Ambient-pressure molecular superconductor with a superlattice containing layers of tris(oxalato)rhodate enantiomers and 18-crown‑6

We report a novel multilayered organic–inorganic hybrid material, β″-(BEDT-TTF)2[(H2O)­(NH4)2Rh­(C2O4)3]·18-crown-6. This is the first molecular superconductor to have a superlattice with layers of both BEDT-TTF and 18-crown-6 and also the first with the anion tris­(oxalato)­rhodate. This is the 2D superconductor with the widest gap between conducting layers, where only a single donor packing motif is observed (β″). The strong 2D nature of this system strongly suggests that the superconducting transition is a Kosterlitz–Thouless transition. A superconducting T c of 2.7 K at ambient pressure was found by transport measurements and 2.5 K by magnetic susceptibility measurements.