Organic-Inorganic Hybrid Noncentrosymmetric (Morpholinium) 2 Cd 2 Cl 6 Single Crystals: Synthesis, Nonlinear Optical Properties, and Stability.

To design nonlinear optical (NLO) materials, we focused on combinations of d 10 metal cation (Cd 2+ )-based chloride and morpholine molecules to form organic-inorganic hybrids. The O of morpholine containing lone-pair electrons can be integrated with Cd 2+ by a ligand-to-metal charge transfer (LMCT) strategy to build acentric structures benefiting from the second-order Jahn-Teller effect. Introduction of the high-electronegativity chlorine can make polyhedrons of acentric crystals more distorted and conducive to a strong second harmonic generation (SHG) response. Therefore, (Morpholinium) 2 Cd 2 Cl 6 crystals were constructed and synthesized by a solvent evaporation method. (Morpholinium) 2 Cd 2 Cl 6 belongs to the orthorhombic P 2 1 2 1 2 1 space group and shows a one-dimensional (1D) structure with distorted [CdCl 6 ] and [CdCl 4 O 2 ] octahedrons. The short cutoff edge of (Morpholinium) 2 Cd 2 Cl 6 was determined to be about 230 nm. The SHG response of (Morpholinium) 2 Cd 2 Cl 6 exhibited an intensity of approximately 0.73 × KDP as estimated by the powder second harmonic generation technique. Furthermore, related theoretical calculations were performed to study the relationship of the band structure, refractive anisotropy, electronic state, and nonlinear optical response. Besides, (Morpholinium) 2 Cd 2 Cl 6 showed relatively good thermal stability. This work can serve as a guide for the design and synthesis of new large NLO hybrid crystals with d 10 transition metals.