Issue 15, 2024

Greatly enhanced optical anisotropy in thiophosphates inspired by rational coupling of tetrahedra and ethane-like [P2S6]4− groups

Abstract

Exploring new potential infrared (IR) birefringent crystals is important for modulating the polarization of light in optical communication, but the rational structural design for the enhancement of optical anisotropy is still a great challenge. For that reason, we have proposed an effective strategy for the design of promising IR birefringent crystals by incorporation of Cu+ or Zn2+ with d10-configuration, or stereochemically active lone-pair (SCALP) Sb3+ cations into structures with the typical ternary thiophosphates as templates (A3PS4 and A4P2S6: A = Na, K), affording the successful synthesis of six new mixed-metal thiophosphates (Na4MgP2S8, A3CuP2S6, KGaP2S6, Na2ZnP2S6, Na3SbP2S8). Systematic research results show that the birefringences (Δn) of A3CuP2S6n, Na: 0.151; K: 0.124), Na2ZnP2S6n = 0.136) and Na3SbP2S8n = 0.107) are much larger than those of Na4MgP2S8n = 0.037) and the typical A3PS4 (0.010 vs. 0.019) and A4P2S6 (0.038 vs. 0.042), which indicates that the d10- or SCALP-cation-centered tetrahedra (CuS4, ZnS4 or SbS4) produce large positive contributions to the enhancement of optical anisotropy; the ethane-like [P2S6]4− dimer appears to have greater contribution than the [PS4]3− unit. Moreover, we extended the research study to the known A(Na/K)–M(Mg/Ga/Al/Cu/Sb/Zn)–P–S systems, and this comprehensive survey illustrates that their Δn values show an increasing trend for thiophosphates based on the order of cation substitutions, from alkaline earth (Ae2+) or alkali (A+) to IIIA (Ga3+/Al3+) to d10 or SCALP cations (Cu+/Zn2+/Sb3+). Special 1D chain or 2D layer structures are more inclined to gain a larger optical anisotropy. Therefore, this study demonstrates a feasible design strategy to achieve greatly enhanced optical anisotropy through the rational coupling of d10- or SCALP-cation-centered tetrahedra and ethane-like [P2S6]4− groups into the structures of thiophosphates.

Graphical abstract: Greatly enhanced optical anisotropy in thiophosphates inspired by rational coupling of tetrahedra and ethane-like [P2S6]4− groups

Supplementary files

Article information

Article type
Research Article
Submitted
08 Apr 2024
Accepted
29 May 2024
First published
30 May 2024

Inorg. Chem. Front., 2024,11, 4603-4610

Greatly enhanced optical anisotropy in thiophosphates inspired by rational coupling of tetrahedra and ethane-like [P2S6]4− groups

N. Zhao, D. Lu, J. Xu, K. Wu, H. Yu and H. Zhang, Inorg. Chem. Front., 2024, 11, 4603 DOI: 10.1039/D4QI00883A

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