Trans Position Research Articles

Trinuclear M3S4 cluster complexes with hemilabile phosphino-thioether ligands: Some experimental and theoretical aspects

Reactions of [W3S4(tu)8(H2O)]Cl4⋅2H2O (tu = thiourea) with (PhCH2CH2)2PCH2CH2SR (R = Ph (PS1) or n-pentyl (PS2), followed by chromatography on silica gel with a solution of KPF6 in acetone as eluent, result in [W3S4Cl3(PS1)3]PF6 ([1]PF6) and [W3S4Cl3(PS2)3]PF6 ([2]PF6) in moderate yields. Crystal structures of [1]PF6 and [2]PF6 were determined by X-ray single crystal analysis. All three phosphine-thioether molecules are bidentately coordinated to tungsten atoms in such a way that the phosphorus atoms are in the trans position to the capping µ3-S atom. The compounds were characterized by 1H, 31P{1H} NMR, and UV–vis spectroscopies and electrospray-ionization mass spectrometry. Unlike similar molybdenum complexes, interaction of [1]PF6 or [2]PF6 with Bu4NCl does not lead to the formation of neutral complexes [W3S4Cl4(PS)2(PS*)] with the monodentate coordination of one of the PS ligands. This indicates weaker hemilabile properties of phosphino-thioether ligands in the tungsten complexes. Consequently, both [1]PF6 and [2]PF6 exhibit significantly lower catalytic activity than the molybdenum analogues in the benchmark reaction of nitrobenzene reduction into aniline with Ph2SiH2. The DFT calculations were performed to determine the relative stability of possible isomers with the chelate, bridging and monodentate manner of coordination of the PS ligands to {M3S4} (M = Mo, W) clusters, taking (CH3)2PCH2CH2SCH3 as a model.

A new PEPPSI type N-heterocyclic carbene palladium(II) complex and its efficiency as a catalyst for Mizoroki-Heck cross-coupling reactions in water

A new air and moisture stable PEPPSI (PEPPSI: pyridine-enhanced pre-catalyst preparation, stabilisation, and initiation) themed palladium N-heterocyclic carbene (NHC) complex [Pd(L)Br2(Py)] (1) [L: 2-flurobenzyl)-1-(4-methoxyphenyl)-1H-imidazolline-2-ylidene] was synthesized and characterized. The structure of complex 1 was determined by X-ray single-crystal analysis. The palladium center in 1 adopted a square planar geometry with carbene and pyridine ligands occupying the mutual trans position. The complex 1 was employed to catalyze the Mizoroki-Heck cross-coupling reactions of aryl bromides/iodides with styrene in water. To the best of our knowledge, this is the first report where a Pd-PEPPSI catalyst was successfully employed in aqueous-phase Mizoroki-Heck reaction. Good to excellent yields of cross-coupling products were obtained with a range of representative aryl bromides/iodides under relatively mild conditions (100 °C, 1 mol% of 1). A new palladium PEPPSI complex was synthesized, characterized and evaluated as catalyst for the Mizoroki-Heck reaction in aqueous medium. Both electron-donating and electron-withdrawing aryl halides (bromides and iodides) reacted with styrene to give corresponding coupling products in moderate to excellent yields.

On utilizing an enhanced object partitioning scheme to optimize self-organizing lists-on-lists

With the advent of “Big Data” as a field, in and of itself, there are at least three fundamentally new questions that have emerged, namely the Artificially Intelligence (AI)-based algorithms required, the hardware to process the data, and the methods to store and access the data efficiently. This paper (The work of the second author was partially supported by NSERC, the Natural Sciences and Engineering Council of Canada. We are very grateful for the feedback from the anonymous Referees of the original submission. Their input significantly improved the quality of this final version.) presents some novel schemes for the last of the three areas. There have been thousands of papers written regarding the algorithms themselves, and the hardware vendors are scrambling for the market share. However, the question of how to store, manage and access data, which has been central to the field of Computer Science, is even more pertinent in these days when megabytes of data are being generated every second. This paper considers the problem of minimizing the cost of retrieval using the most fundamental data structure, i.e., a Singly-Linked List (SLL). We consider a SLL in which the elements are accessed by a Non-stationary Environment (NSE) exhibiting the so-called “Locality of Reference”. We propose a solution to the problem by designing an “Adaptive” Data Structure (ADS), which is created by utilizing a composite of hierarchical data “sub”-structures to constitute the overall data structure (In this paper, the primitive data structure is the SLL. However, these concepts can be extended to more complicated data structures.). In this paper, we design hierarchical Lists-on-Lists (LOLs) by assembling a SLL into a hierarchical scheme that results in SLLs on SLLs (SLLs-on-SLLs) comprising of an outer-list and sublist contexts. The goal is that elements that are more likely to be accessed together are grouped within the same sub-context, while the sublists themselves are moved “en masse” towards the head of the list-context to minimize the overall access cost. This move is carried out by employing the “de-facto” list re-organization schemes, i.e., the Move-To-Front (MTF) and Transposition (TR) rules. To achieve the clustering of elements within the sublists, we invoke the Object Migration Automaton (OMA) family of reinforcement schemes from the theory of Learning Automata (LA). They capture the probabilistic dependence of the elements in the data structure, receiving query accesses from the Environment. We show that SLLs-on-SLLs augmented with the Enhanced OMA (EOMA) minimizes the retrieval cost for elements in NSEs, and are superior to the stand-alone MTF and TR schemes, and also superior to the OMA-augmented SLLs-on-SLLs operating in such Environments.

Intramolecular hydrogen bonding stabilizes trans-configuration in a mixed carbene/isocyanide PdII complexes

Aromatic amidines 1a-e undergo facile reaction with one isocyanide in PdCl2(CNBut)2 giving carbene complexes 2b-d (Scheme 2) in high isolated yields (79–95%). The structures of 2b–d were confirmed by the 1H and 13C NMR spectroscopies, high resolution electrospray ionization mass spectrometry (HRESI-MS), IR, the elemental analyses (C, H, N), and X-ray diffraction analysis for 2c, which revealed that the carbene and unreacted isocyanide ligands were located in a mutually trans position. Such arrangement was unexpected since it did not fit trans effect rule. Stabilization of the unfavorable isomer was rationalized by intramolecular hydrogen bonding. The nature of the intramolecular non-covalent interactions, which were responsible for the stabilization of the trans-isomer, was studied theoretically using DFT calculations and topological analysis of the electron density distribution within the framework of Bader’s theory (QTAIM method).

Synthesis, single crystal X-ray, DFT and HSA of N-donor stabilized complexes of cobalt(II) diphenyldithiophosphate: An experimental and theoretical approach

Monosubstituted diphenyldithiophosphates complexes of cobalt(II) stabilized by nitrogen containing donors, [{(ArO)2PS2}2CoL2] [Ar = 4-(C2H5)C6H4 (1) and 4-C(CH3)3C6H4 (2); L = C5H5N (1) and 4-(C2H5)C5H4N (2)] have been isolated successfully and structurally characterized by single crystal X-ray analysis. The Co(II) metal ion is surrounded by four sulfur atoms from two bidentate dithio ligands leading to a CoS4 core in the equatorial plane. The nitrogen atoms from two donor ligands are coordinated to the Co(II) atom in a mutually trans position. To further assist the experimental studies, a comprehensive theoretical investigation is also performed using density functional theory (DFT) calculations. Hirshfeld Surface analysis and 2D Finger print plots analysis have been employed to explore intermolecular interactions and to quantify the space within the molecule having crystalline environment.

CuEn3]MoO4: Synthesis, Structure, Jahn-Teller Effect, Transformations in the Range 100–1263 K

The crystal structure of [CuEn3]MoO4 (En is ethylenediamine) is studied in a range 100–390 K. The crystallographic data at 100 K are as follows: a = 27.5808(9) A, c = 9.9043(4) A, space group $$P\overline 3 $$ , V = 6524.8(4) A3, Z = 18. The coordination of copper atoms is a distorted square bipyramid. In three crystallographically independent cations. four short Cu-N distances are 2.041(2)–2.093(2) A, two long ones in a trans position are 2.397(2)–2.496(2) A (at 200 K these intervals are 2.039(4)–2.148(4) A and 2.332(2)–2.461(4) A respectively). In a range from 200 K to 298 K, the transition occurs to the space group $$P\overline 3 $$ c1 (a = 15.9992(6) A, c = 9.9385(4) A, V = 2203.17(19) A3, Z = 6) and the Cu-N distances are aligned: 2.086(6) A, 2.162(7) A, 2.273(8) A. At 390 K the Jahn-Teller effect disappears and the Cu-N distances are 2.153(4) A (a = 9.2785(14) A, c = 10.0035(18) A, $$P\overline 3 $$ 1c, V = 745.8(3) A3, Z = 2). It is shown that with increasing temperature from 100 K to 320 K the average Mo-O distances decrease from 1.766 A to 1.699 A. The ex situ powder X-ray diffraction study of the formation process of metal and carbide phases is performed during [CuEn3]MoO4 thermal decomposition in the He atmosphere in the presence of LiH. Starting from 973 K, a mixture of Mo2C and the fcc phase based on the Cu structure (a ≈ 3.65 A) forms.

Preparation of Palladium(II) Complexes of 1-substituted-3-phospholene Ligands and their Evaluation as Catalysts in Hydroalkoxycarbonylation

: A series of palladium(II) complexes incorporating 1-substituted-3-methyl-3- phospholenes as the P-ligands were prepared from phospholene oxides by deoxygenation followed by complexation with PdCl2(PhCN)2. The two 1-substituted-3-methyl-3- phospholene ligands were trans position to each other in the Pd(II)-complexes. As the ligands contain a P-stereogenic center, the Pd-complexes were obtained as a 1:1 mixture of two stereoisomers, the homochiral (R,R and S,S) and the meso (R,S) forms, when racemic starting materials were used. An optically active Pd-complex containing (R)-1-propyl- 3-phospholene ligand was also prepared. Catalytic activity of an aryl- and an alkyl-3- phospholene-palladium(II)-complex was evaluated in hydroalkoxycarbonylation of styrene. The alkyl-derivative showed higher activity and selectivity towards the formation of the esters of 3-phenylpropionic acid. However, the overall activity of these PdCl2(phospholene)2-type complexes was low.

Does geometry matter? Effect of the ligand position in bimetallic ruthenium polypyridine siblings.

In this work, we present the preparation of a complex [(tpy)(bpy)Ru(μ-CN)Ru(py)4(OH2)](PF6)3 (tpy = 2,2',6',2''-terpyridine; bpy = 2,2'-bipyridine; py = pyridine) that combines a ruthenium chromophore linked to another ruthenium ion that bears a labile position trans to the bridge. Substitution in this position is very attractive, as it allows us to place a quencher trans to the chromophore maximizing the separation between them. This complex allowed us to prepare a family of cyanide-bridged ruthenium polypyridines of general formula [Ru(tpy)(bpy)(μ-CN)Ru(py)4(L)]2/3+ (L = Cl-, NCS-, 4-dimethylaminopyridine or acetonitrile) and compare them with the related complexes [Ru(tpy)(bpy)(μ-CN)Ru(bpy)2(L)]2/3+ where the L ligand lies cis to the bridge. The mixed-valence form of these complexes shows evidence of strong coupling between the ruthenium ions and enhanced delocalization as the redox potential of the {Ru(py)4L} fragment increases. (TD)DFT calculations reproduce very well the experimental spectra of these complexes and indicate that when L = acetonitrile, the hole in the mixed-valence complex is almost equally distributed between both ruthenium ions. For L = DMAP and NCS- the π orbitals of the ligands are mixed with dπ orbitals of the Ru ions, resulting in partial delocalization of the charge on the ligands. The latter result illustrates that the trans configuration of these complexes is well-suited to extend the interaction beyond the bridged ruthenium ions.

Reactivity of dihydrobenzothiazole heterocycles: Synthesis, molecular and crystal structure of an organotin compound containing a tridentate Schiff ligand

Dibenzyldibromotin(IV) (2) promoted the ring-opening of 2-methyl-2-pyridyl-2,3-dihydrobenzo[d]thiazole heterocycle (1), with the activation of one C–Sn bond, to release toluene as coproduct. The resultant heteroleptic complex [Sn{L}BnBr2] (3), where {L}− = {SC6H4N(Me)C(C5H4N)}−, displayed a κ3-N,N′,S tridentate coordination pattern of the Schiff base. The 119Sn{1H} chemical shift is consistent with a hexacoordinate tin(IV) species in solution. Single-crystal X-ray studies at 293 K were carried out for the precursor 1 and for complex 3. In the crystal, the SnIV center in 3 displayed a distorted octahedral local geometry, with both bromo ligands in trans position. In the crystal, 1 and 3 displayed diverse intermolecular contacts; 3 was also studied by a Hirshfeld surface analysis.

Crystal structures and DFT analysis of Palladium(II) complexes with Schiff bases derived from N,N-dialkyl-p-phenylenediamines

Herein, new palladium(II) complexes with Schiff bases derived from salicylaldehyde and N,N-dialkyl-p-phenylenediamines were obtained. The ligands 2-((4-(N,N-dimethylamino)aniline)formimidoyl)phenol (N,N-metph-sOH - L1) and 2-((4-(N,N-diethylamino)aniline)formimidoyl)phenol (N,N-etph-sOH - L2) and complexes [Pd(N,N-metph-sO)2] (C1) and [Pd(N,N-etph-sO)2] (C2) were characterized by elemental analysis, infrared (IR) and UV–Vis spectroscopy, 1H and 13C nuclear magnetic resonance (NMR), thermogravimetry (TG) and differential thermal analysis (DTA), and the results agree with the proposed structures. The crystal structures data showed the formation of N,O-chelate with the pairs of phenolate O and imine N occupying the trans positions. Hirshfeld surface analysis was employed to elucidate the intermolecular contacts which drive the different supramolecular assemblies of C1 and C2. In addition, Density Functional Theory (DFT) calculations were also performed to better understand the electronic properties. Additional DFT calculations were also devoted to elucidate the stereochemistry of these palladium complexes toward the cis-trans isomerism among these square-planar Pd(II) N,O-Schiff base complexes. Time-dependent DFT (TD-DFT) analysis was applied to shed light on the nature of the electronic transitions determined in the UV–Vis spectra.

Molecular and Inner Complex Compounds of Dioxomolybdenum(VI) with Disubstituted Salicydenealcoholimines: Crystal Structure of 1 : 1 Dioxo(3,5-Dibromosalicylidenemonoethanoliminato)molybdenum(VI) Solvate with Methanol [MoO2(L1) · MeOH] (L1 = C9H7Br2NO2)

Complexes of dioxomolybdenum(VI) of the molecular (МоО2Сl2 · 2H2L) and inner complex ([MoO2L · Solv]) types are synthesized (H2L are azomethines, derivatives of disubstituted R1,R2-salicylaldehydes (R1, R2 = 3.5-Вr2; R1 = 3-МеО, R2 = 5-Вr) and monoethanolamine; Solv is a methanol, dimethylformamide, pyridine, or α-picoline molecule). The cis-octahedral structure of the complexes is concluded on the basis of the IR spectroscopic data. In the molecular compounds, the ligands are coordinated via the O atom of the carbonyl group of the H2L tautomeric form. In the inner complex compounds, the ligands are coordinated in the deprotonated benzoid form. The structure of [MoO2(L1) · МеОН] (I) (where L1 is C9H7Br2NO2) is determined by X-ray diffraction analysis (СIF file CCDC no. 1898088). In the mononuclear molecule of compound I, the Mo atom has the octahedral coordination by two oxo ligands, two oxygen atoms, the nitrogen atom of the tridentate bis(chelate) two-charge ligand (L1)2–, and the O atom of the methanol molecule. The neutral N(1) and O(1) atoms of the L1 and МеОН ligands, respectively, are arranged in the trans positions to the O(oxo) ligands. The Mo–N(1) (2.265 A) and Мо–О(1) (2.372 A) bonds are substantially elongated due to the structural manifestation of the trans effect of the multiply bonded oxo ligands. The intermolecular hydrogen bonds (МеОН)О–Н···О(oxo) join the molecules into supramolecular 1D chains.

The crystal structure of the triclinic polymorph of 1,4-bis-([2,2':6',2''-terpyridin]-4'-yl)benzene.

The title triclinic polymorph (Form I) of 1,4-bis-([2,2':6',2''-terpyridin]-4'-yl)benzene, C36H24N6, was formed in the presence of the Lewis acid yttrium trichloride in an attempt to obtain a coordination compound. The crystal structure of the ortho-rhom-bic polymorph (Form II), has been described previously [Fernandes et al. (2010 ▸). Acta Cryst. E66, o3241-o3242]. The asymmetric unit of Form I consists of half a mol-ecule, the whole mol-ecule being generated by inversion symmetry with the central benzene ring being located about a crystallographic centre of symmetry. The side pyridine rings of the 2,2':6',2''-terpyridine (terpy) unit are rotated slightly with respect to the central pyridine ring, with dihedral angles of 8.91 (8) and 10.41 (8)°. Opposite central pyridine rings are coplanar by symmetry, and the angle between them and the central benzene ring is 49.98 (8)°. The N atoms of the pyridine rings inside the terpy entities, N⋯N⋯N, lie in trans-trans positions. In the crystal, mol-ecules are linked by C-H⋯π and offset π-π inter-actions [inter-centroid distances are 3.6421 (16) and 3.7813 (16) Å], forming a three-dimensional structure.

Rotamer Jumps, Proton Exchange, and Amine Inversion Dynamics of Dimethylated Lysine Residues in Proteins Resolved by pH-Dependent 1H and 13C NMR Relaxation Dispersion.

Post-translational methylation of lysine side chains is of great importance for protein regulation, including epigenetic control. Here, we present specific 13CHD2 labeling of dimethylated lysines as a sensitive probe of the structure, interactions, and dynamics of these groups, and outline a theoretical and experimental framework for analyzing their conformational dynamics using 1H and 13C CPMG relaxation dispersion experiments. Dimethylated lysine side chains in calcium-loaded calmodulin show a marked pH dependence of their Carr-Purcell-Meiboom-Gill (CPMG) dispersion profiles, indicating complex exchange behavior. Combined analysis of 1H and 13C CPMG relaxation dispersions requires consideration of 12-state correlated exchange of the two methyl groups due to circular three-state rotamer jumps around the Cε-Nζ axis combined with proton exchange and amine inversion. Taking into account a number of fundamental constraints, the exchange model can be reduced to include only three fitted parameters, namely, the geometric average of the rotamer-jump rate constants, the rate constant of deprotonation of Nζ, and the chemical shift difference between the trans and gauge positions of the 13C or 1H nuclei. The pH dependence indicates that protonation of the end group dramatically slows down rotamer exchange for some lysine residues, whereas deprotonation leads to rapid amine inversion coupled with rotamer scrambling. The observed variation among residues in their exchange behavior appears to depend on the structural environment of the side chain. Understanding this type of exchange process is critical to correctly interpreting NMR spectra of methylated lysine side chains. The exchange model presented here forms the basis for studying the structure and dynamics of epigenetically modified lysine side chains and perturbations caused by changes in pH or interactions with target proteins.

Crystal structure of tetra-kis-(tetra-hydro-furan-κO)bis-(tri-fluoro-methane-sulfonato-κO)iron(II).

The title compound, [Fe(CF3SO3)2(C4H8O)4], is octa-hedral with two tri-fluoro-methane-sulfonate ligands in trans positions and four tetra-hydro-furane mol-ecules in the equatorial plane. By the conformation of the ligands the complex is chiral in the crystal packing. The compound crystallizes in the Sohncke space group P212121 and is enanti-omerically pure. The packing of the mol-ecules is determined by weak C-H⋯O hydrogen bonds. The crystal studied was refined as a two-component inversion twin.

Complexation of Cobalt(II), Nickel(II), Copper(II), and Zinc(II) Hexafluorosilicates with Nicotinamide in Aqueous Solution

The new complexes [M(NA)2(H2O)4]SiF6 ⋅ 2H2O, where M2+ = Co, Ni, Zn (complexes I, II, and III, respectively), and NA = C6H6N2O is nicotinamide, [Cu(NA)2(SiF6)(H2O)2] ⋅ 2H2O (IV), and (HNA)2SiF6 (V) have been synthesized from aqueous solutions and studied by chemical, IR spectroscopic, and X-ray diffraction analyses. Their unit cell parameters are a = 16.2448(18) A, b = 6.8834(8) A, c = 10.0767(11) A, β = 102.765(3)°, V = 1098.92 A3, space group C2 for I; a = 16.1591(7) A, b = 6.8777(3) A, c = 10.0314(5) A, β = 102.410(1)°, V = 1088.82 A3, space group C2 for II; a = 16.2265(6) A, b = 6.8965(3) A, c = 10.0696(5) A, β = 102.390(1)°, V = 1100.60 A3, space group C2 for III; a = 6.5915(4) A, b = 7.7670(4) A, c = 10.1506(5) A, α = 110.7390(10)°, β = 105.824(2)°, γ = 95.448(2)°, V = 456.868 A3, space group P $$\overline{1}$$ for IV; and a = 14.1904(7) A, b = 9.0468(4) A, c = 11.8160(7) A, β = 106.277(2)°, V = 1456.1 A3, space group C2/c for V. Complexes I–III are isostructural and represent ionic compounds formed by hexafluorosilicate anions and complex cations. The coordination polyhedron of the metal is a slightly distorted octahedron built of the O atoms of four coordinated water molecules and the two N atoms of two pyridine rings of two nicotinamide molecules in trans positions of the polyhedron. Complex IV has a polymeric chain structure. The coordination polyhedron of the copper cation represents an octahedron, which is elongated along its axis and built of the two N atoms of two pyridine rings of two nicotinamide molecules, the two O atoms of coordinated water molecules, and the two F atoms of hexafluorosilicate anions acting as bridges between neighboring cations. In the structure of complex V, the nitrogen atom of the pyridine ring HNA+ is protonated. The geometry of hexafluorosilicate anions is identical in all the five complexes. The structures have branched networks of hydrogen bonds.

Structural Features of Monomeric Octahedral Monooxo d2-Rhenium(V) Complexes [ReO(Lmono)($$L_{{{\text{tetra}}}}^{n}$$)] with Oxygen Atoms of Tridentate Chelate Ligands OХ3, Х = O, N, or P ($$L_{{{\text{tetra}}}}^{n}$$)

The structural features of six mononuclear octahedral monooxo d2-Re(V) complexes [ReO(Lmono) $$\left( {{\text{L}}_{{{\text{tetra}}}}^{n}} \right)$$ ] with tetradentate chelate (O, Х3; Х = O, N, P) $$\left( {{\text{L}}_{{{\text{tetra}}}}^{n}} \right)$$ and monodentate (Lmono) ligands are discussed. The O $$\left( {{\text{L}}_{{{\text{tetra}}}}^{n}} \right)$$ atoms are always located in the trans positions to the multiply bound O(oxo) ligands.

Switching from a Chromium(IV) Peroxide to a Chromium(III) Superoxide upon Coordination of a Donor in the trans Position.

O2 activation at a chromium(II) siloxide complex in propionitrileleads to a chromium(III) complex with an end-on bound superoxide ligand, while the reaction in tetrahydrofuran leads to a side-on peroxo chromium(IV) compound. The superoxide reacts faster with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl hydroxylamine while the peroxide, unlike the superoxide, proved capable of deformylating aldehydes. The system was found to represent a unique case, where even a switching between the two structures can be achieved via the solvent; its ability to coordinate at the positiontrans to the O2 ligand is decisive, as supported by density functional theory studies. Altogether, the results show that subtle changes can determine for an initially formed metal-dioxygen adduct, whether it exists as a superoxide or a peroxide, which thus merits consideration in discussions on mechanisms and possible reaction routes.

Synthesis, molecular structure, anti-microbial, anti-oxidant and enzyme inhibition activities of 2-amino-6-methylbenzothiazole and its Cu(II) and Ag(I) complexes

Molecular structure of 2-amin-6-methylbenzothiazole, 1 and its coordination complexes with Ag(I) and Cu(II) were determined by X-ray diffraction. The ligand 2-amin-6-methylbenzothiazole (hereafter represented as L in general formula of complexes) and [AgL2]NO3 crystallize in orthorhombic crystal systems and CuL2(OAc)2 complex is monoclinic. Ligand and its Ag(I) complex possess space groups Pbcn and Cu(II) complex has a space group P21/c. Complex bis(2-amino-6-methylbenzothiazole)diacetatocopper(II), 2 and bis(2-amino-6-methylbenzothiazole)silver(I) nitrate, 3 were obtained by reacting ligand with respective metal salt in a molar ratio 2:1, respectively. The coordination environment of copper metal is octahedral where acetate acts as bidentate ligand and 2-amino-6-methylbenzothiazole occupies trans position with respect to each other. The ligand contains three possible coordination sites (endocyclic nitrogen, exocyclic nitrogen and sulphur). Among three nucleophilic centers the endocyclic nitrogen is more basic and readily coordinates to the metal ion (both Cu and Ag). Nitrate group plays an important role in stabilizing the supramolecular structure of Ag complex wherein NO…H2N- interactions are very effective. Non-covalent interactions in molecules make them efficient medicines. On the basis of certain secondary interactions, compounds 1–3 were expected to be biologically active and were studied as antibacterial, antifungal, antioxidant agents and enzyme inhibitors. Moderate activities against selected strains were observed for the ligand and its complexes. It was observed that the antibacterial and antifungal potentials of the ligand were enhanced by complexation with copper(II) and silver(I) metal ions.

Spin state, electronic structure and bonding on C-scorpionate [Fe(II)Cl2(tpm)] catalyst: An experimental and computational study

The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the FeL2,3-edges and NK-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interaction of the complex’s vacant site (the sixth) with a further ligand. Moreover, comparison of the electronic properties of the complex in condensed phase and water solution showed an increased Lewis acidity of the catalyst in solution phase, due to a decreasing of the LUMO energy of about 8 kcal/mol. These results gave an overall picture of the electronic behavior of the complex investigated, on going from condensed to water solution phase, explaining the preferred use of 1 as catalyst in homogeneous catalysis. The NFe(II) interaction has been thoroughly investigated by means of DFT Kohn-Sham and EDA bond analysis applied to i) the isolated [Fe(II)Cl2(tpm)] and ii) the [Fe(II)Cl2(tpm)] interacting with water as a solvent within the Conductor-like Screening Mode (COSMO) framework. Results showed that both tpm→Fe(II) σ and tpm⟵Fe(II) π Charge Transfer (CT) interactions characterize the Fe(II)–tpm interaction. Moreover, the three tpm N atoms do not equally interact with the Fe(II) and one of them shares a suitable available iron-based d virtual orbital, to bind a further ligand in trans position.

The Chemical Bond and s-d Hybridization in Coinage Metal(I) Cyanides.

We present a four-component relativistic density functional theory study of the chemical bond and s-d hybridization in the group 11 cyanides M-CN (M = Cu, Ag, and Au). The analysis is carried out within the charge-displacement/natural orbital for chemical valence (CD-NOCV) scheme, which allows us to single out meaningful contributions to the total charge rearrangement that arises upon bond formation and to quantify the components of the Dewar-Chatt-Duncanson bonding model (the ligand-to-metal donation and metal-to-ligand back-donation). The M-CN bond is characterized by a large donation from the cyanide ion to the metal cation and by two small back-donation components from the metal toward the cyanide anion. The case of gold cyanide elucidates the peculiar role of the relativistic effects in determining the characteristics of the Au-C bond with respect to the copper and silver homologues. In AuCN, the donation and back-donation components are significantly enhanced, and the spin-orbit coupling, removing the degeneracy of the 5d atomic orbitals, induces a substantial split in the back-donation components. A simple spatial analysis of the NOCV-pair density, related to the ligand-to-metal donation component, allows us to quantify, with unprecedented accuracy, the charge rearrangement due to the s-d hybridization occurring at the metal site. The s-d hybridization plays a key role in determining the shape and size of the metal; it removes electron density from the bond axis and induces a significant flattening at the metal site in the position trans to the ligand. The s-d hybridization is present in all noble metal complexes, influencing the bond distances, and its effect is enhanced for Au, which is consistent with the preference of gold to form linear complexes. A comparative investigation of simple complexes [AuL]+/0 of Au+ with different ligands (L = F-, N-heterocyclic carbene, CO, and PH3) shows that the s-d hybridization mechanism is also influenced by the nature of the ligand.