Ligand Geometry Research Articles

Ring-Shaped Phosphinoamido-Magnesium-Hydride Complexes: Syntheses, Structures, Reactivity, and Catalysis.

A series of magnesium(II) complexes bearing the sterically demanding phosphinoamide ligand, L(-) =Ph2 PNDip(-) , Dip=2,6-diisopropylphenyl, including heteroleptic magnesium alkyl and hydride complexes are described. The ligand geometry enforces various novel ring and cluster geometries for the heteroleptic compounds. We have studied the stoichiometric reactivity of [(LMgH)4 ] towards unsaturated substrates, and investigated catalytic hydroborations and hydrosilylations of ketones and pyridines. We found that hydroborations of two ketones with pinacolborane using various Mg precatalysts is very rapid at room temperature with very low catalyst loadings, and ketone hydrosilylation using phenylsilane is rapid at 70 °C. Our studies point to an insertion/σ-bond metathesis catalytic cycle of an in situ formed "MgH2 " active species.

Balanced Dual Emissions from Tridentate Phosphine-Coordinate Copper(I) Complexes toward Highly Efficient Yellow OLEDs.

Dual emissive copper(I) halide complexes TTPPCuX (X = Cl, Br, I) with a triphosphine ligand and stable tetrahedral geometries are constructed, in which TTPPCuI successfully achieves the balanced dual thermally activated delayed fluorescence and phosphorescence (PH) emissions with PH fraction of 39% at ambient temperature, supporting the equal triplet exciton reallocation for the state-of-the-art device performance.

Tailored synthesis of CuS nanodisks from a new macrocyclic precursor and their efficient catalytic properties on methylene blue dye degradation

In this study, CuS nanodisks have been synthesized from a tetraaza (N4) macrocyclic complex precursor by a facile wet chemical method. The crystallinity and morphology of the as-synthesized products were characterized by X-ray diffraction and transmission electron microscopy, which confirm a phase pure crystalline CuS nanostructures with ~15 to 20 nm in dimension with ~5 nm thickness. A possible formation mechanism and growth process of the CuS nanodisks are discussed using thiourea and tetraaza ligand as the sulfur donor and stabilizing agent, respectively. Cyclic N4 ligand also acts as a binding agent to template-guide the oriented growth of CuS nanodisks. The optimized geometry of ligands and complexes was calculated using B3YLP functional, which indicates that the HOMO in the complex located on metal center and N atoms are weakly bonded to the metal center. The catalytic activity of CuS nanodisks toward MB degradation with light displays the higher MB degradation rate than under dark in the presence of H2O2. The C t/C 0 plot as a function of time displays the higher MB degradation activity of CuS nanoparticles with H2O2. The recycle stability of CuS nanoparticles was even found to be >80 % after five cycles studied by repeating the MB degradation with same CuS nanoparticles sample. CuS nanostructures synthesized from a tetraaza macrocyclic complex precursor show the disk-like registry with average lateral dimension between 15 and 20 nm and thickness of 5 nm. The catalytic activity of CuS nanodisks toward MB degradation with light displays the higher MB degradation rate than in dark in the presence of H2O2.

Metallo-Supramolecular Self-Assembly of a Multicomponent Ditrigon Based on Complementary Terpyridine Ligand Pairing.

Predesigned complementary complexation of two 2,2':6',2″-terpyridine-based ligands was established by installing 2,6-dimethoxyphenyl substituents at the terpyridyl 6,6″-positions, which provided ancillary ion-dipole interactions in the coordination process and extra π-stacking stabilization in the resultant heteroleptic complex. The high-fidelity self-recognition ligation afforded facile access to the quantitative self-assembly of multicomponent triangle [Cd6L(3)3L(4)3] and ditrigon [Cd15L(3)6L(5)3] (that is, a hexagon with six 120° angles and two alternating edge lengths). It was found that the linear 6,6″-substituted ditopic motif (L(3)) would be directed by the ligand geometry of L(5) to selectively incorporate into the parallel homoleptic connections in the bilayered framework.

Computer-Aided Molecular Design of Bis-phosphine Oxide Lanthanide Extractants.

Computer-aided molecular design and high-throughput screening of viable host architectures can significantly reduce the efforts in the design of novel ligands for efficient extraction of rare earth elements. This paper presents a computational approach to the deliberate design of bis-phosphine oxide host architectures that are structurally organized for complexation of trivalent lanthanides. Molecule building software, HostDesigner, was interfaced with molecular mechanics software, PCModel, providing a tool for generating and screening millions of potential R2(O)P-link-P(O)R2 ligand geometries. The molecular mechanics ranking of ligand structures is consistent with both the solution-phase free energies of complexation obtained with density functional theory and the performance of known bis-phosphine oxide extractants. For the case where the link is -CH2-, evaluation of the ligand geometry provides the first characterization of a steric origin for the "anomalous aryl strengthening" effect. The design approach has identified a number of novel bis-phosphine oxide ligands that are better organized for lanthanide complexation than previously studied examples.

Energy Landscapes for the Self-Assembly of Supramolecular Polyhedra

We develop a mathematical model for the energy landscape of polyhedral supramolecular cages recently synthesized by self-assembly [Sun et al., Science 2010]. Our model includes two essential features of the experiment: (i) geometry of the organic ligands and metallic ions; and (ii) combinatorics. The molecular geometry is used to introduce an energy that favors square-planar vertices (modeling $\mathrm{Pd}^{2+}$ ions) and bent edges with one of two preferred opening angles (modeling boomerang-shaped ligands of two types). The combinatorics of the model involve $2$-colorings of edges of polyhedra with $4$-valent vertices. The set of such $2$-colorings, quotiented by the octahedral symmetry group, has a natural graph structure, and is called the combinatorial configuration space. The energy landscape of our model is the energy of each state in the combinatorial configuration space. The challenge in the computation of the energy landscape is a combinatorial explosion in the number of $2$-colorings of edges. We describe sampling methods based on the symmetries of the configurations and connectivity of the configuration graph. When the two preferred opening angles encompass the geometrically ideal angle, the energy landscape exhibits a very low-energy minimum for the most symmetric configuration at equal mixing of the two angles, even when the average opening angle does not match the ideal angle.

ChemInform Abstract: Zinc(II)‐ and Cadmium(II)‐Organic Frameworks with 1‐Imidazole‐Containing and 1‐Imidazole‐Carboxylate Ligands

AbstractReview: 155 refs.

An unusual coordination polymer containing Cu(+) ions and featuring possible Cu...Cu `cuprophilic' interactions: poly[di-μ-chlorido-(μ4-3,5-diaminobenzoato-κ(4)O:O':N:N')tricopper(I)(3 Cu-Cu)

Compounds containing copper(I) are of interest for their role in biological processes. The nature of short (< ∼ 3.2 Å) Cu...Cu contacts within these compounds has been debated, being either described as weakly attractive (bonding) `cuprophilic' interactions, or simply as short metal-metal distances constrained by ligand geometry or largely ionic in nature. The title three-dimensional Cu(+)-containing coordination polymer, [Cu3(C7H7N2O2)Cl2]n, was formed from the in situ reduction of CuCl2 in the presence of 3,5-diaminobenzoic acid and KOH under hydrothermal conditions. Its complex crystal structure contains ten distinct Cu(I) atoms, two of which lie on crystallographic inversion centres. The copper coordination geometries include near-linear CuOCl and CuN2, T-shaped CuOCl2 and distorted tetrahedral CuOCl3 groups. Each Cu(I) atom is also associated with two adjacent metal atoms, with Cu...Cu distances varying from 2.7350 (14) to 3.2142 (13) Å; if all these are regarded as `cuprophilic' interactions, then infinite [-101] zigzag chains of Cu(I) atoms occur in the crystal. The structure is consolidated by N-H...Cl hydrogen bonds.

Metal–organic and supramolecular lead(ii) networks assembled from isomeric nicotinoylhydrazone blocks: the effects of ligand geometry and counter-ion on topology and supramolecular assembly

A new series of six structurally diverse lead(II) coordination compounds was assembled from two isomeric nicotinoylhydrazones as neutral ligands and three Pb(II) salts with different monoanions (chloride, nitrate and thiocyanate) as starting materials. The products were isolated in good yields and were fully characterized, including by single-crystal X-ray diffraction and theoretical methods. Within the six compounds, three feature 2D metal–organic networks, two are 1D coordination polymers, and another one comprises discrete 0D dimeric units. The structures of the latter low dimensional compounds are extendable into 2D supramolecular networks. The topology of the coordination or supramolecular networks is primarily dictated by the geometry of the nicotinoylhydrazone used as a main building block. In contrast, supramolecular interactions are greatly influenced by the choice of the anion in the starting lead(II) salt, which is demonstrated by Hirshfeld surface analysis. In fact, the topological analysis and classification of metal–organic or supramolecular underlying networks in the obtained compounds was performed, disclosed the hcb, 2C1, gek1, SP 1-periodic net (4,4)(0,2) and 3,4L83 topological types; the latter topology was documented for three compounds, including both coordination and supramolecular networks. In the two compounds containing thiocyanate moieties, there are supramolecular contacts between the thiocyanate anions and lead centres. These were shown by DFT calculations to be strong tetrel bonds (−15.3 and −16.7 kcal mol−1) between the σ-hole of the lead atom and the π-system of the thiocyanate S–C bond.

Biomimetic Surface Patterning Promotes Mesenchymal Stem Cell Differentiation.

Both chemical and mechanical stimuli can dramatically influence cell behavior. By optimizing the signals cells experience, it may be possible to control the behavior of therapeutic cell populations. In this work, biomimetic geometries of adhesive ligands, which recapitulate the morphology of mature cells, are used to direct human mesenchymal stem cell (HMSC) differentiation toward a desired lineage. Specifically, adipocytes cultured in 2D are imaged and used to develop biomimetic virtual masks used in laser scanning lithography to form patterned fibronectin surfaces. The impact of adipocyte-derived pattern geometry on HMSC differentiation is compared to the behavior of HMSCs cultured on square and circle geometries, as well as adipocyte-derived patterns modified to include high stress regions. HMSCs on adipocyte mimetic geometries demonstrate greater adipogenesis than HMSCs on the other patterns. Greater than 45% of all HMSCs cultured on adipocyte mimetic patterns underwent adipogenesis as compared to approximately 19% of cells on modified adipocyte patterns with higher stress regions. These results are attributed to variations in cytoskeletal tension experienced by cells on the different protein micropatterns. The effects of geometry on adipogenesis are mitigated by the incorporation of a cytoskeletal protein inhibitor; exposure to this inhibitor leads to increased adipogenesis on all patterns examined.

Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1-Hydroxypyridin-2-one Complexes in Aqueous Solution.

A series of 10 tetradentate 1-hydroxy-pyridin-2-one (1,2-HOPO) ligands and corresponding eight-coordinated photoluminescent Eu(III) and Sm(III) complexes were prepared. Generally, the ligands differ by the linear (nLI) aliphatic linker length, from 2 to 8 methylene units between the bidentate 1,2-HOPO chelator units. The photoluminescent quantum yields (Φtot) were found to vary with the linker length, and the same trend was observed for the Eu(III) and Sm(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φtotxε). The change in ligand wrapping pattern between 2LI and 5LI complexes observed by X-ray diffraction (XRD) is further supported by density functional theory (DFT) calculations. The bimodal Φtot trends of the Eu(III) and Sm(III) complexes are rationalized by the change in ligand wrapping pattern as the bridge (nLI) is increased in length.

Resonance Raman and vibrational mode analysis used to predict ligand geometry for docking simulations of a water soluble porphyrin and tubulin

The ability to modify the conformation of a protein by controlled partial unfolding may have practical applications such as inhibiting its function or providing non-native photosensitive properties. A water-soluble porphyrin, meso-tetrakis (p-sulfonatophenyl) porphyrin (TSPP), non-covalently bound to tubulin can be used as a photosensitizer, which upon irradiation can lead to conformational changes of the protein. To fully understand the mechanism responsible for this partial unfolding and determine the amino acid residues and atoms involved, it is essential to find the most likely binding location and the configuration of the ligand and protein. Techniques typically used to analyze atomic position details, such as nuclear magnetic resonance and X-ray crystallography, require large concentrations, which are incompatible with the dilute conditions required in experiments for photoinduced mechanisms. Instead, we develop an atomistic description of the TSPP–tubulin complex using vibrational mode analysis from density functional theory calculations correlated to resonance Raman spectra of the porphyrin paired with docking simulations. Changes in the Raman peaks of the porphyrin molecule correlate with changes in its structural vibrational modes when bound to tubulin. The data allow us to construct the relative geometry of the porphyrin when bound to protein, which are then used with docking simulations to find the most likely configuration of the TSPP–tubulin complex.

Synthesis and spectroscopic properties of a copper(II) binuclear complex of a novel tetradentate asymmetrical Schiff base ligand and its DFT study

A new asymmetrical Schiff base ligand, N,N′-(salicylidene)-5-bromo-2-hydroxybenzaldehyde-p-phenylenediamine (SBHBP), and its binuclear Cu(II) complex have been synthesized. The molecular structures and spectroscopic properties of the ligand and its complex were experimentally characterized by elemental analysis, FT-IR, NMR and UV–Vis spectroscopic techniques and computationally by the density functional theory (DFT) method. The molecular geometry and vibrational frequencies of the SBHBP ligand in the ground state have been calculated using the B3LYP/6-31G(d,p) and 6-31++G(d,p) basis sets. A potential surface scan study was carried out and the most stable geometry of the SBHBP ligand was confirmed. The calculated results show that the optimized geometry can well reproduce the structural parameters, and the theoretical vibrational frequencies are in good agreement with the experimental values. On calculation of the electronic absorption spectra, TD-DFT calculations were carried out in both the gas and solution phases. The energetic behavior of the SBHBP ligand has been examined in solvent media using the B3LYP method with the 6-31G(d,p) and 6-31++G(d,p) basis sets by applying the Onsager method and polarizable continuum model (PCM). Additionally, Mulliken and NBO atomic charges, NMR analysis, molecular electrostatic potential (MEP) and frontier molecular orbitals (FMO) analysis of the SBHBP ligand were investigated using theoretical calculations.

NHC Versus Pyridine: How “Teeth” Change the Redox Behavior of Iron(II) Complexes

A series of octahedral iron(II) complexes with tetradentate NHC/pyridine hybrid ligands containing up to three pyridyl units was designed to study the influence of NHC and pyridine donors on the electronic structure of the metal center. Structural analysis of the iron complexes by NMR spectroscopy and single-crystal X-ray diffraction reveals different coordination modes of the ligand depending on the linkage of the different donor moieties. The oxidation potentials of all complexes correlate linearly with the number of NHC moieties coordinated to iron, as shown by cyclic voltammetry. The influence, although minor, of structural properties on the oxidation potential and (in one case) the influence of the oxidation state of the coordination geometry of the hybrid ligand are also demonstrated.

Crystal structure of di-μ-iodido-bis-[bis(aceto-nitrile-κN)copper(I)

The title compound, [Cu2I2(CH3CN)4], exhibits a centrosymmetric Cu2I2 core [Cu⋯Cu distance = 2.7482 (11) Å], the CuI atoms of which are further coordinated by four mol­ecules of aceto­nitrile. The CuI atom has an overall distorted tetra­hedral coordination environment evidenced by L—Cu—L angles (L = N or I) ranging from 100.47 (10) to 117.06 (2)°. The coordination geometries of the aceto­nitrile ligands deviate slightly from linearity as shown by Cu—N—C angles of 167.0 (2) and 172.7 (2)°. In the crystal, there are no significant hydrogen-bonding inter­actions present, so the crystal packing seems to be formed predominantly by van der Waals forces.

A mononuclear cobalt(III) 3-(2-pyridyl)-5-phenyl-1,2,4-triazolato complex: hydrothermal synthesis, crystal structure, thermostability, and DFT calculations

Abstract Starting with 1H -3-phenyl-5-(pyridin-2-yl)-1,2,4-triazole (1-Hppt), a Co(III) complex, [Co(ppt)3] (1), has been synthesized by reaction with CoF3 under hydrothermal conditions and characterized by its infrared spectrum and elemental analysis. The structure was determined by single-crystal and powder X-ray diffraction. Density functional theory (DFT) was employed to determine the optimized geometry and preferred conformation of the free ligand. A supramolecular network is formed via π–π stacking interactions. The conformation and geometry of the ligands correspond with the calculated results.

Anionic and Mononuclear Phosphinidene and Imide Complexes of Niobium

The reactivity of a terminal methylidene complex of niobium, [(ArO)2Nb═CH2(CH3)(CH2PPh3)] (1), with the primary phosphine PhPH2 results in formation of the anionic phosphinidene complex [H3CPPh3][(ArO)2Nb═PPh(CH3)2] (2), where both the methylidene and ylide ligands of the precursor experience protonation. Multinuclear NMR spectroscopy and X-ray diffraction studies indicate formation of a bent phosphinidene ligand. Similar reactivity is also observed with primary amines, specifically AdNH2 (Ad = 1-adamantyl) and MesNH2 (Mes = 2,4,6-trimethylphenyl), resulting in formation of the corresponding imide complexes [H3CPPh3][(ArO)2Nb═NR(CH3)2] (R = Mes, (3), Ad, (4)). Whereas 2 has a bent phosphinidene ligand and pseudo trigonal bipyramidal structure, the solid-state structure determination of complex 4 reveals a linear imide ligand and square-pyramidal geometry, where the imide enjoys significant Nb–NR multiple-bond character.

Copper(II) ion as modulator of the conformation of non-steroidal anti-inflammatory drugs. Theoretical insight into the structure

Complexes of four non-steroidal anti-inflammatory drugs (NSAIDs): phenylobutazone, nimesulide, diclofenac and meloxicam with Cu2+ have been theoretically investigated using B3LYP/6-31G∗∗ method. The potential copper binding sites for the selected drugs have been found. Complexation of the investigated drug with Cu2+ can significantly change of the ligand geometry as for phenylobutazone and nimesulide or conformation of the drug can be persistent during complexation with Cu2+ as for meloxicam. For the last compound presence of Cu2+ influences the intramolecular OHO hydrogen bond. For the lowest energy complexes interaction of Cu2+ with the drug has been investigated in the frame of Atom in Molecule (AIM) theory.

Two-dimensional assemblies in f-element ion (UO22+, Yb3+) complexes with two cyclohexyl-based polycarboxylates

Three complexes of f-element metal cations, uranyl and ytterbium(III), with either Kemp’s triacid (H3L1) or 1,2,3,4,5,6-cyclohexanehexacarboxylic acid (H6L2) were obtained under solvo-hydrothermal conditions. The trianionic ligand in [H2NMe2][UO2(L1)] (1) is in the very unusual boat conformation, with two equatorial and one axial carboxylate groups. In contrast to the all-axial chair conformation, this ligand geometry is not conducive to the formation of a closed species, and a honeycomb 2D network is formed instead. Adopting the chair conformation, this ligand reacts with ytterbium(III) to give the complex [Yb(L1)(H2O)2] (2), which crystallizes as a 2D network. All-cis H6L2 undergoes isomerization into its all-trans form under the conditions used, with all functional groups equatorial. In the presence of additional nickel(II) nitrate, the complex [Ni(H2O)6][(UO2)2(L2)]·1.5H2O (3) is obtained, in which the unusual coordination mode of the hexa-anionic ligand leads to the formation of a 2D assembly.

Three-dimensional, soft neotissue arrays as high throughput platforms for the interrogation of engineered tissue environments

Local signals from tissue-specific extracellular matrix (ECM) microenvironments, including matrix adhesive ligand, mechanical elasticity and micro-scale geometry, are known to instruct a variety of stem cell differentiation processes. Likewise, these signals converge to provide multifaceted, mechanochemical cues for highly-specific tissue morphogenesis or regeneration. Despite accumulated knowledge about the individual and combined roles of various mechanochemical ECM signals in stem cell activities on 2-dimensional matrices, the understandings of morphogenetic or regenerative 3-dimenstional tissue microenvironments remain very limited. To that end, we established high-throughput platforms based on soft, fibrous matrices with various combinatorial ECM proteins meanwhile highly-tunable in elasticity and 3-dimensional geometry. To demonstrate the utility of our platform, we evaluated 64 unique combinations of 6 ECM proteins (collagen I, collagen III, collagen IV, laminin, fibronectin, and elastin) on the adhesion, spreading and fate commitment of mesenchymal stem cell (MSCs) under two substrate stiffness (4.6 kPa, 20 kPa). Using this technique, we identified several neotissue microenvironments supporting MSC adhesion, spreading and differentiation toward early vascular lineages. Manipulation of the matrix properties, such as elasticity and geometry, in concert with ECM proteins will permit the investigation of multiple and distinct MSC environments. This paper demonstrates the practical application of high through-put technology to facilitate the screening of a variety of engineered microenvironments with the aim to instruct stem cell differentiation.