In their Research Article (e202512618), Congcong Jin, Yang Li, Bingbing Zhang, Joon Ik Jang, Kang Min Ok, and co-workers present a structural fingerprint optimization strategy for ¹[TMOF₄]_∞ chain-based compounds, tuning chain geometry to maximize optical nonlinearity. In the UV NLO crystal (H₃O)(Biu)₂(NbOF₄), ideal structural fingerprints yield a record SHG response (10.8 × KH₂PO₄) among all known transition metal oxyfluorides.