Comparison of copper imine and amine podates: Geometric consequences of podand size and donor type

Article abstract of DOI:10.1107/S0108270106034524

The imine podands tris[(2-nitrobenzylidene)aminoethyl]-amine and tris[(2-nitrobenzylidene)aminopropyl]amine both stabilize copper(I), forming {tris[(2-nitrobenzylidene)amino-ethyl]amine-κ⁴N}copper(I) perchlorate acetonitrile disolvate, [Cu(C

Full text of DOI:10.1107/S0108270106034524

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
In podate and cryptate complexes with potential threefold
symmetry, imine donors typically stabilize CuI and are easily
hydrolysed by CuII (Harding et al., 1995; Arthurs et al., 2001).
Reduction of the imine donors to the corresponding amines
generates a site in which CuI is activated to reaction with
dioxygen, as shown elegantly by Suzuki, Schindler and their
co-workers (Komiyama et al., 2004; Schatz et al., 2001).
However, CuII binds readily to the reduced ligands.
ISSN 0108-2701
Comparison of copper imine and
amine podates: geometric
consequences of podand size and
donor type
Joanne L. Coyle,a Anna Fuller,b Vickie McKeeb* and Jane
Nelsonb
aChemistry Department, The Open University, Milton Keynes MK7 6AA, England,
and bChemistry Department, Loughborough University, Loughborough, Leicester-
shire LE11 3TU, England
Correspondence e-mail: v.mckee@lboro.ac.uk
Received 11 August 2006
Accepted 28 August 2006
Online 12 September 2006
The imine podands tris[(2-nitrobenzylidene)aminoethyl]-
amine and tris[(2-nitrobenzylidene)aminopropyl]amine both
stabilize copper(I), forming {tris[(2-nitrobenzylidene)amino-
ethyl]amine-ꢀ4N}copper(I) perchlorate acetonitrile disolvate,
[Cu(C27H27N7O6)]ClO4Á2CH3CN, (II), and {tris[(2-nitro-
benzylidene)aminopropyl]amine-ꢀ4N}copper(I) perchlorate,
[Cu(C30H33N7O6)]ClO4, (VI), respectively. The larger
propyl-based ligand is a poorer ®t for the CuI ion. The
reduced amine podand tris[(2-nitrobenzyl)aminoethyl]amine
binds CuII and the resulting compound, chloro{tris[(2-nitro-
benzyl)aminoethyl]amine-ꢀ4N}copper(II) chloride ethanol
solvate, [Cu(C27H33N7O6)Cl]ClÁC2H5OH, (IV), shows both
intra- and intermolecular hydrogen bonding, which gives rise
to RRS or SSR conformations in the podand strands rather
than the expected pseudo-threefold symmetry.
The structure of the imine podand tris[(2-nitrobenzyl-
idene)aminoethyl]amine, (I), was reported recently (McKee et
al., 2006). Reaction of (I) with Cu(CH3CN)4ClO4 in acetoni-
trile gave the CuI complex [Cu(I)]ClO4Á2CH3CN, (II), as dark-
brown crystals (Fig. 1). The CuI ion is coordinated to all four N
atoms in an approximately trigonal±pyramidal geometry
(Table 1), although the bonds to the imine N atoms [average
Comment
We have had a long-standing interest in the chemistry of both
imine and amine cryptates derived from tris(aminoethyl)-
amine (tren) and tris(3-aminoisopropyl)amine (trpn) [see, for
example, McKee et al. (2003) and Nelson et al. (1998)]. We
have investigated some simple podate complexes derived from
the same amines in order to clarify the geometric require-
ments associated with each (Coyle, 1999). A search of the
Cambridge Structural Database (Version 5.27; Allen, 2002;
Fletcher et al., 1996) showed that, although many tris(amino-
ethyl)amine/salicylate complexes have been investigated,
surprisingly few simple podates with other substituted benz-
aldehyde derivatives have been structurally characterized to
date. In this paper, we compare the structures of two CuI
podates, one derived from tris(aminoethyl)amine (tren) and
one from tris(aminopropyl)amine (trpn), with the CuII amine
analogue of the smaller tren-based podate.
Ê
2.003 (2) A] are signi®cantly shorter than that to the bridge-
I
head amine [Cu1ÐN1 = 2.196 (1) A], and the Cu ion is
Ê
Ê
0.172 (1) A out of the mean plane of the imine N atoms in the
opposite direction to the bridgehead. The nitro groups are not
involved in the coordination of the metal and the three strands
are arranged fairly tightly about the approximate threefold
axis. There are two important factors controlling this
geometry, namely the essentially planar geometry at the imine
N atoms [angle sums 359.9 (2), 359.9 (2) and 359.8 (2)ꢀ for
atoms N11, N21 and N31, respectively] and the steric demands
imposed by coordination of all four N donors of the ligand.
These result in the CÐN C plane being tilted with respect to
the `default' orientation (parallel to the pseudo-threefold axis
m472 # 2006 International Union of Crystallography
DOI: 10.1107/S0108270106034524
Acta Cryst. (2006). C62, m472±m476

metal-organic compounds
and perpendicular to the plane of the three sp2-hybridized
imine donors); the interplanar angles are 71.6 (1), 73.5 (1) and
74.1 (1)ꢀ for the N11, N21 and N31 strands, respectively. In
other words, the orientation of the conjugated nitrobenzyl-
idene strands is determined by the orientation of the imine
lone pairs. It is therefore not surprising that this geometry is
common for tren-based imine podands in the absence of
additional intra- or intermolecular interactions. There are no
signi®cant interactions between the cation and perchlorate
anion or solvent molecules. The anion is disordered and was
modelled with approximately 10% occupancy of the minor
orientation (Fig. 1).
The amine podand, tris[(2-nitrobenzyl)aminoethyl]amine,
(III), was obtained by reduction of (I) with NaBH4, which
reduced the imine groups but not the nitro substituents.
Reaction of ligand (III) with CuCl2 in ethanol yielded the
amine complex [Cu(III)Cl]ClÁC2H5OH, (IV), as green crystals.
The formula unit of (IV) is shown in Fig. 2. The geometry at
the CuI ion is approximately trigonal±bipyramidal (Table 2),
with the bridghead tertiary amine and the coordinated Cl ion
as apical donors. The coordination geometry is similar to that
observed for the analogous CuII podate derived from
benzaldehyde [tris(benzylaminoethyl)amine; Komiyama et al.,
2004; Schatz et al., 2001).
Two of the nitro groups of (IV) are hydrogen bonded to the
adjacent secondary amines (Table 3), but the third strand is
different, with the amine (N31) hydrogen bonded to the
ethanol solvent molecule. Consequently, the con®guration at
N31 is opposite to that at N11 and N21 (SRR in Fig. 2,
although, since the structure is centrosymmetric, the RSS
con®guration is also present). This difference breaks the
pseudo-threefold symmetry of the cation. The non-coordi-
nated Cl ion Cl2 makes a relatively short hydrogen bond to
Ê
the ethanol solvent molecule [3.105 (4) A] and shows further
interactions with N21 and with N11 of an adjacent molecule.
The latter two interactions are long for hydrogen bonds to
Ê
Cl , at 3.302 (4) and 3.474 (4) A, respectively (Steiner, 2002).
However, both are bifurcated and involve coordinated amines.
The resulting hydrogen-bond pattern links the structure in
chains running parallel to the b axis (Fig. 3). The most notable
Figure 1
The structure of complex (II), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and H
atoms have been omitted for clarity. The minor component of the
disordered ClO4 ion is indicated by open bonds.
Figure 3
Figure 2
A packing plot for complex (IV), viewed down the b axis. Hydrogen
bonds are shown as dashed lines and the ꢁ±ꢁ interactions are indicated by
open bonds linking ring centroids. Key: Cl atoms are shown cross-
hatched, Cu atoms are shaded top left to bottom right, N atoms are
dotted, and O atoms are shaded bottom left to upper right.
The structure of complex (IV), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and
hydrogen bonds are shown as dashed lines. H atoms not involved in
hydrogen bonding have been omitted for clarity.
[Cu(C27H27N7O6)]+, [Cu(C30H33N7O6)]+ and [Cu(C27H33N7O6)Cl]+ m473
ꢁ
Acta Cryst. (2006). C62, m472±m476
Coyle et al.

metal-organic compounds
interaction between these chains is a ꢁ±ꢁ interaction between
the C24±C29 ring and its symmetry equivalent by inversion
under (1 x, y, 1 z); the rings are necessarily parallel, the
We have observed similar patterns in the geometry of Cu
ions in cryptand hosts derived from tren and trpn [see, for
example, Farrar et al. (1995) and Nelson et al. (1998)],
supporting the suggestion that steric constraints mean that the
larger podand has more dif®culty accommodating bonding
between the CuI ion and all four donors than the smaller
analogue. These results also go some way to explaining the
initially counterintuitive ®nding that, in the dinuclear imino-
cryptate series, the shortest internuclear distances between
cationic guests are found for the larger hosts (Drew et al., 2000;
Farrar et al., 1995; Nelson et al., 1998). In the case of the
cryptand ligands, the twist imposed on each strand by the
coordination of the imine donors shortens the distance
between the two metal binding sites.
Ê
interplanar distance is 3.393 (4) A and centroid-to-centroid
Ê
distance is 3.710 (4) A.
Complex (VI), namely {tris[(2-nitrobenzylidene)amino-
propyl]amine}copper(I) perchlorate, is analogous to complex
(II), except that the longer tripodal amine tris(amino-
propyl)amine (trpn) is used in place of tren. As for (II), the Cu
ion is stabliized in the +1 state and has trigonal±pyramidal
geometry (Fig. 4 and Table 4). However, the CuI ion is
Ê
displaced from the imine plane by 0.167 (1) A towards the
bridgehead [i.e. in the opposite sense from complex (II)]. As
observed for complex (II), the requirement to coordinate the
CuI ion to all four N-atom donors results in tilting of the CÐ
N
C planes relative to the plane of the three sp2-hybridized
imine donors. In complex (VI), however, this effect is much
more pronounced [interplanar angles 34.9 (2), 36.3 (2) and
39.4 (2)ꢀ for atoms N11, N21 and N31, respectively].
Experimental
For the preparation of [CuI(I)]ClO4Á2CH3CN, (II), tris[(2-nitro-
The three-dimensional `podand bite' in the two CuI
complexes, (II) and (VI), can be compared by considering the
dimensions of the trigonal pyramid formed by the four N-atom
donors, with the tertiary amine (N1) at the apex and the imine
atoms N11, N21 and N31 in the basal plane. As mentioned
above, the CuI ion is outside the pyramid in complex (II) and
inside for (VI). However, the CuÐN1 distances are identical
benzylidene)aminoethyl]amine, (I) (0.93 g, 1.7 mmol), was dissolved
in dry deoxygenated acetonitrile (30 ml) and
a solution of
Cu(CH3CN)4ClO4 (0.55 g, 1.7 mmol) in deoxygenated acetonitrile
(20 ml) was added slowly with stirring. The red±brown solution was
stirred for 30 min at 313 K and then cooled, during which time an
orange crystalline product precipitated. This was ®ltered off and
dried under nitrogen, losing the acetonitrile solvent in the process
(yield 0.70 g, 52%). Analytical results (available in the archived CIF)
are consistent with the stated composition for all compounds
reported here.
Ê
[2.196 (2) A] and the CuÐN(imine) bonds are only marginally
Ê
Ê
different [mean values 2.003 (2) A for (II) and 2.018 (2) A for
(VI)]. The mean imine±imine distances in the basal plane are
The amine podand tris[(2-nitrobenzyl)aminoethyl]amine, (III),
was prepared by reduction of the imine analogue (Liu et al., 1992).
The imine (I) (2.15 g, 3.9 mmol) was dissolved in methanol (60 ml).
Na2B4O7 (0.81 g, 4.0 mmol) was added, followed by NaBH4 (0.65 g,
17.2 mmol) in small portions over a period of 30 min. The solution
was stirred for 2 h and then the solvent was removed on a rotary
evaporator. NH4Cl (4 g, 76 mmol) in water (40 ml) was added and the
mixture was extracted with CHCl3 (3 Â 60 ml). The CHCl3 solution
was washed with water, dried over MgSO4 and ®ltered. Finally, the
solvent was removed under reduced pressure to yield the amine as a
pale-yellow oil (yield ca 88%). The IR spectrum of the oil con®rmed
that the ligand had been successfully reduced. The imine stretch at ca
Ê
similar [3.456 and 3.483 A for (II) and (VI), respectively], but
the mean base±apex edges are signi®cantly different
Ê
[2.842 (2) A for (II) and 3.103 (2) for (VI)]. An indication of
steric strain in complex (VI) is given by the NÐCÐC and CÐ
CÐC angles in the saturated chain between N1 and the imine
N atoms; the average angle is 114.4 (3)ꢀ, compared with
110.5 (2)ꢀ for complex (II).
1
1630 cm was no longer present, but symmetric and antisymmetric
stretches of the nitro group at 1347 and 1526 cm 1, respectively,
con®rmed that the substituent remained unchanged. The amine was
used in the next step without further puri®cation.
For the preparation of [CuII(III)Cl]ClÁC2H5OH, (IV), the amine
ligand (III) (0.05 g, 0.09 mmol) was dissolved in ethanol (1.5 ml),
forming a pale-orange solution. On addition of a solution containing
CuCl2 (0.013 g, 0.09 mmol) in ethanol (1 ml), a turquoise solution was
formed. Green crystals of (IV) were obtained on allowing the solu-
tion to stand (yield 0.03 g, 48%).
Ligand (V) was prepared by the dropwise addition of tris(3-
aminoisopropyl)amine (0.32 g, 1.7 mmol) in methanol (20 ml) with
stirring to nitrobenzaldehyde (0.77 g, 5.1 mmol) in methanol (20 ml).
The resulting solution was stirred at 313 K for 30 min and the volume
was then reduced to yield a yellow oil, viz. (V). The oil was dissolved
in deoxygenated acetonitrile (30 ml) and Cu(CH3CN)4ÁClO4 (0.55 g,
1.7 mmol) was added. A brown solution formed and dark-red crystals
of [CuI(V)]ClO4, (VI), were obtained on allowing the solution to
stand (yield 0.69 g, 54%).
Figure 4
The structure of complex (VI), showing the atom-numbering scheme.
Displacement ellipsoids are drawn at the 40% probability level and H
atoms have been omitted for clarity.
m474 Coyle et al. [Cu(C27H27N7O6)]+, [Cu(C30H33N7O6)]+ and [Cu(C27H33N7O6)Cl]+
Acta Cryst. (2006). C62, m472±m476
ꢁ

metal-organic compounds
Table 2
Selected geometric parameters (A, ) for (IV).
Compound (II)
ꢀ
Ê
Crystal data
3
Cu1ÐN1
Cu1ÐN31
Cu1ÐN11
2.038 (4)
2.081 (4)
2.105 (4)
Cu1ÐN21
Cu1ÐCl1
2.107 (4)
2.2547 (16)
Ê
V = 1737.8 (2) A
[Cu(C27H27N7O6)]ClO4Á2C2H3N
Mr = 790.65
Triclinic, P1
a = 11.1178 (7) A
Z = 2
Dx = 1.511 Mg m
Mo Kꢂ radiation
3
Ê
Ê
Ê
N1ÐCu1ÐN31
N1ÐCu1ÐN11
N31ÐCu1ÐN11
N1ÐCu1ÐN21
N31ÐCu1ÐN21
84.44 (16)
83.97 (16)
127.92 (16)
84.35 (15)
121.43 (16)
N11ÐCu1ÐN21
N1ÐCu1ÐCl1
N31ÐCu1ÐCl1
N11ÐCu1ÐCl1
N21ÐCu1ÐCl1
107.62 (15)
176.50 (12)
92.13 (12)
97.66 (11)
98.07 (11)
1
b = 13.3595 (9) A
ꢅ = 0.78 mm
T = 150 (2) K
c = 13.7998 (9) A
ꢂ = 111.627 (1)ꢀ
ꢃ = 102.995 (1)ꢀ
ꢄ = 103.648 (1)ꢀ
Tablet, brown
0.37 Â 0.19 Â 0.08 mm
Data collection
Table 3
Hydrogen-bond geometry (A, ) for (IV).
ꢀ
Ê
Bruker SMART 1000 CCD area-
detector diffractometer
' and ! scans
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.762, Tmax = 0.941
15023 measured re¯ections
7856 independent re¯ections
6372 re¯ections with I > 2ꢆ(I)
Rint = 0.019
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
ꢇmax = 28.8ꢀ
N31ÐH31NÁ Á ÁO41
N11ÐH11NÁ Á ÁO12
N11ÐH11NÁ Á ÁCl2i
N21ÐH21NÁ Á ÁO22
N21ÐH21NÁ Á ÁCl2
O41ÐH41Á Á ÁCl2
0.93
0.93
0.93
0.93
0.93
0.84
2.13
2.29
2.63
2.46
2.48
2.28
2.998 (6)
2.882 (6)
3.474 (4)
3.023 (6)
3.302 (4)
3.105 (5)
154
121
152
119
147
170
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.033
wR(F2) = 0.082
S = 1.02
7856 re¯ections
w = 1/[ꢆ2(Fo2) + (0.0325P)2
+ 1.0079P]
1
2
z ‡ 32.
where P = (Fo2 + 2Fc2)/3
(Á/ꢆ)max = 0.025
Symmetry code: (i) x ‡ 1; y
;
3
Ê
Áꢈmax = 0.35 e A
3
Ê
0.45 e A
Compound (VI)
488 parameters
H-atom parameters constrained
Áꢈmin
=
Crystal data
[Cu(C30H33N7O6)]ClO4
Mr = 750.62
Z = 4
Dx = 1.499 Mg m
Mo Kꢂ radiation
ꢅ = 0.80 mm
T = 150 (2) K
Lath, red
0.47 Â 0.17 Â 0.13 mm
Table 1
Selected geometric parameters (A, ) for (II).
3
ꢀ
Ê
Monoclinic, P21=c
1
Ê
a = 9.5361 (7) A
b = 18.6870 (13) A
Cu1ÐN31
Cu1ÐN21
1.9974 (15)
1.9981 (15)
Cu1ÐN11
Cu1ÐN1
2.0127 (16)
2.1965 (15)
Ê
Ê
c = 19.2367 (13) A
ꢃ = 104.044 (1)ꢀ
Ê
V = 3325.5 (4) A
3
N31ÐCu1ÐN21
N31ÐCu1ÐN11
N21ÐCu1ÐN11
120.56 (6)
118.99 (6)
118.25 (6)
N31ÐCu1ÐN1
N21ÐCu1ÐN1
N11ÐCu1ÐN1
85.48 (6)
84.85 (6)
84.86 (6)
Data collection
Bruker SMART 1000 CCD area-
detector diffractometer
' and ! scans
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.704, Tmax = 0.903
28475 measured re¯ections
7892 independent re¯ections
5773 re¯ections with I > 2ꢆ(I)
Rint = 0.028
ꢇmax = 28.8ꢀ
Compound (IV)
Crystal data
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.040
wR(F2) = 0.112
S = 1.00
7892 re¯ections
w = 1/[ꢆ2(Fo2) + (0.0534P)2
+ 2.0893P]
[Cu(C27H33N7O6)Cl]ClÁC2H6O
Z = 4
Dx = 1.512 Mg m
Mo Kꢂ radiation
ꢅ = 0.90 mm
T = 150 (2) K
Plate, green
0.23 Â 0.21 Â 0.07 mm
3
Mr = 732.11
Monoclinic, P21=c
2
where P = (Fo + 2Fc2)/3
1
Ê
Ê
a = 13.183 (5) A
(Á/ꢆ)max = 0.001
3
b = 14.485 (6) A
Ê
Áꢈmax = 0.50 e A
Ê
c = 16.914 (7) A
3
Ê
0.33 e A
455 parameters
H-atom parameters constrained
Áꢈmin
=
ꢃ = 95.319 (7)ꢀ
Ê
V = 3216 (2) A
3
Table 4
Selected geometric parameters (A, ) for (VI).
Data collection
ꢀ
Ê
Bruker SMART 1000 CCD area-
detector diffractometer
' and ! scans
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.819, Tmax = 0.940
22643 measured re¯ections
5657 independent re¯ections
3256 re¯ections with I > 2ꢆ(I)
Rint = 0.103
Cu1ÐN21
Cu1ÐN11
2.0124 (19)
2.0093 (18)
Cu1ÐN31
Cu1ÐN1
2.0326 (17)
2.1965 (19)
ꢇmax = 25.0ꢀ
N21ÐCu1ÐN11
N21ÐCu1ÐN31
N11ÐCu1ÐN31
121.49 (8)
119.13 (7)
117.34 (7)
N21ÐCu1ÐN1
N11ÐCu1ÐN1
N31ÐCu1ÐN1
94.59 (8)
94.67 (7)
95.00 (7)
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.055
wR(F2) = 0.153
S = 0.98
5657 re¯ections
416 parameters
H-atom parameters constrained
w = 1/[ꢆ2(Fo2) + (0.0768P)2]
where P = (Fo2 + 2Fc2)/3
For all three compounds, H atoms were inserted in calculated
positions and re®ned using a riding model. The constrained distances
Ê
were 0.95, 0.99, 0.98, 0.93 and 0.84 A for aryl, methylene, methyl,
amine and alcohol H atoms, respectively. They were re®ned with
(Á/ꢆ)max < 0.001
3
Ê
Áꢈmax = 0.63 e A
3
Ê
0.76 e A
Áꢈmin
=
[Cu(C27H27N7O6)]+, [Cu(C30H33N7O6)]+ and [Cu(C27H33N7O6)Cl]+ m475
ꢁ
Acta Cryst. (2006). C62, m472±m476
Coyle et al.

metal-organic compounds
Bruker (1998). SMART (Version 5.625) and SAINT (Version 6.28). Bruker
AXS Inc., Madison, Wisconsin, USA.
Coyle, J. L. (1999). PhD thesis, Open University, Milton Keynes, England.
Drew, M. G. B., Farrell, D., Morgan, G. G., McKee, V. & Nelson, J. (2000). J.
Chem. Soc. Dalton Trans. pp. 1513±1519.
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Fujinami, S., Suzuki, M. & Kitagawa, T. (2004). Bull. Chem. Soc. Jpn, 77, 59±
72.
Uiso(H) = 1.2Ueq(carrier atom). The value of Rint for complex (IV) is
high (0.103) due to poor crystal quality resulting in broad diffraction
peaks.
For all compounds, data collection: SMART (Bruker, 1998); cell
re®nement: SMART; data reduction: SAINT (Bruker, 1998);
program(s) used to solve structure: SHELXS97 (Sheldrick, 1997);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);
molecular graphics: SHELXTL (Sheldrick, 2001); software used to
prepare material for publication: SHELXTL.
The authors thank the Leverhulme Foundation, Unilever
Research and Development and the Open University for
support. They also acknowledge the use of the EPSRC
Chemical Database Service at Daresbury.
Liu, S., Gelmini, G., Rettig, S. J., Thompson, R. C. & Orvig, C. (1992). J. Am.
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Chim. Acta, 324, 173±179.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SQ3035). Services for accessing these data are
described at the back of the journal.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of
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Gottingen, Germany.
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m476 Coyle et al. [Cu(C27H27N7O6)]+, [Cu(C30H33N7O6)]+ and [Cu(C27H33N7O6)Cl]+
Acta Cryst. (2006). C62, m472±m476
ꢁ