Hard–Soft Acid–Base Principle Drives Rational Synthesis of Super-Dense Rare-Earth-Based Diatomic Sites - Yimeng Cai; Xiuyun Wang; Ke Ma; Dongdong Xiao; Hsiao-Tsu Wang; Yanghua Li; Yibing Yang; Haonan Li; Chi-Feng Lee; Yu-Cheng Shao; Hirofumi Ishii; Nozomu Hiraoka; et al. (Journal of the American Chemical Society, 2026)