Synthesis and Optical Properties of Organic-Inorganic Hybrid [(18-Crown-6)K][MoOCl4(H2O)].

Abstract

Crown ether anchored organic-inorganic hybrid halides have been recently reported as interesting luminescent materials in the visible region of electromagnetic spectrum. Is it possible to develop such crown ether anchored hybrid materials for near infrared emission? Motivated by this question, we designed a new hybrid material, namely, [(18-Crown-6)K][MoOCl₄(H₂O)]. 18-Crown-6 ether bound with K⁺ form the cationic part [(18-Crown-6)K]⁺. The K⁺ of [(18-Crown-6)K]⁺ electrostatically interacts with Cl^- of the anionic part [MoOCl₄(H₂O)]^-, forming the hybrid crystal [(18-Crown-6)K][MoOCl₄(H₂O)]. It crystallizes in orthorhombic crystal system with Pnma space group. The Mo(V) possesses one d-electron (d¹) in $C_{4v}$ point group symmetry in the [MoOCl₄(H₂O)]^- polyhedra. This electronic configuration leads to multiple spin-allowed $d-d$ transitions along with a ligand to metal charge transfer (LMCT) resulting into multiple optical absorption bands in the near UV-visible-near infrared (NIR) region. The lowest energy $d-d$ transition via ²E ( $d_{xz}^1$ , $d_{yz}$ )/²E ( $d_{xz},d_{yz}^1$ ) $\to$ ²B₂ ( $d_{xy}^1$ ) leads to NIR PL with peak at 952 nm, but with a poor intensity at room temperature.