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DALTON
Lanthanoid complexes of a tripodal acetal ligand: synthesis,
structural characterisation and reactivity with 3d metals

Stephen J. Archibald, Alexander J. Blake,*,† Simon Parsons, Martin Schröder *,†

and Richard E. P. Winpenny *
Department of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ,
UK

A novel tripodal ligand (H3L1) has been prepared by condensation of tris(2-aminoethyl)amine with 2,6-
diformyl-4-methylphenol in MeOH. The compound has three equivalent side-arms, each containing four possible
donor groups, an imine N atom, a phenol O atom and two O-donors from an acetal group. The crystal structure
showed the arms to be arranged such that a non-crystallographic three-fold axis passes through the bridgehead N
Published on 01 January 1997 on http://pubs.rsc.org | doi:10.1039/A605154E

atom. Reaction of H3L1 with lanthanoid perchlorate salts resulted in the isolation of two series of complexes. With
early lanthanoids compounds of stoichiometry [Ln(H3L1)(H2O)][ClO4]3 were obtained and the compounds with
Ln = La and Pr have been structurally characterised. The lanthanoid site in these complexes is ten co-ordinate,
with a geometry which can be related to an icosahedron. For later lanthanoids, complexes of stoichiometry
[Ln(H3L1)][ClO4]3 are found in which the lanthanoid site is nine-co-cordinate, with a tricapped trigonal-
prismatic geometry. The complex with Ln = Y has been characterised by diffraction techniques. Mass
spectroscopic studies indicated that the acetal functions within H3L1 are stabilised by co-ordination to the
lanthanoid metals. Reaction of the complex [La(H3L1)(H2O)][ClO4]3 with nickel() perchlorate led to a novel
heterobimetallic complex in which both La and Ni are encapsulated within the tripodal ligand.

Compartmental ligands derived from Schiff-base condensation cedure.15 Tris(2-aminoethyl)amine (tren), lanthanoid salts and
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of 2,6-diformyl- and 2,6-diacetyl-4-methylphenol have received solvents were used as obtained. CAUTION: perchlorate salts are
much attention.1 These types of compound provide a frame- potentially explosive and should be handled with great care and
work from which polymetallic, and especially binuclear, metal in small quantities.
complexes can be generated with considerable control of the Proton NMR spectra in CDCl3 (for H3L1) or CD3NO2 (for
topology and composition of the resulting complex.1,2 In par- metal complexes) were recorded on a Bruker AM-360 MHz
ticular where heterobimetallic compounds are the desired spectrometer referenced to SiMe4, mass spectra by fast-atom
product, design of a suitable polydentate ligand is a more bombardment (FAB) of samples in a 3-nitrobenzyl alcohol
elegant approach than use of simpler, less specific chelates. For matrix on a Kratos MS50 spectrometer, and infrared spectra on
example, Okawa and co-workers 3 have shown how ring expan- a Perkin-Elmer Paragon 1000 FT-IR spectrometer as Nujol
sion of one compartment of a Schiff-base macrocycle can allow mulls. Analytical data were obtained on a Perkin-Elmer 2400
complexation of both 3d and 6p elements by the same ligand. Elemental Analyser by the University of Edinburgh Microana-
Recent work by Costes et al.4 has shown that binuclear 3d/4f lytical Service.
complexes can be made utilising such a route, whereas previous
synthetic methods have always led to larger oligomers when H3L1. 2,6-Diformyl-4-methylphenol (1.0 g, 6 mmol) was dis-
such metals have been mixed.5–9 solved in MeOH (40 cm3) and tren (2 mmol) dissolved in
A second approach to the preparation of mixed-metal com- MeOH (10 cm3) was added dropwise with stirring. The result-
plexes is via the use of tripodal ligands where metals can be ing yellow solution was stirred at 40 8C for 30 min then concen-
encapsulated by the three arms of a suitably designed ligand. In trated to 20 cm3 under reduced pressure. Dimethyl sulfoxide (3
particular, Orvig and co-workers 10 have demonstrated that such cm3) was added with stirring and left to evaporate at room
ligands provide suitable hosts for lanthanoid metals, and the temperature. After 24 h brown-yellow crystals had formed
resulting complexes may be of use as contrast agents for mag- which were filtered off and washed with Et2O. Further crystals
netic resonance imaging (MRI). Related macrocyclic species could be obtained by addition of MeOH and Me2SO to the
have potential use in RNA and DNA cleavage,11 and because of filtrate and continued evaporation at room temperature. Yield:
their photophysical properties.12 McCleverty and co-workers 13 74% (Found: C, 65.5; H, 7.6; N, 7.7. Calc. for C39H54N4O9: C,
have also reported an interesting podand with chelating side- 64.8; H, 7.5; N, 7.8%). IR (Nujol mull), cm21: 1636s, 1601s,
arms which appears ideal for co-ordinating to 4f elements. 1273m, 1252m, 1104s, 1074s, 986m, 936m and 657w. 1H NMR:
We report herein the synthesis and structures of a free tri- δ 2.08 (s, 9 H), 2.81 (t, 9 H), 3.37 (s, 18 H), 3.47 (t, 6 H), 5.69 (s,
podal compartmental ligand and of its complexes with lan- 3 H), 5.89 (d, 3 H), 7.35 (d, 3 H), 7.76 (s, 3 H) and 14.2 (s, 3 H).
thanum, praseodymium and yttrium.14 Additionally we demon- FAB mass spectrum (significant peaks, possible assignments):
strate that its lanthanoid complexes can be deprotonated and a m/z 691, [H3L1 2 OMe]+; 659, [H3L1 2 2OMe]+; and 627,
second metal incorporated within the tripodal host. [H3L1 2 3OMe]+.

Experimental [La(H3L1)(H2O)][ClO4]3 1. The compound H3L1 (0.14 g, 0.19

mmol) was dissolved in methanol (30 cm3) at 40 8C and the
Preparation of compounds solution filtered. Hydrated lanthanum perchlorate (0.11 g, 0.2
2,6-Diformyl-4-methylphenol was prepared by a literature pro- mmol) dissolved in MeOH (10 cm3) was added dropwise; there
was no immediate colour change but on stirring for 5 min a
Present address: Department of Chemistry, The University of yellow precipitate was observed. The temperature was main-
Nottingham, University Park, Nottingham, UK NG7 2RD. tained and the solution stirred for 1 h. The yellow precipitate

J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 173

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was then filtered off and dried in vacuo. Yield: 84% (Found; C, polarisation effects. Semiempirical absorption corrections based
39.3; H, 5.2; N, 4.5. Calc. for C39H56Cl3LaN4O22?CH3OH: C, on azimuthal measurements 18 were applied for all compounds.
39.1; H, 5.1; N, 4.6%). FAB mass spectrum: m/z 879,
[La(H3L1)(H2O)]+, 849, [La(H3L1)(H2O) 2 OMe]+ and 719, Structure analysis and refinement. Structure H3L1 was solved
[H3L1]+. A single crystal suitable for X-ray analysis was by Patterson search techniques: a phenol fragment was located
obtained by diffusion of diethyl ether vapour into a nitrometh- using the ORIENT and TRACOR routines of the DIRDIF
ane solution of complex 1 at 258 K. suite.19 All other structures were solved by direct methods using
SHELXS 86 20 and completed by iterative cycles of ∆F syn-
[Pr(H3L1)(H2O)][ClO4]3 2. This complex was synthesized in theses and full-matrix least-squares refinement. For H3L1 all
an identical manner to that described for 1 but with non-H atoms were refined anisotropically with a similarity re-
Pr(ClO4)3?xH2O in place of lanthanum perchlorate. Yield: 80% straint applied to the three side-arms. In 1–4 the perchlorate
(Found: C, 39.3; H, 5.4; N, 4.5. Calc. for C39H56Cl3N4O22Pr? anions and solvate molecules displayed considerable disorder
CH3OH: C, 39.0; H, 5.0; N, 4.6%). FAB mass spectrum: m/z which was modelled with partial site occupancies of several
881, [Pr(H3L1)(H2O)]+; 851, [Pr(H3L1)(H2O) 2 OMe]+; and 719, sites for oxygen atoms, and two orientations for the solvate
[H3L1]+. A single crystal suitable for X-ray analysis was molecules in 1 and 2. For 1–3 all non-H atoms within cations
obtained by diffusion of diethyl ether vapour into a nitrometh- and the Cl atoms of the anions were refined anisotropically. For
ane solution of 2 at 258 K. 4 only metal atoms were refined anisotropically. For all struc-
tures H atoms were included in idealised positions, allowed to
[Y(H3L1)][ClO4]3 3. This complex was synthesized in an iden- ride on their parent C atoms (C–H 1.08 Å), and assigned iso-
tropic thermal parameters [U(H) = 1.2Ueq(C) for aromatic H
Published on 01 January 1997 on http://pubs.rsc.org | doi:10.1039/A605154E

tical manner to that described for 1, but with Y(ClO4)3?xH2O in

place of lanthanum perchlorate. Yield: 79% (Found: C, 40.1; H, atoms; U(H) = 1.5 Ueq(C) for methyl H atoms]. Structures H3L1
5.6; N, 4.9. Calc. for C39H54Cl3N4O21Y?CH3OH: C, 40.8; H, 5.3; and 1–4 were refined against F2 using SHELXL 93.21
N, 4.8%). FAB mass spectrum: m/z 810, [Y(H3L1)]+. A single
crystal suitable for X-ray analysis was obtained by diffusion of The crystal structure of complex 6 was refined by full-matrix
diethyl ether vapour into an acetonitrile solution of 3 at 258 K. least squares against F using CRYSTALS.22 The long c axis and
broad profiles of the diffraction peaks led to substantial peak
[LaNiL1(H2O)][ClO4]2 4. Compound H3L1 (255 mg, 0.2 overlap, while refinement was complicated by disorder in two of
mmol) was dissolved in MeCN (20 cm3) and hydrated nickel the three anion sites. One of these was modelled as a single
perchlorate (80 mg, 0.2 mmol) in MeCN (10 cm3) was added perchlorate anion disordered over two orientations, while the
dropwise causing a change to light green. Ethyldiisopro- other was modelled as being occupied by 0.83 ClO42, dis-
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pylamine (0.12 cm3) was added with rapid stirring which was ordered over two orientations, and 0.17 chloride, again dis-
continued for 30 min. The solution was then concentrated to 5– ordered over two positions; the sum of the occupancies was
10 cm3. Slow addition of Et2O gave a green solid which was restricted to unity. The perchlorate anions were treated initially
filtered off. Yield: 6% (Found: C, 40.1; H, 4.6; N, 4.8. Calc. for as rigid groups and subsequently with similarity restraints on all
C39H53Cl2LaN4NiO18: C, 40.8; H, 4.7; N, 4.9%). FAB mass Cl]O distances and O]Cl]O angles. Deviations in the angles in
spectrum: m/z 1033, [LaNiL1(H2O)(ClO4)]+; and 1015, [LaNi- the minor components from 1098 attests to the presence of fur-
L1(ClO4)]+. A single crystal suitable for X-ray analysis was ther unresolved disorder. The geometries of the three equiv-
produced by diffusion of Et2O vapour into an MeOH solution alent side-arms of H3L2 were also restrained to be similar, and
of complex 4 over a period of 3 d. full-weight H atoms were placed in calculated positions and
iteratively reidealised during refinement. Only the Gd and
[Gd(H3L2)(H2O)2][ClO4]2.83Cl0.17 6. The complex [Gd(H3L1)- ordered ClO42 atoms were refined with anisotropic displace-
(H2O)][ClO4]3 5 was synthesized in an identical manner to that ment parameters. Restrained anisotropic refinement of the
described for 1, but with Gd(ClO4)3?xH2O in place of lan- ligand atoms, while possible, did not lead to any significant
thanum perchlorate. It (150 mg, 0.12 mmol) was dissolved in improvement, and so these atoms, together with atoms in the
MeCN (50 cm3), then hydrated copper() perchlorate (44 mg, disordered anions and solvent molecules, were refined iso-
0.12 mmol) in MeCN (10 cm3) was added dropwise to give a tropically. The Uiso for the disordered O atoms in the anions was
light green solution. Ethyldiisopropylamine (3.2 cm3 of a restrained to a common value. The two molecules of MeCN
0.1148 mol dm23 solution in MeCN, 0.36 mmol) was added were made subject to explicit geometric restraints. The model-
immediately and the solution stirred for 1 h at room temper- ling of the electron density in the region of the mixed ClO42/Cl2
ature before being filtered and concentrated to half its original site led to difficulties in full-matrix refinement, which diverged
volume. Addition of diethyl ether produced a yellow-green pre- with symptoms associated with ill conditioning of the normal
cipitate in low yield which was filtered off. Yield: ca. 5% matrix. This was alleviated by the use of a combination of
(Found: C, 35.1; H, 4.0; N, 5.4. Calc. for C33H40Cl3GdN4O19.32: C, eigenvalue filtering and the application of shift-limiting
37.2; H, 3.8; N, 5.3%). FAB mass spectrum: m/z 783, restraints on the positional, thermal and occupancy factors of
[Gd(H3L2)(H2O)2]+; and 763, [Gd(H3L2)(H2O)]+. A single crys- the part-occupancy Cl sites.
tal suitable for X-ray analysis was produced by diffusion of Atomic coordinates, thermal parameters and bond lengths
Et2O vapour into an MeCN solution of complex 6 over a period and angles have been deposited at the Cambridge Crystallo-
of 3 weeks. graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
Crystallography CCDC for this material should quote the full literature cit-
ation and the reference number 186/302.
Crystal data and data collection and refinement parameters for
compounds H3L1, 1–4 and 6 are given in Table 1; selected bond
Results and Discussion
lengths in Tables 2 and 3.
Synthesis and characterisation of H3L1
Data collection and processing. Data were collected on a Stoë The compound H3L1 results from a reaction sequence which we
Stadi-4 four-circle diffractometer equipped with an Oxford had envisaged would produce the cryptand H3L3. Reaction of
Cryosystems low-temperature device,16 using graphite- tren with 2,6-diformyl-4-methylphenol in MeOH leads to the
monochromated Mo-Kα radiation (λ 0.710 73 Å) ω–2θ scans expected Schiff-base condensation reaction of one formyl
and on-line profile fitting.17 Data were corrected for Lorentz group with tren, but formation of a dimethyl acetal at the

174 J. Chem. Soc., Dalton Trans., 1997, Pages 173–179

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Fig. 1 Structure of H3L1 in the crystal showing the numbering scheme

Fig. 2 Structure of complex 1 in the crystal showing the numbering

scheme. The latter is common to 2
Published on 01 January 1997 on http://pubs.rsc.org | doi:10.1039/A605154E
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second group. It is worth noting that H3L1 is produced in very

good yield, and that variation of the ratios of the reactants does
not produce the cyclised H3L3 in this solvent, merely producing Fig. 3 The lanthanum co-ordination geometry in complex 1
poorer yields of H3L1 and unreacted tren. The cryptand H3L3
has been made by Gagné and co-workers 23 by a two-step con-
Synthesis and characterisation of lanthanoid complexes of H3L1
densation of tren with 2,6-diformyl-4-methylphenol, and this
synthetic strategy has been used by Nelson and co-workers 24 to Reaction of a hydrated rare-earth-metal perchlorate salt with
produce related cryptands. The intermediate tripodal pro- H3L1 in MeOH produces a yellow precipitate which analyses as
ligand isolated contained aldehyde functions, not acetals as in [Ln(H3L1)(H2O)][ClO4]3 for the larger, early lanthanoids, and as
H3L1. [Ln(H3L1)][ClO4]3 for the later lanthanoids. As representative
Spectroscopic characterisation of H3L1 does not decisively examples of the early lanthanoids we have crystallised com-
indicate its nature. The FAB mass spectrum does not show the plexes where Ln = La and Pr (1 and 2 respectively), and for the
molecular ion, only peaks at m/z 691, 659 and 627 due to loss latter lanthanoids we have crystallised the yttrium complex 3.
of one, two and three methoxy groups respectively. Infrared Yttrium, although a 4d rather than a 4f element, forms com-
spectroscopy confirms the disappearance of the carbonyl pounds which are normally isostructural with those of the
groups of the reactants, while NMR spectroscopy confirms a heavier rare earths.
strong resonance due to the OMe groups of the acetal. Defini- Spectroscopic characterisation is again useful but not con-
tive proof of structure came from a crystallographic clusive. The NMR spectra of 1 and 3 differ little from that of
determination. free H3L1, with a small shift to higher frequency observed for all
The compound crystallises with a non-crystallographic resonances. Assignment of the various methyl resonances is
three-fold axis running through the bridgehead N atom (Fig. complicated due to residual nitromethane in all samples. One
1). This N atom is pyramidal and the lone pair is pointing intriguing change is that the resonance at δ 8.53, assigned to the
towards the cavity formed by the arms of the compound. The CH proton of the imine function, appears as a doublet rather
orientation of the phenol rings within the three side-arms is than as a singlet in the spectrum of H3L1 (δ 7.76). Irradiation of
such that the planes of these rings are at approximately 1208 to the resonance at δ 12.9 causes this splitting to collapse, indicat-
each other and the potential donor groups within the arms, one ing that the CH proton of the imine group is coupled to the
N- and three O-donors in each, are pointing away from the proton involved in the hydrogen bond between the imine N and
central cavity. Although the H atoms were not located, all the phenol O atom of each side-arm. As this coupling is
hydrogen bonding appears to be confined within each side- resolved for 1 and 3, but not for H3L1, it seems likely that this H
arm, with strong interactions likely between the imine N and atom is more firmly located on the N atom in the complex,
the phenol O atom (average N ? ? ? O 2.547 ± 0.020 Å): no sig- consistent with co-ordination of the phenol O atom to a metal
nificant interactions were found between molecules. Crystal- centre. For 2 all resonances are broadened and shifted due to
lisation of H3L1 could only be achieved by addition of Me2SO the paramagnetism of the Pr.
to a MeOH solution yet no molecules of either solvent are The FAB mass spectra of all three complexes show a peak for
found in the crystal lattice. the molecular ion, and fragment peaks for loss of one MeO

J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 175

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Fig. 4 Structure of complex 3 in the crystal showing the numbering

scheme

Fig. 6 Structure of complex 4 in the crystal showing the numbering

scheme
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Fig. 5 The yttrium co-ordination geometry in complex 3

group. By comparison with the spectrum of free H3L1, where

the only peaks observed were for products where methoxy
groups had been lost, these results suggest that co-ordination of
the acetal side-arms to the metal has occurred thus stabilising
the acetal functions. Fig. 7 The co-ordination geometries of La and Ni in complex 4
Single-crystal X-ray diffraction studies show that compounds
1 and 2 are isostructural. In each the 4f metal is ten-co-
is comparatively regular. For example, the upper and lower tri-
ordinate, bound exclusively to oxygen donors. These are derived
angular faces of the prism are essentially equilateral (angle
from all three side-arms, with two acetal and one phenolic oxy-
range 59.0–61.78), and the angles at the corners of the square
gen attached from each leg of the tripod, and the final oxygen
faces are almost right angles (range 83.8–95.58). It is interesting
donated by a water molecule (Fig. 2). There is a non-
that the change in co-ordination number from ten in 1 and 2 to
crystallographic three-fold axis running through the metal site,
nine in 3 is achieved with retention of the three-fold axis
the bridgehead N atom and the bound water molecule.
through the metal centre.
The Ln]O bond lengths depend on the type of oxygen atom,
No significant intermolecular hydrogen-bonding interactions
with bonds to phenol oxygens (for H3L1, average 2.47 Å) signifi-
are found in any of these structures, although strong intra-
cantly shorter than bonds to acetal oxygens (for H3L1, average
molecular hydrogen-bonds between the imine N atom and the
2.65 Å) or to the water (for H3L1, 2.63 Å). There is also a
phenolic O atom in each side-arm are present. The second cav-
predictable general shortening of these bonds moving from La
ity of the compartmental ligand is therefore occupied by three
to Pr due to the lanthanoid contraction. The co-ordination
protons in each of these complexes.
geometry around the Ln can be related to an icosahedron (Fig.
Co-ordination of metal ions to chelate acetal ligands is rela-
3) where the three phenolic oxygens [O(1), O(4) and O(7)] form
tively rare. Binding of Rb I 25 and AgI 26 to chelate acetal-
a triangular face, the six acetal oxygens [O(2), O(3), O(5), O(6),
containing antibiotics has been reported, while other non-
O(8) and O(9)] form a puckered six-membered ring above this
chelate examples include binding of hard metal ions, usually
face and the final oxygen atom [O(10)] is at the centre of what
main-group ions, to cyclic 27 and non-cyclic 28 acetals. However,
would be the final triangular face. The geometry therefore cor-
no previous structural reports of lanthanide metal ions to
responds closely to a trirhombohedron.
acetals have been reported.
For complex 3 the co-ordination number of the metal has
fallen to nine, with loss of the water molecule found in 1 and 2
Reactions of lanthanoid complexes of H3L1
(Fig. 4). Again the molecule has a non-crystallographic C3 axis
running through the metal and the bridgehead nitrogen. The Given the structures of complexes 1–3 we argued that deproto-
Y]O distances show the same dependence on the character nation of [H3L1] to [L1]32 would facilitate insertion of a second
of the O atom, with shorter bonds to the O-donors from the metal into the vacant octahedral cavity formed by the three
phenol groups. The co-ordination geometry about the yttrium imine N- and the three phenolic O-donors. This methodology
centre is now based on a tricapped trigonal prism (Fig. 5), and proves moderately successful for a range of lanthanoids when

176 J. Chem. Soc., Dalton Trans., 1997, Pages 173–179

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Published on 01 January 1997 on http://pubs.rsc.org | doi:10.1039/A605154E

Table 1 Experimental data for the X-ray diffraction studies of compounds H3L1, 1–4 and 6

H3L1 1 2 3 4 6
Formula C39H54N4O9 C39H56Cl3LaN4O22?3CH3NO2 C39H56Cl3N4O22Pr?3CH3NO2 C39H54Cl3N4O21Y?3CH3CN C39H53Cl2LaN4NiO18?CH3OH C33H39GdN4O8?2.83ClO4?0.17 Cl?2CH3CN
M 722.8 1361.3 1363.3 1233.3 1157.3 1152.3
Crystal system Monoclinic Monoclinic Monoclinic Monoclinic Trigonal Monoclinic
Space group P21/n P21/n P21/n P21/c R3 P21/c
a/Å 16.088(9) 13.013(3) 12.998(2) 17.381(13) 34.204(13) 10.845(10)
b/Å 13.353(10) 25.275(17) 25.265(8) 17.070(12) a 11.641(11)
c/Å 18.798(23) 17.869(8) 17.771(3) 19.385(14) 24.59(3) 40.77(2)
β/8 93.92(5) 92.27(5) 92.282(12) 94.74 93.21(7)
U/Å3 4029 5873 5831 5864 24914 5139
T/K 293 150.0(2) 150.0(2) 220.0(2) 150.0(3) 150.0(2)
Z 4 4 4 4 18 4
Dc/ g cm23 1.192 1.510 1.553 1.397 1.388 1.490
Crystal size/mm 0.1 × 0.1 × 0.1 0.2 × 0.2 × 0.2 0.70 × 0.43 × 0.27 0.4 × 0.4 × 0.1 0.55 × 0.15 × 0.08 0.61 × 0.33 × 0.15
µ/mm21 0.085 0.937 1.064 1.208 1.265 1.533
Unique data 6113 7604 10 080 7628 4960 4883
Observed data 1810 5583 8917 4411 2032 2675
Parameters 477 719 760 632 300 576
Maximum ∆/σ 21.99 0.118 20.75 20.27 0.047 0.087
ratio —
R1, wR2a 0.0938, 0.3862 0.0500, 0.1439 0.0372, 0.1609 0.0553, 0.1830 0.1236, 0.5184 —
R, R9 b — — — — — 0.1088, 0.1175
Weighting σ2(Fo2) + σ2(Fo2) + (0.0515P)2 + σ2(Fo2) + (0.0418P) + σ2(Fo2) + (0.0835P)2 + σ2(Fo2) + (0.013P)2 Chebychev three-term
scheme,c w21 (0.1776P)2 40.70P 22.17P 20.71P polynomial
Goodness of fit 1.068 1.034 1.040 0.987 1.201 1.100
Largest 0.54, 20.33 1.07, 20.76 0.75, 20.56 0.72, 20.54 2.00, 21.56 +1.94, 21.50
residuals/e Å23
Common feature: all compounds crystallise as yellow tablets.
a
SHELXL93:21 R1 based on observed data, wR2 on all unique data. b CRYSTALS:22 R and R9 based on observed data. c P = ¹[max(Fo2, 0) + 2Rc].
³̄

J. Chem. Soc., Dalton Trans., 1997, Pages 173–179

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Table 2 Selected bond lengths (Å) for compounds 1–3 and 6

1 2 3 6
Ln = La Pr Y Gd
Ln]O(1) 2.543(5) 2.396(3) 2.240(5) 2.31(1)
Ln]O(2) 2.650(5) 2.567(3) 2.432(5) 2.42(1)
Ln]O(3) 2.663(5) 2.613(3) 2.526(5) 2.31(1)
Ln]O(4) 2.462(5) 2.409(3) 2.230(5) 2.41(1)
Ln]O(5) 2.697(5) 2.658(3) 2.542(5) 2.32(1)
Ln]O(6) 2.631(5) 2.560(3) 2.400(5) 2.37(1)
Ln]O(7) 2.490(5) 2.438(3) 2.243(5) 2.40(2)
Ln]O(8) 2.587(5) 2.531(3) 2.526(5) 2.44(2)
Ln]O(9) 2.674(5) 2.654(3) 2.412(5)
Ln]O(10) 2.626(5) 2.588(3)

Fig. 8 Structure of complex 6 in the crystal showing the numbering Table 3 Selected bond lengths (Å) and angles (8) for compound 4
scheme
Ln]O(1) 2.44(2) Ln]O(9) 2.62(2)
Ln]O(2) 2.72(3) Ln]O(10) 2.60(3)
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Ln]O(3) 2.57(2) Ni]O(1) 2.07(2)

Ln]O(4) 2.45(2) Ni]O(4) 2.07(2)
Ln]O(5) 2.58(2) Ni]O(7) 2.05(2)
Ln]O(6) 2.67(2) Ni]N(2) 2.07(3)
Ln]O(7) 2.43(2) Ni]N(3) 2.08(3)
Ln]O(8) 2.64(2) Ni]N(4) 2.09(3)

O(7)]Ni]N(2) 161.5(10) O(1)]Ni]N(3) 160.9(10)

O(7)]Ni]O(1) 77.4(8) O(4)]Ni]N(3) 84.3(11)
N(2)]Ni]O(1) 84.5(9) O(7)]Ni]N(4) 84.3(10)
O(7)]Ni]O(4) 78.1(9) N(2)]Ni]N(4) 96.3(10)
N(2)]Ni]O(4) 101.9(10) O(1)]Ni]N(4) 103.4(10)
O(1)]Ni]O(4) 77.1(9) O(4)]Ni]N(4) 161.8(10)
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O(7)]Ni]N(3) 103.1(10) N(2)]Ni]N(4) 95.6(11)

N(2)]Ni]N(3) 95.3(11)

confirmed the formation of binuclear [LnNiL1][ClO4] com-

plexes, e.g. for 4 at m/z 1015. Elemental analytical data were less
Fig. 9 The co-ordination geometry of Gd in complex 6. The full lines reassuring, and in most cases indicated the presence of some
show the O ? ? ? O contacts within the mutually perpendicular trapezia of impurity beyond additional solvate molecules. This is reflected
the dodecahedral oxygen array in low values for C, H and N. This suggests that encapsulation
of two metals by H3L1 is difficult, presumably due to the tri-
treated with nickel() salts, but markedly less successful with gonal strain imposed at the 3d-metal site.
copper() salts. The problems associated with addition of nickel to lan-
Addition of 3 molar equivalents of dipropylamine to a 1 : 1 thanoid complexes of H3L1 become much more serious when
molar solution of complex 1 and Ni(ClO4)2?6H2O in MeCN copper() salts are utilised. The second trigonally compressed
gives a green solution from which a green precipitate of a mixed octahedral cavity is clearly incompatible with the require-
La–Ni complex can be precipitated by addition of diethyl ether. ments of the d9 metal ion. All reactions produced compounds
Structural analysis reveals the binuclear complex [LaNiL1- which do not contain both metals, and there is no indication
(H2O)][ClO4]2 4 (Fig. 6). As expected the ligand [L1]32 uses all from mass spectrometry that heterobimetallic complexes are
twelve potential donor atoms to encapsulate a six-co-ordinate formed. For example, reaction of [Gd(H3L1)(H2O)][ClO4]3 5
NiII and a ten-co-ordinate LaIII. The trigonal axis, present in all with Cu(ClO4)2 appears promising, but crystallisation gives
the other structures involving H3L1, is also present in 4. crystals of a mononuclear gadolinium complex 6. These crys-
The NiII is six-co-ordinate, bound to the three imine N- tals diffracted poorly, however the structure demonstrates
donors and three phenolic O-donors (Fig. 7). Significantly, the that incorporation of a second metal has failed and that the
bond angles between the N atoms are markedly different from ligand has been modified, with the acetal groups hydrolysed
those of an ideal octahedron and all trans-N]Ni]O angles are (Fig. 8), which reduces the number of available oxygen-donor
reduced to ca. 1618 by a trigonal compression imposed by the atoms to six; three phenolic oxygens and three O-donors
ligand. The strain within this cavity is perhaps most powerfully from aldehydes. Therefore in order to reach a satisfactory co-
illustrated by considering the angles at the bridgehead sp3-N ordination number at gadolinium two water molecules are
atom [N(1)], which are close to 1208. also present.
The three phenolic O atoms are shared with the LaIII, which The Gd]O distances show a similar variation to that found
has a co-ordination geometry very similar to that in complex 1. for complexes 1–3; bonds to phenolic O atoms are shorter (ca.
Therefore a face is shared by the 3d and 4f metals leading to a 2.32 Å) than those to other O-donors (2.37–2.44 Å). The geom-
Ni ? ? ? La contact of 3.355(5) Å. It is interesting that the geom- etry of the eight-co-ordinated Gd can be related to a dodeca-
etry at La is closely maintained between 1 and 4, with La]O hedron (Fig. 9), with the two intersecting mutually perpendicu-
bond lengths statistically unchanged (Fig. 7). It is the d-block lar trapezia required by this geometry described by O(1), O(8),
metal ion which has a considerable distortion imposed on its O(4), O(6) and O(7), O(2), O(5) and O(3). It is also noticeable
geometry by the requirements of [L1]32. that the three-fold symmetry evident in the structures featuring
Similar products can be obtained for other 4f metals H3L1 has disappeared, which suggests it is the steric require-
investigated (Ln = GdIII, ErIII or PrIII) when treated with ments of the six OMe groups of the acetal functions which were
Ni(ClO4)2?6H2O. The FAB mass spectra of the products always causing the trigonal arrangement of the ligand.

178 J. Chem. Soc., Dalton Trans., 1997, Pages 173–179

 View Online

Conclusion Angew. Chem., Int. Ed. Engl., 1991, 31, 1139; A. J. Blake, P. E. Y.
Milne and R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1993,
Although the reaction to give H3L1 and related Ln–Ni com- 3727; A. J. Blake, V. A. Cherepanov, A. A. Dunlop, C. M. Grant,
plexes works, the strain at the bridgehead N atom in [L1]32 P. E. Y. Milne, J. M. Rawson and R. E. P. Winpenny, J. Chem. Soc.,
incorporating ethylene linkages leads to some loss of the 3d Dalton Trans., 1994, 2719.
7 M. Andruh, I. Ramade, E. Codjovi, O. Giullou, O. Kahn and
metal from the inner co-ordination site during recrystallisation.
J. C. Trombe, J. Am. Chem. Soc., 1993, 115, 1822.
This is further exacerbated by potential instability of the ligand 8 S. Wang, S. J. Trepanier and M. J. Wagner, Inorg. Chem., 1993, 32,
where both the imine linkage and acetal groups are susceptible 833.
to further reaction. Current work is aimed at synthesizing 9 A. J. Blake, C. Benelli, P. E. Y. Milne, J. M. Rawson and R. E. P.
derivatives of [L1]32, especially with longer chain lengths Winpenny, Chem. Eur. J., 1995, 1, 614.
between the bridgehead N atom and the imine donor atoms, 10 S. Liu, L.-W. Yang, S. J. Rettig and C. Orvig, Inorg. Chem., 1993, 32,
2773.
and with saturated amine chains in place of the imine linkers.
11 K. A. O. Chin, J. R. Morrow, C. H. Lake and M. R. Churchill,
It is envisaged that these larger and/or more flexible ligands will Inorg. Chem., 1994, 33, 656.
lead to more stable binuclear complexes. Such complexes might 12 N. Sabbatini, M. Guardigli and J.-M. Lehn, Coord. Chem. Rev.,
also allow us to examine any correlation 9 between Ln ? ? ? M 1993, 123, 201 and refs. therein.
distance and magnetic exchange interactions. 13 A. J. Amoroso, A. M. Cargill Thompson, J. C. Jeffery, P. L. Jones,
J. A. McCleverty and M. D. Ward, J. Chem. Soc., Chem. Commun.,
1994, 2571.
Acknowledgements 14 S. J. Archibald, A. J. Blake, M. Schröder and R. E. P. Winpenny,
J. Chem. Soc., Chem. Commun., 1994, 1669.
We are grateful to the EPSRC for funding a diffractometer and 15 R. R. Gagné, C. L. Spiro, T. J. Smith, C. A. Hamann, W. R. Thies
Published on 01 January 1997 on http://pubs.rsc.org | doi:10.1039/A605154E

for a postdoctoral fellowship (to S. P.), and to the University of and A. K. Shiemke, J. Am. Chem. Soc., 1981, 103, 4073.
Edinburgh for a studentship (to S. J. A.). 16 J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105.
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J. Chem. Soc., Dalton Trans., 1997, Pages 173–179 179