Nonlinear organic-inorganic halide hybrids containing unprecedented linear [MIX

Organic-inorganic halide hybrids are rapidly gaining increased attention owing to their remarkable optoelectronic performance. Amongst these, divalent and trivalent metal cations (Pb2+, Sn2+, Bi3+, and Sb3+) usually link to six halogen X atoms and form an asymmetric [MX6] octahedron with weak optical anisotropy. Herein, we show a first family of monovalent-metal-based hybrid halides [N(CH3)4]MCl2 (M = Ga, In) with a zero-dimensional configuration containing unprecedented linear [MX2] units. Owing to the reduced coordination number, the lone pairs on Ga+ and In+ exhibit quasi-two-dimensional distribution, thereby leading to a narrowed bandgap, enhanced optical anisotropy and strong nonlinear second harmonic response of 1.4 and 1.3 times that of benchmark KH2PO4, respectively.