Atoms Of Ligand Research Articles

Structure and Thermodynamic Hydricity in Cobalt(triphosphine)(monophosphine) Hydrides.

The mononuclear cobalt hydride complex [HCo(triphos)(PMe3)], in which triphos = PhP(CH2CH2PPh2)2, was synthesized and characterized by X-ray crystallography and by 1H and 31P NMR spectroscopy. The geometry of the compound is a distorted trigonal bipyramid in which the axial positions are occupied by the hydride and the central phosphorus atom of the triphos ligand, while the PMe3 and terminal triphos donor atoms occupy the equatorial positions. Protonation of [HCo(triphos)(PMe3)] generates H2 and the Co(I) cation, [Co(triphos)(PMe3)]+, and this reaction is reversible under an atmosphere of H2 when the proton source is weakly acidic. The thermodynamic hydricity of HCo(triphos)(PMe3) was determined to be 40.3 kcal/mol in MeCN from measurements of these equilibria. The reactivity of the hydride is, therefore, well suited to CO2 hydrogenation catalysis. Density functional theory (DFT) calculations were performed to evaluate the structures and hydricities of a series of analogous cobalt(triphosphine)(monophosphine) hydrides where the phosphine substituents are systematically changed from Ph to Me. The calculated hydricities range from 38.5 to 47.7 kcal/mol. Surprisingly, the hydricities of the complexes are generally insensitive to substitution at the triphosphine ligand, as a result of competing structural and electronic trends. The DFT-calculated geometries of the [Co(triphos)(PMe3)]+ cations are more square planar when the triphosphine ligand possesses bulkier phenyl groups and more tetrahedrally distorted when the triphosphine ligand has smaller methyl substituents, reversing the trend observed for [M(diphosphine)2]+ cations. More distorted structures are associated with an increase in ΔGH-°, and this structural trend counteracts the electronic effect in which methyl substitution at the triphosphine is expected to yield smaller ΔGH-° values. However, the steric influence of the monophosphine follows the normal trend that phenyl substituents give more distorted structures and increased ΔGH-° values.

A Theoretical Investigation of Chemical Bonding of a Heterometallic Trinuclear Cluster Containing Iridium and Ruthenium: [(Cp*Ir) (CpRu)2 (μ3-H) (μ-H)3] by QTAIM Approach

Numerous integral and local electron density’s topological parameters of significant metal-metal and metal-ligand bonding interactions in a trinuclear tetrahydrido cluster [(Cp* Ir) (Cp Ru)2 (μ3-H) (μ-H)3]1 (Cp = η5 -C5Me5), (Cp* = η5 -C5Me4Et) were calculated and interpreted by using the quantum theory of atoms in molecules (QTAIM). The properties of bond critical points such as the delocalization indices δ (A, B), the electron density ρ(r), the local kinetic energy density G(r), the Laplacian of the electron density ∇2ρ(r), the local energy density H(r), the local potential energy density V(r) and ellipticity ε(r) are compared with data from earlier organometallic system studies. A comparison of the topological processes of different atom-atom interactions has become possible thanks to these results. In the core of the heterometallic tetrahydrido cluster, the Ru2IrH4 part, the calculations showed that there are no bond critical points (BCPs) or identical bond paths (BPs) between Ru-Ru and Ru-Ir. The distribution of electron densities is determined by the position of bridging hydride atoms coordinated to Ru-Ru and Ru-Ir, which significantly affects the bonds between these transition metal atoms. On the other hand, the results confirm that the cluster under study contains a 7c–11e bonding interaction delocalized over M3H4, as shown by the non-negligible delocalization index calculations. The small values for ρ(b) above zero, together with the small values, again above zero, for Laplacian ∇2ρ(b) and the small positive values for total energy density H(b), are shown by the Ru-H and Ir-H bonds in this cluster is typical for open-shell interactions. Also, the topological data for the bond interactions between Ir and Ru metal atoms with the C atoms of the cyclopentadienyl Cp ring ligands are similar. They show properties very identical to open-shell interactions in the QTAIM classification.

The Role of Non-Covalent Interactions in the Reactions between Palladium Hydrido Complex with Amidoarylphosphine Pincer Ligand and Brønsted Acids

The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols and formic acid) was studied in benzene or toluene as well as in neat alcohols by IR and NMR spectroscopies. The structures of hydrogen-bonded complexes were also optimized at the DFT/ωB97-XD/def2-TZVP level. The nitrogen atom of the amidophosphine pincer ligand readily accepts proton not only from strong Brønsted acids but from relatively weak fluorinated alcohols. That suggests that binding to palladium(II) increases the diarylamine basicity, making it a strong base. Nevertheless, H+ can be taken from [(PN(H)P)PdH]+ (2) by pyridine or hexamethylphosphoramide (HMPA). These observations confirm the need for a shuttle base to form [(PN(H)P)PdH]+ (2) as the result of the heterolytic splitting of H2 by [(PNP)Pd]+. At that, a stoichiometric amount of formic acid protonates a hydride ligand yielding an unstable η2-H2 complex that rapidly converts into formate (PNP)Pd(OCHO), which loses CO2 to restore (PNP)PdH, whereas the relatively high acid excess hampers this reaction through competitive protonation at nitrogen atom.

Synthesis, biological evaluation and molecular docking studies of a new magnesium (II) porphyrin complex

A new bioactive material of magnesium porphyrin complex [Mg(TPP)](H2O)2].2/3(2.2.2).1/3(Bz) (I), (TPP = meso-‑tetraphenylporphyrinato and (2.2.2) = cryptand, and Bz is benzene (C6H6)) has been synthesized and characterized by Single-crystal X-ray diffraction (SCXRD). The title compound crystallizes in trigonal crystal system in space group P-3. The magnesium ion is coordinated to four nitrogen atoms of the porphyrin core and two oxygen atoms of the axial ligands. The crystal packing is stabilized by inter-and intramolecular hydrogen bonds, and by weak C–H…Cg π interactions leading to a bi-dimensional network. In order to confirm the crystal structure, the photophysical properties have been evaluated by infrared (IR), proton nuclear magnetic resonance 1H NMR and UV–Vis spectroscopy. UV–Visible absorption spectrum of complex (I) displayed a red shifted Soret (429 nm) and Q (567 and 609 nm) bands due to the extended conjugation. The IR, and 1H NMR confirm the crystal structure. Finally, bioactivity investigations revealed that free porphyrin H2TPP, [Mg(TPP)] and complex (I) could be used as potential novel significant antibacterial agents. The docking of the free base porphyrins, metallated and the complex (I), in the active sites of bacterial proteins EEscherichia coli (1ECL) and Aspergillus Niger (3K4P) was carried out to detect the degree of antibacterial activity of recognition.

Structural analysis of the coronavirus main protease for the design of pan-variant inhibitors

With the rapid rate of SARS-CoV-2 Main protease (Mpro) structures deposition, a computational method that can combine all the useful structural features becomes crucial. This research focuses on the frequently occurring atoms and residues to find a generalized strategy for inhibitor design given a large amount of protein complexes from SARS-CoV in contrast to SARS-CoV-2 Mpro. By superposing large numbers of the ligands onto the protein template and grid box, we can analyse which part of the structure is conserved from position-specific interaction for both data sets for the development of pan-Mpro antiviral design. The difference in conserved recognition sites from the crystal structures can be used to determine specificity determining residues for designing selective drugs. We can display pictures of the imaginary shape of the ligand by unionising all atoms from the ligand. We also pinpoint the most probable atom adjustments to imitate the frequently found densities from the ligand atoms statistics. With molecular docking, Molecular Dynamics simulation, and MM-PBSA methods, a carbonyl replacement at the nitrile warhead (N5) of Paxlovid’s Nirmatrelvir (PF-07321332) was suggested. By gaining insights into the selectivity and promiscuity regions for proteins and ligands, crucial residues are highlighted, and the antiviral design strategies are proposed.

Efficient discovery of room temperature magnetic transition metal monolayers assisted by artificial neural network

The low-dimensional materials have opened a new window to new emerging science and technological applications. Recently the discovery of new two-dimensional (2D) monolayers with long-range magnetic order by theoretical method gets more attention. The key question is how to effectively explore different possible 2D magnetic configurations. However, the computational cost of optimizing and electronically analyzing a a large number of compounds on the ab initio level is very high. A practical method is the combination of density functional theory and machine learning techniques to explore a large number of 2D monolayers. As a proof of principle, the method is implemented for looking at new high transition point 2D magnetic monolayers among transition metals dichalcogenides, dihalides, and chalcogenides/halides TMXY. Our study is intended to provide physical insights into the magnetic properties in two dimensions and introduce new room-temperature magnetic monolayers. For instance, our results show that the effective electronic screening and magnetic transition temperature in 2D monolayers are strongly dependent on the type of non-magnetic ligand atoms. Three different Neural Network (NN), Random Forest (RF), and Supporting Vector Regression (SVR) algorithms are successfully employed for quick and accurate prediction of Hubbard U, cell parameters, and the magnetic exchange parameter for a large number of TMXY (TM: V, Cr, Fe, Co, Mn, Ni, Nb and X, Y: O, S, Se, Te, Cl, Br, I) monolayers. Moreover, the binary classification is employed to determine the magnetic and atomic structure ground state. Finally, the transition temperature of TMXY monolayers is estimated from the predicted value of effective magnetic exchange parameter. The magnetic monolayers with higher transition temperatures are suggested for further theoretical and experimental investigations.

Cobalt(II) complexes containing mefenamic acid with imidazole and pyridine based auxiliary ligands: Synthesis, structural investigation and cytotoxic evaluation

The interaction between CoCl2.6H2O and mefenamic acid (2-[(2,3-dimethylphenyl)amino]benzoic acid) in the presence of imidazole and pyridine based ligands resulted in the formation of [Co(mef)2(imi)2]; C-1, [Co(mef)2(nic)2(H2O)2].2H2O; C-2, [Co2(µ-H2O)(µ-mef-O,O')2(mef)2(py)4].CH3CN; C-3, and [Co2(µ-mef-O,O')4(apy)2].2CH3CN; C-4, (mef is monodentate mefenamato, µ-H2O is bridging aqua ligand, µ-mef-O, O' is bridging bidentate mefenamato, imi is imidazole, nic is nicotinamide, py is pyridine, and apy is 2-aminopyridine). The complexes were characterized spectroscopically and by physicochemical properties. Single-crystal X-ray diffraction studies confirmed the structures of the complexes. In C-1, Co(II) is in four-coordinate geometry, while in C-2, Co(II) is in hexa-coordination with two mefenamato carboxylate oxygen atoms, two nitrogen atoms, and two oxygen atoms from two solvent ligands. Complex C-3 consists of two cobalt centers linked by an aqua ligand and bridged by two mefenamato ligands. Furthermore, the octahedral geometry in each Co(II) in C-3 was completed by coordinating two monodentate mefenamato ligands and monodentate pyridine ligands. Similarly, in C-4, a Co-Co bond connects two Co(II) centers in six-coordinate geometry, with four bidentate mefenamato ligands acting as bridges between the two Co(II) and two 2-aminopyridine nitrogen, in monodentate coordination to each Co(II). The lattice solvents in C-2 to C-4 participated in intermolecular hydrogen bonding interactions with the mefenamato ligand. FTIR studies showed the presence of both monodentate and bidentate coordination of the deprotonated carboxylate oxygen atoms of the mefenamato ligand, as well as the coordination of the nitrogen donor ligands in the complexes. TG analysis determined the complexes' thermal stability and decomposition steps and ascertained their compositions, which agreed with the analytical and X-ray crystallography studies. Furthermore, the cytotoxicity of mefenamic acid and the cobalt (II) complexes on lung carcinoma cells (NCIH-460) and breast cells (MDAMB) were assessed using MTT assay. The complexes showed higher cytotoxicity than mefenamic acid against the MDAMB cell line.

Synthesis and crystal structure of the copper (II) carboxylate with 2,2-bipyridine, [Cu(4-mba)2(bipy)(H2O)

The new Cu(II) carboxylate complex, aqua(2,2'-bipyridine-κ2N,N')bis(4-methylbenzoato-κO)copper(II) [Cu(4-mba)2(bipy)(H2O)] (4-mba: 4-methylbenzoate, bipy: 2,2'-bipyridine) was synthesized, and the molecular structure of the complex was characterized by the single crystal X-ray diffraction technique. The X-ray diffraction analysis indicated that the asymmetric unit comprises an independent molecule. Crystal data for [Cu(4-meb)2(2,2-bipy)(H2O)]: Triclinic, space group P-1 (no. 2), a = 7.0452(13) Å, b = 11.260(2) Å, c = 16.635(3) Å, α = 103.543(7)°, β = 91.002(7)°, γ = 104.106(6)°, V = 1240.4(4) Å3, Z = 2, T = 296 K, μ(MoKα) = 0.918 mm-1, Dcalc = 1.360 g/cm3, 51364 reflections measured (5.054° ≤ 2Θ ≤ 57.38°), 6258 unique (Rint = 0.0398, Rsigma = 0.0284) which were used in all calculations. The final R1 was 0.0392 (I > 2σ(I)) and wR2 was 0.1021 (all data). The Cu(II) ion was found to be coordinated with two nitrogen atoms of the 2,2'-bipyridine ligand, two oxygen atoms of the 4-methyl benzoate molecule, and one oxygen atom of the aqua ligand. In the three-dimensional supramolecular architecture, molecules are connected through pairs of O-H···O and C-H···O intermolecular interactions, consisting of chains. The molecule also demonstrates Cg···Cg intermolecular interactions between six-membered rings of 2,2'-bipyridine.

Spin-Resolved Band Structure of Hoffman Clathrate [Fe(pz)2Pt(CN)4] as an Essential Tool to Predict Optical Spectra of Metal–Organic Frameworks

Paramount spin-crossover properties of the 3D-Hoffman metalorganic framework (MOF) [Fe(pz)2Pt(CN)4] are generally described on the basis of the ligand field theory, which provides adequate insight into theoretical and simulation analysis of spintronic complexes. However, the ligand field approximation does not take into account the 3D periodicity of the actual complex lattice and surface effects and therefore cannot predict a full-scale periodic structure without utilizing more advanced methods. Therefore, in this paper, the electronic properties of the exemplar MOF were analyzed from the band structure perspective in low-spin (LS) and high-spin (HS) states. The density-of-states spectra determined for both spin-up and spin-down electrons of Fe d6 orbitals indicate spin-orbital splitting and delocalization for HS due to spin polarization in the iron atom ligand field. Presence of the surface states in the real crystal causes a red shift of the metal-metal charge transfer (MMCT) and metal-ligand charge transfer (MLCT) peaks for both HS and LS states. The addition of residual water molecules and disorder among the pyrazine rings reveal additional influences on the positions of the pyrazine band and, therefore, on the absorption spectra of the crystal. The results show a magnification of the peak correlated with the MLCT in the HS state and a significant red shift of the LS characteristic absorption band. The presented approach involving band structure analysis delivers a more complete image of the electronic properties of the [Fe(pz)2Pt(CN)4] crystalline network and can be a landmark for insightful studies of other MOFs.

Synthesis, structure, and catalytic activity of polyoxometalate (C7H15N4)2[Co(H2O)6][C6H12N2CoMo6O24]·4H2O in the azide–alkyne cycloaddition reaction

A new polyoxomolybdate with a formula of (C7H15N4)2 [Co(H2O)6] [C6H12N2CoMo6O24]·4H2O (1) was synthesized and then it was characterized using IR, EDX and X-ray crystallography. The unit cell of 1 consists of two [Co(H2O)6]2+ and one N-methyluroptropine (C7H15N4)+ cations, and one polyanion [C6H12N2CoMo6O24]4- and four lattice water molecules. In the polyanion [C6H12N2CoMo6O24]4-, molybdenum metals are surrounded by two terminal and one bridging oxygen atoms and also one oxygen of the trimethanolamine ligand is coordinated to each Mo metal. Cobalt metal in the center of the polyanion is also bonded to four bridged oxygen atoms and two oxygen atoms of the trimethanolamine ligand. This novel polyoxomolybdate was used as an efficient catalyst for the azide–alkyne cycloaddition reaction to produce various 1,2,3-triazoles in high yields (34–99%).

Crystal structure of [2-({[2-(dimethylamino-κN)ethyl]imino-κN}methyl)phenolato-κO](1,10-phen-anthroline-κ2 N,N')copper(II) perchlorate.

The title compound, [Cu(C11H15N2O)(C12H8N2)]ClO4 or [Cu(L)(phen)](ClO4) {where L refers to the deprotonated form of 2-[(2-di-methyl-amino-ethyl-imino)-meth-yl]phenol} and phen is 1,10-phenanthroline) is a mononuclear mixed ligand copper(II) complex. The CuII atom is coordinated by two N and one O atoms of the tridentate Schiff base ligand (HL) and two N atoms of the 1,10-phenanthroline ligand, resulting in a five-coordinate complex. The asymmetric unit of the title complex contains two crystallographically independent complex cations (a and b) with a slightly different geometry around the CuII ion. The value of the trigonality index τ, indicates that in both cations a and b, the CuII atoms display a square-pyramidal distorted trigonal-bipyramidal (SPDTBP) geometry, although the distortion is greater for cation a.

Classification of GTP-dependent K-Ras4B active and inactive conformational states.

Classifying reliably active and inactive molecular conformations of wildtype (WT) and mutated oncogenic proteins is a key, ongoing challenge in molecular cancer studies. Here, we probe the GTP-bound K-Ras4B conformational dynamics using long-time atomistic molecular dynamics (MD) simulations. We extract and analyze the detailed underlying free energy landscape of WT K-Ras4B. We use two key reaction coordinates, labeled d1 and d2 (i.e., distances coordinating the Pβ atom of the GTP ligand with two key residues, T35 and G60), shown to correlate closely with activities of WT and mutated K-Ras4B. However, our new K-Ras4B conformational kinetics study reveals a more complex network of equilibrium Markovian states. We show that a new reaction coordinate is required to account for the orientation of acidic K-Ras4B sidechains such as D38 with respect to the interface with binding effector RAF1 and rationalize the activation/inactivation propensities and the corresponding molecular binding mechanisms. We use this understanding to unveil how a relatively conservative mutation (i.e., D33E, in the switch I region) can lead to significantly different activation propensities compared with WT K-Ras4B. Our study sheds new light on the ability of residues near the K-Ras4B-RAF1 interface to modulate the network of salt bridges at the binding interface with the RAF1 downstream effector and, thus, to influence the underlying GTP-dependent activation/inactivation mechanism. Altogether, our hybrid MD-docking modeling approach enables the development of new in silico methods for quantitative assessment of activation propensity changes (e.g., due to mutations or local binding environment). It also unveils the underlying molecular mechanisms and facilitates the rational design of new cancer drugs.

Effect of pendent alkyl group of ancillary ligand on molecular structures of new metal(II)-2, 4-dinitro benzoate complexes- spectral, structural and photoluminescence studies

A series of new metal(II) complexes having general formulae, [M (2, 4-dnb)2(L)2] (where 2, 4-dnbH = 2,4-dinitro benzoic acid; M = Co(1), Ni(2), Zn(3) and Cd(4), L = methyl hydrazine carboxylate (mc); M = Co(5), Ni(6), Zn(7) and Cd(8), L = ethyl hydrazine carboxylate (ec)) were prepared and characterized using elemental analysis, UV-Visible, FT-IR, emission spectroscopic and powder XRD techniques. Single crystal X-ray study for 3 and 7 shows that metal ion, in both complexes, adopts distorted MN2O4 geometry arising from a pair of N,O-chelating methyl/ethyl hydrazine carboxylate ligands at equatorial sites and monodendate 2, 4-dnb ions at the axial sites. The pair of nitrogen (or) oxygen atoms of chelating ligands (L) are trans positioned in 3 whereas they are cis positioned in 7. All the complexes exhibit photoluminescence property. On heating all the complexes show explosive nature of decomposition.

Linear response based theories for Dzyaloshinskii-Moriya interactions

We investigate abilities of various linear response based techniques for extracting parameters of antisymmetric Dzyaloshinskii-Moriya (DM) interactions from the first-principles electronic structure calculations. For these purposes, we further elaborate the idea of Sandratskii [Phys. Rev. B 96, 024450 (2017)], which states that $z$ component of the DM vector can be computed by retaining only spin-diagonal part of the spin-orbit (SO) coupling. We start our analysis with the magnetic force theorem (MFT), which relies on additional approximations resulting in the linear dependence of the exchange interactions on the response tensor, and compare it with the exact approach formulated in terms of the inverse response. We propose the downfolding procedure transferring the effect of these ligand spins into parameters of effective interactions between the localized spins. These techniques are applied for the series of CrCl$_3$ and CrI$_3$ based materials, including bulk, monolayer, bilayer, and three-layer systems. Particularly, we discuss how the DM interactions are induced by the inversion symmetry breaking at the surface or by the electric field. As long as the SO interaction of the heavy ligand atoms is taken into account in the calculations of the response tensor between the Cr $3d$ states, the MFT appears to be a good approximation for the DM interactions, being in contrast with the isotropic exchange, for which MFT and the exact method provide quite a different description. Finally, we discuss the relevance of our approach to other techniques ever proposed for calculations of the DM interactions. Particularly, we argue that the spin-current model for the DM interactions can be derived from the MFT based expression and is the relativistic counterpart of the double exchange, occurring in metallic systems in the limit of infinite exchange splitting.

Investigating the Electronic Structure of Prospective Water-Splitting Oxide BaCe0.25Mn0.75O3−δ before and after Thermal Reduction

BaCe$_{0.25}$Mn$_{0.75}$O$_{3-\delta}$ (BCM), a non-stoichiometric oxide closely resembling a perovskite crystal structure, has recently emerged as a prospective contender for application in renewable energy harvesting by solar thermochemical hydrogen generation. Using solar energy, oxygen-vacancies can be created in BCM and the reduced crystal so obtained can, in turn, produce H2 by stripping oxygen from H2O. Therefore, a first step toward understanding the working mechanism and optimizing the performance of BCM, is a thorough and comparative analysis of the electronic structure of the pristine and the reduced material. In this paper, we probe the electronic structure of BCM using the combined effort of first-principles calculations and experimental O K-edge x-ray absorption spectroscopy (XAS). The computed projected density-of-states (PDOS) and orbital-plots are used to propose a simplified model for orbital-mixing between the oxygen and the ligand atoms. With the help of state-of-the-art simulations, we are able to find the origins of the XAS peaks and to categorize them on the basis of contribution from Ce and Mn. For the reduced crystal, the calculations show that, as a consequence of dielectric screening, the change in electron-density resulting from the reduction is strongly localized around the oxygen vacancy. Our experimental studies reveal a marked lowering of the first O K-edge peak in the reduced crystal which is shown to result from a diminished O-2p contribution to the frontier unoccupied orbitals, in accordance with the tight-binding scheme. Our study paves the way for investigation of the working-mechanism of BCM and for computational and experimental efforts aimed at design and discovery of efficient water-splitting oxides.

Exploring cooperative molecular contacts using a PostgreSQL database system.

Cooperative molecular contacts play an important role in protein structure and ligand binding. Here, we constructed a PostgreSQL database that stores structural information in the form of atomic environments and allows flexible mining of molecular contacts. Taking the Ser-His-Asp/Glu catalytic triad as a first test case, we demonstrate that the presence of a carboxylate oxygen atom in the vicinity of a His is associated with shorter Ser-OH..N-His bond in the PDB30 subset. We prospectively mine catalytic triads in unannotated proteins, suggesting catalytic functions for unannotated proteins. As a second test case, we demonstrate that this database system can include ligand atoms, represented by Sybyl atom types, by evaluating the proportion of counter-ions for ligand carboxylate oxygens.

The tritopic phosphanylthiolato ligand P(2-SHC6H4)2(2,4,6-iPr3C6H2) enables formation of a thiolato-bridged dinuclear nickel(II) complex featuring a Ni2S2 butterfly core

The bulky tritopic phosphanylthiolato pincer ligand (Tipp)P(2-SHC6H4)2 (Tipp = 2,4,6-iPr3C6H2) (TippPS2H2) reacts with nickel dichloride to give the dinuclear nickel(II) complex [Ni{(Tipp)P(µ-2-SC6H4)2-κ3S,S',P}]2 (1). The X-ray structure analysis of 1 shows a dinuclear complex consisting of two nickel(II) phosphanyldithiolato units formed with the dianionic tridentate pincer ligand, [Ni(TippPS2)], which dimerise via thiolato bridges involving one of the two sulfur atoms of each pincer ligand. The resulting four-membered central Ni2S2 ring has a butterfly conformation. The molecule is located on a crystallographic twofold axis and displays two chiral phosphorus centres. Only the rac isomer is formed diastereoselectively; both enantiomers of 1 (R,R and S,S) are present in the unit cell.

Enhancing the Magnetization Blocking Energy of Biradical-Metal System by Merging Discrete Complexes into One-Dimensional Chains.

The reaction of nitronyl nitroxide biradical NITPhMeImbis [5-(2-methylimidazole)-1,3-bis(1-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)-benzene] with Ln(hfac)3 ⋅ 2H2 O and Cu(hfac)2 (hfac=hexafluoroacetylacetonate), led to two series of 2p-3d-4f complexes, namely, nona-spin clusters, [Ln2 Cu3 (hfac)12 (NITPhMeImbis)2 ] (Ln=Gd 1, Dy 2), or one-dimensional chains [LnCu2 (hfac)7 (NITPhMeImbis)] (Ln=Y 3, Dy 4, Tb 5) depending on the temperature of the reaction. All five complexes contain a biradical-Ln unit in which the biradical chelates the LnIII ion by the means of one aminoxyl (i. e. NO) group of each NIT unit. For the discrete complexes, a Cu(hfac)2 links two biradical-Ln units via one of the remaining NO groups, while for the chain compounds, the two remaining NO groups of the biradical-Ln moiety are each coordinated to a Cu(hfac)2 unit to form a 1D coordination polymer. Moreover, a terminal Cu(hfac)2 unit is coordinated to the imidazole-N atom of the NITPhMeImbis ligand. Spin dynamics investigations evidenced the onset of slow relaxation of the magnetization for 2, whereas 4 and 5 exhibit a typical single-chain magnet behavior. This highlights the vital role of the 1D spin correlation in the blocking of the magnetization. These results illustrate that from the same basic building blocks, magnetic relaxation can be carefully modulated by structural adjustments.

Nature of NMR Shifts in Paramagnetic Octahedral Ru(III) Complexes with Axial Pyridine-Based Ligands.

In recent decades, transition-metal coordination compounds have been extensively studied for their antitumor and antimetastatic activities. In this work, we synthesized a set of symmetric and asymmetric Ru(III) and Rh(III) coordination compounds of the general structure (Na+/K+/PPh4+/LH+) [trans-MIIIL(eq)nL(ax)2]- (M = RuIII or RhIII; L(eq) = Cl, n = 4; L(eq) = ox, n = 2; L(ax) = 4-R-pyridine, R = CH3, H, C6H5, COOH, CF3, CN; L(ax) = DMSO-S) and systematically investigated their structure, stability, and NMR properties. 1H and 13C NMR spectra measured at various temperatures were used to break down the total NMR shifts into the orbital (temperature-independent) and hyperfine (temperature-dependent) contributions. The hyperfine NMR shifts for paramagnetic Ru(III) compounds were analyzed in detail using relativistic density functional theory (DFT). The effects of (i) the 4-R substituent of pyridine, (ii) the axial trans ligand L(ax), and (iii) the equatorial ligands L(eq) on the distribution of spin density reflected in the "through-bond" (contact) and the "through-space" (pseudocontact) contributions to the hyperfine NMR shifts of the individual atoms of the pyridine ligands are rationalized. Further, we demonstrate the large effects of the solvent on the hyperfine NMR shifts and discuss our observations in the general context of the paramagnetic NMR spectroscopy of transition-metal complexes.

Red emissive β-diketonate Ln(III) complexes for displays: Preparation, spectroscopic and optical investigations

Photophysical and optoelectronic characteristics of a series of ternary lanthanide (Eu, Sm) complexes with diacetylmethane (DAM) and substituted 2,2′-bipyridine derivatives as auxiliary ligands were examined thoroughly by various characterization techniques. Optical and electronic band gap analyses suggest the conducting nature of complexes. Vibrational spectral analysis affirms the binding of lanthanide ions with oxygen and nitrogen atoms of DAM and heteroaromatic auxiliary ligand respectively. Photoluminescence emission spectra indicate that the prepared trivalent complexes give red emission which is further confirmed by Commission Internationale de l′ Eclairage (CIE) color coordinates. Color purity value of complexes shows their luminous nature. Red light emitting materials have found good significance in solid state electronics, flat panel displays and organic light emitting devices (OLEDs).