Abstract
The anhydrous salts of the Lewis base 1,8-di-aza-bicyclo-[5.4.0]undec-7-ene (DBU) with 4-amino-benzoic acid [1-aza-8-azoniabi-cyclo-[5.4.0]undec-7-ene 4-amino-benzoate, C9H17N2 (+)·C7H6NO2 (-) (I)], 3,5-di-nitro-benzoic acid [1-aza-8-azoniabi-cyclo-[5.4.0]undec-7-ene 3,5-di-nitro-benzoate, C9H17N2 (+)·C7H3N2O6 (-), (II)] and 3,5-di-nitro-salicylic acid (DNSA) [1-aza-8-azoniabi-cyclo-[5.4.0]undec-7-ene 2-hy-droxy-3,5-di-nitro-benzoate, C9H17N2 (+)·C7H3N2O7 (-), (III)] have been determined and their hydrogen-bonded structures are described. In both (II) and (III), the DBU cations have a common disorder in three of the C atoms of the six-membered ring moieties [site-occupancy factors (SOF) = 0.735 (3)/0.265 (3) and 0.686 (4)/0.314 (4), respectively], while in (III), there is additional rotational disorder in the DNSA anion, giving two sites (SOF = 0.72/0.28, values fixed) for the phenol group. In the crystals of (I) and (III), the cation-anion pairs are linked through a primary N-H⋯Ocarbox-yl hydrogen bond [2.665 (2) and 2.869 (3) Å, respectively]. In (II), the ion pairs are linked through an asymmetric three-centre R 1 (2)(4), N-H⋯O,O' chelate association. In (I), structure extension is through amine N-H⋯Ocarbox-yl hydrogen bonds between the PABA anions, giving a three-dimensional structure. The crystal structures of (II) and (III) are very similar, the cation-anion pairs being associated only through weak C-H⋯O hydrogen bonds, giving in both overall two-dimensional layered structures lying parallel to (001). No π-π ring associations are present in any of the structures.
Highlights
Crystal structures of three anhydrous salts of the Lewis base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with the ring-substituted benzoic acid analogues 4-aminobenzoic acid, 3,5-dinitrobenzoic acid and 3,5-dinitrosalicylic acid
It finds use as a curing agent for epoxy resins, as a catalyst in organic syntheses, and as a counter-cation in metal complex chemistry, e.g. with the pentabromo(triphenylphosphane)platinum(IV) monoanion (Motevalli et al, 1989). It has found use in binding organic liquids (BOLs), which usually comprise a mixture of amidines or guanidine and alcohol, and are used to reversibly capture and release gases such as CO2, CS2, SO2 or COS (Shannon et al, 2015; Perez et al, 2004; Heldebrant et al, 2009)
No reported crystal structures of salts with simple substituted benzoic acids are found, so in order to examine the hydrogen-bonding in crystals of the DBU salts with some common ring-substituted benzoic acids, a number of these were prepared
Summary
The Lewis base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is an alkaloid isolated from the sponge Niphates digitalis (Regalado et al, 2010) but is commonly synthesized. It finds use as a curing agent for epoxy resins, as a catalyst in organic syntheses, and as a counter-cation in metal complex chemistry, e.g. with the pentabromo(triphenylphosphane)platinum(IV) monoanion (Motevalli et al, 1989). It has found use in binding organic liquids (BOLs), which usually comprise a mixture of amidines or guanidine and alcohol, and are used to reversibly capture and release gases such as CO2, CS2, SO2 or COS (Shannon et al, 2015; Perez et al, 2004; Heldebrant et al, 2009). Suitable crystals were obtained with 4aminobenzoic acid (PABA), (3,5-dinitrobenzoic acid (DNBA) and (3,5-dinitrosalicylic acid (DNSA), giving the anhydrous salts, C9H17N2+ C7H6NO2À (I), C9H17N2+ C7H3N2O6À (II) and C9H17N2+ C7H3N2O7À (III), respectively and their structures and hydrogen-bonding modes are reported
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