Intralayer Molecular\nPacking Coefficient as One Packing\nCharacteristic of Planar Layer-Stacked Crystals and Its Dominators

Planar layer-stacking, as a special stacking mode, is\nattracting\nmuch attention in the fields of some molecular solid materials. In\nthe present work, we propose a special index, the intralayer molecular\npacking coefficient (ILMPC), as the ratio of the sum of sectional\nareas of all molecules on a layer to that of the layer, to deepen\nthe understanding of the planar layer-stacking. Besides, methods for\ncalculating the sectional area (<i>S</i><sub>m,s</sub>)\nand perimeter (<i>C</i><sub>m,s</sub>) of a planar molecule\nalong its plane are proposed to describe molecular size to account\nfor its compact on describing ILMPC by intralayer intermolecular interactions\n(Δ<i>E</i><sub>intralayer</sub>). Regarding 65 planar\nlayer-stacking, it shows a certain correlation of ILMPC with Δ<i>E</i><sub>intralayer</sub>/<i>C</i><sub>m,s</sub> (<i>R</i><sup>2</sup> = 0.30) or Δ<i>E</i><sub>intralayer</sub>/<i>S</i><sub>m,s</sub> (<i>R</i><sup>2</sup> = 0.23) and a significantly linear one of packing coefficient with\nILMPC/<i>d</i><sub>interlayer</sub> (<i>R</i><sup>2</sup> = 0.86) in which <i>d</i><sub>interlayer</sub> represents\nthe interlayer distance. Hopefully, the ILMPC will be an effective\ngeometric descriptor of intralayer molecular compactness and contribute\nto a deeper understanding of planar layer-stacking.