Paramagnetic dithiolene complexes as metallo-ligands: ether/thioether coordination.

International audienceThe secondary coordination ability of a paramagnetic nickel dithiolene complex, bearing an ether coordinating function within a nine-membered flexible ring, has been demonstrated in its [NiCl(DMF)(2)](+) complex, through coordination by both ether and thioether functions, allowing for a ferromagnetic interaction between both paramagnetic entities

Dithiolene complexes as metallo-ligands: a crown-ether approach

International audienceA nickel dithiolene complex substituted with crown ether cyclic moieties incorporating four O atoms, abbreviated as [Ni(S2O4)2]1−,0, is isolated in its radical anionic (as Na+ salt) and neutral forms. The Na+ cation is six-coordinated with short Na[cdots, three dots, centered]O distances (2.46-2.52 Å), involving two crown ether moieties of two different complexes. The oxidized neutral complex [Ni(S2O4)2]0 was also isolated and structurally characterized. In the absence of alkaline cations during the synthesis, a mixed salt associating [Ni(S2O4)2]1− with Ni2+ was isolated, and formulated as (Ni,H2O)[Ni(S2O4)2]2, with the Ni2+ cation weakly bonded to two crown ether moieties. The salt exhibits an unprecedented solid state association with extremely short S[cdots, three dots, centered]S intermolecular contacts [3.332(2) Å], leading to a pairing of the radical [Ni(S2O4)2]− into antiferromagnetic uniform spin chains

Novel Correlations between Spectroscopic and Morphological Properties of Activated Carbons from Waste Coffee Grounds

Massive quantities of spent coffee grounds (SCGs) are generated by users around the world. Different processes have been proposed for SCG valorization, including pyrolytic processes to achieve carbonaceous materials. Here, we report the preparation of activated carbons through pyrolytic processes carried out under different experimental conditions and in the presence of various porosity activators. Textural and chemical characterization of the obtained carbons have been achieved through Brunauer–Emmett–Teller (BET), ESEM, 13C solid state NMR, XPS, XRD, thermogravimetric and spectroscopic determinations. The aim of the paper is to relate these data to the preparation method, evaluating the correlation between the spectroscopic data and the physical and textural properties, also in comparison with the corresponding data obtained for three commercial activated carbons used in industrial adsorption processes. Some correlations have been observed between the Raman and XPS data

Dithiolene and thiolate transition metal complexes: towards an exploration of their multi-functional properties

This work has dealt with the synthesis and characterization of transition metal complexes with two types of sulphur based ligands: 1,2 dithiolato ligands and thiol-carboxylate ligands. The electronic features related to the metal-sulphur interaction, such as the rich redox behaviour associated to the interplay between the sulphur and a redox active metal, the better overlap between sulphur and metal orbitals, the ability of forming coordination compounds in different topologies, from discrete complexes to extended 1-D network, make sulphur-based coordination compounds. We have explored these features starting from non redox innocent metal bis-dithiolene complexes as possible molecular precursors in the field of molecular magnetism, as paramagnetic centers able to organize in more complex coordination compounds. In the first part of this work, “classical” metal bis-dithiolene complexes have been investigated as metallo-ligands towards the coordination of “acceptor” metal complexes, in order to build up coordination compounds of higher nuclearities with paramagnetic centers. Particularly, the investigated dithiolenes were [Cu(mnt)2]2- ,[Cu(tfadt)2]2-and [Ni(dmid)2].- while the “acceptor” metal complexes are Mn(III) porphinato ,Mn(III) salen-like complexes and finally a mixed valence Mn(II)Mn(III) complex. We have observed that the reactivity in solution of metal-bis –dithiolene together with the Mn-based complexes employed has lead to co-crystallization salts where the coordinating group of the dithiolene does not coordinate the Mn center. From these observation, we have decided to synthesize a series of new 1,2 dithiolato ligands bearing a potential coordinating functional group. We have choosen to functionalize them with crown-ether macrocycles with different sizes, in order modulate their selectivity for transition metal ions or lanthanide ions. The corresponding radical nickel(dithiolene) complexes have been synthesized and polymetallic Ni-Na and Ni-Ni chains have been obtained as well as a bimetallic Ni-Ni discrete complex. We have provided their physico-chemical characterizations in order to understand their rich redox behaviour and their magnetic properties. The investigation on these new 1,2 dithiolato ligands is still in progress in order to build up polymetallic assemblies also with lanthanide ions. We have then switched to another class of sulphur-based ligands, the thiol-carboxylate ligands. 2-mercaptonicotinic acid has been considered as versatile ligand towards the synthesis of sulphur-based metal complexes. This polyfunctional ligand can coordinate with N, O or S donor atoms. Under hydrothermal conditions, Zn(II) and 2-mercaptonicotinic acid afforded a coordination polymer where 2-mercaptonicotinic acid is S,O chelating. The electronic properties were studied by means of theoretical calculations and experimental measurments. Under the same reaction conditions, Ni(II) did not led to any crystalline material. By switching the reaction conditions, it has been observed a mononuclear S,O chelated Ni bis(mercaptonicotinate).Questo lavoro di dottorato ha riguardato la sintesi e la caratterizzazione di complessi di metalli di transizione con leganti donatori allo zolfo. In particolare sono stati considerati i leganti 1,2 ditiolato e un legante tipo tiol-carbossilato, l’acido 2-mercaptonicotinico. Lo zolfo presenta una variabilità maggiore di stati di ossidazione rispetto all’ossigeno e a questo si riconduce il particolare comportamento redox dei complessi con legami M-S. Per questo motivo la sintesi di complessi implicanti il legame metallo-zolfo è un’area di ricerca attiva soprattutto per quanto riguarda la progettazione di materiali con proprietà di conduzione, ottiche o magnetiche. In questo contesto sono stati considerati i complessi dei metalli di transizione con i leganti 1,2 ditiolato, altresi detti metallo bis-ditioleni. Nei metallo bis-ditioleni la variabilità degli stati di ossidazione del complesso senza grandi variazioni della geometria di coordinazione li rende adatti per la sintesi di materiali molecolari. In particolare, una via sintetica per l’ottenimento di tali materiali consiste nell’organizzare questi complessi via coordinazione ad un altro centro metallico, in maniera da ottenere composti a più alta nuclearità. Soprattutto per quanto riguarda il magnetismo molecolare, vi è la necessita di organizzare nella stessa molecola più centri paramagnetici. In questo lavoro di tesi, inizialmente dithioleni paramagnetici “classici” come [Cu(mnt)2]2- ,[Cu(tfadt)2]2-and [Ni(dmid)2].-, contenenti gruppi funzionali potenzialmente coordinanti sono stati impiegati come metallo-leganti verso complessi paramagnetici di Mn(III) o a valenza mista Mn(II)/Mn(III). Durante gli esperimenti condotti, è risaltata la reattività in soluzione dei metallo bis-ditioleni verso lo scambio di leganti che non ha condotto alla formazione del complesso polunucleare sperato, sebbene siano stati isolati composti potenzialmente interessanti. Alla luce di tutto cio, è stata intrapresa la sintesi di nuovi leganti 1,2 ditiolato opportunamente funzionalizzati con gruppi coordinanti quali gli eteri corona. La versatilità dei ditioleni verso la funzionalizzazione ha permesso di realizzare una serie di leganti con diverse dimensioni del macrociclo, in modo da poter modulare la selettività verso metalli di transizione ma anche verso ioni di lantanidi trivalenti. Sono stati sintetizzati a partire da questi leganti i complessi ditioleni di nickel, isolandoli in forma di anioni e aventi spin S=1/2. Sono state ottenuti complessi polimetallici Ni-Ni e Ni-Na. Inoltre è stato ottenuto un complesso bimetallico Ni-Ni. Tutti i complessi sono stati caratterizzati chimicamente. Inoltre, le proprietà magnetiche sono state indagate tramite misure di suscettività magnetica in funzione della temperatura, rivelando per il complesso polimetallico Ni-Ni una forte interazione fra le unità ditiolene costituenti il complesso. Il legante tiol-carbossilato acido 2- mercaptonicotinico è stato considerato per la sua versatilità alla coordinazione. In condizioni idrotermali e in presenza di Zn(II) e acido 2-mercaptonicotinico, è stato ottenuto un polimero di coordinazione dove il legante mercaptonicotinato funge da chelante S,O e lega a ponte monoatomico i vicini centri metallici. La stessa topologia non è stata ottenuta con il Ni(II). Cambiando le condizioni di reazione, finora solo il complesso monometallico Ni(II) bis-mercaptonicotinato è stato ottenuto. Le proprietà elettroniche correlate alla situazione di coordinazione S-Zn-O del polimero di coordinazione di Zn(II) sono state investigate per mezzo di calcoli teorici e misure sperimentali

Molecular, Electronic, and Crystal Structures of Self-Assembled Hydrothermally Synthesized Zn(II) 12Mercaptonicotinate: A Combined Spectroscopic and Theoretical Approach

A Zn(II) 2-mercaptonicotinate coordination polymer (Zn1), with Zn(II) ions chelated by both sulfur and oxygen in a distorted square pyramidal environment, and a molecular Zn(II) 2-hydroxynicotinate complex (Zn2) were synthesized by the reaction of zinc acetylacetonate with 2-mercaptonicotinic (Zn1) and 2-hydroxynicotinc (Zn2) acid, respectively, under hydrothermal conditions. The crystal structures of Zn1 and Zn2 were determined by single crystal X-ray diffraction measurements. Dispersion-corrected density functional theory (DFT) calculations reproduce very well the experimental structures and show that Zn1 is stable against hydration, whereas Zn2 is stable against dehydration over wide ranges of temperature and pressure, in agreement with thermogravimetric analysis results. The electronic structure of the two compounds is computed with the DFT+U method. The theoretical valence band agrees well with the X-ray photoelectron spectroscopy experiments. Furthermore, the band gap of Zn1 is found to be narrower than that of Zn1 and is characterized by the presence of sulfur lone pairs at the edge of the valence band

Plasma-Activated Water Triggers Rapid and Sustained Cytosolic Ca2+ Elevations in Arabidopsis thaliana

Increasing evidence indicates that water activated by plasma discharge, termed as plasma-activated water (PAW), can promote plant growth and enhance plant defence responses. Nevertheless, the signalling pathways activated in plants in response to PAW are still largely unknown. In this work, we analysed the potential involvement of calcium as an intracellular messenger in the transduction of PAW by plants. To this aim, Arabidopsis thaliana (Arabidopsis) seedlings stably expressing the bioluminescent Ca2+ reporter aequorin in the cytosol were challenged with PAW generated by a plasma torch. Ca2+ measurement assays demonstrated the induction by PAW of rapid and sustained cytosolic Ca2+ elevations in Arabidopsis seedlings. The dynamics of the recorded Ca2+ signals were found to depend upon different parameters, such as the operational conditions of the torch, PAW storage, and dilution. The separate administration of nitrate, nitrite, and hydrogen peroxide at the same doses as those measured in the PAW did not trigger any detectable Ca2+ changes, suggesting that the unique mixture of different reactive chemical species contained in the PAW is responsible for the specific Ca2+ signatures. Unveiling the signalling mechanisms underlying plant perception of PAW may allow to finely tune its generation for applications in agriculture, with potential advantages in the perspective of a more sustainable agriculture