organic compounds
two independent molecules of compound (III) (Insuasty et al.,
2012). In addition, the exocyclic angles S1—C5—C57 and
C56—C51—C57 are both significantly larger than the corre-
sponding angles C4—C5—C57 and C52—C51—C57, respec-
tively (Table 1). These observations, taken together, indicate
that the nonbonded intramolecular contact S1ꢀ ꢀ ꢀH56 is
strongly repulsive. It appears that distortion of the bond
angles at atoms C5, C51 and C57 is an energetically more
favourable route for accommodating the repulsive Sꢀ ꢀ ꢀH
contact than that provided by a significant rotation of the aryl
ring around the C51—C57 bond. On the other hand, although
the aryl-ring C52—C53 and C55—C56 bond lengths of
˚
1.379 (4) and 1.389 (3) A, respectively, are slightly shorter
than the remaining C—C distances in this ring [range
˚
˚
1.397 (3)–1.412 (3) A; mean 1.405 A], none of the other bond
lengths in (I) (Table 1) provides any evidence for the devel-
opment of a polarized (zwitterionic) electronic structure of
type (Ia) which might lead to restricted rotation about the
C51—C57 bond.
Figure 2
Part of the crystal structure of compound (I), showing the formation of a
1
1
hydrogen-bonded dimer centred at (12, , ). For the sake of clarity, H
2
2
atoms not involved in the motif shown have been omitted. The atom
marked with an asterisk (*) is at the symmetry position (ꢂx + 1, ꢂy + 1,
ꢂz + 1).
(ꢂx + 1, ꢂy, ꢂz + 1) (Table 2). However, not only is the Hꢀ ꢀ ꢀS
˚
distance greater than the sum (2.89 A) of the van der Waals
radii for H and S (Bondi, 1964; Rowland & Taylor, 1996), but
two-connected sulfur has been shown (Allen et al., 1997) to be
an extremely poor acceptor in hydrogen bonds, even from O—
H and N—H as donors; accordingly, this contact cannot be
regarded as structurally significant.
It is of interest to compare briefly the supramolecular
aggregation reported here for compound (I) with that in
compounds (II) and (III). In compound (II) (Low et al., 2007),
symmetry-related pairs of molecules are again linked into
cyclic dimers, but here the component molecules are related
by a twofold rotation axis, rather than by inversion as in
compound (I) and hydrogen bond concerned in (II) is of the
C—Hꢀ ꢀ ꢀO type rather than of the C—Hꢀ ꢀ ꢀꢀ(arene) type
found in (I), Compound (III) (Insuasty et al., 2012) crystallizes
in the space group P1 with Z0 = 2, and in one of the two
independent molecules the chair-form morpholine ring is
conformationally disordered over two sets of sites, with the
two disorder forms exhibiting different orientations of the
ring, while the other molecule is fully ordered. An extensive
series of C—Hꢀ ꢀ ꢀO hydrogen bonds link the molecules of (III)
into a complex two-dimensional structure; it is notable that,
despite the molecular constitution, intermolecular hydrogen
bonds of the C—Hꢀ ꢀ ꢀN type are absent from the structure of
compound (III).
The supramolecular aggregation in compound (I) is very
simple as the crystal structure contains neither conventional
hydrogen bonds nor aromatic ꢀ–ꢀ stacking interactions.
Instead the molecules are linked in pairs by a single C—
Hꢀ ꢀ ꢀꢀ(arene) hydrogen bond (Table 2) to form centrosym-
metric dimers, with the reference dimer centred across (12, 21, 21)
(Fig. 2). There are two such dimers per unit cell, but there are
no direction-specific interactions between adjacent dimers.
The only other potentially significant intermolecular contact is
of the C—Hꢀ ꢀ ꢀS type between the molecules at (x, y, z) and
Experimental
To a mixture of 4-(dimethylamino)benzaldehyde (1.1 mmol) and
rhodanine (1.0 mmol) in dry ethanol (10 ml) was added one drop of
piperidine. This mixture was then heated under reflux for 6 h. After
cooling the mixture to ambient temperature, the resulting solid
ꢃ
Acta Cryst. (2013). C69, 74–76
Insuasty et al. C17H21N3OS 75
Insuasty, Alberto
