Zinc and cadmium complexes of an 18-membered N4O2 oxaaza-Schiff base macrocycle and the corresponding reduced form

Article abstract of DOI:10.1039/a906372b

The metal templated (Cd and Zn) cyclocondensation of 2,6-pyridinedicarbaldehyde and 1,5-bis(2-aminophenoxy)-3-azapentane is reported together with the crystal structures of two mononuclear cadmium macrocyclic Schiff base complexes, [CdL¹(NO

Full text of DOI:10.1039/a906372b

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Zinc and cadmium complexes of an 18-membered N4O2 oxaaza-
Schiff base macrocycle and the corresponding reduced form†
Harry Adams,a Rufina Bastida,b David E. Fenton,*a Alejandro Macías,b Sharon E. Speya and
Laura Valenciab
a Department of Chemistry, Dainton Building, The University of Sheffield, Sheffield,
UK S3 7HF
b Departamento de Química Inorgánica, Universidad de Santiago de Compostela,
Avenida de las Ciencias s/n, 15706 Santiago de Compostela, Spain
Received 5th August 1999, Accepted 6th October 1999
The metal templated (Cd and Zn) cyclocondensation of 2,6-pyridinedicarbaldehyde and 1,5-bis(2-aminophenoxy)-3-
azapentane is reported together with the crystal structures of two mononuclear cadmium macrocyclic Schiff base
complexes, [CdL1(NO3)2] 1 and [CdL1(H2O)2][ClO4]2 2 and a dinuclear, µ-hydroxy-bridged zinc macrocyclic Schiff
base complex [Zn2L1 (OH)][ClO4]3ؒCH3CN 3ؒCH3CN. The corresponding reduced macrocycle, L2, has been
2
synthesised by using the MnII-templated cyclocondensation of 2,6-pyridinedicarbaldehyde and 1,5-bis(2-amino-
phenoxy)-3-azapentane in methanol followed by an in situ reductive demetallation of the Schiff base macrocyclic
manganese() complex using excess sodium borohydride. The crystal structures of the free macrocycle L2,
[CdL2(NO3)2] 4 and [CdL2(CH3CN)2][ClO4]2 5 are reported.
balance between cationic size, the bonding preference of the
cation, the nature of the donor atoms present and their dis-
position within the macrocyclic framework is therefore required
to effect cyclocondensation.
Introduction
The synthesis of oxaaza Schiff base macrocyclic ligands by the
metal templated cyclocondensation of 2,6-dicarbonylpyridines
and α,ω-diaminoethers is well documented.1,2 Metal complexes
In the present study we have modified the donor atom
of both ‘1 ϩ 1’ diimine and ‘2 ϩ 2’ tetraimine macrocycles were
sequence of the precursor diamine for macrocycle LB by
reported and it was first suggested that for 18-membered ring
replacing the oxygen atom present at the 3-position of the ether
linker with a secondary amino-group. This change was made to
macrocycles (La, generated from 1,5-diamino-3-oxapentane,
and Lb, generated from 1,5-bis(2-aminophenoxy)-3-oxapent-
enhance the opportunity to use templates other than ‘hard’
ane) the ionic size of the templating cation exercised a major
metals and introduces into the macrocycle a functional group
influence on macrocycle formation.3 Alkaline earth cations
to which pendant arms can be attached. In the present work
we report the application of zinc(), cadmium() and man-
such as Ca2ϩ, Sr2ϩ and Ba2ϩ, the trivalent lanthanide cations
and Pb2ϩ were all shown to be effective at producing complexes
ganese() as templating devices together with the X-ray crystal
of La and Lb by this route whereas the transition metals did not
structures of the Schiff base macrocyclic complexes [CdL1-
do so.
(NO3)2] 1, [CdL1(H2O)2][ClO4]2 2, and [Zn2L1 (OH)][ClO4]3ؒ
2
CH3CN 3ؒCH3CN. The structure of the reduced macrocycle
L2 and its cadmium complexes, [CdL2(NO3)2] 4 and [CdL2-
Recently it has been shown that if 1,13-diamino-4,7,10-
trioxatridecane is reacted with 2,6-pyridinedicarbaldehyde in
(CH3CN)2][ClO4]2 5 are also reported.‡
the presence of copper() and nickel() templates then copper
can serve to produce a 20-membered ‘1 ϩ 1’ macrocycle and
nickel() will generate a 40-membered ‘2 ϩ 2’ macrocycle.4 The
reaction paths are dominated by the binding of the metal to the
pyridinyl head units. It is therefore necessary to think beyond
a simple size control parameter. In this case the additional
methylene groups give the macrocycle an extra mobility which
allows the metal to attain a preferential site geometry. A
Experimental
Elemental analyses were carried out on a Carlo Erba Ea 1108.
IR Spectra were recorded as KBr discs using a Bruker IFS-66V
spectrophotometer. 1H NMR spectra were recorded using
‡ L1 = 10,16-dioxa-3,13,23,29-tetraazatetracyclo[23.3.1.04,9.017,22]nona-
cosa-1(29),2,4(9),5,7,17,19,21,23,25,27-undecaene. L2 = 10,16-dioxa-
3,13,23,29-tetraazatetracyclo[23.3.1.04,9.017,22]nonacosa-1(29),4(9),5,7,
17,19,21,25,27-nonaene.
† Supplementary data available: rotatable 3-D crystal structure diagram
in CHIME format. See http://www.rsc.org/suppdata/dt/1999/4131/
J. Chem. Soc., Dalton Trans., 1999, 4131–4137
This journal is © The Royal Society of Chemistry 1999
4131

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Bruker DPX250 and Bruker AMX300 spectrometers. Mass
spectra were recorded using a Kratos-MS-50 spectrometer
with 3-nitrobenzyl alcohol used as the matrix for FAB spectra.
Conductivity measurements were recorded on a WTW LF-3
spectrometer using 10Ϫ3 M acetonitrile solutions of the com-
plexes.
The metal-free reduced macrocycle L2. 2,6-Pyridinedicarb-
aldehyde (1 mmol) and Mn(NO3)2ؒ4H2O (1 mmol) were dis-
solved in methanol (50 ml). The solution was stirred vigorously
and heated while a solution of 1,5-bis(2-aminophenoxy)-3-
azapentane (1 mmol) in methanol (50 ml) was added. The
resultant solution was refluxed for 2 hours and cooled. Sodium
borohydride (4 mmol) was then added slowly and carefully. The
resulting precipitate was filtered off and recrystallised from hot
acetonitrile. Yield: 65% (Found: C, 70.3; H, 6.3; N, 14.1. Calc.
for C23H26N4O2: C, 70.8; H, 6.7; N, 14.4%). Mass spectral
parent ion: m/z 391. IR (KBr disc): ν(NH) 3354, 3282 cmϪ1. 1H
NMR (CD3CN), δ 7.75 (t, 1H, py), 7.35 (d, 2H, py), 6.93–6.59
(m, 8H, C6H4), 5.42 (t, 4H, NH), 4.42 (d, 4H, NHCH2),
4.12 (t, 4H, OCH2CH2NH), 3.07 (t, 4H, OCH2CH2NH);
13C NMR, δ 156.4 (py), 137.6 (py), 120.5 (py), 47.5 (NHCH2),
109.8, 110.0, 116.1, 120.7, 146.2 (C6H4), 67.0 (OCH2), 26.3
(NHCH2).
Synthetic procedures
2,6-Pyridinedicarbaldehyde was prepared by the literature
method5 as was N,N-bis-[2-(2-aminophenoxy)ethyl]form-
amide.6
1,5-Bis(2-aminophenoxy)-3-azapentane.
This
triamine
precursor was prepared by deformylation of N,N-bis-[2-(2-
aminophenoxy)ethyl]formamide. 4 mmol of N,N-bis-[2-(2-
aminophenoxy)ethyl]formamide were dissolved in ethanol (30
ml), NaOH (0.6 g) was added and the solution was refluxed for
12 hours. When cold the solution was evaporated to dryness
under reduced pressure and the residue dissolved in water (50
ml) prior to extraction with CHCl3 (3 × 50 ml). The combined
extracts were dried over magnesium sulfate, filtered and evapor-
ated, under reduced pressure, to leave a cream powder. Yield:
95% (Found: C, 66.7; H, 7.3; N, 14.7. Calc. for C16H21N3O2: C,
66.9; H, 7.3; N, 14.6%). Mass spectral parent ion: m/z 288. IR
(KBr disc): ν(NH2) 3360, 3450 cmϪ1. 1H NMR (CDCl3), δ 6.91–
6.70 (m, 8H, C6H4), 4.26 (t, 4H, OCH2CH2NH), 3.09 (t, 4H,
OCH2CH2NH), 3.71 (br, 4H, NH2).
Metal complexes of the reduced macrocycle. The following
procedure was used in all cases. The ligand (0.05 mmol) and
appropriate hydrated metal salt (nitrate or perchlorate) (0.05
mmol) were mixed in warm acetonitrile (50 ml). The solution
was refluxed for 2 hours and filtered while hot. The volume of
the filtrate was reduced to 20 ml and the solution was left
standing for crystallisation.
[ZnL2][NO3]2. Yield: 43% (Found: C, 46.6; H, 4.1; N, 14.1.
Calc. for C23H26N6O8Zn: C, 47.6; H, 4.5; N, 14.5%). Mass spec-
tral parent ion: m/z 391. IR (KBr disc): ν(NH) 3360, 3390 cmϪ1
,
ν(NO3Ϫ) 1318, 1384, 1400 cmϪ1. H NMR (CD3CN), δ 8.12
(t, 1H, py), 7.55 (d, 2H, py), 7.26–6.88 (m, 8H, C6H4), 6.14
(t, 2H, NH), 4.63 (d, 4H, NHCH2), 4.33 (t, 4H, OCH2CH2NH),
3.64 (t, 4H, OCH2CH2NH). ΛM (acetonitrile): 114 ΩϪ1 cm2
molϪ1 (1:1 electrolyte).
1
Metal complexes of the diimine macrocycle. 2,6-Pyridine-
dicarbaldehyde (0.5 mmol) and the requisite metal nitrate or
perchlorate (0.5 mmol) were dissolved in refluxing acetonitrile
(30 ml). To this a solution of 1,5-bis(2-aminophenoxy)-3-aza-
pentane (0.5 mmol) in acetonitrile (20 ml) was added dropwise.
The resultant solution was refluxed for 2 hours, cooled, and
filtered. The volume of the filtrate was reduced to 20 ml and the
solution was left standing for crystallisation.
[ZnL2(H2O)2][ClO4]2. Yield: 40% (Found: C, 40.2; H, 4.0;
N, 8.3. Calc. for C23H30N4O12Cl2Zn: C, 40.0; H, 4.3; N, 8.1%).
Mass spectral parent ion: m/z 553, 453. IR (KBr disc): ν(NH)
3264 cmϪ1, ν(ClO4Ϫ) 1121, 1089, 624 cmϪ1. 1H NMR (CD3CN),
δ 8.08 (t, 1H, py), 7.54 (d, 2H, py), 7.31–7.09 (m, 8H, C6H4),
5.66 (t, 2H, NH), 4.61 (d, 4H, NHCH2), 4.44 (t, 4H, OCH2-
CH2NH), 3.13 (t, 4H, OCH2CH2NH). ΛM (acetonitrile): 294 ΩϪ1
cm2 molϪ1 (2:1 electrolyte).
[Zn2L1 (OH)][ClO4]3 3. Yield: 61% (Found: C, 44.1; H, 3.6;
2
N, 9.3. Calc. for C46H45N8O17Cl3Zn2: C, 45.3; H, 3.7; N, 9.2%).
Mass spectral parent ion: m/z 549, 449. IR (KBr disc): ν(C᎐N)
᎐
1621 cmϪ1, ν(ClO4Ϫ) 1103, 624 cmϪ1. 1H NMR (CD3CN), δ 8.44
(t, 1H, py), 8.07 (d, 2H, py), 7.55–7.13 (m, 8H, C6H4), 8.84 (s,
[CdL2(NO3)2] 4. Yield: 76% (Found: C, 41.4; H, 4.0; N, 12.6.
Calc. for C23H26N6O8Cdؒ2H2O: C, 41.6; H, 4.7; N, 12.7%).
Mass spectral parent ion: m/z 566, 501. IR (KBr disc): ν(NH)
2H, HC᎐N), 4.10, 3.75 (m, 4H, OCH CH NH) 2.76, 2.54 (m,
᎐
2
2
4H, OCH2CH2NH). ΛM (acetonitrile): 407 ΩϪ1 cm2 molϪ1 (3:1
electrolyte).
3226, 3267, 3321 cmϪ1, ν(NO3Ϫ) 1036, 1302, 1384, 1410 cmϪ1
.
1H NMR (CD3CN), δ 8.08 (t, 1H, py), 7.58 (d, 2H, py), 7.11–
6.87 (m, 8H, C6H4), 5.54 (t, 2H, NH), 4.52 (d, 4H, NHCH2),
4.30 (t, 4H, OCH2CH2NH), 3.23 (t, 4H, OCH2CH2NH). ΛM
(acetonitrile): 146 ΩϪ1 cm2 molϪ1 (1:1 electrolyte).
[ZnL1(NO3)2]. Yield: 43% (Found: C, 46.2; H, 4.0; N, 13.3.
Calc. for C23H22N6O8ZnؒH2O: C, 46.5; H, 4.0; N, 14.2%). Mass
spectral parent ion: m/z 512, 450. IR (KBr disc): ν(C᎐N) 1620
᎐
1
cmϪ1, (NO3Ϫ) 1384, 1449 cmϪ1. H NMR (CD3OD), δ 8.57 (t,
[CdL2(CH3CN)2][ClO4]2 5. Yield: 78% (Found: C, 41.0; H,
4.6; N, 10.6. Calc. for C27H32N6O10Cl2Cd: C, 41.3; H, 4.1; N,
10.7%). Mass spectral parent ion: m/z 603, 501. IR (KBr disc):
1H, py), 8.29 (d, 2H, py), 7.77–7.30 (m, 8H, C6H4), 9.16 (s,
2H, HC᎐N), 4.44 (br, 4H, OCH CH NH), 3.03 (br, 4H,
᎐
2
2
OCH2CH2NH). ΛM (acetonitrile): 139 ΩϪ1 cm2 molϪ1 (1:1
electrolyte).
1
ν(NH) 3239, 3281 cmϪ1, ν(ClO4Ϫ) 1121, 623 cmϪ1. H NMR
(CD3CN), δ 8.18 (t, 1H, py), 7.67 (d, 2H, py), 7.18–6.84 (m, 8H,
C6H4), 5.31 (t, 2H, NH), 4.43 (d, 4H, NHCH2), 4.76, 3.78 (m,
4H, OCH2CH2NH), 3.21 (t, 4H, OCH2CH2NH). ΛM (aceto-
nitrile): 284 ΩϪ1 cm2 molϪ1 (2:1 electrolyte).
[CdL1(H2O)2][ClO4]2 2. Yield: 78% (Found: C, 37.9; H, 3.5;
N, 7.9. Calc. for C23H26N4O12Cl2Cd: C, 37.6; H, 3.5; N, 7.6%).
Mass spectral parent ion: m/z 599, 498. IR (KBr disc): ν(C᎐N)
᎐
1625 cmϪ1, ν(ClO4Ϫ) 1093, 623 cmϪ1. 1H NMR (CD3CN), δ 8.53
(t, 1H, py), 8.27 (d, 2H, py), 7.70–7.19 (m, 8H, C6H4), 9.13 (s,
X-Ray crystallography
2H, HC᎐N), 4.58, 4.45 (br, 4H, OCH CH NH), 3.30, 3.17 (br,
᎐
2
2
4H, OCH2CH2NH). ΛM (acetonitrile): 298 ΩϪ1 cm2 molϪ1 (2:1
electrolyte).
All crystals were obtained by slow recrystallisation of the
compound from acetonitrile. The details of the X-ray crystal
data, and of the structure solution and refinement, are given
in Table 1. Measurements were made on a Siemens SMART
CCD area diffractometer for the free macrocycle L2, a
Siemens P4 four-circle diffractometer for complex 4, and a
Bruker SMART CCD area diffractometer for complexes 1, 2,
3ؒCH3CN and 5.
[CdL1(NO3)2] 1. Yield: 76% (Found: C, 44.2; H, 4.0; N, 13.4.
Calc. for C23H22N6O8Cd: C, 44.3; H, 3.5; N, 13.5%). Mass
spectral parent ion: m/z 562, 499. IR (KBr disc): ν(C᎐N) 1628
᎐
cmϪ1, (NO3Ϫ) 1309, 1384, 1419 cmϪ1
.
1H NMR (CD3OD),
δ 8.46 (t, 1H, py), 8.22 (d, 2H, py), 7.63–7.13 (m, 8H, C6H4),
9.15 (s, 2H, HC᎐N), 4.47 (br, 4H, OCH CH NH), 3.30 (br, 4H,
᎐
2
2
OCH2CH2NH). ΛM (acetonitrile): 117 ΩϪ1 cm2 molϪ1 (1:1
The programs used were Siemens SMART and SAINT for
control and integration software and SHELXTL as imple-
electrolyte).
4132
J. Chem. Soc., Dalton Trans., 1999, 4131–4137

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Table 1 Crystal data, structure solution and refinement
[CdL1(NO3)2]
1
[CdL1(H2O)2]-
[ClO4]2 2
[Zn2L1 (OH)][ClO4]3ؒ Free macrocycle [CdL2(NO3)2]
[CdL2(CH3CN)2]-
[ClO4]2 5
2
CH3CN 3ؒCH3CN
L2
4
Chemical formula
Formula weight
T/K
Crystal system,
space group
a/Å
C23H22CdN6O8 C23H26CdCl2N4O12 C48H48Cl3N9O17Zn2
C23H28N4O3
408.49
293(2)
Orthorhombic,
Cmc21
21.7074(3)
12.1388(2)
7.9913(2)
C23H26CdN6O8
626.90
293(2)
Monoclinic,
P2(1)/n
11.891(5)
12.824(6)
16.724(7)
105.48(3)
2457.7(19)
4
C27H32CdCl2N6O10
783.89
293(2)
Orthorhombic,
P2(1)2(1)2(1)
8.72260(5)
10.5384(6)
34.657(2)
622.87
150(2)
733.78
150(2)
1260.04
293(2)
Monoclinic,
P2(1)/n
7.9479(13)
12.605(2)
23.682(4)
95.467(18)
2361.7(7)
4
Monoclinic,
C2/c
Monoclinic,
P21/c
31.382(7)
10.683(2)
18.127(4)
116.983(6)
5415.2(19)
8
19.5154(10)
12.2075(6)
22.3744(12)
96.8220(10)
5292.6(5)
4
b/Å
c/Å
β/Њ
V/Å3
2105.72(7)
4
0.087
3187.0(3)
4
0.917
Z
µ/mmϪ1
0.988
1.076
1.139
0.950
Reflections collected
Independent
reflections
Final R1, WR2
indices [I > 2σ(I)]
(all data)
15442
5685
(Rint = 0.0587)
17448
6471
(Rint = 0.0735)
34249
12571
(Rint = 0.0698)
7640
2338
(Rint = 0.0217)
5413
4296
(Rint = 0.0957)
21043
2338
(Rint = 0.0217)
0.0370, 0.0897 0.0453, 0.1053
0.0478, 0.0952 0.0623, 0.1134
0.0534, 0.1337
0.0903, 0.1539
0.0365, 0.0856
0.0471, 0.0947
0.0657, 0.1715
0.1153, 0.2119
0.0349, 0.0731
0.0430, 0.0826
mented on the Viglen Pentium computer; XSCANS was used
for the P4.7
CCDC reference number 186/1686.
See http://www.rsc.org/suppdata/dt/1999/4131/ for crystallo-
graphic files in .cif format.
Results and discussion
Macrocyclic Schiff base complexes
The diimine macrocyclic complexes were synthesised by the
metal templated cyclocondensation of 2,6-pyridinedicarb-
aldehyde and 1,5-bis(2-aminophenoxy)-3-azapentane in reflux-
ing acetonitrile in the presence of the appropriate zinc() or
cadmium() salt demonstrating that it is indeed possible to use
metals other than the alkaline earth metals as templates when
the donor set in the 18-membered ring macrocycle is changed
from N3O3 to N4O2. The complexes were characterised by
elemental analysis, IR, NMR (1H and 13C) and FAB MS. The
IR of the complexes showed no bands corresponding to NH2
Fig. 1 The molecular structure of complex 1, [CdL1(NO3)2]. Selected
bonds and angles: Cd(1)–O(3), 2.376(2); Cd(1)–N(2), 2.556(2); Cd(1)–
N(1), 2.389(2); Cd(1)–O(7), 2.595(2); Cd(1)–N(3), 2.397(2); Cd(1)–
N(4), 2.658(2); Cd(1)–O(8), 2.544(2) Å. O(3)–Cd(1)–N(1), 83.90(8);
O(3)–Cd(1)–O(7), 145.17(7); O(3)–Cd(1)–N(3), 119.60(8); N(1)–Cd(1)–
O(7), 81.91(7); N(1)–Cd(1)–N(3), 155.98(7); N(3)–Cd(1)–O(7),
75.61(7); O(3)–Cd(1)–O(8), 155.82(7); O(8)–Cd(1)–O(7), 49.23(6);
N(1)–Cd(1)–O(8), 79.82(7); N(2)–Cd(1)–O(7), 121.73(6); N(3)–Cd(1)–
O(8), 79.14(7); O(3)–Cd(1)–N(4), 75.64(7); O(3)–Cd(1)–N(2), 80.18(7);
N(1)–Cd(1)–N(4), 64.83(7); N(1)–Cd(1)–N(2), 66.30(7); N(3)–Cd(1)–
N(4), 113.58(7); N(3)–Cd(1)–N(1), 119.37(7); O(8)–Cd(1)–N(4),
112.55(7); O(8)–Cd(1)–N(2), 79.95(6); N(2)–Cd(1)–N(4), 127.02(7)Њ.
and C᎐O groups and were consistent with the formation of
᎐
imine linkages. For the perchlorate complexes absorptions
attributable to ionic perchlorate were found,8 and for the
nitrate complexes it was possible to distinguish the vibrations
associated with coordinated nitrate as well as a band at 1384
cmϪ1 arising from ionic nitrate;9 the ν1–ν4 separation sug-
gested that at least one nitrate would be bidentate. The FAB
MS of the complexes gave highest peaks corresponding to
[MLX]ϩ; in the case of [Zn2L1 (OH)][ClO4]3 3 the hydroxide
The structures of the cadmium complexes of L1
2
bridge is cleaved and no higher peaks were detected. The
molar conductivity of complex 1 in acetonitrile indicated that
this nitrate complex is a 1:1 electrolyte; in the crystalline
state, as discussed below, the nitrate anions in 1 are coordin-
ated to the metal but one is more distant than the other and
so might be more readily displaced in solution. The cadmium
perchlorate complex 2 is a 2:1 electrolyte and the zinc per-
chlorate complex 3 is a 3:1 electrolyte.10 This reflects the
weaker coordinating ability of perchlorate relative to nitrate
and this is further shown in the crystalline state where the
perchlorate anions are non-coordinated. The NMR spectra
of the complexes are unremarkable and are reported in the
Experimental section.
The X-ray structure analyses of three of the complexes con-
firm that the metal cation has been incorporated on complex-
ation to generate endomacrocyclic complexes; both cadmium
complexes 1 and 2 are mononuclear whereas the zinc perchlor-
ate complex is an uncommon µ-hydroxo-bridged dinuclear
species 3.
The molecular structures of the cationic unit present in the
cadmium complexes, 1 and 2, are given in Figs. 1 and 2 respec-
tively, together with selected bond lengths and angles relating
to the coordination environment of the metal. In 1 the metal is
seven-coordinate with a distorted capped trigonal prismatic
(1:4:2) geometry arising from coordination by the four N
atoms of the macrocycle, and three O atoms from a mono-
dentate nitrate [Cd(1)–O(3), 2.38 Å] and an asymmetric, biden-
tate nitrate [Cd(1)–O(8), 2.54 Å; Cd(1)–O(7), 2.60 Å] sited
trans to the macrocyclic plane and in 2 the metal is six-
coordinate with a distorted octahedral geometry arising from
coordination by the four N atoms of the macrocycle, and two O
atoms from water molecules sited trans to the macrocyclic
plane. These O atoms are asymmetrically bound, Cd(1)–O(11),
2.26 Å and Cd(1)–O(12), 2.36 Å. The perchlorate anions are
non-coordinating and so the cadmium structures reflect the
relative coordinating abilities of the nitrate and perchlorate
anions.
J. Chem. Soc., Dalton Trans., 1999, 4131–4137
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Table 2 Structures of zinc complexes with single hydroxide bridges
Compound
Zn ؒ ؒ ؒ Zn/Å
Zn–O–Zn/Њ
Coordination numbers (and geometries)
Ref.
22
[(LA)Zn2(µ-OH)(2-hydroxypyridinate)][ClO4]3
3.46
n/ra
6 (distorted Oh) and 5 (intermediate between square
bipyramid and trigonal bipyramid)
6 and 6 (both distorted trigonal prisms)
4 and 4 (both distorted tetrahedra)
6 and 6 (both distorted octahedra)
4 and 4 (both distorted tetrahedra)
5 and 5 (both trigonal bipyramid)
b
[(LB)Zn2(µ-OH)][ClO4]3 b
3.54
3.63
3.08
3.54
3.40
3.41
3.60
137.1
140.2
131
23
15
24
14
25
b
[(LC)Zn2(µ-OH)][ClO4]3
[(LDH)2Zn2(µ-OH)][PF6]b
[(LE)3Zn-(µ-OH)-Zn(LE)3][ClO4]3
137
b
[(LF)Zn4(µ-OH)2(µ-O2CMe)2][ClO4]2ؒ2H2Ob
n/ra
[(L1)2Zn-(µ-OH)-Zn][ClO4]3
141
5 and 5 (both distorted square coplanar)
This work
b
a n/r = not reported. b Abbreviations of ligands: LA = 4,7,10,23-tetramethyl-17-oxa-1,4,7,10,13,23-hexaazabicyclo[11.7.5]pentacosane, LB = 1,4,7,
16,19,22-hexaaza-10,13,25,28-tetraoxacyclotriacontane, LC = α,αЈ-bis(bis(2-pyridylethyl)amino)-m-xylene, LD = 4,7-di(2-hydroxybenzyl)-1-oxa-4,7-
dioxacyclononane, LE = 5-tert-butylpyrazole, L1 = 10,16-dioxa-3,13,23,29-tetraazatetracyclo[23.3.1.04,9.017,22]nonacosa-1(29),2,4(9),5,7,17,19,21,23,
25,27-undecaene, LF = [2 ϩ 2] macrocycle derived from 2,6-diformyl-4-methylphenol and 1,11-diamino-3,6,9-trioxaundecane.
Fig. 2 The molecular structure of the cation from complex 2, [CdL1-
(H2O)2][ClO4]2, viewed in the plane of the pyridinyl head group.
Selected bonds and angles: Cd(1)–O(11), 2.256(2); Cd(1)–N(3),
2.371(3); Cd(1)–O(12), 2.359(2); Cd(1)–N(4), 2.540(3); Cd(1)–N(1),
2.363(3); Cd(1)–N(2), 2.585(3) Å. O(11)–Cd(1)–N(1), 177.71(9); N(1)–
Cd(1)–N(4), 66.80(9); O(11)–Cd(1)–N(3), 99.17(9); N(3)–Cd(1)–N(4),
122.75(9); O(12)–Cd(1)–N(3), 80.46(9); O(11)–Cd(1)–N(2), 93.97(8);
O(11)–Cd(1)–O(8), 96.56(9); O(12)–Cd(1)–N(2), 83.80(8); O(12)–
Cd(1)–O(8), 83.52(8); N(1)–Cd(1)–N(2), 67.45(6); N(1)–Cd(1)–O(8),
162.56(9); N(3)–Cd(1)–N(2), 104.08(8); O(11)–Cd(1)–N(2), 83.64(9);
N(4)–Cd(1)–N(2), 133.12(8); O(12)–Cd(1)–N(2), 98.25(9)Њ.
The geometric distortion in the complexes arises in part from
Fig. 3 The molecular structure of the cation from complex 3ؒCH3CN,
[Zn2L1 (OH)][ClO4]3ؒCH3CN. Selected bonds and angles: Zn(1)–O(5),
the distortion of the rectangular arrangement of the ligand N
atoms. This is imposed by rigidity of the pyridinyldiimino-
fragment within the ligand framework. In 1 the plane contain-
ing N(1)N(2)N(3)N(4) has an r.m.s. deviation from planarity of
0.308 Å and the Cd(1) is displaced from this towards the
monodentate nitrate by 0.1826 (0.0012) Å. In 2 the correspond-
ing plane containing N(1)N(2)N(3)N(4) has a smaller r.m.s.
deviation from planarity of 0.179 Å and the Cd(1) is now
displaced from this towards the water molecule containing
O(12) by 0.1276 (0.0013) Å [N(2)Cd(1)N(4)]. In both complexes
the Cd–Nimine distances (2.5–2.6 Å) are longer than the Cd–Npy
(ca. 2.37 Å) and Cd–Namine (ca. 2.38 Å) and the Oether atoms at
the distances of Cd–O(1), 2.90 Å and Cd–O(2), 2.77 Å in 1 and
Cd–O(1), 2.97 Å and Cd–O(2), 2.72 Å in 2 from the metal
leading to weak, long range interactions.
2
1.904(2); Zn(2)–O(5), 1.910(2); Zn(1)–N(3), 2.066(3); Zn(2)–N(5),
2.107(3); Zn(1)–N(1), 2.094(3); Zn(2)–N(7), 2.108(3); Zn(1)–N(2),
2.249(3); Zn(2)–N(8), 2.279(3); Zn(1)–N(4), 2.426(3); Zn(2)–
N(6), 2.323(3) Å. O(5)–Zn(1)–N(3), 136.14(11); O(5)–Zn(2)–N(5),
129.92(10); O(5)–Zn(1)–N(1), 121.73(10); O(5)–Zn(2)–N(7), 128.95(10);
N(3)–Zn(1)–N(1), 101.24(11); N(5)–Zn(2)–N(7), 101.12(11); O(5)–
Zn(1)–N(2), 97.98(10); O(5)–Zn(2)–N(8), 97.81(10); N(3)–Zn(1)–N(2),
101.65(11); N(5)–Zn(2)–N(8), 73.50(11); N(1)–Zn(1)–N(2), 74.77(10);
N(7)–Zn(2)–N(8), 97.60(10); O(5)–Zn(1)–N(4), 96.82(9); O(5)–Zn(2)–
N(6), 95.19(10); N(3)–Zn(1)–N(4), 87.73(10); N(5)–Zn(2)–N(6),
72.37(11); N(1)–Zn(1)–N(4), 72.06(10); N(7)–Zn(2)–N(6), 99.99(10);
N(2)–Zn(1)–N(4), 146.69(10); N(8)–Zn(2)–N(6), 143.95(10); Zn(1)–
O(5)–Zn(2), 141.50 (12)Њ.
y Ϫ 1/2, Ϫz), 2.81 Å and O(12)–H(4W) ؒ ؒ ؒ O(4) (Ϫx ϩ 1, y,
Ϫz ϩ 3/2), 2.97 Å.
The pyridine and benzenes are all coplanar and the bonds
and angles within the macrocyclic framework are as expected.
The macrocycle is somewhat buckled in each case. For 1 the
plane derived from N(2)C(6)C(5)N(1)C(1)C(23)N(4) and the
phenyl rings C(7)–C(12) and C(17)–C(22) are inclined at 43.7
and 23.7Њ respectively to this plane and the dihedral angle
between the two aromatic rings is 53.1Њ. In 2 the plane derived
from N(2)C(6)C(5)N(1)C(1)C(23)N(4) and the phenyl rings
C(7)–C(12) and C(17)–C(22) are more shallowly inclined at
13.7 and 28.8Њ; the dihedral angle between the two aromatic
rings is now 33.5Њ.
One of the noncoordinated perchlorate anions in 2 is weakly
involved in hydrogen bonding with a coordinated water mole-
cule, O(7) ؒ ؒ ؒ O(11), 2.76 Å and there are further weak hydro-
gen bonds from the water molecules to perchlorate anions
in the symmetry related positions shown—O(11) ؒ ؒ ؒ O(9)
(Ϫx ϩ 1, y, Ϫz ϩ 3/2), 2.84 Å, O(12)–H(3W) ؒ ؒ ؒ O(5) (x Ϫ 1/2,
The structure of the dinuclear zinc complex of L1
The molecular structure of the cationic unit present in the
dinuclear zinc complex, 3ؒCH3CN, is given in Fig. 3, together
with selected bond lengths and angles relating to the coordin-
ation environment of the metal. The zinc atoms are 3.60 Å
apart and the Zn–O–Zn angle is 141.5Њ. Although there are
numerous examples of zinc complexes with multiple hydroxo
bridges instances of unsupported, or single, µ-hydroxo bridged
complexes are less evident.12,13 Details of the structures of such
complexes are given in Table 2. It is noted that for the first four
complexes the dinuclear moiety is held within a single ligand
framework and so a direct structural comparison can only be
made with [(LE)3Zn–OH–(LE)3][ClO4]3 in which the two zinc
atoms are four coordinate, there is a Zn ؒ ؒ ؒ Zn separation of
3.54 Å and the Zn–O–Zn angle is 137Њ.14 In the complex
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[(LC)Zn2OH][ClO4]3 the two zinc atoms are both in distorted
tetrahedral environments but slight differences in the bonds and
angles lead to inequivalent zinc-containing sites.15 A similar
situation exists in 3ؒCH3CN where although the Zn–OH dis-
tances are similar [Zn(1)–O(5), 1.904(2) Å and Zn(2)–O(5),
1.910(2) Å] the molecule is not symmetric as there are differ-
ences in the metal coordination geometries and the macrocyclic
configurations as discussed below.
Fig. 4 The molecular structure of the free macrocycle L2.
Addison et al. have formulated an algebraic expression which
has proven to be extremely useful for assessing the degree of
trigonality (τ) in a given five-coordinate transition metal com-
plex. τ is considered as the index of trigonality within the struc-
tural continuum between ideal square pyramidal and perfectly
trigonal bipyramidal geometry and is defined by the expression
τ = ( β Ϫ α)/60.16 In a typical square pyramidal molecule there is
an apex A and an equatorial plane defined by BCDE. The
apical donor atom A should not be designated as any of the
atoms which are associated with the two largest angles (α,β ) at
the metal centre. Consequently the limiting cases are τ = 0 for
the square pyramid and τ = 1 for the trigonal bipyramid. In the
present case, where the zinc atoms are both five coordinated by
four macrocycle N atoms and the bridging O atom of the
coordinated hydroxide, it is possible to use this formula to show
that the geometry at Zn(2) is distorted square pyramidal with
τ = 0.23. The geometry is such that the amino nitrogen atom
N(7) is at the apex and the base is provided by the plane
O(5)N(5)N(8)N(6) which has an r.m.s. deviation from planarity
of 0.178 Å. Applying the same criteria to Zn(1) gives a less clear
result. The differences of largest angles gives a τ value of 0.18
with the pyridine nitrogen atom N(1) at the apex and
O(5)N(2)N(3)N(4) as the basal plane. This plane however is
considerably distorted with a r.m.s. deviation from planarity of
0.699 Å. If the second largest angular difference is used then the
amino nitrogen N(3) becomes the apex and so the ligand
configuration is similar to that found at Zn(2). The τ factor is
now 0.41 indicating a significant distortion towards trigonal
bipyramidal and the basal plane, formed by O(5)N(2)N(1)N(4),
has a much reduced mean displacement of 0.293 Å. For com-
pleteness it is noted that the second largest angular differences
found at Zn(2) give rise to a τ value of 0.25 with pyridine nitro-
gen atom N(5) at the apex and O(5)N(6)N(7)N(8) as the basal
plane, the deviation from planarity of which is 0.781 Å. The
ambiguity in using the τ formula in this case is ascribed to the
distortions caused by geometric constraints imposed by the
semi-flexible macrocyclic ligand.
derived from N(8)C(29)C(28)N(5)C(24)C(46)N(6) has the
phenyl rings C(30)–C(35) and C(40)–C(45) inclined at 36.6 and
38.6Њ respectively to this plane; the dihedral angle between the
two aromatic rings is now 57.5Њ.
The three non-coordinated perchlorate anions are disordered
with occupancies of 53 and 47% for the two components of
Cl(1)O4, 71 and 29%, for the two components of Cl(2)O4 and 54
and 46%, for the two components of Cl(3)O4.
The free reduced macrocycle L2
Tetrahydroborate reduction of a range of Schiff base diimine
macrocyclic complexes, prepared by template synthesis on
manganese() or lead() has afforded a useful route to the
corresponding metal-free macrocycles.11 In the present study
the manganese() templated cyclocondensation of 2,6-pyrid-
inedicarbaldehyde and 1,5-bis(2-aminophenoxy)-3-azapentane
in methanol followed by an in situ reductive demetallation of
the Schiff base macrocyclic manganese() complex using excess
sodium borohydride readily gave the metal-free macrocyclic lig-
and L2—it is possible to isolate the Schiff base complex but
crystals suitable for X-ray analysis have so far proved elusive.
The reduced form of macrocycle LB was only obtained when
lead() was used as the template and so the change in donor set
is important in modifying the conditions required to produce
L2. Macrocycle L2 was characterised by elemental analysis, IR,
NMR (1H and 13C) and FAB MS. The IR showed no bands
corresponding to NH , C᎐O or C᎐N groups and bands were
᎐
᎐
2
observed ascribable to the secondary amines present in L2. The
FAB MS gave a parent peak at m/z 391 [L2 ϩ 1]ϩ confirming
that a macrocycle derived from a 1 ϩ 1 condensation had been
formed. The NMR data are summarised in the Experimental
section.
The X-ray crystal structure of the ligand L2, recrystallised
from acetonitrile, confirmed the macrocyclic nature of the
product (Fig. 4). The bond lengths and angles do not show any
significant deviations from the expected values. The macro-
cyclic ring is somewhat bent, having a butterfly shape, with the
benzene rings forming a dihedral angle of 57.3Њ and the
pyridine ring lying at an angle of 48.4Њ to them. There is a water
of crystallisation a hydrogen atom of which undergoes a weak
hydrogen bonded interaction with N(3), [N(3) ؒ ؒ ؒ O(2), 2.86 Å].
In both macrocyclic units the Zn–Nimine distances (2.25–2.42
Å) are longer than the Cd–Npy (ca. 2.1 Å) and Cd–Namine (ca.
2.1 Å) with the Oether atoms at distances of Zn(1)–O(1) 2.81 Å,
Zn(1)–O(2) 2.84 Å, Zn(2)–O(3) 2.86 Å, and Zn(2)–O(4), 2.90 Å
suggesting weaker interactions. The pyridine and benzenes are
all coplanar and the bonds and angles within the macrocyclic
framework are as expected. Each of the macrocycles are
buckled; in the macrocycle ligating Zn(1) the plane derived
from N(2)C(23)C(1)N(1)C(5)C(6)N(4) has the phenyl rings
C(7)–C(12) and C(17)–C(22) inclined at 12.1 and 28.3Њ respec-
tively to this plane with a dihedral angle between the two aro-
matic rings of 20.6Њ. In the macrocycle ligating Zn(2) the plane
The metal complexes of L2
The zinc(II) and cadmium(II) complexes of L2 were synthesised
by reaction of the ligand and the appropriate metal salt in
refluxing acetonitrile. The complexes were characterised by
J. Chem. Soc., Dalton Trans., 1999, 4131–4137
4135

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elemental analysis, IR, NMR (1H and 13C) and FAB MS. The
IR of the complexes showed no bands corresponding to
NH , C᎐O or C᎐N groups but gave bands ca. 3250 cmϪ1 corres-
᎐
᎐
2
ponding to the secondary amine present. For the perchlorate
complexes a splitting of the band at 1100 cmϪ1 suggests that
there could be a possible coordination of the perchlorate group
but such a splitting can also arise from hydrogen bonding to
anion-coordinated perchlorate, loss of symmetry occurring in
both cases. As found for the Schiff base complexes the vibra-
tions associated with a coordinated nitrate were noted together
with a band arising from ionic nitrate. The FAB MS of the
complexes gave highest peaks corresponding to [MLX]ϩ and
the molar conductivities of the complexes in acetonitrile indi-
cated that the nitrate complexes were 1:1 electrolytes and that
the perchlorate complexes were 2:1 electrolytes suggesting a
similar solution behaviour as found for the complexes of L1.
The NMR spectra of the complexes showed, in general, down-
field shifts of signals on coordination suggesting an interaction
of the metal with all available donor atoms. No clear pattern of
shift emerged to support the metal–donor interactions noted in
the crystal structures. The 1:1 stoichiometry of the complexes
in solution was established by NMR titrimetry in CD3CN. For
the cadmium complexes 5 and 6 the metal ion must be strongly
complexed because there is an immediate ingrowth of the sig-
nals due to the metal complex when the metal salt solution is
added to the ligand solution. In contrast only broad signals
occur as the formation of [ZnL2(NO3)2] procedes; this may be
due to an exchange process indicating a weaker coordination of
the zinc although the presence of different conformers in solu-
tion cannot be discounted. Certain oxaazamacrocycles have
been shown to exhibit a marked preference for cadmium over
zinc and it has been suggested that this arises from ‘structural
dislocations’, abrupt changes in coordination geometry,
between the respective complexes.17–21 It is possible to speculate
that this is the case here but in the absence of crystals of the
zinc complex it has not been possible to determine the precise
nature of the bonding to the macrocycle.
Fig. 5 The molecular structure of complex 4, [CdL2(NO3)2]. Selected
bonds and angles: Cd(1)–N(3), 2.370(7); Cd(1)–O(3), 2.530(11); Cd(1)–
N(1), 2.378(6); Cd(1)–N(4), 2.558(7); Cd(1)–O(6), 2.385(8); Cd(1)–
O(4), 2.610(11); Cd(1)–N(2), 2.466(7) Å. N(3)–Cd(1)–N(1), 154.4(3);
N(3)–Cd(1)–O(3), 83.1(3); N(3)–Cd(1)–O(6), 83.2(3); N(1)–Cd(1)–
N(4), 90.9(3); N(1)–Cd(1)–O(6), 81.4(3); N(3)–Cd(1)–N(4), 68.3(2);
N(3)–Cd(1)–N(2), 129.4(2); O(8)–Cd(1)–N(4), 87.8(3); N(1)–Cd(1)–
N(2), 68.6(2); N(2)–Cd(1)–N(4), 136.8(2); O(6)–Cd(1)–N(2), 83.1(2);
O(3)–Cd(1)–N(4), 120.6(3); O(3)–Cd(1)–O(3), 84.4(2); N(1)–Cd(1)–
O(4), 120.2(3); N(3)–Cd(1)–O(3), 118.5(3); N(3)–Cd(1)–O(4), 74.9(3);
N(1)–Cd(1)–O(3), 149.1(3)Њ.
The structures of the cadmium complexes of L2
X-Ray structure analysis confirmed that both 4 and 5, were
mononuclear endomacrocyclic complexes. The molecular struc-
tures of the cationic unit present in the cadmium complexes, 4
and 5, are given in Figs. 5 and 6 respectively, together with
selected bond lengths and angles relating to the coordination
environment of the metal. In 4 the metal is again seven-
coordinate with a distorted capped trigonal prismatic (1:4:2)
geometry arising from coordination by the four N atoms of
the macrocycle, and three O atoms from a monodentate nitrate
[Cd(2)–O(6), 2.38 Å] and an asymmetric, bidentate nitrate
[Cd(2)–O(3), 2.53 Å; Cd(2)–O(4), 2.61 Å] sited trans to the
macrocyclic plane and in 5 the metal is also seven-coordinate
but with a pentagonal bipyramidal geometry arising from
coordination by the four N atoms and one ether oxygen atom,
O(2), of the macrocycle, and two N atoms from acetonitrile
molecules sited trans to the macrocyclic plane. These N atoms
are symmetrically bound, Cd(1)–N(5), 2.44 Å and Cd(1)–N(6),
2.41 Å. The perchlorate anions are non-coordinating and so the
structures again reflect the relative coordinating abilities of the
nitrate and perchlorate anions. One of the perchlorate cations
is disordered with occupancies of 60 and 40%, for the two
components present. The Flack parameter for 5 is Ϫ0.040(19).
The geometric distortion in 4 again arises in part from the
distortion of the rectangular arrangement of the ligand N
atoms. In 4 the plane containing N(1)N(2)N(3)N(4) has an
r.m.s. deviation from planarity of 0.067 Å and the Cd is dis-
placed from this by 0.2665 (0.0045) Å towards the bidentate
nitrate anion, in contrast to the pattern observed for 1. In 4 the
corresponding plane containing N(1)N(2)N(3)N(4) has an
r.m.s. deviation from planarity of 0.021 Å and the Cd is now
Fig. 6 The molecular structure of the cation from complex 5, [CdL2-
(CH3CN)2][ClO4]2, viewed along the plane of the pyridinyl head group.
Selected bonds and angles: Cd(1)–N(1), 2.330(3); Cd(1)–N(5), 2.438(3);
Cd(1)–N(3), 2.368(3); Cd(1)–O(2), 2.486(2); Cd(1)–N(6), 2.413(3);
Cd(1)–N(4), 2.583(3); Cd(1)–N(2), 2.423(3) Å. N(11)–Cd(1)–N(1),
153.55(10); N(1)–Cd(1)–O(2), 135.63(9); N(11)–Cd(1)–N(3), 91.35(10);
N(3)–Cd(1)–O(2), 69.95(9); N(12)–Cd(1)–N(3), 84.82(11); N(6)–Cd(1)–
O(2), 83.05(10); N(11)–Cd(1)–N(8), 70.67(9); N(2)–Cd(1)–O(2),
65.20(9); N(12)–Cd(1)–N(8), 135.11(10); N(5)–Cd(1)–O(2), 89.92(10);
N(1)–Cd(1)–N(8), 88.20(11); N(1)–Cd(1)–N(4), 68.69(9); N(11)–
Cd(1)–N(2), 92.89(10); N(3)–Cd(1)–N(4), 85.25(9); N(11)–Cd(1)–N(2),
93.87(10); N(6)–Cd(1)–N(4), 91.77(11); N(11)–Cd(1)–N(2), 172.88(12);
N(2)–Cd(1)–N(4), 139.34(9); N(11)–Cd(1)–N(2), 87.81(10); N(5)–
Cd(1)–N(4), 95.09(10)Њ.
displaced from this by 0.0819 (0.0015) Å towards the N(5) atom
of a coordinated acetonitrile molecule. In both complexes the
Cd–Namine distances, relating to the amines derived from the
reduced imines, (2.4–2.6 Å) are longer than the Cd–Npy (ca.
2.36 Å) and remaining Cd–Namine (ca. 2.37 Å). The Cd–Oether
4136
J. Chem. Soc., Dalton Trans., 1999, 4131–4137

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distance in 5 is 2.49 Å and the remaining Oether atoms lie at
distances from the metal of 3.93 Å [Cd–O(1)] in 5 and 3.44 Å
[Cd–O(1)] and 2.68 Å [Cd–O(2)] in 4; the latter may be viewed
as a weak long range interaction.
an enhancement of ligand flexibility on reduction which is
manifest by the more ‘cleft’-like conformation found in the
complexes of L2. The nitrate anions are metal coordinated
whereas the perchlorate anions are not, clearly indicating their
The pyridine and benzenes are each coplanar and the bonds
and angles within the macrocyclic framework are as expected.
The macrocycle L2 is significantly buckled in each complex
relative to the buckling of L1 in its complexes, thus reflecting the
greater flexibility inherent in the reduced ligand. For 4 the plane
derived from N(4)C(6)C(5)N(1)C(1)C(23)N(2) and the phenyl
rings C(7)–C(12) and C(17)–C(22) are inclined at 72.0 and
20.4 Å respectively; the dihedral angle between the phenyl rings
is much increased from that in the complexes of L1 at 88.2 Å. In
5 the plane derived from N(2)C(23)C(1)N(1)C(5)C(6)N(4) and
the phenyl rings C(7)–C(12) and C(17)–C(22) are inclined at
94.7 and 163.0 Å respectively; the dihedral angle between the
phenyl rings is again much increased from that in the complexes
of L1 at 101.4 Å.
relative coordinating strengths. The complex [Zn2L1 (OH)]-
2
[ClO4]3ؒCH3CN provides a rare example of an unsupported
dinuclear µ-hydroxy-bridged complex.
Acknowledgements
We thank the EPSRC and the Xunta de Galicia (XUGA
20903B96) for financial support.
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M. G. Williams, P. A. Tasker, A. J. Leong and L. F. Lindoy, J. Chem.
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22 C. Bazzicalupi, A. Bencini, A. Bianchi, V. Fusi, L. Mazzanti, P.
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23 C. Bazzicalupi, A. Bencini, A. Bianchi, V. Fusi, P. Paoletti, G.
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The structures of the cadmium complexes may be compared
with that of [CdLG(MeOH)0.5(H2O)0.5(NO3)][ClO4] derived
from the related macrocycle LG.20 In this complex a more sym-
metric coordination environment is found even though the
ligand adopts a very twisted conformation. The cadmium is
eight coordinated by all six donor atoms of the ligand together
with a monodentate nitrate anion in one ‘axial’ site with the
remaining axial site occupied by a water molecule in one half
of the molecules and a methanol in the remaining half. The
Cd–N distances in this molecule range from 2.43 to 2.58 Å and
the Cd–O distances from 2.35–2.42 Å. It is possible that
the presence of the two pyridine groups in LG allow a more
cadmium compatible macrocyclic cavity to be formed than can
occur with the more flexible macrocycle L2.
Conclusions
Mononuclear cadmium() macrocyclic Schiff base complexes
and a dinuclear, µ-hydroxy-bridged zinc() macrocyclic Schiff
base complex have been prepared by the metal templated
cyclocondensation of 2,6-pyridinedicarbaldehyde and 1,5-(2-
aminophenoxy)-3-azapentane. This has provided a new oxaaza
macrocyclic ligand and the opportunity to utilise the amino-
group in the linker unit to introduce a range of pendant arms.
Mononuclear cadmium() and zinc() complexes of the corre-
sponding reduced macrocycle, L2, have also been synthesised.
Comparison of the crystal structures of the cadmium()
complexes [CdL1(NO3)2] 1, [CdL1(H2O)2][ClO4]2 2, [CdL2-
(NO3)2] 4 and [CdL2(CH3CN)2][ClO4]2 5 show that there is
25 E. Asato, H. Furutachi, T. Kawahashi and M. Mikuriya, J. Chem.
Soc., Dalton Trans., 1995, 3897.
Paper 9/06372B
J. Chem. Soc., Dalton Trans., 1999, 4131–4137
4137