Elementary Graph-Set Descriptors in Crystal Structure Comparison of 2‑Methyl-4-Nitroanilinium Hexachloridostannate(IV), Bromide and Two Noncentrosymmertic Chlorides. X‑Ray, Vibrational and Theoretical Studies

Crystal
structures of two polymorphs of [H2m4na]Cl (1α,1β) and (H2m4na)2SnCl6·H2O (2), where 2m4na = 2-methyl-4-nitroaniline are shown and comparison
of these crystal structures with the bromide salt reported earlier
is presented. In all the presented crystal structures, alternatively
arranged cations and anions form chain and ring hydrogen-bonding patterns
of weak unconventional N–H···Cl hydrogen bonds.
Interrelations among the elementary graph-set descriptors and descriptors
of the hydrogen-bonding patterns are presented. Nonhydrogen bonding
interactions between the nitro groups are also described using graph-set
descriptors. Comparison of the experimental, also for deuterated 1α polymorph, and theoretical, for H2m4na+ ion with B3LYP/6-31G­(d,p), spectra showed good agreement among the
frequencies due to very weak interactions existing in studied compounds.
Detailed analysis of the spectra revealed that the interaction between
adjacent −NO2 groups in 1α is
stronger than the other types involving the nitro group. The bands
were assigned on the basis of theoretical calculations of vibrational
frequencies for H2m4na+ ion and PED analysis.