Towards a system for the systematic structural study of intermolecular interactions in crystals of transition metal complexes

Article abstract of DOI:10.1039/b503381k

Pseudo-macrocyclic complexes of copper(II), and in one instance nickel(II), incorporating the bidentate ligands methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro- 1H-imidazol-2-yl)imidocarbamateand N,N-dimethyl-N′-(4-oxo-5,5-diphenyl-4, 5-dihydro-1H-imidazol-2-yl)guanidine are reported and their X-ray structures compared with those previously reported for related complexes of two N-(4-oxo- 5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)alkanimidamides. A feature of these complexes is that they are capable of forming hydrogen bonded chains or chains in which adjacent complexes are linked by phenyl 'embraces'. Changes in supramolecular structure arising from small changes in ligand structure or on crystallisation from different solvents are also discussed. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b503381k

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F U L L P A P E R
Towards a system for the systematic structural study of
intermolecular interactions in crystals of transition metal complexes†
Michael M. Bishop,a,b Leonard F. Lindoy,*a Andrew Parkina,c and Peter Turnera
a Centre for Heavy Metals Research, School of Chemistry, University of Sydney, NSW, 2006,
Australia
b Sydney Grammar School, College Street, Darlinghurst, NSW, 2010, Australia
c Department of Chemistry, University of Glasgow, Glasgow, UK G12 8QQ
Received 7th March 2005, Accepted 7th June 2005
First published as an Advance Article on the web 29th June 2005
Pseudo-macrocyclic complexes of copper(II), and in one instance nickel(II), incorporating the bidentate ligands methyl
N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)imidocarbamate and N,N-dimethyl-Nꢀ-(4-oxo-5,5-diphenyl-
4,5-dihydro-1H-imidazol-2-yl)guanidine are reported and their X-ray structures compared with those previously
reported for related complexes of two N-(4-oxo- 5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)alkanimidamides. A
feature of these complexes is that they are capable of forming hydrogen bonded chains or chains in which adjacent
complexes are linked by phenyl ‘embraces’. Changes in supramolecular structure arising from small changes in ligand
structure or on crystallisation from different solvents are also discussed.
Introduction
There has been a growing interest in the rational design
of crystals incorporating transition metal complexes that are
present as metal coordination polymers or for which hydrogen
bonding and/or other interactions link coordinated ligands.1
Such products constitute a category of new materials that show
promise for a range of applications that include the uptake or
exchange of guest molecules and ions for separation or sensing
applications and the potential to act as catalytic frameworks
of the ‘synthetic zeolite’ type. Clearly the need for the targeted
design (and synthesis) of new products of this type, displaying
specific structures, remains an activity of more than intrinsic
interest.
In earlier papers we have described the incorporation of
a number of transition metal complexes into supramolecu-
lar arrays that incorporate complementary hydrogen bonding
motifs.2–6 In these arrays the complexes occur in two- or three-
component subunits, or as chains, which then interact further
by hydrogen bonding or other intermolecular interactions to
form more elaborate structures. For example, we have previously
investigated complexation by selected members of the ligand
series listed in Scheme 1—a series that seems well suited for use in
a comparative structural study of supramolecular interactions in
crystals of transition metal complexes. Thus we have reported the
synthesis and structures of the copper(II) complexes 1, 2a and 2b
(see Scheme 2) containing two bidentate N-(4-oxo-5,5-diphenyl-
4,5-dihydro-1H-imidazol-2-yl)alkanimidamide ligands.6
Scheme 2
properties, are also readily available allowing one to ‘tune’
the system, with changes being possible both close to and
remote from the metallo-rings. Nevertheless, it needs to be noted
that one synthetic limitation in the preparation of individual
members of such a ligand family is that the diketone precursor
must be capable of undergoing a benzilic acid rearrangement;
Scheme 1
this rules out, for example, the use of butanedione and pyridil.7,8
On coordination, ligands of the present type will readily
The synthesis of the ligands of the latter type is straight-
lose a proton from N(3) (see Scheme 1) to form neutral
forward and the related ligand derivatives of the type shown
complexes with a suitable metal ion. The generation of neutral
in Scheme 1, differing only slightly in steric and electronic
complexes will tend to limit additional structural complexity
(from hydrogen bonding, solvation and/or steric effects) arising
from the presence of counter ions in the crystal.9 For example,
† Electronic supplementary information (ESI) available: Additional
crystallographic data. See http://dx.doi.org/10.1039/b503381k
T h i s j o u r n a l i s
each coordinated ligand in 1, 2a and 2b has only one metal bound
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 2 5 6 3 – 2 5 7 1
2 5 6 3
©

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=
NH group and in the bis-ligand complexes the hydrogen from
(Dimethyl sulfoxide)bis(methyl N-(4-oxo-5,5-diphenyl-4,5-
this group is hydrogen bonded to the carbonyl group of the
second ligand, forming a pseudo-macrocyclic ring (Scheme 2).
This neatly removes these hydrogens from being potential
hydrogen bond donors to neighbouring molecules or ions.
It also means that the self-complementary donor–acceptor
(DA) motif encompassing N(2) and N(3) is the only potential
(intermolecular) hydrogen bonding group present on the ligand.
The above self-complementary motif can be ‘switched off’
by protonation of N(3) or by steric influence arising from the
presence of a bulky X group (Scheme 1). Such steric interference
will always be present when X = –NR2 but will depend on the
conformation adopted when X = –OR. The above doublet motif
can be expanded to a triplet, DDD or DAD, depending on the
protonation present and if X = –NHR and the R group is syn
with respect to the coordinated imino group.
dihydro-1H-imidazol-2-yl)imidocarbamato)copper(II), 3c, and
bis(methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-
yl)imidocarbamato)copper(II)-2-dimethyl sulfoxide, 3d
Cu(ClO4)2·6H2O (0.094 g, 0.25 mmol) was dissolved in methanol
(15 mL) at room temperature and the solution heated to boiling.
Ligand 6 (0.139 g, 0.5 mmol) was added to the boiling solution.
The mixture was heated under reflux for 4 h. The solution was
removed from the heat and conc. aqueous ammonia (2 mL)
was added slowly. A pink powder, which formed immediately,
was isolated and washed with methanol (2 × 5 mL) and Et2O
(2 × 5 mL) and air-dried. Yield: 0.074 g, 44%. Drying over
silica gel at room temperature gave a solid that analysed as the
hemihydrate of bis(methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-
1H-imidazol-2-yl)imidocarbamato)copper(II) (Found: C, 59.42;
H, 4.55; N, 16.31. Calc. for C34H30CuN8O4.1 H2O: C, 59.25;
H, 4.49; N, 16.14%). Crystallisation of the pi2nk powder from
DMSO gave purple crystals of 3c mixed with a small amount
of a second pink phase 3d. X-Ray diffraction studies (see
later) showed that 3c was [Cu(C17H15N4O2)2DMSO] and 3d was
[Cu(C17H15N4O2)2]·2DMSO.
Whether hydrogen bonding is present or not, phenyl–phenyl
interactions, offset face-to-face (OFF), edge-to-face (EF) or
more complicated supramolecular motifs such as an (OFF)(EF)2
‘embrace’ may occur; it is noted that the energies of such
interactions can approach that for hydrogen bonding. Alkyl to
p-facial interactions may also occur.10 Solvent may also play
a role in the crystal and will have its own steric requirements;
typically it may be present coordinated to the metal or hydrogen
bonded to the coordinated ligands or, alternatively, may simply
interact with the ligand phenyl groups.
In this paper we present the results of an investigation of
structure–function relationships with respect to the supramolec-
ular structures of four complexes (3a–d) of methyl-N-(4-oxo-
5,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)imidocarbamate in
both its neutral and anionic forms, and two (4a, 4b) of the an-
ionic form of the ligand N,N-dimethyl-N’-(4-oxo-5,5-diphenyl-
4,5-dihydro-1H-imidazol-2-yl)guanidine (Scheme 2). In this
context we also discuss methoxyiminocimetidine-N,Nꢀ,Nꢀꢀ,S-
perchloratocopper(II) perchlorate, 5, whose X-ray structure was
re-determined as part of the present study.
Bis(N,N-dimethyl-Nꢀ-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-
imidazol-2-yl)guanidino)copper(II)-2-dimethyl sulfoxide, 4a, and
bis(N,N-dimethyl-Nꢀ-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-
imidazol-2-yl)guanidino)nickel(II)-2-dimethyl sulfoxide, 4b
Complexes 4a and 4b were prepared by the same method. The
ligand, 7, (0.321 g, 1 mmol) was dissolved in boiling ethanol
(60 mL). To this solution was added an aqueous ammoniacal
solution of the hydrated metal chloride (0.5 mmol). A purple
precipitate formed immediately and was filtered off when the
precipitation was complete. The solid was washed with alcohol
(2 × 5 mL) and Et2O (2 × 5 mL) and air dried. Yields: 4a,
0.300 g, 43%; 4b, 0.295 g, 42%. (4a, Found: C, 56.05; H, 5.55;
N, 16.33. Calc. for C36H36CuN10O2·2DMSO: C, 55.83; H, 5.62;
N, 16.28%; 4b, Found: C, 56.47; H, 5.61; N, 16.35. Calc. for
C36H36NiN10O2·2DMSO: C, 56.14; H, 5.65; N, 16.37%.).
Experimental
4-Oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-ylcyanamide, 6
Methoxyimino-cimetidine-N,Nꢀ,Nꢀꢀ,S-perchloratocopper(II)
perchlorate, 5
This was prepared in 66% yield from benzil and dicyandiamide
as described previously.11
This was prepared by the literature procedure13 and involved the
heating a 1 : 1 mixture of cimetidine and copper(II) perchlorate
in methanol at reflux temperature.
N,N-Dimethyl-Nꢀ-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-
imidazol-2-yl)guanidine, 7
CAUTION: perchlorate complexes are potentially explosive
and appropriate caution should be exercised in their synthesis
and handling.
This was prepared in 85% yield by the reaction of benzil and
N,N-dimethylbiguanide in the presence of sodium ethoxide as
reported previously.12
Bis(methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-
yl)imidocarbamate)copper(II) perchlorate-2-methanol, 3a, and
bis(methyl N-(4-oxo-5,5-diphenyl-4,5-dihydro-1H-imidazol-2-
yl)imidocarbamato) copper(II)-1-methanol, 3b
X-Ray structure determinations
Data for the seven crystal structures were collected at 150 K
˚
to approximately 0.75 A resolution, on a Bruker SMART
1000 CCD diffractometer equipped with an Oxford Cryostems
Cu(ClO4)2·6H2O (0.095 g, 0.25 mmol) was dissolved in boiling
methanol (15 mL) and 6 (0.138 g, 0.5 mmol) was added to
the boiling solution. The mixture was heated under reflux for
3 h during which time a deep blue colour developed. The
solution was allowed to cool and large blue crystals of 3a
formed. A crystal from this batch was employed for an X-
ray structure determination. Pink crystals of a second product,
3b, also subsequently formed on letting the methanol solution
containing the blue crystals of 3a stand. Over time the blue
crystalline solid disappeared and was replaced by the pink. A
(pink) crystal from this batch was also employed for a second X-
ray structure determination. The methanol solvate present in the
crystals was lost on drying over silica gel at room temperature
(Found: C, 60.24; H, 4.58; N, 16.60. Calc. for C34H30CuN8O4: C,
60.21; H, 4.46; N, 16.53%).
cryostat14 and employed graphite monochromated MoKa radi-
˚
ation (0.71073 A) from a sealed tube. Data were integrated using
SAINT15 and subsequent computations were carried out with
the teXsan,16 WinGX17 and XTAL18 graphical user interfaces. A
Gaussian absorption correction15,19 was applied to compounds
3a, 3c, 4a, 4b and 5, and a multi-scan absorption correction20
based on the method of Blessing21 was applied to 3b and 3d. All
structures were solved by direct methods using either SIR9722
(3a, 3c, 4a, 4b and 5) or SHELXS23 (3b and 3d) and extended and
refined against F2 using SHELXL97.23 Final refinement data
are listed in Table 1, and details of hydrogen bond geometries
are given in Table 3. ORTEP24 depictions are shown in Figs. 1
and 2. The non-hydrogen atoms were modelled with anisotropic
displacement parameters and a riding atom model was used
for the hydrogen atoms. Amine hydrogen sites were located and
2 5 6 4
D a l t o n T r a n s . , 2 0 0 5 , 2 5 6 3 – 2 5 7 1

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modelled with isotropic displacement parameters. Refinement
variations are given below for individual structures.
3a. The asymmetric unit contains the complex located on
an inversion centre, a perchlorate counter ion and a methanol
solvate molecule. Distance restraints were used for H(2N) and
H(3N).
3b. The non-hydrogen atoms in the asymmetric unit were
modelled with anisotropic displacement parameters. Idealised
hydrogen positions were calculated for the methanol and allowed
to ride on the parent atoms. The methanol solvent was refined
as disordered over a crystallographic inversion centre, and the
hydroxyl hydrogen atom was geometrically placed in a position
so that it was oriented towards the nearest region of high electron
density (O1), thus forming a long hydrogen bond. This hydrogen
atom was refined as a riding group.
4a. The asymmetric unit contains the complex located on
an inversion centre, and a dimethyl sulfoxide solvate molecule.
Distance restraints were used for H(2N) and H(4N).
The asymmetric unit contains the complex located on an
inversion centre, and a dimethyl sulfoxide solvate molecule.
Distance restraints were used for H(2N) and H(4N).
5. The asymmetric unit contains the complex molecule and
two perchlorate counter ions. Distance restraints were required
for H(11), H(3N) and H(6N).
CCDC reference numbers 265654–265660.
See http://dx.doi.org/10.1039/b503381k for crystallographic
data in CIF or other electronic format.
Results and discussion
Crystallographic details for the structurally characterised com-
plexes are listed in Table 1, pertinent geometrical details are
given in Table 2 and a summary of hydrogen bond interactions
is given in Table 3. More detailed geometric data is available as
ESI.† ORTEP24 depictions are provided in Fig. 1 and Fig. 2. The
methods employed for preparation of the ligands and complexes
are summarised in Scheme 3.
Scheme 3
Structure 3a contains a square planar, pseudo-macrocyclic
copper(II) complex dication, with the metal residing on an
inversion site. The copper–N(imidazole) bonds are slightly
longer than for copper–N(imine) (Table 2a) and there is weak
perchlorate ion coordination, with O(6) occupying a distorted
˚
octahedral site 2.8147(14) A from the metal centre. Each ligand
is approximately planar and the methoxy group lies in the plane
in its syn conformation, as expected.25 The ligand atoms N(1),
C(1), C(2), N(2), C(3), N(3), C(4), N(4) are approximately co-
planar, with minimum and maximum deviations of 0.1668(16)
˚
˚
A and 0.1037(13) A respectively; the accordingly defined least
D a l t o n T r a n s . , 2 0 0 5 , 2 5 6 3 – 2 5 7 1
2 5 6 5

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Table 2 Selected metal environment geometry details for compounds 3a–d and 4a and 4b. M represents Cu in structures 3a–d and 4a, and Ni in 4b
˚
(a) Coordination bond (M–N) lengths in A
M(1)–N(1)
2.0396(12)
2.0322(16)
2.0468(17)
2.034(2)
M(1)–N(4)
1.9367(13)
1.9251(16)
1.931(2)
1.897(2)
1.9041(17)
1.8679(19)
M(1)–N(5)
—
—
2.0495(18)
2.033(2)
—
M(1)–N(8)
—
—
1.936(2)
1.908(2)
—
3aa,b
3ba
3cc
3d
4aa
4ba
2.0458(15)
1.9652(18)
—
—
(b) Coordination bond angles in ◦
N(1)–M(1)–N(4)
N(1)–M(1)–N(5)
180
180
176.69(7)
174.28(8)
180
N(1)–M(1)–N(8)
91.99(5)
92.33(7)
93.16(8)
93.32(9)
92.52(7)
91.88(8)
N(4)–M(1)–N(5)
—
—
91.85(8)
92.15(8)
—
N(4)–M(1)–N(8)
180
N(5)–M(1)–N(8)
—
3aa
3ba
3c
88.00(5)
87.67(7)
87.12(8)
87.24(9)
87.53(7)
88.12(8)
180
—
171.74(8)
175.74(10)
180
87.41(8)
87.71(8)
—
3d
4aa
4ba
180
—
180
—
a Structures 3a, 3b, 4a and 4b all contain the metal atom sited on a crystallographic inversion centre; in these cases N5 is symmetry related by
this inversion centre to N1 and N4 is symmetry related to N8. Values are not reported for non-independent values. Note that in these cases angles
N(1)–M(1)–N(5) and N(4)–M(1)–N(8) are constrained to be 180◦, and N(4)–M(1)–N(5) is constrained to be the same as N(1)–M(1)–N(8). b Structure
3a also contains a perchlorate oxygen atom in an apical coordination site, with a Cu(1)–O(6) bond length of 2.815(2) A. c Structure 3c also contains
˚
˚
an oxygen in an apical coordination site, with a Cu(1)–O(5) bond length of 2.4013(17) A.
Table 3 Hydrogen bond summary
DHA Angle/◦
˚
˚
˚
Donor
Hydrogen
Acceptor
D–H/A
H–A/A
D–A/A
3a
O(7)
O(7)
N(2)
N(3)
N(4)
3b
H(7O)
H(7O)
H(2N)
H(3N)
H(4N)
O(3a)
O(5a)
O(5a)
O(7)
0.84
0.84
0.806(16)
0.797(16)
0.80(2)
2.10
2.52
2.035(17)
1.974(17)
2.01(2)
2.928(2)
3.022(2)
2.8278(18)
2.7633(18)
2.7576(17)
167.6
119.5
167.5(18)
170.7(18)
156.3(19)
O(1b)
N(4)
N(2)
3c
N(2)
N(4)
N(8)
N(6)
3d
H(4N)
H(2N)
O(1c)
N(3d)
0.83(3)
0.84(3)
1.99(3)
2.15(3)
2.748(2)
2.987(2)
152(2)
172(3)
H(2N)
H(4N)
H(8N)
H(6N)
N(7e)
O(3)
O(1)
N(3f)
0.72(2)
0.80(2)
0.79(2)
0.799(16)
2.23(2)
2.05(2)
2.07(2)
2.144(17)
2.938(3)
2.788(2)
2.782(3)
2.938(3)
170(2)
153(2)
150(2)
173(3)
N(8)
N(4)
N(2)
N(6)
H(8)
H(4)
H(2)
H(6)
O(1)
O(3)
O(6)
O(5)
0.88
0.88
0.88
0.88
2.03
1.95
1.95
1.92
2.788(3)
2.748(3)
2.777(3)
2.764(3)
144.0
150.0
155.6
160.4
Symmetry operators: a x − 1/2, −y + 1/2, z − 1/2; b −x + 2, −y, −z + 1; c −x, −y, −z; d −x, −y, −z − 1; e x, −y + 1/2, z − 1/2; f x, −y + 1/2,
z + 1/2.
4a
N(2)
N(4)
4b
H(2N)
H(4N)
O(2)
0.806(19)
0.773(18)
2.115(19)
2.084(19)
2.913(2)
2.798(2)
171(2)
154(2)
O(1a)
N(2)
N(4)
H(2N)
H(4N)
O(2)
0.840(10)
0.837(10)
2.050(11)
1.941(15)
2.882(3)
2.717(2)
171(3)
154(3)
O(1a)
Symmetry operators: a −x, −y + 1, −z + 1.
5
N(2)
N(1)
N(3)
N(6)
N(6)
H(2N)
H(1N)
H(3N)
H(6N)
H(6N)
O(8a)
O(6)
0.77(2)
2.51(2)
3.240(3)
3.055(2)
3.194(3)
3.190(3)
3.190(3)
160(2)
151(2)
145(2)
148(2)
144(2)
0.819(15)
0.806(15)
0.788(16)
0.788(16)
2.314(18)
2.502(19)
2.50(2)
O(7b)
O(2c)
O(4c)
2.52(2)
Symmetry operators: a −x + 1, y + 1/2, −z + 1/2; b x − 1, y, z; c −x + 1, −y, −z.
squares ligand plane makes an angle of 9.67(4)◦ with the plane
The supramolecular structure shows the complexity that can
of the four nitrogen donor atoms. The structure also exhibits a
long contact between the central metal atom and the perchlorate
counterion, forming a [4 + 2] coordination sphere, with Cu(1)–
attend the inclusion of counter ions in the crystal. The perchlo-
rate ion and a methanol solvent molecule are hydrogen bonded
to the protonated nitrogen atoms N(2) and N(3) in a R3 (10)
3
˚
O(6) distance of 2.815(2) A. Further details of the geometry are
pattern as shown in Fig. 1. This results in an extended layer of
pseudo-macrocycles in two different orientations linked into a
listed in Tables 2 and 3.
2 5 6 6
D a l t o n T r a n s . , 2 0 0 5 , 2 5 6 3 – 2 5 7 1

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Fig. 1 ORTEP24 depictions of complexes 3a–3d, showing 20% displacement ellipsoids. A methanol molecule in b, which is disordered over a
crystallographic inversion centre, has been omitted. Dotted lines indicate hydrogen bonds.
network by hydrogen bonding and electrostatic (weak) coordi-
nation interactions with the perchlorate ions and methanol. The
layers are ‘linked’ to one another by centrosymmetric methyl–
p facial interactions between ligands; the average C(methyl)–
C(phenyl) distance is 3.79 A. The complexes so linked form
chains quasi-parallel to the a-axis. It is worth noting that the
are further involved in OFF and EF interactions between the
chains.
The methanol in the crystal, which lies on an inversion site
and is disordered, is not coordinated or involved in hydrogen
bonding but lies amongst the phenyl rings as shown in Fig. 4.
The change of conformation from that expected for the above
system prompted us to re-determine the structure of 5, in which
hydrogen bonding might be expected to occur but for which the
crystal data only, but not the atomic coordinates, were available
in the Cambridge Structural Database.27 From the structure
it is clear that the methoxy methyl conformation is syn, as
is expected for the coordinated neutral ligand (protonated on
N(3)) and different from the anti conformation observed for the
anionic ligand 628 (Scheme 4). The N-methyl group is anti; all the
hydrogen bonds are rather long (Table 3). The supramolecular
structure is depicted in Fig. 5.
˚
most advantageous intermolecular C–C distance is not the sum
˚
˚
of the van der Waals radii (3.4 A) but some 0.3–0.4 A longer.
For offset face-to-face interactions the distance is even greater.
In fact, the intermolecular potential becomes zero, or slightly
destabilising, at the van der Waals distance.26
Structure 3b forms spontaneously at the expense of 3a when
the latter is allowed to stand in the crystal growth solution. Like
3a, 3b contains square planar copper(II), with each copper at an
inversion site, but this time each complex is neutral. The least
squares ligand plane makes an angle of 5.24(6)◦ with the plane
of the four nitrogen donor atoms (see also Table 2b). The supra-
molecular structure, however, is much simpler than before and
much simpler too than that of the apparently similar 2a. The
latter contains three crystallographically distinct complexes and
two different chains intricately interlocked.6 The DA (donor–
acceptor) hydrogen bonding motif is self-complementary so that
When 2a was crystallised from DMSO, the hydrogen bonded
chains did not re-form but instead crystals of 2b grew from the
solution.
in 3b chains of complexes, linked by R2 (8) patterns, form quasi-
2
parallel to the c-axis (Fig. 3).
The formation of the chains results in the methoxy group
being in its syn conformation instead of being anti as would
be expected for the corresponding anionic ligand. The methyl
group is twisted 8◦ out of the plane of the ligand. It is also
interesting that the conformations of the phenyl rings are quite
different from those present in 1, 2a and 2b. In the present case
one of the phenyl groups forms a C(11)H · · · O(2) interaction
◦
˚
(3.36 A, 165 ) while the other makes a p-facial interaction with
˚
the terminal methyl group (average C–C distance: 4.05 A). This
suggests that the twisting of the chains observed for 2a reflect the
steric requirements of the ethyl side chain. The phenyl groups
Scheme 4
D a l t o n T r a n s . , 2 0 0 5 , 2 5 6 3 – 2 5 7 1
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Fig. 3 A PLATON29 depiction of part of a chain in 3b and the
interactions between neighbouring complexes within a chain.
Fig. 4 A PLATON29 depiction of the unit cell of 3b, viewed down the
c-axis. The hydrogen atoms of the disordered methanol molecules are
not shown.
Fig. 2 An ORTEP24 depiction of complexes 4a, 4b and 5 showing 20%
displacement ellipsoids. Dotted lines indicate hydrogen bonds.
The neutral complexes of type 3, which have methoxy instead
of ethyl groups, behave differently to the above. The major
crystalline form, 3c, contains hydrogen bonded chains. There
is also a small amount of a second phase, 3d, formed (Table 2).
This minor phase resembles 2b in that it consists of discrete three-
component units made up of the complex and two molecules
of DMSO hydrogen bonded to the protons on N(2) and N(6).
This behaviour is also consistent with the postulate that it will be
more difficult to accommodate the ethyl group than the methoxy
group in the hydrogen bonded chains.
Interestingly each copper ion in 3c is five coordinate, with a
DMSO molecule occupying its apical site. This arrangement
resembles that present in 1. The maximum and minimum
Fig. 5 A PLATON29 depiction of 5 showing the complex–perchlorate
chains quasi-parallel to the b-axis and the long hydrogen bonded
NH · · · O chains quasi-parallel to the a-axis.
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Fig. 6 A PLATON29 depiction of the unit cell of 3c, viewed down the a-axis.
deviations of the four nitrogen donor atoms from their least
the nitrogen donor atoms from their least squares plane being
˚
˚
˚
squares plane are 0.046(3) and 0.036(2) A and Cu(1) lies
0.094(3) and 0.078(3)A; Cu(1) lies 0.0229(10) A from the plane.
The least squares ligand planes subtend angles of 6.44(7)◦ and
3.60(6)◦ with the nitrogen donor plane. The conformation of
the methoxy group is now anti as expected for the presence
of an anionic ligand (and contrasts with the syn conformation
observed in 3b and 3c).
The three-component unit in 2b is interesting in that the two
‘ends’ of the unit differ with respect to the orientation of the
hydrogen bonded DMSO, the X side chain conformation as
well as the orientation of the phenyl groups. In the absence of
hydrogen bonding between complexes, chains linked by phenyl–
phenyl interactions are formed. Two such types of interaction
alternate: a centrosymmetric CH–p facial dimer interaction and
an OFF(EF)2 embrace.
˚
0.0932(10) A from the plane. The least squares ligand plane make
angles of 10.82(6)◦ and 12.63(6)◦ with the plane of the nitrogen
donor atoms. The hydrogen bonded chains have a slightly wave-
like disposition relative to the c-axis (Fig. 6) and the orientation
of the coordination pyramids in the chains has a different pattern
from that in 1 (Scheme 5).
Although the two ends of the three-component unit of 3d are
crystallographically distinct, both DMSO molecules in the unit
are oriented in a similar manner, with the DMSO methyl groups
pointing back towards the centre of the complex and with one
of the methyl groups of each DMSO making a methyl–p-facial
phenyl contact within the unit. The methoxy methyl group is
in the anti conformation. This arrangement is similar to that
found in 2b which is associated with the OFF(EF) embrace;
in the present case, the same motif is observed and leads to
the formation of chains running quasi-parallel to the a-axis.
The motif is not centrosymmetric. The chains are illustrated in
Fig. 7 and a space-filling model of the motif is shown in Fig. 8.
Between the chains there are further methyl–p facial interactions
involving both DMSO molecules, C(37), and methoxy, C(5),
methyl groups and again both faces of the benzene ring interact
with methyl groups.
Scheme 5
The hydrogen bonds in 3c are slightly shorter than those
in 1 but similar to those in 3b. The orientation of the phenyl
groups is different from that in 3b; they interact with others
from neighbouring chains as well as with the DMSO methyl
groups of adjacent complexes. Adjacent chains appeared linked
by DMSO methyl to phenyl p-facial interactions and by phenyl
EF and OFF interactions.
Structure 3d, at least superficially, resembles that of 2b, in that
the complexes are not linked into chains but rather form three-
component systems with DMSO molecules acting as hydrogen
bond acceptors. The copper coordination is approximately
square planar, with the maximum and minimum deviation of
The crystal structures of 4a and 4b show them to be
isostructural (Tables 1, 2 and 3). The metal ions again have
square planar geometries with the metal ions located at inversion
sites. In both complexes the least squares ligand planes make
angles of 6.11(6)◦ (4a) and 7.73(7)◦ (4b) with the nitrogen donor
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form three-component units with DMSO molecules hydrogen
bonded to the proton on N(2), with the orientation of the
DMSO molecules differing from that in 3d. In 4, the DMSO
methyl groups are oriented away from the metal (in the same
manner as the disordered DMSO methyl groups in 2b and
there are no methyl–phenyl–p-facial contacts within the three
component units).
Instead of hydrogen bonded chains, the complexes form
chains linked by centrosymmetric pairs of aromatic CH · · · p-
facial interactions as shown in Fig. 8 and Fig. 9. The interactions
are of the same type as observed in 2b. In addition, each of the
remaining six faces of the four phenyl rings in the motif has
a methyl group (–NMe from a ligand, C(5), the anti methyl,
or –SMe from a DMSO molecule C(19)) interacting with it
(Fig. 10).
Fig. 9 A PLATON29 depiction of one of the chains of complexes for 4a
linked by the synthon consisting of a centrosymmetric pair of aromatic
CH to p-facial interactions.
Concluding remarks
Fig. 7 A PLATON29 depiction of 3d looking down the b-axis. Chains,
quasi-parallel to the a-axis, formed by (OFF)(EF)2 interactions and the
methyl–p facial–methyl interactions between neighbouring chains are
also shown.
The structures of six pseudo-macrocyclic complexes of similar
ligands that possess potential self-complementary hydrogen
bonding doublet DA motifs have been examined. Where linking
of these motifs is not prevented by solvation of the motif or
by the steric requirements of the ligand, the complexes form
chains involving R2 (8) hydrogen bond patterns. When hydrogen
2
bonding is not possible, phenyl embraces link the complexes
together. In all cases, the chains are offset from one another
in the crystal rather than forming ‘channels’. The rational
modification of the alignment of these chains by making small
structural changes to the ligand remains a goal of planned future
studies.
Other points of interest arising from the studies include: (i)
Hydrogen bonded chains in which the hydrogen bonded ligands
of adjacent complexes are approximately coplanar (1a, 3b, 3c)
were observed but the steric requirements of the ligands can
also cause twisting of the chains (2a). (ii) The five coordinate
complexes 1a and 3c show different ‘orientational’ motifs
within the chains. (iii) Where hydrogen bonding of the neutral
complexes is not possible because of solvation (2b, 3d) or the
steric requirements of the ligand (4), the complexes yield chains
involving the phenyl substituents in (OFF)(EF)2 embraces or
involve centrosymmetric aromatic CH to p-facial interactions,
or both. (iv) Complexes of different ligands differ in the ease
with which the hydrogen bonded form can be isolated from
a solution of the strong hydrogen bond acceptor, DMSO (2a,
2b and 3c, 3d). (v) Variation of the solvent or conditions of
crystallisation can also give rise to different supramolecular
structures (3a, 3b, 3c, 3d) with molecules of the respective
solvents incorporated in different ways. Finally, (iv) it is noted
that methyl groups attached to heteroatoms (O, N, S) exhibit
a tendency to form CH to p-facial contacts with ligand phenyl
rings.
Fig. 8 A PLATON29 depiction (CPK-style) of the two four-phenyl
motifs linking complexes into chains in 3b and 4a. DMSO molecules are
not shown.
planes. Although potential complementary doublet motifs are
present, the formation of hydrogen bonded chains is inhibited by
steric interference from the ligand-NMe2 groups. The complexes
Acknowledgements
We thank the Australian Research Council for support.
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Fig. 10 A PLATON29 depiction of 4a showing the intermolecular interactions. For clarity, only two DMSO molecules are shown.
16 teXsan for Windows: Single Crystal Structure Analysis Software,
Molecular Structure Corporation, The Woodlands, TX, USA, 1997–
1998.
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