Calculation of van der Waals radii of atoms from bond distances

Mechanochemical preparation of strongly emissive monosubstituted triarylphosphane gold(i) compounds activated by hydrogen bonding driven aggregations

Gold(i) triarylphosphane compounds are a well-known class of coordination compounds displaying from mild to strong emissive properties. Mechanochemical approaches to the preparation, spectroscopic characterization, X-ray diffraction structural determination, and photophysical studies of green emissive neutral linear monophosphane or neutral pseudo-T-shaped or cationic bis-phosphane gold(i) compounds, are herein discussed. The mechanochemical approach to the preparation of gold(i) derivatives was particularly successful for ligands bearing the carboxylic group, while the preparation with esterified ligands yields better results with solvent-mediated methods. The introduction of carboxyl or ester substituents in one aryl group favors the ligand-centered emissions. The analysis of the origin of the emissions was elucidated on the basis of DFT calculations, addressing the emissive behavior to ligand-centered excited states, strongly affected by supramolecular reversible hydrogen bonding aggregation. The study indicates that the ligand with the carboxylic group is particularly suitable for the mechanochemical preparation of emissive gold(i) complexes for material science applications.

Clustering of metal dopants in defect sites of graphene-based materials

Single-atom catalysts are promising candidates for many industrial reactions. However, making true single-atom catalysts is an experimental dilemma, due to the difficulty of keeping dopant single atoms stable at temperature and under pressure. This difficulty can lead to clustering of the metal dopant atoms in defect sites. However, the electronic and geometric structure of sub-nanoscale clusters in single-atom defects has not yet been explored. Furthermore, recent studies have proven sub-nanoscale clusters of dopants in single-atom defect sites can be equally good or better catalysts than their single-atom counterparts. Here, a comprehensive DFT study is undertaken to determine the geometric and electronic structure effects that influence clustering of noble and p-block dopants in C₃- and N₄-defect sites in graphene-based systems. We find that the defect site is the primary driver in determining clustering dynamics in these systems.

Spodium Bonds in Biological Systems: Expanding the Role of Zn in Protein Structure and Function

Understanding the structural and functional implications of metal ions is of pivotal significance to chemical biology. Herein, we report first time the evidence of spodium bonds (SpB's, an attractive noncovalent force involving elements from group 12 and electron-rich species) in tetrahedral Zn-binding sites. Through a combined crystallographic (PDB analysis) and computational (ab initio calculations) study, we demonstrate that Zn SpB's are abundant and might be involved in protein structure and enzyme inhibition.

Preparation and properties of a dual-function cellulose nanofiber-based bionic biosensor for detecting silver ions and acetylcholinesterase

A dual-function cellulose nanofiber (CNF)-based bionic biosensor with good biocompatibility was developed for detecting Ag⁺ and acetylcholinesterase (AChE) by grafting deoxyribonucleic acid (DNA) onto CNF. The Ag⁺ ions captured by the biosensor acted as recognition sites for the detection of AChE. The CNF-based bionic biosensor (CNF-DNA) could detect Ag⁺ concentrations as low as 10^-6 nM in the presence of interference metal ions (Hg²⁺, Ba²⁺, Cd²⁺, Mg²⁺, Mn²⁺, Pb²⁺, and Zn²⁺). DNA-template silver nanoclusters (DNA-AgNCs) were formed on the surface of CNF-DNA during the detection of Ag⁺ (CNF-DNA-AgNCs). This new strategy yielded CNF-DNA-AgNCs through the adsorption of Ag⁺ ions onto the cytosine base of the single-stranded DNA in CNF-DNA without the use of any additional reducer. Meanwhile, the CNF-DNA-AgNCs exhibited excellent sensitivity and selectivity for trace levels (0.053 mU/mL) of AChE in the presence of interference reagents. The novel strategy proposed in this paper may establish a foundation for further research on DNA-template AgNCs for developing biosensors and biomarkers for in vivo and in vitro detection.

Spodium bonding in five coordinated Zn(ii): a new player in crystal engineering?

This highlight evidences the existence and importance of spodium bonds (SpB) in solid state structures involving five-coordinated square-pyramidal Zn(ii) spodium atom.

Synthesis, X-ray characterization and regium bonding interactions of a trichlorido(1-hexylcytosine)gold(iii) complex

Herein we report the synthesis and X-ray characterization of a gold(iii) complex of 1-hexylcytosine via N(3). The AuCl₃N complexes stack on top of each other by reciprocal [AuCl] regium bonding interactions. After the first example 35 years ago, this is the second available structure of a cytosine nucleobase model complexed to gold(iii).

Diferrocenylmercury diphosphine diastereomers with unique geometries: trans-chelation at Pd(ii) with short Hg(ii)Pd(ii) contacts

Diphosphine chelate ligands are essential in many catalytic processes with both the electronic structure and bite angle having a dramatic influence on the coordination behavior and catalytic performance. The synthesis of a new class of diferrocenylmercury-supported diphosphine chelate ligands was accomplished by the reaction of (ortho-diphenylphosphino)ferrocenyl sulfinate (2) with t-BuLi, followed by treatment with mercury(ii) chloride. Two diastereomers, 4a (pSpR-, meso-isomer) and 4b (pSpS-isomer), differ in the orientation of the ferrocene moiety relative to the central Ph₂PC₅H₃-Hg-C₅H₃PPh₂ bridging entity. They were isolated independently and fully characterized in solution and in the solid state by single crystal X-ray diffraction analysis. Key characteristics of these ligands are their exceptionally wide and flexible bite angles and the unique stereochemical environment that is achieved upon coordination to transition metals. Complexation to Pd(ii)Cl₂ gives rise to unusual square-planar trans-chelate complexes 5a (meso) and 5b (pSpS). In competition reactions, 4a and 4b show similar reactivity toward Pd(ii)Cl₂. The molecular structures of 5a and 5b exhibit short PdHg contacts, possibly indicating secondary metallophilic interactions as further evidenced by bond-critical points between Pd and Hg that were identified by AIM analyses.

Planar-chiral ferrocenylphosphine-borane complexes featuring agostic-type B–H⋯E (E = Hg, Sn) interactions

Ferrocenylphosphine-borane adducts with Lewis acidic organotin and organomercury substituents inortho-position show rare agostic-type B–H⋯E (E = Sn, Hg) interactions that have been studied by single crystal XRD, multinuclear solution NMR, and computational methods.

Phenylmercury(ii) sulfanylpropenoates: an example of symmetrization with the 3-(2-methoxyphenyl)-2-sulfanylpropenoato ligand

Some new phenylmercury(ii) sulfanylpropenoate complexes were prepared and characterized. The identification of diphenylmercury(ii) reveals the existence of a symmetrization process, which was followed in solution by NMR.

Weak aurophilic interactions in a series of Au(iii) double salts

In this work, several new examples of rare Au^III⋯Au^IIIaurophilic contacts are reported.

Steric effect of the dithiolato linker on the reduction mechanism of [Fe2(CO)6{μ-(XCH2)2CRR′}] hydrogenase models (X = S, Se)

Investigations of the electrochemical properties of [Fe₂(CO)₆{μ-(XCH₂)₂CRR′}] (X = S, Se; R or R′ = H or Me) showed that the complex with the bulkiest CMe₂moiety undergoes reduction with potential inversion.

The enthalpies of formation of AsX(n) molecules, where X=H, F or Cl, and n=1, 2 or 3, by RCCSD(T) and UCCSD(T)-F12x calculations

RCCSD(T) and UCCSD(T)-F12x calculations were performed on AsX(n) molecules, where X = H, F or Cl, and n = 1, 2 or 3, and related species, in order to evaluate their enthalpies of formation (ΔH(f)(Ø)). The recommended ΔH(f)(Ø) values obtained from the present investigation are AsH, 57.7(2); AsF, -7.9(3); AsCl, 27.2(4); AsH(2), 39.8(4); AsF(2), -96.6(9); AsCl(2), -17.8(10); AsH(3), 17.1(4); AsF(3)-196.0(5) and AsCl(3), -59.1(27) kcal mole(-1). These values are anchored only on one thermodynamic quantity, namely, ΔH(f)(Ø)(As) (= 70.3 kcal mole(-1)). In the calculations, the fully-relativistic small-core effective core potential (ECP10MDF) was used for As. Contributions from outer core correlation of As 3d(10) electrons were computed explicitly in both RCCSD(T) and UCCSD(T)-F12 calculations with additional tight basis functions designed for As 3d(10) electrons. Basis sets of up to augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality were used in RCCSD(T) calculations and computed relative electronic energies were extrapolated to the complete basis set (CBS) limit. For the simplified, explicitly correlated UCCSD(T)-F12x calculations, basis sets of up to quadruple-zeta (QZ) quality were employed. Based on the RCCSD(T)/CBS benchmark values, the reliability of available theoretical and experimental values have been assessed.

A Theoretical Study of Properties and Reactions Involving Arsenic and Selenium Compounds Present in Coal Combustion Flue Gases

Species of arsenic and selenium thought to be present in coal combustion flue gases were studied using density functional theory and a broad range of ab initio methods. At each level of theory, the calculated geometries and vibrational frequencies of each species as well as the reaction enthalpies of anticipated reactions were compared with experimental data where available. Comparisons between each calculation are given along with a discussion of the better performance of some theoretical calculations for a given species/reaction.

Structures and Thermochemistry of Calcium-Containing Molecules

A variety of theoretical procedures, including the high-level ab initio methods G3, G3[CC](dir,full), and W2C//ACQ, have been used to predict the structures and heats of formation of several small calcium-containing molecules (CaH, CaH2, CaO, CaOH, Ca(OH)2, CaF, CaF2, CaS, CaCl, and CaCl2). B3-LYP and CCSD(T) with both the (aug-)cc-pWCVQZ and (aug-)cc-pWCVQ+dZ basis sets are found to give molecular geometries that agree well with the experimental results. The CCSD(T)(riv)/(aug-)cc-pWCVQ+dZ results are found to be the most accurate, with a mean absolute deviation from experiment of just 0.008 angstroms. Zero-point vibrational energies (ZPVEs) and thermochemical corrections are found to be relatively insensitive to the level of theory, except in the case of molecules with highly anharmonic calcium-centered bending modes (CaH2, Ca(OH)2, CaF2, CaCl2), where special procedures need to be employed in order to obtain satisfactory results. Several potential improvements to the W2C method were investigated, most of which do not produce significant changes in the heats of formation. It was observed, however, that for CaO and CaS the scalar relativistic corrections are unexpectedly large and highly basis set dependent. In these cases, Douglas-Kroll CCSD(T)/(aug-)cc-pWCV5Z calculations appear to give a converged result. The G3[CC](dir,full) and best W2C-type heats of formation are both found generally to agree well with experimental values recommended in recent critical compendia. However, in some cases (CaO, Ca(OH)2, and CaF2), they differ from one another by more than their predicted error margins. The available experimental data are not sufficiently precise to distinguish definitively between the two sets of results although, in general, when discrepancies exist the W2C heats of formation are lower in energy and tend to be in better agreement with experiment. In the case of CaO, the W2C heat of formation (20.7 kJ mol(-1)) is approximately 20 kJ mol(-1) lower than the G3[CC](dir, full) result and most of the experimental data. Extensive investigation of possible refinements of the W2C method has failed to reveal any weaknesses that could account for this discrepancy. We therefore believe that the heat of formation of CaO is likely to lie closer to the more recent direct experimental determination of 27 kJ mol(-1) than to the value of approximately 40 kJ mol(-1) recommended in recent thermochemical reviews.

Coordination Polymers of Copper(I) Halides and Neutral Heterocyclic Thiones with New Coordination Modes

Reaction of copper(I) chloride or bromide with equimolar amounts of the neutral pyrimidine-2-thione ligand (pymtH) afforded linear chain polymers [Cu(pymtH)X]n (X = Cl, Br) with the pymtH ligand acting as a bridging N, S donor. In contrast, copper(I) iodide under the same conditions gave the dimeric complex [Cu(pymtH)2I]2 with the pymtH ligand adopting monodentate coordination mode through the exocyclic sulfur atom in terminal and bridging modes. Reactions of the heterocyclic thione ligand 2,4,6-trimercaptotriazine (H3TMT) with copper(I) halides afforded novel three-dimensional polymers, which crystallized in the cubic space group Pa. Each copper(I) ion is coordinated by three S atoms of three distinct H3TMT ligands, and each H3TMT acts as a tridentate bridging ligand linking three copper(I) ions through its sulfur atoms, thus forming two independent three-dimensional (3D) networks. The network belongs to a three-connected (10, 3)-a topology, which is enantiometric and interpenetrating. In all complexes the ligands are present in the thione form, and all halides are terminally coordinated to copper(I) ions. The photoluminescent and thermal properties of the complexes have also been investigated.

Effect of Substituents on the Strength of A−Cl- (A = Si, Ge, and Sn) Bonds in Hypervalent Systems: ACl5-, ACl4F-, and A(CH3)3Cl2-

The gas-phase strengths of the A-Cl(-) bonds in ACl(5)(-), ACl(4)F(-), and A(CH(3))(3)Cl(2)(-) (A = Si, Ge, and Sn) have been determined by measuring thresholds for collision-induced dissociation in a flowing afterglow-tandem mass spectrometer. Bond dissociation energies increase in the order Si < Ge < Sn. Replacement of the three equatorial chlorides with methyl groups weakens the bonds, while replacing one axial chloride with a fluoride strengthens the bonds. Computational results using the B3LYP model with several basis sets parallel the experimental periodic trends, but provide bond dissociation energies lower than experiment by 7-44 kJ mol(-1). MP2 computational results are in better agreement with experiment. The results are consistent with steric hindrance and electrostatic effects playing significant roles in the bonding energetics.