N-benzoyl-N′,N′-dibutylselenourea and its palladium(II) complex

Article abstract of DOI:10.1107/S0108270107053711

The crystal and molecular structures of N-benzoyl-N′,N′- dibutylselenourea (HL), C₁₆H₂₄N₂OSe, and the corresponding complex bis(N-benzoyl-N′,N′-dibutylselenoureato- κ²Se,O)-palladium(II), [Pd(C₁₆H₂₃N ₂OSe)₂], are reported. The selenourea molecule is characterized by intermolecular hydrogen bonds between the selenoamidic H atom and the Se atom of a neighbouring molecule forming a dimer, presumably as a consequence of resonance-assisted hydrogen bonding or π-bonding co-operativity. A second dimeric hydrogen bond is also described. In the palladium complex, the typical square-planar coordination characteristic of such ligands results in a cis-[Pd(L-Se,O)₂] complex.

Full text of DOI:10.1107/S0108270107053711

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
ingly, relatively few crystal structures of the unbound ligand
N,N-dialkyl-N0-benzoylthiourea and analogous N,N-dialkyl-
N0-benzoylselenoureas are available in the literature. We
report here the crystal and molecular structures of N,N-
dibutyl-N0-benzoylselenourea (HL), (I) (Figs. 1 and 2), and its
PdII complex, cis-[Pd(L-Se,O)2], (II) (Fig. 3).
ISSN 0108-2701
N-Benzoyl-N0,N0-dibutylselenourea
and its palladium(II) complex
Jocelyn C. Bruce and Klaus R. Koch*
Department of Chemistry, University of Stellenbosch, Private Bag X1, Matieland
7602, South Africa
Correspondence e-mail: krk@sun.ac.za
Received 11 September 2007
Accepted 27 October 2007
Online 14 December 2007
The crystal and molecular structures of N-benzoyl-N0,N0-
dibutylselenourea (HL), C16H24N2OSe, and the corresponding
complex bis(N-benzoyl-N0,N0-dibutylselenoureato-ꢀ2Se,O)-
palladium(II), [Pd(C16H23N2OSe)2], are reported. The seleno-
urea molecule is characterized by intermolecular hydrogen
bonds between the selenoamidic H atom and the Se atom of a
neighbouring molecule forming a dimer, presumably as a
consequence of resonance-assisted hydrogen bonding or ꢁ-
bonding co-operativity. A second dimeric hydrogen bond is
also described. In the palladium complex, the typical square-
planar coordination characteristic of such ligands results in a
cis-[Pd(L-Se,O)2] complex.
Compound (I) (Fig. 1) crystallizes in the space group P21/c.
The O and Se donor atoms adopt an anti orientation relative
to each other as a result of twisting about the N1ÐC8 bond, to
give torsion angles O1ÐC7ÐN1ÐC8 = 0.5 (4)ꢀ and C7Ð
N1ÐC8ÐSe1 = 121.1 (2)ꢀ. The CÐN bonds are all shorter
Ê
than the average CÐN bond length of 1.472 (5) A (Allen et
al., 1987) (Table 1); the alkyl-substituted selenourea CÐN
Ê
bond [C8ÐN2 = 1.316 (3) A] is signi®cantly shorter than the
Ê
amide bond [C7ÐN1 = 1.397 (3) A] and the acyl-substituted
Ê
selenourea CÐN bond [C8ÐN1 = 1.399 (3) A]. This re¯ects
the trend observed in the sulfur analogues, where N,N-dibutyl-
N0-naphthoylthiourea (Koch et al., 1995) and, more recently,
N-acetyl-N0,N0-(butane-1,4-diyl)thiourea (Dillen et al., 2006a)
and N,N-di-n-butyl-N0-pivaloylthiourea (Dillen et al., 2006b),
show that the R,RNÐC(S) bond length is, on average, the
shortest, followed by the amidic R0C(O)ÐN bond, while the
HNÐC(S) thiourea bond is the longest. Moreover, these
molecules usually adopt a conformation in the solid state such
that the S and O donor atoms assume opposing orientations,
the molecule being usually signi®cantly twisted around the
longest HNÐC(S) thiourea bond.
Comment
The use of metal complexes in which the ligands contain either
S or Se as single-source precursors for the synthesis of semi-
conducting quantum dots has recently attracted interest (Nair
et al., 2005; Malik et al., 2005). In this context, we have recently
reported the use of [N0-benzoyl-N,N-diethylthio(seleno)-
urea]cadmium(II) complexes as single-source precursors for
the successful synthesis of CdS and CdSe nanoparticles (Bruce
et al., 2007). As part of our interest in extending this study to
include other metal ions, we have prepared several N,N-
dialkyl-N0-benzoylselenoureas and corresponding metal
complexes with a view to using these as single-source
precursors for nanoparticle synthesis. The related N,N-dialkyl-
N0-benzoylthiourea ligands have been studied extensively and
are well known to coordinate to a wide variety of ®rst-row
transition metal ions (Schuster & Koenig, 1987; Dietze et al.,
1991; Beyer et al., 1981). The corresponding N,N-dialkyl-N0-
benzoylselenoureas are relatively rare, although some metal
complexes of NiII and PdII derived from N,N-dialkyl-N0-
benzoylselenourea have been structurally characterized
(Kampf et al., 2004; Bensch & Schuster, 1994). Generally, both
N,N-dialkyl-N0-benzoylthioureas and N,N-dialkyl-N0-ben-
zoylselenoureas readily coordinate to metal ions with loss of a
thioamidic or selenoamidic H atom, resulting in bidentate
coordination through the S(Se) and O donor atoms. Surpris-
Figure 1
The molecular structure of (I), showing the atomic numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level.
Acta Cryst. (2008). C64, m1±m4
DOI: 10.1107/S0108270107053711
# 2008 International Union of Crystallography m1

metal-organic compounds
As shown in Fig. 2, the molecules of (I) are linked through a
hydrogen bond between the selenoamidic H atom of one
molecule and the Se atom of its neighbour (see Table 2), so
giving rise to a dimer linked through such hydrogen bonds in
the crystal structure. The formation of this dimer represents an
example of resonance-assisted hydrogen bonding (RAHB) or
ꢁ-bond co-operativity (Steiner, 2002) since, in terms of
hydrogen bonding, the selenourea moiety consists of donor±
acceptor pairs which are connected by a resonant ꢁ system,
manifested by the shortening of the amide and acyl-substi-
tuted CÐN bonds. Such an arrangement is also observed in
the closely related diethyl analogue, N0-benzoyl-N,N-diethyl-
selenourea (Bruce et al., 2007). This dimer forms an eight-
membered ring structure where atoms H1/N1/C8/Se1/H1i/N1i/
C8i/Se1i [symmetry code: (i) x, 1 y, 1 z] lie in a plane,
82.36 (2)ꢀ. It is interesting to note that the second hydrogen
bond is not evident in the solid-state structures of other
N0-benzoyl-N,N-dialkylselenoureas that have previously been
analysed (N0-benzoyl-N,N-dihexylselenourea, N0-benzoyl-
N,N-dioctylselenourea and N0-benzoyl-N-benzyl-N-methyl-
selenourea; Bruce & Koch, 2007). These two dimers give rise
to the hydrogen-bonded chains shown in Fig. 2 that form in the
direction of the c axis. There is little interaction apparent
between these chains.
The molecular structure of cis-[Pd(L-Se,O)2], (II), which
crystallizes in the space group P1, is shown in Fig. 3. The
generally expected mode of coordination of HL, with loss of
an H atom and yielding a cis-square-planar complex, is
observed. The four donor atoms and Pd metal centre lie in a
single coordination plane involving atoms Se1A/O1A/Pd1/
Se1B/O1B, with a mean deviation from planarity of only
Ê
with a maximum deviation of 0.119 (2) A for atom H1. A
second dimeric hydrogen bond is present in (I) between the
carbonyl O atom and a H atom on the benzene residue at ( x,
Ê
0.024 A; the two chelate rings are twisted at an angle of
4.6 (1)ꢀ relative to each other, and deviate slightly from
Ê
perfect planarity by 0.096 and 0.085 A for atoms Se1A/C8A/
1
y, z) (see Table 2). Similarly to the ®rst dimer, this forms
a ten-membered ring structure where atoms O1/C7/C1/C6/H6/
O1ii/C7ii/C1ii/C6ii/H6ii [symmetry code: (ii) x, 1
y, z]
N1A/C7A/O1A and Se1B/C8B/N1B/C7B/O1B, respectively.
The reduced planarity in the chelate rings is re¯ected in a
puckering of the C7A/N1A/C8A and the C7B/N1B/C8B
planes, with atoms N1A and N1B, respectively, lying
Ê
again lie in a plane, with a maximum deviation of 0.241 (2) A
for atom O1, the angle between these two planes being
Ê
Ê
0.486 (2) A below and 0.336 (2) A above the Se1A/O1A/Pd1/
Se1B/O1B plane.
The average PdÐSe and PdÐO bond lengths (Table 3) of
Ê
2.345 (3) and 2.041 (1) A, respectively, in (II) compare well
with those reported previously for bis[N0-(2-¯uorobenzoyl)-
N,N-diisobutylselenoureato]palladium(II) (Kampf et al., 2004)
and its di¯uoro analogue, bis[N0-(2,6-di¯uorobenzoyl)-N,N-
diisobutylselenoureato]palladium(II) (Kampf et al., 2005). The
C
O and C Se bonds in (II) are somewhat longer than the
corresponding bonds in the ligand HL, as a result of a slight
loss of double-bond character in these bonds, presumably due
to electron delocalization in the six-membered chelate ring of
the metal complex. The relative reduction in the C Se bond
Figure 2
Neighbouring molecules of (I), showing the weak NÐHÁ Á ÁSe and CÐ
HÁ Á ÁO intermolecular hydrogen bonds (dashed lines). Displacement
ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i)
x, 1 y, 1 z; (ii) x, 1 y, z.]
Figure 3
The molecular structure of (II), showing the atomic numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level.
ꢁ
m2 Bruce and Koch
C16H24N2OSe and [Pd(C16H23N2OSe)2]
Acta Cryst. (2008). C64, m1±m4

metal-organic compounds
order of (I) on coordination to PdII in the complex is also
re¯ected by a signi®cant reduction of the 1J(77Se 13C)
coupling constant, from 222 Hz in the ligand to 177 Hz in (II),
in the 13C NMR spectra of these substances in CDCl3. The
electron delocalization in the chelate ring of (II) is, in turn,
shown by the slight shortening of the CÐN bond lengths
compared with the corresponding bonds in the unbound
ligand.
Data collection
Bruker APEX CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
Tmin = 0.651, Tmax = 0.732
10228 measured re¯ections
3775 independent re¯ections
3031 re¯ections with I > 2ꢆ(I)
Rint = 0.038
Re®nement
R[F2 > 2ꢆ(F2)] = 0.037
wR(F2) = 0.085
S = 1.02
H atoms treated by a mixture of
independent and constrained
re®nement
3
Ê
3775 re¯ections
187 parameters
Áꢇmax = 0.55 e A
Experimental
3
Ê
0.33 e A
Áꢇmin
=
The ligand synthesis was formed according to a previously published
procedure (Douglass, 1937).
Table 1
Selected bond lengths (A) for (I).
Ê
For the synthesis of (II), a dichloromethane solution (25 ml) of (I)
(1.278 mmol) was added to an aqueous solution (25 ml) of K2PdCl4
(0.639 mmol). The solutions were shaken together in a separating
funnel after which an aqueous solution (10 ml) of sodium acetate
(2.558 mmol) was added, followed by gentle shaking. Extraction and
drying of the organic layer was followed by the addition of ethanol.
Slow evaporation from this mixture yielded crystals suitable for
analysis. 1H NMR chemical shifts are quoted relative to the residual
CHCl3 solvent resonance at 7.26 p.p.m., and 13C NMR chemical shifts
are quoted relative to the CDCl3 triplet at 77.0 p.p.m. (centre peak).
Elemental analyses were performed on a Heraeus Universal
Combustion Analyser, model CHN-Micro.
Se1ÐC8
O1ÐC7
C7ÐN1
C7ÐC1
1.848 (2)
1.212 (3)
1.397 (3)
1.492 (3)
N1ÐC8
N2ÐC8
N2ÐC13
N2ÐC9
1.399 (3)
1.314 (3)
1.470 (3)
1.480 (3)
Compound (II)
Crystal data
[Pd(C16H23N2OSe)2]
Mr = 783.05
Triclinic, P1
ꢈ = 81.867 (1)ꢀ
3
For N-benzoyl-N0,N0-dibutylselenourea, (I): yield 57.5%, m.p.
392.5±394.0 K. Analysis found: C 56.6, H 7.1, N 8.2%; C16H24N2OSe
requires: C 56.6, H 7.1, N 8.3%. 1H NMR (400 MHz, CDCl3): ꢂ 0.90 (t,
Ê
V = 1632.0 (2) A
Z = 2
Ê
a = 9.9302 (8) A
b = 10.9315 (9) A
Mo Kꢄ radiation
1
Ê
ꢅ = 2.83 mm
T = 173 (2) K
3
3
3H, JHH = 7.4 Hz, H12/H16), 0.99 (t, 3H, JHH = 7.4 Hz, H12/H16),
Ê
c = 15.4119 (13) A
ꢄ = 80.216 (1)ꢀ
ꢃ = 88.291 (1)ꢀ
3
3
1.28 (m, 2H, JHH = 7.5 Hz, H11/H15), 1.45 (m, 2H, JHH = 7.5 Hz,
H11/H15), 1.67 (q, 2H, 3JHH = 7.4 Hz, H10/H14), 1.83 (q, 2H, 3JHH
0.09 Â 0.08 Â 0.08 mm
=
3
7.4 Hz, H10/H14), 3.55 (t, 2H, JHH = 7.4 Hz, H9/H13), 4.08 (t, 2H,
3JHH = 7.6 Hz, H9/H13), 7.46 (t, 2H, H3, H5), 7.57 (t, 1H, H4), 7.83 (d,
2H, H2, H6), 8.54 (br s, 1H, NÐH); 13C NMR (100 MHz, CDCl3): ꢂ
13.6 (C12/C16), 13.8 (C12/C16), 19.9 (C15/C11), 20.0 (C15/C11), 28.7
(C14/C10), 29.7 (C14/C10), 53.7 (C13/C9), 56.4 (C13/C9), 127.8 (C3,
C5), 128.8 (C2, C6), 132.5 (C4), 133.0 (C1), 162.1 (C7), 180.9 (C8);
1J(77Se 13C) = 222.1 Hz.
For cis-bis(N-benzoyl-N0,N0-dibutylselenoureato)palladium(II),
(II): yield 94.2%, m.p. 423.5±424.4 K. Analysis found: C 49.1, H 5.8,
N 7.1%; C32H46N4O2PdSe2 requires: C 49.1, H 5.9, N 7.2%. 1H NMR
(400 MHz, CDCl3): ꢂ 0.93 (t, 6H, 3JHH = 7.4 Hz, H12A/B or H16A/B),
Data collection
Bruker APEX CCD area-detector
diffractometer
Absorption correction: multi-scan
(SADABS; Bruker, 2002)
Tmin = 0.785, Tmax = 0.797
18809 measured re¯ections
7329 independent re¯ections
6802 re¯ections with I > 2ꢆ(I)
Rint = 0.017
Re®nement
R[F2 > 2ꢆ(F2)] = 0.022
wR(F2) = 0.056
S = 1.05
374 parameters
H-atom parameters constrained
3
Ê
Áꢇmax = 0.55 e A
3
Ê
0.38 e A
7329 re¯ections
Áꢇmin
=
0.98 (t, 6H, 3JHH = 7.4 Hz, H12A/B or H16A/B), 1.38 (m, 8H, 3JHH
=
7.6 Hz,H11A/B,H15A/B),1.67(q,4H,3JHH =7.7 Hz,H10A/BorH14A/
Table 2
Hydrogen-bond geometry (A, ) for (I).
ꢀ
Ê
3
H14A/B), 1.76 (q, 4H, JHH = 7.8 Hz, H10A/B or H14A/B), 3.78 (m,
3
8H, JHH = 7.8 Hz, H9A/B, H13A/B), 7.40 (t, 4H, H3A/B, H5A/B),
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
7.49 (t, 2H, H4A/B), 8.23 (d, 4H, H2A/B, H6A/B); 13C NMR
(101 MHz, CDCl3, ꢂ): 13.8, 13.9 (C12A/B, C16A/B), 20.2, 20.3 (C11A/
B, C15A/B), 29.9, 30.0 (C10A/B, C14A/B), 51.8, 54.7 (C9A/B, C13A/
B), 127.9 (C3A/B, C5A/B), 129.7 (C2A/B, C6A/B), 131.4 (C4A/B),
137.2 (C1A/B), 166.7 (C8A/B), 170.8 (C7A/B). 1J(77Se 13C) =
176.5 Hz.
N1ÐH1Á Á ÁSe1i
0.83 (3)
0.93
2.76 (3)
2.48
3.539 (2)
3.407 (3)
159 (2)
174
C6ÐH6Á Á ÁO1ii
Symmetry codes: (i) x; y ‡ 1; z ‡ 1; (ii) x; y ‡ 1; z.
Table 3
Selected bond lengths (A) for (II).
Ê
Compound (I)
Pd1ÐO1A
Pd1ÐO1B
Pd1ÐSe1B
Pd1ÐSe1A
Se1AÐC8A
Se1BÐC8B
O1BÐC7B
O1AÐC7A
N2AÐC8A
2.0395 (12)
2.0439 (12)
2.3411 (3)
2.3489 (3)
1.9076 (17)
1.9006 (16)
1.260 (2)
N2AÐC13A
N2AÐC9A
C9BÐN2B
N1BÐC8B
N1BÐC7B
N2BÐC8B
N2BÐC13B
C8AÐN1A
C7AÐN1A
1.469 (2)
1.478 (2)
1.481 (2)
1.334 (2)
1.335 (2)
1.338 (2)
1.473 (2)
1.333 (2)
1.329 (2)
Crystal data
3
Ê
C16H24N2OSe
Mr = 339.33
V = 1639.4 (5) A
Z = 4
Monoclinic, P21=c
Mo Kꢄ radiation
1
Ê
a = 10.3880 (17) A
ꢅ = 2.29 mm
T = 273 (2) K
Ê
b = 15.715 (3) A
1.266 (2)
1.341 (2)
Ê
c = 10.1518 (16) A
0.20 Â 0.16 Â 0.14 mm
ꢃ = 98.423 (3)ꢀ
ꢁ
Acta Cryst. (2008). C64, m1±m4
Bruce and Koch
C16H24N2OSe and [Pd(C16H23N2OSe)2] m3

metal-organic compounds
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H atoms involved in hydrogen bonding were located in difference
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Ê
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ꢁ
m4 Bruce and Koch
C16H24N2OSe and [Pd(C16H23N2OSe)2]
Acta Cryst. (2008). C64, m1±m4