  Pressure induced phase transitions of MIAgIIF3 perovskites where M = K, Rb,
Cs, have been predicted theoretically for the first time for pressures up to
100 GPa. The sequence of phase transitions for M = K and Rb consists of an
orthorhombic to monoclinic and back to orthorhombic transition, associated with
progressive bending of infinite chains of corner sharing [AgF6]4 minus
octahedra and their mutual approaching via secondary Ag...F contacts. In stark
contrast, only a single phase transition i.e. tetragonal to triclinic, is
predicted for CsAgF3, associated with substantial deformation of the Jahn
Teller-distorted first coordination sphere of AgII and association of the
infinite [AgF6]4 minus chains into a polymeric sublattice. The phase
transitions markedly decrease the coupling strength of intra-chain
antiferromagnetic superexchange in MAgF3 hosts lattices.
