Shape‐Topology‐Driven Design of Deep Ultraviolet Nonlinear Optical Crystals: Engineering [CH ₃ PO ₃ ]–Metal‐Oxo Layered Frameworks for Enhanced SHG, DUV Transparency

ABSTRACT Designing deep ultraviolet (DUV) nonlinear optical (NLO) crystals that balance high nonlinear coefficients, moderate birefringence, and DUV transparency remains a major challenge. Here, we introduce a shape‐topology‐driven strategy to design novel layered DUV NLO materials using polar covalent tetrahedral groups with C 3 v symmetry. By selecting the [CH 3 PO 3 ] 2− group as a key building block, which exhibits outstanding optical properties, including an ultra‐wide HOMO‐LUMO gap and high hyperpolarizability (180 a.u.), far surpassing conventional D 3h π ‐conjugated units like [CO 3 ] and [BO 3 ]. The combination of [CH 3 PO 3 ] 2− with Mg 2+ and Zn 2+ metal‐oxo polyhedra led to the synthesis of two new non‐centrosymmetric crystals, Mg(CH 3 PO 3 )·H 2 O (CPM) and Zn(CH 3 PO 3 )·H 2 O (CPZ). Benefiting from their NLO‐active [M(CH 3 PO 3 )·H 2 O (M = Mg, Zn)] ∞ layers, these crystals exhibit exceptional DUV transparency (< 200 nm), moderate birefringence, and impressive SHG responses (1.8 × KDP for CPM and 3.1 × KDP for CPZ), representing a significant advancement in DUV NLO material design.