Tetra­methyl­ammonium borohydride from powder data

In the crystal structure of the title compound, C4H12N+·BH4 −, the tetra­methyl­ammonium cations are situated on special positions with site symmetry m2. The borohydride anions are situated on special positions with 4mm site symmetry and show rotational disorder around the fourfold axis

A unique two-dimensional silver(II) antiferromagnet Cu[Ag(SO4)2] and perspectives for its further modifications

Copper(II) silver(II) sulfate crystallizes in a monoclinic CuSO4-related structure with P21/n symmetry. This quasi-ternary compound features [Ag(SO4)2]2- layers, while the remaining cationic sites may be occupied either completely or partially by Cu2+ cations, corresponding to the formula of (CuxAg1-x)[Ag(SO4)2], x = 0.6-1.0. CuAg(SO4)2 is antiferromagnetic with large negative Curie-Weiss temperature of -84.1 K and shows two characteristic ordering phenomena at 19 K and 40 K. Density functional theory calculations reveal that the strongest superexchange interaction is a two-dimensional antiferromagnetic coupling within [Ag(SO4)2]2- layers, with the superexchange constant J2D of -11.1 meV. This renders CuAg(SO4)2 the rare representative of layered Ag2+-based antiferromagnets. Magnetic coupling is facilitated by the strong mixing of Ag d(x2-y2) and O 2p states. Calculations show that M2+ sites in MAg(SO4)2 can be occupied with other similar cations such as Zn2+, Cd2+, Ni2+, Co2+, and Mg2+.Comment: 9 pages, 4 Tables, 9 Figures, and electronic supplement of 21 page

Structural phase transitions and magnetic superexchange in MIAgIIF3 perovskites at high pressure

Pressure induced phase transitions of MIAgIIF3 perovskites where M = K, Rb, Cs, have been predicted theoretically for the first time for pressures up to 100 GPa. The sequence of phase transitions for M = K and Rb consists of an orthorhombic to monoclinic and back to orthorhombic transition, associated with progressive bending of infinite chains of corner sharing [AgF6]4 minus octahedra and their mutual approaching via secondary Ag...F contacts. In stark contrast, only a single phase transition i.e. tetragonal to triclinic, is predicted for CsAgF3, associated with substantial deformation of the Jahn Teller-distorted first coordination sphere of AgII and association of the infinite [AgF6]4 minus chains into a polymeric sublattice. The phase transitions markedly decrease the coupling strength of intra-chain antiferromagnetic superexchange in MAgF3 hosts lattices.Comment: 7 pages, 3 figures, and electronic supplement of 25 page

Ag(II) as spin super-polarizer in metal fluoride clusters

Using quantum mechanical calculations, we examine magnetic (super)exchange interactions in prototypal molecular fluoride clusters containing late transition metals or selected lanthanides, as well as Ag(II). By referencing to analogous species comprising closed shell Cd(II) we provide evidence that the presence of Ag(II) may modify the magnetic properties of such systems (including metal metal superexchange) to an unprecedented degree, specifically both coupling sign and strength may markedly change. Remarkably, this happens in spite of the fact that the fluoride ligand is the least susceptible to spin polarization among all monoatomic ligands known in chemistry. Ag(II), with one hole in its d shell, stands as spin superpolarizer, and this feature could be exploited in spintronics and diverse molecular devices.Comment: 6 pages, 3 figures, 2 tables, and 19 pages of supplementary informatio