Inverted Ligand Field in a Pentanuclear Bow Tie Au/Fe Carbonyl Cluster

Gold chemistry has experienced in the last decades exponential attention for a wide spectrum of chemical applications, but the +3 oxidation state, traditionally assigned to gold, remains somewhat questionable. Herein, we present a detailed analysis of the electronic structure of the pentanuclear bow tie Au/Fe carbonyl cluster [Au{η2-Fe2(CO)8}2]- together with its two one-electron reversible reductions. A new interpretation of the bonding pattern is provided with the help of inverted ligand field theory. The classical view of a central gold(III) interacting with two [Fe2(CO)8]2- units is replaced by Au(I), with a d10 gold configuration, with two interacting [Fe2(CO)8]- fragments. A d10 configuration for the gold center in the compound [Au{η2-Fe2(CO)8}2]- is confirmed by the LUMO orbital composition, which is mainly localized on the iron carbonyl fragments rather than on a d gold orbital, as expected for a d8 configuration. Upon one-electron stepwise reduction, the spectroelectrochemical measurements show a progressive red shift in the carbonyl stretching, in agreement with the increased population of the LUMO centered on the iron units. Such a trend is also confirmed by the X-ray structure of the direduced compound [Au{η1-Fe2(CO)8}{η2-Fe2(CO)6(μ-CO)2}]3-, featuring the cleavage of one Au-Fe bond

The Competition Between Chemistry and Biology in Assembling Iron–Sulfur Derivatives: Molecular Structures and Electrochemistry. Part VI. {[Fe 4 S 4 ](S γ Cys ) 3 (nonthiolate ligand)} Proteins

2noWithin a couple of years we have planned to systematically update structure/electrochemistry of the different classes of metalloproteins harboring iron–sulfur clusters. In this picture we have so far dealt with {Fe(Cys)4}, {[Fe2S2](Cys)4}, {[Fe2S2](Cys)3(X)} (X = Asp, Arg, His), {[Fe2S2](Cys)2(His)2}, {[Fe3S4](Cys)3}, and {[Fe4S4](Cys)4} cores. Since a significant number of structurally characterized [4Fe–4S] proteins harbor {[Fe4S4](SγCys)3(nonthiolate ligand)} iron–sulfur centers, the aim of the present review paper is to complement our paper review on {[Fe4S4](Cys)4} cores with structure and electrochemistry of {[Fe4S4](SγCys)3(nonthiolate ligand)} proteins in order to gain a panoramic overview of the state-of-the-art of structure/electrochemistry of all the [4Fe–4S] proteins (excluding obviously those proteins which harbor mixed iron–sulfur clusters such as [4Fe–4S] + [2Fe–2S], [4Fe–4S] + [3Fe–4S], [4Fe–4S] + [3Fe–4S] + [2Fe–2S], and [4Fe–4S] + [3Fe–4S] + [4Fe–3S]).nonemixedZanello, Piero; Corsini, MaddalenaZanello, Piero; Corsini, Maddalen

Synthesis, and electrochemical and density functional studies of new copper(II)- and manganese(II) -oxicam drugs. Redox potentials and MOs compatible with SOD-like activity and unusual six-membered rings of water molecules bridging complex units

The synthesis and rare structures of Mn-II and Cu-II complexes with OXI drugs (oxicam, a family of non-steroidal anti-inflammatory drugs) are reported. On mixing Mn-II acetate with piroxicam (H2PIR) pale yellow single crystals of trans,trans-[Mn-II(O-N,N-DMF)(2)(N,O-HPIR)(2)], 1, dimethylformamide (DMF), were obtained. The structure shows two HPIR- anions chelate through pyridyl nitrogen and amide oxygen, and two positions around the metal atom are occupied by the two DMF molecules. The Mn-O(amide, HPIR) vector is much shorter than the two other coordination vectors, a novelty for M-II(L)(2)(HOXI)(2) molecules. Single crystals of trans,trans-[Cu-II(H2O)(2)(N,O-HTEN)(2)]center dot 4H(2)O center dot 2DMF, 2, (H2TEN, tenoxicam,) were obtained by long storage from DMF solutions of Cu-II(HTEN)(2) during loading smart synthetic hydrogels. Compound 2 is the first example for M-II(HOXI)(2) units, linked to H2O molecules ever reported, and extensive networks of H2O center dot center dot center dot OH2 hydrogen bonds and Cu center dot center dot center dot OH2 bonds that involve six member cycles of water molecules arranged as puckered rings bridging M-II(HOXI)(2) entities. Infrared bands related to amide groups for HOXI- ligands are significantly influenced by the strength of M-O bonds in agreement with bond length trends. Electrochemical studies for Cu-II(HTEN)(2) in tetrahydrofuran are in agreement with a SOD-like scavenger activity at least for superoxide oxidation to molecular oxygen, E degrees(Cu-II/Cu-I, SCE) -0.31V. Furthermore, density functional investigation at the gas phase reproduces well the structure for trans,trans-[Mn-II(O-DMF)(2)(N,O-HPIR)(2)] sextuplet molecule and for trans,trans-[Cu-II(H2O)(2)(N,O-HTEN)(2)] doublet molecule. Even a model of the {Cu-II(HTEN)(2)(OH2)center dot center dot center dot(H2O)(4)center dot center dot center dot(H2O)Cu-II(HTEN)(2)} entity found for 2 is well reproduced by theory. The estimate stabilization energy brought about by the six water molecules ring between two Cu-II(HTEN)(2) molecules is 69 kcal

Redox Chemistry and Electrochemistry of Homoleptic Metal PhenolatesPATAI'S Chemistry of Functional Groups

The redox chemistry of aryl alcohols, or phenols, is of great interest because of their involvement in important biological and industrial processes. Phenol and its substituted analogs are facile one-electron reducing agents that are often involved in electrochemical, photochemical and radiation chemical electron transfer reactions. For these and many other reasons the interest of chemists in the metal phenolates has always been lively and a huge number of these complexes are known. In this chapter we describe the redox behavior of the more restricted set of homoleptic aryloxide complexes. The peculiarities of phenolates as ligands make them usually unable to stabilize a metal in different redox states and, very often, reduction of the metal is accompanied by the release of one or more of the ligands and/or by the formation of polynuclear compounds. This may give rise to a complicated pattern in the redox chemistry of these complexes, but may also open the way to a rich, redox-driven, chemistry of this class of compounds, which, apparently, is still largely unexplored

Mononuclear Metallacarboranes of Groups 6-10 Metals. Analogues of Metallocenes: Electrochemical and X-Ray Structural Aspects

Metallacarboranes containing carborane ligands possessing a pentagonal open face can coordinate metal atoms in a η5-manner quite similar to the cyclopentadienyl monoanion, thus affording metallocene analogues. By virtue of such an analogy, their electron transfer aptitude plays an important role in their physico-chemical characterisation. We review such an aspect, also providing evidence for the structural consequences of their electron transfer processes. At variance with metallocenes, electrochemical investigations on the metallacarboranes have not yet become a routine tool to search for their potential application in fields which require electronic mobility

Unusual hetero-atomic RhSCNSb(Rh) co-ordination ring. Synthesis and X-ray structure of [Rh(N1,S2-2-thiopyrimidinato)2(S2(Rh),N1(Sb)-2-thiopyrimidinato){Sb(C6H5)3}] and long time sought structure of mer-[RhCl3{Sb(C6H5)3}3],

The reaction of RhCl3 center dot 3H(2)O with SbPh3 (Ph, C6H5) in ethanol produced mer-[RhCl3(SbPh3)(3)] (1), as the main product, together with trans-[RhCl2(Ph)(SbPh3)(3)](2) (R. Cini, G. Giorgi, L. Pasquini, Inorg. Chim. Acta 196 (1992) 7; A. Cavaglioni, R. Cini, J. Chem. Soc., Dalton Trans. (1997) 1149). Ways to improve the yield for 1 and 2 were a subject of further works by this laboratory during the past decade and the reactivity of the organometallic compound 2 was investigated towards a variety of bases. Long sought single crystals of 1 suitable for X-ray diffraction have been obtained from hot acetone solution. The metal centre has a pseudo-octahedral coordination environment with the three chloride anions and the three SbPh3 molecules in mer positions. The Rh-Cl bond trans to Sb is significantly weakened by the high trans influence by antimony itself. This gives the rationale for the formation of 2 from RhCl3 and SbPh3 via the preliminary formation of 1, followed by dissociation of the activated chloride anion, and the subsequent formation of the Rh-C(Ph) linkage. The reaction of 1 with 2-thio-1,3-pyrimidine (Htpym) in ethanol produces crystalline [Rh((NS2)-S-1-tpym)(2)(N-1(Sb),S-2(Rh)-tpym)(SbPh3)] (3). Single crystals suitable for X-ray diffraction studies as obtained from ethanol/diethyl-ether contain a complex molecule and a quarter of an ethanol molecule in the asymmetric unit. Two out of three tpym(-) anions chelate the metal centre via the N-1 and S-2 atoms, whereas the third tpym- anion behaves as mono-dentate through the S-2 atom only. The sixth co-ordination position is occupied by the Sb atom. Interestingly, one of the N atoms of the monodentate tpym- anion behaves as electron donor to Sb and a Sb-N linkage forms (d((sb-N)), 2.846 angstrom). As a consequence, an unusual totally hetero-atomic five-membered co-ordination ring of the type RhSCNSb(Rh) forms. A molecular modelling analysis at the hybrid density functional level DFT-B3LYP was performed on selected coordination molecules

Water isotopes in landslide research (WIsLaR)

In the last decade, the scientific community is trying to integrate multidisciplinary approaches to gain further insights in the knowledge of landslide initiation and evolution. In particular, isotope geochemistry is a useful investigation tool to define landslide groundwater recharge origin, groundwater flow paths, mixing phenomena between different water bodies, type of aquifer, type of groundwater transfer processes (only pressure or pressure and mass). This paper aims at pointing out the potentiality of stable and radiogenic isotopic analyses in the study of large and deep rock landslides located in north Apennines. In the studied landslides, the continuous monitoring of groundwater levels, groundwater flow rate from springs or mitigation works, groundwater electrical conductivity and temperature are coupled with groundwater sampling followed by determination of major and tracers ions (such as: Na+, K+, Mg2+, Ca2+, Cl-, HCO3-, SO42-,Btot, Sr2+), and stable (delta 18O, delta 2H,) and radiogenic isotopes (87Sr/86Sr, 3H). In this study isotopic investigations are decisive to understand hydrological processes in landslide body. More in details delta 18O, delta 2H, 87Sr/86Sr and 3H allow to define subsurface architecture, groundwater origin, groundwater flow paths and mixing phenomena between different groundwater bodies. Recharge zones are identify by means of delta 18O and delta 2H isotopes. 3H gives information about groundwater age and allows to identify deep confined layer characterized by low circulation of water and to investigate subsurface transfer processes. In the current research 3H allows to identify a deep confined aquifer in which pressure transfer prevails on mass transfer. Subsurface layers with prevalent horizontal or vertical flux are identified by means simultaneous application of delta 18O, delta 2H and 3H. The simultaneous application of delta 18O, delta 2H, 3H and 87Sr/86Sr allows to recognize hydraulic connections between groundwater and surface water. Moreover, 87Sr/86Sr coupled with 3H allow to identify multilayer aquifer within the landslide body

More about the redox behavior of late transition metal triple-decker complexes with cyclo-triphosphorus

The syntheses of the new triple-decker complexes [(triphos)Co(mu,etha3:3-P3)Ru(triphos)](BPh4)2; (CoP3Ru)(BPh4)2, [(triphos)Co(mu,etha·3:3-P3)Os(triphos)](BPh4)2; (CoP3Os)(BPh4)2 and [(triphos)Ru(mu,etha3:3-P3)Ru(triphos)]PF6·(CH3)2CO; (RuP3Ru)PF6·(CH3)2CO, three new members of the [(tripod)M(mu-P3)M'(tripod)]n+ (MP3M' n+ ) family are described. The structure of the homodinuclear complex (RuP3Ru)PF6·(CH3)2CO is also reported. This latter compound has a structure similar to that of the other members of the series and shows an M-M separation among the longest hitherto found in these compounds. An electrochemical study shows that they are stable in various oxidation states with a VEN value ranging between 28 and 34. A reasoning around the redox data shows a progressive shift of two pairs of redox processes, corresponding to the VEN variation 30/31-31/32 and 32/33-33/34, which almost rigidly moves in the cathode direction as the overall charge of the homoelectronic compound decreases