Polar Oxalate Fluoride KMn(C ₂ O ₄ )F with Triangular Arrangements of Mn ²⁺ –F–Mn ²⁺ Spin Chains: Nonlinear Optical and Magnetic Properties

Multifunctional materials including magnetism and nonlinear optical activity are of great interest due to their wide applications. Herein, we report a novel polar mixed-anion oxalate fluoride KMn(C 2 O 4 )F 1 with one-dimensional (1D) Mn 2+ –F–Mn 2+ spin chains arranged in triangular geometry, exhibiting both 1D magnetism and nonlinear optical activity. Compound 1 crystallizes in the polar Cmc 2 1 space group and is a nonlinear optical material with the efficiency of second harmonic generation (SHG) ∼0.2 times that of KH 2 PO 4 (KDP). Magnetic measurement results indicate typical low-dimensional magnetism, with a broad maximum around 25 K, which suggests strong intrachain interactions with a Weiss temperature of −60(1) K. Additionally, 1 undergoes a long-range antiferromagnetic ordering at ∼11 K, which is further confirmed by the heat capacity result. Our work demonstrates the potential of using mixed anions to design and develop multifunctional materials with both low-dimensional magnetism and nonlinear optical activity.