Controlled formation and topologies of thiophenolate-based macrocycles: Rings, cylinders and bowls

Article abstract of DOI:10.1039/b512068c

The Schiff-base condensations of 1,3-diaminopropane with a protected thiophenol dialdehyde in the presence of Ni²⁺, Pd²⁺ or Zn²⁺ can be controlled to yield either mononuclear acyclic, or 2 + 2 and 4 + 4 macrocyclic complexes by the choice of both metal cation and counteranion. The Ni²⁺ complex of the 2 + 2 macrocycle contains two square-planar nickel ions and shows an arrangement similar to one observed previously: the μ-S atoms of the thiophenolate groups are pyramidal and lie on the same side of the plane defined by the four N atoms of the macrocycle to give a V-shaped molecule. By contrast, the Zn²⁺ complex of the 2 + 2 macrocycle undergoes oligomerisation to yield a bowl-shaped hexanuclear complex that includes a μ₃-carbonate anion. Essential for this topology is the presence of three μ₃-S-thiophenolato groups that link the three macrocyclic units to form a Zn₃S₃ ring that seals the bottom part of the bowl. In this arrangement, one of the pyramidal μ₃-S atoms in each dinuclear Zn²⁺ complex is inverted relative to the arrangement observed for the dinickel complexes. Molecular modelling suggests that inversion about the μ-S atoms of the 2 + 2 macrocyclic complexes is readily accessible at room temperature and that the contrasting arrangements observed for the Ni²⁺ and Zn²⁺ complexes are those energetically most favourable for the respective metal ions. Rare 4 + 4 macrocyclic complexes are isolated as neutral dinuclear complexes for Ni²⁺ and Pd²⁺ and as a tetranuclear complex cation for Zn²⁺. The topologies of these systems contrast significantly: those with two square-planar Ni²⁺ or Pd²⁺ ions form extended rings, while that with Zn²⁺ forms a sulfur-lined cylinder which hosts acetonitrile molecules in the crystalline state. Reaction conditions can also be optimised to produce 2 + 1 acyclic ligands as their mononuclear Ni ²⁺ and Pd²⁺ complexes, providing potentially useful building blocks for production of more complicated macrocyclic and supramolecular systems. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b512068c

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PAPER
www.rsc.org/dalton | Dalton Transactions
Controlled formation and topologies of thiophenolate-based macrocycles:
rings, cylinders and bowls
Aase Christensen, Christoph Mayer, Frank Jensen, Andrew D. Bond* and Christine J. McKenzie*
Received 24th August 2005, Accepted 14th October 2005
First published as an Advance Article on the web 7th November 2005
DOI: 10.1039/b512068c
The Schiff-base condensations of 1,3-diaminopropane with a protected thiophenol dialdehyde in the
presence of Ni2+, Pd2+ or Zn2+ can be controlled to yield either mononuclear acyclic, or 2 + 2 and 4 + 4
macrocyclic complexes by the choice of both metal cation and counteranion. The Ni2+ complex of the
2 + 2 macrocycle contains two square-planar nickel ions and shows an arrangement similar to one
observed previously: the l-S atoms of the thiophenolate groups are pyramidal and lie on the same side
of the plane defined by the four N atoms of the macrocycle to give a V-shaped molecule. By contrast,
the Zn2+ complex of the 2 + 2 macrocycle undergoes oligomerisation to yield a bowl-shaped
hexanuclear complex that includes a l3-carbonate anion. Essential for this topology is the presence of
three l3-S-thiophenolato groups that link the three macrocyclic units to form a Zn3S3 ring that seals the
bottom part of the bowl. In this arrangement, one of the pyramidal l3-S atoms in each dinuclear Zn2+
complex is inverted relative to the arrangement observed for the dinickel complexes. Molecular
modelling suggests that inversion about the l-S atoms of the 2 + 2 macrocyclic complexes is readily
accessible at room temperature and that the contrasting arrangements observed for the Ni2+ and Zn2+
complexes are those energetically most favourable for the respective metal ions. Rare 4 + 4 macrocyclic
complexes are isolated as neutral dinuclear complexes for Ni2+ and Pd2+ and as a tetranuclear complex
cation for Zn2+. The topologies of these systems contrast significantly: those with two square-planar
Ni2+ or Pd2+ ions form extended rings, while that with Zn2+ forms a sulfur-lined cylinder which hosts
acetonitrile molecules in the crystalline state. Reaction conditions can also be optimised to produce
2 + 1 acyclic ligands as their mononuclear Ni2+ and Pd2+ complexes, providing potentially useful
building blocks for production of more complicated macrocyclic and supramolecular systems.
The relative paucity to date of thiophenolate macrocyclic
Introduction
systems may be attributed at least in part to synthetic difficulties
Multi-metallic macrocyclic complexes and metallomacrocycles are
associated with thiolates, particularly in the presence of redox-
of importance in diverse fields such as bioinorganic chemistry and
active metal ions. Thiolates are generally “non-innocent” ligands
supramolecular chemistry. They find numerous applications, for
with radical states that are readily accessible, especially if they
are attached to aromatic systems.4 In addition, they commonly
undergo oxygenation, also while bound to metal ions; such
behaviour is observed in the metalloenzyme nitrile hydratase,5 for
example, and also in its model complexes.6 Sulfur protecting-group
chemistry may be used to overcome these synthetic problems to
some extent. For example, we,7 and others,8,9 have described previ-
ously the preparation of dinickel complexes of ditopic macrocycles
containing two thiophenolate units (R = CH3 for the 2 + 2 ligands
depicted in Scheme 1). Our study produced the first example of
a macrocycle (LMe4+4) containing four thiophenolate units from
a 4 + 4 Schiff-base condensation. Further examples of 4 + 4
thiophenolate macrocycles have been reported since by Kersting
et al., incorporating amine nitrogen donors rather than imine.10
These latter compounds were prepared in a stepwise manner,
first by linking two thiophenolate dialdehyde moieties via an
ethylene bridge, then effecting reductive amination between two
of these units and four aliphatic diamines, amounting to a 2 + 4
reaction under high-dilution conditions. Metal complexes can be
prepared subsequently from the pre-formed macrocycle, and one
tetrametallic complex was isolated (Scheme 2). This elegant, but
rather more complicated, procedure contrasts to our one-pot 4
example in molecular magnetic materials and in metal-ion recog-
nition/binding for environmental purposes. In the last 40 years,
considerable work has been undertaken with Schiff-base macro-
cycles that contain phenolate bridging groups between metal
ions.1 By comparison, the chemistry of the related thiophenolate
macrocyclic systems has been less well explored. One expectation
is that these macrocycles will show a higher affinity for “soft”
transition-metal ions. Mononuclear transition-metal complexes of
soft metal ions (e.g. Wilkinson’s catalyst) are of tremendous impor-
tance as stereospecific catalysts in industrial and synthetic organic
chemistry. Catalysis by a dipalladium acyclic thiophenolate-based
complex with one exchangeable coordination site on each metal
ion has been demonstrated.2 A more recent important result in
this area is the report by Heyduk and Nocera3 who showed that
a dinuclear Rh complex catalyses reduction of protons to hydro-
gen. In general, however, development of effective multinuclear
transition-metal complexes as catalysts remains less advanced.
University of Southern Denmark, Department of Chemistry, Campusvej
55, 5230, Odense M, Denmark. E-mail: adb@chem.sdu.dk, chk_chem@
chem.sdu.dk; Fax: +45 6615 8780; Tel: +45 6550 2518
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constrained within a single molecule. In this report, we describe
further refinements of our one-pot procedure using slightly more
soluble homologues of the earlier systems (R = C(CH3)3 for the
ligands depicted in Scheme 1). We show that some control can be
achieved over the oligomerisation of the thiophenolate building
blocks in the presence of transition metal cations, providing multi-
metallic macrocyclic complexes directly.
Experimental
CAUTION! Although we encountered no problems during prepa-
ration of the perchlorate salts, care should be exercised when
handling these potentially explosive compounds. Solvents and
starting materials were used as supplied from commercial sources
and reactions were carried out in air unless otherwise specified.
Syntheses
(S)-(2,6-Diformyl-4-tert-butylphenyl)dimethylthiocarbamate.
2,6-Diformyl-4-tert-butylphenol14 is reacted with dimethylthio-
carbamoyl chloride to give the thiocarbamoyl-protected phenol.9
This compound undergoes a thermal rearrangement to the desired
◦
product by heating 8 g, 0.027 mol at 170 C under N2 for 1 h to
give a red melt. This is cooled to give a dark solid material, which
is dissolved in minimum CH2Cl2 (ca. 10 mL). EtOH is added until
onset of product precipitation and the mixture is left to stand in
an open flask. Yield (last step) 61%. Mp 132–133 ◦C. Anal. Calc.
for C15H19NO3S: C, 61.41; H, 6.53; N, 4.77; S, 10.93. Found: C,
1
61.47; H, 6.58; N, 4.72; S, 11.01%. H NMR (CDCl3) d 1.38 (s,
9H, CH3), 3.05 (s, 3H, CH3), 3.25 (s, 3H, CH3), 8.27 (s, 2H, ArH),
10.57 (s, 2H, CHO). 13C NMR (CDCl3) d 30.76 (C(CH3)3), 35.00
(C(CH3)3), 36.76 (N–CH3), 36.78 (N–CH3), 130.75 (ArC), 132.10
(SCN), 138.17 (ArCCHO), 154.37 (ArCC(CH3)3), 163.91 (ArCS),
190.67 (CHO). FABMS: m/z 316 ([C15H19NO3S + Na]+, 12%),
294 ([C15H19NO3S + H]+, 100%), 221 ([C15H19NO3S − C3H6NO]+,
39%).
Scheme
1
Ligands produced from metal-ion-templated Schiff-base
condensation of 1,3-propanediamine and (S)-(2,6-diformyl-4-tert-butyl-
phenyl)dimethylthiocarbamate (after removal of the sulfur protecting
groups, –CON(CH3)2).
[(10,23-Di-tert-butyl-13,26-dimercapto-2,6,15,19-tetraaza-1,7,
14,20-tetraene[7.7.7.7]metacyclophane)dinickel(II)] diperchlorate,
[Ni2(L2+2)](ClO4)2. 1,3-Diaminopropane,
(S)-(2,6-diformyl-4-
tert-butylphenyl)dimethylthiocarbamate and Ni(ClO4)2·6H2O
in (0.4 : 0.2 : 0.2 mmol) dissolved in 3–5 mL of methanol or
acetonitrile or MeOH–DMF (1 : 1) mixture was heated to boiling
point or ca. 100 ◦C for 15 min. The product crystallized in 30–50%
yield as red blocks. Three different crystalline solvates of the same
salt were obtained, depending on the solvent system. MALDI MS:
m/z 634 ([C30H38N4S2Ni2]+, 100%), 735 ([C30H38N4S2Ni2(ClO4)]+,
25%).
Scheme 2 Tetranickel tetrathiocyanato complex of the tetrathiolate
macrocycle prepared by Kersting et al. (n = 2 or 3).10
[ N,Nꢀ - Propane - 1,3 - diyl( 6 - formyl-4-tert-butyl-2-methylimin-
atothiophenolato)]nickel( II ), Ni( pfbtp ). 1,3-Diaminopropane
(0.1315 g, 1.78 mmol) and Ni(ClO4)2·6H2O (0.3227 g, 0.88 mmol)
were mixed in 5 mL DMF. (S)-(2,6-diformyl-4-tert-butylphenyl)-
dimethylthiocarbamate (0.301 g, 1.03 mmol) in 8 mL DMF was
added and the mixture was warmed at ca 100 ◦C for 10 min,
during which time the colour changed from olive green to dark
brown. The product was deposited as golden brown plates
over three days. Yield 203 mg, 43%. Anal. Calc. for Ni(pfbtp),
C27H32N2O2S2Ni: C, 60.12; H, 5.98; N, 5.19; S, 11.89. Found: C,
+ 4 condensation reactions in the presence of metal ions. To
our knowledge, the Kersting system and our system are the only
known M4(SR)4 systems in which all the bridging sulfur atoms
are part of a single organic ligand. Numerous examples exist
in the literature in which thiolate ligands and metal ions form
clusters of various nuclearities, with interesting topologies such as
cubanes,11 ladders12 and cyclized ladders.13 In general, however, the
thiolate donors in these cases originate from separate ligands so
that the self-assembly process has many more degrees of freedom
compared to the multitopic ligands in which the sulfur atoms are
1
60.19; H, 6.03; N, 5.27; S, 11.85%. H NMR (CDCl3) d 1.30 (s,
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18H, CH3), 2.11 (m, 2H, CH2); 3.99 (t, 4H, CH2), 7.44 (s, 2H,
ArH), 7.89 (s 2H, ArH), 7.91 (s, 2H, imine CH), 10.99 (s, 2H,
CHO). 13C NMR (CDCl3) d 26.57 (2C, C(CH3)4) 30.87 (6C, CH3)
34.23 (1C, CH2) 56.57 (2C, CH2) 129.70 (2C, Ar) 133.19 (2C, Ar)
135.62 (2C, Ar), 136.03 (2C, Ar), 145.19 (2C, Ar), 146.47 (2C,
Ar), 165.20 (2C, imine C), 192.25 (2C, CHO). FABMS: m/z 539.0
([C27H32N2O2S2Ni + Na+, 100%).
Tris[(10,23-di-tert-butyl-13,26-dimercapto-2,6,15,19-tetraaza-
1,7,14,20-tetraene[7.7.7.7]metacyclophane)dizinc]carbonato tetra-
perchlorate, [Zn6(L2+2)3(CO3)](ClO4)4. A mixture of (S)-(2,6-
diformyl-4-tert-butylphenyl)dimethylthiocarbamate (47 mg,
0.2 mmol) and 1,3-diaminopropane (14.8 mg, 0.2 mmol) in 3 mL
methanol was heated at reflux for 15 min during which time the
solution changed from orange to red. Zn(ClO4)2·6H2O (74 mg,
0.2 mmol) in 1 mL methanol was added and the colour changed
to an intense yellow. The mixture was heated under reflux for
30 min, and yellow crystals of the product were deposited on
standing in an open vessel. Yield 29 mg, 45%. ESIMS: m/z
324.7 ([Zn2(L2+2)]2+, 100%), 501.6 ([Zn6(L2+2)3(CO3)]4+, 90%),
679.4 ([Zn4(L2+2)2(CO3)]2+, 95%), 749.0 ([(Zn2(L2+2))(ClO4)]+,
[N,N-Propane-1,3-diyl(6-formyl-4-tert-butyl-2-methyliminato-
thiophenolato)]palladium(II), Pd(pfbtp). PdCl2 (34 mg, 0.2 mmol)
and 1,3-diaminopropane (45 mg, 0.6 mmol) were mixed in 10 mL
DMF and (S)-(2,6-diformyl-4-tert-butylphenyl)dimethylthiocar-
bamate (116 mg, 0.4 mmol) in 2 mL DMF was added. The
mixture was heated at ca. 100 ◦C for 15 min to give a dark
orange solution from which orange crystals of the product were
deposited. Yield 38 mg, 57%. MALDI MS: m/z 609.0 ([Pd(C27H32-
N2O2S2) + Na+, 100%), 587.0 ([Pd(C27H32N2O2S2)+, 30%), 627.0
([Pd(C27H32N2O2S2) + K+, 5%).
2+
70%), 1103.6 ({[Zn6(L2+2)3(CO3)](ClO4)2} , 8%), 1457.3
+
({[Zn4(L2+2)2(CO3)](ClO4)} , 6%).
Physical measurements
(10,23,36,49-Tetra-tert-butyl-13,26,39,52-tetramercapto-2,6,15,
1H and 13C NMR spectra were recorded on 300 MHz Varian
Gemini 2000 instrument, using TMS as an internal reference. IR
spectra were measured as KBr discs using a Hitachi 270–30 IR
spectrometer. UV-visible absorption spectra were recorded on a
Shimadzu UV-3100 spectrophotometer. FAB Mass spectra were
recorded on a Kratos MS-50 instrument. MALDI mass spectra
were obtained using a 4.7-T Ultima instrument (Ionspec, Irvine,
CA), using dihydroxybenzoic acid as matrix. ESI mass spectra
were recorded on a Finnigan TSQ 700 MAT triple quadrupole
instrument equipped with a nanoelectrospray source. Spectra were
obtained by spraying an acetonitrile solution from a coated needle
held at 0.8 kV, introduced to the mass spectrometer through
a capillary tube heated to 150 ◦C. Sample concentrations were
typically 0.3 mM. Although it may not be explicitly stated,
the isotope patterns of all m/z assignments have been checked
by comparison to the calculated theoretical patterns. Elemental
analyses were performed at the Chemistry Department II, Copen-
hagen University, Denmark and Atlantic Microlab, Inc., Norcross,
Georgia, USA.
19,28,32,41,45 - octaaza - 1,7,14,20,27,33,40,46 - octaene[ 7.7.7.7 ] -
metacyclophane)dinickel(II), Ni2(L4+4).
A
mixture of 1,3-
diaminopropane (118 mg, 1.6 mmol) and ammonium chloride
(9.7 mg, 0.18 mol) in methanol (10 L) was added to a solution
of Ni(pfbtp) (48.1 mg, 0.089 mol) dissolved in 7 mL warm
DMF. The mixture was heated under reflux for 15 min and
filtered. On standing, the product deposited as a dark brown
solid. Yield 30 mg, 58%. Anal. Calc. for C60H76N8S4Ni2: C, 62.40;
H, 6.63; N, 9.70. Found: C, 61.91; H, 6.78; N, 9.90%. FABMS:
m/z 1155 ([C60H76N8S4Ni2 + H]+, 100%), 1121 ([C60H76N8S4Ni +
Na + 2H]+, 22%), 528.0 ([C30H38N4S2Ni + 2H]+, 30%).
(10,23,36,49-Tetra-tert-butyl-13,26,39,52-tetramercapto-2,6,15,
19,28,32,41,45 - octaaza - 1,7,14,20,27,33,40,46 - octaene[ 7.7.7.7 ] -
metacyclophane)dipalladium(II), Pd2(L4+4). (S)-(2,6-Diformyl-
4-tert-butylphenyl)dimethylthiocarbamate (35 mg, 0.12 mmol)
in 6 mL DMF was added to a mixture of 1,3-diaminopropane
(178 mg, 2.4 mmol) and PdCl2 (21 mg, 0.119 mmol) in 5 mL
DMF. The reaction mixture was heated at ca. 150 ◦C for 15 min,
during which time the mixture clarified to a dark orange/red.
The solution was filtered and allowed to stand, depositing orange
crystals over several days. Yield 26 mg, 35%. Anal. Calc. for
C60H76N8S4Pd2·3DMF: C, 56.37; H, 6.66; N, 10.49; S, 8.73.
Found: C, 56.32; H, 6.59; N, 10.50, S, 8.69%. FABMS: m/z
1250.5 ([C60H76N8S4Pd2 + H]+, 47%), 625.0 ([C30H38N4S2Pd +
H]+, 100%).
Single-crystal X-ray diffraction
X-Ray diffraction data for Pd2(L4+4)·3DMF were collected at
120(2) K using a Siemens SMART CCD diffractometer (Technical
University of Denmark). All other diffraction data were collected
using a Bruker-Nonius X8APEX-II diffractometer, in most in-
stances at 180(2) K. In the case of Zn4(L4+4)(NO3)4·5CH3CN, the
crystal was cooled further in an effort to enhance the intensity of
the diffraction data, but cooling below ca. 150 K led to crystal
degradation; the reported data collection represents a viable
compromise. In all instances, graphite-monochromated Mo-Ka
(10,23,36,49-Tetra-tert-butyl-13,26,39,52-tetramercapto-2,6,15,
19,28,32,41,45 - octaaza - 1,7,14,20,27,33,40,46 - octaene[ 7.7.7.7 ] -
metacyclophane)tetrazinc(II) tetranitrate, Zn4(L4+4)(NO3)4.
A
mixture of (S)-(2,6-diformyl-4-tert-butylphenyl)dimethylthio-
carbamate (58 mg, 0.2 mmol) and 1,3-diaminopropane (14.8 mg,
0.2 mmol) in 2 mL methanol was heated at reflux for 15 min
during which time the solution changed from orange to red.
Zn(NO3)2·6H2O (56 mg, 0.2 mmol) in 1 mL methanol was
added and the colour changed to an intense yellow. After further
heating for 15 min, a solid began to precipitate. All solvent was
removed and the residue was dissolved in 5 mL acetonitrile. On
standing, crystals of Zn4(L4+4)(NO3)4·5CH3CN were deposited.
Yield 20 mg, 76%. Anal. Calc. for C60H76N12S4O12Zn4·5CH3CN:
C, 47.98; H, 5.23; N, 13.59. Found: C, 47.45; H, 5.00; N, 11.90%.
˚
radiation (k = 0.7107 A) was used. The structures were solved
by direct methods and refined against F2 using SHELXTL.15
H
atoms bound to C and N atoms were placed geometrically and
refined using a riding model. Selected crystallographic data are
summarized in Table 1.
The analysis and structure refinement of each nickel complex
was straightforward. In the refinement of [Ni2(L2+2)](ClO4)2·
1
1 DMF· CH3OH, both solvent molecules were included with 50%
2
2
site occupancy to provide satisfactory displacement parameters.
Partial site occupancy is not a physical requirement—there are no
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unacceptable contacts between the solvent molecules—and most
likely reflects some degree of solvent loss from the crystal studied.
The analysis of Pd(pfbtp) was performed using a plate-like crystal
with a minimum dimension of only ca. 0.005 mm. The data were
weak with only ca. 50% observed at the I > 2r(I) level (Rint
=
˚
0.106) to 0.85 A resolution. Anisotropic refinement was possible
only for Pd, S and N atoms. For Pd2(L4+4)·3DMF, the crystal
used for data collection was somewhat larger and less isotropic
in shape than might be desirable for a Pd2+ complex, and the
data suffer from severe effects related to anisotropic absorption.
Numerous attempts to prepare new crystals to repeat the analysis
were unsuccessful. The resulting refinement for Pd2(L4+4)·3DMF is
therefore of relatively low quality; the data establish connectivity,
but do not permit anisotropic refinement. The large peak and
hole in the difference electron density are associated with the Pd
atom. Analysis of both zinc complexes presented some challenging
aspect, largely related to weak diffraction and modelling of diffuse
lattice solvent. For [Zn6(L2+2)3(CO3)](ClO4)4·4H2O, the solvent
molecules are poorly modelled, but correction via a continuous
solvent area model16 is prevented by relatively large voids in the
structures coupled with relatively poor data. The C atom of the
central carbonate moiety could be refined only with an isotropic
2−
displacement parameter. Assignment of this moiety as CO3
,
−
rather than NO3 for example, was made on the basis of charge
balance within the structure, coupled with observation of ions
assignable to carbonate-containing complex cations in the ESI-MS
data; the X-ray data themselves do not permit definitive distinction
between C and N on the basis of bond lengths or displacement
parameters. For Zn4(L4+4)(NO3)4·5CH3CN, the combination of
a relatively small crystal and a large primitive unit cell gave
˚
rise to weak diffraction which was truncated to 1 A resolution,
with ca. 50% observed at the I > 2r(I) level (Rint = 0.149).
As a result, the structure is of relatively low precision. The two
crystallographically distinct complexes were tightly restrained to
have comparable geometries and only Zn, S and O atoms were
refined anisotropically. The acetonitrile moieties in the lattice were
surprisingly well resolved, although the distinction between the N
terminus and the CH3 terminus of each molecule is not clear;
the relative orientations of these molecules (in particular those
within the cavities of the macrocycles) should be considered highly
uncertain.
CCDC reference numbers 282070–282076.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b512068c
Results and discussion
The Schiff-base condensation reaction of 1,3-diaminopropane
and (S)-(2,6-diformyl-4-tert-butylphenyl)dimethylthiocarbamate,
with metal-promoted concurrent sulfur deprotection, in the pres-
ence of Ni2+, Pd2+ or Zn2+ gives four observed products: 1 + 2
acyclic ligands (pfbtp2−, pabtp2−), a 2 + 2 macrocycle (L2+2) and a
4 + 4 macrocycle (L4+4) (Scheme 1).† The products were character-
ized as metal complexes: mononuclear complexes of pfbtp2− were
isolated for Ni2+ and Pd2+; a mononuclear complex of pabtp2− was
† Notably, the analogous 4 + 4 macrocyclic product has not been observed
to date for the corresponding Schiff-base adducts of 1,3-diaminopropane
and the phenolate analogue, 2,5-phenoldialdehyde.
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isolated for Ni2+,17 dinuclear complexes of L2+2 were isolated for
Ni2+; dinuclear complexes of L4+4 were isolated for Ni2+ and Pd2+;
tetranuclear complexes of L4+4 were isolated for Zn2+. In addition,
a hexanuclear complex comprising three L2+2 units linked by l3-
thiolate bridges between three of the six metal ions was isolated for
Zn2+. Scheme 3 summarizes the synthetic pathways to the isolated
compounds. Distinguishing these visibly similar products (for a
given metal ion) was not entirely straightforward, since there are
Scheme 3 Summary of the products obtained from Schiff-base condensation of 1,3-diaminopropane with (S)-(2,6-diformyl-4-tert-butylphenyl)-
dimethylthiocarbamate in the presence of divalent ions: (a) reactions with Ni(ClO4)2 and PdCl2; (b) reactions with Zn(NO3)2 and Zn(ClO4)2.
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no salient spectroscopic signature differences between L2+2, L4+4
and the diacetal 1 + 2 system, pabtp2−. Complexes of the acyclic
dialdehyde pfbtp2− are less problematic, being distinguished by
a strong band at 1681 cm−1 in IR spectra. Mass spectrometry
was useful for distinguishing between the mononuclear complexes
of pfbtp2− and the dinuclear macrocyclic complexes, but X-ray
crystallography was the mainstay for characterization.
perchlorate, the 2 + 2 macrocycle is formed, similar to the
reactions observed with Ni2+ in methanol or acetonitrile. When
this reaction mixture is allowed to crystallize slowly under ambient
conditions, carbon dioxide is fixed from the atmosphere to form
the hexanuclear [Zn6(L2+2)3CO3](ClO4)4. ESI MS (but not MALDI
MS) furnishes conditions mild enough to observe the carbonated
hexanuclear species (Fig. 1). Monomeric [Zn2(LMe2+2)2(H2O)2]2+,19
and dimeric [Zn4(LMe2+2)2(OH)2]2+,20 have been reported previ-
ously, where (LMe2+2) is the homologous ditopic ligand with R =
CH3 (Scheme 1). The observation here of [Zn6(L2+2)3CO3](ClO4)4
may be considered to extend this series. The pseudo-pH of
the reaction will clearly influence the outcome with respect to
whether a fifth ligand might be water or hydroxide or consequent
carbonate after CO2 fixation. The fact that the l3-carbonato
system crystallizes in our case rather than a di-l-hydroxo system
homologous to [Zn4(LMe2+2)2(OH)2]2+, presumably is due to some
factor such as concentration of adventitious CO2.§ It is possible
that the presence of tert-butyl substituents rather than methyl
groups may influence the reaction outcome, although there are no
obvious steric constraints in the structure of [Zn4(LMe2+2)(OH)2]2+
(e.g. between methyl groups) that might prevent formation of the
analogous complex with tert-butyl groups.
Since the original anticipated targets were metal-ion-templated
2 + 2 macrocycles, the three reactants (S)-(2,6-diformyl-4-tert-
butylphenyl)dimethylthiocarbamate, 1,3-diaminopropane and a
metal-ion salt were mixed in equimolar proportions in the initial
experiments. Only for zinc and nickel were products observed in
which the reactants emerge in equimolar proportions.‡ For the
reactions incorporating Ni2+, the solvent is an important factor
for determining the reaction outcome. In DMF, acyclic Ni(pfbtp)
is obtained despite an excess of 1,3-diaminopropane relative to
the product. In methanol or acetonitrile, [Ni2(L2+2)](ClO4)2 is
recovered, even in the presence of relatively fewer equivalents
of 1,3-diaminopropane. Since imine bond formation is reversible,
the principal factor that determines the product may simply be
solubility: [Ni2(L2+2)](ClO4)2 is more soluble than Ni(pfbtp) in
DMF, and the reverse is true in methanol and acetonitrile. The
dinickel complex of the 4 + 4 macrocycle, Ni2(L4+4), was obtained
by reaction of Ni(pfbtp) with 1,3-diaminopropane in methanol,
thus amounting to a stepwise synthesis rather than a 4 + 4 ligand
assembly. We have no satisfactory explanation for why this reaction
occurred most effectively in the presence of ammonium chloride:
in the absence of ammonium chloride, the aldehyde groups are
converted to methyl acetals and Ni(pabtp) is isolated despite the
presence of excess diamine. We note that a related ethyl acetal
formation has been observed previously.18
The conditions required for isolating Pd(pfbtp) or Pd2(L4+4
)
differ only marginally in the ratios of the reactants:
Pd(pfbtp) is formed by reaction of (S)-(2,6-diformyl-4-tert-
butylphenyl)dimethylthiocarbamate, 1,3-diaminopropane and
PdCl2 in 2 : 3 : 1 proportions in DMF (i.e. an excess of 1,3-
diaminopropane compared to the product stoichiometry), while
Pd2(L4+4) is formed from the same reactants in a 1 : 2 : 1 stoichiome-
try in DMF (i.e. an excess of Pd and 1,3-diaminopropane). Both of
these compounds are neutral species that can be distinguished by
IR spectroscopy and mass spectrometry. The FAB mass spectrum
of Pd2(L4+4) shows m/z 625 ([(PdC30H38N4S2) + H]+, 100%) as the
major ion, corresponding to half the macrocyclic complex after
cleavage of two C–N bonds originating from two different (proba-
bly the non-coordinated) 1,3-diaminopropane units. A significant
molecular ion is also observed at m/z 1250.5 ([(Pd2C60H76N8S4) +
H]+, 47%). In the spectrum of Pd(pfbtp), the molecular ion is the
major peak at m/z 586, ([PdC27H32N2O2S2]+, 100%).
Fig. 1 ESI mass spectrum of [Zn6(L2+2)3CO3](ClO4)4. Assignments:
324.7, [Zn2(L2+2)(CH3CN)(H2O)]2+; 361.0, [Zn2(L2+2)]2+; 501.6, [Zn6(L2+2)3-
+
(CO3)]4+; 679.4, [Zn4(L2+2)2(CO3)]2+; 749.0, {[Zn2(L2+2)](ClO4)} ; 1103.6,
+
{[Zn6(L2+2)3(CO3)](ClO4)2}2+; 1457.3, {[Zn4(L2+2)2(CO3)](ClO4)} .
Crystal structures
2
[Ni2(L2+2)](ClO4)2·2CH3CN, [Ni2(L2+2)](ClO4)2· CH3OH and
3
1
2
1
2
[Ni2(L2+2)](ClO4)2· DMF· CH3OH. The dinickel(II) complex of
the 2 + 2 macrocycle has been characterized as three different
crystalline solvates. In addition, a diethyl ether/water solvate has
been described previously.9 In each case, the [Ni2(L2+2)]2+ complex
displays a “V-shaped” (syn) conformation, in which the S atoms of
the thiophenolate groups lie to the same side of the plane defined
by the four N atoms of the macrocycle (Fig. 2). The dihedral
angles between the least-squares planes of the phenyl rings of the
thiophenolate units are 83.9(1), 83.4(2)/86.4(1) and 89.2(2)◦ in
the three structures respectively. The conformation of the complex
is closely comparable in all three solvated forms: the 28 non-
H atoms of the complexes (excluding the C atoms of the CH3
groups in tert-butyl substituents, which are prone to rotational
variation) may be overlaid with a maximum rms deviation of only
For the reactions incorporating Zn2+, the outcome is influenced
by the identity of the counteranion. This is likely to be attributable
to the anion’s coordinating ability: nitrate is more strongly
coordinating in methanol and acetonitrile than is perchlorate.
Thus, if zinc nitrate is used as the starting salt, nitrate remains
coordinated to Zn2+, leading to precipitation of a neutral complex
Zn2(L4+4)(NO3)4. In the presence of the less strongly coordinating
§ It is not explicitly stated in ref. 20 whether an inert atmosphere was used
in the preparation of [Zn4(LMe2+2)2(OH)2]2+. The presence of CO2 might
be the key difference that leads to production of [Zn6(L2+2)3CO3]4+ rather
than [Zn4(LMe2+2)2(OH)2]2+ in these otherwise similar preparations.
‡ Where the stoichiometry of the reactions in the Experimental section
differ from equimolar, it is because yields were improved using the reported
ratios.
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Fig. 2 Ni2(L2+2) complex in [Ni2(L2+2)](ClO4)2·2CH3CN showing the syn
conformation in which the S atoms of the thiophenolate groups lie to the
same side of the plane defined by the four N atoms of the macrocycle.
Displacement ellipsoids are shown at 50% probability and H atoms are
omitted. The Ni2(L2+2) complexes in the other two solvated forms are
comparable.
Fig. 3 Back-to-back arrangements of [Ni2(L2+2)]2+ in (a) [Ni2(L2+2)]-
1
1
(ClO4)2·2CH3CN and (b) [Ni2(L2+2)](ClO4)2· DMF· CH3OH. In both
2
2
cases, the solvent molecules occupy comparable positions on the concave
side of the V-shaped [Ni2(L2+2)]2+ complexes. H atoms (except in the
methanol moiety) and perchlorate anions are omitted.
˚
0.25 A. In each case, the complexes display approximate C2v point
symmetry, with the two-fold axis lying perpendicular to the N4
plane and passing through the centroid of the complex, and two
perpendicular mirror planes passing through the two S atoms and
the two Ni atoms, respectively. In the monoclinic structure of
[Ni2(L2+2)](ClO4)2·2CH3CN, the two-fold axis is crystallographic.
coordinated via their O atoms, with Ni · · · O distances of 2.840(1)
˚
and 2.646(2) A, respectively (Fig. 3(b)). The H atom of the
methanol moiety forms a hydrogen bond to the O atom of DMF,
approximately parallel to the Ni · · · Ni vector of the complex.
Similar axial interactions with solvent, in these otherwise
square-planar nickel complexes, have been noted previously.9
2
3
In [Ni2(L2+2)](ClO4)2· CH3OH, two independent complexes exist,
2
In the third solvate, [Ni2(L2+2)](ClO4)2· CH3OH, adjacent
one lying on the crystallographic two-fold axis and one lying
3
1
1
on a general position. In [Ni2(L2+2)](ClO4)2· DMF· CH3OH, the
Ni2(L2+2) complexes again adopt back-to-back arrangements. Two
distinct arrangements exist, giving rise to two crystallographically
distinct complexes. For the complex sited on a general position
in the crystal structure, one end forms an arrangement identical
to that described previously, i.e. thiophenolate groups adopt an
offset face-to-face arrangement with their C–S bond vectors lying
anti-parallel (as in Fig. 3). This arrangement blocks approach
2
2
complex lies on a general position.
The crystal structures of [Ni2(L2+2)](ClO4)2·2CH3CN
1
1
and [Ni2(L2+2)](ClO4)2· DMF· CH3OH show considerable
2
2
similarity.¶ In each case, adjacent complexes adopt “back-to-
back” arrangements in which the phenyl rings of the thiophenolate
groups adopt offset face-to-face orientations with interplane
˚
towards one Ni2+ cation from the convex side of the Ni2(L2+2
)
separations of ca 3.6 A and their C–S bond vectors lying
anti-parallel (Fig. 3). Similar arrangements are observed for the
related systems.8,9 In this arrangement, the tert-butyl groups of
the thiophenolate rings lie above the Ni2S2 centres, effectively
preventing further coordination of the Ni2+ cations from the
convex side of each complex. In each structure, the solvent
molecules lie on the concave side. In [Ni2(L2+2)](ClO4)2·2CH3CN,
each acetonitrile molecule is oriented so that its N atom
occupies the axial coordination site of a square pyramid about
complex. At the other end of the same complex, the thiophenolate
groups again adopt face-to-face arrangements, but in this case
with their C–S bond vectors lying approximately perpendicular,
i.e. adjacent complexes are rotated by ca. 90◦ with respect to
each other (Fig. 4(a)). This arrangement leaves the convex side
of the Ni2(L2+2) complexes exposed, and the perchlorate anions
complete an essentially square-pyramidal coordination geometry
of the Ni2+ cation with Ni · · · O separations of 2.819(4) A. The
˚
2+
˚
Ni2+ cation that has its convex face blocked by the tert-butyl group
is coordinated by methanol solvent molecules on the concave
Ni , with an Ni · · · N distance of 3.155(4) A (Fig. 3(a)). In
1
2
1
2
[Ni2(L2+2)](ClO4)2· DMF· CH3OH, comparable axial sites are
occupied either by DMF or by methanol, both moieties being
˚
side, with a Ni · · · O separation of 2.777(14) A. This methanol
moiety displays some orientational disorder within the concave
cavity. The coordination of two methanol molecules per six Ni2+
¶ The centered monoclinic lattice of [Ni2(L2+2)](ClO4)2·2CH3CN can be
cations (i.e. per three Ni2(L2+2) complexes) gives rise to 2 CH3OH
˚
described by a primitive unit cell a = 11.460, b = 13.042, c = 16.038 A,
3
a = 112.42, b = 110.93, c = 116.06◦. This description (although failing to
per Ni2(L2+2) in the empirical formula. For the Ni2(L2+2) complex
lying on the crystallographic two-fold axis, both of its ends adopt
the perpendicular arrangement and both of its Ni2+ cations are
take proper account of the symmetry in the structure) highlights clearly
1
1
the similarity to the triclinic lattice of [Ni2(L2+2)](ClO4)2· DMF· CH3OH
2
2
(see Table 1).
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Fig. 4 Environments of the two crystallographically distinct complexes
2
in [Ni2(L2+2)](ClO4)2· CH3OH: (a) at one end of the complex (left), the
3
thiophenolate rings form an offset face-to-face arrangement with the
C–S bond vectors lying anti-parallel, while the at the other end (right)
the C–S bond vectors lie perpendicular and one Ni atom is further
coordinated by a perchlorate moiety; (b) both ends of the complex (related
by a crystallographic two-fold rotation axis) adopt the perpendicular
arrangement and both Ni atoms are further coordinated by perchlorate
moieties. H atoms are omitted.
Fig. 5 Metal complexes in (a) Ni(pftp)7 and (b) Pd(pfbtp) showing
projections along the two-fold rotation axis (top) and the direction
approximately perpendicular to it, along the long axis of the molecule
(bottom). In (a), the planes of the phenyl rings are approximately parallel,
while in (b) they form a dihedral angle of 16.5(4)◦.
coordinated by perchlorate moieties on the convex side, with
˚
equivalent Ni · · · O distances of 2.858(4) A (Fig. 4(b)).
˚
separations of 5.719(2) A. The offset of adjacent molecules within
the stacks is such that the structure in this case might be better
described in terms of two-dimensional layers in the bc planes, with
the long axes of the complexes lying close to perpendicular to the
plane of the layers (Fig. 6(a)). The tert-butyl groups present an
approximately centred rectangular arrangement (defined by the
bc face of the unit cell) at the surface of each layer (Fig. 6(b)), and
adjacent layers stack along the a direction so that the tert-butyl
groups project into the hollows in the surface of the neighbouring
layer.
Pd(pfbtp). The crystal structure of Pd(pfbtp) is closely
comparable to that of the Ni2+ complex Ni(pftp) (pftp2− = N,N-
propane-1,3-diyl(6-formyl-4-methyl-2-methyliminatothiophenolato,
C21H20N2O2S2) reported previously.7 The presence of Pd2+ rather
than Ni2+ in the N2S2 coordination site gives rise to subtle changes
in the geometry of the complex on account of the differing M–N
and M–S bond distances in the two cases. For Ni(pftp), the
square-planar geometry of Ni2+ coupled with the (CH2)3 linkage
between the two N atoms accommodates an anti conformation
for the thiophenolate rings (i.e. the thiophenolate rings lie on
opposite sides of the NiN2S2 square plane), with the ring planes
approximately parallel (Fig. 5(a)). The complex displays C2
point symmetry in the solid state, with the two-fold axis passing
through Ni and the C atom of the central CH2 group in the
(CH2)3 linkage. In the Pd2+ complex, the relatively longer Pd–N
and Pd–S distances impose a slight “twist” on the molecule so
that there is a small but discernible distortion of the N2S2 unit
away from planarity (Fig. 5(b)). The twist is manifested most
clearly by the thiophenolate groups, which form a dihedral angle
of 16.5(4)◦ between the least-squares planes of their phenyl rings.
The complex retains C2 point symmetry in the solid state.
Pd2(L4+4)·3DMF. The crystal structure of Pd2(L4+4)·3DMF
is again closely comparable to the analogous Ni2+ complex,
Ni2(LMe4+4)·xH2O, reported previously.7 The two Pd2+ cations in
the complex Pd2(L4+4) occupy opposed coordination sites in the
4 + 4 macrocycle. The complex displays crystallographic C2 point
symmetry with the two-fold axis passing through the centre of the
macrocycle, perpendicular to the least-squares plane of the four
S atoms (Fig. 7). The two Pd(pfbtp) units within the macrocycle
resemble closely those in the crystal structure of Pd(pfbtp) itself:
the Pd–S and Pd–N bond distances are comparable, and the phenyl
rings of the thiophenolate rings are twisted with respect to each
other to form a dihedral angle of 20(1)◦ between the least-squares
planes. The complex as a whole resembles an extended ring,
In a manner similar to Ni(pftp), the Pd(pfbtp) complexes may
be considered to stack along the crystallographic c direction. In
Ni(pftp), the complexes lie directly one on top of the other (rotated
180◦ for each adjacent complex), forming Ni · · · Ni separations
=
=
folded via the N–(CH2)3–N linkages to form an approximate
“V-shaped” conformation. The bending angle of approximately
82◦ (defined as the dihedral angle between the two PdN2S2 square
planes) is slightly greater than the 77◦ angle observed in the
7
˚
of 3.96 A. In Pd(pfbtp), such direct stacking is precluded by the
=
presence of the tert-butyl substituents, and adjacent complexes are
offset laterally with respect to one another, giving rise to Pd · · · Pd
comparable Ni2+ complex.7 The non-coordinated N–(CH2)3–
=
N
linkages are oriented so that lone pairs associated with N(3)
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and N(4) may be envisaged to point towards the outside of
the macrocycle.
The packing arrangements of Pd2(L4+4)·3DMF and
Ni2(L4+4)·xH2O are also closely comparable, viewed most
clearly in projection along the crystallographic b direction, i.e.
along the two-fold rotation axes of the complexes (Fig. 8). In
Pd2(L4+4)·3DMF, adjacent complexes may be considered to be
arranged into layers in the (200) planes, with the Pd(pfbtp)
portions adopting offset stacked arrangements along b. This
stacking arrangement is more closely comparable to that observed
in Ni(pftp), but with a much larger lateral offset to accommodate
the tert-butyl substituents, giving rise to Pd · · · Pd separations
˚
of 6.365(3) A. There is a clear distinction between Pd(pfbtp)
portions stacked within layers and the boundary between layers.
In Ni2(L4+4)·xH2O, the complexes are translated relative to
each other along a so that the Ni(pfbtp) portions form more
extended two-dimensional arrangements and the distinction
between layers is less clear (Fig. 8(b)).7 This lateral translation
gives rise to Ni · · · Ni separations of 7.53 A. In Pd2(L4+4)·3DMF,
˚
a DMF moiety (displaying some orientational disorder) lies
at the centre of each complex, towards the concave side, and
further DMF moieties occupy the regions between the layers.
The comparable regions are also occupied by solvent molecules
Fig. 6 Packing arrangement in Pd(pfbtp): (a) projection along the b
direction showing the complexes arranged into layers lying in the (200)
planes; (b) projection onto a single layer along the direction indicated by
the arrow in (a), showing the offset stacking arrangement of the complexes
and the approximate centred rectangular arrangement (defined by the
dashed lines) presented by the tert-butyl groups on the surface of the layer.
Fig. 8 Packing arrangements in (a) Pd2(L4+4)·3DMF and (b) Ni2(L4+4)·
xH2O. In (a), layers can be clearly distinguished in the (200) planes, while
in (b) the complexes are shifted relative to each other along the a direction
so that the distinction is less clear. The solvent molecules in each case
adopt comparable positions.
Fig.
7
Perpendicular views of the dinuclear metal complex in
Pd2(L4+4)·3DMF, showing the “V-shaped” conformation of the extended
ring. H atoms are omitted and only unique C atoms are labelled.
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in Ni2(LMe4+4)·xH2O, although the electron density in that case
is diffuse and the identity of the solvent remains somewhat
uncertain (modelled as numerous water molecules).7
˚
macrocycle compared to the other pair (ca. 9.2–9.4 A), so that
one end of the cylinder is relatively more open than the other,
and the overall arrangement approaches a “bowl”. Acetonitrile
molecules lie within the “bowl”. In the second crystallographically
distinct macrocycle, the cross-complex separation between Zn2+
Zn4(L4+4)(NO3)4·5CH3CN. The tetranuclear Zn2+ complex of
the 4 + 4 macrocycle adopts a conformation dramatically different
from those of the dinuclear Ni2+ and Pd2+ complexes (Fig. 9).
The macrocycle is folded to form a cylinder-like arrangement
in which the Zn2+ cations are coordinated to two N atoms and
one S atom, which in this case is not bridging. The cations in
each case adopt an essentially tetrahedral coordination geometry,
with NO3−occupying the fourth coordination site. The nitrate
anions form either monodentate or bidentate arrangements. The
macrocycle exhibits approximate S4 point symmetry (although
sited on a general position in each crystal structure). The
four Zn2+ cations lie in a tetrahedral arrangement which is
“flattened” along the direction of the approximate S4 axis. Two
crystallographically distinct complexes exist, displaying slightly
different conformations. In one complex, two of the Zn2+ cations
˚
cations is comparable (ca. 9.1 A) at both ends, so that the
macrocycle resembles more closely a regular cylinder. In this case,
two acetonitrile molecules are threaded through the cylinder: thus,
the bowl shape can become more cylindrical to accommodate
the acetonitrile molecules. Although these CH3CN molecules are
surprisingly well resolved, the X-ray data do not permit definitive
distinction between the CH3 terminus and the N terminus of each
molecule, and it is not possible to specify with any confidence the
orientations of the CH3CN molecules within the macrocycle cavity.
However, we could speculate that the two N termini are unlikely
to be brought into close contact on account of the electrostatic
repulsion that would arise between them.
The folding of the macrocycle in Zn4(L4+4)(NO3)4, compared to
the extended ring conformation in the dinuclear Ni2+ and Pd2+
complexes, can be viewed as a requirement for coordination of
the two additional Zn2+ cations: a dinuclear complex comparable
to that of Ni2+ or Pd2+ must fold if its previously uncoordinated
N atoms are to wrap around the two additional Zn2+ cations.
It is clear that such an arrangement cannot accommodate a
metal cation in a square-planar geometry, which may offer some
rationalization for the absence of tetranuclear Ni2+ and Pd2+
complexes of L4+4. The overall topology of Zn4(L4+4)(NO3)4, con-
trasts with that of the only other known tetrametallic complexes
of tetrathiophenolate macrocycles, namely the tetranickel system
depicted in Scheme 2.10 This latter system resembles a covalently
linked dimer of dinuclear [Ni2(L2+2)]2+ moieties, in which the
conformation of each dinuclear unit resembles closely that of
[Ni2(L2+2)]2+ itself.
˚
are brought relatively closer together (ca. 8.0–8.2 A) across the
The packing arrangement of Zn4(L4+4)(NO3)4·5CH3CN is con-
veniently considered in terms of 2-D layers parallel to the (001)
planes (Fig. 10). Within an individual layer, the macrocycles
are arranged so that the cavities through their centres lie either
within or perpendicular to the layer plane (Fig. 10(b)). Adjacent
macrocycles turned perpendicular to each other interact in a
Fig. 9 Two conformations observed for Zn4(L4+4)(NO3)4: (a) “bowl”
shape in which the Zn(1) · · · Zn(3) distance is significantly shorter than the
Zn(2) · · · Zn(4) distance. (b) “Cylinder” shape in which the Zn(5) · · · Zn(7)
and Zn(6) · · · Zn(8) distances are comparable. The cylinder in (b) is shown
with two acetonitrile molecules threaded through it. Acetonitrile molecules
also lie within the bowl, but are not shown in (a).
Fig. 10 View along the a direction in Zn4(L4+4)(NO3)4·5CH3CN showing
layers parallel to the ab face of the unit cell. Macrocycles adopt a
perpendicular alignment with their neighbours within layers, and adjacent
layers are offset laterally so that there are no channels running through the
structure.
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manner similar to that seen in the [Ni2(L2+2)]2+ complexes: the
thiophenolate rings come into face-to-face contact with their C–S
vectors approximately perpendicular. The layers are stacked in an
ABAB manner, offset so that the macrocycles lie perpendicular to
their neighbours in adjacent layers. Thus, there are no channels
running through the structure and the acetonitrile molecules in
the macrocycle cavities are effectively trapped.
˚
significantly longer than the other two (4.450(2) and 4.539(2) A).
The coordination geometry around Zn2+ is again approximately
trigonal bipyramidal, with the two S atoms and two N atoms
of a given [Zn2(L2+2)]2+ unit occupying two equatorial and two
axial positions. The remaining equatorial coordination site is
occupied by O from a l3-carbonate anion that lies approximately
within the upper Zn3 plane. The geometry of the three individual
[Zn2(L2+2)]2+ units in [Zn6(L2+2)3(CO3)]4+ differs from that observed
in the isolated [Ni2(L2+2)]2+ units described previously: the S atoms
of the thiophenolate groups lie on opposite sides of the plane
defined by the four N atoms of the macrocycle, giving rise to
an anti conformation. The dihedral angles between the least-
squares planes of the phenyl rings of the thiophenolate units are
60.1(4), 69.0(4) and 66.4(4)◦ in the three distinct [Zn2(L2+2)]2+ units,
respectively. The Zn3S3 ring effectively closes one side of the
macrocycle, forming the bowl shape within which the carbonate
anion lies.
The crystal structure of [Zn6(L2+2)3(CO3)](ClO4)4·4H2O is conve-
niently described by considering layers in (010) (Fig. 12). Within a
given layer, all of the complexes are aligned with their approximate
local C3 axes parallel. In an adjacent layer, related to the primary
layer by a centre of inversion, the C3 axes are also aligned along
the same direction, with the bowls adopting a “back-to-back”
arrangement. In the adjacent layer on the other side of the primary
layer, the bowls are aligned in a side-on manner so that their C3
axes point in approximately perpendicular directions. The bowls
are relatively loosely packed–there are no face-to-face contacts
between thiophenolate rings, for example–and the perchlorate an-
ions and water solvent molecules occupy the voids between them.
[Zn6(L2+2)3(CO3)](ClO4)4·4H2O. The hexanuclear complex
[Zn6(L2+2)3(CO3)]4+ consists of three distinct [Zn2(L2+2)]2+ units,
linked via further Zn–S bonds, displaying approximate (non-
crystallographic) C3 point symmetry (Fig. 11). The coordination
geometry around three of the six Zn2+ cations resembles trigonal
bipyramidal, with the two S atoms and two N atoms of a
given [Zn2(L2+2)]2+ unit occupying two equatorial and two axial
positions, and the S atom from an adjacent [Zn2(L2+2)]2+ unit
occupying one equatorial position. The S atoms of the thiophe-
nolate rings that bridge between these two Zn2+ centres adopt
l3-coordination, in an approximate trigonal-planar arrangement.
The three Zn2+ cations and three S atoms form a six-membered
Zn3S3 ring that is approximately planar and very close to three-
fold symmetric. The remaining three Zn2+ cations lie in second
plane, that is close to parallel to the plane of the Zn3S3 ring
(actual dihedral angle 3.9(1)◦), with an approximate perpendicular
˚
separation of ca. 2.6 A. The triangular arrangement of these
Zn2+ cations is distorted, with one Zn · · · Zn distance (4.817(2) A)
˚
Fig. 12 Perspective view of the crystal structure of [Zn6(L2+2)3-
(CO3)](ClO4)4·4H2O along the a direction showing layers envisaged
parallel to the (100) planes. In adjacent layers, the bowl-shaped complexes
lie either back-to-back with their neighbour so that their local C3 axes
are parallel, or side-on so that their local C3 axes are approximately
perpendicular.
Fig. 11 View of the [Zn6(L2+2)3(CO3)]2+ complex: (a) along its approxi-
mate C3 rotation axis and (b) perpendicular to it, highlighting the Zn3S3
ring in the lower plane and the CO32− anion complexed between three Zn2+
cations in the upper plane.
Modelling studies
In the l-thiolate bridged systems with L2+2, the two metal ions
and the ipso-carbon of the phenyl ring are located at three
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apices of a tetrahedron around each S atom, with a lone pair
of electrons occupying the fourth. Two possibilities exist for
the relative orientations of the two tetrahedra in the [M(L2+2)]2+
macrocyclic complex: a syn orientation of the sulfur lone pairs
leads to a V-shaped molecule in which both phenyl rings lie on
the same side of the N4 plane of the macrocycle, while an anti
conformation causes the phenyl rings to lie on opposite sides of
the N4 plane (Scheme 4). Both conformations are observed in
the present series. In the discrete dinickel complexes of the 2 +
2 macrocycles7–9 the syn conformation is observed exclusively. In
contrast the anti orientation is observed in the dinuclear units of
[Zn6(L2+2)3(CO3)]4+ (Fig. 11(a)). Likewise the anti conformation
was seen in [Zn2(LMe2+2)2(H2O)2]2+.19 Both the syn and the anti
conformation are seen in the dimeric [Zn4(LMe2+2)2(OH)2]2+.20 The
question arises as to whether these conformations can interconvert
in solution via a fluxional sulfur-inversion process. Inversion might
occur at one sulfur atom to change the observed conformer, or at
both to give an inversion of the entire M2S2 core (Scheme 4).
These processes could take place by either dissociative or non-
dissociative mechanisms. It is well known that thiolate sulfur can
invert when attached to a metal centre as a monodentate donor,
and when it is part of an organic ring.21 The possibility of inversion
in this system is addressed by considering calculated energies
for each of the limiting forms. The coordinates obtained in the
structure analysis of [Ni2(L2+2)]2+ and a dimeric unit taken from
[Zn6(L2+2)3(CO3)]4+ were used as starting points for the calculations
and the structures were fully optimized at the B3LYP level using
the 6-31G(d,p) basis set. Both Ni2+ and Zn2+ were found to
favour the geometries observed: for Zn2+, the syn conformer is
destabilized by approximately 80 kJ mol−1 relative to the observed
anti conformer, while for Ni2+, the anti conformer is 50 kJ mol−1 less
stable than the syn conformer. In the non-dissociative transition
structures, the inverting sulfur atom lies almost in the plane of
the surrounding atoms. The activation energy relative to the most
stable conformer is calculated to be 105 kJ mol−1 for the Zn2+
complex and 90 kJ mol−1 for the Ni2+ complex, indicating that
interconversion should occur readily at room temperature.
entities is influenced by the identity of the metal ion, solvent
and counteranions in the synthetic procedure. The rare 4 + 4
thiophenolate macrocycles show dramatically different topologies
in their dinuclear and tetranuclear metal complexes. The dinuclear
complexes Ni2(L4+4) and Pd2(L4+4) resemble extended rings folded
into “V-shaped” conformations, in which the local environment
of each square-planar metal ion resembles closely that in the
isolated mononuclear complexes, Ni(pftp) and Pd(pfbtp). By
contrast, the tetranuclear complex Zn4(L4+4)(NO3)4, displays a
cylindrical conformation that can distort to become more “bowl-
like”. The cavities within the macrocycle are essentially sulfur-
lined rather than metal-lined, presenting the possibility that these
systems might be developed as electron-rich hosts for host–guest
chemistry. In particular, we intend to investigate the uptake of
gases by these materials; we might speculate that the sulfur-lined
cavities would show particular affinity for dihydrogen, for example.
A hexanuclear complex [Zn6(L2+2)3(CO3)]4+ is also formed by
oligomerisation of three dinuclear 2 + 2 macrocyclic complexes.
This complex exhibits a bowl shape, and is occupied by a carbonate
anion derived from CO2 fixation.
Acknowledgements
We are grateful to Dr Inger Søtofte for collecting X-ray diffraction
data for Pd2(L4+4)·3DMF at Technical University of Denmark
and to the Danish Natural Science Research Council (SNF) and
Carlsbergfondet for provision of the X-ray diffraction equipment.
A. D. B. also thanks SNF for funding via a Steno stipend. The
computational studies were supported by grants from the Danish
Center for Scientific Computing to F. J.
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