Engineering Short, Strong, Charge-Assisted Hydrogen Bonds in Benzoic Acid Dimers through Cocrystallization with Proton Sponge

Abstract

A series of molecular complexes of the proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) with mono-substituted halobenzoic acids are reported, illustrating the designed exploitation of the characteristics of the proton sponge to induce short, charge-assisted hydrogen bonds in a predictable and reproducible manner. In every case, a DMAN molecule extracts a proton from the carboxylic acid group of the benzoic acid, as a result of which a recurrent supramolecular unit between a neutral and a 2 deprotonated benzoic acid molecule is formed featuring an extremely short, strong O-H···O hydrogen bond, within a predominant crystallisation ratio of 1:2 (DMAN:benzoic acid). KEYWORDS (Word Style "BG_Keywords"). If you are submitting your paper to a journal that requires keywords, provide significant keywords to aid the reader in literature retrieval.

Exploring short strong hydrogen bonds engineered in organic acid molecular crystals for temperature dependent proton migration behaviour using single crystal synchrotron X-ray diffraction (SCSXRD)

“…However, it is clear that from this set, the combination of isonicotinamide with either orthosubstituted or dinitrobenzoic acids is a good route to forming shorter hydrogen bonding interactions. As is the case for the O-H⋯O SSHBs, this may be a result of the increased acidity of the carboxylic acid group 32,50-52 and thus an enhanced charge-assisted component of the HB 55,56 for these types (nitro) or positions (ortho) of substituent group.…”

Tuning charge-assisted and weak hydrogen bonds in molecular complexes of the proton sponge DMAN by acid co-former substitution

“…This is as found in other DMAN organic acid systems. 11,15,16,18 The O-H⋯O − CAHBs (Table S3 †) are nearly all asymmetric with respect to the refined hydrogen atom positions. Exceptions to this are the O-H⋯O − CAHBs in 3; the hydrogen atom in these cases is constrained to take a symmetrical position within the HB, lying on a centre of inversion.…”

“…27 Crystallisation stoichiometries of 1 : 2 DMAN : acid co-former were trialled initially to target the formation of an ACID − dimer as formed commonly in known DMAN benzoic acid molecular complexes. 16 Where this 1 : 2 stoichiometry did not yield single crystals, a 1 : 1 stoichiometry was trialled. The starting stoichiometry was not always carried through to the molecular complex.…”

“…9,10 Such complexes studied previously include DMAN in combination with benzene-1,2,4,5tetracarboxylic acid, 4,5-di-chlorophthalic acid, 11 maleic acid, 12 benzene-1,2,3-tricarboxylic acid, 13 chloranilic acid, 14 1,2-dichloromaleic acid 15 and a range of halo benzoic acids. 16,17 In these complexes, DMAN typically extracts a proton from the organic acid inducing the formation of O-H⋯O − charge-assisted hydrogen bonds (CAHBs) between acid molecules. 11,15,16,18 The extracted proton is held by the DMAN molecule in an asymmetric [19][20][21][22] intramolecular [N-H⋯N] + hydrogen bond (IHB).…”

“…16,17 In these complexes, DMAN typically extracts a proton from the organic acid inducing the formation of O-H⋯O − charge-assisted hydrogen bonds (CAHBs) between acid molecules. 11,15,16,18 The extracted proton is held by the DMAN molecule in an asymmetric [19][20][21][22] intramolecular [N-H⋯N] + hydrogen bond (IHB). 11 The association of the DMAN : acid components in the crystal packing consistently occurs via weak HB interactions in an assembly where the hydrogen bonded acid (ACID − ) unit is oriented towards the DMAN cation methyl groups and IHB (Scheme 1).…”