Pb0.65Mn2.85Ga3S8 and Pb0.72Mn2.84Ga2.95Se8: Two Quaternary Metal Chalcognides with Open-Tunnel-Framework Structures Displaying Intense Second Harmonic Generation Responses and Interesting Magnetic Properties

By combining different nonlinear optical-active structural chromophores with transition metal Mn into a crystal structure, two novel quaternary metal chalcogenides Pb0.65Mn2.85Ga3S8 (1) and Pb0.72Mn2.84Ga2.95Se8 (2) were successfully synthesized. Compounds 1 and 2 are isostructural, and they represent a new structure type that crystallizes in the space group P (6) over bar (No. 174) in the hexagonal system. Their structures feature an interesting three-dimensional open tunnel framework composed of bridged infinite chains with Pb2+ cations filling in the biggest tunnels. Interestingly, both 1 and 2 demonstrate intense second harmonic generation responses at 2.09 mu m that is about 1.5 and 4.4 times, respectively, of that of the benchmark material AgGaS2. However, 1 and 2 possess different optical diffuse reflectance spectra: 1 displays an evident multiband absorption characteristic with two distinguishing absorption edges of 738 and 551 nm, corresponding to two band gaps of 1.68 and 2.25 eV, respectively, while 2 exhibits only one sharp edge, and the corresponding band gap was estimated to be 1.65 eV. Moreover, apart from the considerable structural similarity between 1 and 2, the dc temperature dependent susceptibility measurements indicate that compound 1 is paramagnetic, while compound 2 exhibits spin-glass-like behavior.