Flexibility of the MPS-4 Chains of the KMPS4 (M=Ni, Pd) Compounds Studied by Molecular Orbital Calculations and Atomic Force Microscopy Measurements

The flexibility of the MPS-4 chains of KMPS4 (M=Ni, Pd) was examined by performing contact mode atomic force microscopy (AFM) measurements for the (001) surface of KNiPS4 and also by performing extended Hückel tight binding calculations for the [M(PS4)2]4- entities of KMPS4. The observed AFM images were analyzed by calculating the total electron density plots for an isolated [NiPS4]- slab of the (001) surface. Our calculations show that the PS3-4 ions are more strongly bound to the Pd2+ ions in KPdPS4 than to the Ni2+ ions in KNiPS4, and that the bonding between the PS3-4 anions and M2+ (M=Ni, Pd) cations is flexible with respect to the rotational motions of the PS3-4 anions. The AFM images recorded for the (001) surface of KNiPS4 indicate that the PS3-4 anions on the surface undergo a rotational relaxation when the scanning tip passes by.