Synthesis of the terpyridyl pendant-arm azamacrocycle 4′-(p-1,4,7-triazacyclonon-1-ylmethylphenyl)-2,2′ :6′,2″-terpyridine (L) and complexes of L with copper(II) and nickel(II). Crystal structure of [Cu(HL)(H2O)2][PF6]<sub

Article abstract of DOI:10.1039/a907717k

The azamacrocyclic ligand 4′-(p-1 ,4,7-triazacyclonon-l-ylmethylphenyl)-2,2′ : 6′,2″-terpyridine (L) has been prepared, and some of the complexes it forms with hydrated copper(n) and nickel(n) have been isolated as the [PF₆]^- salts.

Full text of DOI:10.1039/a907717k

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Synthesis of the terpyridyl pendant-arm azamacrocycle 4Ј-(p-1,4,7-
triazacyclonon-1-ylmethylphenyl)-2,2Ј:6Ј,2Љ-terpyridine (L) and
complexes of L with copper(II) and nickel(II). Crystal structure
of [Cu(HL)(H2O)2][PF6]3
Mary L. Turonek, Peter Moore* and William Errington
Department of Chemistry, University of Warwick, Coventry, UK CV4 7AL.
E-mail: p.moore@warwick.ac.uk
Received 24th September 1999, Accepted 21st December 1999
The azamacrocyclic ligand 4Ј-(p-1,4,7-triazacyclonon-1-ylmethylphenyl)-2,2Ј:6Ј,2Љ-terpyridine (L) has been
prepared, and some of the complexes it forms with hydrated copper() and nickel() have been isolated as the
[PF6]Ϫ salts. X-Ray crystallography has been used to determine the solid state structure of the distorted trigonal
bipyramidal complex [Cu(HL)(H2O)2][PF6]3, in which the copper() is co-ordinated to the terpyridyl group and
the azamacrocycle is monoprotonated and non-co-ordinating. A bis(2,2Ј:6Ј,2Љ-terpyridine)nickel() complex,
[Ni(H2L2)2][PF6]6 has also been isolated, in which each azamacrocycle is diprotonated.
Recent attention has focused on the production of suitably
designed supramolecular multicomponent systems to obtain
photoinduced migration of electronic energy and/or charge
separation by covalently linked photosensitizers.1,2 Although
ruthenium() complexes of bipyridine-type ligands, such as
[Ru(bipy)3]2ϩ (bipy = 2,2Ј-bipyridine), are well documented
photosensitisers, their chirality causes problems from the
geometric viewpoint for the construction of well defined
supramolecular systems. In contrast, the complexes of the
[Ru(terpy)2]2ϩ family (terpy = 2,2Ј:6Ј,2Љ-terpyridine) offer sev-
eral synthetic and structural advantages, while exhibiting less
favourable photophysical properties. However, suitable sub-
stituents in the 4Ј position of terpy can yield ruthenium()
complexes which display room temperature luminescence.3
Attention has now been directed towards the derivatization of
terpyridyl ligands, the formation of homo- and hetero-leptic
[Ru(terpy)2]2ϩ-type complexes, and the formation of back-to-
back mixed metal polynuclear complexes.3–7
and molecular structure of [Cu(HL)(H2O)2][PF6]3 determined
by X-ray crystallography.
Experimental
Materials
Reagent grade commercial compounds were used as starting
materials, and their purity was checked by 1H and 13C NMR.
To date the attachment of terpyridyl derivatives to novel
subunits displaying contrasting metal complex co-ordination
geometries has received little attention. For example, the modes
of co-ordination of macrocycles with transition metals are
diverse, and often vary with changing metal cation for the same
macrocyclic ligand. It is our intention to combine derivatized
terpyridyl ligands with polyaza macrocycles of increasing ring
size, systematically to develop polynuclear complexes of mixed
geometry. The systematic increase of repeating subunits has the
potential to produce oligomeric species, and may give rise to the
self assembly of new inorganic materials.7
In this paper we report the synthesis of a new azamacrocyclic
ligand, 4Ј-(p-1,4,7-triazacyclonon-1-ylmethylphenyl)-2,2Ј:6Ј,2Љ-
terpyridine (L), that has both a meridionally co-ordinating
subunit (terpy), and a facially co-ordinating triazamacrocycle
(1,4,7-triazacyclononane). This new ligand has been synthesized
using an approach developed by Weisman et al.,8 where the ter-
pyridylbenzyl pendant arm is introduced into the macrocyclic
structure by reaction with the tricyclic orthoamide of 1,4,7-
triazacyclononane.8 Copper() and nickel() complexes of L of
formulae [Cu(HL)(H2O)2][PF6]3 and [Ni(H2L)2][PF6]6ؒH2O have
been isolated, and characterized by elemental analyses, liquid
secondary ion mass spectrometry (LSIMS) and electrospray
mass spectrometry. The complexes were further investigated by
UV/VIS spectroscopy and cyclic voltammetry, and the crystal
Spectra, analyses and other procedures
The 250 MHz 1H NMR and proton-decoupled 62.9 MHz
13C NMR spectra were obtained with a Bruker AC250 spec-
trometer, UV/VIS and electron-impact mass spectra with
Shimadzu 365 and Kratos MS80 spectrometers respectively
and LSIMS spectra obtained with a Kratos Concept II HH
four-sector tandem mass spectrometer (Kratos Analytical
Ltd, Manchester, UK). Elemental analyses were made with a
Leeman Laboratories CE 440 elemental analyser. Cyclic vol-
tammetry was performed under argon at 20 ЊC with an Oxford
Electrodes potentiostat and triangular wave generator (Oxford,
UK) and an Advance Bryons X-Y chart recorder. The working
electrode was a platinum electrode, with a platinum wire
counter electrode and a saturated calomel reference electrode.
The supporting electrolyte was NaClO4 (0.1 mol dmϪ3).
Preparations
The synthetic route to L is outlined in Scheme 1.
4Ј-(p-Tolyl)-2,2Ј:6Ј,2Љ-terpyridine (ttpy). The procedure was
modified from those described by Collin and Constable.6,9
A mixture of acetamide (183 g, 3.1 mol), ammonium acetate
(118 g, 1.5 mol), p-tolualdehyde (12.4 g, 103 mmol) and
DOI 10.1039/907717k
J. Chem. Soc., Dalton Trans., 2000, 441–444
This journal is © The Royal Society of Chemistry 2000
441

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2-acetylpyridine (25 g, 206 mmol) was refluxed for 2 h. The
mixture was then cooled to 120 ЊC, and a solution of sodium
hydroxide (90 g) in water (200 cm3) added. After standing for 2
h at 120 ЊC, the solution was cooled to room temperature and
left to stand overnight. A dark brown solidified “glass” was
broken up and separated from the quickly solidifying solution,
washed with water and dissolved in glacial acetic acid (60 cm3).
The hydrogen bromide salt was precipitated by adding 48%
HBr (60 cm3), and the resulting solid filtered from the solution
and dissolved in water (200 cm3). The aqueous solution was
made alkaline to pH 10 with KOH, and the resulting suspen-
sion extracted into CH2Cl2 (3 × 200 cm3). After drying the
combined extracts with anhydrous MgSO4, the solvent was
removed under reduced pressure, and the residue recrystallized
from ethanol (400 cm3) to give white needles (8.4 g). The
product was dissolved in EtOH–CH2Cl2 (1:1, 380 cm3), and a
solution of ammonium iron() sulfate hexahydrate (4.5 g) in
water (76 cm3) added to give a deep purple solution. The
dichloromethane was removed under reduced pressure and then
a solution of KPF6 (4.27 g) in water (38 cm3) added. The purple
precipitate was collected by suction filtration and extracted with
toluene (3 × 100 cm3). The combined toluene extracts were
dried with anhydrous MgSO4, filtered, then taken to dryness
under reduced pressure to isolate the minor by-product, 6Ј-p-
tolyl-2,2Ј:4Ј,2Љ-terpyridine (2 g, 6% yield). δH (250 MHz,
solvent CDCl3) 8.89 (1 H, d), 8.79 (1 H, d), 8.74–8.69 (2 H, m),
8.51 (1 H, d), 8.18 (2 H, d), 8.03 (1 H, d), 7.84 (2 H, q), 7.34 (4
H, m) and 2.36 (3 H, s); δC (62.9 MHz, solvent CDCl3) 157.2,
156.2 (2C), 155.1, 149.9, 148.9, 148.1, 139.0, 136.9, 136.8, 136.4,
129.3 (2C), 126.9 (2C), 123.7, 123.6, 121.4, 121.2, 117.6, 116.4
and 21.3. The remaining purple precipitate was dissolved in
acetonitrile (100 cm3) and an equal volume of water added. The
pH of the aqueous layer was increased to pH > 12 with KOH.
Hydrogen peroxide (30%) was then added dropwise (CARE:
this reaction is accompanied by copious effervescence) until the
purple acetonitrile layer had disappeared to form one layer
containing a heavy orange precipitate and a flocculent pale
lavendar precipitate that cannot be removed or decolourized by
further addition of hydrogen peroxide. The solution was filtered
and the pale lavendar precipitate scraped from the top of the
remaining residue and discarded. The remainder was boiled
with decolourizing charcoal and chloroform (50 cm3). The
solution was filtered, and then taken to dryness under reduced
pressure to give a bright white powder (6 g, 18% yield). δH (250
MHz, solvent CDCl3) 8.73 (2 H, s), 8.70 (2 H, m), 8.62 (2 H, d),
7.82 (4 H, m), 7.30 (4 H, m) and 2.40 (3 H, s); δC (62.9 MHz,
solvent CDCl3) 156.2 (2C), 155.7 (2C), 150.0, 149.0 (2C), 139.0,
136.7 (2C), 135.3, 129.6 (2C), 127.0 (2C), 123.6 (2C), 121.2
(2C), 118.5 (2C) and 21.2.
(10 cm3) was refluxed for 3.5 h, then cooled to 0 ЊC and
made basic (pH 10) by dropwise addition of NaOH (8 mol
dmϪ3). The solution was immediately extracted with CHCl3
(5 × 20 cm3). The combined organic extracts were dried with
anhydrous MgSO4, filtered and taken to dryness under reduced
pressure to yield the ligand precursor as a viscous pale yellow
oil (0.40 g, 96% yield). δH (250 MHz, solvent CDCl3) 8.64 (4 H,
m), 8.58 (2 H, d), 8.02 (1 H, d), 7.78 (4 H, m), 7.35 (2 H, d), 7.25
(2 H, m), 3.64 (2 H, s), 3.38–3.27 (3 H, m), 3.11 (1 H, m), 2.99
(3 H, m), 2.89 (1 H, m), 2.81 (1 H, m), 2.67 (1 H, m), 2.57 (2 H,
s) and 2.47 (1 H, m); δC (62.9 MHz, solvent CDCl3) 163.7,
163.6, 156.0, 155.8, 155.7, 149.7, 149.6, 149.0, 140.6, 140.4,
137.2, 137.0, 136.7 (2C), 129.5, 129.4, 127.2, 127.1, 123.7, 121.2,
118.6, 61.8 (2C), 57.4, 55.6, 53.2, 52.4, 52.2, 50.2, 49.2, 48.0,
47.9, 47.1 and 46.7. A solution of the ligand precursor (0.40 g,
0.835 mmol) and KOH (1 g, 18 mmol) in ethanol (15 cm3) and
water (5 cm3) were refluxed for 48 h, cooled and taken to
dryness under reduced pressure. The residue was dissolved in
the minimum volume of water and extracted with CHCl3
(5 × 20 cm3). The combined organic extracts were dried over
anhydrous MgSO4, filtered and evaporated to yield a yellow oil
(0.31 g, 6.89 mmol, 82% yield). δH (250 MHz, solvent CDCl3)
8.69 (2 H, s), 8.67 (2 H, m), 8.60 (2 H, d), 7.80 (4 H, m), 7.42
(2 H, d), 7.28 (2 H, m), 3.71 (2 H, s), 2.74 (4 H, s), 2.61 (8 H, s)
and 2.23 (2 H, br s); δC (62.9 MHz, solvent CDCl3) 156.1 (2C),
155.8 (2C), 149.9, 149.0 (2C), 140.9, 137.0, 136.7 (2C), 129.4
(2C), 127.1 (2C), 123.6 (2C), 121.2 (2C), 118.6 (2C), 61.3, 53.2
(2C), 47.1 (2C) and 46.7 (2C). Electron-impact mass spectrum:
found, m/z 451; calc. for Mϩ, 451.
[Cu(HL)(H2O)2][PF6]3. A solution of Cu(NO3)2ؒ3H2O (48
mg) in ethanol (4 cm3) was added to a cooled, filtered solution
of ligand L (0.18 g) in ethanol (4 cm3). The reaction mixture
was refluxed for 1 h, and upon cooling to room temperature
afforded a blue-green insoluble precipitate (0.13 g). The precip-
itate was suspended in ethanol–water (1:1, 5 cm3) and three
drops of concentrated HPF6 were slowly added. The reaction
mixture was gently heated until the solution turned turquoise
and a pale lavender precipitate formed. The precipitate was
filtered from the solution, rinsed with water (20 cm3) followed
by ethanol (20 cm3) and diethyl ether (3 × 20 cm3), then air
dried (yield: 60 mg). The remaining turquoise filtrate was
heated to reflux then allowed to cool to room temperature over-
night. In this way, turquoise rectangular crystals of [Cu(HL)-
(H2O)2][PF6]3 suitable for X-ray analysis were produced. The
crystals were collected by filtration, washed with ethanol (20
cm3) then diethyl ether (3 × 20 cm3), and allowed to air dry
(yield: 0.10 g, 51%). LSIMS: found, m/z 694; calc. for Mϩ, 694.
Found: C, 34.0; H, 3.5; N, 8.3. C28H35CuF18N6O2P3 requires C,
34.1; H, 3.6; N, 8.5%.
4Ј-(p-Bromomethylphenyl)-2,2Ј:6Ј,2Љ-terpyridine. This was
prepared from 4Ј-(p-tolyl)-2,2Ј:6Ј,2Љ-terpyridine using the
procedure described by Collin et al.9 (yield: 37%). δH (250 MHz,
solvent CDCl3) 8.72 (4 H, m), 8.65 (2 H, d), 7.86 (4 H, m), 7.52
(2 H, d), 7.34 (2 H, m) and 4.55 (2 H, s); δC (62.9 MHz, solvent
CDCl3) 156.0 (2C), 155.9 (2C), 149.3, 149.0 (2C), 138.5 (2C),
136.8 (2C), 129.5 (2C), 127.7 (2C), 123.8 (2C), 121.3 (2C), 118.7
(2C) and 32.9.
[Ni(H2L)2][PF6]6ؒH2O. A solution of Ni(NO3)2·6H2O (30 mg)
in ethanol (2 cm3) was added to a cooled, filtered solution of
ligand L (90 mg) in ethanol (2 cm3). The reaction mixture was
refluxed for 1 h, and upon cooling to room temperature
afforded a pale yellow powder. The precipitate was suspended
in ethanol–water (1:1, 2 cm3) and three drops of concentrated
HPF6 were slowly added. The reaction mixture was gently
refluxed until the precipitate dissolved, then allowed to cool very
slowly to room temperature to afford a golden microcrystalline
powder. The powder was collected by filtration, washed with
ethanol (10 cm3) then diethyl ether (3 × 10 cm3), and allowed to
air dry (yield: 0.15 g, 80%). Electrospray MS: found, m/z 1105;
calc. for [Ni(L)2(PF6)]ϩ, 1105. Found: C, 36.6; H, 3.9; N, 8.8.
C56H66F36N12NiOP6 requires C, 36.3; H, 3.6; N, 9.1%.
4Ј-(p-1,4,7-Triazacyclonon-1-ylmethylphenyl)-2,2Ј:6Ј,2Љ-
terpyridine (L). A solution of “capped” 1,4,7-triazacyclononane
(0.15 g, 1.07 mmol; prepared as described8) and 4Ј-(p-bromo-
methylphenyl)-2,2Ј:6Ј,2Љ-terpyridine (0.433 g, 0.886 mmol) in
tetrahydrofuran (30 cm3) was stirred at room temperature for 24
h. The resulting white precipitate of the bromide salt was
filtered off and washed with diethyl ether (yield: 480 mg, 0.886
mmol, 83%). δH (250 MHz, solvent D2O) 7.66 (2 H, d), 7.15
(4 H, m), 6.89–6.71 (8 H, m), 5.45 (1 H, s), 4.16 (2 H, s), 3.50
(4 H, m), 3.18 (2 H, m), 2.97 (4 H, m) and 1.64 (2 H, m). A
solution of the bromide salt (0.47 g, 8.68 mmol) in water
Crystal structure analysis of [Cu(HL)(H2O)2][PF6]3
Crystals of [Cu(HL)(H2O)2][PF6]3ؒ4H2O suitable for single
crystal X-ray diffraction studies were obtained as turquoise
rectangular plates by slow recrystallization from ethanol–water
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(1:1). Data were collected using a Delft Instruments FAST TV
area-detector diffractometer. No absorption correction was
applied. The structure was solved by direct methods and refined
by full-matrix least-squares on F2 for all data using SHELXL
97.10 A difference electron density plot failed to locate the H
atoms associated with the water molecules, and hence they were
not included in the final refinement.
Crystal data. C28H43CuF18N6O6P3, M = 1058.13, triclinic,
a = 8.654(2), b = 11.277(2), c = 21.593 Å, α = 74.93(3), β =
79.94(3), γ = 86.42(3)Њ, U = 2003.2(7) Å3, T = 150(2) K, space
group P1, Z = 2, µ(Mo-Kα) = 0.799 mmϪ1, 9155 reflections
¯
measured, 5832 unique (Rint = 0.097). The final values of R1
[I > 2σ(I)] and wR2 were 0.057 and 0.116 respectively. Selected
bond lengths and angles are given in Table 1.
CCDC reference number 186/1788.
See http://www.rsc.org/suppdata/dt/a9/a907717k/ for crystal-
lographic files in .cif format.
Results and discussion
Ligand synthesis
The ligand, L, was prepared (Scheme 1) by reaction of 4Ј-
(p-bromomethylphenyl)-2,2Ј:6Ј,2Љ-terpyridine with the tricyclic
orthoamide of 1,4,7-triazacyclononane (9N3). This general
approach allows controlled stepwise addition of pendant arms
to the macrocycle. Aqueous hydrolysis affords the formyl
derivative that is then subjected to base hydrolysis to give the
desired ligand. This strategy produces the ligand in fairly good
yield. The ligand is characterized by its 1H, 13C NMR and mass
spectra, and by the analytical data for its metal complexes.
On repeating the synthesis of 4Ј-(p-tolyl)-2,2Ј:6Ј,2Љ-ter-
pyridine (ttpy) described by Collin et al.6 we frequently found
thatduringattemptstoextracttheminorby-product,6Ј-(p-tolyl)-
2,2Ј:4Ј,2Љ-terpyridine, the purple acetonitrile solutions of [Fe-
(ttpy)2][PF6]2 were miscible with toluene, and separation of the
by-product proved unsuccessful. We were able successfully to
isolate the by-product by repeatedly washing the purple [Fe-
(ttpy)2][PF6]2 precipitate with toluene, and then combining the
washings. This modified procedure still yielded reasonable
amounts of 4Ј-(p-tolyl)-2,2Ј:6Ј,2Љ-terpyridine. It is then easily
converted into the reactive bromomethyl derivative.2
Scheme 1 (i) thf, r.t. 24 h; (ii) water, 100 ЊC, 3.5 h; (iii) KOH (20 mol.
equivalents), EtOHؒwater (3:1), 100 ЊC, 48 h.
ible spectrum is very similar to that reported for [Ni(terpy)2]2ϩ
(λmax 785 nm, ε 32.3 dm3 molϪ1 cmϪ1).11 The presence of co-
ordinated water molecules in [Cu(HL)(H2O)2][PF6]3 is confirmed
by a broad O–H band in the infrared spectrum at 3000 cmϪ1
.
Metal complexes of L
Cyclic voltammetry of millimolar solutions of the [Cu(HL)-
(H2O)2][PF6]3 and [Ni(H2L)2][PF6]6ؒH2O complexes in aqueous
solution were run in the scan range Ϫ1.0 to ϩ1.0 V (vs. SCE). A
reversible one electron process (Fig. 1) was observed at Ϫ0.445
V (vs. SCE, ∆Ep = 80 mV) for [Ni(H2L)2][PF6]6 and is attributed
to the NiII–NiI redox couple. Two irreversible waves, a cathodic
and an anodic one electron process, were observed for
[Cu(HL)(H2O)2][PF6]3. The irreversible cathodic process at
Ϫ0.6 V (vs. SCE) is attributed to the one electron reduction of
[Cu(HL)(H2O)2][PF6]3 to the copper() species, and its sub-
sequent rearrangement within the co-ordination sphere. The
solvolysis of the copper() species and its resulting dispropor-
tionation to aqueous copper() and elemental copper was not
observed. The irreversible anodic process at Ϫ0.355 V (vs. SCE)
is related to the cathodic process and may be the oxidation of
the rearranged copper() species to copper() followed by its
rearrangement back to [Cu(HL)(H2O)2][PF6]3.
These are obtained from reactions of the appropriate stoichio-
metric amounts of L and the hydrated metal() nitrate salts
in ethanol, followed by the addition of hexafluorophosphoric
acid to a suspension of the resulting metal() complex nitrate
salts in ethanol and water (1:1). It was the production of seem-
ingly intractable nitrate salts of the metal() complexes that
prompted us to redissolve them in dilute HPF6 and recrystallize
them from that medium. It is not surprising that under these
conditions the resulting complexes, [Cu(HL)(H2O)2][PF6]3 and
[Ni(H2L)2][PF6]6, are isolated with partial protonation of the
1,4,7-triazacyclononane macrocyclic subunit. This procedure
led to the isolation of two copper() complexes from the same
reaction mixture, the crystalline turquoise [Cu(HL)(H2O)2]-
[PF6]3 and an intractable purple powder. Attempts to charac-
terize this latter material by elemental analysis and mass
spectroscopy proved unsuccessful. The UV/VIS spectrum of
each complex is consistent with the given formulations. The
copper() complex shows a broad d–d band at 680 nm (ε = 120
dm3 molϪ1 cmϪ1) in the visible region, and does not allow a
distinction to be made between either five- or six-co-ordination
in solution. The UV/VIS spectrum of the nickel() complex
Crystal structure
To gain further insight into the structure of the copper()
complex, the crystal structure of [Cu(HL)(H2O)2][PF6]3 was
determined (Fig. 2). The cation geometry is approximately
trigonal bipyramidal, where two water molecules and the
central pyridyl nitrogen atom of ligand L occupy the three sites
of the equatorial plane and the two axial sites of the poly-
hedron are occupied by each terminal pyridyl nitrogen atom of
shows a broad d–d band at 800 nm (ε = 37.4 dm3 molϪ1 cmϪ1
and a very broad shoulder of lower intensity around 550 nm.
In the UV region there are two intense bands at 330 (ε =
3.87 × 104) and 291 nm (5.77 × 104 dm3 molϪ1 cmϪ1). The vis-
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J. Chem. Soc., Dalton Trans., 2000, 441–444
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Table 1 Selected bond lengths (Å) and angles (Њ) for [Cu(HL)-
(H2O)2]3ϩ ion
Cu1–N1
Cu1–N2
Cu1–N3
2.062(7)
1.914(6)
1.989(7)
Cu1–O1
Cu1–O2
2.201(6)
1.999(5)
N2–Cu1–N1
79.7(3)
79.4(3)
158.9(3)
119.8(2)
152.7(2)
O2–Cu1–O1
O2–Cu1–N3
O2–Cu1–N1
N3–Cu1–O1
N1–Cu1–O1
87.3(2)
95.4(3)
101.7(3)
96.4(2)
96.6(2)
N2–Cu1–N3
N3–Cu1–N1
N2–Cu1–O1
N2–Cu1–O2
Fig. 1 Cyclic voltammogram of [Ni(H2L)2][PF6]6·H2O in water at a
platinum working electrode (0.1 mol dmϪ3 NaClO4 supporting electro-
lyte; 20 ЊC) at scan rate 50 mV sϪ1 vs. SCE.
illustrates that the conformation of the triazacyclononane
subunit of the complex is ideally suited for facial co-ordination
to another transition metal ion. Recent work has exploited the
contrasting co-ordination modes of the ligand L by forming the
heterobinuclear heteroleptic complex [Ru(ttpy){LNi(SCN)3}]-
SCN, where the heteroleptic mer-[Ru(ttpy)2]2ϩ fragment is
covalently linked by the CH2 spacer to the fac-tris(thio-
cyanato)triazacyclononanenickelate() fragment. One envisages
that the heterotrinuclear homoleptic complex [Ru{LNi-
(SCN)3}2] could also be synthesized, and it is towards this end,
and the production of more extended oligomeric species based
on the successful coupling of two 9N3 fragments of L with
nickel() and other first-row transition metal ions, that our
future work is directed.
Acknowledgements
Fig. 2 Crystal structure of the [Cu(HL)(H2O)2]3ϩ ion showing the
We thank the EPSRC for financial assistance, and for provision
of X-ray and mass spectrometry services at Cardiff and
Swansea respectively. Dr R. Gallagher and Mr P. A. Moore
are thanked for their assistance with LSIMS and elemental
analyses, respectively.
atomic numbering.
L. The N–Cu–N angles are lower than those required for an
idealized trigonal bipyramid by about 10Њ, presumably as a con-
sequence of the restricted ligand bite. The equatorial Cu–N2
bond distance of 1.914(6) Å is significantly shorter than the the
two axial Cu–N distances (mean 2.026(3) Å). As is usual in
complexes formed with terpy the ligand remains planar, and
the bond lengths and angles the terpy makes with the CuII are
similar to those found in other mono(terpyridyl)copper()
complexes.12–14 The plane of the Cu1, O1 and O2 atoms is at
88.6(2)Њ to the best fit plane through Cu1 and the terpy subunit.
There is also very little deviation of the Cu–O bond lengths
from those found in related compounds.12–14 However, in con-
trast to other mono(terpyridyl)copper() complexes, the cation
[Cu(HL)(H2O)2]3ϩ adopts a trigonal bipyramidal rather than a
square pyramidal geometry. A distortion in the direction of a
trigonal bipyramidal geometry for fivefold co-ordination is
expected for weaker ligands such as H2O. Indeed, the geometry
of complexes of the type [Cu(terpy)X2], where XϪ is IϪ, BrϪ or
NCSϪ, lies between trigonal bipyramidal and square pyramidal
in what is known as “reverse” geometry.15,16 In the present case,
distortions from a regular trigonal bipyramidal geometry are
evident from the N1–Cu–N3, O2–Cu–N2, and O1–Cu–O2
bond angles of 158.9(3), 152.7(2), and 87.3(2)Њ respectively.
The phenyl ring is not coplanar with the terpyridyl fragment,
but is twisted about the interannular bond such that its plane
makes an angle of 24.2(3)Њ with the plane of the central pyridyl
ring. This twist simultaneously maximizes both van der Waals
H ؒ ؒ ؒ H repulsion and π overlap, and minimizes π conjugation
and non-bonded H ؒ ؒ ؒ H contacts between the ortho protons of
the phenyl ring and those of the central pyridyl ring.
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The triazacyclononane subunit of the complex adopts a con-
formation where all the electron lone pairs of the ring nitrogen
atoms are pointing in the same direction (endodentate). The
torsion angles of N4–C23–C24–N5, N5–C25–C26–N6, and
N6–C27–C28–N4 ethyl linkages are Ϫ49(1), Ϫ62(1), and
Ϫ43(1)Њ respectively, and are indicative of gauche conform-
ation. The solid state structure of [Cu(HL)(H2O)2][PF6]3
Paper a907717k
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J. Chem. Soc., Dalton Trans., 2000, 441–444