Raman and single-crystal X-ray diffraction evidence of pressure-induced phase transitions in a perovskite-like framework of [(C3H7)4N] [Mn(N(CN)2)3]

We report complementary high-pressure Raman and single-crystal X-ray diffraction studies of a perovskite-like dicyanamide framework of [(C3H7)4N][Mn(N(CN)2)3] ([TPrA][Mn(dca)3]). Our studies show that the bulk modulus of the ambient pressure P21c phase is B0 = 8.1(11) GPa, and the ab-plane compresses by 54.4(15) × 10−3 GPa−1 and the c-axis by 8.0(12) × 10−3 GPa−1, indicating the low stiffness of the framework and its highly anisotropic nature. [TPrA][Mn(dca)3] transforms near 0.4 GPa into the Pbcn phase. The driving forces for this symmetry change are partial ordering of the dicyanamide (dca) linkers, off-center shifts of TPrA+ cations and large changes in the columnar shifts of the MnN6 octahedra within the ab-plane. Upon further increase of pressure, [TPrA][Mn(dca)3] undergoes symmetry-lowering transitions into a monoclinic phase (space group P21/n) near 3 GPa and a triclinic phase near 5 GPa. The observed structural changes are, however, very subtle.