1J Values Research Articles

Synthesis, anticancer, α-glucosidase inhibition, molecular docking and dynamics studies of hydrazone-Schiff bases bearing polyhydroquinoline scaffold: In vitro and in silico approaches

A series of hydrazone-Schiff base derivatives of polyhydroquinoline (PHQ) nucleus have been synthesized, structurally deduced by NMR (13C- and 1H-) and HR-ESI-MS spectroscopic methods and finally subjected for anti-cancer and α-glucosidase inhibitory activities. The MTT assay's results exposed that these eight compounds (2j, 2u, 2t, 2w, 2s, 2r, 2x, and 2d) presented notable activity against breast cancer MDA-MB-231 cells having IC50 in the range of 11.4 ± 0.2 to 15.1 ± 0.4 µM, while the remaining fourteen compounds displayed significant to good anti-breast cancer activity. In case of α-glucosidase inhibition, eight compounds (2n, 2j, 2e, 2o, 2w, 2q, 2v, and 2l) exhibited superior inhibition against α-glucosidase enzyme with IC50 values ranging from 8.72 ± 0.14 to 16.16 ± 0.17 µM, compare with the standard acarbose. Additionally, the remaining eighteen derivatives showed significant to least inhibitory activity. The in silico docking, and molecular dynamic displayed the minimal divergence in MM-PBSA values for 2n, 2j, 2e, and 2o which suggests a strong and stable interaction with the protein's amino acid backbone. Pharmacokinetic profiles and anti-glucosidase ability suggested them as potential drug candidates for further studies.

MA'AT Analysis: Probability Distributions of Molecular Torsion Angles in Solution from NMR Spectroscopy.

ConspectusMonosaccharides adopt multiple conformations in solution, and this structural complexity increases significantly when they are assembled into oligosaccharides and polysaccharides. Characterization of the conformational properties of saccharides in solution by NMR spectroscopy has been hampered by several complicating factors, including difficulty interpreting spectra because of significant signal overlap, population averaging of NMR parameters, and unique properties of the spectra that make accurate measurements of NMR parameters prone to error (e.g., non-first-order effects on J-couplings). Current conformational assignments rely heavily on theoretical calculations, especially molecular dynamics (MD) simulations, to interpret the experimental NMR parameters. While these studies assert that the available experimental data fit the calculated models well, a lack of independent experimental validation of the force fields from which MD models are derived and an inability to test all possible models that might be compatible with the experimental data in an unbiased manner make the approach less than ideal.NMR spin couplings or J-couplings have been used as structure constraints in organic and other types of molecules for more than six decades. The dihedral angle dependence of vicinal (three-bond) 1H-1H spin couplings (3JHH) first described by Karplus led to an explosion of applications for a wide range of conformational problems. Other vicinal J-couplings (e.g., 3JCCOP, 3JHCOP, and 3JCOCH) have been found to exhibit similar dihedral angle dependencies. 3J values have been used to assign the preferred conformation in molecules that are conformationally homogeneous. However, many molecules, particularly those in biological systems, are conformationally flexible, which complicates structural interpretations of J values in solution. Three-state staggered models are often assumed in order to deconvolute the conformationally averaged J values into conformer populations. While widely applied, this approach assumes highly idealized models of molecular torsion angles that are likely to be poor representations of those found in solution. In addition, this treatment often gives negative populations and neglects the presence of librational averaging of molecular torsion angles.Recent work in this research group has focused on the development of a hybrid experimental-computational method, MA'AT analysis, that provides probability distributions of molecular torsion angles in solution that can be superimposed on those obtained by MD. Ensembles of redundant NMR spin couplings, including 3J (vicinal), 2J (geminal), and sometimes 1J (direct) values, are used in conjunction with circular statistics to provide single- and multistate models of these angles. MA'AT analysis provides accurate mean torsion angles and circular standard deviations (CSDs) of each mean angle that describe the librational motion about the angle. Both conformational equilibria and dynamics are revealed by the method. In this Account, the salient features of MA'AT analysis are discussed, including some applications to conformational problems involving saccharides and peptides.

Theoretical study of the influence of solvent polarity on the 31P and 13C NMR parameters of the Ru(PH3)4(η2-benzyne) complex

In this study, using the wB97XD method, quantum chemical calculations were used to analyze the effect of solvent on 31P and 13C NMR parameters of the Ru(PH3)4(η2-benzyne) complex. The solvent effects were examined using the self-consistent reaction field theory (SCRF) based on the Polarizable Continuum Model (PCM). The stability of this complex was studied in the singlet and triplet states. The 31P and 13C NMR chemical shifts of the complex were calculated for both gas and solution phases. One-bond nuclear spin–spin coupling constants of RhC and RuP bonds as well as two-bond nuclear spin–spin coupling constants of P⋯P were estimated. The correlations of these parameters and solvent polarity functions including both the dielectric constant (ε) and refractive index (nD) of the liquid medium were explored further. In addition, the most significant Ramsey terms involved significantly in 1J(RuP), 1J(RuC) and 2J(P⋯P) values were determined. Finally, the correlations between 1J(RuP), 1J(RuC) and the APT net charge on the Ru atom were studied.

A New Series of Antileukemic Agents: Design, Synthesis, In Vitro and In Silico Evaluation of Thiazole-Based ABL1 Kinase Inhibitors.

After the approval of imatinib, more than 25 antitumor agents targeting kinases have been approved, and several promising candidates are at various stages of clinical evaluation. Due to the importance of the thiazole scaffold in targeted anticancer drug discovery, the goal of this work is to identify new thiazolyl hydrazones as potent ABL1 kinase inhibitors for the management of Chronic Myeloid Leukemia (CML). New thiazolyl hydrazones (2a-p) were synthesized and investigated for their cytotoxic effects on the K562 CML cell line. Compounds 2h, 2j and 2l showed potent anticancer activity against K562 cell line. The cytotoxic effects of these compounds on other leukemia (HL-60, MT-2 and Jurkat) and HeLa human cervical carcinoma cell lines were also investigated. Furthermore, their cytotoxic effects on Mitogen-Activated Peripheral Blood Mononuclear Cells (MA-PBMCs) were evaluated to determine their selectivity. Due to its selective and potent anticancer activity, compound 2j was benchmarked for its apoptosis-inducing potential on K562 cell line and inhibitory effects on eight different Tyrosine Kinases (TKs), including ABL1 kinase. In order to investigate the binding mode of compound 2j into the ATP binding site of ABL1 kinase (PDB: 1IEP), a molecular docking study was conducted using MOE 2018.01 program. The QikProp module of Schrödinger's Molecular modelling package was used to predict the pharmacokinetic properties of compounds 2a-p. 4-(4-(Methylsulfonyl)phenyl)-2-[2-((1,3-benzodioxol-4-yl)methylene)hydrazinyl]thiazole (2j) showed antiproliferative activity against K562 cell line with an IC50 value of 8.87±1.93 μM similar to imatinib (IC50= 6.84±1.11μM). Compound 2j was found to be more effective than imatinib on HL-60, Jurkat and MT-2 cells. Compound 2j also showed cytotoxic activity against HeLa cell line similar to imatinib. The higher selectivity index value of compound 2j than imatinib indicated that its antiproliferative activity was selective. Compound 2j also induced apoptosis in K562 cell line more than imatinib. Among eight TKs, compound 2j showed the strongest inhibitory activity against ABL1 kinase enzyme (IC50= 5.37±1.17μM). According to molecular docking studies, compound 2j exhibited high affinity to the ATP binding site of ABL1 kinase, forming significant intermolecular interactions. On the basis of in silico studies, this compound did not violate Lipinski's rule of five and Jorgensen's rule of three. Compound 2j stands out as a potential orally bioavailable ABL1 kinase inhibitor for the treatment of CML.

New tri- and di-alkylstannyl 2-(1H-indol-3-yl)ethanoates: synthesis, characterization and biological screenings

A series of triorganotin(IV) compounds {Me3SnL (1), Bu3SnL (2), Ph3SnL (3)} and di-organotin(IV) complexes {Me2SnL2 (4), Bu2SnL2 (5) and Ph2SnL2 (6)}, where Me = methyl, Bu = butyl, Ph = phenyl and L = 2-(1H-indole-3-yl)acetate) have been synthesized and characterized by FT-IR and multinuclear NMR (1H-, 13C- and 119Sn-NMR) spectroscopy. Tri- and diorganotin(IV) derivatives exhibited five- and six-coordinate geometries, respectively, in solid state as evident from the Δν value. Five-coordinate trigonal bipyramidal and six-coordinate octahedral geometry was assigned to 1 and 4 in solution state based on NMR data as evident from 2J(119Sn,1H) and 1J(119Sn-13C) coupling constant values, which was further attested by 119Sn NMR. Single crystal XRD analysis on 1 revealed that it exhibited polymeric crystal structure with distorted trigonal bipyramidal geometry around the tin center with two unequal Sn–O bonds. The screening of the synthesized compounds for cytotoxicity showed good activity in comparison to cis-platin. They have also displayed moderate to good antimicrobial activities.

Crystal structure and nontrivial magnetic properties of CuII binuclear complex based on 4-methyl-2,6-bis{[2-(4,6-dimethyl-pyrimidin-2-yl)hydrazono]methyl}phenol

The new complex [Cu2(H2L)Cl3] with axial chloride ions coordination based on 4-methyl-2,6-bis{[2-(4,6-dimethyl-pyrimidin-2-yl)hydrazono]methyl}phenol was obtained and its crystal structure was determined. Magnetic studies revealed the presence of antiferromagnetic exchange interaction of −193 cm−1 that is extremely high for such type of complexes. The quantum chemical calculation of 2J value has perfectly matched an experiment.

Pnicogen bonds in complexes with CO and CS: differentiating properties

ABSTRACTAb initio MP2/aug’-cc-pVTZ calculations have been performed on pnicogen-bonded complexes with CO and CS as electron-pair donors to PH2X, for X = F, NC, OH, CN, CCH, and H. CO:PH2X and OC:PH2X complexes are stabilised by traditional pnicogen bonds. CS is an electron-pair donor through its in-plane π system to four PH2X molecules. It forms C··· P phosphorus-shared bonds with some ion-pair character with PH2F, PH2(OH-Z), and PH2(OH-E), and traditional pnicogen bonds with all PH2X except PH2F. C-O and C-S stretching frequencies are blue-shifted for C···P pnicogen bonds, and red-shifted for O···P and S···P bonds. EOM-CCSD spin-spin coupling constants 1pJ(P-C) for OC:PH2X and 1pJ(P-O) for CO:PH2X are characteristic of complexes stabilised by traditional pnicogen bonds. Coupling constants 1pJ(P-C) as a function of the P-C distance for SC:PH2X illustrate the evolution of the C···P pnicogen bond. They increase as the P-C distance decreases in complexes with traditional bonds, reach a maximum for SC:PH2OH transition structures as the P-C distance further decreases and the bonds gain phosphorus-shared character, and then change sign and continue to decrease as the P-C distance further decreases and the phosphorus-shared pnicogen bonds gain ion-pair character. They approach the values of 1J(P-C) for the cation (H2PCS)+.

Neutron-hole states in 131Sn and spin-orbit splitting in neutron-rich nuclei

In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of 132Sn. The spectroscopic strength of single-hole states in 131Sn was determined from the measured differential cross sections of the tritons from the neutron-removing 132Sn(d, t)131Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3/2+, 1/2+ and 5/2+ states were found to be consistent with their maximal values of (2j+1), confirming the robust N=82 shell closure at 132Sn. We compared the spin-orbit splitting of neutron single-hole states in 131Sn to those of single-particle states in 133Sn determined in a recent measurement of the 132Sn(d, p)133Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength.

Delitpyrones: α-Pyrone Derivatives from a Freshwater Delitschia sp.

In research focused on the discovery of new chemical diversity from freshwater fungi, a peak library was built and evaluated against a prostate cancer cell line, E006AA-hT, which was derived from an African American, as this population is disproportionately affected by prostate cancer. The chemical study of the bioactive sample accessioned as G858 (Delitschia sp.) led to the isolation of eight new α-pyrone derivatives (1: - 7: , and 11: ), as well as the new 3S*,4S*-7-ethyl-4,8-dihydroxy-3,6-dimethoxy-3,4-dihydronaphthalen-1(2H)-one (15: ). In addition, the known compounds 5-(3-S-hydroxybutyl)-4-methoxy-6-methyl-2H-pyran-2-one (8: ), 5-(3-oxobutyl)-4-methoxy-6-methyl-2H-pyran-2-one (9: ), pyrenocine I (10: ), 5-butyl-6-(hydroxymethyl)-4-methoxy-2H-pyran-2-one (12: ), sporidesmin A (13: ), 6-ethyl-2,7-dimethoxyjuglone (14: ), artrichitin (16: ), and lipopeptide 15G256ε (17: ) were also obtained. The structures of the new compounds were elucidated using a set of spectroscopic (NMR) and spectrometric (HRMS) methods. The absolute configuration of the most abundant member of each subclass of compounds was assigned through a modified Mosher's ester method. For 15: , the relative configuration was assigned based on analysis of 3 J values. Compounds 1, 2, 5: - 14, 16: , and 17: were evaluated against the cancer cell line E006AA-hT under hypoxic conditions, where compound 13: inhibited cell proliferation at a concentration of 2.5 µM.

Influence of non-bridging donor atoms on the value of exchange interaction in binuclear CuII complexes with bis-hydrazones based on 2,6-diformylphenol

The quantum chemical simulation of exchange interaction according to the broken symmetry approach was performed for a series of binuclear CuII complexes containing the asymmetric exchange moiety based on bis-hydrazones of 2,6-diformylphenol. The calculated values were compared between themselves and with the experimental values of the exchange parameter 2J for the binuclear copper(II) complexes with bis-hydrazones based on 2,6-diformylphenol in order to reveal the influence pattern of the nature of nonbridging donor atoms X (O, N, S, and Se) onto the exchange interaction. The strength of exchange interaction of the antiferromagnetic type depends significantly on the nature of nonbridging donor atoms, increasing in the series of X = O, NH, S, and Se.

Lone-Pair Hole on P: P···N Pnicogen Bonds Assisted by Halogen Bonds.

Ab initio MP2/aug'-cc-pVTZ calculations have been performed on the binary complexes XY:PH3 for XY = ClCl, FCl, and FBr; and PH3:N-base for N-base = NCH, NH3, NCF, NCCN, and N2; and the corresponding ternary complexes XY:PH3:N-base, to investigate P···N pnicogen bond formation through the lone-pair hole at P in the binary complexes and P···N pnicogen-bond formation assisted by P···Y halogen bond formation through the σ-hole at Y. Although the binary complexes PH3:N-base that form through the lone-pair hole have very small binding energies, they are not equilibrium structures on their potential surfaces. The presence of the P···Y halogen bond makes PH3 a better electron-pair acceptor through its lone-pair hole, leading to stable ternary complexes XY:PH3:N-base. The halogen bonds in ClCl:PH3 and ClCl:PH3:NCCN are traditional halogen bonds, but in the remaining binary and ternary complexes, they are chlorine- or bromine-shared halogen bonds. For a given nitrogen base, the P···N pnicogen bond in the ternary complex FCl:PH3:N-base appears to be stronger than that bond in FBr:PH3:N-base, which is stronger than the P···N bond in the corresponding ClCl:PH3:N-base complex. EOM-CCSD spin-spin coupling constants for the binary and ternary complexes with ClCl and FCl are also consistent with the changing nature of the halogen bonds in these complexes. At long P-Cl distances, the coupling constant 1xJ(P-Cl) increases with decreasing distance but then decreases as the P-Cl distance continues to decrease, and the halogen bonds become chlorine-shared bonds. At the shorter distances, 1xJ(P-Cl) approaches the value of 1J(P-Cl) for the cation +(Cl-PH3). The coupling constants 1pJ(P-N) are small and, with one exception, are greater in ClCl:PH3:N-base complexes compared to that in FCl:PH3:N-base, despite the shorter P-N distances in the latter.

Structure and Antiferromagnetism of Trinuclear Heterometallic Strings Containing MnII–MII–MnII Frameworks (M = Ni, Pd, Pt)

The syntheses, crystal structures, and magnetic properties of three trinuclear, symmetric, heterometal string complexes stabilized by four dipyridylamide (dpa) ligands were explored. MnNiMn(dpa)4Cl2 (1), MnPdMn(dpa)4Cl2 (2), and MnPtMn(dpa)4Cl2 (3) were found to exhibit an approximate D4 symmetry and a linear metal framework helically wrapped by four syn–syn‐type ligands. The center metal ions bond with the amide part of dpa– in a square‐planar environment, and the outer Mn ions bond with Cl– and the pyridyl part of dpa– in a square‐pyramidal environment. The magnetic susceptibilities of these three compounds showed antiferromagnetic interactions (2J = –13.7 cm–1 for 1, –29.7 cm–1 for 2, and –66.2 cm–1 for 3 in the Heisenberg exchange framework) between the MnII magnetic centers. The value of 2J increased with increasing atomic number of the central metal ion. The antiferromagnetic properties were further confirmed by electron paramagnetic resonance spectroscopy studies in variable‐temperature measurements.

Unusual traits of cis and trans-2,3-dibromo-1,1-dimethylindane on the way from 1,1-dimethylindene to 2-bromo-, 3-bromo-, and 2,3-dibromo-1,1-dimethylindene.

Do not rely on the widely accepted rule that vicinal, sp3-positioned protons in cyclopentene moieties should always have more positive 3J NMR coupling constants for the cis than for the trans arrangement: Unrecognized exceptions might misguide one to wrong stereochemical assignments and thence to erroneous mechanistic conclusions. We show here that two structurally innocent-looking 2,3-dibromo-1,1-dimethylindanes violate the rule by means of their values of 3J(cis) = 6.1 Hz and 3J(trans) = 8.4 Hz. The stereoselective formation of the trans diastereomer from 1,1-dimethylindene was improved with the tribromide anion (Br3−) as the brominating agent in place of elemental bromine; the ensuing, regiospecific HBr elimination afforded 3-bromo-1,1-dimethylindene. The addition of elemental bromine to the latter compound, followed by thermal HBr elimination, furnished 2,3-dibromo-1,1-dimethylindene, whose Br/Li interchange reaction, precipitation, and subsequent protolysis yielded only 2-bromo-1,1-dimethylindene.

Unusual acid-base properties of the P4 molecule in hydrogen-, halogen-, and pnicogen-bonded complexes.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate hydrogen bonding, halogen bonding, and pnicogen bonding involving tetrahedral P4 and the FH, ClH, and FCl molecules. P4 has three unique interaction sites: at a vertex (designated the P1 atom); at an edge (the P2-P3 bond); and at the P2-P3-P4 face. The uniqueness of molecular P4 is its ability to act as an electron donor and an electron acceptor at the same site, except for the P2-P3 bond, which is only an electron donor. FCl and FH form five different complexes with P4, but ClH forms only three. The type of complex formed and its binding energy depend on both the interaction site of molecular P4 and the interacting molecule. For all complexes with FH, ClH, and FCl, the binding energies at a given site with the P4 molecule acting as the base are greater than the binding energies when P4 is the acid. Thus, P4 is a better electron donor than an electron acceptor. Charge-transfer interactions and EOM-CCSD spin-spin coupling constants across hydrogen, halogen, and pnicogen bonds are reported for all of the P4 complexes. Relative to 1J(Pi-Pj) in molecular P4, 1J(P1-P2) coupling constants decrease in absolute value and 1J(P2-P3) coupling constants increase in pnicogen-bonded complexes and the complex with FCl that has a PF halogen bond. Absolute values of 1J(P1-P2) increase and those of 1J(P2-P3) decrease in hydrogen-bonded complexes and complexes with PCl halogen bonds. 1J(P1-P2) and 1J(P2-P3) exhibit a single linear correlation with the corresponding Pi-Pj distances.

Exploring the (H2C═PH2)(+):N-Base Potential Surfaces: Complexes Stabilized by Pnicogen, Hydrogen, and Tetrel Bonds.

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the structures, binding energies, and bonding properties of complexes involving the cation (H2C═PH2)(+) and a set of sp-hybridized nitrogen bases including NCCH3, NP, NCCl, NCH, NCF, NCCN, and N2. On each (H2C═PH2)(+):N-base surface, four types of unique equilibrium structures exist: a complex with a P···N pnicogen bond formed through the π system of (H2C═PH2)(+) (ZB-π); a complex with a P···N pnicogen bond formed through the σ system of (H2C═PH2)(+) (ZB-σ); a hydrogen-bonded complex with a P-H···N hydrogen bond (HB); and a tetrel-bonded complex with a C···N bond (TB). Binding energies of complexes stabilized by the same type of intermolecular interaction decrease in the order NCCH3 > NP > NCCl > NCH > NCF > NCCN > N2. For a given base, binding energies decrease in the order ZB-π > HB > ZB-σ > TB, except for a reversal of HB and ZB-σ with the weakest base N2. Binding energies of ZB-π, HB, and ZB-σ complexes increase exponentially as the corresponding P-N distance decreases, but the correlation is not as good between the binding energies of TB complexes and the intermolecular C-N distance. Charge-transfer energies stabilize all complexes and also exhibit an exponential dependence on the corresponding intermolecular distances. EOM-CCSD spin-spin coupling constants (1p)J(P-N) for ZB-π and ZB-σ complexes, and (2h)J(P-N) for HB complexes increase quadratically as the corresponding P-N distance decreases. Values of (1t)J(C-N) for TB are small and show little dependence on the C-N distance. (1)J(P-H) values for the hydrogen-bonded P-H bond in HB complexes correlate with the corresponding P-H distance, whereas values of (1)J(P-H) for the non-hydrogen-bonded P-H correlate with the P-N distance.

Sulfadiazine/dimethylsulfadiazine transition metal complexes: Synthesis, crystal structures and magnetic properties

Sulfadiazine (Hsulf) and dimethylsulfadiazine (Hdmsulf) were used to assemble divalent transition metal complexes (Cu, Ni or Co). Solvated complexes 1–4, dinuclear 1 (Cu2), tetranuclear 2 (Ni4) and 3 (Co4), and two-dimensional polymeric 4, were synthesized by controlling the metal ions, ligands and solvents. For complex 1, two Cu(II) ions are bridged by four NCN groups of four sulf− ligands, while for complex 2, four Ni(II) ions are alternatively bridged by the pyrimidine rings of four sulfadiazine ligands, forming a neutral square Ni4 molecule. In complex 3, four Co(II) ions are bridged by four μ3-OMe− groups, yielding a Co4O4 cubane. Complex 4 possesses a 2D grid structure with the Co(II) ions bridged by the remote amino groups of the ligand dmsulf−. Magnetic susceptibility measurements show that the desolvated complex (1d) exhibits antiferromagnetic coupling between adjacent Cu(II) ions with the 2J value of −90.0cm−1, and the pyrimidine rings transmit weak antiferromagnetic coupling in complex 2. Complex 3·8H2O shows ferromagnetic coupling via the methoxido bridges with the bridging CoOCo bond angles of 96–99°. Complex 4 displays a magnetic property for mononuclear cobalt(II) complexes due to the remote separation of Co(II) ions.

Inducing magnetic communication in caged dinuclear Co(II) systems.

The synthesis, structural, electronic and magnetic characterization of five dinuclear Co(II) azacryptand compounds (1-5) bridged through different ions are reported. The magnetic exchange interactions, 2J values, obtained from theoretical computations show that the variation of the intermetallic angles and distances lead to antiferromagnetic behaviours. Magneto-structural correlations show a trend, where the angles Co(II)-bridge-Co(II) closer to 180° favour an increase in the superexchange pathway leading to higher AF interaction values.

Structural, magnetic and quantum-chemical study of dinuclear copper(II) thiophenecarboxylate and furancarboxylate complexes

The synthesis, spectral and magnetic properties, crystal and electronic structures of five dimeric copper(II) carboxylates, [Cu2(2-tpc)4(H2O)2] (1), [Cu2(2-tpc)4(DMSO)2] (2) (where 2-tpc is 2-thiophenecarboxylate and DMSO is dimethylsulfoxide), [Cu2(5-Me-2-tpc)4(DMSO)2]·2caffeine (3), [Cu2(5-Me-2-tpc)4(H2O)2]·0.488[(5-Me-2-tpcH·H2O)2]·0.012[Cu(5-Me-2-tpc)2(H2O)2] (4) (where 5-Me-2-tpcH and 5-Me-2-tpc are 5-methyl-2-tiophenecarboxylic acid and its deprotonated anion, respectively) and [Cu2(2-fuc)4(H2O)2]·2.5H2O (5) (where 2-fuc is 2-furancarboxylate), are reported. All five complexes adopt dimeric paddle-wheel cage structures as revealed by X-ray analyses. Moreover, the crystal structure of 4 contains, apart from dimeric paddle-wheel molecules, also other molecules that exist as a result of substitutional disorders. EPR spectra and magnetic measurements for 1, 4 and 5 confirmed an antiferromagnetic intramolecular interaction between the Cu(II) ions with −2J coupling constants of 319, 334 and 327cm−1, respectively. Density functional calculations (B3LYP hybrid functional) have been carried out on the experimental geometries in order to study the magnetic properties of the respective complexes. The computed values of 2J are overestimated by ca 110–180cm−1. Our calculations show that the coexistence of various conformers can be the source of different exchange coupling constants, despite their similar electronic structure parameters.

Pnicogen Bonds between X═PH3 (X = O, S, NH, CH2) and Phosphorus and Nitrogen Bases

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the pnicogen bonded complexes formed between the acids O═PH3, S═PH3, HN═PH3, and H2C═PH3 and the bases NH3, NCH, N2, PH3, and PCH. All nitrogen and phosphorus bases form complexes in which the bases are lone pair electron donors. The binding energies of complexes involving the stronger bases NH3, NCH, and PH3 differentiate among the acids, but the binding energies of complexes with the weaker bases do not. These complexes are stabilized by charge transfer from the lone pair orbital of N or P to the σ*P═A orbital of X═PH3, where A is the atom of X directly bonded to P. PCH also forms complexes with the X═PH3 acids as a π electron donor to the σ*P═A orbital. The binding energies and the charge-transfer energies of the π complexes are greater than those of the complexes in which PCH is a lone pair donor. Whether the positive charge on P increases, decreases, or remains the same upon complex formation, the chemical shieldings of (31)P decrease in the complexes relative to the corresponding monomers. (1p)J(P-N) and (1p)J(P-P) values correlate best with the corresponding P-N and P-P distances as a function of the nature of the base. (1)J(P-A) values do not correlate with P-A distances. Rather, the absolute values of (1)J(P-O), (1)J(P-S), and (1)J(P-N) decrease upon complexation. Decreasing (1)J(P-A) values correlate linearly with increasing complex binding energies. In contrast, (1)J(P-C) values increase upon complexation and correlate linearly with increasing binding energies.

Synthesis, crystal structures, spectral, electrochemical and magnetic properties of di-µ-phenoxido-bridged dinuclear copper(II) complexes with N-salicylidene-2-hydroxybenzylamine derivatives: axial coordination effect of dimethyl sulphoxide molecule

AbstractThe template reaction of salicylaldehyde and its substituted derivatives and 2-hydroxy-5-bromobenzylamine or 2-hydroxy-5-chlorobenzylamine with copper(II) acetate in dimethyl sulphoxide (dmso) afforded eight dinuclear Cu(II) complexes, [Cu2(L)2(dmso)2] (H2 L = N-salicylidene-2-hydroxy-5-bromobenzylamine, N-salicylidene-2-hydroxy-5-chlorobenzylamine and their 5-bromo, 5-nitro and 5-methyl-substituted salicylidene derivatives). These Cu(II) complexes were characterised by IR and UV-VIS-NIR spectroscopy, electric conductivity, cyclic voltammetry, and temperature dependence of magnetic susceptibilities (4.5–300 K). In the THF solution, the complexes are nonelectrolytes and exhibit a characteristic CT band due to phenoxido-bridging at 360–384 nm. In the cyclic voltammograms, an irreversible reduction process was observed at −1.18–1.54 V vs Fc/Fc+. Single-crystal X-ray crystallography revealed that two Cu(II) ions were bridged by the two phenoxido-oxygen atoms of the two Schiff-base ligands with axial coordination of dmso molecules forming a square pyramid with a Cu-Cu distance of 3.0628(8)–3.0931(6) °A. In accordance with the crystal structures, the magnetic interaction between the two Cu(II) ions is relatively anti-ferromagnetic with −2J value of 386–575 cm−1. The axial coordination effect of the dmso molecule was discussed in relation to the correlation between the Cu-O-Cu angle and the −2J value.