Nonlinear organic–inorganic halide hybrids containing unprecedented linear [MIX2]− coordination units and quasi-two-dimensional lone pairs

Abstract

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.