[Ag(NH3)2]2SO4: A coordination strategy on the cationic-moiety to design nonlinear optical materials

TL;DR

This paper introduces a novel cationic-moiety coordination strategy in nonlinear optical materials, demonstrating significant property enhancements through structural modifications driven by cationic coordination, which has been largely overlooked in prior research.

Contribution

The study pioneers a cationic-moiety coordination approach to design nonlinear optical materials, exemplified by [Ag(NH3)2]2SO4, leading to improved SHG and birefringence properties.

Findings

[Ag(NH3)2]2SO4 exhibits stronger SHG intensity than KDP.

Large birefringence (delta(n)=0.102) observed at 1064 nm.

Cationic coordination induces noncentrosymmetric structure and permanent dipole moment.

Abstract

Over decades, guided by the anionic group theory, the majority work has been focused on the anionic-moiety of a nonlinear optical material, however, the property guided structure modification and design on the cationic-moiety has long been neglected. Herein, we report for the first time a coordination strategy on the cationic-moiety, as demonstrated by the first exmple, [Ag(NH3)2]2SO4 vs Ag2SO4, the coordination of the plus one Ag+ cation by the neutral ligand forming the [Ag(NH3)2]+ cationic-moiety drives the formation of the noncentrosymmetric tetragonal P-421c structure which exhibits a remarkable property improvement, including a strong SHG intersity (1.4*KDP vs 0 @1064 nm), and a large birefringence (delta(n)cal.: 0.102 vs 0.012 @1064 nm). Furthermore, we discover that owing to the strong hydrogen bonds and spatial confinement of [SO4]2- anions, the cation [Ag(NH3)2]+ bends parallel to the crystallographic c axis with a bond angle of N-Ag-N = 174.35deg, generating a permenant dipole moment z = -0.12 D that is responsible for the large birefringence that enlarges the range of the phase matching SHG laser output. We believe what we discover is only a glimpse of the long been neglected crystal engineering on the cationic-moiety. Encourage by this work, exciting works on other ionic compound systems shall flood in.