organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
an acid, can be deprotonated in a polar medium. Recently, it
0
was reported that some 5,5 -derivatives of 3-diethylamino-
0
methyl-2,2 -biphenol exist as zwitterions in the crystalline
ISSN 0108-2701
state (Ng et al., 2002; Bartoszak-Adamska et al., 2000; Brze-
zinski et al., 1998, 1995). The reason for the formation of the
zwitterions, con®rmed by experimental and theoretical
methods, is that the ±CH N(C H ) group, as a relatively
A zwitterion of 1,5-bis(2-hydroxy-
benzamido)-3-azapentane: a two-
dimensional hydrogen-bonding
network involving dimers
2
2
5 2
strong base, causes deprotonation of the nearby phenol group
and thereby builds a short intramolecular hydrogen bond
involving a six-membered ring. Other zwitterionic species,
such as the salicylideneimine Schiff bases (Mondal et al., 2002;
Hazell et al., 1997), are also formed as the result of an intra-
molecular proton transfer. These results prompted us to look
into the structure of the bhap molecule, which also bears both
aliphatic amine and phenol groups. We present here the
crystal structure of the title compound, (I), which is the
zwitterion of bhap obtained by recrystallization from
methanol/water.
Hui-Min Liu, Lei He, Xiao-Lan Luo and Wen-Qin Zhang*
Department of Chemistry, Tianjin University, Tianjin 300072, People's Republic of
China
Received 1 November 2005
Accepted 13 January 2006
Online 31 January 2006
The title compound, 2-{N-[2-(2-hydroxybenzamido)ethyl-
ammonioethyl]aminocarbonyl}phenolate, C H N O , crys-
1
8
21
3
4
tallizes in a zwitterionic form as a result of intermolecular
proton transfer and possesses a negatively charged phenolate
group and a protonated amino group. The 2-hydroxy-
benzamide and 2-(aminocarbonyl)phenolate moieties
attached to the two ends of the CÐCÐNÐCÐC backbone
adopt a cis conformation in relation to this backbone. All N-
and O-bound H atoms are involved in hydrogen-bond
formation; the zwitterions are ®rst linked into head-to-tail
dimers, which are further organized into a two-dimensional
network parallel to the crystallographic bc plane.
The structure of compound (I) (Fig. 1) is composed of a
2-hydroxybenzamide group and
a
2-(aminocarbonyl)-
phenolate moiety linked by a protonated 3-azapentanediyl
chain. The zwitterionic nature is con®rmed by the location and
free re®nement of the relevant H atoms. The two pendant
moieties attached to the ends of the CÐCÐNÐCÐC back-
bone adopt a cis conformation, as shown by the N1ÐC8Ð
ꢀ
C9ÐN2 [65.1 (2) ] and N2ÐC10ÐC11ÐN3 torsion angles
ꢀ
0
[78.6 (2) ]. Similar to the previously studied 5,5 -derivatives of
0
3-diethylaminomethyl-2,2 -biphenol, (I) exists as a zwitterion,
a H atom from one phenol hydroxy group having been
transferred to the 3-azapentanediyl N atom. The C8ÐC9Ð
Comment
There is considerable interest in complexes that are capable of
mimicking the active sites of metalloproteins (Cao et al., 2004;
Tolman & Spencer, 2001; Xing & DeRose, 2001). Generally,
these model complexes are obtained from bulky multidentate
ligands in order to construct an environment similar to that
found in the proteins. 1,5-Bis(2-hydroxybenzamido)-3-aza-
pentane, bhap, is a potentially pentadentate coordinating
ligand containing N- and O-donor atoms, and has been
synthesized in order to study its coordination behavior with
2
+
2+
2+
several transition metal ions (e.g. Zn , Cu and Co , which
are the most abundant and important metals in biology;
Lipscomb & Str aÈ ter, 1996). In previous reports, this compound
exhibited different chelating modes in the formation of
mononuclear or binuclear complexes with copper(II) (Sure-
shan & Bhattacharya, 1999) and iron(III) ions (Dash & Rath,
2
004; Rath et al., 2002). However, to the best of our knowl-
edge, there are no published data related to the crystal
structure of either bhap or its complexes mentioned above.
It is commonly accepted that the aliphatic amino group acts
as a comparatively strong base, whereas the phenol group, as
Figure 1
A view of the structure of (I), showing the atom-numbering scheme and
displacement ellipsoids at the 30% probability level. The dashed lines
represent intramolecular hydrogen bonds.
o104 # 2006 International Union of Crystallography
DOI: 10.1107/S0108270106001545
Acta Cryst. (2006). C62, o104±o106
Liu, Hui-Min
