °C in THF in the presence of DBU as a base to isolate [DBU+H][OC(O)H] salt as the final product. Using catalyst loadings down to 0.01 mol%, it was possible to hydrogenate gaseous CO2 with TONs up to 9900.

Single-Crystal X-ray Structure Determination of Tris(pyrazol-1-yl)methane Triphenylphosphine Copper(I) Tetrafluoroborate, Hirshfeld Surface Analysis and DFT Calculations

The tetrafluoroborate salt of the cationic Cu(I) complex [Cu(CHpz3)(PPh3)]+, where CHpz3 is the tridentate N-donor ligand tris(pyrazol-1-yl)methane and PPh3 is triphenylphosphine, was synthesized through a displacement reaction on the acetonitrile complex [Cu(NCCH3)4][BF4]. The compound crystallizes in the monoclinic P21/c space group. The single-crystal X-ray diffraction revealed that the copper(I) centre is tetracoordinated, with a disposition of the donor atoms surrounding the metal centre quite far from the ideal tetrahedral geometry, as confirmed by continuous shape measures and by the τ4 parameter. The intermolecular interactions at the solid state were investigated through the Hirshfeld surface analysis, which highlighted the presence of several non-classical hydrogen bonds involving the tetrafluoroborate anion. The electronic structure of the crystal was modelled using plane-wave DFT methods. The computed band gap is around 2.8 eV and separates a metal-centred valence band from a ligand-centred conduction band. NMR spectroscopy indicated the fluxional behaviour of the complex in CDCl3 solution. The geometry of the compound in the presence of chloroform as implicit solvent was simulated by means of DFT calculations, together with possible mechanisms related to the fluxionality. The reversible dissociation of one of the pyrazole rings from the Cu(I) coordination sphere resulted in an accessible process.

Solution-State Studies, X-ray Structure Determination and Luminescence Properties of an Ag(I) Heteroleptic Complex Containing 2,9-Bis(styryl)-1,10-phenanthroline Derivative and Triphenylphosphine

A novel heteroleptic Ag(I) compound, formulated as [AgL(PPh3)]BF4 (1) (where L represents 2,9-bis((E)-4-methoxystyryl)-1,10-phenanthroline and PPh3 stands for triphenylphosphine), was successfully synthesized and thoroughly characterized. The compound’s stability in solution was confirmed through 1D and 2D nuclear magnetic resonance (NMR). The photo-irradiation of the complex in a CDCl3 solution, utilizing a common portable UV lamp emitting at λ = 365 nm, led to the partial transformation of the E,E-geometric isomer to E,Z, ultimately yielding a 1:1.4 molar ratio of isomers. Its molecular structure was determined via X-ray crystallography, while molecular packing was assessed using Hirshfeld calculations. The most notable interactions (51%) within the cationic inner sphere involved H···H bonds. The photophysical characteristics of the complex and L were evaluated both in the solid state and in solution (dichloromethane). Compound 1 is a weak emitter, with photoluminescence quantum yields of 8.6% and 4.3% in solution and the solid state, respectively.

Lewis Acid-Base Adducts of α-Amino Acid-Derived Silaheterocycles and N-Methylimidazole

In chloroform solution, the reaction of bis(tert-butylamino)dimethylsilane ((tBuNH)2SiMe2) and an α-amino acid (α-amino isobutyric acid, H2Aib; D-phenylglycine, H2Phg; L-valine, H2Val) in the presence of N-methylimidazole (NMI) gave rise to the formation of the pentacoordinate silicon complexes (Aib)SiMe2-NMI, (Phg)SiMe2-NMI and (Val)SiMe2-NMI, respectively. Therein, the amino acid building block was a di-anionic bidentate chelator at the silicon atom. In solution, the complexes were involved in rapid coordination–dissociation equilibria between the pentacoordinate Si complex (e.g., (Aib)SiMe2-NMI) and its constituents NMI and a five-membered silaheterocycle (e.g., (Aib)SiMe2), as shown by 29Si NMR spectroscopy. The energetics of the Lewis acid-base adduct formation and the competing solvation of the NMI molecule by chloroform were assessed with the aid of computational methods. In CDCl3 solution, deuteration of the silaheterocycle NH group proceeded rapidly, with more than 50% conversion within two days. Upon cooling to −44 °C, the chloroform solvates of the adducts (Aib)SiMe2-NMI and (Phg)SiMe2-NMI crystallized from their parent solutions and allowed for their single-crystal X-ray diffraction analyses. In both cases, the Si atom was situated in a distorted trigonal bipyramidal coordination sphere with equatorial Si–C bonds and an equatorial Si–N bond (the one of the silaheterocycle). The axial positions were occupied by a carboxylate O atom of the silaheterocycle and the NMI ligand’s donor-N-atom.

A Comprehensive Computational NMR Analysis of Organic Polyarsenicals including the Marine Sponge-Derived Arsenicins A-D and Their Synthetic Analogs.

The adamantane structure of arsenicin A and nor-adamantane structures of arsenicins B-D have gained attention as unique natural polyarsenicals, as well as hits showing promising anticancer activity. The purpose of this study is to apply the predictive power of NMR DFT calculations in order to identify a valid tool to be used in the structural elucidation of similar molecules. 1H- and 13C-NMR chemical shifts of twelve natural and synthetic polyarsenical analogs were calculated and validated by comparison with experimental data acquired in CDCl3 solutions, in regard to mean absolute error (MAE) values under various combinations of two methods (GIAO and CSGT), four functionals and five basis sets, also considering relativistic effects. The best computational approaches are highlighted for predicting the chemical shifts of 1H and 13C nuclei and J(1H,1H) coupling constants in the series of O- and S-polyarsenicals. This comprehensive analysis contributes to making NMR spectroscopy appealing for the structural elucidation of such molecules, contrary to the first structural elucidation of natural arsenicin A, in which the experimental NMR analysis was limited by the poor presence of proton and carbon atoms in its structure and by the shortage of reference data.

Molecular structure of 3,3-pentamethylenediaziridine in gas and solution phases

The equilibrium molecular structure of the 3,3-penta-methylenediaziridine (PMDA) molecule in the gas phase was determined by gas-phase electron diffraction in combination with quantum chemical calculations up to the CCSD(T)-AE/cc-pwCVQZ level and estimation of the mean amplitudes and anharmonic vibrational corrections using quadratic and cubic force fields. 1D and 2D 1H and 13C NMR spectra of PMDA in a CDCl3 solution recorded at different temperatures revealed the temperature dependence of the chemical shifts of NH protons. Nonempirical simulations of small PMDA clusters, carried out at the DFT-B3LYP/6-31++G(2d,p) level, enabled us to suggest an interpretation of the NMR data

Molecular structure of 1,2,3-triethyldiaziridine: Gas-phase electron diffraction and theoretical calculations

For the first time, the equilibrium molecular structure and conformational composition (6 to 8 conformers) of 1,2,3-triethyl-diaziridine in the gas phase were determined by gas-phase electron diffraction. Using 1D and 2D 1H and 13C NMR spectro-scopy, it was shown that in a CDCl3 solution under normal conditions on the NMR time scale, the molecule exists only as one conformer. The enthalpy of formation ΔfH0298 of the studied molecule in the gas phase was calculated by the method of atomization reactions and is equal to 92.2 ± 1.7 kJ mol−1.

Hexahexyloxycalix[6]arene, a Conformationally Adaptive Host for the Complexation of Linear and Branched Alkylammonium Guests.

Hexahexyloxycalix[6]arene 2b leads to the endo-cavity complexation of linear and branched alkylammonium guests showing a conformational adaptive behavior in CDCl3 solution. Linear n-pentylammonium guest 6a+ induces the cone conformation of 2b at the expense of the 1,2,3-alternate, which is the most abundant conformer of 2b in the absence of a guest. In a different way, branched alkylammonium guests, such as tert-butylammonium 6b+ and isopropylammonium 6c+, select the 1,2,3-alternate as the favored 2b conformation (6b+/6c+&sub;2b1,2,3-alt), but other complexes in which 2b adopts different conformations, namely, 6b+/6c+&sub;2bcone, 6b+/6c+&sub;2bpaco, and 6b+/6c+&sub;2b1,2-alt, have also been revealed. Binding constant values determined via NMR experiments indicated that the 1,2,3-alternate was the best-fitting 2b conformation for the complexation of branched alkylammonium guests, followed by cone > paco > 1,2-alt. Our NCI and NBO calculations suggest that the H-bonding interactions (+N-H···O) between the ammonium group of the guest and the oxygen atoms of calixarene 2b are the main determinants of the stability order of the four complexes. These interactions are weakened by increasing the guest steric encumbrance, thus leading to a lower binding affinity. Two stabilizing H-bonds are possible with the 1,2,3-alt- and cone-2b conformations, whereas only one H-bond is possible with the other paco- and 1,2-alt-2b stereoisomers.

Molecular Switching through Chalcogen-Bond-Induced Isomerization of Binuclear (Diaminocarbene)PdII Complexes

Binuclear diaminocarbene complexes, which form as a regioisomer mixture in the reaction between isocyanide–palladium(II) complex cis-[PdCl2(CNXyl)2] and 1,3-thiazol-2-amine, are able to exchange an anionic chloride ligand with other halides, such as Br or I. This process also affords binuclear complexes as mixtures of kinetically and thermodynamically controlled regioisomers. In CDCl3 solutions, we observed interconversion of kinetically and thermodynamically controlled regioisomers. The results of the DFT calculations revealed that in CHCl3 solution, each pair of the isomers exhibited two different types of chalcogen bonding such as S···X or S···N; the presence of CBs for two complexes in the solid state was also proven through X-ray crystallographic study. Based on the combined experimental and theoretical data, it could be concluded that thermodynamic favorability for the formation of thermodynamically controlled regioisomers increases in the Cl &lt; Br ≈ I row and correlate well with the energy difference between S···N and S···X (X = Cl, Br, I) chalcogen bonds in kinetically and thermodynamically controlled products. This means that it is possible to change the structure of metallocycles in binuclear diaminocarbene complexes by simply replacing one halide ligand with another.

Multistep sequence-controlled supramolecular polymerization by the combination of multiple self-assembly motifs

The precise sequence control of polymer chain is an important research topic of polymer chemistry. Although some methods such as iterative synthesis and supramolecular polymerization have been developed to fabricate sequence-controllable polymer, it is still a great challenge to consecutively prepare multiple supramolecular polymers with different sequence structures. In this work, through the reasonable utilization of assembly motifs, we integrated multiple host-guest recognitions and metal coordination interactions to prepare different sequence-controlled supramolecular polymers by a multistep assembly strategy. This research provides inspiration for the design and preparation of supramolecular polymers with different sequence structures.

New organic ionic plastic crystals based on pyrrolidinium dication for a solid‐phase electrolyte

AbstractA series of 1,4‐bis(N‐alkylpyrrolidinium)butane salts combined with Br−, I−, PF6−, and Tf2N− anions were newly designed and synthesized. In nonpolar CDCl3 solution, the axial and equatorial proton peaks of the bis‐pyrrolidinium cation ring are distinguished in 1H NMR. Also, the strengths of ion paring could be estimated from the 1H NMR chemical shift changes of the bridge and pyrrolidinium proton peaks. 1,4‐Bis(N‐hepthylpyrrolidinium)butane I− is an organic ionic plastic crystal showing the lowest fusion entropy value (ΔSf = 3.4 J K·mol−1). Softer crystalline morphologies were found by polarized optical microscope images at plastic crystal phase of each sample and the results were corresponding to differential scanning calorimetry results. 1,4‐Bis(N‐ethylpyrrolidinium)butane Tf2N− showed the softest crystal phase. Ionic conductivity changes and electrochemical stabilities of the bis‐pyrrolidinium PF6− and Tf2N− salts were also measured, and they were stable up to 4.3 V (vs. Li/Li+) and expected to be applied as an electrolyte component.

Acrylamide derivatives: A dynamic nuclear magnetic resonance study.

Substituted acrylamides have found an extensive application in organic and medical chemistry; therefore, it is very important to get insight into their features such as electronic structure, spectral properties, and stereochemical transformations. A correct interpretation of the chemical behavior and biological activity of these heteroatomic systems is impossible without knowledge of the structure of stereodynamic forms and factors determining their relative stability. The structure and peculiarities of stereodynamic behavior of substituted acrylamides and their model compounds were studied by dynamic and multinuclear 1 H, 13 C, and 15 N nuclear magnetic resonance (NMR) spectroscopy in CDCl3 and DMSO-d6 solution. It has been established that acrylamides in solution are realized as Z- and E-isomers, with the E-rotamer being somewhat predominant. The obtained experimental values of the free activation energy of rotamers vary within 15-17 kcal/mol, depending on the stereochemical structure of the molecule. 15 N NMR spectroscopy is the most reliable and fastest method for determining the structural and stereochemical features of nitrogen-containing compounds.

Molecular structure of 1,1',6,6'-tetraaza-7,7'-bi(bicyclo[4.1.0]heptane) in gas, solid and solution phases: GED, XRD and NMR data combined with quantum chemical calculations

The equilibrium molecular structure of 1,1',6,6'-tetraaza-7,7'-bi(bicyclo[4.1.0]heptane) in the gas phase has been determined from the data of the gas phase electron diffraction method using quantum chemical calculations up to the RI-MP2/def2-QZVPP level of theory. Structure studies were also carried out in CDCl3 solution using 1D and 2D 1H and 13C NMR spectroscopy and in the solid state using X-ray diffraction analysis. In the gas phase, three conformers of the molecule have been identified, while only one conformer is present in the CDCl3 solution and in the solid state, in which the substance crystallizes in space group P1¯.

СТРУКТУРА И ВНУТРИМОЛЕКУЛЯРНАЯ ПОДВИЖНОСТЬ НЕКОТОРЫХ ПРОИЗВОДНЫХ БИС(ТИО)ФОСФОРИЛИРОВАННЫХ АМИДОВ В РАСТВОРАХ CCl4, CD2Cl2 И CD3CN

The structure and intramolecular mobility of some derivatives of bis(thio)phosphorylated amides in CCl4, CD2Cl2, and CD3CN solutions were examined by 1H and 31P NMR spectroscopy. A comparative analysis of the temperature-dependent 1H and 31P NMR spectra of the studied compounds with symmetric and asymmetric substitution at phosphorus atoms was carried out. Various intramolecular processes were identified – rotation around C-N bonds, conformational transformations of molecules, tautomerism, and phosphorylotropic rearrangement with the formation of various conformational forms. It was shown that a dynamic equilibrium of several forms is reached, with the amide (phosphazo-) form having a clear advantage.

Synthesis, structure, and cytotoxicity of some triorganotin(iv) complexes of 3-aminobenzoic acid-based Schiff bases

Abstract Six new triorganotin(iv) complexes of 3-aminobenzoic acid-based Schiff bases, 3-(R′-CH═N)C6H4COOSnR3 (1–6) (R′, R = 5-Br-2-HOC6H3, Ph (1); 3,5-Br2-2-HOC6H2, Ph (2); 4-NEt2-2-HOC6H3, Cy (3); 3-OCH3-2-HOC6H3, Cy (4); 2-HOC10H6, Ph (5); 2-HOC10H6, Cy (6)), have been synthesized by the one-pot reaction of equimolar 3-aminobenzoic acid, substituted 2-hydroxybenzaldehyde (or 2-hydroxy-1-naphthaldehyde) and triorganotin(iv) hydroxide, and characterized by elemental analysis, FT-IR, NMR spectroscopy, and X-ray single crystal diffraction. The NMR data (1 J(119Sn–13C) and 119Sn chemical shifts) suggested that these organotin(iv) complexes are all four-coordinated in CDCl3 solution. In the crystalline state, the tin atoms in 1–4 and 6 are four-coordinated and possess a distorted tetrahedral geometry. Complex 5 with crystalline solvents (CH3OH and CHCl3) exhibits a zigzag chain, and the five coordination atoms on the tin atom are arranged in a trigonal bipyramidal geometry in which the carboxylate oxygen atom and the phenolic oxygen atom of the adjacent ligand occupy the axial positions. In all complexes, the 3-(arylmethyleneamino)benzoate ligands are coordinated with tin atoms in monodentate mode. Their cytotoxicity against two human cancer cell lines (A549 and HeLa), UV-Vis, and fluorescence have been determined, and the results reveal that complexes 1–6 have higher cytotoxicity than cisplatin and may be explored for potential blue luminescent materials.