Divalent first-row transition metal complexes of the rigid pendantarm ligand l,4,7-tris(2-aminophenyl)-l,4,7-triazacyclononanef

Article abstract of DOI:10.1039/b005402j

The rigid pendant-arm macrocyclic ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane (L¹) has been synthesized. It reacts with divalent first row transition metal perchlorate salts to yield complexes of general formula [M^II(L

Full text of DOI:10.1039/b005402j

View Article Online / Journal Homepage / Table of Contents for this issue
Divalent first-row transition metal complexes of the rigid pendant-
arm ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane†
Ian A. Fallis,* Richard D. Farley, K. M. Abdul Malik, Damien M. Murphy and
Hayley J. Smith
Department of Chemistry, Cardiff University, PO Box 912, Cardiff, UK CF10 3TB
Received 5th July 2000, Accepted 6th September 2000
First published as an Advance Article on the web 3rd October 2000
The rigid pendant-arm macrocyclic ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triazacyclononane (L1) has been
synthesized. It reacts with divalent first row transition metal perchlorate salts to yield complexes of general formula
[MII(L1)][ClO4]2 (M = FeII, NiII, CuII or ZnII). Single crystal X-ray crystallography indicated that [FeII(L1)][ClO4]2
and [NiII(L1)][ClO4]2 are isostructural with both complex cations consisting of distorted pseudo-octahedral six-co-
ordinate metal centres with three macrocyclic N-donors and three anilino donors. The mean Fe–N bond length
in [FeII(L1)][ClO4]2 was found to be 2.10 Å, which is intermediate between the normal ranges of high and low
spin FeIIN6 species. Magnetometry and EPR measurements indicated that single crystals of [FeII(L1)][ClO4]2 were
predominately low spin, with approximately 5% of a low spin iron() species present in the lattice. It is postulated
that this latter species is the mono anilido complex [FeIII(L1 Ϫ H)][ClO4]2. The crystal structure of [NiII(L1)][ClO4]2
indicated a short mean Ni–N bond length of 2.09 Å. The ligand field strength for this material was found to have a
very high value of 12,330 cmϪ1 (B = 850 cmϪ1) and is compared to that of some related trigonal NiIIN6 species. The
crystal structure of [CuII(L1)][ClO4]2 was also determined and indicated a distorted six-co-ordinate metal centre.
The X-band EPR spectrum of this complex in magnetically dilute solid solution indicated a predominantly axial
species, although a slight rhombic distortion may be present. The variable temperature 1H NMR of [ZnII(L1)][ClO4]2
in CD3CN solution revealed a non-fluxional six-co-ordinate complex. Electrochemical analyses of the complexes
indicated only irreversible oxidation and reduction processes for [NiII(L1)][ClO4]2 and [CuII(L1)][ClO4]2. [FeII(L1)]-
[ClO4]2 displays at least two reversible oxidation processes with the first at ϩ0.181 V (vs. Fc–Fcϩ) being assigned
as a metal centred FeII → FeIII process and the second at ϩ0.475 V as a ligand centred process.
Introduction
The synthesis of rigid pendant-arm derivatives of aza-macro-
cyclic ligands provides a useful means of controlling the ligand
environment about transition metal ions.1 In recent years
Wieghardt and co-workers have described the synthesis and co-
ordination chemistry of a 1,4,7-triazacyclonane (tacn) based
macrocyclic ligand bearing pendant anilino donors (ligand
structure L).2 In L the pendant donor group, as with most
pendant-arm donor systems, is linked to the macrocyclic
donors via a methylene group which imparts a high degree of
ligand conformational flexibility. We felt it would be interesting
to examine the effect of attaching aniline donor groups directly
to the macrocyclic secondary amine positions. Not only would
this make the ligand more rigid but would also be expected to
increase the strength of metal–ligand interactions by reducing
the size of the pendant chelate rings from 6 to 5 membered. To
this end we have devised a simple synthesis of the rigid
pendant-arm ligand 1,4,7-tris(2-aminophenyl)-1,4,7-triaza-
cyclonane (L1) and have begun to explore its transition metal
co-ordination chemistry. To the best of our knowledge L1 repre-
sents the first example of an N-aryl triazacyclononane deriv-
ative. Two examples of tetraaza-macrocyclic ligands bearing
N-aryl substituents have been reported with Kimura and co-
in co-ordination, but acts as a sensitiser or a reporter moiety
for spectroscopic measurements. There are of course
many examples of triazacyclononane derivatives with pendant
workers describing the preparation and complexation proper-
ties of 1-(2,4-dinitrophenyl)-1,4,7,10-tetraazacyclododecane3
and Collins and co-workers examining the spectroscopic prop-
anilines, phenols, benzenethiols and heterocyclic donors, but
erties of 4-(1,4,8,11-tetraazacyclotetradec-1-yl)benzonitrile.4 In
in all these ligand types the aromatic functionalities are bound
both these cases however the aryl group does not participate
to the ring nitrogen donors via methylene linkages, which
confer considerable conformational flexibility upon these sys-
tems.5 We wish to compare these ligands to systems in which
aromatic pendant donor groups were linked directly to the
macrocycle.
† Electronic supplementary information (ESI) available: X-band EPR
spectra of [FeL1][ClO4]2 and electronic spectra of nickel() complexes.
See http://www.rsc.org/suppdata/dt/b0/b005402j/
3632
J. Chem. Soc., Dalton Trans., 2000, 3632–3639
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b005402j

View Article Online
L1 also represents an example of an N,N-disubstituted
o-phenylenediamine ligand. ortho N-Substituted aromatics are
of interest due to their ‘non-innocent’ acid–base and redox
behaviour upon co-ordination.6 There are remarkably few well
defined complexes of o-phenylenediamine itself7 although a
cobalt() templated synthesis of a 21-membered macrocyclic
(tribenzo-1,4,8,11,15,18-hexaazacyclohenicosane) containing
alternating phenylene and propane bridges derivative has been
reported.8 This paper reports the first examples of structurally
characterised tris chelates containing the phenylenediamine
moiety.
H, 4.8; N, 17.0%. Mass spectrum: molecular ion peak at m/z
492 (calc. 492.49).
Method B. To a solution of 1,4,7-triazacyclononane trihydro-
bromide (1 g, 2.7 mmol) in water (5 ml) was added sodium
hydroxide (0.645 g, 16.1 mmol). 2-Fluoronitrobenzene (1.14 g,
8 mmol) dissolved in 5 ml of dichloromethane was added and
the resulting two phase reaction mixture stirred vigorously
overnight. The orange organic layer was separated, diluted with
dichloromethane and washed with water, NaHCO3 (sat.) and
water. The organic phase was dried (MgSO4) and the solvent
removed to afford a bright orange solid. This material was
purified by entrainment with several portions of warm ethanol.
Yield 0.78 g (59%). This material had identical properties to that
prepared by method A.
Experimental
CAUTION! On one occasion a small sample of a metal per-
chlorate salt of L1 detonated whilst being manipulated as a dry
solid. In a separate incident a sample of the ligand mono-
hydroperchlorate salt ([HL1][ClO4]) exploded under similar
circumstances. Whilst no damage or injury was incurred in
these incidents it is recommended that perchlorates be prepared
and manipulated in very small quantities.
1,4,7-Tris(2-aminophenyl)-1,4,7-triazacyclononane (L1). To a
solution of 1,4,7-tris(2-nitrophenyl)-1,4,7-triazacyclonane (1 g,
2 mmol) in tetrahydrofuran–ethanol (10:1, 100 ml) was added
palladium (10%) on carbon (100 mg). Hydrogen was bubbled
through the stirred reaction mixture for 20 hours during which
a fresh portion of catalyst was added. The reaction was filtered
under nitrogen through a pad of Celite and the solvent removed
under reduced pressure. The residue was recrystallised from a
small volume of hot oxygen-free ethanol to afford the required
product as an off-white crystalline solid. Yield 0.51 g (62%). 1H
NMR (400 MHz, CDCl3): δ 6.97 (d, 3 H, Ar), 6.78 (t, 3 H, Ar),
6.60 (m, 6 H, Ar), 4.17 (s (br), 6 H, NH2) and 3.39 (12 H, s, CH2
1,4,7-Triazacyclonane was prepared by standard methods9
and purified (twice) by bulb-to-bulb distillation prior to use. All
other reagents (Aldrich) were used as received. Solvents were
purified by standard literature methods.10 All metal complexes
were prepared under a nitrogen atmosphere using standard
Schlenk techniques. Mass spectra were obtained in FAB
(Fast Atom Bombardment) mode in a 3-nitrobenzyl alcohol
matrix, IR spectra in KBr discs using a Nicolet 510 series
spectrometer and electronic spectra in acetonitrile solution
using Perkin-Elmer Lambda 20 or Lambda 900 spectrophoto-
meters. Electrochemical measurements were performed using a
Windsor Scientific Eco Chemie Autolab PGSTAT12 potentio-
meter equipped with a cell consisting of a platinum disc (3 mm)
working electrode, a platinum wire counter electrode and a non-
aqueous 0.01 M AgNO3–Ag–0.1 M Bu4NPF6–CH3CN–glass
frit reference electrode. All electrochemical measurements were
performed in Bu4NPF6 (0.1 M) supporting electrolyte under an
argon atmosphere and the data were analysed using the Eco
Chemie GPES suite of software (v. 4.7). Electrochemical poten-
tials are quoted with reference to a ferrocene–ferrocenium
internal standard. NMR spectra were obtained on Brüker
Avance AMX 400 or JEOL Eclipse 300 spectrometers and
referenced to external TMS. EPR spectra were recorded on a
Brüker ESP 300-E X-band spectrometer. The g values were
determined using a Brüker NMR gaussmeter calibrated using
the perylene radical anion generated in concentrated sulfuric
acid, g = 2.002569.
1
of macrocycle). H NMR (300 MHz, CD3CN): δ 6.97 (d, 3 H,
Ar), 6.78 (t, 3 H, Ar), 6.60 (m, 6 H, Ar), 4.17 (s (br), 6 H, NH2)
and 3.39 (12 H, s, CH2 of macrocycle). 13C NMR (100 MHz,
CDCl3): δ 141.3 (C of Ar), 140.4 (C of Ar), 123.8 (CH of Ar),
122.1 (CH of Ar), 117.6 (CH of Ar) and 114.6 (CH of Ar). IR
(KBr disc, cmϪ1) 3449, 3331, 3045, 2854, 2822, 1606, 1497,
1452, 1374, 1318, 1300, 1149, 1129, 1042, 745 and 611. Calc. for
C24H30N6: C, 71.6; H, 7.5; N, 20.9%. Found: C, 71.4; H, 7.3; N,
20.7%. Mass spectrum: molecular ion peak at m/z 402 (calc.
402.54).
[FeII(L1)][ClO4]2 1. To suspension of L1 (40 mg, 0.1 mmol) in
thoroughly degassed ethanol (20 ml) was added an excess of
Fe(ClO4)2ؒ6H2O (40 mg, 1.1 mmol). The reaction mixture was
slowly heated to reflux during which time the ligand dissolved
to precipitate pale blue micro-crystals. Removal of the super-
natant by cannula and subsequent drying in vacuo afforded the
required complex (59 mg, 90%) as small faintly blue crystals.
Crystals of X-ray quality were grown by dissolving this material
in hot thoroughly degassed ethanol (60 ml) and allowing the
solution to cool slowly and stand for several weeks at room
temperature. IR (KBr disc, cmϪ1): 3287, 3240, 3163, 2971, 2943,
1615, 1568, 1497, 1477, 1455, 1280, 1260, 1090, 920, 808, 769,
737, 709, 625, 572 and 455. UV/vis (MeCN, nm): 710. Calc. for
C24H30Cl2FeN6O8: C, 43.9; H, 4.6; N, 12.8%. Found: C, 44.0;
H, 4.7; N, 12.9%.
Preparations
1,4,7-Tris(2-nitrophenyl)-1,4,7-triazacyclononane
(LЈ).
Method A. To a solution of 1,4,7-triazacyclononane (1.29 g, 10
mmol) in dry acetonitrile (100 ml) was added 2-fluoronitro-
benzene (4.23 g, 30 mmol) and finely ground potassium
carbonate (4.14 g, 30 mmol). The reaction mixture was refluxed
under a nitrogen atmosphere for 8 hours and subsequently
filtered, whilst hot, through a fluted filter paper. The residual
solid was washed with dichloromethane (2 × 50 ml) and the
combined acetonitrile filtrate and dichloromethane washings
were evaporated to dryness to yield a bright orange solid. This
material was purified by washing with several portions of warm
ethanol. Yield 3.52 g (72%). 1H NMR (CDCl3): δ 7.53 (d, 3 H,
Ar), 7.33 (m, 3 H, Ar), 7.08 (d, 3 H, Ar), 6.88 (m, 3 H, Ar) and
3.46 (s, 12 H, CH2 of macrocycle). 13C NMR (CDCl3): δ 145.1
(C of Ar), 143.3 (C of Ar), 133.6 (CH of Ar), 126.3 (CH of Ar),
122.3 (CH of Ar), 121.2 (CH of Ar) and 55.2 (CH2 of macro-
cycle). IR (KBr disc, cmϪ1): 3052, 2920, 1610, 1561, 1513,
1480, 1435, 1339, 1297, 1255, 1240, 1221, 1178, 732 and 707.
Calc. for C24H24N6O6: C, 58.5; H, 4.9; N, 17.1%. Found: C, 58.6;
[NiII(L1)][ClO4]2 2. This material was prepared in a similar
manner to that of 1 by treating L1 (40 mg, 0.1 mmol) with an
excess of Ni(ClO4)2ؒ6H2O (40 mg, 1.1 mmol). Yield 59 mg
(90%) of a pink crystalline powder. Crystals of X-ray quality
were grown by dissolving this material in hot degassed ethanol
(40 ml) and allowing the solution to cool slowly and stand for
several days at room temperature. IR (KBr disc, cmϪ1): 3315,
3264, 3179, 2872, 1619, 1575, 1495, 1478, 1455, 1278, 1231,
1092, 947, 931, 920, 900, 810, 770, 734, 714, 621, 595, 576, 556
and 457. UV/vis (MeCN, nm (ε/dm3 molϪ1 cmϪ1)): 869 (sh) (13),
811 (17), 521 (11) and 326 (sh) (26). Calc. for C24H30Cl2N6NiO8:
C, 43.7; H, 4.6; N, 12.7%. Found: C, 43.4; H, 4.8; N, 12.0%.
[CuII(L1)][ClO4]2ؒEtOH 3. The method used to prepare this
material was analogous to that for 1 using 40 mg of Cu(ClO4)2ؒ
6H2O. Yield 48 mg (68%). UV/vis (MeCN, nm (ε/dm3 molϪ1
J. Chem. Soc., Dalton Trans., 2000, 3632–3639
3633

View Article Online
cmϪ1)): 695 (103) and 1200 (30). Calc. for C26H36Cl2CuN6O9: C,
43.9; H, 5.1; N, 11.8%. Found: C, 43.5; H, 5.3; N, 11.7%. Mass
spectrum: molecular ion peak at m/z 464.4 (566 {[CuII(L1)]-
[ClO4]}Ϫ also observed).
[ZnII(L1)][ClO4]2 4. The method used to prepare this material
was analogous to that for [NiII(L1)][ClO4]2, using 100 mg (2.5
mmol) of L1 and 100 mg Zn(ClO4)2ؒ6H2O. Yield 110 mg (66%).
1H NMR (400 MHz , CD3CN): δ 7.57 (d, 3 H, Ar), 7.35 (t, 3 H,
Ar), 7.24 (m, 6 H, Ar), 4.56 (s (br), 6 H, NH2), 3.60 (6 H, m,
CH2 of macrocycle) and 2.99 (6 H, m, CH2 of macrocycle). 13
C
NMR(CD3CN): δ 147.03 (C), 134.05 (C), 129.31 (CH), 128.28
(CH), 127.81 (CH), 125.40 (CH) and 53.62 (CH2). Calc. for
C24H30Cl2N6O8Zn: C, 43.2; H, 4.5; N, 12.6%. Found: C, 43.0; H,
4.6; N, 12.5%.
[CuII(L1)][ClO4]2 doped in [ZnII(L1)][ClO4]2. [CuII(L1)][ClO4]2ؒ
EtOH (5 mg) and [ZnII(L1)][ClO4]2 (95 mg) were dissolved in
dry oxygen free acetonitrile (1 ml). The resulting suspension
was warmed to effect dissolution and cold diethyl ether (5 ml)
added to precipitate a grey solid. The supernatant liquid was
removed by cannula and the residue washed first with ether
(3 ml) and then light petroleum (bp 40–60 ЊC) (3 ml). The
sample was dried in vacuo to afford the required product as a
blue-grey powder. Yield 84 mg (84%).
Scheme 1 Reagents and conditions: (i) o-FC6H4NO2, K2CO3, MeCN,
reflux 8 hours; (ii) 10% Pd/C, H2(g), THF–EtOH; (iii) MII(ClO4)2ؒ
X-Ray crystallography
6H2O, EtOH.
X-Ray intensity data for the complexes of Fe, Ni and Cu (1, 2
and 3 respectively) were collected on a CAD4 diffractometer
using monochromated Mo-Kα radiation (λ = 0.71073 Å).
Allowances were made for crystal decay for 2 and 3 which,
respectively, showed a 24 and 25% fall in the intensities of the
standard reflections during the period of data collection. The
structures were solved by direct methods (SHELXS 86)11 and
refined on F 2 by full-matrix least squares (SHELXL 96)12 using
all unique data. The complexes of Fe and Ni were isostructural;
one of the two independent ClO4Ϫ anions showed orientational
disorder with two partially occupied positions for each oxygen
atom. The disordered group in both structures was refined with
one common Cl–O distance and the anisotropic displace-
ment coefficients of the oxygen atoms constrained to remain
‘approximately isotropic’ by using an ISOR = 0.012 parameter
in SHELXL 96. The copper complex contained an ethanol
and anaerobic work-up of LЈ affords L1 in 62% (isolated) yield
as a crystalline solid. Solutions of L1 prepared by this method
were found rapidly to darken upon exposure to air. Attempts to
increase the scale of this reaction resulted in reduced yields and
difficult work up procedures. In preparing complexes of L1 it
was essential to use anaerobic conditions. For example, solu-
tions of [ZnII(L1)][ClO4]2 became red upon exposure to air,
although no change in the NMR spectrum of this material was
observed. In addition no electrochemical oxidation (0.1 M
Bu4NPF6, MeCN 0–1.5 V vs. Fc–Fcϩ) of this complex or the
“free” ligand was observed. We are currently investigating
alternative reaction conditions for the hydrogenation step
in order to increase the scale and improve the yield of this
procedure.
Ϫ
solvate per complex cation. One O atom of one ClO4 anion
[FeII(L1)][ClO4]2. Initial reaction of L1 with Fe(ClO4)2ؒ6H2O
under anaerobic conditions afforded colourless solutions which
upon cooling yielded pale blue micro-crystals of the required
product. Recrystallisation of the initial product from ethanol
yielded pale blue X-ray quality crystals. The structure of the
[FeII(L1)]2ϩ cation is shown in Fig. 1 with selected bond lengths
and angles collected in Table 2. The complex is monomeric with
all six N-ligators bound to a distorted octahedral metal centre.
The structure as shown is that of the Λ isomer in which the
macrocyclic chelate rings are of δ configuration. This material
crystallises in a non-enantiomorphous space group, and thus
[FeII(L1)][ClO4]2 in the solid state consists of equal quantities of
Λ(δδδ) and ∆(λλλ) cations. An examination of the metal–
ligand bond distances indicates a mean Fe–N bond length of
2.10 Å. A selection of FeN6 systems for which crystallographic
data are available is collected in Table 3. It can be seen that the
mean Fe–N distance is intermediate between typical values
observed for high (≈2.20 Å) and low-spin (≈2.00 Å) FeII–N6
systems and is significantly longer than those in iron() systems
and from the crystallography data alone the assignment of a
spin state is somewhat ambiguous.
and the methyl C of the ethanol molecule were refined with an
ISOR = 0.015. The non-H atoms in all the structures were
anisotropic. The H atoms were included in calculated positions
(riding model) with Uiso = nUeq (n = 1.2 for NH2, CH2 and ring
H; 1.5 for CH3 in 3) of the parent atom. Pertinent crystallo-
graphic data, and selected bond distances and angles are given
in Tables 1 and 2 respectively.
CCDC reference number 186/2173.
See http://www.rsc.org/suppdata/dt/b0/b005402j/ for crystal-
lographic files in .cif format.
Results and discussion
Ligand synthesis and complex preparation
L1 and its complexes are prepared according to reaction
Scheme 1. Using method A the initial nucleophilic aromatic
substitution reaction of 1,4,7-triazacyclononane with 3 mole
equivalents of 2-fluoronitrobenzene in refluxing acetonitrile in
the presence of anhydrous potassium carbonate affords the
intermediate 1,4,7-tris(2-nitrophenyl)-1,4,7-triazacyclononane
(LЈ) in 72% (isolated) yield. By method B a lower yield was
obtained but the synthesis proceeds via tacnؒ3HBr and as such
is more convenient. These reactions are not optimised and we
are currently investigating a range of different conditions in
order to improve yields. Hydrogenation (10% Pd/C, thf–EtOH)
Ethanolic solutions of complex 1 are very air-sensitive and
upon exposure to air rapidly become deep blue with the elec-
tronic spectrum indicating a broad, intense band at 710 nm. All
attempts at observing a well resolved 1H NMR spectrum of the
[FeII(L1)]2ϩ cation failed. The spectra obtained were broad with
3634
J. Chem. Soc., Dalton Trans., 2000, 3632–3639

View Article Online
Table 1 Crystallographic data for complexes 1, 2 and 3
1
2
3
Chemical formula
Formula weight
C24H30Cl2FeN6O8
657.29
C24H30Cl2N6NiO8
660.15
C26H36Cl2CuN6O9
711.05
Crystal system
Space group
Orthorhombic
Pbca
Orthorhombic
Pbca
Triclinic
P1
¯
a/Å
b/Å
c/Å
α/Њ
β/Њ
γ/Њ
T/K
14.298(2)
13.759(2)
28.230(4)
14.282(4)
13.765(5)
28.182(4)
11.064(6)
11.197(4)
13.814(7)
75.13(3)
74.41(4)
67.95(3)
293
293
293
Z
8
8
2
µ(Mo-Kα)/cmϪ1
No. of reflections measured
No. of unique data
Rint
0.795
5498
4931
0.0344
0.1044
0.0413
0.953
6316
5618
0.0650
0.1801
0.0672
0.966
6059
5265
0.0425
0.2153
0.0838
wR2 (on F2, all data)
R1 (on, F, observed data)
Table 2 Selected bond lengths (Å) and angles (Њ) in complexes 1, 2
and 3
1 (M = Fe)
2 (M = Ni)
3 (M = Cu)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1)–N(4)
M(1)–N(5)
M(1)–N(6)
2.102(3)
2.101(3)
2.112(3)
2.099(3)
2.113(3)
2.092(3)
2.087(5)
2.088(4)
2.083(5)
2.083(5)
2.116(5)
2.089(5)
2.218(9)
2.024(9)
2.193(8)
2.211(9)
2.081(9)
2.032(8)
N(1)–M(1)–N(2)
N(1)–M(1)–N(3)
N(1)–M(1)–N(4)
N(1)–M(1)–N(5)
N(1)–M(1)–N(6)
N(2)–M(1)–N(3)
N(2)–M(1)–N(4)
N(2)–M(1)–N(5)
N(2)–M(1)–N(6)
N(3)–M(1)–N(4)
N(3)–M(1)–N(5)
N(3)–M(1)–N(6)
N(4)–M(1)–N(5)
N(4)–M(1)–N(6)
N(5)–M(1)–N(6)
83.92(11)
83.30(11)
82.10(11)
164.24(12)
99.68(12)
84.30(11)
101.36(12)
81.15(12)
164.65(11)
163.66(12)
100.13(12)
81.34(11)
95.90(13)
93.93(12)
96.06(13)
84.6(2)
84.6(2)
82.7(7)
165.9(2)
100.2(2)
85.6(2)
100.3(2)
82.4(2)
166.3(2)
165.5(2)
99.7(2)
82.1(2)
94.3(2)
93.2(2)
93.8(2)
83.2(3)
80.8(3)
78.0(3)
161.6(3)
98.3(3)
84.5(3)
100.1(3)
83.8(3)
164.3(3)
157.6(3)
110.9(3)
80.9(3)
91.5(3)
95.1(3)
97.6(3)
Fig. 1 Ortep 313 plot of [FeII(L1)]2ϩ 1 viewed down the approximate
3-fold axis. Ellipsoids are drawn at 40%. Hydrogen atoms are omitted
for clarity.
peaks interpreted as macrocyclic ring methylene groups at
δ 2.1 and 2.4 and those for the aryl groups at δ 11.4 and 14.55.
It is believed that the blue coloration observed in the original
complex is due to a trace of oxidation of [FeII(L1)]2ϩ to the
corresponding iron() species, the paramagnetism of which
results in the broadening of the NMR spectra. Alternatively it
is possible that the source of FeIII may be a small impurity in the
original iron() perchlorate hexahydrate starting material. It
was also observed that this oxidation process occurred more
slowly in dry acetonitrile solution. The magnetic moment of
single crystals of 1 have been measured by variable temper-
ature SQUID magnetometry by Professor Andrew Harrison
(University of Edinburgh). This study indicated that 1 contains
a low spin iron() centre but also that a small (≈5%) quantity of
a low-spin iron() species was present in the lattice. We also
observed that the darkening of solutions of 1 was accelerated
by addition of trace amounts of a weak base (e.g. triethyl-
amine), which we interpret as a deprotonation of a pendant
anilino donor [see ref. 2(c)] to yield a corresponding anilido
complex [FeIII(L1 Ϫ nH)](3 Ϫ n)ϩ. We therefore tentatively suggest
that single crystals of 1 contain approximately 5% of [FeIII-
(L1 Ϫ H)][ClO4]2 (low spin) dispersed in a lattice of [FeII(L1)]-
[ClO4]2 (low spin). This is perhaps not unreasonable given that
[FeII(L1)]2ϩ and [FeIII(L1 Ϫ H)]2ϩ would be expected to have very
similar structures, not dissimilar molecular volumes, and would
not be distinguishable from pure [FeII(L1)][ClO4]2 using micro-
analytical data. In order to support this suggestion the X-band
Table 3 Mean Fe–N distances and spin states of a range of FeN6
complexes
Complex
Mean M–N/Å
Spin state
Ref.
[FeII(tacn)2]2ϩ
[FeIII(tacn)2]3ϩ
[FeII(L)]2ϩ
2.03
1.99
Not reported
2.10
2.23
Low
Low
High
Lowa
High
14
14
2(b)
This work
15
[FeII(L1)]2ϩ
[FeII(en)3]2ϩ
a Contains ≈5% of low spin [FeIII(L1 Ϫ H)]2ϩ
.
EPR spectrum of 1 in a frozen dimethylformamide glass was
measured at 10 K (see ESI supplementary information). 1 (20
mg) was dissolved in degassed anhydrous DMF (1.0 ml) and the
solution divided into two approximately equal portions. A drop
of dimethylformamide containing a trace of triethylamine was
added to one portion under aerobic conditions. The spectrum
obtained for the initial (i.e. base free) solution was found to be
rather low in intensity and to be typical of a low spin d5 species
with g values centred about that of the free electron. Low spin
d5 species would be expected to display a small Jahn–Teller
distortion that explains a weak rhombicity observed in this
spectrum. The spectrum of 1 in the presence of triethylamine
J. Chem. Soc., Dalton Trans., 2000, 3632–3639
3635

View Article Online
Fig. 2 Cyclic voltammogram of [FeII(L1)][ClO4]2 in 0.1 M [n-Bu4N]-
PF6 in acetonitrile vs. Fc–Fcϩ.
indicated that the initial low spin iron() spectrum is only
slightly altered but that a new feature centred at g = 4.3 appears.
This latter signal is typical of that of a high-spin iron() com-
plex. This seemingly contradictory result may be explained by
considering that the addition of triethylamine is likely to gener-
ate the neutral tris-anilido species [FeIII(L1 Ϫ 3H)]0 [see ref. 2(c)].
Anilido ligands are strong σ and π donors and as such may
be regarded as weak field ligands. Therefore the formation of
a tris anilido species converts this system from a strong into a
weak field case with a corresponding shift from low to high
spin. These results corroborate the assignment of 1 as consist-
ing of predominantly diamagnetic low spin [FeII(L1)][ClO4]2
with a small amount of a low spin mono-anilido species
[FeII(L1 Ϫ H)][ClO4]2 present in the lattice. The above EPR results
also imply that in the presence of base (and under aerobic
conditions) there is an equilibrium between a range of [FeIII-
(L1 Ϫ nH)](3 Ϫ n)ϩ species which vary in their degree of protonation
and hence in spin state. In an additional experiment [FeIII-
(H2O)6][ClO4]3 was added to L1 dissolved in oxygenated DMF
solution. An immediate deep blue coloration was observed
(λ = 710 nm) and the EPR spectrum of this solution was found
to be identical to that of [FeII(H2O)6][ClO4]2 prior to the addi-
tion of base. Subsequent addition of Et3N yielded a spectrum
identical to that of [FeII(H2O)6][ClO4]2 basified under aerobic
conditions. It seems likely that here the initial reaction yields
[FeIII(L1 Ϫ nH)](3 Ϫ n)ϩ type species in various degrees of proton-
ation, and that addition of base again generates the neutral
high spin complex [FeIII(L1 Ϫ 3H)]0. The blue coloration of single
crystals of 1 can also be attributed to the presence of [FeIII-
(L1 Ϫ H)]2ϩ if the strong absorption observed at 710 nm in solu-
tion is assigned as an anilido ligand-to-metal charge transfer
band. Owing to its intensity this charge transfer band obscures
Fig. 3 Ortep plot of [NiII(L1)]2ϩ 2 viewed normal to the plane defined
by the macrocyclic donors. Other details as in Fig. 1.
To date all attempts at the preparation of [FeII(L1)][ClO4]2,
[FeIII(L1 Ϫ H)][ClO4]2 and [FeIII(L1 Ϫ 3H)]0 as discrete, analytically
pure substances have failed.
[NiII(L1)][ClO4]2. The single crystal structure of this
material, which is isostructural to 1, was obtained as shown in
Fig. 3. The metal centre is six-co-ordinate with the macrocycle
is in its typical face-capping mode and all three pendant aniline
donors co-ordinated. The twist angle of the complex is 16Њ
(octahedral twist angle = 0Њ) indicating that the bite angle of the
N-2-aminophenyl pendant group is not sufficient to span two
cis sites of an undistorted octahedron. The complex has no
crystallographic symmetry but has approximate C3 molecular
symmetry. A comparison of the mean metal–ligand distances in
[NiII(L1)]2ϩ (Ni–N 2.09 Å) to those of [NiII(L)]2ϩ (Ni–N 2.16
Å)2b reveals a significantly stronger metal–ligand interaction in
the case of L1. In addition the metal–ligand distances are short
in comparison to those of other nickel() hexaamine species
contained in the Cambridge crystallography database.
The electronic spectrum of [NiII(L1)][ClO4]2 was measured in
acetonitrile solution (see ESI supplementary information for
this spectrum and related NiIIN6 chromophores). Typically the
ligand field splitting parameter 10Dq for octahedral nickel()
3
complexes is given by the energy of the lowest T2g ← 3A1g
transition, which in most cases is seen to consist of two com-
ponents. For the purposes of calculating ∆ in the cases of [NiII-
(bipy)3]2ϩ 16 and [NiII(tacn)2]2ϩ 17 the higher energy component
1
1
3
the expected T1g ← 1A1g and T2g ← 1A1g transitions
has normally been assigned as the spin-allowed T2g ← 3A1g
normally observed in low spin iron() species.
(Oh) transition, whilst the lower energy component is attributed
to the spin-forbidden 1Eg ← 3A1g transition. By following this
convention a ligand field splitting value ∆ of 12,330 cmϪ1 and a
Racah B parameter of 850 cmϪ1 (as calculated from the
3T2g ← 3A1g and 3T1g(F) ← 3A1g transitions) is obtained for
[NiII(L1)]2ϩ. This value is significantly greater than that of the
isoleptic complexes [NiII(L)]2ϩ (10Dq = 10,900 cmϪ1 2b) and
[NiII(en)3]2ϩ indicating that the more rigid ligand enforces a
stronger metal–ligand interaction. However Jørgensen18 and
Hancock and McDougall19 have pointed out that the
The electrochemical behaviour of [FeII(L1)][ClO4]2 was
measured by cyclic voltammetry (CV) in acetonitrile solution
(Fig. 2). The complex displays two strong fully reversible oxid-
ation processes at ϩ 0.181 (∆Ep = 60 mV) and ϩ 0.475 V
(∆Ep = 60 mV) and weaker reversible processes at ϩ0.695 V
(∆Ep = 72 mV). The reductive electrochemistry proved to be
complex with three irreversible oxidation processes occuring at
Ϫ1.03, Ϫ1.585 and Ϫ1.906 V. The reversibility of the more
prominent oxidation processes was confirmed by recording the
CV data at a range of sweep rates. A plot of (sweep rate)1/2 vs.
cathodic current yielded a straight line, indicating truly revers-
ible behaviour for each process. We can currently only speculate
on the nature of the oxidised species although it seems likely
that the first oxidative processes at ϩ 0.181 V may be assigned
to a metal based FeII → FeIII process. The other oxidations
are presumably ligand based and may result in the generation
of a ligand centred radical species. It is also possible that these
oxidations involve concomitant deprotonation of the ligand to
an anilido species.
1
3T2g ← 3A1g and Eg ← 3A1g transitions are scrambled in
complexes with Dq/B values significantly greater than unity and
therefore it not possible unequivocally to assign either compon-
ent to a specific transition. In addition, for complexes in which
there is a noted degree of trigonal distortion the lower energy
band is also split into two components as seen in Gillum et al.’s
analysis of the [NiII{(py)3(tach)}]2ϩ system ((py)3(tach) =
cis,cis-1,3,5-tris{2-pyridylmethyleneamine}cyclohexane).
In
this case the {(py)3(tach)] ligand was found to dictate almost
perfect trigonal prismatic co-ordination geometry about NiII.20
3636
J. Chem. Soc., Dalton Trans., 2000, 3632–3639

View Article Online
Table 4 Mean Ni–N distances and 10 Dq values of a range of NiIIN6
complexes
Complex
Mean Ni–N/Å
10Dq/cmϪ1
Ref.
[NiII(bipy)3]2ϩ
[NiII(tacn)2]2ϩ
2.09
2.08
12,650
12,500, 12,350
23, 24
25
22
This work
2(b)
26, 18
[NiII(L1)]2ϩ
[NiII(L)]2ϩ
[NiII(en)3]2ϩ
2.09
2.16
2.13
12,330
10,900
11,700
The electronic spectra for the lower energy T2g ← A1g
transition for [NiII{(py)3(tach)}]2ϩ and [NiII(L1)]2ϩ are very
similar, and whilst simple model building studies indicate
that L1 will not support trigonal prismatic co-ordination geom-
etry this observation implies that the rigorous assignment of
the two components of the lower energy band is a non-trivial
task.
The 10Dq value of [NiII(L1)]2ϩ is not very much smaller that
of [NiII(bipy)3]2ϩ (10Dq = 12,650 cmϪ1), which is the largest
reported ligand-field splitting parameter for an octahedral
nickel() species21 (see Table 4). The high ligand-field splitting
value in [NiII(bipy)3]2ϩ is partly due to the π acidity of the bipy
ligand, but since L1 may be described as a pure σ donor, steric
factors must account for the high ligand field strengths
observed. It is has been argued by Hancock that the high ligand
field splitting value of [NiII(tacn)2]2ϩ (mean Ni–N distance 2.08
Å, 10Dq = 12,350 cmϪ1; note 10Dq values for this complex vary
from author to author) is due to this complex having the
minimum possible ‘cage’ size for nickel() cations and that the
metal–ligand distances would be shorter were it not for the
non-bonded repulsive interactions between pairs of methylene
groups on adjacent macrocyclic rings.22 In L1 the 3 anilino
donor groups (primary amino donors) would be expected to be
sterically more efficient than an additional tacn moiety
(secondary amino donors) and thus it appears that the rigidity
of the pendant arms in [NiII(L1)]2ϩ prevents the closer approach
of the anilino donor atoms to the metal centre and places it at a
ligand field strength slightly less than that of [NiII(tacn)2]2ϩ and
considerably higher than that of the more flexible tris chelates
such as [Ni(en)3]2ϩ (mean N–Ni 2.13 Å, ∆ = 11,700 cmϪ1).18 An
alternative way of stating this notion is that L1 has an appropri-
ate cavity size for the nickel() ion.
Fig. 4 Ortep plot of [CuII(L1)]2ϩ 3 viewed normal to the plane defined
by the macrocyclic donors. Other details as in Fig. 1.
The rhombic distortion was also confirmed spectroscopically
(Q-band EPR).
The structure of the cation [CuII(L1)]2ϩ is illustrated in Fig. 4,
with selected bond lengths and angles collected in Table 2.
This complex also displays six-co-ordinate geometry with the
macrocycle facially co-ordinated and all anilino donors bound
to the metal centre. An examination of the metal–ligand bond
lengths indicates that despite the high symmetry of the ligand
three relatively short (Cu–N2, Cu–N5, Cu–N6) and three
long (Cu–N1, Cu–N3, Cu–N4) metal–nitrogen distances are
observed, indicating that the complex is rhombically, not tetra-
gonally, distorted. The three axes are defined as x N3–Cu–N4
(long), y N1–Cu–N5 (intermediate) and z N2–Cu–N6 (short).
It is worth noting that the two sets of short and long metal–
ligand bond lengths are not restricted to those of macrocyclic
donors and pendant-arm donors (which would maintain tri-
gonal symmetry), but involve two pendant-arm donors and one
macrocyclic donor and vice versa. The mean Cu–N distance is
2.12 Å, which is particularly short compared to related CuN6
species in the Cambridge Crystallography database, indicating
a compression of the metal–ligand bond lengths. The electronic
spectrum of [CuII(L1)][ClO4]2 in acetonitrile solution indi-
cated a broad band at 695 nm (ε = 107 dm3 molϪ1 cmϪ1),
We speculated that a nickel() complex of L1 might be
accessible. However upon examination of the electrochemical
behaviour of [NiII(L1)][ClO4]2 only an irreversible oxidation at
ϩ1.05 V (vs. Fc–Fcϩ) was observed.
2 Ϫ y2
dx
← t2g) and a weaker broad feature at 1200 nm (ε = 30
dm3 molϪ1 cmϪ1 dx
← dz ), suggesting that the pseudo
2
2 Ϫ y2
[CuII(L1)][ClO4]2. The above results suggest that L1 permits
the formation of six-co-ordinate C3 symmetric complexes and
that the ligand rigidity, to some extent, dictates the metal–
ligand bond lengths. Copper() centres have a marked tendency
to form five-co-ordinate complexes or six-co-ordinate Jahn–
Teller distorted complexes, typically by elongation of one
ligand–metal–ligand axis.27 In an interesting example reported
by Parker and co-workers it was shown that the Jahn–Teller
distortion of copper() species can be suppressed in a C3 sym-
metric tacn based system in which the pendant arm has the
appropriate bite angle.28 The ligand in this study was however a
pendant arm phosphinic acid derivative and it could be argued
that the stronger anionic ligand–metal interaction is partly
responsible for dampening out of the Jahn–Teller distortion.
We postulated that L1 as a neutral, rigid N6 donor would
not permit the typical tetragonal distortion. Halcrow and co-
workers have demonstrated that by using rigid sterically
demanding ligands (3,3Ј-disubstituted 2,6-di(pyrazol-1-yl)-
pyridines), compressed rhombic distortions may be promoted.29
In this system three distinct axes were observed crystallo-
graphically with a mean Cu–N distance found to be 2.11 Å.
octahedral structure was maintained in solution. The presence
of a near infrared band implies tetragonal distortion, although
this distortion is not observed in the solid state structure. Simi-
lar observations were noted by Bernhardt and co-workers in the
structure and electronic spectroscopy of the hexaamine cage
complex [Cu{(NH3)2sar}][NO3]4ؒH2O (sar = 3,6,10,13,16,19-
hexaazabicyclo[6.6.6]eicosane).30 It should be noted that the
mean Cu–N bond distance in the Cu–sar system is rather long
at 2.17 Å and that ligand is likely to be more flexible than in the
present case. It imposes trigonal symmetry but in this case an
additional tetragonal elongation is also observed with a further
small, but distinct, orthorhombic distortion. This latter distor-
tion was evidenced by the observation of three distinct g values
in the Q-band EPR spectrum. The X-band EPR of [CuII(L1)]-
[ClO4]2 doped into [ZnII(L1)][ClO4]2 measured at 100 K is shown
in Fig. 5. The spectrum is essentially that of an axial d9 species
with g|| = 2.26 (A|| = 147 G) and g⊥ = 2.058 (A⊥ = unresolved).
The solution spectrum as measured in a frozen DMF–toluene
glass was found be very similar with comparable g and A values.
The shoulder to higher field on the perpendicular component
may be interpreted as a so called “overshoot” feature resulting
J. Chem. Soc., Dalton Trans., 2000, 3632–3639
3637

View Article Online
Research Council (EPSRC) for financial support, and the
EPSRC Mass Spectrometry Service (Swansea, UK) for valuable
experimental assistance. We would also like to thank Dr
Angelo J. Amoroso (Cardiff), Dr Athanasia Dervisi (Cardiff)
and Professor Andrew Harrison (Edinburgh) for valuable
discussion.
References
1 P. Chaudhuri and K. Wieghardt, Prog. Inorg. Chem., 1987, 35,
329; P. V. Bernhardt and G. A. Lawrance, Coord. Chem. Rev.,
1990, 104, 297; K. P. Wainwright, Coord. Chem. Rev., 1997, 35,
166.
˜
2 (a) O. Schlager, K. Wieghardt, H. Grondey, A. RufiOska and
B. Nuber, Inorg. Chem., 1995, 34, 6440; (b) O. Schlager, K.
Wieghardt and B. Nuber, Inorg. Chem., 1995, 34, 6449; (c) O.
Schlager, K. Wieghardt and B. Nuber, Inorg. Chem., 1995, 34, 6456.
3 T. Koike, T. Gotoh, A. Aoki, E. Kimura and M. Shiro, Inorg. Chim.
Acta, 1998, 270, 424.
4 (a) L.-S. Choi and G. E. Collins, Chem. Commun., 1998, 893;
(b) G. E. Collins, L. S. Choi and J. H. Callahan, J. Am. Chem. Soc.,
1998, 120, 1474.
Fig. 5 (a) X-Band EPR spectrum of [CuII(L1)][ClO4]2 doped in [ZnII-
(L1)][ClO4]2 at 100 K.
from the relative magnitudes of the g and A anisotropies. Alter-
natively this may be interpreted as a rhombic feature. This sys-
tem is currently the subject of an ENDOR and multi-frequency
EPR study which will be described in a subsequent paper.
A plausible analysis for the distortion in [Cu(L1)]2ϩ may be
made by noting that the co-ordination polyhedra as defined by
the six nitrogen donor atoms of [Fe(L1)]2ϩ, [Ni(L1)]2ϩ and
[Cu(L1)]2ϩ are very similar with the mean M–N bond lengths
spanning a narrow range (2.09–2.12 Å). Here it appears that by
confining three donors within a macrocycle, and by having rigid
aryl pendant arms bearing the remaining three donors, the
degrees of torsional freedom available to the ligand are greatly
restricted. As a final indicator of the inflexibility of L1, the co-
ordination geometry observed for [CuII(L1)]2ϩ is in contrast to
that of [CuII(L)]2ϩ, with the latter complex found to be five-co-
ordinate in the solid state with distorted square pyramidal
geometry.2b In [CuII(L)]2ϩ the additional methylene group
between the pendant aniline and the macrocycle permits one of
the pendant groups to rotate away from the metal centre to
yield a five-co-ordinate metal centre. This is not possible in
the case of L1, in which rotation of the pendant arm about
the N–Ar bond results in an unfavourable steric interaction of
the pendant amine group and the macrocyclic methylene
residues.
5 For recent examples see: B. Albela, E. Bill, O. Brosch, T.
Weyhermüller and K. Wieghardt, Eur. J. Inorg. Chem., 2000, 139;
M. Di Vaira, F. Mani and P. Stoppioni, Inorg. Chim. Acta, 2000, 297,
61; S. J. Brudenell, L. Spiccia, A. M. Bond, G. D. Fallon, D. C. R.
Hockless, G. Lazarev, P. J. Mahon and E. R. T. Tiekink, Inorg.
Chem., 2000, 39, 881; L. M. Berreau, J. A. Halfen, V. G. Young, Jr.
and W. B. Tolman, Inorg. Chim. Acta, 2000, 297, 115; J. Müller,
A. Kikuchi, E. Bill, T. Weyhermüller, P. Hiderbrandt, L. Ould-
Moussa and K. Wieghardt, Inorg. Chim. Acta, 2000, 297, 265; M. Di
Vaira, F. Mani and P. Stoppioni, Eur. J. Inorg. Chem., 1999, 833;
T. Glaser, F. Kesting, T. Beissel, E. Bill, T. Weyhermüller, W. Meyer-
Klaucke and K. Wieghardt, Inorg. Chem., 1999, 38, 722; T. Glaser,
E. Bill, T. Weyhermüller, W. Meyer-Klaucke and K. Wieghardt,
Inorg. Chem., 1999, 38, 2632; B. Albela, E. Bothe, O. Brosch,
K. Mochiazuki, T. Weyhermüller and K. Wieghardt, Inorg. Chem.,
1999, 38, 5131; R. Schnepf, A. Sololowski, J. Müiller, V. Bachier,
K. Wieghardt and P. Hildebrandt, J. Am. Chem. Soc., 1998, 120,
2352; F. N. Penkert, T. Weyhermüller and K. Wieghardt, Chem.
Commun., 1998, 557; H. Weller, T. A. Kaden and G. Hopfgarten,
Polyhedron, 1998, 17, 4543; M. Koikawa, K. B. Jensen, H.
Matsushima, T. Tokii and H. Toflund, J. Chem. Soc., Dalton Trans.,
1998, 1085; M. Di Vaira, F. Mani and P. Stoppioni, J. Chem. Soc.,
Dalton Trans., 1998, 3209; S. J. Brudenell, L. Spiccia, A. M.
Bond, P. C. Mahon and D. C. R. Hockless, J. Chem. Soc., Dalton
Trans., 1998, 3919; A. Sokolowski, B. Adam, T. Weyhermüller,
A. Kikuchi, K. Hildenbrand, R. Schnepf, P. Hildebrandt, E. Bill
and K. Wieghardt, Inorg. Chem., 1997, 36, 3702; B. Adam, E. Bill,
E. Bothe, B. Goerdt, G. Haselhorst, K. Hildenbrand, A.
Sokolowski, S. Steenken, T. Weyhermüller and K. Wieghardt,
Chem. Eur. J., 1997, 3, 308; M. Di Vaira, F. Mani and P. Stoppioni,
J. Chem. Soc., Dalton Trans., 1997, 1375; T. Beissel, F. Birkelbach,
E. Bill, T. Glaser, F. Kesting, C. Krebs and K. Wieghardt, J. Am.
Chem. Soc., 1996, 118, 12376.
6 D. A. House, in Comprehensive Co-ordination Chemistry, eds.
G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon Press,
Oxford, 1987, vol. 2, p. 59.
7 D. R. Marks, D. J. Phillips and J. P. Redfern, J. Chem. Soc. A, 1967,
1464.
8 G. J. Grant and D. J. Royer, J. Am. Chem. Soc., 1981, 103, 867.
9 K. Wieghardt, W. Schmidt, B. Nuber and J. Weiss, Chem. Ber., 1979,
112, 2220.
10 D. D. Perrin and W. F. A. Amarego, Purification of Laboratory
Chemicals, Pergamon, Oxford, 1988.
11 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
12 G. M. Sheldrick, SHELXL 96, Program for Crystal Structure
Refinement, University of Göttingen, 1996.
13 Ortep 3 for Windows, A Version of ORTEP III with a Graphical
User Interface (GUI), L. J. Farrugia, J. Appl. Crystallogr., 1997, 30,
565.
14 J. C. A. Boeyens, A. G. S. Forbes, R. D. Hancock and K. Wieghardt,
Inorg. Chem., 1985, 24, 19226.
15 J. Li, Z. Chen, J. J. Emge and D. M. Proserpio, Inorg. Chem., 1997,
36, 1437.
[ZnII(L1)][ClO4]2 4. Reaction of L1 with Zn(ClO4)2ؒ6H2O in
refluxing ethanol afforded [ZnII(L1)][ClO4]2 4 as colourless
microcrystals. Despite repeated attempts, crystals of [ZnII(L1)]-
[ClO4]2 failed to yield workable X-ray crystallographic data.
The 1H NMR spectrum of the complex in acetonitrile solution
indicated that it is C3 symmetric in solution. All three aromatic
pendant groups are equivalent and the macrocyclic methylene
groups have been resolved into two complex multiplets at δ 3.60
and 2.99. These latter resonances are tentatively assigned as due
to endo- and exo- protons of the macrocyclic chelate rings. The
pendant aniline NH2 groups in the “free” ligand occur as a
broad singlet at δ 4.17 (in CD3CN solution) and shift to a broad
singlet at δ 4.56 upon co-ordination. This implies that in solu-
tion all six N-donors are co-ordinated. The 1H NMR was found
not to change significantly when recorded over the temperature
range of Ϫ40 to ϩ70 ЊC. This observation suggests that over
the experimental temperature range the [ZnII(L1)]2ϩ cation is
non-fluxional in solution. This is in contrast to the behaviour of
[ZnII(L)]2ϩ which displayed a complex, temperature-dependant
NMR spectrum.2a Again it can be seen that the larger pendant
chelate rings of L1 permit greater torsional flexibility in the
co-ordinated ligand system.
16 R. A. Palmer and T. S. Piper, Inorg. Chem., 1966, 5, 864.
17 L. J. Zompa, Inorg. Chem., 1978, 17, 2531.
18 C. K. Jørgensen, Acta Chem. Scand., 1955, 9, 1362.
19 R. D. Hancock and G. J. McDougall, J. Chem. Soc., Dalton Trans.,
1977, 67.
Acknowledgements
We wish to thank the Engineering and Physical Sciences
3638
J. Chem. Soc., Dalton Trans., 2000, 3632–3639

View Article Online
20 W. O. Gillum, R. A. D. Wentworth and R. P. Childers, Inorg. Chem.,
1970, 9, 1825.
21 A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier,
Amsterdam, 1984, p. 508.
22 V. J. Thom, G. J. McDougall, J. C. A. Boeyens and R. D. Hancock,
J. Am. Chem. Soc., 1984, 106, 3198; R. D. Hancock, Prog. Inorg.
Chem., 1989, 37, 187.
and A. B. P. Lever, Inorganic Electronic Structure and Spectroscopy,
Wiley, New York, 1999, vol. II, p. 76; M. Milnik, M. Kabesova,
L. Macaskova and C. E. Holloway, J. Coord. Chem., 1998, 45, 31;
L. R. Falvello, J. Chem. Soc., Dalton Trans., 1997, 4463; B. J.
Hathaway, in Comprehensive Co-ordination Chemistry, eds. G.
Wilkinson, J. McCleverty and R. D. Gillard, Pergamon, Oxford,
1987, vol. 5, p. 610.
23 C. K. Jørgensen, Adv. Chem. Phys., 1963, 5, 33.
24 D. J. Chestnut, R. C. Haushalter and J. Zubieta, Inorg. Chim. Acta,
1999, 292, 41.
25 L. J. Zompa and T. N. Margulis, Inorg. Chim. Acta, 1980, 45, L263.
26 J. D. Korp, I. Bernal, R. A. Palmer and J. C. Robinson, Acta
Crystallogr., Sect. B, 1980, 36, 560.
27 B. N. Figgis and M. A. Hitchman, Ligand Field Theory Theory and
Applications, Wiley, New York, 2000, p. 298; C. E. Holloway
and M. Melnik, Rev. Inorg. Chem., 1995, 15, 147; E. I. Solomon
28 E. Cole, D. Parker, G. Ferguson, J. F. Gallagher and B. Kaitner,
J. Chem. Soc., Chem. Commun., 1991, 1473.
29 N. K. Solanki, E. J. McInnes, F. E. Mabbs, S. Radojevic,
M. McPartlin, N. Feeder, J. E. Davies and M. A. Halcrow, Angew.
Chem., Int. Ed., 1998, 37, 2221.
30 P. V. Bernhardt, R. Bramley, L. M. Engelbrandt, J. M. Harrowfield,
D. C. R. Hockless, B. R. Korybut-Daszkiewicz, E. R. Krause,
T. Morgan, A. M. Sargeson, B. W. Skelton and A. H. White,
Inorg. Chem., 1995, 34, 3589.
J. Chem. Soc., Dalton Trans., 2000, 3632–3639
3639