Search

Coordinatively unsaturated dithiophosphato complex [Cd((MeO)2PS2)2] (1) was reacted with the bifunctional ligands 3,5-di-(4-pyridyl)-1,2,4-thiadiazole (L1) and 3,5-di-(3-pyridyl)-1,2,4-thiadiazole (L2) to give the helicoidal coordination polymer (1·L1)∞ and the paddle-wheel dimer (1·L2)2, both characterised by single-crystal X-ray diffraction. A comparison of the structures with the different supramolecular constructs obtained by reacting L1 and L2 with differently P-substituted dithiophosphoric NiII complexes allowed to evaluate the role of the metal ion for the predictable assembly of this class of coordination polymers. Cadmium dithiophosphato complex [Cd((MeO)2PS2)2] (1) was reacted with bis-functional dipyridyl-thiadiazole ligands L1 and L2 to give the helicoidal coordination polymer (1·L1)∞ and the discrete dimeric paddle-wheel (1·L2)2. A comparison of the structures with different supramolecular constructs previously obtained is presented.

Five coumarin derivatives, able to coordinate Fe(III) and exhibit a ratiometric and turn-on fluorescence response, were prepared and tested. The derivative with the –OCH3 substituent exhibited a high fluorescence enhancement in the presence of Fe(III), Ga(III), Au(III) and Y(III). Thanks to the higher stability of the Fe(III) complexes, this molecule could be proposed as a selective fluorescent sensor for the detection of Fe(III) in CH3CN and CH3CN : H2O (1 : 1, v/v) solutions, showing a linear response up to 35.0 μM Fe(III) concentration and a limit of detection of 2.4 μM Fe(III) concentration. The fluorescence response towards this ion was also tested on a solid surface with a simple cellulose paper-strip test. The peculiarity of the proposed sensor lies in its easy and low-cost synthesis, relevant ratiometric response and, since it is derived from a natural product, low impact on the environment and its organisms.

The reactivity of thiomorpholinium P-(4-methoxyphenyl)-N-thiomorpholin-amidodithiophosphonate (S-MorH+2)(S-Mor-adtp−) and morpholinium P-(4-methoxyphenyl)-N-morpholin-amidodithiophosphonate (O-MorH+2)(O-Mor-adtp−) towards nickel (II) dichloride hexahydrated is presented and the hydrolysis of the relevant metal complexes investigated. The hydrolytic products (S-MorH+2)2 [Ni(dtp)2]2− and (O-MorH+2)2[Ni(dtp)2]2− were characterized by means of FT-IR, 1H, and 31P NMR and XRD and the experimented P–N cleavage investigated and elucidated by means of DFT calculations. The antimicrobial activity of the neutral nickel complex [Ni(S-Mor-adtp)2] was tested against a set of Gram-positive and Gram-negative bacteria alongside with its nanodispersion in a silica matrix. The complex [Ni(S-Mor-adtp)2] did not show antibacterial activity, whilst the nano-dispersed sample [Ni(S-Mor-adtp)2]_SiO2 demonstrated inhibition to growth of Staphylococcus aureus. The nanocomposites were fully characterized by means of XRPD, TGA, SEM and dinitrogen sorption techniques.

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.

Sulphur and nitrogen oxide pollutants cause acid rain that can eventually lead to the dissolution of calcite in marble and limestones. Calcium oxalate is an inorganic protective agent, which is obtained by treatment with ammonium oxalate. The functionalization of oxalic acid to give monoesters and monoamides (oxamates) allows tailoring the solubility of the relevant ammonium and calcium salts. In this context, theoretical calculations carried out at the Density Functional Theory (DFT) level were exploited to investigate the capability of oxalate, methyloxalate, phenyloxalate, oxamate, methyloxamate, and phenyloxamate to interact with the calcium carbonate lattice. An in-depth validation based on the structural data showed that DFT calculations with the PBE0 functional along with a single or triple-zeta def2 basis set allow understanding the different reactivity of the oxalate and oxamate derivatives and their efficiency in interacting with stones containing calcium carbonate, such as Carrara marble and biomicritic limestones.

The reaction of (C^Npz^C)AuCl with C-H acidic compounds H2CR1R2 in the presence of base readily affords the corresponding alkyl complexes (C^Npz^C)AuCHR1R2 [2a, R1 = R2 = CN; 3a, R1 = R2 = C(O)Me; 4, R1 = R2 = CO2Et; 5, R1 = R2 = C(O)Ph; 6a, R1 = H, R2 = C(O)Me]. The analogous pyridine-pincer complexes 2b, 3b and 6b were obtained similarly [C^Npz^C = 2,6-bis(4′-tBuC6H3)2pyrazine dianion; C^Npy^C = 2,6-bis(4′-tBuC6H3)2pyridine dianion]. The reactions of (C^Npz^C)AuOAcF (7a) and (C^Npy^C)AuOAcF (7b) with MeMgI gave the methyl complexes (C^Npz^C)AuMe (8a) and (C^Npy^C)AuMe (8b), respectively. The crystal structures of 2a, 2b, 3a, 6a, and 7a have been determined. The photophysical properties of the new complexes and those of the previously reported gold hydride (C^Npz^C)AuH (AuH) are reported. The lower-energy absorption and the emission maxima follow the energy sequence 2a < 3a < 4 < 5 < 6a < AuH ≈ 8a for the pyrazine series, and 2b < 3b < 6b ≈ 8b for the pyridine series. These values provide a correlation with the pKa values of the corresponding ancillary ligand precursors. In agreement with DFT calculations, the emissions are assigned to 3IL(C^N^C)/3ILCT {(C6H4tBu-4’)→pz/py*} transitions, dominated by the HOMO and the LUMO orbitals. The LUMO is located in the heterocycle (py/pz) in trans position to the ancillary ligand, which makes this orbital more sensitive to the electronic nature of the ancillary ligand than the HOMO. The calculations establish that the charge transfer from the tBuC6H3 ligand fragments to the central heterocycle ring in the dominant transition explains the modulation of the properties with the σ-donor characteristics of the alkyl or hydride ligands.

The novel heteroleptic cyclometalated complex [AuIII(pyb-H)(mnt)] (1; pyb-H=C-deprotonated 2-benzylpyridine; mnt =1,2-dicyanoethene-1,2-dithiolate) was tested against a panel of ten Gram positive (belonging to the Staphylococcus, Streptococcus spp. and Bacillus clausii), Gram negative (E. coli, K. pneumoniae, P. aeruginosa) bacteria and three yeasts belonging to the Candida spp. Complex 1 showed a remarkable bacteriostatic antimicrobial activity against staphylococci, with Minimum Inhibitory Concentration (MIC) values of 1.56 and 3.13μg/mL for S. haemoliticus and S. aureus, respectively. Spectroscopic and electrochemical measurements, supported by Density Functional Theory (DFT) calculations, were exploited to fully investigate the electronic structure of complex 1 and its relationship with the antimicrobial activity.

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.

The hydroauration of internal and terminal alkynes by gold(III) hydride complexes [(C^N^C)AuH] was found to be mediated by radicals and proceeds by an unexpected binuclear outer‐sphere mechanism to cleanly form trans‐insertion products. Radical precursors such as azobisisobutyronitrile lead to a drastic rate enhancement. DFT calculations support the proposed radical mechanism, with very low activation barriers, and rule out mononuclear mechanistic alternatives. These alkyne hydroaurations are highly regio‐ and stereospecific for the formation of Z‐vinyl isomers, with Z/E ratios of >99:1 in most cases.

The synthesis of 5-hydroxy-2-(hydroxymethyl)pyridin-4(1H)-one (P1) is presented, together with the evaluation of its coordination ability towards Fe(3+), studied by a combination of chemical, computational, and animal approaches. The use of complementary analytical techniques has allowed us to give evidence of the tautomeric changes of P1 as a function of pH, and to determine their influence on the coordinating ability of P1 towards Fe(3+). The pFe(3+) value 22.0 of P1-iron complexes is noticeably higher than that of deferiprone (20.6), one of the three clinical chelating agents in therapeutic use for iron overload diseases. This is due on one side to the tautomeric change to the catechol form, and on the other to the lower protonation constant of the OH group. Bio-distribution studies on mice allowed us to confirm in vivo the efficacy of P1. Furthermore the coordinating ability toward Al(3+), Cu(2+) and Zn(2+) has been studied to evaluate the possible use of P1 against a second toxic metal ion (Al(3+)), and to envisage its potential influence on the homeostatic equilibria of essential metal ions. The chelating ability of P1 toward these ions, not higher than that of the corresponding deferiprone, contributes to render P1 a more selective iron chelator.

The reactions of 2,4-bis(4-methoxyphenyl)-1,3-dithio-2,4-diphosphetane-2,4-disulfide (Lawesson&rsquo, 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&ndash, N bond cleavage.

Isocyanides insert into gold(iii)-hydrogen bonds to give the first examples of gold iminoformyl complexes. The reaction is initiated by catalytic amounts of radicals; DFT calculations indicate that this is an equilibrium reaction driven forward by isocyanide in sufficient excess to trap the Au(ii) intermediate.

The hydroauration of functionalised 1-alkenes by the gold(III) hydride (C^NOMe^C)AuH is initiated by organic radicals and proceeds via (C^N^C)Au(II) radical intermediates following a bimolecular outer-sphere mechanism. The outcome of these reactions is determined by the stability of the gold-substituted radicals, and chemoselectivity correlates with the degree of spin delocalisation in the alkylgold radical intermediates. The reaction is sensitive to steric as well as electronic factors; disubstituted alkenes and alkenes that form unstable radicals give product mixtures or are unreactive. As DFT calculations show, the reactions agree well with the calculated reaction enthalpies and the standard free energy change for the reaction of the gold(II) radical with the respective alkene.

The coordination properties and photochemical response of two fluorescent ligands 2,5-bis{2-[bis(2-pyridylmethyl)aminomethyl]phenyl}[1,3,4]oxadiazole (L1) and 2,5-bis{2-[(1,4,7-triazacyclononane-1-yl)methyl]phenyl}[1,3,4]oxadiazole (L2) towards ZnII and CdII are reported. The ligands contain the 2,5-diphenyl[1,3,4]oxadiazole (PPD) fluorescent probe linked to two coordinating units, namely dipicolylamine (DPA) for L1 and 1,4,7-triazacyclononane (TACN) for L2, through a methylene spacer. Both ligands form mononuclear and dinuclear complexes with these metal ions in aqueous or hydro-alcoholic media. With regard to L1, only the mononuclear CdII complex is highly fluorescent at 368 nm, while the mononuclear ZnII and dinuclear CdII and ZnII complexes are not emissive. Ligand L2 forms an excimer emitting at 474 nm only in the presence of one equivalent of CdII, and potentiometric, spectrophotometric, spectrofluorimetric, and NMR studies and DFT calculations were performed to explain this peculiarity. The discrimination between CdII and ZnII is mainly due to the different coordination environments of the metal ions in the mononuclear complexes; namely CdII is coordinated by both the side arms of each ligand, while ZnII is bound only to one coordinating unit.

The reactivity of the 2-arylselanyl pyridine derivatives L1–L4 towards dihalogens X2 (X = I, Br) and interhalogens IX (X = Cl, Br) was studied in CHCl3 or CH3CN. The solid products obtained were structurally characterized and their nature points out the preference for CT spoke adducts and for seesaw insertion adducts to be formed at the N-donor and Se-donor site, respectively. DFT calculations were performed to provide a rationale for the structural diversity observed in the products obtained.

The Dipartimento di Scienze Chimiche e Geologiche of the Università degli Studi di Cagliari and Banco di Sardegna, Italy are kindly acknowledged for financial support (PRID 2015). The choice of the metal ion M and the terminal Y and donor X chalcogen species (M = Ni, Pt; X, Y = S, Se) in square-planar complexes with 1,3-dimethyl-2-chalcogenoxo-imidazoline-4,5-dichalcogenolates allows fine-tuning both the redox stability and the energy of the peculiarly intense NIR electrochromic absorption, thanks to the subtle contribution of M, X, and Y to the relevant frontier molecular orbitals, investigated at IEF-PCM DFT and TD-DFT level. Publisher PDF

International audience; Eighteen new [PtII(N∧N)(S∧S)] complexes [23-40; N∧N = diimine: 2,2′-bipyridine, 1,10-phenanthroline and alkyl/aryl-substituted derivatives; S∧S = arylethylene-1,2-dithiolate (R-edt2-: R = phenyl, 2-naphthyl, 1-pyrenyl), N-substituted 2-thioxothiazoline-4,5-dithiolate (R-dmet2-: R = methyl, ethyl, phenyl)] have been synthesized and characterized by spectroscopic (UV/Vis/NIR, fluorescence) and electrochemical (CV) measurements. Single-crystal X-ray diffraction analysis allowed structural characterization of five of the complexes (27-29, 31, and 37). Structural modifications capable of affecting the nature and energies of the frontier molecular orbitals in these systems were assessed and hybrid DFT and time-dependent (TD) DFT calculations, carried out both in the gas phase and in the presence of several solvents (CH2Cl2, CHCl3, CH3CN, acetone, thf, dmf, dmso, and toluene), allowed the trends observed in the voltammetric data and in the energies of the peculiar solvatochromic visible absorption bands to be rationalized. In addition, to evaluate the second-order nonlinear optical properties of 23-40, first static hyperpolarizability values βtot were calculated both in the gas phase and in CH2Cl2, the highest values being obtained for [Pt(N∧N)(Me-dmet)] complexes (N∧N = 4,4′-diphenyl-2,2′-bipyridine and 4,7-diphenyl-1,10-phenanthroline; βtot = 691 × 10-30 and 604 × 10-30 esu, respectively).

Two new diimine-diselenolate PtII chromophores [Pt(bipy)(Me-dset)] (1) and [Pt(phen)(Me-dset)] (2) (Me-dset2- = N-methyl-2-thioxothiazoline-4,5-diselenolate) were synthesized and characterized. The effect of replacing sulfur with selenium was investigated by comparing the UV/Vis spectroscopic and electrochemical properties of 1 and 2 with those of the corresponding sulfur analogues, [Pt(bipy)(Me-dmet)] (3) and [Pt(phen)(Me-dmet)] (4), with a particular focus on their linear and nonlinear optical properties. Postprint Postprint