Probing the Reactivity of the Potent AgF2Oxidizer. Part 2: Inorganic Compounds

Charge doping to flat AgF2 monolayers in a chemical capacitor setup

Flat monolayers of silver(II) fluoride, which could be obtained by epitaxial deposition on an appropriate substrate, have been recently predicted to exhibit very strong antiferro-magnetic superexchange and to have large potential for ambient pressure superconductivity if doped to an optimal level. It was shown that AgF₂ could become a magnetic glue-based superconductor with a critical superconducting temperature approaching 200 K at optimum doping. In the current work we calculate the optimum doping to correspond to 14% of holes per formula unit, i.e. quite similar to that for oxocuprates(II). Furthermore, using DFT calculations we show that flat [AgF₂] single layers can indeed be doped to a controlled extent using a recently proposed "chemical capacitor" setup. Hole doping associated with the formation of Ag(III) proves to be difficult to achieve in the setup explored in this work as it falls at the verge of charge stability of fluoride anions and does not affect the d(x² - y²) manifold. However, in the case of electron doping, manipulation of different factors - such as the number of dopant layers and the thickness of the separator - permits fine tuning of the doping level (and concomitantly T_C) all the way from the underdoped to overdoped regime (in a similar manner to chemical doping for the Nd₂CuO₄ analogue).

Separation-Controlled Redox Reactions

In the era of molecular devices and nanotechnology, precise control over electron-transfer processes is strongly desired. However, redox reactions are usually characterized by reaction equilibrium constants strongly departing from unity. This leads to strong favoring of either reactants or products and does not permit subtle control of transferred charge (doping). Here we propose, based on theoretical studies for periodic systems, how charge transfer between reactants could be finely manipulated in the epitaxially grown system composed of extremely strong oxidizer, reducing agent, and an inert separator-the key factor of control.

Gigantic work function in layered AgF2

AgF2 is a layered material and a correlated charge transfer insulator with an electronic structure very similar to the parent compounds of cuprate high-TC superconductors. It is also interesting as it is a powerful oxidizer. Here we present a first principles computation of its electronic properties in a slab geometry including its work function for the (010) surface (7.76 eV) which appears to be the highest among known materials with non-dipolar surfaces, and surpassing even that of fluorinated diamond (7.24 eV). We demonstrate that AgF2 will show a "broken-gap" type alignment becoming electron doped and promoting injection of holes in many wide band gap insulators if chemical reaction can be avoided. Novel junction devices involving p type and n type superconductors have been proposed. The issue of chemical reaction is discussed in connection with the possibility to create flat AgF2 monolayers achieving high-TC superconductivity. As a first step in this direction, we studied the stability and properties of an isolated AgF2 monolayer.

[Ag(OH2 )2 ][Ag(SO4 )2 ]: A Hydrate of a Silver(II) Salt

When exposed to air at ambient conditions, AgSO₄ slowly reacts with moisture, yielding AgSO₄ ⋅H₂ O. The crystal structure determination (powder data) shows that it may be described as [Ag(OH₂ )₂ ][Ag(SO₄ )₂ ], with some sulfate groups being shared between different Ag²⁺ cations, resembling in that way its Cu²⁺ analogue. [Ag(OH₂ )₂ ][Ag(SO₄ )₂ ], the first hydrate of a compound of Ag²⁺ , was extensively characterized using many physicochemical methods.

Synthesis of a highly reactive form of WO2Cl2, its conversion into nanocrystalline mono-hydrated WO3 and coordination compounds with tetramethylurea

A new form of WO₂Cl₂ was prepared from WCl₆. Conversion of WO₂Cl₂ into nanocrystalline WO₃·H₂O occurred upon air exposure at room temperature. The first coordination complexes of WO₂Cl₂ with an alkylurea are reported.

Chemistry of silver(II): a cornucopia of peculiarities†

Silver is the heavier congener of copper in the Periodic Table, but the chemistry of these two elements is very different. While Cu(II) is the most common cationic form of copper, Ag(II) is rare and its compounds exhibit a broad range of peculiar physico-chemical properties. These include, but are not limited to: (i) uncommon oxidizing properties, (ii) unprecedented large mixing of metal and ligand valence orbitals, (iii) strong spin-polarization of neighbouring ligands, (iv) record large magnetic superexchange constants, (v) ease of thermal decomposition of its salts with O-, N- or C-ligands, as well as (vi) robust Jahn-Teller effect which is preserved even at high pressure. These intriguing features of the compounds of Ag(II) will be discussed here together with (vii) a possibility of electromerism (electronic tautomerism) for a certain class of Ag(II) salts.

Probing the Reactivity of the Potent AgF2 Oxidizer. Part 1: Organic Compounds

The reactivity of Ag(II)F2 towards a variety of organic compounds of a high degree of fluorination has been investigated. AgF2 readily fluorinates P(C6F5)3 to PF2(C6F5)3, and attacks the isothiocyanate functional group, -NCS, yielding Ag2S. Perfluorinated aliphatic nitriles resist the action of AgF2, but aromatic C6F5CN undergoes a radical-initiated oligomerization; byproducts include C6F6CN• and C6F5N2• (after intramolecular rearrangement following the bimolecular reaction). AgF2 oxidizes higher fluorosulfonic acids (C4F9SO3H, C8F17SO3H) at or close to the room temperature and triflic acid (CF3SO3H) at its boiling point to the corresponding peroxides. CF3COOH and CF3CONH2 are also decomposed in redox reactions, but the gaseous products have not been identified. Surprisingly, AgF2 is kinetically inert to perfluorinated aromatic hydrocarbons and to CCl4, but it decomposes CBr4 with vigorous elimination of Br2. CI4 decomposes explosively in the presence of AgF2. C6F5OH and CF3COOH are readily oxidized with AgF2 but, surprisingly, t-C4F9OH is kinetically resistant under similar conditions. Coordination complexes of perfluorinated aza and oxa Lewis bases (including perfluorinated 15-crown-5 ether) and AgF2 are not formed under the experimental conditions.