Raising the (metastable) bar: 100% photo-switching in [Pd(Bu₄dien)(η¹-NO₂)]⁺ approaches ambient temperature

100% nitro-nitrito linkage isomerism is reported in single-crystals of the Pd(ii)-nitrite system [Pd(Bu₄dien)(η¹-NO₂)]BPh₄ (Bu₄dien = N,N,N′,N′-tetrabutyldiethylenetriamine, BPh₄ = tetraphenylborate). Complete conversion to a metastable endo-nitrito-(η¹-ONO) isomer is achieved after just 15 min irradiation with 400 nm LED light. The system is entirely metastable below 240 K, while pseudo-steady-state photocrystallographic experiments confirm that the excited state isomer is retained, at substantial conversion levels, under continuous illumination until 260 K. These results show promise for new linkage isomer systems, based on heavier transition metal centres, which display full functionality under near-ambient conditions.