Near‐Infrared Light‐Induced Spin‐State Switching Based on Fe(II)−Hg(II) Spin‐Crossover Network

≈102 K. Photomagnetic studies conducted at 10 K with lasers ranging from 405 to 1310 nm evidence light-induced excited spin-state trapping (LIESST) and reverse-LIESST effects, with a unique near-infrared-responsive LIESST phenomenon at 1064 and 1310 nm. Advanced photocrystallographic studies at 40 K provide precise structural evidence for these metastable states. The optical and vibrational properties consistently corroborate with magnetic and photomagnetic studies. Additionally, temperature- and light-dependent terahertz (THz) absorptions are associated with phonon vibrations around Fe2 centers, through SCO behavior, as supported by ab initio calculation. The Fe(II)-Hg(II) systems can be promising benchmarks for exploring synergistic switching effects in structural, magnetic, and spectroscopic properties.