Binding of inorganic oxoanions to macrocyclic ligands: Interactions of sulfate and dithionate with protonated forms of [18]aneN6

Article abstract of DOI:10.1039/b409088h

Three sulfate-macrocycle adducts [H₆L(HSO₄) ₄(SO₄)] · H₂O (1), [H ₆L(SO₄)₃] (2) and [H₆L(HSO ₄)₂Cl₄] · 2H₂O (3) (where L = [18]aneN₆) were crystallized from solutions containing the macrocycle and the appropriate inorganic acids, and [H₄L(S ₂O₆)₂] · 2H₂O (4) from an aqueous solution of the macrocycle and sodium dithionate. All four structures show that the polyammonium groups on the protonated macrocycle participate in 'co-ordination' or supramolecular interactions with one or more oxygen atoms from the polyoxoanions (i.e., SO₄^2-, HSO₄ or S₂O₆^2-). In 3, the protonated macrocyclic cavity holds the two chloride anions in preference to the oxoanions. The sulfate anions show remarkable versatility in their interactions with the macrocycle. Of particular note is a unique η-5 N-H...O cluster involving the sole sulfate anion in 1, but there are many common features throughout the structures, such as the inclusion of one anion on either side of the macrocycle and the participation of all ammonium protons in H-bonding interactions.

Full text of DOI:10.1039/b409088h

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P A P E R
Binding of inorganic oxoanions to macrocyclic ligands: interactions
of sulfate and dithionate with protonated forms of [18]aneN6
Andrew C. Warden,a Mark Warren,a Milton T. W. Hearnb and Leone Spiccia*a
a School of Chemistry, Monash University, Victoria, 3800 Australia.
E-mail: leone.spiccia@sci.monash.edu.au; Fax: þ61 3 99054597; Tel: þ61 3 99054526
b Centre for Green Chemistry, Monash University, Victoria, 3800 Australia
Received (in Durham, UK) 15th June 2004, Accepted 19th August 2004
First published as an Advance Article on the web 19th October 2004
Three sulfate-macrocycle adducts [H6L(HSO4)4(SO4)] ꢀ H2O (1), [H6L(SO4)3] (2) and [H6L(HSO4)2Cl4] ꢀ 2H2O
(3) (where L ¼ [18]aneN6) were crystallized from solutions containing the macrocycle and the appropriate
inorganic acids, and [H4L(S2O6)2] ꢀ 2H2O (4) from an aqueous solution of the macrocycle and sodium
dithionate. All four structures show that the polyammonium groups on the protonated macrocycle
participate in ‘co-ordination’ or supramolecular interactions with one or more oxygen atoms from the
ꢁ
polyoxoanions (i.e., SO42ꢁ, HSO4 or S2O62ꢁ). In 3, the protonated macrocyclic cavity holds the two
chloride anions in preference to the oxoanions. The sulfate anions show remarkable versatility in their
interactions with the macrocycle. Of particular note is a unique Z-5 N–Hꢀ ꢀ ꢀO cluster involving the sole
sulfate anion in 1, but there are many common features throughout the structures, such as the inclusion
of one anion on either side of the macrocycle and the participation of all ammonium protons in H-bonding
interactions.
hexacyanocobaltate,18 trifluoromethane sulfonate19 and pyro-
Introduction
phosphate20 salts. We recently reported the structures of a
series of adducts formed by the [18]aneN6 macrocycle with the
halide ions21 and various protonated forms of the phosphate
ions.22 We herein have extended our investigation to adducts
formed by tetra- and hexaprotonated forms of [18]aneN6 and
sulfate and dithionate. Four complexes, [H6L(HSO4)4(SO4)] ꢀ
H2O (1), [H6L(SO4)3] (2), [H6L(HSO4)2Cl4] ꢀ 2H2O (3) and
[H4L(S2O6)2] ꢀ 2H2O (4), have been prepared and characterized
and X-ray crystallography used to determine their structures
and to elucidate the predominant anion–cation and anion–
anion interactions and how these are influenced by pH.
Anion co-ordination, or recognition, is an area that has been
receiving increased attention in the past two decades,1,2 with
particular emphasis on the thermodynamics of interactions
between the anions and a wide variety of synthetic hosts.
Interest in the co-ordination of biologically relevant oxoa-
nions, such as sulfate and phosphate, has sparked efforts
towards the elucidation of the features of the host that would
result in strong affinity and high selectivity. The selectivity
exhibited by proteins that bind these anions has provided a
strong basis for the study of interactions between non-natural
hosts and oxoanions. These efforts have resulted in the synth-
esis of a range of hosts including cyclic3,4 and non-cyclic
amides,5 azacryptands,6 mixed polyaza-ferrocene constructs,7
porphyrins,8 guanidinium compounds,9 mixed oxo-aza macro-
cycles10,11 and azamacrocycles.12–14 The solution characteriza-
tion of adducts formed by the receptors and oxoanions has
involved the use of conductometric, potentiometric (pH titra-
tion) and NMR studies and on fewer occasions the solid state
structures have been determined by X-ray crystallography.
One system that has attracted interest is the hexaazamacro-
cycle, 1,4,7,10,13,16-hexaazacyclooctadecane ([18]aneN6, L,
sometimes referred to as hexacyclen or 18-azacrown-6).
Experimental methods
Reagents.
All reagents were purchased from commercial suppliers and
used as supplied with the exception of 1,4,7,10,13,16-hexaaza-
cyclooctadecane ([18]aneN6), which was prepared via a pre-
viously reported method.22
Physical Measurements.
Microanalyses were performed by the Campbell Microanaly-
tical Service of the University of Otago in New Zealand.
Infrared spectra were recorded using KBr pellets on a Per-
kin-Elmer 1600 FTIR spectrometer at a resolution of 8 cmꢁ1
.
Synthesis.
.
[H6L(HSO4)4(SO4)] H2O (1). [18]aneN6 (26 mg, 0.10 mmol)
was dissolved in water (300 mg) and sulfuric acid (conc., 300
mg, 3.2 mmol) was added to the solution. The solution was left
to slowly evaporate over a few days to produce clear crystals of
1. Yield ¼ 43 mg, 56%. Microanalysis (%) Found: C 18.9, H
6.0, N 11.6. Calc. for C12H42N6O21S5: C 18.8, H 5.5, N 11.0. IR
bands (n, cmꢁ1) 3400 m, 3106 s, 3036 s, 2950 s, 2856 s, 2491 m,
Until this year, however, only six structures of [18]aneN6/anion
adducts had been published: nitrate/chloride,15,16 nitrate,17
T h i s j o u r n a l i s & 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 a n d t h e
C e n t r e N a t i o n a l d e l a R e c h e r c h e S c i e n t i f i q u e 2 0 0 4
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 3 0 1 – 1 3 0 8
1301

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Table 1 Crystal structure and refinement data for 1–4
1
2
3
4
Empirical formula
FW, g molꢁ1
Crystal system
C12H42N6O21S5
766.82
C12H36N6O12S3
552.65
C12H42Cl4N6O10S2
636.44
C12H38N6O14S4
618.72
Orthorhomic
Pca21
Monoclinic
P21/c
Monoclinic
P21/n
Monoclinic
C2/m
Space group
a/A
20.5271(4)
8.3909(1)
16.6116(2)
7.9597(2)
11.2322(3)
12.5897(4)
100.673(1)
1106.11(5)
2
6.4044(2)
20.6316(5)
10.1970(4)
94.455(1)
1343.29(7)
2
13.1554(3)
11.4761(4)
8.7203(3)
97.56(3)
1305.07(7)
2
b/A
c/A
b/1
Volume/A3
2861.20(7)
4
1.780
Z
r
calcd/g cmꢁ3
1.659
0.409
1.573
0.653
1.574
0.439
m/mmꢁ1
0.507
y range/1
2.43 to 28.28
23302
6691
2.45 to 28.28
9553
2718
2.23 to 28.29
9801
3306
3.48 to 28.31
4485
1684
Reflections collected
Independent reflections
Goodness-of-fit on F2
R1a, wR2b [I 4 2s(I)]
0.98
0.0448, 0.0860
1.032
0.0428, 0.0972
1.043
0.0412, 0.0844
1.086
0.0509, 0.1389
a
b
2
S||Fo|ꢁ|Fc||/S|Fo|. [Sw(Fo ꢁFc2)2/Sw(Fo2)2]1/2
.
2444 m, 2365 m, 1588 m, 1544 w, 1494 m, 1464 m, 1418 m, 1322
s, 1289 s, 1236 s, 1205 s, 1167 s, 1133 s, 1057 s, 1021 s, 934 w,
885 s, 866 s, 763 m, 589 s, 571 s.
tion is employed, and all hydrogen bonds drawn as dashed
lines. In the discussion, hydrogen bond distances given are
between donor and acceptor heteroatoms. A summary of the
crystal data and structure refinement for 1–4 is given in Table
1. Across the series, all non-hydrogen atoms were refined
anisotropically without restraint. In 1, all hydrogen atoms
were located on Fourier difference maps and refined isotropi-
cally without restraint with the exception of those on the water
molecule, which were restrained to idealized geometries. In 2,
all hydrogen atoms were located on Fourier difference maps
and refined without restraint. In 3, all methylene and ammo-
nium hydrogen atoms were assigned in calculated positions
and refined isotropically with U(H) ¼ 1.2 Ueq (C). The water
and hydrogen sulfate protons were located on Fourier differ-
ence maps but were restrained to idealized geometries during
refinement. In 4, all macrocyclic hydrogen atoms were located
on Fourier difference maps and refined isotropically without
restraint. The water molecule (12 per symmetric unit) was
[H6L(SO4)3] (2). [18]aneN6 (26 mg, 0.10 mmol) was dis-
solved in water (300 mg) and sulfuric acid (conc., 300 mg, 3.2
mmol) was added. The pH was adjusted to 2 using sodium
hydroxide solution (5 M) after which the solution was left to
slowly evaporate. Clear crystals of 2 were produced after
several days. Yield ¼ 20 mg, 36%. Microanalysis (%) Found
C 26.2, H 7.0, N 15.2. Calc. for C12H36N6O12S3: C 26.1, H 6.6
N 15.2. IR bands (n, cmꢁ1) 3501 m, 3036 m, 3008 m, 2855 m,
1619 m, 1605 m, 1522 m, 1495 w, 1464 w, 1430 w, 1418 w, 1322
m, 1300 m, 1150 s, 1087 s, 1058 s, 1030 s, 620 s.
.
[H6L(HSO4)2Cl4] 2H2O (3). Crystals of 3 were originally
found to crystallize in the filtrate from the synthesis of 1,4,7-
triazacyclononane trihydrochloride which was produced via
the classic Richman-Atkins route.23 A few crystals of 3 were
separated from the mixture and used in X-ray structure
determination. A clean synthetic route to 3 has not yet been
devised.
1
modelled as two oxygen atoms each with occupancy. The
4
minor component of the disordered pair was refined isotropi-
cally with its counterpart being refined anisotropically. The
hydrogen atoms on the water molecule were unable to be
located. CCDC reference numbers 246843–246846.w
Results and discussion
.
[H4L(S2O6)2] 2H2O (4). [18]aneN6 (18 mg, 0.06 mmol) was
dissolved in water (2 ml). Sodium dithionate (100 mg, 0.48
mmol) added and the solution was left to slowly evaporate.
Clear crystals of 4 were produced after several days. Yield ¼ 10
mg, 38%. Microanalysis (%) Found C 22.9, H 5.9, N 13.2.
Calc. for C12H38N6O14S4: C 23.3, H 6.2, N 13.6. IR bands (n,
cmꢁ1) 3376 m, 3246 w, 3016 m, 2846 m, 1457 m, 1397 m, 1320
m, 1247 s, 1214 m, 1144 m, 1050 w, 1025 w, 997 s, 943 w, 914 w,
853 w, 790 m, 755 w, 577 s.
The crystallization of adducts 1, 2 and 4 was achieved by slow
evaporation of aqueous solutions containing [18]aneN6 and an
excess of the appropriate anion as the acid for 1 and 2, and the
sodium salt for 4. Intergrowth of the crystals of 3 with other
crystalline products in the reaction vessel made isolation and
thorough analysis impractical. Further attempts to recreate the
product also resulted in an intergrown mixture of crystals
which included the known [H6LCl6] ꢀ 4H2O species21 and 1.
The IR spectra of the adducts showed absorbances that
indicated the presence of the macrocycle and anions and
microanalyses for 1, 2 and 4 corresponded to calculated values
based on the compositions elucidated from crystal structure
determinations.
X-ray crystallography.
Single crystal X-ray data for 1–4 were collected on an Enraf-
Nonius-Kappa CCD diffractometer with monochromated Mo
Ka radiation (l ¼ 0.71073 A) at 123(2) K using phi and/or
omega scans. Data were corrected for Lorentz and polarization
effects. The structures were solved by the direct methods and
refined using the full matrix least-squares method of the
programs SHELXS-9724 and SHELXL-97,25 respectively.
The program X-Seed26 was used as an interface to the SHELX
programs, and to prepare the figures with thermal ellipsoids
drawn at the 50% probability level where ORTEP representa-
.
Structure determinations. [H6L(HSO4)4(SO4)] H2O (1).
The asymmetric unit in 1 consists of a hexaprotonated macro-
cycle whose charge is balanced by four hydrogen sulfate
w See http://www.rsc.org/suppdata/nj/b4/b409088h/ for crystallo-
graphic data in .cif or other electronic format.
1302
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 3 0 1 – 1 3 0 8

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2ꢁ
SO4 anion. The remaining ammonium group (N(1)) is
pushed out of the plane of the other five, donating a hydrogen
2ꢁ
bond to an oxygen atom of a symmetry related SO4 anion
(N(1)–H(2)ꢀ ꢀ ꢀO(2) 2.824(4) A, 125(3)1) and an oxygen atom of
ꢁ
a HSO4 anion bound on the opposite side of the ring to the
sulfate anion (N(1)–H(1)ꢀ ꢀ ꢀO(11) 2.705(4) A, 168(3)1, see Fig.
1). The anions are hydrogen bonded to water, macrocyclic
ammonium groups and each other in a variety of ways, the
most notable of which is the Z-5 coordinated sulfate anion
(S(1)) mentioned above. The penta-coordinated O(1) lies just
0.668(3) A from the least squares plane of the ring defined by
the six nitrogen atoms and is reminiscent of a protonated
sapphyrin–phosphate complex reported recently,27 in which
an oxygen atom of a phosphate anion interacts with all fivꢁe
ammonium groups of the sapphyrin ring. The S(3) HSO4
anion provides a unique example of co-operative C–Hꢀ ꢀ ꢀO
hydrogen bonding (Fig. 2) whose existence has been estab-
lished for other systems.28,29 Two of the oxygen atoms on this
anion each interact with two N–H and one C–H donors, with
the C–Hꢀ ꢀ ꢀO contacts being particularly short but sacrificing
some directionality by sharing the accepting oxygen atom. The
remaining oxygen atoms on S(1), O(4) and O(2), are accepting
H-bonds from an OH and a NH donor, respectively, while
O(3) appears to be participating in a short C–Hꢀ ꢀ ꢀO contact
(C(7)–H(25)ꢀ ꢀ ꢀO(3) 3.151(5) A, 127(3)1) with a neighbouring
macrocycle. Interestingly, the next-closest contact to this oxy-
gen is another carbon atom on the host macrocycle (C(7)–
Fig. 1 ORTEP plot of the asymmetric unit in 1. C–H hydrogen atoms
have been removed for clarity.
anions, one sulfate anion and there is one water molecule of
crystallization (Fig. 1). The ability to locate all hydrogen atoms
gave unequivocal evidence for the degree of protonation of the
macrocycle and the configuration of the oxoanions. Hydrogen
bonding distances and close contacts are listed in Table 2 and
discussed herein.
In 1, [18]aneN6 adopts the most asymmetrical conformation
seen so far for this macrocycle. This arises from the interaction
of five ammonium groups with a single oxygen atom of the
ꢁ
H(15)ꢀ ꢀ ꢀO(3) 3.237(5) A, 134(3)). The HSO4 anion (S(3)) on
the other side of the ring stands astride three of the macrocyclic
Table 2 Hydrogen bond lengths (A) and angles (1) in 1 with esd’s given in parentheses
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
o (DHA)
N(1)–H(1)ꢀ ꢀ ꢀO(11)
O(1)W–H(2)Wꢀ ꢀ ꢀO(6)#1
N(1)–H(2)ꢀ ꢀ ꢀO(2)#2
N(1)–H(2)ꢀ ꢀ ꢀO(13)
N(2)–H(3)ꢀ ꢀ ꢀO(1)
0.93(4)
0.898(10)
0.82(4)
0.82(4)
0.88(5)
0.88(5)
0.91(5)
0.88(4)
0.88(4)
0.88(5)
1.00(5)
1.00(5)
0.90(5)
1.03(5)
1.03(5)
0.86(5)
1.09(5)
0.88(5)
0.88(5)
0.84
1.79(4)
1.92(2)
2.27(4)
2.54(4)
2.15(5)
2.58(5)
1.88(5)
2.08(4)
2.40(4)
1.95(5)
2.02(5)
2.62(5)
1.90(5)
1.98(4)
2.26(4)
1.88(5)
1.87(6)
2.02(5)
2.57(5)
1.67
2.705(4)
2.792(4)
2.824(4)
3.215(4)
3.011(4)
3.101(4)
2.785(4)
2.939(4)
2.870(4)
2.798(4)
3.020(4)
3.165(4)
2.763(4)
2.966(4)
2.818(4)
2.726(4)
2.950(4)
2.822(4)
3.020(4)
2.503(3)
2.590(4)
3.223(4)
2.546(4)
2.615(4)
2.850(4)
3.384(5)
3.230(5)
3.151(5)
3.282(5)
3.384(5)
3.237(5)
3.017(5)
3.085(5)
3.065(5)
3.103(5)
168(3)
163(6)
125(3)
141(3)
165(4)
118(4)
169(4)
165(3)
114(3)
163(4)
173(4)
114(3)
161(4)
159(3)
113(3)
170(4)
171(4)
151(5)
113(4)
170.9
N(2)–H(3)ꢀ ꢀ ꢀO(10)
N(2)–H(4)ꢀ ꢀ ꢀO(18)
N(3)–H(5)ꢀ ꢀ ꢀO(1)
N(3)–H(5)ꢀ ꢀ ꢀO(10)
N(3)–H(6)ꢀ ꢀ ꢀO(20)#3
N(4)–H(7)ꢀ ꢀ ꢀO(1)
N(4)–H(7)ꢀ ꢀ ꢀO(2)
N(4)–H(8)ꢀ ꢀ ꢀO(16)#4
N(5)–H(9)ꢀ ꢀ ꢀO(1)
N(5)–H(9)ꢀ ꢀ ꢀO(12)
N(5)–H(10)ꢀ ꢀ ꢀO(7)#3
N(6)–H(11)ꢀ ꢀ ꢀO(1)
N(6)–H(12)ꢀ ꢀ ꢀO(8)
N(6)–H(12)ꢀ ꢀ ꢀO(12)
O(13)–H(3)Sꢀ ꢀ ꢀO(4)#2
O(5)–H(1)Sꢀ ꢀ ꢀO(14)#5
O(5)–H(1)Sꢀ ꢀ ꢀO(15)#5
O(9)–H(2)Sꢀ ꢀ ꢀO(1)W
O(17)–H(4)Sꢀ ꢀ ꢀO(15)#6
O(1)W–H(1)Wꢀ ꢀ ꢀO(19)#7
C(11)–H(33)ꢀ ꢀ ꢀO(17)#8
C(1)–H(13)ꢀ ꢀ ꢀO(16)
C(7)–H(25)ꢀ ꢀ ꢀO(3)#9
C(4)–H(20)ꢀ ꢀ ꢀO(6)#1
C(2)–H(16)ꢀ ꢀ ꢀO(8)#10
C(2)–H(15)ꢀ ꢀ ꢀO(3)
C(9)–H(30)ꢀ ꢀ ꢀO(12)
C(8)–H(28)ꢀ ꢀ ꢀO(12)
C(4)–H(20)ꢀ ꢀ ꢀO(10)
C(5)–H(21)ꢀ ꢀ ꢀO(10)
1.08(5)
1.08(5)
1.003(10)
0.73(6)
0.895(10)
0.87(4)
1.07(4)
1.00(3)
0.96(4)
1.04(4)
0.92(4)
1.03(4)
0.88(4)
0.96(4)
1.00(4)
1.51(6)
2.65(5)
1.544(12)
1.89(6)
1.972(19)
2.53(4)
2.38(4)
2.44(3)
2.40(4)
2.55(4)
2.53(4)
2.50(4)
2.57(3)
2.59(4)
2.54(4)
177(5)
113(3)
177(6)
171(6)
166(6)
166(3)
135(3)
127(3)
153(3)
137(3)
134(3)
110(3)
119(3)
111(3)
115(3)
Symmetry transformations used to generate equivalent atoms: #1 x þ 1/2, ꢁy þ 1, z #2 x, y þ 1, z #3 x, y ꢁ 1, z #4 ꢁx þ 2, ꢁy þ 1, z þ 1/2 #5 ꢁx þ
3/2, y, z þ 1/2 #6 x þ 1/2, ꢁy þ 2, z #7 ꢁx þ 5/2, y, z þ 1/2 #8 x ꢁ 1/2, ꢁy þ 1, z #9 ꢁx þ 2, ꢁy, z þ 1/2 #10 ꢁx þ 2, ꢁy þ 1, z ꢁ 1/2.
N e w J . C h e m . , 2 0 0 4 , 2 8 , 1 3 0 1 – 1 3 0 8
1303

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Fig. 2 Interactions between the S(3) HSO4ꢁ anion and the macrocycle
in 1. Only selected C–H hydrogen atoms are shown.
Fig. 4 ORTEP plot showing the hydrogen bonding environment
around the macrocycle in 2. Only one of the symmetry related half
occupancy sulfate anions is shown. C–H hydrogen atoms have been
removed for clarity.
ammonium groups, each hydrogen bonded to one of the three
non-protonated oxygen atoms. The OH group on this anion
donates a hydrogen bond to a water molecule in a very short
interaction (O(9)–H(2)Sꢀ ꢀ ꢀꢁO(1)W 2.546(4) A, 177(6)1).
and N(3)–H(6) by O(2). The remaining oxygen, O(4), is
involved in three interactions: one sharing the N(2)–H(4)
hydrogen bond to O(2) and the other two involving short
C–Hꢀ ꢀ ꢀO contacts (C(1)–H(7)ꢀ ꢀ ꢀO(4) 3.119(4) A, 164.2(18)1,
C(5)–H(15)ꢀ ꢀ ꢀO(4) 3.101(3) A, 135(2)1). The other sulfate (S(2))
is bound to its host macrocycle by two interactions through
two oxygen atoms (N(2)–H(3)ꢀ ꢀ ꢀO(5) 2.880(3) A, 164(2)1,
N(1)–H(1)ꢀ ꢀ ꢀO(7) 2.742(2) A, 175(2)1), with an almost-linear
third interaction with an adjacent macrocycle occupying a
third oxygen (N(3)–H(5)ꢀ ꢀ ꢀO(6) 2.694(3) A, 179(2)1) in con-
junction with a short C–Hꢀ ꢀ ꢀO contact (C(2)–H(10)ꢀ ꢀ ꢀO(6)
3.221(3) A, 149(2)1). The fourth oxygen atom on S(2), O(8),
does not participate in significant interactions with the possible
exception of a weak C–Hꢀ ꢀ ꢀO contact (C(3)–H(11)ꢀ ꢀ ꢀO(8)
3.340(3) A, 153(2)1).
The other three HSO4 anions, S(2), S(4) and S(5) are
similar to S(3) in that each of their three non-protonated
1
oxygens are accepting just one hydrogen bond from NH2 or
OH functions, and the OH groups are donating solely to
oxygen atoms. All five sulfate moieties and the water molecule
assemble into 1D chains that run parallel to the b axis (Fig. 3),
separated by macrocycles. The components all pack together to
form a complex and quite dense H-bonded 3D network. There
is a remarkablꢁe difference in the preferred interaction modes
for the HSO4 anions compared to their isostructural but
2ꢁ
doubly charged HPO4
when associating with the same
macrocycle.22 The phosphates tend to have more than one
(often more than two) H-bonds to each of their non-proto-
nated oxygen atoms whereas the sulfates in this structure have
only one, most likely a result of the increased electrostatic
attraction afforded by the extra negative charge on the phos-
phates. There is also a notable difference in the average
O–Hꢀ ꢀ ꢀO bonds involving the sulfate and phosphate anions,
with the latter usually being around 0.1–0.2 A shorter.
The anions are all isolated from one another in the lattice,
owing to their lack of H-bond donating groups, and in contrast
to 1, there are no solvent molecules in the lattice (Fig. 5). The
macrocycle has all twelve of its ammonium protons involved in
N–Hꢀ ꢀ ꢀO interactions. The closest oxygen atom (O(7)) to the
least squares plane of the macrocycle lies 0.876(3) A above it.
[H6L(SO4)3] (2).
Table 3 Hydrogen bond lengths (A) and angles (1) in 2 with esd’s
given in parentheses
2 contains a hexaprotonated macrocycle lying around a two-
fold axis of symmetry with three sulfate anions balancing the
charge (Fig. 4). A list of hydrogen bonds and close contacts for
2 is presented in Table 3.
D–Hꢀ ꢀ ꢀA
d(D–H) d(Hꢀ ꢀ ꢀA) d(Dꢀ ꢀ ꢀA) o(DHA)
N(1)–H(1)ꢀ ꢀ ꢀO(7)
N(1)–H(2)ꢀ ꢀ ꢀO(5)#3
N(1)–H(2)ꢀ ꢀ ꢀO(6)#3
N(2)–H(3)ꢀ ꢀ ꢀO(5)
N(2)–H(3)ꢀ ꢀ ꢀO(7)
N(2)–H(4)ꢀ ꢀ ꢀO(4)#1
N(2)–H(4)ꢀ ꢀ ꢀO(1)
N(2)–H(4)ꢀ ꢀ ꢀO(3)
N(2)–H(4)ꢀ ꢀ ꢀO(2)#1
N(3)–H(5)ꢀ ꢀ ꢀO(6)#4
N(3)–H(5)ꢀ ꢀ ꢀO(8)#4
N(3)–H(6)ꢀ ꢀ ꢀO(1)#5
N(3)–H(6)ꢀ ꢀ ꢀO(2)#6
N(3)–H(6)ꢀ ꢀ ꢀO(3)#6
C(1)–H(7)ꢀ ꢀ ꢀO(4)#7
0.93(3)
0.91(2)
0.91(2)
0.86(3)
0.86(3)
0.92(3)
0.92(3)
0.92(3)
0.92(3)
0.93(3)
0.93(3)
0.91(3)
0.91(3)
0.91(3)
0.94(2)
1.81(3)
2.06(2)
2.52(2)
2.04(3)
2.55(3)
1.81(3)
1.94(3)
2.40(3)
2.41(3)
1.76(3)
2.60(3)
2.00(3)
2.08(3)
2.31(3)
2.20(2)
2.36(2)
2.41(2)
2.33(2)
2.42(2)
2.742(2)
2.892(2)
3.309(3)
2.880(3)
3.222(2)
2.643(3)
2.831(3)
3.090(3)
3.169(3)
2.694(3)
3.133(2)
2.906(3)
2.786(3)
3.039(4)
3.119(4)
3.221(3)
3.340(3)
3.101(3)
3.019(2)
175(2)
151(2)
145(2)
164(2)
135(2)
148(2)
160(2)
132(2)
140(2)
179(2)
117(2)
178(2)
133(2)
137(2)
164(2)
149(2)
153(2)
135(2)
119(2)
One of the sulfates (S(1)) present in the asymmetric unit has
one half occupancy, with expansion of the asymmetric unit
revealing the other half with perfectly superimposed sulfur
atoms but with its oxygen atoms lying directly on the opposite
side of the sulfur atom (i.e. O(1)–S(1)–O(1)* ¼ 1801). Each has
O(1) bridging neighbouring macrocycles through N(2)–
H(4)ꢀ ꢀ ꢀO(1)ꢀ ꢀ ꢀH(6)–N(3). O(2) acts in a similar manner utiliz-
ing N(2) and N(3) on two separate macrocycles to those
bridged by O(1) while O(3) bridges two macrocycles through
N(2) and N(3), however the N(2)–H(4) donor is shared by O(1)
C(2)–H(10)ꢀ ꢀ ꢀO(6)#3 0.97(2)
C(3)–H(11)ꢀ ꢀ ꢀO(8)#8 1.01(2)
C(5)–H(15)ꢀ ꢀ ꢀO(4)#5 0.98(2)
C(5)–H(15)ꢀ ꢀ ꢀO(5)#6 0.98(2)
Symmetry transformations used to generate equivalent atoms: #1 ꢁx,
ꢁy, ꢁz #3 ꢁx, ꢁy þ 1, ꢁz #4 ꢁx þ 1, y ꢁ 1/2, ꢁz þ 1/2 #5 ꢁx þ 1, ꢁy,
ꢁz #6 x þ 1, y, z #7 ꢁx, y þ 1/2, ꢁ z ꢁ 1/2 #8 x, ꢁy þ 1/2, z ꢁ 1/2.
2ꢁ
Fig. 3 ORTEP plot of the 1D chains formed by the HSO4ꢁ and SO4
anions, and water in 1. Macrocycles have been removed for clarity.
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Table 4 Hydrogen bond lengths (A) and angles (1) in 3 with esd’s
given in parentheses
D–Hꢀ ꢀ ꢀA
d(D–H) d(Hꢀ ꢀ ꢀA) d(Dꢀ ꢀ ꢀA) 4(DHA)
N(1)–H(1)ꢀ ꢀ ꢀCl(2)
N(1)–H(2)ꢀ ꢀ ꢀO(2)#2
N(1)–H(2)ꢀ ꢀ ꢀO(1)W#3
N(2)–H(4)ꢀ ꢀ ꢀCl(1)
N(2)–H(3)ꢀ ꢀ ꢀCl(2)
N(3)–H(6)ꢀ ꢀ ꢀO(3)#4
N(3)–H(6)ꢀ ꢀ ꢀO(2)#4
N(3)–H(5)ꢀ ꢀ ꢀCl(1)#5
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
2.16
2.11
2.29
2.24
2.33
2.11
2.52
2.19
3.0573(18) 165
2.887(2)
2.982(2)
141
132
3.1173(18) 160
3.1658(18) 151
2.842(2)
3.000(2)
136
113
3.0916(19) 165
170(3)
3.2293(16) 153(3)
O(1)W–H(1)Wꢀ ꢀ ꢀO(4)#6 0.994(10) 1.746(11) 2.731(2)
O(1)W–H(2)Wꢀ ꢀ ꢀCl(1)
O(1)–H(19)ꢀ ꢀ ꢀO(1)W
C(6)–H(17)ꢀ ꢀ ꢀCl(2)
0.991(10) 2.31(2)
0.998(10) 1.573(14) 2.554(2)
0.99 2.66 3.605(2)
166(4)
160
Symmetry transformations used to generate equivalent atoms: #2 x ꢁ 1
/2, ꢁy þ 1/2, z þ 1/2 #3 x þ 1/2, ꢁy þ 1/2, z þ 1/2 #4 ꢁx þ 1, ꢁy, ꢁz þ
1 #5 ꢁx, ꢁy, ꢁz þ 1 #6 x ꢁ 1/2, ꢁy þ 1/2, z ꢁ 1/2.
Fig. 5 Packing of the structure in 2 viewed down the b axis. Both parts
1
of the occupancy sulfate are shown. Hydrogen atoms have been
removed for clarity.
2
(Fig. 7), which lie parallel to each other (but out of direct
contact) to form 2D sheets that are separated by layers of
macrocycle-bound chlorides. Cl(1) has the only interaction
between the chloride anions and the water–sulfate chains
(O(1)W–H(2)Wꢀ ꢀ ꢀCl(1) 3.2293(16) A, 153(3)1). It also shows
the trigonal pyramid motif, acting as a bridge between macro-
cycles (N(2)ꢀ ꢀ ꢀCl(1)ꢀ ꢀ ꢀN(3)*). The distances from the planes of
their H-bond donors are 1.279(1) A and 1.731(2) A for Cl(1)
and Cl(2), respectively.
.
[H6L(HSO4)2Cl4] 2H2O (3)
The structure of 3 contains a hexaprotonated macrocycle, two
hydrogen sulfate anions and four chlorides, with two waters of
crystallization (Fig. 6). Table 4 contains a list of hydrogen
bonds and close contacts in the structure.
The macrocycle lies around a two-fold crystallographic axis
of symmetry, and is elongated along the axis defined by N(3)
and N(3)*. Preference is given to chloride as a cavity guest, in
spite of fact that a weak C–Hꢀ ꢀ ꢀCl contact (C(6)–H(17)ꢀ ꢀ ꢀCl(2)
3.605(2) A, 1601) completes the trigonal co-ordination geome-
try often adopted by chlorides.30 [18]aneN6 was observed to
chelate chloride anions in preference to nitrates in a structure
reported by Cullinane et al.,15 leaving the nitrates to form
hydrogen bonded networks with water molecules much like
those formed by sulfate and water in the present structure.
Cl(2) lies 1.9221(6) A from the least squares plane of the
macrocycle, significantly further out than the chelated oxygen
atoms in 1, 2 and 4, due to its larger van der Waals radius. The
hydrogen sulfate and water moieties link up to form 1D chains
ꢁ
The two O–Hꢀ ꢀ ꢀO contacts between the water and HSO4
anions are very different, with the interaction involving hydro-
gen sulfate as donor being significantly shorter than its coun-
terpart: 2.554(2) A, 166(4)1 for O(1)–H(19)ꢀ ꢀ ꢀO(1)W compared
to 2.731(2) A, 170(3)1 for O(1)W–H(1)Wꢀ ꢀ ꢀO(4). The hydro-
gen sulfate itself shows a different overall co-ordination geo-
metry to the four found in 1, with one of its oxygen atoms,
O(3), accepting two hydrogen bonds from adjacent macro-
cycles whereas the HSO4ꢁ anions in 1 only accept one H-bond
to each of their three non-protonated oxygen atoms.
.
[H4L(S2O6)2] 2H2O (4).
The structure of 4 (Fig. 8) consists of a tetraprotonated
macrocycle lying on a four-fold crystallographic axis of sym-
metry, two disordered waters and two dithionate anions which
are involved in hydrogen bonding to the ammonium groups,
one above and one below the ring. In the asymmetric unit, the
dithionate is one half dithionate split along a plane defined by
O(1)–S(2)–S(1)–O(3), with these atoms all having half occu-
pancy. The water molecule is lying in the middle of a hydro-
phobic hole formed from the CH2 groups of surrounding
macrocycles, with its closest and only interaction being with
Fig. 6 ORTEP plot of the hydrogen bonding environment around the
macrocycle in 2. Non-interacting C–H hydrogen atoms have been
removed for clarity. All hydrogen atoms participating in hydrogen
bonds to chloride anions are included.
Fig. 7 Packing diagram of 3 highlighting the 2D sheets formed by
sulfate anions and water.
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Table 5 Hydrogen bond lengths (A) and angles (1) in 4 with esd’s
given in parentheses
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
d(Dꢀ ꢀ ꢀA)
o(DHA)
N(2)–H(3)ꢀ ꢀ ꢀO(2)
N(2)–H(3)ꢀ ꢀ ꢀO(2)#4
N(2)–H(2)ꢀ ꢀ ꢀO(3)#5
N(2)–H(2)ꢀ ꢀ ꢀO(3)
N(2)–H(2)ꢀ ꢀ ꢀN(1)
0.94(4)
0.94(4)
0.87(3)
0.87(3)
0.87(3)
2.12(4)
2.64(4)
2.11(3)
2.58(3)
2.41(3)
2.966(3)
3.181(3)
2.911(3)
3.106(3)
2.823(3)
150(3)
117(3)
154(3)
120(2)
110(2)
Symmetry transformations used to generate equivalent atoms: #4 ꢁx þ
1/2, ꢁy þ 1/2, ꢁz þ 2 #5 ꢁx þ 1, ꢁy, ꢁz þ 2.
symmetry generated, N(2)–H(2)ꢀ ꢀ ꢀN(1) 2.823(3) A, 110(2)1)
which help to maintain the orientation of the amines, with the
main driving force of the macrocyclic elongation being the two
bridges (N–Hꢀ ꢀ ꢀOꢀ ꢀ ꢀH–N and N–Hꢀ ꢀ ꢀO–S–Oꢀ ꢀ ꢀH–N) running
perpendicular to its longest N–N axis. A list of the hydrogen
bonds in 4 is given in Table 5. The packing of the structure
(Fig. 10) shows the macrocycles all oriented in the same way
within the lattice forming stacks of alternating macrocycle–
dithionate moieties, separated by solvent water molecules.
Fig. 8 ORTEP plot of the hydrogen bonding environment surround-
ing the macrocycle in 4. The dashed line connecting O(3) and O(3)*
through the macrocyclic cavity indicates a close contact rather than a
hydrogen bond.
one of the dithionate oxygen atoms (O(1)W–O(1) 2.803(20) A),
with O(1) presumably acting as a hydrogen bond acceptor.
The dithionate anion sits above the macrocycle and is
supported by four N–Hꢀ ꢀ ꢀO interactions. The mode of inter-
action of the macrocycle with the dithionate anion is somewhat
reminiscent of that seen in the analogous CF3SOꢁ3 adduct with
[18]aneN6 which had the anion bound to the cavity by a single
oxygen atom as in 4, with two separate N–Hꢀ ꢀ ꢀF interactions
at the other end of the macrocycle.19 In that example, the
shortness of the C–S bond compared to the S–S bond in the
present structure allowed the two ammonium groups chelating
the fluorines to use their other protons to provide two addi-
tional N–Hꢀ ꢀ ꢀO interactions to the already doubly-bound
oxygen atom (N–Hꢀ ꢀ ꢀO B2.9 A). The same interactions are
not possible in the present structure due to the two N(2)–
H(3)ꢀ ꢀ ꢀO(2) bonds stretching the macrocycle and leaving the
Nꢀ ꢀ ꢀO distance to the chelated oxygen atom at around 3.1 A.
Notably, the O(3)ꢀ ꢀ ꢀO(3)* distance through the plane of the
macrocycle is quite short, 2.652(5) A, and suggestive of an O–
Hꢀ ꢀ ꢀO interaction, however there is no evidence supporting the
presence of a proton between these two oxygen atoms. The
anions and water molecules form 1D chains that run parallel to
the a–b–c plane, threading through the macrocycle with the
short O(3)ꢀ ꢀ ꢀO(3)* contact (Fig. 9).
Hydrogen bonding modes of sulfur oxoanions.
Fig. 11 shows the hydrogen bonding modes for ꢁthe hydrogen
sulfate anions found in 1 and 3. For each HSO4 anion, each
oxygen atom is accepting only one hydrogen bond with the
notable exception of the tripodal hydrogen bonding involving
C–H and N–H donors for the anion in 1. The OH group of
each anion invariably donates a hydrogen bond to an oxygen
atom of either another anion or a water molecule.
The sulfate and dithionate anions behave differently to the
hydrogen sulfate anions in that there is a tendency towards
multiple hydrogen bonds to one oxygen atom (Fig. 12). Inter-
estingly, three of the six dithionate oxygen atoms are not
participating in any hydrogen bonds, and one oxygen atom
on each sulfate anion is also completely free of H-bond
interactions. In the case of the sulfate participating in the Z-5
hydrogen bonding motif there are two oxygen atoms devoid of
H-bond interactions, however, there is a particꢁularly strong O–
Hꢀ ꢀ ꢀO interaction with a neighbouring HSO4 anion with an
Oꢀ ꢀ ꢀO distance of 2.503(3) A. Whilst most of the N–Hꢀ ꢀ ꢀO
interactions have Nꢀ ꢀ ꢀO distances of between 2.7 A and 3.0 A
there are stronger interactions down to 2.64 A. The C–Hꢀ ꢀ ꢀO
All four of the macrocyclic ammonium groups are involved
in O–Hꢀ ꢀ ꢀO interactions with dithionate groups with the
macrocyclic amines finding no suitable acceptors. The macro-
cycle is elongated along its N(1)–N(1)* axis (which is also the
S(1)–S(2) axis of the anions on either side of the ring) and in
contrast to the hexaprotonated macrocycles in 2 and 3, has all
of its nitrogen atoms directed in towards the center of the
macrocycle. This is not surprising as the positive charge of the
macrocycle is neutralized solely by the two anions chelated
within the ring, hence there is no requirement for charge
distribution to an external negatively-charged component.
There is a total of four internal N–Hꢀ ꢀ ꢀN interactions (three
Fig. 9 1D chain formed by the disordered water molecules and
dithionate.anions in 4 (ORTEP) threaded through the macrocycles
(stick representation).
Fig. 10 Packed view of the macrocycles and dithionate anions in 4
viewed down the b axis. Water molecules are not shown for clarity.
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dithionate and sulfate, including an Z-5 hydrogen bonding
motif to a single sulfate oxygen atom with a unique asymmetric
conformation of the macrocycle and a series of co-operative C–
Hꢀ ꢀ ꢀO hydrogen bonding interactions contributing to the
tripodal binding of a hydrogen sulfate anion to the other side
of the macrocyclic cavity. In the dithionate adduct there is a
very close Oꢀ ꢀ ꢀO contact between dithionate anions through a
macrocyclic cavity with (surprisingly) no hydrogen bond di-
rectly connecting the two, highlighting the ability of [18]aneN6
to bring two negatively charged atoms to within the sum of
their van der Waals radii. When presented with the option of
chelating to a chloride anion, the macrocycle binds it in
preference to sulfate (and nitrate15,16), allowing anions with a
greater number of hydrogen bonding possibilities to form
networks beyond the macrocycle to stabilize the chloride
binding motif in the solid state.
Acknowledgements
This work was supported by the Australian Research Council.
ACW gratefully acknowledges the award of a Teaching fellow-
ship and Departmental Scholarship from Monash University.
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