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2.2. Refinement
SD anion are also well represented in the literature. These
include the structure of the commercially utilized AgI complex
(Baenziger & Struss, 1976) and of many transition-metal
complexes, especially those involving the heavier first-row
transition metals Co, Ni, Cu and Zn (e.g. Shi et al., 2015; Sun et
al., 2016; Pan et al., 2012). Salt structures of SD with organic
cations are also well known (e.g. Elacqua et al., 2013; Heren et
al., 2006). Somewhat strangely, there are very few structural
studies of s-block metal complexes of SD. As far as we are
aware, the only known s-block metal structure is that of a Ca
salt form (Tommasino et al., 2011). Given the ubiquity of
s-block metal salt usage in pharmaceutical materials in
general, and the long-standing commercial use of [Na][SD] in
particular, this seemed an odd omission (Stahl & Wermuth,
2008; Preskey & Kayes, 1976). The current study adds to our
Crystal data, data collection and structure refinement
details are summarized in Table 1. For all structures, H atoms
bound to C atoms were placed in the expected geometric
positions and treated in riding modes (aromatic and methyl-
˚
ene C—H = 0.95 A), with Uiso(H) = 1.2Ueq(C). All H atoms
bound to N atoms were refined freely and isotropically, as
were H atoms bound to O atoms in structure (VI). Water H
atoms in (I), (III) and (IV) were located by difference
syntheses and required restraints to be applied, i.e. O—H =
˚
˚
0.88 (1) A and Hꢀ ꢀ ꢀH = 1.33 (2) A. For these atoms of (III),
Uiso(H) = 1.5Ueq(O), whilst for (I) and (IV), Uiso(H) values
were refined. For (IV), after several trial calculations, the
three noncoordinated water molecules were given site-occu-
pancy factors of 0.5. For (III), the H atoms of one water ligand
were modelled as disordered over three sites.
knowledge of sulfadiazine structural chemistry by reporting
the structures of three alkali metal salt forms of SD with Li, Na
and K, i.e. structures (I), (II) and (III), respectively, as well as
the structure formed when the sulfonated azo dye sodium
Orange G (OG) crystallizes in the presence of SDH to give a
form containing both Na and SDH2 cations, (IV) (see Schemes
1 and 2). Finally, the structures of two new organic salt forms,
(V) and (VI), prepared by reaction of SDH with the bases
2-aminopyridine and ethanolamine, are also presented for
comparison.
3. Results and discussion
The structure of lithium salt (I) was found to consist of a
simple discrete coordination compound of type [Li(SD)-
(H2O)2] (see Fig. 1). Extensive hydrogen bonding creates a
three-dimensional hydrogen-bonding network (Table 2). The
SD anion acts in a chelating fashion to form a six-membered
[LiOSNCN] ring through Li-to-O and Li-to-heterocyclic N
bonds. Thus, although the Li coordination geometry is tetra-
hedral, the bond angles are considerably distorted due to the
small bite angle of the chelate [90.91 (18)–126.9 (2)ꢂ] (see
2. Experimental
2.1. Synthesis and crystallization
The simple salt forms were prepared by reacting 1:1 molar
mixtures of sulfadiazine and MOH (M = Li, Na or K) or the
organic base in water–ethanol (50:50 v/v). The mixtures were
stirred and heated to give clear solutions, before being left to
cool to room temperature. Partial evaporation of these reac-
tion mixtures over periods of 4–7 d gave suitable crystals of
(I), (III), (V) and (VI), but a fine powder of Na salt (II).
Good-quality crystals of (II) were obtained by vapour diffu-
sion of ethanol into an aqueous solution of sodium sulfadia-
zine. Na Orange G (OG) complex (IV) was obtained by
dissolving NaOG (0.20 g, 0.44 mmol) in the minimum amount
of water. A slight excess of sulfadiazine (0.12 g, 0.48 mmol)
was also dissolved in the minimum amount of water. The two
solutions were mixed together with stirring and acidified with
concentrated HCl. After 3 d, orange crystals of (IV) had
grown.
Figure 1
The molecular structure of Li salt (I), with non-H atoms shown as 50%
probability displacement ellipsoids.
ꢁ
474 Campbell et al.
Salt forms of sulfadiazine
Acta Cryst. (2018). C74, 472–479
Campbell, Gemma
