A new metal pnictidehalide (Hg₆P₄)(CrCl₆)Cl has been prepared by solid-state reaction. Its structure features a 3-D perovskite-like host octahedral network and discrete octahedral (CrCl₆)³⁻ and Cl⁻ guest ions assembled by weak van der Waals interactions. The nearest neighboring Cr³⁺ ions are antiferromagnetically coupled with each other, and the complex can be regarded as a geometric spin frustrated system. Electronic structure, optical dielectric constants and magnetic coupling parameters were calculated using the LDA+U method. The complex exhibits good resistive humidity sensitivity with humidity response as big as four orders of magnitude, quick resistance response, fast recovery, and good reproducibility. The complex provides a new way to realize multifunctional properties driven by weak van der Waals interactions.