High-Pressure Synthesis of Quantum-Stabilised Manganese Superhydride MnH7.

Through high-temperature, high-pressure diamond anvil cell studies combined with in situ synchrotron powder x-ray diffraction, we investigate the reactivity between manganese and hydrogen up to 182 GPa. Laser heating manganese in an H 2 medium at 118 GPa yields body-centred tetragonal MnH 7 , which has the highest hydrogen content ever observed in the binary hydrides of group IV-XII transition metals. In addition, we also observe two other new hydrides as minor phases, MnH ∼ 2 with a tetragonal crystal structure and cubic MnH 3.67 , formed at the pressures of 105 and 118 GPa, respectively. Upon decompression, MnH 3.67 and MnH 7 remain stable down to ∼ 30 GPa before decomposing into the monohydride. Our ab initio quantum chemistry computations employing density-functional theory reveal that the key stabilisation factor of MnH 3.67 and MnH 7 is zero-point energy, however, no isotope effect is observed on the crystal structures of the deuterated samples.