[AuIII(N

A series of new complexes of general formula [AuIII(N^N)Br2](PF6) (N^N = 2,2'-bipyridine and 1,10-phenanthroline derivatives) were prepared and characterized by spectroscopic, electrochemical, and diffractometric techniques and tested against Gram-positive and Gram-negative bacterial strains (Staphylococcus aureus, Streptococcus intermedius, Pseudomonas aeruginosa, and Escherichia coli), showing promising antibacterial and antibiofilm properties.

Fluorescent sensing of non-steroidal anti-inflammatory drugs naproxen and ketoprofen by dansylated squaramide-based receptors.

Bis-squaramide receptors L1-L4 bearing a dansyl moiety were synthesised and their potential applications as fluorescent probes towards non steroidal anti-inflammatory drugs naproxen and ketoprofen was investigated. A detailed photophysical characterization in CH3CN/DMSO solution (9 : 1 v/v) was conducted and demonstrated that the two macrocyclic receptors L1 and L2 show good sensitivity towards ketoprofen with an ON-OFF fluorescent response, while the two open chain receptors L3 and L4 behave similarly with the three guests considered. DFT theoretical calculations carried out on L2 and L4 as model receptors allowed to propose a possible coordination mode towards the guests. Finally, 1H-NMR spectroscopy in DMSO-d6/0.5% water solution demonstrated that the four receptors interact with the considered guests via H-bonds.

A Structural Approach to the Strength Evaluation of Linear Chalcogen Bonds.

The experimental structural features of chalcogen bonding (ChB) interactions in over 34,000 linear fragments R-Ch⋯A (Ch = S, Se, Te; R = C, N, O, S, Se, Te; A = N, O, S, Se, Te, F, Cl, Br, I) were analyzed. The bond distances dR-Ch and the interaction distances dCh⋯A were investigated, and the functions δR-Ch and δCh⋯A were introduced to compare the structural data of R-Ch⋯A fragments involving different Ch atoms. The functions δR-Ch and δCh⋯A were calculated by normalizing the differences between the relevant bond dR-Ch and ChB interaction dCh⋯A distances with respect to the sum of the relevant covalent (rcovR + rcovCh) and the van der Waals (vdW) radii (rvdWCh + rvdWA), respectively. A systematic comparison is presented, highlighting the role of the chalcogen involved, the role of the R atoms covalently bonded to the Ch, and the role of the A species playing the role of chalcogen bond acceptor. Based on the results obtained, an innovative approach is proposed for the evaluation and categorization of the ChB strength based on structural data.

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam): A Novel Precursor of Calcium Oxalate Coating for Carbonate Stone Substrates.

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam), synthesized from O-methyl-N-(pyridin-2-ylmethyl)oxamate, was spectroscopically and structurally characterized and assayed as a novel precursor for the protection and consolidation of carbonate stone substrates. An in-depth characterization of treated and untreated biomicritic limestone and white Carrara marble samples was carried out by means of SEM microscopy, X-ray powder diffraction, helium pycnometry, determination of water transport properties, and pull-off tests. The improved solubility (1.00 M, 16.5% w/w) of the title compound with respect to ammonium oxalate (0.4 M, 5% w/w) results in the formation of a thicker protective coating of calcium oxalate (CaOx) dihydrate (weddellite) on marble and biomicrite samples after the treatment with 5% and 12% w/w water solutions, producing a reduction in the stone porosity and increased cohesion. Theoretical calculations were carried out at the DFT level to investigate both the electronic structure of the N-(pyridin-2-ylmethyl)oxamate anion and the hydrolysis reaction leading from AmPicOxam to CaOx.

Chelating Phosphorus-An O, C, O-Coordinating Pincer-Type Ligand Coordinating PIII and PV Centres.

The sequence of reactions of the phosphorus-containing aryllithium compound 5-t-Bu-1,3-[(P(O)(O-i-Pr)2 ]2 C6 H2 Li (ArLi) with Ph2 PCl, KMnO4 , elemental sulfur and elemental selenium, respectively, gave the aryldiphenylphosphane chalcogenides 5-t-Bu-1,3-[(P(O)(O-i-Pr)2 ]2 C6 H2 P(E)Ph2 (1, E=O; 2, E=S; 3, E=Se). Compound 1 partially hydrolysed giving [5-t-Bu-1-{(P(O)(O-i-Pr)2 }-3-{(P(O)(OH)2 }C6 H2 ]P(O)Ph2 (4). The reaction of ArLi with PhPCl2 provided the benzoxaphosphaphosphole [1(P), 3(P)-P(O)(O-i-Pr)OPPh-6-t-Bu-4-P(O)(O-i-Pr)2 ]C6 H2 P (5i) as a mixture of the two diastereomers. The oxidation of 5i with elemental sulfur gave the benzoxaphosphaphosphole sulfide [1(P), 3(P)-P(O)(O-i-Pr)OP(S)Ph-6-t-Bu-4-P(O)(O-i-Pr)2 ]C6 H2 (5) as pair of enantiomers P1(R), P3(S)/P1(S), P3(R) of the diastereomer (RS/SR)-5 (5b). The aryldiphenylphosphane 5-t-Bu-1,3-[(P(O)(O-i-Pr)2 ]2 C6 H2 PPh2 (6) was obtained from the reaction of the corresponding aryldiphenylphosphane sulfide 2 with either sodium hydride, NaH, or disodium iron tetracarbonyl, Na2 Fe(CO)4 . The oxidation of the aryldiphenylphosphane 6 with elemental iodine and subsequent hydrolysis yielded the aryldiphenyldioxaphosphorane 9-t-Bu-2,6-(OH)-4,4-Ph2 -3,5-O2 -2,6-P2 -4λ5 -P-[5.3.1.0]-undeca-1(10),7(11),8-triene (7). Both of its diastereomers, (RR/SS)-7 (7a) and (RS/SR)-7 (7b), were separated as their chloroform and i-propanol solvates, 7a⋅2CHCl3 and 7b⋅i-PrOH, respectively. DFT calculations accompanied the experimental work.

Role of the Solvent in the Reactivity of Bis-4-imidazoline-2-selone Derivatives toward I2: An Experimental and Theoretical Approach.

The reactivity of 1,1'-bis(3-methyl-4-imidazolin-2-selone)methane (L1) and 1,2-bis(3-methyl-4-imidazolin-2-selone)ethane (L2) toward I2 has been explored in MeCN under different experimental conditions and compared with that in CH2Cl2. The compounds [L1'](I)2 (I), [L1I]n(I)n (II), [L1(µ-Se)](I)2·1/2H2O (III), [L1I](I3)·2I2 (IV), and [L2](I)2·MeCN (V) were obtained and characterized. X-ray diffraction analyses point out an ionic nature for these compounds, which is presumably favored by the polarity of the solvent used. In particular, [L1I]n(I)n (II) represents the first example of an iodonium complex of imidazoline-2-selone derivatives, while [L1(µ-Se)](I)2·1/2H2O (III) represents a unique example of a dicationic [RSeSeSeR] triselane. Density functional theory calculations have allowed us to better understand the nature of the obtained compounds and to justify their formations in polarizing reaction conditions rather than in low polar solvents.

Self-Assembly of Supramolecular Architectures Driven by σ-Hole Interactions: A Halogen-Bonded 2D Network Based on a Diiminedibromido Gold(III) Complex and Tribromide Building Blocks.

The reaction of the complex [Au(phen)Br2](PF6) (phen = 1,10-phenanthroline) with molecular dibromine afforded {[Au(phen)Br2](Br3)}∞ (1). Single crystal diffraction analysis showed that the [Au(phen)Br2]+ complex cations were bridged by asymmetric tribromide anions to form infinite zig-zag chains featuring the motif ···Au-Br···Br-Br-Br···Au-Br···Br-Br-Br···. The complex cation played an unprecedented halogen bonding (XB) donor role engaging type-I and type-II XB noncovalent interactions of comparable strength with symmetry related [Br3]- anions. A network of hydrogen bonds connects parallel chains in an infinite 2D network, contributing to the layered supramolecular architecture. DFT calculations allowed clarification of the nature of the XB interactions, showing the interplay between orbital mixing, analyzed at the NBO level, and electrostatic contribution, explored based on the molecular potential energy (MEP) maps of the interacting synthons.

Switching-On Fluorescence by Copper (II) and Basic Anions: A Case Study with a Pyrene-Functionalized Squaramide.

The new symmetric acyclic N,N'-bis(1-pyrenyl) squaramide (H2L) functionalized with the pyrene moiety as a fluorogenic fragment has been designed and its ability to selectively detect specific anions and metals investigated. H2L selectively binds Cl- both in solution (DMSO 0.5% H2O and MeCN) and in the solid state, and allows to selectively detect Cu2+ in MeCN with the formation of a 2:1 metal-receptor complex, with a green intense emission appreciable by naked eye under the UV lamp. The H2L copper complex preserves its emission properties in the presence of Cl-. The addition of basic anions (OH-, CN-, and F-) up to 10 equivalents caused the deprotonation of the squaramide NHs and a dramatic change of the emission properties of the H2L copper complex.

Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic Ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal Ions PdII, PtII, and RhIII.

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L1-L3 towards Platinum Group metal ions PdII, PtII, and RhIII. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H2O or MeOH/H2O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and 1H- and 13C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L1)Cl]2[Pd2Cl6], [Pt(L1)Cl](BF4), [Rh(L1)Cl2](PF6), and [Rh(L3)Cl2](BF4)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the PdII/PtII, and RhIII complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L3 with PtCl2 in MeCN/H2O gave by serendipity the complex [Pt(L3)(m-1,3-MeCONH)PtCl(MeCN)](BF4)2·H2O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d8-d8 PtII-PtII ground-state nature for this compound, rather than the alleged d9-d7 PtI-PtIII mixed-valence character reported for related dinuclear Pt-complexes.

Diradical Character of Neutral Heteroleptic Bis(1,2-dithiolene) Metal Complexes: Case Study of [Pd(Me2timdt)(mnt)] (Me2timdt = 1,3-Dimethyl-2,4,5-trithioxoimidazolidine; mnt2- = 1,2-Dicyano-1,2-ethylenedithiolate).

The reaction of the bis(1,2-dithiolene) complex [Pd(Me2timdt)2] (1; Me2timdt•- = monoreduced 1,3-dimethyl-2,4,5-trithioxoimidazolidine) with Br2 yielded the complex [Pd(Me2timdt)Br2] (2), which was reacted with Na2mnt (mnt2- = 1,2-dicyano-1,2-ethylenedithiolate) to give the neutral mixed-ligand complex [Pd(Me2timdt)(mnt)] (3). Complex 3 shows an intense solvatochromic near-infrared (NIR) absorption band falling between 955 nm in DMF and 1060 nm in CHCl3 (ε = 10700 M-1 cm-1 in CHCl3). DFT calculations were used to elucidate the electronic structure of complex 3 and to compare it with those of the corresponding homoleptic complexes 1 and [Pd(mnt)2] (4). An in-depth comparison of calculated and experimental structural and vis-NIR spectroscopic properties, supported by IEF-PCM TD-DFT and NBO calculations, clearly points to a description of 3 as a dithione-dithiolato complex. For the first time, a broken-symmetry (BS) procedure for the evaluation of the singlet diradical character (DC) of heteroleptic bis(1,2-dithiolene) complexes has been developed and applied to complex 3. The DC, predominant for 1 (nDC = 55.4%), provides a remarkable contribution to the electronic structures of the ground states of both 3 and 4, showing a diradicaloid nature (nDC = 24.9% and 27.5%, respectively). The computational approach developed here clearly shows that a rational design of the DC of bis(1,2-ditiolene) metal complexes, and hence their linear and nonlinear optical properties, can be achieved by a proper choice of the 1,2-dithiolene ligands based on their electronic structure.

Photoconducting Devices with Response in the Visible-Near-Infrared Region Based on Neutral Ni Complexes of Aryl-1,2-dithiolene Ligands.

Metal bis(1,2-dithiolene) complexes belonging to the class [Ni(Ar-edt)2]x- [Ar-edt2- = arylethylene-1,2-dithiolate; Ar = phenyl, (1x-), 2-naphthyl (2x-); x = 0 and 1] were fully characterized by NMR, UV-visible-near-infrared (UV-vis-NIR), diffuse reflectance, and FT-IR spectroscopy, as well as cyclic voltammetry and single-crystal X-ray diffraction analysis. These complexes have emerged as new photoconducting materials that allowed for the development of a prototype of photodetectors with response in the vis-NIR region. The photodetecting devices showed in some cases quantum efficiencies orders of magnitude higher than those of previously reported 1,2-dithiolene systems.

Antibacterial Activity of Amidodithiophosphonato Nickel(II) Complexes: An Experimental and Theoretical Approach.

The reactions of 2,4-bis(4-methoxyphenyl)-1,3-dithio-2,4-diphosphetane-2,4-disulfide (Lawesson's Reagent, LR) with benzylamine (BzNH2) and 4-phenylbutylamine (PhBuNH2) yield benzylammonium P-(4-methoxyphenyl)-N-benzyl-amidodithiophosphonate (BzNH3)(BzNH-adtp) and 4-phenylbutylammonium P-(4-methoxyphenyl)-N-(4-phenylbutyl)-amidodithiophosphonate (PhBuNH3)(PhBuNH-adtp). The relevant nickel complexes [Ni(BzNH-adtp)2] and [Ni(PhBuNH-adtp)2] and the corresponding hydrolysed derivatives (BzNH3)2[Ni(dtp)2] and (PhBuNH3)2[Ni(dtp)2] were prepared and fully characterized. The antimicrobial activity of the aforementioned amidodithiophosphonates against a set of Gram-positive and Gram-negative pathogen bacteria was evaluated, and [Ni(BzNH-adtp)2] and [Ni(PhBuNH-adtp)2] showed antiproliferative activity towards Staphylococcus aureus and Staphylococcus haemolyticus strains. density functional theory (DFT) calculations were performed to shed some light on the activity of reported compounds related to their tendency towards P-N bond cleavage.

New Variations on the Theme of Gold(III) C∧N∧N Cyclometalated Complexes as Anticancer Agents: Synthesis and Biological Characterization.

A series of novel (C∧N∧N) cyclometalated AuIII complexes of general formula [Au(bipydmb-H)X][PF6] (bipydmb-H = C∧N∧N cyclometalated 6-(1,1-dimethylbenzyl)-2,2'-bipyridine) were prepared with a range of anionic ligands X in the fourth coordination position, featuring C (alkynyl)-, N-, O-, or S-donor atoms. The X ligands are varied in nature and include three coumarins, 4-ethynylaniline, saccharine, and thio-ß-d-glucose tetraacetate, the tripeptide glutathione (GSH), and a coumarin-substituted amide derived from 4-ethynylaniline. The gold(I) complex [Au(C2ArNHCOQ)(PPh3)] (HC2ArNHCOQ = N-(4-ethynylphenyl)-2-oxo-2 H-chromene-3-carboxamide) was also prepared for comparison. The new compounds were fully characterized by means of analytical techniques, including NMR, absorption, and emission spectroscopy. The crystal structures of three cyclometalated AuIII complexes and of the AuI derivative were solved by single-crystal X-ray diffraction. The antiproliferative activity of the new AuIII cyclometalated derivatives was evaluated against cancer cells in vitro. According to the obtained results, only complexes 3-PF6 and 5-PF6, featuring coumarins as ancillary ligands and endowed with high redox stability in solution, display antiproliferative effects, with 5-PF6 being the most potent, while all of the others are scarcely active to nonactive in the selected cell lines. In order to study the reactivity of the compounds with biomolecules, the interaction of complexes 3-PF6 and 5-PF6 with the protein cytochrome c and the amino acids cysteine and histidine was analyzed by electrospray ionization mass spectrometry (ESI MS), showing adduct formation only with Cys after at least 1 h incubation. Furthermore, the parent hydroxo complex [Au(bipydmb-H)(OH)][PF6] (1OH-PF6) was investigated in a competitive assay to determine the protein vs oligonucleotide binding preferences by capillary zone electrophoresis (CZE) coupled to ESI-MS. Of note, the compound was found to selectively form adducts with the oligonucleotide over the protein upon ligand exchange with the hydroxido ligand. Adduct formation occurred within the first 10 min of incubation, demonstrating the preference of 1OH-PF6 for nucleotides in this setup. Overall, the obtained results point toward the possibility to selectively target DNA with gold(III) organometallics.

Synthesis of 2,2-bis(pyridin-2-yl amino)cyclobutanols and their conversion into 5-(pyridin-2-ylamino)dihydrofuran-2(3H)-ones.

A two-step protocol is presented for the preparation of 5-(pyridin-2-ylamino)dihydrofuran-2(3H)-ones from 2-hydroxycyclobutanone and some 2-aminopyridines via a catalyst-free synthesis of 2,2-bis(pyridin-2-ylamino)cyclobutanols followed by Dess-Martin periodinane mediated ring expansion.

Acid-catalyzed reaction of 2-hydroxycyclobutanone with benzylic alcohols.

The acid-promoted syntheses of 2-(benzyloxy)cyclobutanones and bis(benzyloxy)dioxatricyclo decanes were achieved starting from 2-hydroxycyclobutanone and variously functionalized benzyl alcohols. The reaction sequences afforded the desired products in good to high yields and in a solvent-dependent chemoselective fashion.

Atom Efficient Preparation of Zinc Selenates for the Synthesis of Selenol Esters under "On Water" Conditions.

We describe here an atom efficient procedure to prepare selenol esters in good to excellent yields by reacting [(PhSe)2Zn] or [(PhSe)2Zn]TMEDA with acyl chlorides under "on water" conditions. The method is applicable to a series of aromatic and aliphatic acyl chlorides and tolerates the presence of other functionalities in the starting material.

Structure-activity relationships in cytotoxic Au(I)/Au(III) complexes derived from 2-(2'-pyridyl)benzimidazole.

Gold(I) and gold(III) complexes derived from 2-(2'-pyridyl)benzimidazole (pbiH) were proven to be a promising class of in vitro antitumor agents against A2780 human ovarian cancer cells. In this paper, a comparative electrochemical, UV-vis absorption, and emission spectroscopic investigation is reported on pbiH, the two mononuclear Au(III) complexes [(pbi)AuX2] (X = Cl (1), AcO (2)), the four mononuclear Au(I) derivatives [(pbiH)AuCl] (3), [(pbiH)Au(PPh3)]PF6 ((4(+))(PF6(-))), [(pbi)Au(PPh3)] (5), and [(pbi)Au(TPA)] (6), the three mixed-valence Au(III)/Au(I) complexes [(µ-pbi)Au2Cl3] (7), [(Ph3P)Au(µ-pbi)AuX2]PF6 (X = Cl ((8(+))(PF6(-))), AcO ((9(+))(PF6(-)))), and the binuclear Au(I)-Au(I) compound [(µ-pbi)Au2(PPh3)2]PF6 ((10(+))(PF6(-))). All complexes feature irreversible reduction processes related to the Au(III)/Au(I) or Au(I)/Au(0) processes and peculiar luminescent emission at about 360-370 nm in CH2Cl2, with quantum yields that are remarkably lower ((0.7-14.5) × 10(-2)) in comparison to that determined for the free pbiH ligand (31.5 × 10(-2)) in the same solvent. The spectroscopic and electrochemical properties of all complexes were interpreted on the grounds of time-dependent PBE0/DFT calculations carried out both in the gas phase and in CH2Cl2 implicitly considered within the IEF-PCM SCRF approach. The electronic structure of the complexes, and in particular the energy and composition of the Kohn-Sham LUMOs, can be related to the antiproliferative properties against the A2780 ovarian carcinoma cell line, providing sound quantitative structure-activity relationships and shedding a light on the role played by the global charge and nature of ancillary ligands in the effectiveness of Au-based antitumor drugs.

Crystal structure of 4,4'-(disulfanedi-yl)dipyridinium chloride triiodide.

4,4'-(Disulfanedi-yl)dipyridinium chloride triiodide, C10H10N2S2 2+·Cl-·I3 -, (1) was synthesized by reaction of 4,4'-di-pyridyl-disulfide with ICl in a 1:1 molar ratio in di-chloro-methane solution. The structural characterization of 1 by SC-XRD analysis was supported by elemental analysis, FT-IR, and FT-Raman spectroscopic measurements.

A new class of third-order nonlinear optical materials: laser pulse-duration dependant saturable absorption and nonlinear refraction in platinum(II) diimine-dithiolate complexes.

The third-order nonlinear optical (NLO) properties of a series of platinum diimine-dithiolate complexes [Pt(N^N)(S^S)] were investigated by means of Z-scan measurements, revealing second hyperpolarizability values up to 10-29 esu, saturable absorption properties, and nonlinear refractive behaviour, which were rationalized also by means of DFT calculations.

An Experimental and Theoretical Insight into I2 /Br2 Oxidation of Bis(pyridin-2-yl)Diselane and Ditellane.

The reactivity between bis(pyridin-2-yl)diselane o Py2 Se2 and ditellane o Py2 Te2 (L1 and L2, respectively; o Py=pyridyn-2-yl) and I2 /Br2 is discussed. Single-crystal structure analysis revealed that the reaction of L1 with I2 yielded [(HL1+ )(I- )⋅5/2I2 ]∞ (1) in which monoprotonated cations HL1+ template a self-assembled infinite pseudo-cubic polyiodide 3D-network, while the reaction with Br2 yielded the dibromide Ho PySeII Br2 (2). The oxidation of L2 with I2 and Br2 yielded the compounds Ho PyTeII I2 (3) and Ho PyTeIV Br4 (6), respectively, whose structures were elucidated by X-ray diffraction analysis. FT-Raman spectroscopy measurements are consistent with a 3c-4e description of all the X-Ch-X three-body systems (Ch=Se, Te; X=Br, I) in compounds 2, 3, Ho PyTeII Br2 (5), and 6. The structural and spectroscopic observations are supported by extensive theoretical calculations carried out at the DFT level that were employed to study the electronic structure of the investigated compounds, the thermodynamic aspects of their formation, and the role of noncovalent σ-hole halogen and chalcogen bonds in the X⋅⋅⋅X, X⋅⋅⋅Ch and Ch⋅⋅⋅Ch interactions evidenced structurally.