In Situ Generation of a Coordinatively Unsaturated Nickel Site Enabling Reversible H ₂ Sorption in the Solid State

Developing molecular materials capable of storing hydrogen reversibly under ambient conditions is a long-standing goal in sustainable energy chemistry. Here, we present a solid-state H2 sorption material based on a square-planar d8 nickel dihydrogen complex, [(t-BuPCP)Ni(H2)]BPhF4 (Ni–H2, PhF = C6F5), stabilized by a rigid PCP pincer framework. Controlled evacuation of Ni–H2 at 343 K generates the T-shaped unsaturated species [(t-BuPCP)Ni]BPhF4 (Ni-unsat), which was confirmed by 31P CP/MAS NMR spectroscopy. The Ni-unsat complex exhibits fully reversible Langmuir-type H2 adsorption between 323 and 343 K, with a binding enthalpy of −61.0 ± 0.9 kJ mol–1, representing an intermediate between physisorption and chemisorption. DFT analysis supports preferential coordination of H2O over H2, accounting for the observed residual Ni–H2O signal. This work demonstrates, for the first time, a square-planar d8 system enabling reversible solid-state H2 storage, paving the way toward molecularly engineered hydrogen sorbents with tunable thermodynamics.