Metal ion recognition. Interaction of a series of successively N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane (cyclam) with selected transition and post-transition metal ions

Article abstract of DOI:10.1039/b300002h

The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four N-benzyl groups with cobalt(II), zinc(II), cadmium(II), lead(II) and silver(I) nitrates is reported; the results are compared with those obtained in a prior study involving the formation of the corresponding complexes of nickel(II) and copper(II) with this ligand series. The isolation of a selection of 1:1 (metal: ligand) complexes has been carried out and X-ray diffraction structures of five such products have been determined. In each complex the metal ion is coordinated to the N₄-donor set of the cyclam ring with the latter adopting either a trans-I or a trans-V configuration; monodentate or bidentate nitrato ligands complete the respective coordination spheres. Coordination numbers range from five in a zinc(II) complex, through six in two cadmium(II) complexes, to eight in two lead(II) complexes. Competitive bulk membrane transport experiments (water/chloroform/ water) have been carried out in which each of the five benzylated ligands were in turn employed as the ionophore in the chloroform phase. The respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) nitrates. The aqueous receiving phase was buffered at pH 3.0. Under these conditions, high selectivity for copper(II) was observed for each of the ionophores incorporating one or two N-benzyl groups whereas no transport for any of the seven metals present in the source phase was observed for the tribenzylated derivative. In marked contrast to the above behaviour, the tetra-N-benzyl derivative yielded sole transport selectivity for silver(I) under similar conditions. ¹H NMR and ¹³C NMR titration experiments in CD₃CN-CDCl₃ confirmed the 1:1 stoichiometry of the silver(I) tetra-N-benzylcyclam complex in this solvent mixture. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b300002h

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Metal ion recognition. Interaction of a series of successively
N-benzylated derivatives of 1,4,8,11-tetraazacyclotetradecane
(cyclam) with selected transition and post-transition metal ions
Ying Dong,a Sandra Farquhar,b Karsten Gloe,c Leonard F. Lindoy,*a Brendan R. Rumbel,b
Peter Turnera and Kathrin Wichmannc
a Centre for Heavy Metals Research, School of Chemistry, The University of Sydney,
N.S.W. 2006, Australia
b School of Biomedical and Molecular Science, James Cook University, Townsville, Qld. 4811,
Australia
c Institute of Inorganic Chemistry, TU Dresden, D-01062 Dresden, Germany
Received 2nd January 2003, Accepted 26th February 2003
First published as an Advance Article on the web 11th March 2003
The interaction of a series of N-benzylated cyclam ligand derivatives incorporating from one to four N-benzyl groups
with cobalt(), zinc(), cadmium(), lead() and silver() nitrates is reported; the results are compared with those
obtained in a prior study involving the formation of the corresponding complexes of nickel() and copper() with
this ligand series. The isolation of a selection of 1 : 1 (metal : ligand) complexes has been carried out and X-ray
diffraction structures of five such products have been determined. In each complex the metal ion is coordinated to the
N4-donor set of the cyclam ring with the latter adopting either a trans-I or a trans-V configuration; monodentate or
bidentate nitrato ligands complete the respective coordination spheres. Coordination numbers range from five in a
zinc() complex, through six in two cadmium() complexes, to eight in two lead() complexes. Competitive bulk
membrane transport experiments (water/chloroform/water) have been carried out in which each of the five benzylated
ligands were in turn employed as the ionophore in the chloroform phase. The respective aqueous source phases
(buffered at pH 4.9) contained an equimolar mixture of cobalt(), nickel(), copper(), zinc(), cadmium(), silver()
and lead() nitrates. The aqueous receiving phase was buffered at pH 3.0. Under these conditions, high selectivity for
copper() was observed for each of the ionophores incorporating one or two N-benzyl groups whereas no transport
for any of the seven metals present in the source phase was observed for the tribenzylated derivative. In marked
contrast to the above behaviour, the tetra-N-benzyl derivative yielded sole transport selectivity for silver() under
similar conditions. 1H NMR and 13C NMR titration experiments in CD3CN–CDCl3 confirmed the 1 : 1
stoichiometry of the silver() tetra-N-benzylcyclam complex in this solvent mixture.
Introduction
Owing to the presence of a central cavity, macrocyclic ligands
have long been employed as selective hosts for a wide range of
guest molecules and ions.1 Thus, macrocyclic systems have been
employed as selective extractants/ionophores for transition and
post-transition metal ions in a range of solvent extraction2,3
and bulk membrane transport studies.3,4 In this context, the
modification of tetraaza macrocyclic ligands to control and
tune the properties of coordinated metal centres has also been
the subject of much interest.1 For example, in previous studies
we have documented that N-benzylation of the nitrogen
donors in individual mixed oxygen–nitrogen donor macrocycles
leads to enhanced metal ion determination for silver() relative
to cobalt(), nickel(), copper(), zinc(), cadmiun() and
lead()—a phenomenom we refer to as ‘selective detuning’.5,6
In a recent study7 we have investigated the interaction of
nickel() and copper() with N-benzylated derivatives 1–5
(Scheme 1), with emphasis on the relationship between the elec-
trochemical, spectrophotometric and structural features of the
corresponding complexes. The present report represents an
extension of this latter study.
Experimental
Where available, commercial reagents and solvents were of
analytical (or HPLC) grade. The preparation of ligands 1–5
have been reported previously.8
Scheme 1
obtained on a Finnigan LCQ-8 spectrometer. AAS data were
collected on a SpectrAAؒ800, solid state UV-Vis spectra were
measured on a CARY 1E UV-Visible Spectrophotometer,
and solution UV-Vis spectra on a CARY 5E UV-Vis-NIR
Physical methods
1H and 13C NMR spectra were recorded on a Bruker Avance
DPX300 spectrometer. Low resolution (ES) spectra were
D a l t o n T r a n s . , 2 0 0 3 , 1 5 5 8 – 1 5 6 6
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 2 0 0 3
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Table 1 Pertinent geometry details (bond lengths in Å angles in Њ) for
[Pb(1)(NO3)2]
Spectrophotometer. X-Ray diffraction data were obtained on a
Bruker SMART 1000 CCD diffractometer.
Pb(1)–N(4)
Pb(1)–N(3)
Pb(1)–O(4)
Pb(1)–O(2)
Pb(2)–N(8)
Pb(2)–N(9)
Pb(2)–O(10)
Pb(2)–O(8)
2.445(3)
2.505(3)
2.820(3)
3.044(3)
2.452(2)
2.552(3)
2.842(2)
3.059(2)
Pb(1)–N(2)
Pb(1)–N(1)
Pb(1)–O(1)
Pb(1)–O(5)
Pb(2)–N(10)
Pb(2)–N(7)
Pb(2)–O(11)
Pb(2)–O(7)
2.502(3)
2.646(3)
2.829(2)
3.057(3)
2.483(3)
2.657(2)
2.975(2)
3.102(3)
Membrane transport
The transport experiments employed a ‘concentric cell’ in
which the aqueous source phase (10 cm3) and receiving phase
(30 cm3) were separated by a chloroform phase (50 cm3). Details
of the cell design have been reported elsewhere.9 For each
experiment both aqueous phases and the chloroform phase
were stirred separately at 10 rpm; the cell was enclosed by a
water jacket and thermostated at 25 ЊC. The aqueous source
phase was buffered (CH3CO2H–CH3CO2Na) at pH 4.9 ( 0.1)10
and contained an equimolar mixture of the nitrate salts of
cobalt(), nickel(), copper(), zinc(), cadmium(), lead()
and silver(), each at a concentration of 1 × 10Ϫ2 mol dmϪ3. The
chloroform phase contained the ligand (1 × 10Ϫ3 mol dmϪ3),
as well as palmitic acid (4 × 10Ϫ3 mol dmϪ3). The receiving
phase consisted of a buffer (HCO2H–HCO2Na) solution10 at
N(4)–Pb(1)–N(2)
N(4)–Pb(1)–N(3)
N(2)–Pb(1)–N(3)
N(4)–Pb(1)–N(1)
N(2)–Pb(1)–N(1)
N(3)–Pb(1)–N(1)
N(4)–Pb(1)–O(4)
N(2)–Pb(1)–O(4)
N(3)–Pb(1)–O(4)
N(1)–Pb(1)–O(4)
N(4)–Pb(1)–O(1)
N(2)–Pb(1)–O(1)
N(3)–Pb(1)–O(1)
N(1)–Pb(1)–O(1)
O(4)–Pb(1)–O(1)
N(4)–Pb(1)–O(2)
N(2)–Pb(1)–O(2)
N(3)–Pb(1)–O(2)
N(1)–Pb(1)–O(2)
O(4)–Pb(1)–O(2)
O(1)–Pb(1)–O(2)
N(4)–Pb(1)–O(5)
N(2)–Pb(1)–O(5)
N(3)–Pb(1)–O(5)
N(1)–Pb(1)–O(5)
O(4)–Pb(1)–O(5)
O(1)–Pb(1)–O(5)
O(2)–Pb(1)–O(5)
80.18(9)
79.33(9)
71.12(9)
70.49(8)
77.78(8)
139.68(8)
155.58(8)
79.85(9)
81.02(9)
118.33(9)
95.59(8)
150.09(8)
78.99(8)
128.97(7)
94.73(9)
74.53(8)
153.55(8)
110.90(8)
86.48(7)
126.56(8)
42.89(7)
149.95(8)
88.69(8)
123.33(9)
79.92(7)
42.83(8)
107.34(7)
109.52(7)
N(8)–Pb(2)–N(10)
N(8)–Pb(2)–N(9)
N(10)–Pb(2)–N(9)
N(8)–Pb(2)–N(7)
N(10)–Pb(2)–N(7)
N(9)–Pb(2)–N(7)
N(8)–Pb(2)–O(10)
N(10)–Pb(2)–O(10)
N(9)–Pb(2)–O(10)
N(7)–Pb(2)–O(10)
N(8)–Pb(2)–O(11)
N(10)–Pb(2)–O(11)
N(9)–Pb(2)–O(11)
N(7)–Pb(2)–O(11)
O(10)–Pb(2)–O(11)
N(8)–Pb(2)–O(8)
N(10)–Pb(2)–O(8)
N(9)–Pb(2)–O(8)
N(7)–Pb(2)–O(8)
O(10)–Pb(2)–O(8)
O(11)–Pb(2)–O(8)
N(8)–Pb(2)–O(7)
N(10)–Pb(2)–O(7)
N(9)–Pb(2)–O(7)
N(7)–Pb(2)–O(7)
O(10)–Pb(2)–O(7)
O(11)–Pb(2)–O(7)
O(8)–Pb(2)–O(7)
81.33(9)
77.79(8)
70.33(8)
70.61(8)
78.24(8)
138.14(7)
87.48(8)
145.70(7)
75.64(7)
128.04(7)
74.22(8)
153.67(8)
112.80(7)
84.49(7)
43.78(6)
143.24(7)
86.66(8)
129.99(7)
72.97(7)
119.62(7)
107.20(7)
156.52(8)
75.69(9)
89.87(8)
108.68(8)
108.94(8)
129.24(7)
40.66(6)
pH 3.0
0.1. Atomic absorption spectroscopy was used to
determine the amount of metal ion transported over this
period. Transport rates (J values) are in mol/24 h; they repre-
sent the total number of moles of each metal ion present in the
aqueous receiving phase at the end of the 24 h period used for
the experiment divided by 24. The transport results are quoted
as the average values obtained from duplicate runs (errors ca.
10% of reported value). The hydrophilicity of 6 (cyclam) led
to bleeding of this ionophore to the aqueous phases and, as a
consequence, runs involving this species were aborted. A ‘con-
trol’ experiment containing only palmitic acid in the chloro-
form membrane phase confirmed that no metal ion transport
took place in the absence of the macrocyclic ionophore.
X-Ray structure determinations
Full sphere data were collected at 150(2) K, with the exception
of the Pb complex with 3 for which data were collected at
294(2) K. Data were collected with ω scans to 56Њ 2θ using a
Bruker SMART 1000 CCD diffractometer employing graphite-
monochromated Mo-Kα radiation generated from a sealed
tube (0.71073 Å). The data integration and reduction were
undertaken with SAINT and XPREP,11 and subsequent com-
putations were carried out with the teXsan,12 WinGX13 and
XTAL14 graphical user interfaces. A recollection of the reflec-
tions in the first 50 CCD frames at the end of the collection
showed no significant change in intensities. A Gaussian absorp-
tion correction was applied to the data for the Pb(1), Cd(3) and
Zn(4) complexes with XPREP,15,16 and a multiscan empirical
correction was applied to these data for the Cd(2) and Pb(3)
complexes using SADABS.17,18
The structure of [Pb(1)(NO3)2] was solved by direct methods
using SHELXS-9719 and the other structures were solved using
SIR97.20 The structures were extended and refined with
SHELXL-97.19 In general, the non-hydrogen atoms were
modelled with anisotropic thermal parameters and a riding
atom model was used for the hydrogen atoms. ORTEP21
depictions of the molecule with 20% displacement ellipsoids are
provided in Figs. 1–5, and pertinent geometry details are pro-
vided in Tables 1–5.
λ(Mo-Kα)
=
0.71073 Å, µ(Mo-Kα)
=
7.717 mmϪ1
,
T (Gaussian)min,max = 0.069, 0.603, 2θmax = 56.20, hkl range
Ϫ15 to 15, Ϫ16 to 16, Ϫ19 to 19, N = 20115, Nind = 9607 (Rmerge
= 0.0314), Nobs = 8472 (I > 2σ(I )), Nvar = 565, residuals R1(F) =
0.0194, wR2(F 2) = 0.0454 (A = 0.02, B = 0.5), GoF(all) = 1.201,
∆ρmin,max = Ϫ0.830, 0.968 eϪ ÅϪ3
.
Specific details: the amine hydrogens were located and mod-
elled isotropically.
[Cd(2)(NO3)]NO3ؒ0.5MeOH: C24.5H38CdN6O6.5, M = 633.01,
¯
triclinic, space group P1 (#2), a = 9.537(6), b = 11.146(7),
c = 13.097(8) Å, α = 94.789(11), β = 93.115(11), γ = 93.292(11)Њ,
V = 1382.6(15) Å3, Dc = 1.521 g cm,Ϫ3, Z = 2, crystal size 0.389 ×
0.354 × 0.160 mm, colour colourless, habit prism, temperature
150(2) K, λ(Mo-Kα) = 0.71069 Å, µ(Mo-Kα) = 0.841 mmϪ1
,
T (SADABS)min,max = 0.84, 1.00, 2θmax = 56.40, hkl range Ϫ12 to
12, Ϫ14 to 14, Ϫ17 to 17, N = 13482, Nind = 6350 (Rmerge
=
0.0212), Nobs = 5702 (I > 2σ(I )), Nvar = 334, residuals R1(F) =
0.0297, wR2(F 2) = 0.0685 (A = 0.02, B = 0.05), GoF(all) = 1.369,
∆ρmin,max = Ϫ0.800, 0.968 eϪ ÅϪ3
.
Specific details: the asymmetric unit contains a complex
molecule with a coordinated nitrate counter ion, a disordered
non-coordinated nitrate counter ion and a partially occupied
methanol solvate site. The disordered nitrate counter ion was
modelled with three rigid bodies having partial occupancies
that were refined and then fixed. The methanol molecule site
occupancies were also refined and then fixed. The partially
occupied non-hydrogen sites were modelled with isotropic dis-
placement parameters, and the two amine hydrogen sites were
located and modelled isotropically.
The refinement residuals are defined as R1 = Σ||Fo| Ϫ |Fo||/
2
Σ|Fo| for Fo > 2σ(Fo) and wR2 = (Σw(Fo Ϫ Fc2)2/Σ(wFc2)2)1/2 all
2
2
reflections where w = 1/[σ2(Fo ) ϩ (AP)2 ϩ BP], P = (Fo2 ϩ 2Fo )/
3] and A and B are as listed below.
Crystal data
[Pb(1)(NO3)2]: C17H30N6O6Pb, M = 621.66, triclinic, space
[Cd(3)(NO3)]NO3ؒMeOH: C25H40CdN6O7, M = 649.03,
¯
group P1 (#2), a = 11.847(3), b = 12.448(3), c = 14.959(4) Å,
monoclinic, space group P21/c (#14), a = 8.330(2), b = 15.976(4),
c = 22.011(6) Å, β = 97.475(4), V = 2904.3(14) Å3, Dc = 1.484 g
cmϪ3, Z = 4, crystal size 0.442 × 0.397 × 0.375 mm, colour
colourless, habit priamatic, temperature 150(2) K, λ(Mo-Kα) =
α = 86.322(4), β = 89.620(4), γ = 87.247(4)Њ, V = 2199.0(10) Å3,
Dc = 1.878 g cmϪ3, Z = 4, crystal size 0.508 × 0.187 × 0.066
mm, colour colourless, habit tabular, temperature 150(2) K,
D a l t o n T r a n s . , 2 0 0 3 , 1 5 5 8 – 1 5 6 6
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Table 2 Pertinent geometry details (bond lengths in Å angles in Њ) for [Cd(2)(NO3)]NO3ؒ0.5MeOH
Cd(1)–N(3)
Cd(1)–N(1)
Cd(1)–O(1)
2.283(2)
2.320(2)
2.369(2)
Cd(1)–N(4)
Cd(1)–N(2)
Cd(1)–O(2)
2.307(2)
2.364(2)
2.460(2)
N(3)–Cd(1)–N(4)
N(3)–Cd(1)–N(1)
N(4)–Cd(1)–N(1)
N(3)–Cd(1)–N(2)
N(4)–Cd(1)–N(2)
N(1)–Cd(1)–N(2)
N(3)–Cd(1)–O(1)
N(4)–Cd(1)–O(1)
92.40(8)
129.59(8)
80.78(9)
78.41(7)
163.66(8)
94.59(7)
87.43(8)
95.91(9)
N(1)–Cd(1)–O(1)
N(2)–Cd(1)–O(1)
N(3)–Cd(1)–O(2)
N(4)–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
N(2)–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
142.78(6)
97.14(8)
140.06(7)
95.29(8)
90.34(7)
100.42(7)
52.84(6)
Hydrogen bond geometry
Donor
Hydrogen
Acceptor
D–H/Å
H ؒ ؒ ؒ A/Å
D ؒ ؒ ؒ A/Å
D–H ؒ ؒ ؒ A/Њ
N(3)
N(4)
N(4)
N(4)
O(13)
O(13)
H(3N)
H(4N)
H(4N)
H(4N)
H(13A)
H(13A)
O(1a)
O(6)
O(5)
O(10)
O(10)
O(7)
0.84(3)
0.82(3)
0.82(3)
0.82(3)
0.84
2.23(3)
2.26(3)
2.32(3)
2.47(3)
1.96
2.936(3)
2.947(5)
3.114(5)
3.152(6)
2.770(9)
2.891(8)
143(2)
142(3)
162(3)
141(2)
161.7
0.84
2.15
146.7
a 1 Ϫ x, 1 Ϫ y, Ϫz .
Table 3 Pertinent geometry details (bond lengths in Å angles in Њ) for [Cd(3)(NO3)]NO3ؒMeOH
Cd(1)–N(4)
Cd(1)–N(3)
Cd(1)–O(1)
2.2589(16)
2.3718(16)
2.3603(14)
Cd(1)–N(2)
Cd(1)–N(1)
Cd(1)–O(2)
2.2671(16)
2.3692(16)
2.4837(14)
N(4)–Cd(1)–N(2)
N(4)–Cd(1)–O(1)
N(2)–Cd(1)–O(1)
N(4)–Cd(1)–N(1)
N(2)–Cd(1)–N(1)
O(1)–Cd(1)–N(1)
N(4)–Cd(1)–N(3)
N(2)–Cd(1)–N(3)
127.40(6)
138.81(5)
93.79(5)
80.06(6)
93.10(6)
99.77(5)
91.12(6)
80.22(5)
O(1)–Cd(1)–N(3)
N(1)–Cd(1)–N(3)
N(4)–Cd(1)–O(2)
N(2)–Cd(1)–O(2)
O(1)–Cd(1)–O(2)
N(1)–Cd(1)–O(2)
N(3)–Cd(1)–O(2)
96.81(5)
162.51(5)
86.18(5)
146.17(5)
52.76(4)
88.61(5)
105.98(5)
Hydrogen bond geometry
Donor
Hydrogen
Acceptor
D–H/Å
H ؒ ؒ ؒ A/Å
D ؒ ؒ ؒ A/Å
D–H ؒ ؒ ؒ A/Њ
N(2)
N(4)
N(4)
O(7)
H(2N)
H(4N)
H(4N)
H(7O)
O(6a)
O(5)
O(4)
O(6)
0.82(2)
2.42(2)
2.624(19)
2.23(2)
2.21(3)
3.139(3)
3.331(2)
2.931(2)
3.054(3)
146.0(18)
151.5(17)
150.5(17)
155(3)
0.781(19)
0.781(19)
0.91(3)
a Ϫx, y ϩ 1/2, 3/2 ϩ z.
Table 4 Pertinent geometry details (bond lengths in Å angles in Њ) for [Pb(3)(NO3)2]ؒH2O
Pb(1)–N(2a)
Pb(1)–N(1)
Pb(1)–O(2)
2.448(2)
2.583(2)
2.968(3)
Pb(1)–N(2)
Pb(1)–N(1)
Pb(1)–O(1)
2.448(2)
2.583(2)
3.066(3)
N(2a)–Pb(1)–N(2)
N(2)–Pb(1)–N(1)
N(2)–Pb(1)–N(1a)
N(1)–Pb(1)–N(1a)
N(2a)–Pb(1)–O(2)
N(2)–Pb(1)–O(2)
N(1)–Pb(1)–O(2)
80.47(11)
78.20(7)
71.86(7)
140.51(10)
155.58(8)
76.58(8)
N(1a)–Pb(1)–O(2)
N(2a)–Pb(1)–O(1)
N(2)–Pb(1)–O(1)
N(1)–Pb(1)–O(1)
N(1a)–Pb(1)–O(1)
O(2)–Pb(1)–O(1)
86.77(8)
155.15(8)
99.68(10)
83.78(9)
125.75(8)
40.58(8)
110.89(8)
Hydrogen bond geometry
Donor
Hydrogen
Acceptor
D–H/Å
H ؒ ؒ ؒ A/Å
D ؒ ؒ ؒ A/Å
D–H ؒ ؒ ؒ A/Њ
O(4)
N(2)
H(4O)
H(2N)
O(3)
0.909(19)
0.91
1.98(3)
2.13
2.823(4)
3.028(5)
155(6)
167.1
O(4b)
a 1 Ϫ x, y, 3/2 Ϫ z. b x, 1 ϩ y, z.
D a l t o n T r a n s . , 2 0 0 3 , 1 5 5 8 – 1 5 6 6
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Table 5 Pertinent geometry details (bond lengths in Å angles in Њ) for
[Zn(4)(NO3)]NO3ؒ0.5MeOH
of acetone, methanol and ether to give dark-purple crystals
(0.052 g, 45%) (Found: C, 36.48; H, 5.58; N, 12.36. Calc. for
C17H30CoF6N5PO3: C, 36.70; H, 5.44; N, 12.59%).
Zn(1)–O(1)
Zn(1)–N(1)
Zn(1)–N(3)
2.0442(17)
2.204(2)
2.306(2)
Zn(1)–O(2)
Zn(1)–N(2)
Zn(1)–N(4)
2.837(2)
2.109(2)
2.061(2)
[Zn(1)](NO3)2. Zinc() nitrate hexahydrate (0.045 g, 0.172
mmol) in methanol (5 cm3) was added to 1 (0.05 g, 0.172 mmol)
in hot methanol (15 cm3). The solution was wamed for 30 min
then allowed to stand at room temperature. The required prod-
uct formed as colourless crystals (0.046 g, 56%) after recrystal-
lization from methanol (Found: C, 42.48; H, 6.33; N, 17.29.
O(1)–Zn(1)–N(4)
O(1)–Zn(1)–N(2)
N(4)–Zn(1)–N(2)
O(1)–Zn(1)–N(1)
N(4)–Zn(1)–N(1)
N(2)–Zn(1)–N(1)
O(1)–Zn(1)–N(3)
N(4)–Zn(1)–N(3)
120.91(8)
102.15(8)
136.78(8)
96.41(7)
84.04(8)
95.42(7)
89.69(7)
91.69(8)
N(2)–Zn(1)–N(3)
N(1)–Zn(1)–N(3)
O(1)–Zn(1)–O(2)
N(4)–Zn(1)–O(2)
N(2)–Zn(1)–O(2)
N(1)–Zn(1)–O(2)
N(3)–Zn(1)–O(2)
84.55(7)
173.75(7)
49.81(6)
71.14(7)
151.44(7)
93.50(6)
89.42(6)
1
Calc. for C17H30N6O6Zn: C, 42.55; H, 6.30; N, 17.51%). H
NMR (DMSO-d6): δ 1.58–1.86 (m, CH2CH2NH, 4 H), 2.22–
3.08 (m, overlapping signals, CH2N, 16 H), 3.96–4.02 (m,
CH2C6H5, 1 H), 4.15–4.25 (m, CH2C6H5, 1 H), 7.25–7.55 (m,
ArH, 5 H). 13C NMR (DMSO-d6): δ 23.71, 23.90, 24.11, 27.62,
28.30, 43.96, 44.52, 44.72, 45.42, 46.34, 46.78, 47.41, 48.14,
48.42, 48.54, 49.18, 49.48, 49.71, 50.51, 50.77, 51.06, 51.31,
52.16, 53.64, 53.91, 54.36, 128.41, 128.55, 128.67, 128.74,
130.77, 131.22, 131.76, 132.42, 132.71.
0.71073 Å, µ(Mo-Kα) = 0.804 mmϪ1, T (Gaussian)min,max = 0.74,
0.85, 2θmax = 56.62, hkl range Ϫ11 to 11, Ϫ21 to 21, Ϫ29 to 29,
N = 28544, Nind = 6914 (Rmerge = 0.0259), Nobs = 5815 (I > 2σ(I )),
Nvar = 365, residuals R1(F) = 0.0260, wR2(F 2) = 0.0588
(A = 0.02, B = 0.0), GoF(all) = 1.471, ∆ρmin,max = Ϫ0.419, 0.804
eϪ ÅϪ3
.
[Cd(1)](NO3)PF6. Cadmium() nitrate tetrahydrate (0.054 g,
0.172 mmol) in methanol (5 cm3) was added to a solution of 1
(0.050 g, 0.172 mmol) in methanol (10 cm3). The solution was
stirred and heated for 0.5 h, then the solvent was reduced to 10
cm3 and excess saturated NH4PF6 in methanol was added. The
white powder that formed was filtered off and recrystallized
from acetonitrile–isopropanol to yield colourless crystals
(0.067 g, 64%) (Found: C, 33.69; H, 5.03; N, 11.50. Calc. for
Specific details: the amine hydrogen sites were located and
modelled with isotropic displacement parameters.
[Pb(3)(NO3)2]ؒH2O: C24H38N6O7Pb, M = 729.79, ortho-
rhombic, space group Pbcn (#60), a = 16.1228(13), b =
9.4321(7), c = 18.4865(15) Å, V = 2811.3(4) Å3, Dc = 1.724 g
cmϪ3, Z = 4, crystal size 0.326 × 0.294 × 0.264 mm, colour
colourless, habit prism, temperature 294(2) K, λ(Mo-Kα) =
0.71073 Å, µ(Mo-Kα) = 6.053 mmϪ1, T (SADABS)min,max = 0.79,
1.00, 2θmax = 56.54, hkl range Ϫ21 to 21, Ϫ12 to 12, Ϫ23 to 23,
N = 27909, Nind = 3412 (Rmerge = 0.0244), Nobs = 2361 (I > 2σ(I )),
Nvar = 177, residuals R1(F) = 0.0176, wR2(F 2) = 0.0553
(A = 0.02, B = 1.0), GoF(all) = 1.350, ∆ρmin,max = Ϫ0.427, 0.744
1
C17H30CdF6N5PO3: C, 33.48; H, 4.96; N, 11.48%). H NMR
(CD3CN): δ 1.57–1.88 (m, CH2CH2NH, 4 H), 2.61–3.25 (m,
CH2N, 16 H), 3.88–3.93 (d, CH2C6H5, 1 H), 4.23–4.28 (d,
CH2C6H5, 1 H), 7.26–7.40 (dm, ArH, 5 H). 13C NMR
(CD3CN): δ 25.62, 29.15, 46.59, 47.71, 47.94, 52.00, 52.85,
53.26, 53.85, 55.03, 56.24, 129.39, 129.54, 131.70, 132.65.
eϪ ÅϪ3
.
Specific details: the water hydrogen atom site was located and
modelled with a group isotropic displacement parameter.
[Pb(1)](NO3)2. Lead nitrate (0.048 g, 0.145 mmol) in water
(2 cm3) was added to a solution of 1 (0.042 g, 0.145 mmol)
in methanol (10 cm3). The solution was heated for 0.5 h and
filtered. The filtrate was left to stand in the air overnight and
colourless crystals were obtained (0.018 g, 20%). Single crystals
suitable for X-ray diffraction were obtained from methanol–
water (Found: C, 32.68;H, 4.99: N, 13.67. Calc. for C17H30N6-
O6Pb: C, 32.85; H, 4.86; N, 13.52%).
[Zn(4)(NO3)]NO3ؒ0.5MeOH: C31.5H44.75N6O6.5Zn,
M
=
676.85, monoclinic, space group C2/c (#15), a = 25.741(14),
b = 20.796(11), c = 13.212(7) Å, β = 108.425(9), V = 6710(6) Å3,
Dc = 1.340 g cmϪ3, Z = 8, crystal size 0.487 × 0.132 × 0.055 mm,
colour colourless, habit blade, temperature 150(2) K, λ(Mo-Kα)
= 0.71073 Å, µ(Mo-Kα) = 0.784 mmϪ1, T (Gaussian)min,max
=
0.74, 0.96, 2θmax = 56.56, hkl range Ϫ34 to 32, Ϫ27 to 27, Ϫ17 to
17, N = 33034, Nind = 7959 (Rmerge 0.0483), Nobs = 5235 (I >
2σ(I )), Nvar = 416, residuals R1(F) = 0.0410, wR2(F 2) = 0.1097
(A = 0.05, B = 0.0), GoF(all) = 1.056, ∆ρmin,max = Ϫ0.374, 1.395
[Co(2)](NO3)PF6. Using
a similar procedure to that
described for [Co(1)](NO3)PF6, cobalt() nitrate hexahydrate
(0.038 g, 0.132 mmol) and 2 (0.050 g, 0.132 mmol) produced the
product as a dark-purple powder (0.034 g, 40%) (Found: C,
44.38; H, 5.82; N, 10.99. Calc. for C24H36CoF6N5PO3: C, 44.59;
H, 5.61; N, 10.83%).
eϪ ÅϪ3
.
Specific details: the asymmetric unit contains a complex mole-
cule with a coordinated nitrate ion, a non-coordinated nitrate
counter ion and a disordered solvent region modelled with two
methanol molecules having occupancies refined and fixed at
0.25. The solvate sites were modelled with isotropic displace-
ment parameters, and the amine hydrogen site was located and
modelled with an isotropic displacement parameter.
CCDC reference numbers 200929–200933.
See http://www.rsc.org/suppdata/dt/b3/b300002h/ for crystal-
lographic data in CIF or other electronic format.
[Zn(2)](NO3)2. Using a similar procedure to that described
for [Zn(1)](NO3)2, zinc() nitrate tetrahydrate (0.035 g, 0.132
mmol) and 2 (0.050 g, 0.132 mmol) yielded the product as
colourless crystals (0.025 g, 33%) (Found: C, 50.29; H, 6.25; N,
14.62. Calc. for C24H36N6O6Zn: C, 50.58; H, 6.37; N, 14.74%).
1H NMR (DMSO-d6): δ 1.56–1.73 (m, CH2CH2NH, 2H), 2.25–
2.37 (m, CH2CH2NH, 2H), 2.61–3.13 (m, CH2N, 16 H), 4.17–
4.36 (m, CH2C6H5, 4 H), 7.37–7.44 (m, ArH, 10 H). 13C NMR
(DMSO-d6): δ 20.62, 28.16, 44.42, 44.70, 48.60, 50.97, 52.78,
53.00, 53.45, 54.21, 56.65, 128.45, 128.51, 128.63, 130.74,
132.67, 133.16.
Metal complex syntheses
All complexes were dried over P4O10 in a vacuum before
microanalysis.
[Co(1)(NO3)]PF6. Cobalt() nitrate hexahydrate (0.06 g,
0.207 mmol) in methanol (5 cm3) was added to a solution of 1
(0.06 g, 0.207 mmol) in methanol (15 cm3). The solution was
refluxed for 1 h under nitrogen and then cooled to room tem-
perature. The volume of the solution was reduced by one third
and excess saturated NH4PF6 in methanol was added, followed
by the dropwise addition of ether to produce an oily solid.
The latter was purified by recrystallization from a mixture
[Cd(2)](NO3)PF6. Using
a similar procedure to that
described for [Cd(1)](NO3)PF6, cadmium() nitrate tetra-
hydrate (0.033 g, 0.105 mmol) and 2 yielded the product as
colourless crystals (0.024 g, 32%). Single crystals suitable for
X-ray diffraction were obtained by diffusion of ether vapour
into a methanol solution of the complex (Found: C, 40.99; H,
5.32; N, 9,87. Calc. for C24H36CdF6N5O3P: C, 41.18; H, 5.18; N,
D a l t o n T r a n s . , 2 0 0 3 , 1 5 5 8 – 1 5 6 6
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Table 6 Conductance valuesa for the complexes of cobalt(), zinc(),
cadmium() and lead() of 1–5 in methanol at 25 ЊC
10.01%). 1H NMR (CD3CN): δ 1.80–1.84 (m, CH2CH2NH,
2 H), 2.01–2.06 (m, CH2CH2NH, 2 H), 2.73–3.28 (m, CH2N,
16 H), 4.02–4.05 (d, CH2C6H5, 4 H), 5.98 (br s, NH, 2 H), 7.38–
7.45 (m, ArH, 10 H). 13C NMR (CD3CN): δ 22.67, 25.58, 25.63,
46.13, 50.44, 51.63, 52.45, 52.74, 54.27, 55.36, 55.93, 58.09,
129.43, 129.72, 130.03, 130.07, 131.69, 133.04, 133.26.
Complex
Colour
Λa/S cm2 molϪ1
[Co(1)(NO3)]PF6
Dark purple
Dark purple
Pink
121
–
75
92
84
–
76
75
–
108
84
81
87
84
–
[Co(2)(NO3)]PF6
[Co(3)(NO3)]NO3
[Co(3)](NO3)2. Cobalt() nitrate hexahydrate (0.154 g, 0.526
mmol) in methanol (10 cm3) was added to a solution of 3 (0.200
g, 0.526 mmol) in methanol (20 cm3). The solution was refluxed
for 1 h under nitrogen and then cooled to room temperature.
After filtration, the clear filtrate was left to stand overnight
during which time pink–purple crystals of product formed
(0.184 g, 62%) (Found: C, 51.30; H, 6.37; N, 14.95. Calc. for
C24H36CoN6O6: C, 51.15; H, 6.44; N, 14.91%).
[Co(4)(NO3)]PF6
Pink
[Zn(1)(NO3)]NO3
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
Colourless
[Zn(2)](NO3)2
[Zn(3)](NO3)]NO3
[Zn(4)](NO3)2ؒ0.5H2O
[Zn(5)](NO3)2ؒ2H2O
[Cd(1)[(NO3)]PF6
[Cd(2)(NO3)]PF6
[Cd(3)(NO3)]NO3ؒ0.5MeOH
[Cd(4)(NO3)]PF6ؒ0.75H2O
[Cd(5)(NO3)]]NO3ؒEtOHؒH2O
[Pb(1)(NO3)2]
[Zn(3)](NO3)2. This was prepared using a similar procedure
to that described for [Zn(1)](NO3)2. The initial product was
recrystallized from methanol to yield colourless crystals (46%)
(Found: C, 50.36; H, 6.17; N, 14.60. Calc. for C24H36N6O6Zn:
C, 50.58; H, 6.37; N, 14.74%). 1H NMR (DMSO-d6): δ 1.64–1.80
(m, CH2CH2NH, 3 H), 2.33–3.08 (m, CH2CH2NH, CH2N,
17 H), 3.72–3.84 (dd, CH2C6H5, 2 H), 4.21–4.34 (dd, CH2C6H5,
2 H), 7.31–7.44 (m, ArH, 10 H). 13C NMR (DMSO-d6): δ 22.89,
23.87, 44.52, 44.85, 45.25, 49.16, 49.59, 51.86, 52.94, 53.97,
54.92, 56.17, 128.02, 128.19, 128.36, 130.31, 130.69, 131.42,
132.31.
[Pb(3)(NO3)]NO3ؒ0.25H2O
98
a Conductance at 25 ЊC in methanol at ∼10Ϫ3 mol dmϪ3; expected range
for a 1 : 1 electrolyte in methanol is 80–115 S cm2 molϪ1 while that for a
2 : 1 electrolyte is 160–220 S cm2 molϪ1
.
Calc. for C31H43.5CdF6N5O3.75P: C, 46.33; H, 5.46; N, 8.72%).
1H NMR (CD3CN): δ 1.73–1.83 (m, CH2CH2NH, 2 H), 2.09–
2.29 (m, CH2CH2NH, 2 H), 2.42–2.50 (m, CH2NH, 2 H), 2.60–
3.34 (m, CH2N, 14 H), 3.63 (br s, NH, 1 H), 3.95–4.58 (m,
CH2C6H5, 6 H), 7.35–7.51 (m, ArH, 15 H). 13C NMR
(CD3CN): δ 22.25, 25.32, 46.63, 51.66, 52–58 (overlapping sig-
nals), 129.39, 129.44, 129.71, 129.86, 131.28, 131.44, 132.75,
132.95, 133.47.
[Cd(3)](NO3)2ؒ0.5MeOH. Using a similar procedure to that
described for [Zn(1)](NO3)2, colourless crystals (58%) were
obtained following recrystallization of the initial product from
methanol (Found: C, 46.28; H, 6.07; N, 13.09. Calc. for
C24.5H38CdN6O6.5: C, 46.49; H, 6.05; N, 13.28%). 1H NMR
(DMSO-d6): δ 1.73 (br s, CH2CH2NH, 4 H), 2.42–3.09 (m, over-
lapping signals, CH2N, 16 H), 3.88–3.93 (d, CH2C6H5, 2 H),
4.20–4.25 (d, CH2C6H5, 2 H), 7.32–7.43 (m, ArH, 10 H). 13C
NMR (DMSO-d6): δ 24.10, 24.77, 44.67, 44.93, 45.51, 49.11,
50.60, 52.42, 54.04, 55.54, 55.96, 56.68, 128.02, 128.20, 130.46,
131.52, 2.11.
[Zn(5)](NO3)2ؒ2H2O. S similar procedure to that described
for [Zn(1)](NO3)2 yielded colourless needle-like crystals on
recrystallizaton of the initial product from absolute ethanol
(43%) (Found: C, 58.23; H, 6.47; N, 10.43. Calc. for C38H52N6-
O8Zn: C, 58.05; H, 6.67; N, 10.69%).
[Cd(5)](NO3)2ؒEtOHؒH2O. A similar procedure to that
described for [Cd(3)](NO3)2 was employed except that the reac-
tion solvent was changed from methanol to absolute ethanol.
Colourless crystals were obtained after recrystallization of the
initial product from absolute ethanol (40%) (Found: C, 56.40;
H, 6.15; N, 9.87. Calc. for C40H56CdN6O8: C, 56.49; H, 6.32; N,
10.13%).
[Pb(3)](NO3)2ؒ0.25H20. A similar procedure to that described
for [Pb(1)(NO3)2] yielded colourless crystals (yield 67.8%).
Single crystals suitable for X-ray diffraction were obtained
from methanol–water (Found: C, 40.14; H, 4.99; N, 11.67. Calc.
for C24H36.5N6O6.25Pb: C, 40.24; H, 5.14; N, 11.73%).
CAUTION: perchlorate-containing complexes are poten-
tially explosive and appropriate precautions should be in place
for their preparation, handling and storage.
[Co(4)](NO3)PF6. A similar procedure to that described for
[Co(1)](NO3)PF6 given a product which was recrystallized from
acetone–isopropanol to yield pink–purple crystals (44%)
(Found: C, 50.67; H, 5.99; N, 9.36. Calc. for C31H42CoF6N5O3P:
C, 50.55; H, 5.75; N, 9.51%).
Results and discussion
Synthesis of complexes
[Zn(4)](NO3)2ؒ0.5H2O. A similar procedure to that described
for [Zn(1)](NO3)2 was employed. The initial product was
recrystallized from methanol–isopropanol to yield colourless
crystals (54%). Single crystals suitable for X-ray diffraction
were obtained from the same solvent mixture (Found: C, 55.42;
H, 6.24; N, 12.34. Calc. for C31H43N6O6.5Zn: C, 55.65; H, 6.48;
N, 12.56%). 1H NMR (CD3OD): δ 1.71–1.84 (m, CH2CH2NH,
2 H), 2.29–2.56 (m, CH2CH2NH, CH2NH, 4 H), 2.68–3.27
(m, CH2N, 13 H), 3.61–3.72 (m, CH2N, 1 H), 3.78–4.61 (m,
CH2C6H5, 6 H), 7.35–7.49 (m, ArH, 15 H). 13C NMR
(CD3OD): δ 21.87, 24.89, 25.28, 47.24, 51.15, 51.75, 52.11,
52.24, 53.45, 54.20, 55.35, 56.82, 57.89, 58.40, 129.58, 129.69,
129.82, 130.35, 131.62, 132.25, 132.69, 133.14, 133.92.
In an effort to obtain crystalline complexes that were suitable
for X-ray analysis, the isolation of selected solid complexes of
cobalt(), zinc(), cadmium(), silver() and lead() with 1–5
was attempted. The 1 : 1 (metal : ligand) complexes listed in
Table 6 were successfully obtained in pure form by mixing hot
solutions of the required metal nitrate salt and ligand in
methanol, with in some instances excess ammonium hexa-
fluorophosphate being added to induce precipitation. While
the copper()7 and palladium()22 complexes of the tetraben-
zylated derivative 5 have been reported previously, only
zinc() and cadmium() complexes of this ligand were obtained
in the present study. Interestingly, while this later ligand has
been employed in
a range of host–guest investigations
[Cd(4)](NO3)PF6ؒO.75H2O. A similar procedure to that
described for [Cd(1)](NO3)PF6 was employed. The initial
product was recrystallized from acetone–isopropanol to yield
colourless crystals (52%) (Found: C, 46.44; H, 5.30; N, 8.55.
(including studies of alkali, alkaline earth and other metal
ion binding),23–26 it has been proposed that it shows low affin-
ity for cobalt(), nickel(), copper() and zinc() under a
variety of reaction conditions,27,28 with the latter behaviour
D a l t o n T r a n s . , 2 0 0 3 , 1 5 5 8 – 1 5 6 6
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being ascribed to the sterically demanding nature of the four
pendant benzyl groups.28
As with cyclam itself, silver() complexes of 1–5 proved prone
to decomposition and none were obtained in pure form from
the synthetic conditions employed.
ions present in the source phase was observed. Clearly, this
ligand is a poor ionophore for all seven metal ions under the
conditions employed. In contrast, the tetrabenzylated deriv-
ative 5 was found to show high transport selectivity towards
silver()—a J value of 169 × 10Ϫ7 mol/24 h was obtained, with
no evidence for transport of any of the other six metals present
in the source phase.
In the above context it is noted that a series of single
(individual) metal solvent extraction (water/chloroform)25 and
membrane (water/dichloromethane/water)26 experiments have
been reported previously. In parallel with the present findings,
Where values were obtained, each of the cobalt(), zinc(),
cadmium() and lead()] complexes yielded conductances in
methanol (Table 6) which approximated these expected for a
1 : 1 electrolyte;29 thus indicating that, on average, at least one
of the anionic groups is coordinated (or ion-paired) with the
cation under the conditions employed.
1
The H and 13C NMR spectra of the zinc(), cadmium()
it was reported that 5 was the most efficient extractant for
ϩ
complexes of 1–5 were recorded in CD3CN, CD3OD or
DMSO-d6 (see Experimental section). All spectra showed
induced chemical shifts relative to the corresponding free
ligands, with the 1H NMR signals shifted up-field in the
spectra of the complexes, as is commonly observed for other
diamagnetic metal-containing systems. Both the 1H and 13C
NMR spectra of the respective complexes are more compli-
cated (reflecting peak broadening and/or splitting) relative to
those for the free ligands. For example, the singlets observed for
the benzyl methylene protons in the free ligands are split on
complex formation to ‘doublets’ or ‘multiplets’, in accordance
with inhibition of ligand flexibility occurring on metal
binding.
AgClO4 relative to the perchlorates of Liϩ, Naϩ, Kϩ, NH4
,
Csϩ, Ba2ϩ and Pb2ϩ. Similarly, the above silver salt was the only
one transported when compared with the attempted transport
of the individual perchlorates of Liϩ, Naϩ, Kϩ, NH4ϩ, Csϩ,
Ba2ϩ, Pb2ϩ, Ca2ϩ, Mg2ϩ, Co2ϩ, Ni2ϩ, Cu2ϩ and Zn2ϩ in separate
experiments. Clearly these results support the present finding
that the tetrabenzyl derivative 5 has a prepensity for Agϩ select-
ivity which persists across the respective experiment types just
discussed.
Crystal structures
Single crystal X-ray diffraction studies have been undertaken
to determine the crystal structures of [Pb(1)(NO3)2], [Cd(2)-
(NO3)]NO3ؒ0.5MeOH, [Cd(3)(NO3)]NO3ؒMeOH, [Pb(3)-
(NO3)2]ؒH2O and [Zn(4)(NO3)]NO3ؒ0.5MeOH.
As mentioned above, no solid complexes of Ag() were iso-
lated free of contamination; however, in view of our interest in
the effect of N-benzylation on silver() selectivity (see below),
1
both H NMR and 13C NMR titration studies of the inter-
The structure of [Pb(1)(O2NO) 2] is illustrated in Fig. 1, and
the asymmetric unit contains two crystallographically inde-
pendent complex molecules, each with two weakly coordinated
nitrate counter ions. The cyclam ring adopts the unusual trans-
V configuration (RRRR),1 presumably reflecting that lead() is
too large to fit within the macrocyclic ring. The lead ion in this
complex is eight coordinated, and the Pb–N bond lengths range
from 2.445(3) to 2.657(2) Å (Table 1) and are typical of such
Pb–N bond lengths in other related complexes.30 The benzyl
substituent on N(1) atom is responsible for a longer Pb–N
coordination bond length. The nitrato oxygen to metal bond
distances vary from 2.820(3) to 3.102(3) Å and are slightly
longer than the mean length of 2.71 Å recorded on the CSD
database.31
action of silver() nitrate with 5 in CD3CN–CDCl3 were per-
formed. The incremental addition of solid silver() nitrate to a
solution of 5 held in the NMR tube yielded clear 1 : 1 end-
points in both sets of spectra (no evidence for other species was
obtained up to a molar ratio of [Agϩ] : [5] of 3.5), confirming
the 1 : 1 stoichiometry of this Ag() complex.
In accord with the observations discussed above, both the 1H
NMR and 13C NMR spectra exhibited a doubling of the benzyl
methylene resonance and particular aromatic resonances of the
free ligand on addition of silver ion with significant broadening
of the proton spectrum also being evident.
Bulk membrane transport
The asymmetric unit of the cadmium() complex of 2 con-
tains a complex molecule with a coordinated nitrate counter
ion, a non-coordinated nitrate counter ion disordered over
three sites and a partially occupied methanol solvate site. Fig. 2
shows that the complex adopts a trans-I (RSRS) configuration1
with bidentate coordination of a nitrato ligand to cadmium().
The coordination number of the cadmium cation is six. The
Cd–N bond lengths (to NCH2Ph) of 2.320(2) and 2.364(2) Å
are slightly longer than those of 2.283(2) and 2.307(2) Å (to
NH), while the Cd–O distances are 2.369(2) and 2.460(2) Å
respectively.
The cadmium() complex of 3, [Cd(3)(O2NO)]]ؒNO3ؒMeOH,
incorporates 3 in a trans-I (RSRS) configuration1 (Fig. 3). The
Cd–N distances range from 2.2589(16) to 2.3718(16) Å, while
the Cd–O bond lengths are 2.3603(14) and 2.4837(14) Å,
respectively. The coordination number of the cadmium cation is
six, consisting of four non-coplanar nitrogen atoms from the
macrocycle and two oxygens from one (bidentate) nitrato
ligand. There are hydrogen bonding interactions between the
hydrogens attached to N(2) and N(4) and the nitrate counter
ion, as well as between this nitrate and a methanol solvate mol-
ecule (Fig. 3 and Table 3).
Competitive mixed metal transport experiments (water/chloro-
form/water) have been undertaken, with the chloroform mem-
brane phase containing an ionophore at 10Ϫ3 mol dmϪ3 chosen
from 1–5, respectively. The aqueous source phase contained
equimolar concentrations of the nitrate salts of cobalt(),
nickel(), copper(), zinc(), cadmium(), silver() and lead(),
with individual metal ion concentrations being 1 × 10Ϫ2 mol
dmϪ3. As mentioned in the Experimental section, transport was
performed against a back gradient of protons, with palmitic
acid (4 × 10Ϫ3 mol dmϪ3) also being present in the organic
phase. A main role of the latter is to aid the transport process
by providing a lipophilic counter ion in the organic phase (after
proton loss to the aqueous source phase) for charge neutralis-
ation of the metal cation being transported; in this manner the
need for uptake of hydrophilic nitrate anions into the organic
phase may be avoided. Under the conditions employed (and
ignoring any apparent transport showing J values of >20 ×
10Ϫ7 mol/24 h as being within experimental error of zero), sole
selectivity for copper() was observed for the systems incorpor-
ating the dibenzylated species 2 (J = 83 × 10Ϫ7 mol/24 h) and 3
(J = 63 × 10Ϫ7 mol/24 h); as might be expected, the values for
these isomeric systems are quite similar. While 1 also solely
delivered a significant amount of copper() to the receiving
phase, in this case a precipitate was observed to form in the
organic phase and the results for this system were not con-
sidered further. On moving to the system incorporating the
tribenzylated species 4, no transport of any of the seven metal
The asymmetric unit of the lead() complex of 3 contains the
complex molecule (located on a 2-fold axis), a weakly coordin-
ated nitrate counter ion and a water molecule (Fig. 4). The mac-
rocycle ring, again, adopts the unusual trans-V configuration1
with the lead ion being again eight coordinated. The substi-
tuents on the N(1) atoms are once again reflected by Pb–N
D a l t o n T r a n s . , 2 0 0 3 , 1 5 5 8 – 1 5 6 6
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Fig. 3 ORTEP21 depiction of [Cd(3)(O2NO)]NO3ؒMeOH, with 20%
displacement ellipsoids. Hydrogen bond interactions are indicated with
a dashed line.
Fig. 1 ORTEP21 depiction with 20% displacement ellipsoids, of the
two independent complex molecules present in the crystal structure of
[Pb(1)(O2NO)2].
Fig.
4
ORTEP21 depiction of [Pb(3)(O2NO)2]ؒH2O, with 20%
displacement ellipsoids.
bond length (to NCH2Ph) of 2.583(2) Å that are slightly longer
than that of 2.448(2) Å (to NH).
For the zinc() complex of the tribenzyl derivative 4, the
asymmetric unit contains a complex molecule with a coordin-
ated nitrato ion, and a non-coordinated nitrate counter ion. In
each [Zn(4)(ONO2)]NO3ؒ0.5MeOH, the macrocycle adopts a
trans-I configuration1 (Fig. 5). The Zn–N bond length to the
secondary amine is 2.061(2) Å and, for the zinc to the tertiary
amine lengths, the range is 2.109(2)–2.306(2) Å; these lengths
are similar to those present in other related zinc cyclam
Fig. 2 ORTEP21 depiction of [Cd(2)(O2NO)]NO3ؒ0.5MeOH, with
20% displacement ellipsoids.
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particular situation, other examples of N-alkylation leading to
enhanced selectivity and related behaviour have been reported.
Based on studies involving tetraaza cyclam and its tetra-
N-methylated derivative, it has been proposed by Meyerstein
et al.38,39 that N-alkylation will tend to favour stabilisation of
metals in their lower oxidation states—behaviour exemplified
electrochemically by the above workers with respect to the
stabilisation of copper() over copper() by the N-tetramethyl-
cyclam derivative. In view of the latter, it also seems likely that a
similar effect may contribute to the enhanced recognition for
silver() observed for the tetra-N-benzylated derivative 5 in both
the present and past studies.
Acknowledgements
We thank the Australian Research Council and the Deutsche
Forschungsgemeinschalft for support.
Fig. 5 ORTEP21 depiction of [Zn(4)(ONO2)]NO3ؒ0.5MeOH, with 20%
displacement ellipsoids.
derivatives.32 It is interesting that the Zn–O(1) bond length
(2.0442(17) Å) is somewhat shorter than the normal range. The
overall coordination geometry of this five-coordinated complex
is distorted square pyramidal.
References
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In summary, the five X-ray structures described above show
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Concluding remarks
In the present study we report the results of an investigation of
the interaction of 1–5 with the above metal ions with emphasis
on the effect of successive N-benzylation on the properties of
their respective complexes. In contrast to the (competitive)
membrane transport behaviour of the partially N-benzylated
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silver() from the aqueous source phase to the aqueous receiving
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of secondary amine donors in macrocyclic ligands can give
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