Dicyclohexylaminium 4-nitroanthranilate

# 2004 International Union of Crystallography Printed in Great Britain ± all rights reserved The crystal structure of dicyclohexylamnium 4-nitroanthranilate, C12H24N + C7H5N2O4, shows a three-dimensional hydrogen-bonded network polymer in which the protonated amine groups of both of the independent molecules of dicyclohexylamine give similar hydrogen-bonding interactions with oxygen acceptors of four separate anthranilate carboxylate groups [N O = 2.730 (3)±2.782 (2) AÊ ]. Secondary centrosymmetric peripheral hydrogen-bonding linkages involve the amine groups of the anthranilate anions with nitro and carboxylate O-atom acceptors, while these groups are also involved in intramolecular NÐH O(carboxylate) associations [2.663 (3) and 2.679 (3) AÊ ].

The crystal structure of dicyclohexylamnium 4-nitroanthranilate, C 12 H 24 N + ÁC 7 H 5 N 2 O 4 À , shows a three-dimensional hydrogen-bonded network polymer in which the protonated amine groups of both of the independent molecules of dicyclohexylamine give similar hydrogen-bonding interactions with oxygen acceptors of four separate anthranilate carboxylate groups [NÁ Á ÁO = 2.730 (3)±2.782 (2)

Comment
Nitro-substituted benzoic acids such as 3,5-dinitrosalicylic acid (DNSA) (pK a = 2.2) readily protonate the nitrogen functional groups of most Lewis bases, giving compounds which have moderately to extensively hydrogen-bonded structures Smith et al., 2003). 4-Nitroanthranilic acid (4-NAA; pK a = 3.9) is slightly weaker than DNSA but similar protonation of Lewis bases might be expected. However, structures of proton-transfer compounds with 4±NAA are not common. We have previously prepared and reported the structure of only one such compound, that of ethylenediaminium 4-nitroanthranilate dihydrate [(EN) 2+ Á2(4-NAA) À Á2H 2 O] , in which both amine functional groups of the EN molecule (pK a1 = 6.9 and pK a2 = 9.9) are protonated and are involved in an extensive hydrogen-bonded array, giving a three-dimensional network polymer structure. We report here the crystal structure of the proton-transfer compound of 4-NAA with the secondary amine dicyclohexylamine (DCHA; pK a = 11.4), (I).
The structure determination of (I) shows the presence of two independent but similar 4-nitroanthanilate anions (A and B) and two dicyclohexylaminium cations (C and D) in the asymmetric unit. Fig. 1 shows an associated pair (cation C and anion B). Each of the anion and cation pairs is conformationally and associatively similar. The 4-NAA anions are essentially planar, with both the carboxylate group and the nitro group <10 away from coplanarity with the benzene ring.

Experimental
The synthesis of the title compound, (I), was carried out by heating under re¯ux for 10 min 1 mmol quantities of 2-amino-4-nitrobenzoic acid (4-nitroanthranilic acid, 4-NAA) and N-cyclohexylcyclohexanamine (dicyclohexylamine, DCHA) in 50 ml of 80% ethanol±water. After concentration to ca 30 ml, partial room-temperature evaporation of the hot-®ltered solution gave orange crystal masses (m.p. 394.2±395.1 K).  Symmetry codes: (i) 1 À xY 1 À yY 1 À z; (ii) xY 1 yY z; (iii) 2 À xY 1 À yY Àz; (iv) 1 À xY 1 À yY Àz. A and B), and H11 and H12 (cations C and D)] were located by difference methods and their positional and isotropic displacement parameters were re®ned. Others were included in the re®nement at calculated positions as riding models (CÐH = 0.95 A Ê ), with U iso = 1.2U eq of the parent atom. For re®ned H atoms, the NÐH range is 0.83 (3) The molecular con®guration and atom-naming scheme for one of the independent associated 4-NAA anion (B) and DCHA cation (C) pairs in (I). Atoms are shown as 30% probability ellipsoids

Figure 2
Packing in the unit cell, viewed down a, showing hydrogen-bonding associations as broken lines.