[C(NH₂)₃]Y(HCOO)₄: Constructing 3D Framework for Guanidine-Based UV Nonlinear Optical Crystals with Good Performance.

Area of Science:

• Materials Science
• Crystallography
• Optics

Background:

• The guanidine group ([C(NH2)3]+) is a promising π-conjugated unit for nonlinear optical (NLO) materials.
• Weak hydrogen bonding and zero-dimensional structures limit the stability and mechanical strength of guanidine-based NLO materials.

Purpose of the Study:

• To design and synthesize a novel 3D guanidine-based compound with enhanced stability and NLO properties.
• To explore a new strategy for constructing non-centrosymmetric (NCS) frameworks for guanidine-based NLO materials.

Main Methods:

• Utilizing formate anions ((HCOO)-) and rare-earth cations to construct a 3D framework for [C(NH2)3]+.
• Synthesizing the novel 3D guanidine-based compound [C(NH2)3]Y(HCOO)4.
• Characterizing the compound's NLO properties, UV cutoff, birefringence, and thermal stability.

Main Results:

• Successfully synthesized a novel 3D guanidine-based compound, [C(NH2)3]Y(HCOO)4.
• The compound exhibits a strong second-harmonic generation (SHG) response (1.7 × KH2PO4).
• The crystal shows a short UV cutoff edge (236 nm), appropriate birefringence (0.099@546 nm), and good thermal stability.

Conclusions:

• The developed strategy effectively immobilizes the [C(NH2)3]+ unit and induces an NCS arrangement.
• The synthesized [C(NH2)3]Y(HCOO)4 crystal fulfills critical requirements for UV NLO applications.
• This work provides a new avenue for developing high-performance guanidine-based UV NLO materials.