Tetrahedral frameworks TX2 with T–X–T angle = 180°: Rationalization of the structures of MOF-500 and of MIL-100 and MIL-101

It is shown that the TX2 structures adopted by the giant MOFs MOF-500, MIL-100 and MIL-101 are uniquely determined as a result of the requirement of regular TX4 tetrahedra, T–X–T angles of 180° and appropriate X–T–T–X dihedral angles.