(IUCr) Crystal structure analysis, Hirshfeld surface analysis and DFT calculations of a one-dimensional neutral manganese(II) coordination polymer [(CH<span class="inf"><sub>3</sub></span>)<span class="inf"><sub>3</sub></span>NH][MnCl<span class="inf"><sub>2</sub></span>(H<span class="inf"><sub>2</sub></span>O)<span class="inf"><sub>2</sub></span>]Cl