18-Crown-6 Coordinated Metal Halides with Bright Luminescence and Nonlinear Optical Effects

The crown-ether coordination compounds Zn X 2 (18-crown-6), Eu X 2 (18-crown-6) ( X : Cl, Br, I), MnI 2 (18-crown-6), Mn 3 Cl 6 (18-crown-6) 2 , Mn 3 I 6 (18-crown-6) 2 , and Mn 2 I 4 (18-crown-6) are obtained by ionic-liquid-based synthesis. Whereas MX 2 (18-crown-6) ( M : Zn, Eu) show conventional structural motives, Mn 3 Cl 6 (18-crown-6) 2 , Mn 3 I 6 (18-crown-6) 2 , and Mn 2 I 4 (18-crown-6) exhibit unusual single Mn X 4 etrahedra coordinated to the crown-ether complex. Surprisingly, some compounds show outstanding photoluminescence. Thus, rare Zn 2+ -based luminescence is observed and unexpectedly efficient for ZnI 2 (18-crown-6) with a quantum yield of 54%. Unprecedented quantum yields are also observed for Mn 3 I 6 (18-crown-6) 2 , EuBr 2 (18-crown-6), and EuI 2 (18-crown-6) with values of 98, 72, and 82%, respectively, which can be rationalized based on the specific structural features. Most remarkable, however, is Mn 2 I 4 (18-crown-6). Its specific structural features with finite sensitizer-activator couples result in an extremely strong emission with an outstanding quantum yield of 100%. Consistent with its structural features, moreover, anisotropic angle-dependent emission under polarized light and nonlinear optical (NLO) effects occur, including second-harmonic generation (SHG). The title compounds and their optical properties are characterized by single-crystal structure analysis, X-ray powder diffraction, chemical analysis, density functional theory (DFT) calculations, and advanced spectroscopic methods.