Is AlCl3 a trigonal planar

Answer 1

It depends on the phase and the temperature

Solid AlCl3 has each aluminium is 6 coordinate, surrounded by 6 chlorine atoms in an octahedral formation. The best description here is a ionic bonding. Interestingly just below melt temperature the conductivity rises indicating free ions.

AlCl3 in the melt is found as dimer Al2Cl6 with four coordinate aluminium. Two chlorines bridging the aluminium atoms. In this aluminium achieves its octet and the bond angles are in line with VSEPR theory.

At high temperature the dimers dissociate to monomeric AlCl3 which is trigonal planar, following VSEPR theory.