Struct Chem (2011) 22:1267–1279
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remaining solid crystallized. Specific data for the com-
pounds are given below.
procedure [30]. The dibenzil azines 2a and 2b were syn-
thesized by condensation of a 2:1 mixture of the corre-
sponding benzils with hydrazine hydrochloride. The
dibenzil azines 2c and 2d were prepared from the benzil
monohydrazones 1c and 1d, respectively, by oxidation with
copper(II) acetate.
4,40-Difluorobenzil azine (2c): Crystallization from
acetone yielded 87% yellow crystals, m.p. 225 °C. Anal.
Calc. (%) for C28H16F4N2O2 (488.43): C, 68.85; H, 3.30;
N, 5.74. Found (%): C, 68.79; H, 3.37; N, 5.73; m/z (GC–
MS) 488 [M]?. IR (KBr): 3072, 1682, 1597, 1505, 1413,
1318, 1230, 1157, 903, 850, 805, 755, 736, 606, 508 cm-1
.
=
=
Structural study
3
3
1H NMR (CDCl3): 6.96, 6.98 (2d, JHH = 9.0 Hz, JFH
3
8.4 Hz, 4H, ArH), 7.18, 7.20 (2d, JHH = 8.9 Hz, JFH
3
Crystal structures of the benzil monohydrazones 1a and 1d,
of dibenzil azine (2a) and its substituted derivatives 2b–2d
have been determined by X-ray diffraction. Crystal data
and details of the refinement of the structures are summa-
rized in Table 1. The conformation of the molecules in
their solid state structures can be described by the torsion
angles around the a-ketohydrazone (1a, 1d) or the
bis(ketazine) fragment (2a–2d) as well as the dihedral
angle between the planes of the aromatic rings, designated
as A and B in the illustrations of the molecular structures.
These geometric parameters together with selected bond
lengths are listed in Table 2. Information regarding non-
covalent interactions is given in Table 3. ORTEP plots of
the molecular structures including atom labelling are
shown in Figs. 1, 4, 6 and 9, while illustrations of the
packing structures are presented in Figs. 2, 3, 5, 7, 8
and 10.
3
8.3 Hz, 4H, ArH), 7.48, 7.49 (2d, JHH = 9.0 Hz,
3
4JFH = 5.3 Hz, 4H, ArH), 7.95, 7.96 (2d, JHH = 9.0 Hz,
4JFH = 5.3 Hz, 4H, ArH). 13C NMR (CDCl3): 116.0 (d,
2JFC = 22.1 Hz, Ar), 116.4 (d, 2JFC = 22.6 Hz, Ar), 128.0
4
(d, JFC = 2.8 Hz, Ar), 130.1 (d, JFC = 9.2 Hz, Ar),
3
4
131.6 (d, JFC = 2.7 Hz, Ar), 131.8 (d, JFC = 9.5 Hz,
3
1
Ar), 164.6 (d, JFC = 174.2 Hz, Ar), 165.6 (C=N), 166.6
(d, JFC = 177.5 Hz, Ar), 195.2 (C=O). 19F NMR
1
(CDCl3): -102.9, -106.9.
4,40-Dichlorobenzil azine (2d): Crystallization from
toluene yielded 76% yellowish orange crystals, m.p.
191 °C. Anal. Calc. (%) for C28H16Cl4N2O2 (554.52): C,
60.68; H, 2.91; N, 5.05. Found (%): C, 60.54; H, 2.85; N,
4.92; m/z (GC–MS) 554 [M]?. IR (KBr): 3088, 1676, 1587,
1486, 1401, 1318, 1220, 1176, 1093, 1013, 900, 840, 758,
739, 489 cm-1. 1H NMR (CDCl3): 7.26 (d, 3JHH = 8.8 Hz,
3
4H, ArH), 7.40 (d, JHH = 8.7 Hz, 4H, ArH), 7.49 (d,
3
3JHH = 8.7 Hz, 4H, ArH), 7.84 (d, JHH = 8.6 Hz, 4H,
Crystal structures of the benzil monohydrazones 1a and 1d
ArH). 13C NMR (CDCl3): 129.2, 129.3, 129.6, 130.1,
130.5, 133.5, 138.6, 141.1 (Ar), 166.0 (C=N), 195.5 (C=O).
The benzil monohydrazone 1a crystallizes in the mono-
clinic space group P21/c with one molecule in the asym-
metric part of the unit cell. A perspective view of the
molecular structure is presented in Fig. 1a, showing
E-configuration around the C=N bond. Not only the C=N
X-ray crystallography
The intensity data of 1a, 1d and 2a–2d were collected on a
Bruker APEX II diffractometer with Mo Ka radiation
˚
[1.307(1) A], N–N [1.321(1) A] and C=O bond lengths
˚
˚
˚
[1.235(1) A] are within the range observed for other dione
(k = 0.71073 A) using x- and /-scans. Reflections were
corrected for background, Lorentz and polarization effects.
Preliminary structure models were derived by application
of direct methods [36] and were refined by full-matrix
least-squares calculation based on F2 for all reflections
[36]. With the exception of the amino hydrogens H(2A)
and H(2B) in 1a und 1d, all other hydrogen atoms were
included in the models in calculated positions and were
refined as constrained to bonding atoms.
monohydrazones [21, 22] but also the C(7)–C(8) bond
˚
distance of 1.467(1) A, being approximately the value
expected for a C(sp2)–C(sp2) single bond. As depicted in
Fig. 1a, the carbonyl and hydrazone groups adopt a tran-
soid conformation with a torsion angle of 172.9(1)° for the
atomic sequence O(1)–C(7)–C(8)–N(1), which indicates
approximate planarity of the a-ketohydrazone moiety. The
carbonyl and hydrazone group are inclined at angles of
40.9(1)° and 54.2(1)° with respect to the aromatic rings to
which they are attached. The dihedral angle between the
phenyl rings is 79.5(1)°. The crystal structure of 1a (Fig. 2)
is constructed of supramolecular strands extending along
the crystallographic a-axis. Within a given strand, one of
the amino hydrogens is connected with the carbonyl oxy-
Results and discussion
Synthesis
˚
The benzil monohydrazones 1a–1d were prepared by
simple 1:1 condensation reaction of the corresponding
benzils with hydrazine hydrate following the standard
gen of a consecutive molecule [N(2)–H(2A)ꢀꢀꢀO(1) 1.91 A,
174°], whereas the second amino hydrogen H(1A) is
excluded from non-covalent bonding. Interstrand
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