Mateusz Domański

We report the archetypal representatives of single-molecule magnets (SMMs) based on the “most prolate” lanthanide ion: Yb(BHT)3 (1) and Yb(DBP)3 (2) (BHT = 2,6-di-tert-butyl-4-methylphenolate, DBP = 2,6-di-tert-butylphenolate). The coordination sphere of the metal center was designed to accommodate only three aryloxide ligands yielding highly symmetric nearly trigonal planar geometry which maximizes the magnetic anisotropy associated with the prolate character of the mJ = |7/2| of YbIII. Detailed magnetic and optical studies combined with cantilever torque magnetometry measurements and ab initio calculations, unambiguously unravel the giant magnetic easy axis anisotropy, with the easy magnetization axis perpendicular to the trigonal coordination plane. Our results highlight an exceptional magnetic splitting of the 2F7/2 state (> 1500 cm-1), close to the maximum theoretical value, as well as extremely pure composition of the wavefunction describing each Kramers doublets (KD). This best possible electrostatic environment for the stabilization of the prolate f-electron density does not favour Orbach relaxation, but rather a Raman relaxation process. Nevertheless, the low temperature emission spectra demonstrate that the very strong YbIII anisotropy indeed induces an extremely rare and strong splitting of the 2F7/2 KD in both compounds, as the near infra-red (IR) emissions arising from radiative deexcitation toward the 2F7/2 ground state span over 1695 (1) and 1573 cm−1 (2) at 4 K. Based on this observation, a direct link between the YbIII position with respect to the trigonal coordination environment created by the oxygen atoms and the IR emission can be drawn in solid-state, but also in solution. This allows for going well beyond the crystal structure determination and provides hints about the geometry of such systems in solution.

Hydrides are famous for the possibility of reaching high- T c superconductivity under high pressure within a conventional mechanism. Here we propose ternary nickel hydrides M Ni H 2 ( M = Li , Na) as materials that mirror key aspects of unconventional superconducting cuprates and nickelates while presenting unique characteristics. Compared to Ni oxides, Ni-H bands are wider due to shorter bond lengths and show a smaller charge-transfer energy. This leads to a larger scale of magnetic interactions than for LaNi O 2 , which previous works in cuprates suggest should lead to a larger T c . The presence of an interstitial anionic electron orbital, which hybridizes with the d z 2 band, induces self-doping in the Ni d x 2 − y 2 band, enabling metallicity and superconductivity in stoichiometric forms. A t − J model computation yields dominant d x 2 − y 2 superconducting symmetry for all doping levels. This, combined with the improved thermodynamic stability over known N i 1 + oxides, positions M Ni H 2 as compelling materials for unconventional high- T c superconductivity under standard conditions.

Copper(II) silver(II) sulfate crystallizes in a monoclinic CuSO₄‐related structure with P2₁/n symmetry. This quasi‐ternary compound features Ag(SO₄)₂²⁻ layers, while the remaining cationic sites may be occupied either completely or partially by Cu²⁺ cations, corresponding to the formula of (Cu_xAg_1−x)[Ag(SO₄)₂], x=0.6−1.0. CuAg(SO₄)₂ is antiferromagnetic with large negative Curie‐Weiss temperature of −140 K and shows characteristic ordering phenomenon at 40.4 K. Density functional theory calculations reveal that the strongest superexchange interaction is a two‐dimensional antiferromagnetic coupling within Ag(SO₄)₂²⁻ layers, with the superexchange constant J_2D 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⁺.

High‐temperature solid‐state reaction between orthorhombic AgF₂ and monoclinic CuF₂ (y=0.15, 0.3, 0.4, 0.5) in a fluorine atmosphere resulted in coexisting solid solutions of Cu‐poor orthorhombic and Cu‐rich monoclinic phases with stoichiometry Ag_1−xCu_xF₂. Based on X‐ray powder diffraction analyses, the mutual solubility in the orthorhombic phase (AgF₂ : Cu) appears to be at an upper limit of Cu concentration of 30 mol % (Ag_0.7Cu_0.3F₂), while the monoclinic phase (CuF₂ : Ag) can form a nearly stoichiometric Cu : Ag=1 : 1 solid solution (Cu_0.56Ag_0.44F₂), preserving the CuF₂ crystal structure. Experimental data and DFT calculations showed that AgF₂ : Cu and CuF₂ : Ag solid solutions deviate from the classical Vegard's law. Magnetic measurements of Ag_1−xCu_xF₂ showed that the Néel temperature (T_N) decreases with increasing Cu content in both phases. Likewise, theoretical DFT+U calculations for Ag_1−xCu_xF₂ showed that the progressive substitution of Ag by Cu decreases the magnetic interaction strength |J_2D| in both structures. Electrical conductivity measurements of Ag_0.85Cu_0.15F₂ showed a modest increase in specific ionic conductivity (3.71 ⋅ 10⁻¹³±2.6 ⋅ 10⁻¹⁵ S/cm) as compared to pure AgF₂ (1.85 ⋅ 10^−13±1.2 ⋅ 10⁻¹⁵ S/cm), indicating the formation of a vacancy‐ or F adatom‐free metal difluoride sample.

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+.

Silver(II) compounds exhibit powerful oxidizing properties and strong magnetic superexchange, but most of them comprise fluoride ligands. AgSO₄ is a rare fluorine‐free salt of Ag(II) which found some application in organic chemistry. Here, we report a discovery of a new AgSO₄ polymorph (β). The distinct nature of the two polytypes of AgSO₄ is established using powder X‐ray diffraction, vibrational spectroscopy and theoretical calculations. The β polymorph crystallizes in the monoclinic system (P2₁/n) and shows structural similarities with CuSO₄. DFT calculations indicate very small differences in the energy of the two AgSO₄ polymorphs and that the relative stability of the β polymorph should increase with temperature. The monoclinic distortion of the orthorhombic CuSO₄ prototype originates from an unprecedented strong antiferromagnetic interaction between Ag sites along the unit cell diagonal.