organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
competitive solvent systems (Best et al., 2003). We elucidate
here the possible mechanism of N,N-dimethylbiguanide
interacting with target molecules by reporting the crystal
structures of N,N-dimethylbiguanidium oxalate mono-
hydrate, (I), and N,N-dimethylbiguanidium sulfate mono-
hydrate, (II).
ISSN 0108-2701
Two N,N-dimethylbiguanidium salts
displaying double hydrogen bonds to
the counter-ions
Li-Ping Lu,a,b Hong-Mei Zhang,a Si-Si Fenga and Miao-Li
Zhua,b
*
Some features of the molecular geometries of (I) and (II)
are listed in Tables 1 and 3. The molecular conformation is
illustrated in Figs. 1 and 2. Compound (I) contains one N,N-
dimethylbiguanidium dication, one oxalate anion and one
water molecule. Compound (II) consists of one N,N-dime-
thylbiguanidium dication, one sulfate anion and one water
molecule. Both compounds thus contain the same N,N-dime-
thylbiguanidium dication. The CÐN bonds of the biguanidium
aInstitute of Molecular Science, Key Laboratory of Chemical Biology and Molecular
Engineering of the Education Ministry, Shanxi University, Taiyuan, Shanxi 030006,
People's Republic of China, and bState Key Laboratory of Coordination Chemistry,
Nanjing University, Nanjing 210093, People's Republic of China
Correspondence e-mail: miaoli@sxu.edu.cn
Received 23 March 2004
Accepted 21 July 2004
Online 18 September 2004
Ê
moiety range from 1.302 (3) to 1.374 (3) A in (I) and 1.308 (4)
Ê
to 1.383 (4) A in (II); this situation differs from that in N,N-
dimethylbiguanidium nitrate, in which the CÐN bonds are
Ê
more uniform [1.324 (3)±1.343 (3) A; Zhu et al., 2003]. The
dihedral angles between the two guanidine group planes are
52.8 (1) and 56.1 (1)ꢀ in (I) and (II), respectively. Therefore,
the anions slightly in¯uence the structure of N,N-dimethylbi-
guanide.
The hydrogen-bonding geometries in (I) and (II) are listed
in Tables 2 and 4 and illustrated in Figs. 3 and 4. A number of
intra- and intermolecular hydrogen bonds stabilize the crystal
structure of each compound. These hydrogen bonds are
formed mainly between the biguanidium groups and the
oxalate or sulfate anions, between the biguanidium groups and
the water molecules, as well as between the carboxylate or
sulfate anions and water molecules. Strong double hydrogen
bonds are formed between either the carboxylate groups of
the oxalate anion or the sulfate groups and atoms N3 and N5
The crystal structures of N,N-dimethylbiguanidium oxalate
2+
2
monohydrate, C4H13N5 ÁC2O4 ÁH2O, (I), and N,N-dimethyl-
2+
2
biguanidium sulfate monohydrate, C4H13N5 ÁSO4 ÁH2O,
(II), show that both compounds contain the same N,N-
dimethylbiguanidium dication. In (I), two independent
oxalate ions lie about inversion centres. Strong double
hydrogen bonds, with DÁ Á ÁA distances of 2.658 (2) and
Ê
Ê
2.830 (3) A in (I), and 2.722 (3) and 2.815 (3) A in (II), are
present between N atoms of the N,N-dimethylbiguanidium
moieties and either the carboxylate group of the oxalate anion
or the sulfate anion.
Comment
An N-substituted derivative of biguanide, viz. metformin
(N,N-dimethylbiguanide), is a powerful oral antihyper-
glycaemic drug that has been used in many countries for
over 40 years for treating diabetic patients with non-insulin-
dependent diabetes mellitus. However, the mechanism of
action of this drug is still unknown. Because this compound
contains a biguanidium group, it can form complexes with
many metal ions (Ray, 1961; Zhu et al., 2002, 2002a,b; Lu, Yang
et al., 2004). Recently, we found that N,N-dimethylbiguanide
loses its ability to lower blood glucose levels when forming a
monodentate complex with Zn2+ ions, but retains this ability
when forming bidentate complexes with Cu2+ and Ni2+ ions
(Zhu et al., 2004). On the other hand, guanidium may play an
important role in recognizing anions, such as carboxylates,
phosphates, sulfates and nitrates, in biological systems (Baggio
et al., 1997; Liu et al., 2001; Lu et al., 2001; Best et al., 2003). It
has been proven that a strong interaction between the
guanidium groups and anions through charge pairing and
hydrogen bonding facilitates the recognition of small target
anions by receptors containing guanidinium groups in
Figure 1
The structure of (I), with displacement ellipsoids drawn at the 30%
probability level for non-H atoms. [Symmetry codes: (*) 2 x, 2 y,
z; (#) x, 12 + y, 12 z; symmetry codes (i) and (iii) are as de®ned in
2
Table 2.]
o740 # 2004 International Union of Crystallography
DOI: 10.1107/S010827010401786X
Acta Cryst. (2004). C60, o740±o743