Building Fe(iii) clusters with derivatised salicylaldoximes

Article abstract of DOI:10.1039/b924143d

The syntheses, structures and magnetic properties of nine new iron complexes containing salicylaldoxime (saoH₂) or derivatised salicylaldoximes (R-saoH₂), [Fe₃O(OMe)(Ph-sao)₂ Cl₂(py)₃]·2MeOH (1·2MeOH), [Fe ₃O(OMe)(Ph-sao)₂Br₂(py)₃] ·Et₂O (2·Et₂O), [Fe₄(Ph-sao) ₄F₄(py)₄]·1.5MeOH (3·1.5MeOH), [Fe₆O₂(OH)₂(Et-sao)₂(Et-saoH) ₂(O₂CPh)₆] (4), [HNEt₃] ₂[Fe₆O₂(OH)₂(Et-sao) ₄(O₂CPh(Me)₂)₆]·2MeCN (5·2MeCN), [Fe₆O₂(O₂CPh) ₁₀(3-^tBut-5-NO₂-sao)₂(H ₂O)₂]·2MeCN (6·2MeCN), [Fe₆O ₂(O₂CCH₂Ph)₁₀(3-^tBut-sao) ₂(H₂O)₂]·5MeCN (7·5MeCN), {[Fe₆Na₃O(OH)₄(Me-sao)₆(OMe) ₃(H₂O)₃(MeOH)₆]·MeOH} _n (8·MeOH) and [HNEt₃]₂[Fe ₁₂Na₄O₂(OH)₈(sao) ₁₂(OMe)₆(MeOH)₁₀] (9) are discussed. The predominant building block appears to be the triangular [Fe₃O(R-sao) ₃]⁺ species which can self-assemble into more elaborate arrays depending on reaction conditions. An interesting observation is that the R-saoH^-/R-sao^2- ligand system tends to adopt coordination modes similar to carboxylates. The most unusual molecule is the [Fe ₄F₄] molecular square, 3. While Cl^- and Br ^- appear to act only as terminal ligands, the F^- ions bridge making a telling impact on molecular structure and topology. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b924143d

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www.rsc.org/dalton | Dalton Transactions
Building Fe(III) clusters with derivatised salicylaldoximes†
Kevin Mason, Ian A. Gass, Simon Parsons, Anna Collins, Fraser J. White, Alexandra M. Z. Slawin,
Euan K. Brechin* and Peter A. Tasker*
Received 17th November 2009, Accepted 6th January 2010
First published as an Advance Article on the web 3rd February 2010
DOI: 10.1039/b924143d
The syntheses, structures and magnetic properties of nine new iron complexes containing
salicylaldoxime (saoH2) or derivatised salicylaldoximes (R-saoH2), [Fe3O(OMe)(Ph-sao)2
Cl2(py)3]·2MeOH (1·2MeOH), [Fe3O(OMe)(Ph-sao)2Br2(py)3]·Et2O (2·Et2O), [Fe4(Ph-sao)4F4(py)4]·
1.5MeOH (3·1.5MeOH), [Fe6O2(OH)2(Et-sao)2(Et-saoH)2(O2CPh)6] (4), [HNEt3]2[Fe6O2(OH)2(Et-
sao)4(O2CPh(Me)2)6]·2MeCN (5·2MeCN), [Fe6O2(O2CPh)10(3-tBut-5-NO2-sao)2(H2O)2]·2MeCN
(6·2MeCN), [Fe6O2(O2CCH2Ph)10(3-tBut-sao)2(H2O)2]·5MeCN (7·5MeCN), {[Fe6Na3O(OH)4(Me-
sao)6(OMe)3(H2O)3(MeOH)6]·MeOH}n (8·MeOH) and [HNEt3]2[Fe12Na4O2(OH)8(sao)12(OMe)6-
(MeOH)10] (9) are discussed. The predominant building block appears to be the triangular
[Fe3O(R-sao)3]+ species which can self-assemble into more elaborate arrays depending on reaction
conditions. An interesting observation is that the R-saoH-/R-sao2- ligand system tends to adopt
coordination modes similar to carboxylates. The most unusual molecule is the [Fe4F4] molecular square,
3. While Cl- and Br- appear to act only as terminal ligands, the F- ions bridge making a telling impact
on molecular structure and topology.
The coordination chemistry of MnIII with such ligands has
been extensively studied for its relevance to the field of single
Salicylaldoxime ligands have been studied extensively for their
molecule magnetism, resulting in many structures with remarkable
Introduction
use in extractive hydrometallurgy.1 They show great selectivity
properties. The coordination chemistry of salicylaldoximates with
FeIII has been less extensively reported - a CCDC search reveals
only nineteen Fen+-salicylaldoximate complexes with nuclearities
ranging from 2-8.15-24 Our interest in Fe-salicylaldoximate com-
plexes is in part due to their role as anti-corrosives in protective
coatings. Phenolic oximes have been used to treat lightly oxidised
Fe surfaces and it is postulated that the corrosion inhibition is due
to the formation of polynuclear complexes on the surface.24 An
extensive knowledge of the coordination of such ligands with Fe
would tell us more about possible modes-of-action of the corrosion
inhibition ability of the ligands. There is also potential for the
complexes to have large spin ground states due to the relatively
large spin of the FeIII ion (s = 5/2) which could have application in
molecular magnetism. The aim of this work therefore is to expand
the current family of Fe-salicylaldoxime structures and investigate
the coordination modes and magnetism of the complexes based
on the ligands shown in Scheme 1.
for Cu(II) in particular and account for a quarter of the world’s
copper production.2,3 This selectivity is due to the size of the cavity
created by two singly deprotonated phenolic oximes hydrogen
bonding to form a pseudomacrocyclic arrangement (Chart 1)
which provides an almost ideal fit for the square planar Cu2+ ion.
Once a phenolic oxime has been doubly deprotonated however,
it has the possibility to bind through the phenolate oxygen, the
oxime nitrogen and the oximato oxygen, giving great potential
for polynuclear complex formation and, as a consequence, a large
number of complexes of metals such as Mn,4-12 Co,4,13,14 Ni,4,13 and
Fe have been reported.4,15-24
Chart 1 The pseudo-macrocyclic structure formed by mono-deproto-
nated phenolic oxime copper extractants.
School of Chemistry, The University of Edinburgh, West Mains Road,
Edinburgh, UK EH9 3JJ. E-mail: ebrechin@staffmail.ed.ac.uk, Peter.
Tasker@ed.ac.uk; Tel: +44 (0) 131-650-7545
† Electronic supplementary information (ESI) available: Additional data.
CCDC reference numbers 755035, 755036, 755037, 755038, 755039,
755040, 755041, 755042 and 755043. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b924143d
Scheme 1 General structure of derivatised salicylaldoximes where for
saoH2, Me-saoH2, Et-saoH2, Ph-saoH2 (R1 = H, Me, Et and Ph
t
respectively and R2 = H); and for tBut-saoH2 (R1 = H and R2 = But).
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Found (calc.%): C84H85Fe6N5O24; C 53.87 (53.56), H 4.72 (4.55),
N 3.96 (3.72). IR data (KBr pellet; cm-1): 1599 s, 1560 s, 1400 s,
1313 m, 1254 m, 1070 m, 1016 m, 935 m, 839 m, 752 m, 717 s,
671 m, 638 m, 586 m, 513 m, 467 s.
Experimental
Syntheses
All manipulations were performed under aerobic conditions using
chemicals as received, unless otherwise stated.
[HNEt3]2[Fe6O2(OH)2(Et-sao)4(O2CC6H3(Me)2)6]·2MeCN (5·
2MeCN). FeCl3·6H2O (270 mg, 1.0 mmol), Et-saoH2 (165 mg,
1.0 mmol) and NaO2CC6H3(Me)2 (sodium 3,5-dimethylbenzoate,
158 mg, 1.0 mmol) were dissolved in MeCN (30 ml) in the presence
Caution
◦
Care should be taken when using the potentially explosive
perchlorate salts. 2-Hydroxyacetophenone oxime (Me-saoH2),
2-hydroxypropiophenone oxime (Et-saoH2) and 2-hydroxy-
benzophenone oxime (Ph-saoH2) were synthesised via the reaction
of the appropriate ketone with hydroxylamine and sodium acetate
in EtOH, as described in the literature.25
of NEt3 (1.0 ml, 8.0 mmol) and heated to 50 C. After 120 mins
stirring the solution was filtered and the solution left to evaporate
slowly at room temperature. X-ray quality crystals formed in
2 weeks. The crystals were collected by filtration and dried in vacuo.
The yield was approximately 30%. The dried sample analysed as
5·MeCN. Found (calc.%): C104H127Fe6N7O24; C 56.49 (56.93), H
5.81 (5.83), N 4.72 (4.47). IR data (KBr pellet; cm-1): 1568 s,
1431 s, 1398 s, 1309 m, 1267 m, 1076 m, 1053 m, 931 m, 841 m,
789 m, 752 s, 648 m, 598 m, 509 m, 465 s.
[Fe3O(OMe)(Ph-sao)2Cl2(py)3]·2MeOH (1·2MeOH)
FeCl3·6H2O (405 mg, 1.50 mmol) and Ph-saoH2 (213 mg,
1.00 mmol) were dissolved in a mixture of MeOH (25 ml) and
pyridine (5 ml). After 120 mins stirring the solution was filtered
and left to evaporate slowly, producing X-ray quality crystals after
3 days in approximately 50% yield. The dried sample analysed as
1·MeOH. Found (calc.%): C43H40Cl2Fe3N5O7; C 52.39 (52.85), H
3.91 (4.13), N 7.45 (7.17). IR data (KBr pellet; cm-1): 1593 s,
1557 m, 1514 m, 1487 s, 1429 s, 1314 s, 1249 m, 1148 m, 1037 s,
959 s, 855 m, 758 s, 699 s, 665 s, 582 m, 462 m.
[Fe6O2(O2CPh)10(3-tBut-5-NO2-sao)2(H2O)2]·4MeCN
(6·4MeCN)
[Fe3O(O2CPh)6(H2O)3]NO3 (500 mg, 0.48 mmol) and tBut-saoH2
(94 mg, 0.48 mmol) were dissolved in MeCN (25 ml). After 120 min
stirring the solution was filtered and left to evaporate slowly
producing X-ray quality crystals after 1 week in approximately
30% yield. The dried sample analysed as 6·MeCN. Found (calc.%):
C92H78Fe6N4O32; C 52.69 (52.95), H 3.74 (3.77), N 2.87 (2.68). IR
data (KBr pellet; cm-1): 1599 s, 1554 s, 1493 s, 1408 s, 1306 s,
1176 m, 1113 m, 1026 m, 843 m, 717 s, 673 m, 615 m, 480 s.
[Fe3O(OMe)(Ph-sao)2Br2(py)3]·Et2O (2·Et2O)
FeBr3 (296mg, 1.00 mmol) and Ph-saoH2 (213 mg, 1.00 mmol)
were dissolved in a mixture of MeOH (25 ml) and pyridine (5 ml).
After 120 mins stirring the solution was filtered and diffused
with Et2O, producing X-ray quality crystals after 2 weeks in
approximately 30% yield. The dried sample analysed as 2. Found
(calc.%): C42H36Br2Fe3N5O6; C 49.15 (48.78), H 3.94 (3.51), N 6.55
(6.77). IR data (KBr pellet; cm-1): 1592 s, 1558 m, 1514 m, 1487 s,
1428 s, 1310 s, 1248 m, 1148 m, 1037 s, 958 s, 854 m, 758 s, 700 s,
665 s, 582 m, 462 m.
[Fe6O2(O2CCH2Ph)10(3-tBut-sao)2(H2O)2]·5MeCN (7·5MeCN)
[Fe3O(O2CCH2Ph)6(H2O)3]NO3 (100 mg, 0.09 mmol) and 3-tBut-
saoH2 (18 mg, 0.09 mmol) were dissolved in MeCN (25 ml). After
180 mins stirring the solution was filtered and left to evaporate
slowly producing X-ray quality crystals after 1 week in approxi-
mately 30% yield. The dried sample analysed as 7·MeCN. Found
(calc.%): C102H100Fe6N2O28; C 56.98 (57.33), H 4.25 (4.72), N 1.68
(1.31). IR data (KBr pellet; cm-1): 1576 s, 1496 m, 1410 s, 1298 m,
1194 m, 999 m, 962 m, 876 m, 752 m, 727 m, 642 m, 575 m, 546 m,
501 m.
[Fe4(Ph-sao)4F4(py)4]·1.5MeOH (3·1.5MeOH)
FeF3·3H2O (167 mg, 1.00 mmol) and Ph-saoH2 (213 mg,
1.00mmol) were dissolved in a mixture of MeOH (25 ml) and
pyridine (5 ml). After 180 mins stirring, the solution was filtered
and left to evaporate slowly, producing X-ray quality crystals after
1 week, in approximately 30% yield. The dried sample analysed
as 3. Found (calc.%): C72H56F4Fe4N8O8; C 58.95 (59.21), H 3.47
(3.86), N 7.45 (7.67). IR data (KBr pellet; cm-1): 1592 s, 1560 m,
1521 m, 1488 m, 1433 s, 1319 s, 1255 m, 1147 m, 1039 s, 957 s,
855 m, 750 s, 696 s, 660 s, 546 m, 460 m.
{[Fe6Na3O(OH)4(Me-sao)6(OMe)3(H2O)3(MeOH)6]·MeOH}n
(8·MeOH)
Method 1. Fe(ClO4)2·6H2O (182.5 mg, 0.5 mmol), Me-saoH2
(151 mg, 1.0 mmol) and NaO2CHCl3 (185 mg, 1.0 mmol) were
dissolved in MeOH (25 ml) in the presence of NEt3 (1.0 ml,
8 mmol). After 180 mins stirring the solution was filtered and
then left to evaporate slowly, producing X-ray quality crystals in
4 days. The crystals were collected by filtration and dried in vacuo.
The yield was approximately 65%. The dried sample analysed as
8. Found (calc.%): C57H84Fe6Na3N6O29; C 39.43 (39.77), H 4.54
(4.92), N 5.18 (4.88). IR data (KBr pellet; cm-1): 1630 m, 1593 m,
1568 m, 1531 m, 1473 m, 1435 s, 1306 s, 1250 m, 1130 m, 1024 s,
962 m, 856 m, 752 s, 665 s, 611 m, 449 m, 415 m.
[Fe6O2(OH)2(Et-sao)2(Et-saoH)2(O2CPh)6] (4)
FeCl3·6H2O (135 mg, 0.5 mmol), Et-saoH2 (82.5 mg, 0.5 mmol),
NaO2CPh (216 mg, 1.5 mmol) were dissolved in MeCN (25 ml)
in the presence of NEt3 (0.25 ml, 0.2 mmol) and heated to
50 ◦C. After 90 mins stirring the solution was filtered and then
layered with Et2O to produce X-ray quality crystals in 2 weeks.
The crystals were collected by filtration and dried in vacuo. The
yield was approximately 55%. The dried sample analysed as 4.
Method 2. Fe(O2CMe)2·6H2O (174 mg, 1.0 mmol), Me-saoH2
(151 mg, 1.0 mmol) and NaOMe (324 mg, 6.0 mmol) were
dissolved in MeOH (25 ml). After 120 mins stirring the solution
was filtered and then left to evaporate slowly, producing X-ray
2728 | Dalton Trans., 2010, 39, 2727–2734
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Table 1 Crystallographic details for complexes 1-9
1·2MeOH
2·Et2O
3·1.5MeOH
4
5·2MeCN
6·4MeCN
7
8
9
M, g mol-1
Crystal system Monoclinic
1009.29
1108.25
Monoclinic
P 21/c
14.6095(5)
18.2293(6)
18.2766(6)
90
1508.71
Monoclinic
P 21/c
26.0878(16) 12.8061(8)
20.7755(12) 13.5584(9)
27.5991(17) 14.0247(9)
90
115.9810(10) 78.955(4)
90 78.812(4)
13446.6(14) 2239.6(3)
1835.66
Triclinic
P-1
2235.32
Monoclinic
P 21/c
14.6892(6)
19.6643(9)
19.2762(9)
90
104.153(2)
90
5399.0(4)
150
2250.90
Triclinic
P-1
2342.26
Monoclinic
P 21/c
13.8956(6)
18.6592(8)
21.4730(9)
90
96.520(2)
90
5531.5(4)
150
1753.41
Hexagonal
P63/m
12.40610(10) 23.1511(7)
12.40610(10) 13.5740(4)
28.8478(6)
90
90
120
3845.16(9)
150
2
1.51
3262.67
Monoclinic
P21/c
Space group
P 21/c
˚
a/A
14.2027(3)
18.0542(4)
18.0473(4)
90
98.0570(10) 98.945(2)
90 90
4581.98(17) 4808.2(3)
150
4
1.463
Black rod
12.272(5)
14.458(4)
16.754(7)
69.97(8)
71.74(8)
69.68(6)
2554.5(16)
173(2)
˚
b/A
˚
c/A
23.7570(8)
90
95.223
90
7434.7(4)
150
2
1.45
Dark red
block
a (◦)
b (◦)
g (◦)
V/A
T/K
71.209(4)
3
˚
150
4
1.531
150
8
1.490
150
1
1.322
Z
r
2
1.37
1
2
calc/g cm-3
1.436
1.406
Crystal shape
and colour
Crystal
Black block Black plate
Black block Black block Red rod
Black block Red block
0.48 ¥ 0.15 ¥ 0.66 ¥ 0.37 ¥ 0.44 ¥ 0.13 ¥ 0.24 ¥ 0.11 ¥ 0.20 ¥ 0.15 ¥ 0.50 ¥ 0.20 ¥ 0.41 ¥ 0.17 ¥ 0.38 ¥ 0.28 ¥ 0.21 ¥ 0.20 ¥
0.15
1.110
42560
7742
size/mm
0.32
0.07
0.10
0.12
0.50
0.16
0.15
0.15
m/mm-1
2.608
41924
7249
0.923
72924
14464
1.015
7881
4615
0.859
11117
6311
7.366
34298
8714
0.844
44591
8893
1.199
3379
2110
1.227
15221
6186
unique data
unique data,
(I > 2s(F))
R1,a wR2b
0.0636,
0.1527
0.0421,
0.1073
1.030
0.0803,
0.1741
1.118
0.0617,
0.1741
0.9039
0.0536,
0.1660
0.6354
0.1084,
0.2984
1.056
0.0935,
0.1936
1.1351
0.0297,
0.0322
0.9647
0.0753,
0.2685
1.4701
goodness of fit 1.142
ꢀ
ꢀ
ꢀ
ꢀ
1/2
a R1) (|Fo| - |Fc|)/ (|Fo|) for observed reflections. b wR2) { [w(Fo2 - Fc2)2]/ [w(Fo2)2]} for all data.
quality crystals in 3 days. The crystals were collected by filtration
and dried in vacuo. The yield was approximately 50%. The dried
sample analysed satisfactorily as solvent-free 3.
X-Ray crystallography and structure solution
Diffraction data were collected on a Bruker Smart Apex CCD
diffractometer equipped with an Oxford Cryosystems LT device,
using Mo radiation. Data collection parameters and structure
solution and refinement details are listed in Table 1. Full details can
be found in the CIF files provided in the supporting information,
along with lists of bond lengths and angles.
Method 3. FeCl3·6H2O (270 mg, 1.0 mmol), Me-saoH2
(302 mg, 2.0 mmol) and NaOMe (216 mg, 4.0 mmol) were
dissolved in MeOH (25 ml). After 120 mins stirring the solution
was filtered and then left to evaporate slowly, producing X-ray
quality crystals in 4 days. The crystals were collected by filtration
and dried in vacuo. The yield was approximately 50%. The dried
sample analysed satisfactorily as solvent-free 3.
Physical measurements
Elemental analyses (C, H, N) were performed by the EaStCHEM
microanalysis service. IR spectra were recorded as KBr pellets in
the 4000-400 cm-1 range on a JASCO FT/IR-410 spectrometer.
Variable temperature magnetic susceptibility measurements were
made on a Quantum Design MPMS-XL SQUID magnetometer
equipped with a 7 T magnet. Data were collected on powdered
samples restrained in eicosane to prevent torquing. Diamagnetic
corrections were applied using Pascal’s constants.
Method 4. Fe(ClO4)2·6H2O (182.5 mg, 0.5 mmol), Me-saoH2
(151 mg, 1.0 mmol) and NaO2CHBr3 (319 mg, 1.0 mmol) were
dissolved in MeOH (25 ml) in the presence of NEt4OH (1.0M in
water; 0.125 ml, 0.125 mmol). After 120 mins stirring the solution
was filtered and then left to evaporate slowly, producing X-ray
quality crystals in 3 days. The crystals were collected by filtration
and dried in vacuo. The yield was approximately 55%. The dried
sample analysed satisfactorily as solvent-free 3.
Results and discussion
[HNEt3]2[Fe12Na4O2(OH)8(sao)12(OMe)6(MeOH)10] (9)
Synthesis
Fe(ClO4)2·6H2O (365 mg, 1.0 mmol), saoH2 (137 mg, 1.0 mmol)
and NaO2CCBr3 (319 mg, 1.0 mmol) were dissolved in MeOH
in the presence of NEt3 (0.125 ml, 1 mmol). After 180 mins
stirring the solution was filtered and then left to evaporate
slowly producing X-ray quality crystals in 3 days. The crystals
were collected by filtration and dried in vacuo. The yield was
approximately 30%. The dried sample analysed as 9. Found
(calc.%): C112H156Fe12Na4N14O50; CHN; C 40.92 (41.26), H 4.46
(4.82), N 5.83 (6.01). IR data (KBr pellet; cm-1): 1593 s, 1543 m,
1473 m, 1437 m, 1321 m, 1290 s, 1200 m, 1153 m, 1120 m, 1018 m,
916 s, 818 m, 764 s, 665 m, 607 m.
The reaction of FeCl3·6H2O with Ph-saoH2 in a 3 : 2 molar
ratio in a MeOH/pyridine solution yields the trinuclear complex
[Fe3O(OMe)(Ph-sao)2Cl2(py)3] (1). Repeating the reaction with
FeBr3 in place of FeCl3·6H2O affords the bromide analogue
[Fe3O(MeO)(Ph-sao)2Br2(py)3] (2), but the use of FeF3·3H2O in
the same reaction leads to the tetranuclear complex [Fe4(Ph-
sao)4F4(py)4] (3), in which the halide ions bridge between metals
rather than bonding terminally as in 1 and 2. A combination of
the bulky Ph-sao2- ligand and the coordinating pyridine appears
to favour the production of low nuclearity complexes, but the
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introduction of carboxylates tends to favour larger species. For ex-
ample reaction of FeCl3·6H2O with Et-saoH2 and NaO2CPh in the
presence of NEt3 yields the hexanuclear complex [Fe6O2(OH)2(Et-
sao)2(Et-saoH)2(O2CPh)6] (4). The low ratio of base employed
results in 4 containing two singly deprotonated Et-saoH- ligands.
Increasing this ratio allows us to fully deprotonate all four lig-
ands yielding the hexanuclear complex [HNEt3]2[Fe6O2(OH)2(Et-
sao)4(O2CC6H3(Me)2)6] (5). The increase in the amount of base
employed also leads to the presence of two bridging hydroxides
which link the two triangles (vide infra). This type of structure has
been seen in previously reported carboxylate-only [FeIII6] clusters,
suggesting that oximes could potentially be employed as direct
replacements for carboxylates in many other known polymetallic
Fe-carboxylate clusters.19,20 The similarity between the carboxylate
coordination in 4 and 5 and the basic Fe(III) carboxylates of general
formula [Fe3O(O2CR)6L3]+ (L = solvent) led to the idea that we
could start with pre-made iron carboxylate triangles and replace
the carboxylates with oximes, to create similar complexes. In-
deed treatment of [Fe3O(O2CPh)6(H2O)3]NO3 with 3-tBut-saoH2
yields the complex [Fe6O2(O2CPh)10(3-tBut-5-NO2-sao)2(H2O)2]
(6). Four carboxylates have been replaced with two oximes which
crosslink the two triangles (vide infra), in a manner identical to
work previously reported by Boudalis et al.20 A peculiar anomaly
in this instance is that the 3-tBut-sao2- ligand has undergone an
in situ nitration at the 5 position. Although never seen before in
our work there is precedent for this in organic literature.26,27 Re-
peating this reaction with [Fe3O(O2CCH2Ph)6(H2O)3]NO3 yields
the analogous complex [Fe6O2(O2CCH2Ph)10(3-tBut-sao)2(H2O)2]
(7) in which there is no ligand nitration.
Fig. 1 The molecular structure of 1. Colour code: Fe = olive green; O =
red; N = blue; C = gold; Cl = bright green.
The reaction of Fe(ClO4)2·4H2O with Me-saoH2 and
NaO2CCBr3 and NEt3 yields the polymeric ([Fe6Na3O(OH)4(Me-
sao)6(OMe)3(H2O)3(MeOH)6]·MeOH)n (8·MeOH), in which car-
boxylate does not feature. This is presumably a result of its
highly acidic nature, acting solely as a source of Na. Indeed
the complex can also be obtained by introducing the Na+ using
excess NaOMe. Repeating the reaction but reducing the bulk of
the oxime produces the related, but unusual, molecular complex
[HNEt3]2[Fe12Na4O2(OH)8(sao)12(OMe)6(MeOH)10] (9).
Description of structures
Complexes 1-9 are shown in Fig. 1-6. Full details of the bond
lengths and angles are given in the supplementary information.†
1 and 2 are isostructural, differing only in the identity of the
halide and so here we describe only complex 1 (Fig. 1) in
detail. This crystallises in the monoclinic space group P21/c
with four molecules in the unit cell. It consists of a [FeIII3(m3-
O)] triangular unit where the Fe1-Fe2 and Fe1-Fe3 edges are each
Fig. 2 The molecular structure of 3 (top) and its magnetic core (bottom).
Colour code: Fe = olive green; O = red; N = blue; C = gold; F = yellow.
bridged by a fully deprotonated Ph-sao2- ligand in a h :h :h :m2
fashion. The Fe2-Fe3 edge is bridged by one m-MeO- ion (Fe2-
O1F-Fe3, 98.84(13)◦). The remaining coordination sites on Fe1
are occupied by three pyridine molecules. Fe2 and Fe3 are five
coordinate and the remaining site in each is occupied by a halide
(1 = Cl, 2 = Br). The Fe ◊ ◊ ◊ Fe separations and Fe- m3-O–Fe angles
1
1
1
square based pyramidal geometry with a t value of 0.190 (where
t = (b-a)/60),28 their oxidation states were assigned using charge
balance considerations, bond lengths and BVS calculations.29,30
In the crystal lattice there are no intermolecular hydrogen bonds,
with the closest contacts being between a pyridine ligand and the
◦
˚
˚
˚
˚
are unequal (3.3552(8) A, 3.3834(8) A, 3.0133(8) A, 128.1(2) ,
126.6(2)◦, 105.3(1)◦) and so the triangle is truly scalene rather
than isosceles. Fe1 is in a distorted octahedral geometry with
cis angles in the range 81.7(1)-97.4(1)◦, and trans angles in the
range 166.5(1)-176.6(1)◦. Fe2 and Fe3 are both in a distorted
phenolic O-atom (C ◊ ◊ ◊ O, 3.347(7) A); Cl and the solvent MeOH
2-
˚
(Cl ◊ ◊ ◊ O, 3.365(6) A); MeOH and a phenyl ring of the Ph-sao
ligand (O ◊ ◊ ◊ C, 3.457(8) A). Complex 3 (Fig. 2) crystallises in the
˚
monoclinic space group P21/c with eight molecules in the unit
cell, it contains two independent molecules in the asymmetric unit
2730 | Dalton Trans., 2010, 39, 2727–2734
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Fig. 3 The molecular structures of 4 (left) and 6 (right). Colour code as previous Figures.
which vary slightly in bond lengths and angles but are structurally
equivalent. The FeIII ions are connected by a combination of four
lattice there are inter-molecular hydrogen bonding interactions
between two phenolic O-atoms and the two cations (N ◊ ◊ ◊ O,
fully deprotonated Ph-sao2- ligands in a h : h : h : m2-fashion and
four m2-F- ions creating an unusual [Fe4] square. The remaining
coordination site on each FeIII is occupied by a pyridine molecule.
Each FeIII ion is in a distorted octahedral geometry (cis, 82.1(2)-
102.1(2)◦; trans, 166.9(2)-178.3(2)◦). The structure is unique in that
it is the first case of a FeIII square bridged through fluoride, and
to the best of our knowledge is one of only five fluoride-bridged
first row transition metal squares.31-34 In the crystal lattice there
are no intermolecular hydrogen bonds, with the closest contacts
being between pyridine ligands and phenolic O-atoms (C ◊ ◊ ◊ O,
2.793(8) A) and close contacts between a phenolic O-atom and
1
1
1
˚
the cation (C ◊ ◊ ◊ O, 3.533(8) A) and between a (Me)2PhCO2- ligand
˚
˚
and the cation (C ◊ ◊ ◊ O, 3.271(11) A). This results in the formation
of 2D sheets lying in the bc plane, with the closest intermolecular
˚
Fe ◊ ◊ ◊ Fe distance being 8.925(10) A.
The molecule in complex 6 (Fig. 3) is similar in structure to
that in 4 except that the bridging between the two [FeIII3(m3-O)2]
triangular units occurs only through the two oximate O atoms,
i.e. there are no m-OH- ions present, as in 4. The oxime used in 6
was 3-tBut-saoH2, but under the reaction conditions the benzene
ring has become nitrated at the 5 position giving 3-tBut-5-NO2-
sao2-.26,27 There are only two oximes present in 6 compared to the
˚
3.008(8)-3.380(1) A).
¯
Complex 4 was obtained as triclinic crystals, space group P1
with one molecule in the unit cell (Fig. 3). The molecule contains
a [FeIII6(m3-O)2(m-OH)2]12+ core, whose topology consists of two
centrosymmetrically related off-set [FeIII3(m3-O)] triangular units
linked at one Fe2 edge (Fe1-Fe3) by two m-OH- ions and two
1
1
1
four in 4, the edges that were bridged by one h :h :h :m2-Et-sao2-
-
-
and one PhCO2 ligand in 4, are now bridged by two PhCO2
ligands in their familiar, syn, syn, m-mode in 6. In the crystal
lattice there are intermolecular hydrogen bonds between the NO2
oximate O atoms from two h :h :h :m3-Et-saoH- ligands. Two
salicylaldoxime and the H2O (O ◊ ◊ ◊ O, 2.803(1) A) and between the
1
1
2
˚
˚
Fe2 edges (Fe2-Fe3) are each bridged by one oximate oxygen
H2O and the MeCN solvent (N ◊ ◊ ◊ O, 2.924(2) A).
1
1
1
-
atom from one h :h :h :m2-Et-sao2- and one PhCO2 ligand in its
familiar syn, syn, m2-mode. The remaining two Fe2 edges (Fe1-Fe2)
are bridged by two PhCO2- ligands. Each FeIII ion lies in a distorted
octahedral geometry (cis, 81.47(16)-105.51(17)◦; trans, 161.79(16)-
178.37(18)◦). In the crystal lattice there are no intermolecular
hydrogen bonds, with the closest contacts being between two Et-
The molecule in 7 has a similar structure to 6 with the exception
that there has been no nitration of the benzene ring. In the crystal
lattice there are again intermolecular hydrogen bonds between the
˚
H2O and the MeCN solvent (N ◊ ◊ ◊ O, 2.875(9) A) and also between
˚
the H2O and a carboxylate O-atom (O ◊ ◊ ◊ O, 2.963(6) A).
8 crystallises in the hexagonal space group P63/m with two
molecules in the unit cell and has a 2D framework structure
(Fig. 4-5). The metallic skeleton of the [Fe6] unit (composed of two
linked [Fe3(m3-O)0.5(m3-OH)0.5]7.5+ triangles) (Fig. 4) within the 2D
framework describes a trigonal prism of FeIII ions connected along
the square faces via three m3-OH- ions and three m-MeO- ions to
form an [FeIII6(m3-O)(m3-OH)4(m-OMe)3]9+ core. BVS calculations
on O3 and symmetry equivalent (s.e) of the [Fe3(m3-O)0.5(m3-
OH)0.5]+7.5 triangles reveal values that lie between those expected
for O2- and OH- suggesting that a proton is shared between O3
and s.e. This is reasonable considering the short O ◊ ◊ ◊ O distance
sao2- ligands and two phenolic O- atoms (C ◊ ◊ ◊ O, 3.406(7) A)
˚
which result in the formation of pseudo 1D chains in the bc-plane
(Fig. SI1).
5 has a similar structure to 4 with the following differences: the
two singly deprotonated Et-saoH- ligands in 4 are replaced by two
fully (doubly) deprotonated Et-sao2- ligands, which is perhaps to
be expected given the larger amount of base used in the synthesis,
with charge balance being maintained by the presence of two
[HNEt3]+ cations. Again, the FeIII ions lie in distorted octahedral
geometries with cis angles in the range 80.46(15)-103.24(15)◦ and
trans angles in the range 164.76(16)-177.27(15)◦). In the crystal
˚
of 2.472(3) A between O3 and s.e indicative of a hydrogen bonding
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complementary hydrogen bonds: two between the terminally
bound MeOH molecules and the oximato O-atoms (O ◊ ◊ ◊ O,
˚
2.742(3) A); two between the phenolic O-atoms and bridging H2O
molecules; and one between a OH- ion and a bridging MeO- ion.
9 (Fig. 6) contains two [Fe6Na] units linked by a single
central [Na2] unit forming an unusual S-shaped molecule. This is
structurally very similar to 8 except that a single Na+ is connected
Fig. 4 The [Fe6] trigonal prismatic unit present in 8, viewed parallel to
the [Fe3] planes. Colour code: Fe = green; O = red; N = blue; C = gold.
interaction. The six Fe2 edges (Fe1-Fe1¢ and s.e) of the triangular
faces of the trigonal prism are each linked by a fully deprotonated
Me-sao2- ligand bridging in a h :h :h :m2 fashion. Each Fe ion
has a distorted octahedral geometry (cis, 76.94(6)-97.07(7)◦; trans,
169.42(6)-172.01(6)◦) with a 3+ oxidation state assigned using
charge balance considerations, bond lengths and BVS calculations.
The triangle of Na+ ions in the [Na3] unit (Fig. 5) within the
framework is connected via three m-H2O molecules on each edge.
Each Na+ ion is linked to the [Fe6] unit via a m3-OH- ion; with
six terminal methanol molecules completing the coordination
sphere. The Na+ ions define a distorted trigonal bipyramid with
a t value of 0.955.28 Each [FeIII6O(OH)4(Me-sao)6(OMe)4] unit
is linked to three [Na3(m2-H2O)3(MeOH)6] units forming a non
interpenetrated 2D network (Fig. SI2†) with the centroid of
O3 and s.e of the [FeIII6O(OH)4(Me-sao)6(OMe)4] unit and the
centroid of the three Na+ ions of the [Na3(m-OH2)3(MeOH)6] unit
forming two 3-connecting nodes of a (6,3) 2D net in the ab-
plane. In the crystal lattice there are significant numbers of
1
1
1
Fig. 6 The molecular structure of 9 viewed perpendicular (top) and
parallel to the [Fe3] planes. The lower picture shows only the [Fe6Na] unit.
Colour code: Fe = green; Na = cyan O = red; N = blue; C = gold.
Fig. 5 The structure of the [Fe3Na3] unit in 8 (left) and the respective packing in the crystal as viewed down c-axis (right). Colour code: Fe = green;
Na = cyan O = red; N = blue; C = gold.
2732 | Dalton Trans., 2010, 39, 2727–2734
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to one edge of the trigonal prism via one m3-OH- and two sao2-
behaviour is indicative of antiferromagnetic exchange between the
metal centres and an S = 5/2 ground state. The 300-25 K data for 1
2
1
1
ligands bridging in a h :h :h :m3-fashion forming the [Fe6Na] unit.
Three Fe2 edges (Fe1-Fe2, Fe2-Fe3, Fe5-Fe6) of the triangular
faces of the trigonal prism are linked by fully deprotonated sao2-
ˆ
ˆ
ˆ
were simulated employing the spin-Hamiltonian H = -2J1(S1·S2 +
ˆ
ˆ
ˆ ˆ
S1·S3) -2J2(S2·S3) affording the parameters S = 5/2, g = 2.02,
J1 = -40.0 cm-1, J2 = -5.5 cm-1. Magnetic measurements were
not made on 2 as it is isostructural with 1 differing only in the
nature of the coordinating halides. For complex 3 (Fig. 8) the room
temperature cMT value of approximately 15 cm3 K mol-1 is lower
than expected for four non-interacting FeIII ions (~17.5 cm3 K
mol-1). Upon cooling, the value of cMT decreases almost linearly
to approximately ~2 cm3 K mol-1 at 5 K, indicative of relatively
strong antiferromagnetic exchange with a diamagnetic ground
state. Despite appearing to be a very simple molecule, each of the
Fe–Fe interactions is unique and there are in fact two different
[Fe4] clusters per unit cell, requiring a total of eight separate
J-values. Attempts to fit the data employing simple 1, 2 and 3 J
models all failed to produce a satisfactory result.
1
1
1
ligands bridging in a h :h :h :m2-fashion, while the remaining
three Fe2 edges (Fe1-Fe3, Fe4-Fe5, Fe4-Fe6) are linked by a
2
1
1
fully deprotonated sao2- ligand bridging in a h :h :h :m3-fashion.
Each FeIII ion has a distorted octahedral geometry (cis, 76.4(3)-
100.6(3)◦; trans, 166.4(3)-173.9(3)◦). In 8 the [Fe6] units are
connected by [Na3] units whereas in 9 the linkers are [Na2] units.
These are connected via two m-MeOH molecules which are then
connected to each of the two [Fe6Na] units via one m3-OH- ion
2
1
1
and the phenolate oxygen of a h :h :h :m3 sao2- ligand (Fig. 6).
Terminal MeOH molecules complete the coordination of the Na+
ions in the [Na2] unit forming a discrete molecular complex in
contrast to the coordination polymer found in 9. The Na+ ions in
the [Fe6Na] unit have a distorted octahedral geometry (cis, 68.1(3)–
117.7(11)◦; trans, 147.66(3)-170.57(3)◦), while the Na+ ions in the
[Na2] unit are square pyramidal with a t value of 0.119.28 In the
crystal lattice there are significant numbers of intra-molecular
hydrogen bonds: two between oximic O-atoms and bridging
˚
MeOH molecules (O ◊ ◊ ◊ O, 2.615(0) A); two between phenolate
˚
O-atoms and terminal MeOH molecules (O ◊ ◊ ◊ O, 2.814(11) A);
four between m3-OH- ions and bridging OMe- ions (O ◊ ◊ ◊ O,
-
2-
˚
2.693(7), 2.633(0) A); and two between m3-OH ions and m3-O
˚
ions (O ◊ ◊ ◊ O, 2.526(7) A). The packing of 9 in the crystal can be
found in Fig SI3. The closest intermolecular Fe ◊ ◊ ◊ Fe distance is
˚
8.751(2) A.
Magnetic properties
Direct current (dc) magnetic susceptibility studies were performed
on microcrystalline samples of 1, 3-6, 8, 9 in the 5-300 K range
under an applied field of 0.1 T. For 1 (Fig. 7) the room temperature
cMT value of approximately 4.8 cm3 K mol-1 is lower than expected
for three non-interacting FeIII ions (~13 cm3 K mol-1). Upon
cooling, the value of cMT initially decreases to approximately
~4.3 cm3 K mol-1 at 125 K before increasing to a value of
~4.5 cm3 K mol-1 at 25 K. Below this temperature there is a rapid
decrease to approximately 4.1 cm3 K mol-1 at 5 K - presumably
due to inter-molecular interactions and/or Zeeman effects. This
Fig. 8 Plot of cMT vs. T for complex 3.
For complexes 4-6 and 8-9 (Fig. 9) the room temperature cMT
values of approximately 6.4, 6.1, 5.2, 11.0 and 10.2 cm3 K mol-1
respectively are lower than that expected for six non-interacting
FeIII ions (26.25 cm3 K mol-1). On cooling, the values of cMT
decrease to approximately 0.3, 1.1, 0.6, 0.26 and 0.22 cm3
K
mol-1 at 5 K respectively. This behaviour is consistent with
antiferromagnetic exchange between the metal centres and small
(probably S = 0) ground states.
Fig. 7 Plot of cMT vs. T for complex 1. The solid red line represents the
simulation of the experimental data - see text for details.
Fig. 9 Plot of cMT vs. T for complexes 4 (magenta); 5 (red); 6 (green); 8
(blue); and 9 (olive).
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The complexity of structures of 4-6, 8 and 9 precludes the fitting
of the susceptibility data by standard procedures.
9 P. L. Feng, C. Koo, J. J. Henderson, M. Nakano, S. Hill, E. del Barco
and D. N. Hendrickson, Inorg. Chem., 2008, 47, 8610.
10 C.-I. Yang, W. Wernsdorfer, K.-H. Cheng, M. Nakano, G.-H. Lee and
H.-L. Tsai, Inorg. Chem., 2008, 47, 10184.
11 C. P. Raptopoulou, A. K. Boudalis, K. N. Lazarou, V. Psycharis, N.
Panopoulos, M. Fardis, G. Diamantopoulos, J.-P. Tuchagues, A. Mari
and G. Papavassiliou, Polyhedron, 2008, 27, 3575.
12 A. Prescimone, C. J. Milios, S. Moggach, J. E. Warren, A. R. Lennie, J.
Sanchez-Benitez, K. Kamenev, R. Bircher, M. Murrie, S. Parsons and
E. K. Brechin, Angew. Chem., Int. Ed., 2008, 47, 2828.
13 W.-K. Dong, J.-G. Duan, L.-Q. Chai, G.-L. Liu and H.-L. Wu, J. Coord.
Chem., 2008, 61, 1306.
14 W.-K. Dong, J.-G. Duan, Y.-H. Guan, J.-Y. Shi and C.-Y. Zhao, Inorg.
Chim. Acta, 2009, 362, 1129.
15 C. N. Verani, E. Bothe, D. Burdinski, T. Weyhermuller, U. Florke and
P. Chaudhuri, Eur. J. Inorg. Chem., 2001, 2161.
16 I. A. Gass, C. J. Milios, A. G. Whittaker, F. P. A. Fabiani, S. Parsons,
M. Murrie, S. P. Perlepes and E. K. Brechin, Inorg. Chem., 2006, 45,
5281.
17 E. Bill, C. Krebs, M. Winter, M. Gerdan, A. X. Trautwein, U. Florke,
H.-J. Haupt and P. Chaudhuri, Chem.–Eur. J., 1997, 3, 193.
18 P. Chaudhuri, E. Rentschler, F. Birkelbach, C. Krebs, E. Bill, T.
Weyhermuller and U. Florke, Eur. J. Inorg. Chem., 2003, 541.
19 C. P. Raptopoulou, Y. Sanakis, A. K. Boudalis and V. Psycharis,
Polyhedron, 2005, 24, 711.
20 C. P. Raptopoulou, A. K. Boudalis, Y. Sanakis, V. Psycharis, J. M.
Clemente-Juan, M. Fardis, G. Diamantopoulos and G. Papavassiliou,
Inorg. Chem., 2006, 45, 2317.
21 P. Chaudhuri, M. Winter, P. Fleischhauer, W. Haase, U. Florke and
H.-J. Haupt, Inorg. Chim. Acta, 1993, 212, 241.
Conclusions
The nine new iron(III) cluster compounds assembled using sali-
cylaldoxime derivatives range in nuclearity from three to twelve.
The results support the proposition that salicylaldoximates favour
the formation of polynuclear complexes with higher oxidation
state transition metal ions, whilst the coordination chemistry
with M(II) ions is dominated by mononuclear complexes.4 The
predominant building block in the new clusters - as also seen
in Mn(III) chemistry5-8 - appears to be the triangular [Fe3O(R-
sao)3]+ species, which can assemble into more elaborate arrays
depending on reaction conditions. An interesting observation is
that R-saoH-/R-sao2- ligand system tends to adopt coordination
modes similar to carboxylates, and given that the latter have
been deployed successfully in making magnetically interesting
molecules, it is timely to extend that range of oximate-based
Fe(III) clusters. The most unusual molecule is 3 which contains
the [Fe4F4] molecular square. Whilst Cl- and Br- appear to act
only as terminal ligands, the F- ions bridge thus making a major
impact on molecular structure and topology–affording the square
rather than the “expected” (oxo-centered) triangles. F- bridges
have been used with great success in recent Cr(III) chemistry35-36
but their use in building Fe(III) clusters is extremely rare,37 again
suggesting potential future routes to novel Fe molecules.
22 I. A. Gass, C. J. Milios, A. Collins, F. J. White, L. Budd, S. Parsons, M.
Murrie, S. P. Perlepes and E. K. Brechin, Dalton Trans., 2008, 2043.
23 P. Chaudhuri, M. Winter, P. Fleischhauer, W. Haase, U. Florke and
H.-J. Haupt, J. Chem. Soc., Chem. Commun., 1993, 566.
24 J. M. Thorpe, R. L. Beddoes, D. Collison, C. D. Garner, M. Helliwell,
J. M. Holmes and P. A. Tasker, Angew. Chem., Int. Ed., 1999, 38, 1119.
25 R. Dunsten and T. A. Henry, J. Chem. Soc. Trans., 1899, 75, 66.
26 V. Anuradha, P. V. Srinivas, P. Aparna and J. Madhusudana Rao,
Tetrahedron Lett., 2006, 47, 4933.
Acknowledgements
The authors would like to thank SHEFC for a SPIRIT studentship
(KM) and EaStCHEM for fellowships (AC and FJW).
27 R. R. Bak and A. J. Smallridge, Tetrahedron Lett., 2001, 42, 6767.
28 A. W. Addison, T. N. Rao, J. Reedijk, J. Van Rijn and G. C. Verschoor,
J. Chem. Soc., Dalton Trans., 1984, 1349.
29 I. D. Brown and D. Altermatt, Acta Crystallogr., Sect. B: Struct. Sci.,
1985, 41, 244.
References
30 H. H. Thorp, Inorg. Chem., 1992, 31, 1585.
1 P. A. Tasker, P. G. Plieger and L. C. West, Compr. Coord. Chem. II,
2004, 9, 759.
2 G. A. Kordosky, Int. Solvent Extr. Conf., 2002, 853.
3 P. J. Mackey, Canadian Institute of Mining, Metallurgy and Petroleum
Magazine, 2007, 2, 35.
31 R. Basta, B. G. Harvey, A. M. Arif and R. D. Ernst, J. Am. Chem. Soc.,
2005, 127, 11924.
32 D. W. Aldous, N. F. Stephens and P. Lightfoot, Dalton Trans., 2007,
2271.
33 (a) W. S. Sheldrick, J. Fluorine Chem., 1974, 4, 415; (b) D. A. Straus, M.
Kamigaito, A. P. Cole and R. M. Waymouth, Inorg. Chim. Acta, 2003,
349, 65.
4 A. G. Smith, P. A. Tasker and D. J. White, Coord. Chem. Rev., 2003,
241, 61.
5 R. Inglis, L. F. Jones, C. J. Milios, S. Datta, A. Collins, S. Parsons,
W. Wernsdorfer, S. Hill, S. P. Perlepes, S. Piligkos and E. K. Brechin,
Dalton Trans., 2009, 3403.
6 R. Inglis, L. F. Jones, K. Mason, A. Collins, S. A. Moggach, S. Parsons,
S. P. Perlepes, W. Wernsdorfer and E. K. Brechin, Chem.–Eur. J., 2008,
14, 9117.
7 L. F. Jones, R. Inglis, M. E. Cochrane, K. Mason, A. Collins, S. Parsons,
S. P. Perlepes and E. K. Brechin, Dalton Trans., 2008, 6205.
8 C. C. Stoumpos, R. Inglis, G. Karotsis, L. F. Jones, A. Collins, S.
Parsons, C. J. Milios, G. S. Papaefstathiou and E. K. Brechin, Cryst.
Growth Des., 2009, 9, 24.
34 A. Bottcher, H. Elias, J. Glerup, M. Neuburger, C. E. Olsen, H. Paulus,
J. Springborg and M. Zehnder, Acta Chem. Scand., 1994, 48, 967.
35 S. T. Ochsenbein, F. Tuna, M. Rancan, R. S. G. Davies, C. A. Muryn, O.
Waldmann, R. Bircher, A. Sieber, G. Carver, H. Mutka, F. Fernandez-
Alonso, A. Podlesnyak, L. P. Engelhardt, G. A. Timco, H. U. Gudel
and R. E. P. Winpenny, Chem.–Eur. J., 2008, 14, 5144.
36 L. P. Engelhardt, C. A. Muryn, R. G. Pritchard, G. A. Timco, F. Tuna
and R. E. P. Winpenny, Angew. Chem., Int. Ed., 2008, 47, 924.
37 A. Bino, M. Ardon, D. Lee, B. Spingler and S. J. Lippard, J. Am. Chem.
Soc., 2002, 124, 4578.
2734 | Dalton Trans., 2010, 39, 2727–2734
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The Royal Society of Chemistry 2010
©