Superconductivity at 4.8 K and Violation of Pauli Limit in La2IRu2 Comprising Ru Honeycomb Layer.

We discovered superconductivity at 4.8 K in the hexagonal layered compound La2IRu2 comprising a triangular lattice of the La and a honeycomb lattice of the Ru atoms. First-principles calculations reveal a two-dimensional band structure made up of La 5d and Ru 4d electrons and formal oxidation states +1.5 for the La and the uncommon oxidation state -1 for the Ru atoms. The temperature dependence of the specific heat indicates fully gapped superconductivity. Nevertheless, the upper critical field of this compound violates the Pauli limit. We argue that the high upper critical field is ascribed to an antisymmetric spin-orbit coupling in the unique multilayer structure.

Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism.

We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)2(µ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and µ-bpym = 2,2'-bipyrimidine). The synthesis is performed by reacting Co2(CO)8 and µ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co(II)(SQ)2] with a transition temperature (T1/2) of 215 K. Photomagnetic studies, performed via both SQUID magnetometry and X-band electron paramagnetic resonance, show the clear presence of photoinduced valence tautomerism, at temperatures considerably higher than previous systems. A metastable charge distribution is observed, strengthening previous investigations on the character of mixed valence ligands. Entropy-driven valence tautomeric interconversion is observed, and drives the transition to the most stable charge distribution. The complex has the ability to coordinate and can be used as a photoswitchable building block, with the photomagnetic characterisation evidencing a metastable state lifetime of the photo-induced valence tautomeric process of ca. 2.9 × 10(4) s below 20 K. The observed yields are higher than ones in similar systems, showing that tiny changes in the molecular structures may have a huge impact.