  Two-dimensional (2D) van der Waals (vdW) magnetic $3d$-transition metal
trihalides are a new class of functional materials showing exotic physical
properties useful for spintronic and memory storage applications. In this
article, we report the synthesis and electromagnetic characterization of
single-crystalline vanadium trichloride, VCl$_3$, a novel 2D layered vdW Mott
insulator, which has a rhombohedral structure (R$\overline{3}$, No. 148) at
room temperature. VCl$_3$ undergoes a structural phase transition at 103 K and
a subsequent antiferromagnetic transition at 21.8 K. Combining core levels and
valence bands x-ray photoemission spectroscopy (XPS) with first-principles
density functional theory (DFT) calculations, we demonstrate the Mott Hubbard
insulating nature of VCl$_3$ and the existence of electron small 2D magnetic
polarons localized on V atom sites by V-Cl bond relaxation. The polarons
strongly affect the electromagnetic properties of VCl$_3$ promoting the
occupation of dispersion-less spin-polarized V-3d $a_{1g}$ states and band
inversion with $e^{'}_{g}$ states. Within the polaronic scenario, it is
possible to reconcile different experimental evidences on vanadium trihalides,
suggesting that also VI$_3$ hosts polarons. Our results highlight the complex
physical behavior of this class of crystals determined by charge trapping,
lattice distortions, correlation effects, mixed valence states, and magnetic
states.
