Question #44343

VSEPR theory predicts an ideal tetrahedral geometry ($109.5^\circ$) for the $3d$-transition metal complexes \ce{[FeCl4]^{-}}, \ce{[CoCl4]^{2-}}, \ce{[NiCl4]^{2-}}, and \ce{[CuCl4]^{2-}} because the central metal ions lack ligand-directed lone pairs in the VSEPR sense. However, Crystal Field Theory (CFT) dictates that one of these complexes undergoes a severe Jahn-Teller distortion, flattening to a $D_{2d}$ symmetry due to the asymmetric occupation of the $t_2$ orbital set. Identify this highly distorted complex and calculate its Crystal Field Stabilization Energy (CFSE) in terms of the tetrahedral splitting parameter $\Delta_t$ (ignoring pairing energy).