Sr 3 [SnOSe 3 ][CO 3 ]: A Heteroanionic Nonlinear Optical Material Containing Planar π‐conjugated [CO 3 ] and Heteroleptic [SnOSe 3 ] Anionic Groups

Inorganic heteroanionic materials are attracting increasing attention for exploring new nonlinear optical (NLO) materials because they could better satisfy the necessary but conflicting properties of NLO crystals, e.g. large SHG response and wide band‐gap. Up to now, the reports on heteroanionic NLO materials have mainly focused on ultraviolet or visible oxide‐based fluoroborates, fluorophosphates, borate‐phosphates and borate‐iodates. However, chalcogenides containing different kinds of anionic groups have barely been reported. Herein, we have synthesized the first oxychalcogenide‐carbonate, Sr 3 [SnOSe 3 ][CO 3 ] that contains two different kinds of anionic groups, [SnOSe 3 ] and [CO 3 ]. It crystallizes in a noncentrosymmetric space group and exhibits fascinating NLO properties, including a large SHG response (≈1×AGS), sufficient birefringence (0.12 @1064 nm), wide band‐gap (3.46 eV) and high laser damage threshold (240 MW cm −2 ). These make Sr 3 [SnOSe 3 ][CO 3 ] a promising NLO crystal.