Systematic structural studies on cobalt(II) complexes of tricyclohexylphosphine oxide and related ligands

Article abstract of DOI:10.1016/j.poly.2011.08.005

The new cobalt(II) phosphine oxide complexes Co(Cy₃PO) ₂Cl₂ (1), Co(Cy₃PO)₂Br₂ (2), Co(Cy₃PO)₂I₂ (3), Co(Ph ₂CyPO)₂Cl₂ (4),

Full text of DOI:10.1016/j.poly.2011.08.005

Polyhedron 30 (2011) 2832–2836
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Systematic structural studies on cobalt(II) complexes of tricyclohexylphosphine
oxide and related ligands
b
b
d
Rafael Bou-Moreno a, Simon A. Cotton b,c, , Verity Hunter , Kathryn Leonard , Andrew W.G. Platt ,
⇑
Paul R. Raithby e, , Stefanie Schiffers e
⇑
a Department of Chemistry, University College London, WC1H 0AJ, UK
b Uppingham School, Uppingham, Rutland LE 15 9QE, UK
c School of Chemistry, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
d Faculty of Sciences, Staffordshire University, College Road, Stoke on Trent, ST4 2DE, UK
e Department of Chemistry, The University of Bath, Bath, BA2 7AY, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The new cobalt(II) phosphine oxide complexes Co(Cy3PO)2Cl2 (1), Co(Cy3PO)2Br2 (2), Co(Cy3PO)2I2 (3),
Co(Ph2CyPO)2Cl2 (4), Co(Ph2CyPO)2Br2 (5), Co(Ph2CyPO)2I2 (6), Co(Ph2EtPO)2Br2 (7), Co(Cy3PO)2(NCS)2
(8) and Co(Cy3PO)2(NO3)2 (9) have been prepared mainly by the reaction of anhydrous CoX2 (X = Cl, Br,
I, NCS, NO3) with the appropriate phosphine oxide. The complexes were characterised by single-crystal
X-ray crystallography supported by IR and UV–Vis absorption spectroscopy. The structural analyses show
that the cobalt(II) centre adopts a distorted tetrahedral coordination geometry except for 9 which dis-
plays an octahedral geometry. Systematic structural features of these complexes are explained within
this paper.
Received 13 July 2011
Accepted 7 August 2011
Available online 31 August 2011
Keywords:
Phosphine oxide
Cobalt (II) complex
X-ray structures
Tetrahedral
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
other phosphine oxides were obtained as commercial products and
were used without further purification.
We previously reported the structures of the cobalt(II) complexes
Co(Ph3PO)2Cl2, Co(Ph3PO)2Br2, Co(Ph3PO)2I2, Co(Ph3AsO)2Br2 and
Co(Ph3AsO)2(NO3)2 [1]; all exhibited distorted tetrahedral coordina-
tion of cobalt. Clear trends were seen in metal-halogen bond lengths
in Co(Ph3PO)2X2 (X = Cl, Br, I), whilst the cobalt–oxygen bond length
was relatively insensitive to the nature of the halogen. We wished to
establish whether such patterns might be found in other simple
transition metal complexes and we therefore prepared analogous
complexes with other phosphine oxides, which to our knowledge,
have not been reported previously, particularly those of tricyclohex-
ylphosphine oxide. In this paper, we report the syntheses and struc-
ture of 2:1 complexes of Cy3PO and Ph2CyPO with CoX2 (X = Cl, Br, I);
of the analogous complex of Ph2EtPO with CoBr2; and also the 2:1
complexes of Cy3PO with Co(NCS)2 and Co(NO3)2.
2.2. Synthesis of the complexes
[Co(Cy3PO)2Cl2] (1) was prepared by mixing warm ethanolic
solutions of anhydrous CoCl2 (0.12 g; 0.92 mmol) and Cy3PO
(0.60 g; 2.0 mmol). Blue crystals formed on cooling. Compounds
2, 4, 5, 7, 8 and 9 were obtained similarly; all formed blue crystals,
except 9 which is violet. 9 was prepared using hydrated Co(NO3)2.
Compounds 3 and 6 were prepared in a similar procedure, but the
initial products of the reactions of CoI2 with Cy3PO and Ph2CyPO
were dark green crystals; their exact composition has not been
established. However, on leaving the solutions for several weeks
to crystallize further, a few green–blue crystals of Co(Cy3PO)2I2
(3) and Co(Ph2CyPO)2I2 (6) formed; these were insufficient for
analysis except for X-ray diffraction.
2. Experimental
2.3. X-ray crystallography
2.1. Material and methods
Crystals were obtained from the mother liquor and mounted on
a glass fibre with oil and transferred to a diffractometer. The crystal
data, data collection parameters, and structure solution and refine-
ment details for the crystal structures determined are summarised
in Tables 1 and 2.
Tricyclohexylphosphine oxide was synthesised [2] by hydrogen
peroxide oxidation of tricyclohexylphosphine. Cobalt salts and the
⇑
Corresponding authors. Fax: +44 1223 336033.
E-mail addresses: s.cotton@bham.ac.uk (S.A. Cotton), p.r.raithby@bath.ac.uk (P.R.
Data collections were carried out using either Bruker Nonius
Kappa CCD diffractometers, equipped with an Oxford Cryostream
Raithby).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.005

R. Bou-Moreno et al. / Polyhedron 30 (2011) 2832–2836
2833
Table 1
Crystal data, data collection parameters and refinement parameters for the complexes 1–5.
Compound reference
(1)
(2)
(3)
(4)
(5)
Chemical formula
Formula mass
Crystal system
a (Å)
b (Å)
c (Å)
C
36H66Cl2CoO2P2
C36H66Br2CoO2P2
811.58
C36H66CoI2O2P2
905.56
C36H42Cl2CoO2P2
698.47
C36H42Br2CoO2P2
787.39
722.66
orthorhombic
16.2750(2)
18.3150(2)
25.6890(3)
90
orthorhombic
16.3730(2)
18.4280(3)
25.8840(3)
90
orthorhombic
20.1463(14)
9.6082(3)
20.3167(7)
90
90
90
3932.7(3)
150(2)
Pca21
monoclinic
9.3230(1)
16.5790(3)
22.3780(4)
90
99.634(1)
90
3410.10(9)
150(2)
monoclinic
9.4690(2)
16.6590(5)
22.3690(4)
90
98.702(2)
90
3487.96(14)
150(2)
a
(°)
b (°)
(°)
90
90
90
90
c
Unit cell volume (Å3)
Temperature (K)
7657.29(15)
150(2)
Pcab
7809.76(18)
150(2)
Pcab
Space group
P21/n
P21/n
No. of formula units per unit cell, Z
Size
Diffractometer
No. of reflections measured
No. of independent reflections
Rint
8
8
4
4
4
0.40 Â 0.40 Â 0.35
0.5 Â 0.2 Â 0.2
0.17 Â 0.14 Â 0.11
Gemini
29957
12549
0.0413
0.0292
0.037
0.0539
0.0391
0.80 Â 0.35 Â 0.25
0.40 Â 0.35 Â 0.30
Kappa
Kappa
Kappa
Kappa
110431
11623
94571
10964
0.0999
0.0587
0.1094
0.1251
0.1331
55284
9357
0.1015
0.0551
0.1255
0.1285
0.1837
51344
9551
0.1378
0.0486
0.1087
0.1117
0.1562
0.0544
0.0407
0.1028
0.0599
0.1195
Final R1 values (I > 2
r
(I))
r
Final wR(F2) values (I > 2
Final R1 values (all data)
(I))
Final wR(F2) values (all data)
Flack parameter
À0.030(8)
Table 2
Crystal data, data collection parameters and refinement parameters for the complexes 6–9.
Compound reference
(6)
(7)
(8)
(9)
Chemical formula
Formula mass
Crystal system
a (Å)
b (Å)
c (Å)
C
36H42CoI2O2P2
C28H30Br2CoO2P2
679.21
C38H66CoN2O2P2S2
767.92
triclinic
C36H66CoN2O8P2
775.78
881.37
monoclinic
9.6375(3)
16.8434(5)
22.3267(7)
90
97.296(3)
90
3594.91(19)
150(2)
monoclinic
9.6940(2)
14.6690(3)
20.5910(4)
90
96.856(1)
90
2907.13(10)
150(2)
monoclinic
9.2520(1)
21.2490(4)
20.3010(4)
90
95.318(1)
90
3973.91(12)
150(2)
9.4220(4)
12.2400(3)
19.5100(7)
101.628(2)
96.622(2)
109.748(2)
2032.74(12)
150(2)
a
(°)
b (°)
(°)
c
Unit cell volume (Å3)
Temperature (K)
ꢀ
Space group
P21/n
P21/n
P21/c
P1
No. of formula units per unit cell, Z
Size
Diffractometer
No. of reflections measured
No. of independent reflections
Rint
4
4
2
4
0.19 Â 0.15 Â 0.08
Gemini
51076
0.55 Â 0.5 Â 0.5
0.35 Â 0.30 Â 0.30
0.3 Â 0.2 Â 0.2
Kappa
Kappa
Kappa
46751
8688
0.167
0.0663
0.1619
0.0826
0.1772
36201
10817
66958
10954
0.1049
0.0509
0.0985
0.1216
0.1183
12367
0.0408
0.0333
0.076
0.0631
0.0803
0.1302
0.0592
0.1185
0.1386
0.1462
Final R1 values (I > 2
r
(I))
r
Final wR(F2) values (I > 2
Final R1 values (all data)
(I))
Final wR(F2) values (all data)
cooling apparatus [3] or using an Oxford Diffraction Gemini A Ultra,
equipped with a CryojetXL cooling device. In all cases graphite
O
PCy3
O
Cy3P
R2(R1)2P
O
X
O
X
X = Cl, Br, I, NCS
P(R1)2R2
Co
O
O
Co
R
1 = Cy, Ph
O
monochromated MoKa radiation was used. The structures were
O
N
O
N
R2 = Cy, Et
O
solved using Sir92 [4], SHELX-86 [5] and refined by full-matrix least-
squares F2 using SHELXL-97 [6]. All non-hydrogen atoms were refined
with anisotropic displacement parameters and H-atoms were
placed in idealised positions and allowed to ride on the relevant
C-atom. Isotropic displacement parameters were set at 1.2 Ueg. Refine-
ments were continued until convergence was reached and the residual
electron density maps showed no significant residual features.
Scheme 1.
Co(Cy3PO)2(NCS)2 (8) and Co(Cy3PO)2(NO3)2 (9) were prepared by
the reaction of anhydrous CoX2 (X = Cl, Br, I, NCS) and hydrated
Co(NO3)2 with the appropriate phosphine oxide using a method
previously described for the synthesis of Co(Ph3PO)2X2 (X = Cl, Br,
I) [1] (Scheme 1). The were initially characterised by IR spectros-
copy (see Supplementary information) and by comparison with
the data reported for Co(Ph3PO)2X2.
3. Results and discussion
3.1. Preparation
3.2. X-ray structures of the compounds 1–9
The new cobalt(II) phosphine oxide complexes Co(Cy3PO)2Cl2
(1), Co(Cy3PO)2Br2 (2), Co(Cy3PO)2I2 (3), Co(Ph2CyPO)2Cl2 (4),
Co(Ph2CyPO)2Br2 (5), Co(Ph2CyPO)2I2 (6), Co(Ph2EtPO)2Br2 (7),
In the four complexes with tricyclohexylphosphine oxide (1–3,
8), cobalt has distorted tetrahedral coordination, being bound to

2834
R. Bou-Moreno et al. / Polyhedron 30 (2011) 2832–2836
Fig. 1. (a) Structures of 1, (b) 3 and (c) 8 with hydrogens and disorder in 1 removed for clarity and ellipsoids set at 50 % probability.
the oxygen atoms of two tricyclohexylphosphine oxides and two
halogens or thiocyanate ligands. An analysis of the packing in these
four structures showed no short intermolecular interactions, the
molecules being separated by normal van-der-Waals distances.
Compounds 1–2 crystallize in the orthorhombic space group Pcab,
with one molecule per asymmetric unit and the structures are iso-
morphous and isostructural (Fig. 1a). Compound 3, on the other
hand, crystallizes in the orthorhombic space group Pca21, again
with one molecule per asymmetric unit (Fig. 1b). The structure of
1 displays disorder in one of the cyclohexyl rings (C12–C17) in a
ratio of ca. 90:10, which is not found within the other two struc-
tures. It is treated as a disorder model with the total occupancy
of each atom being summed to unity. Only the major compound
is refined with anisotropic displacement parameters. The closely
related thiocyanate complex, Co(Cy3PO)2(NCS)2 8, crystallizes in
ꢀ
the triclinic space group P1 with one molecule in the asymmetric
unit (Fig. 1c).
Fig. 2. Structure of
ellipsoids set at 50% probability.
4 with hydrogens and disorder removed for clarity and
The three structures 4–6 are isomorphous and isostructural and
crystallize in the monoclinic space group P21/n, with one molecule
per asymmetric unit (Fig. 2). Again the molecules are separated by
normal van-der-Waals distances and there is no indication of any
significant intermolecular interactions. The distorted tetrahedral
Co(II) centre is coordinated by two phosphine oxide ligands and
two halogen atoms.
Compound 7 crystallizes in the monoclinic space group P21/n.
The structure shows no obvious intermolecular packing interac-
tions in the crystal. The distorted tetrahedral cobalt centre is bound
to two phosphine oxide ligands and two bromides (Fig. 3).
The complex Co(Cy3PO)2(NO3)2 (9) crystallizes in the mono-
clinic space group P21/c with one molecule per asymmetric unit.
The cobalt ion is bound to two bidentate oxygens of each nitrate
group and to the two oxygens of the phosphine oxides (Fig. 4). 9
has octahedral coordination of cobalt, with the phosphine
oxide ligands adopting a cis arrangement, as also found in
Co(Ph3PO)2(NO3)2 [7] and Ni(NO3)2(Cy3PO)2 [8], but in contrast
to tetrahedral Co(Ph3AsO)2(NO3)2 [1], where the nitrate groups
exhibit a monodentate coordination mode. The molecules within
the crystal structure are separated by normal van-der-Waals dis-
tances and there is no evidence for any significant intermolecular
interactions.

R. Bou-Moreno et al. / Polyhedron 30 (2011) 2832–2836
2835
Co(Ph3PO)2Cl2, respectively, whilst the O–Co–O angles of
101.85(5)° in 1 and 102.6(1)° in 4 are intermediate between the
values of 105.6(2)° and 97.86(16)° in Co(Me3PO)2Cl2 and Co(Ph3-
PO)2Cl2, respectively (Table 3).
For the bromide complexes, average Co–O bond lengths of
1.964 Å in 2, 1.959 Å in 5 and 1.947 Å in 7 are very comparable
with the values of 1.957 and 1.970 Å in Co((Me2N)3PO)2Br2 [10]
and Co(Ph3PO)2Br2 [1], respectively. Similarly average Co–Br bond
lengths of 2.391 Å in 2, 2.386 Å in 5 and 2.387 Å in 7 are likewise
close to the respective values of 2.404 and 2.385 Å in Co(Me3-
PO)2Br2 and Co(Ph3PO)2Br2. The O–Co–O angles of 102.7(1)° in 2,
103.5(1)° in 5 and 102.9(1)° in 7 are similar to that in Co(Ph3-
PO)2Br2 (103.9(2)°), but much less than the value of 110.7(3)° in
Co((Me2N)3PO)2Br2. There is in most cases very significant devia-
tion from regular tetrahedral geometry in the Br–Co–Br bond an-
gles of 114.22(3)° in 2, 119.16(3)° in 5 and 109.10(3)° in 7, as in
Co(Ph3PO)2Br2 (113.72(5)°) and 117.97(6)° in Co((Me2N)3PO)2Br2.
For the iodide complexes, average Co–O bond lengths of 1.953 Å
in 3 and 1.954 Å in 6 are virtually identical to the values of 1.952
Fig. 3. Structure of
ellipsoids set at 50% probability.
7 with hydrogens and disorder removed for clarity and
i
and 1.958 Å in Co(Ph2 PrPO)2I2 [11] and Co(Ph3PO)2I2 [1], respec-
tively. Similarly, average Co–I bond lengths of 2.554 Å in 3 and
2.591 Å in 6 are closely comparable to the respective values of
i
2.576 and 2.578 Å in Co(Ph2 PrPO)2I2 and Co(Ph3PO)2I2. The I–Co–
I angles of 120.68(1)° in 3 and 115.99(1)° in 6 reveal considerable
i
distortion from the tetrahedral ideal; values for Co(Ph2 PrPO)2I2
and Co(Ph3PO)2I2 are 117.11(5)° and 112.46(3)° respectively. The
O–Co–O angles of 104.12(8)° in 3 and 104.24(7)° in 6 are similar
i
to the values of 102.7(3)° and 105.12(12)° in Co(Ph2 PrPO)2I2 and
Co(Ph3PO)2I2, respectively.
The structure of Co(Cy3PO)2(NCS)2 (8) is also slightly distorted
tetrahedral, with an O–Co–O angle of 107.2(1)° and an N–Co–N an-
gle of 111.9(1)°. The Co–O distance averages 2.034 Å, whilst the
average Co–N bond is 1.952 Å, similar to the value of 1.939 Å in
Co(3,5-dimethylpyrazole)2(NCS)2 [12] and 1.964 Å in K2[Co(N-
CS)4]ÁH2OÁ2CH3NO2 [13]. The IR spectrum of 8 has the characteristic
C–N stretching vibration at 2062 cmÀ1. The molecular structure of
Co(Cy3PO)2(NCS)2 contrasts with Co(Ph3PO)2(NCS)2, which, in the
solid state at least, adopts an ‘‘auto-ionised’’ structure,
[Co(OPPh3)4]2+ {[Co(OPPh3)(NCS)3]À}2 [14]. The identity of the com-
plex isolated is due to a balance of many factors, not least the solu-
bility of each species present in solution, as well as its concentration.
The average distances in the complex 9 are 2.166 Å for the
metal-oxygen (nitrate) and 1.985 Å for the metal-oxygen
(phosphine oxide) distances, similar to those in Co(Ph3PO)2(NO3)2;
comparison is difficult, because of the large standard deviations in
Co(Ph3PO)2(NO3)2. The metal-oxygen (phosphine oxide) distances
average 1.985 Å in Co(Cy3PO)2(NO3)2 and 1.984 Å in the nickel
analogue, Ni(Cy3PO)2(NO3)2, with metal-oxygen (nitrate) distances
of 2.166 and 2.106 Å, respectively. There is a close correspondence
between the m3 (asymmetric stretching) vibration of coordinated
Fig. 4. Structure of
ellipsoids set at 50% probability.
9 with hydrogens and disorder removed for clarity and
3.3. Comparison of bond parameters across the series 1–9
For the chloride complexes, average Co–O bond lengths of
1.974 Å in 1 and 1.964 Å in 4 are similar to the values of 1.972 Å
and 1.971 Å in Co(Me3PO)2Cl2 [9] and Co(Ph3PO)2Cl2 [1] respec-
tively; similarly average Co–Cl bond lengths of 2.251 Å in both 1
and 4 are likewise comparable to the respective values of 2.262
and 2.227 Å in Co(Me3PO)2Cl2 and Co(Ph3PO)2Cl2. The Cl–Co–Cl an-
gles of 116.58(2)° in 1 and 117.97(4)° in 4 are rather greater than
the values of 113.6(1)° and 112.76(6)° in Co(Me3PO)2Cl2 and
Table 3
Principal bond lengths and angles for the coordination sphere of the complexes 1–9.
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
Co–X
2.2464(5)
2.2562(5)
2.3847(6)
2.3964(7)
2.5530(4)
2.5543(4)
2.2462(11)
2.2559(11)
2.3830(6)
2.3884(7)
2.5915(4)
2.5915(4)
2.3808(6)
2.3940(7)
1.947(2)
1.957(3)
2.1077(16)
2.1171(19)
2.1916(18)
2.2461(17)
1.9703(15)
1.9996(14)
Co–O
1.9648(12)
1.9827(12)
116.58(2)
101.85(5)
109.21(4)
1.960(2)
1.968(2)
114.22(3)
102.7(1)
108.98(8)
111.48(8)
111.61(8)
107.26(8)
1.9461(17)
1.9601(17)
120.68(1)
104.12(8)
106.68(6)
113.72(5)
107.61(6)
107.78(5)
1.961(2)
1.966(2)
117.97(4)
102.6(1)
111.58(8)
107.81(8)
106.38(8)
109.41(8)
1.954(3)
1.964(3)
119.16(3)
103.5(1)
110.32(9)
107.58(8)
105.58(8)
109.65(9)
1.9422(16)
1.9655(16)
115.99(1)
104.24(7)
109.13(6)
107.23(5)
105.01(5)
109.47(5)
1.937(3)
1.957(3)
1.9413(19)
1.9660(18)
111.9(1)
107.22(8)
108.22(9)
110.08(9)
110.25(9)
109.10(9)
X–Co–X
O–Co–O
O–Co–X
109.10(3)
102.9(1)
108.67(10)
113.24(9)
110.94(10)
111.81(9)
99.75(6)
111.35(4)109.74(4)
107.09(4)

2836
R. Bou-Moreno et al. / Polyhedron 30 (2011) 2832–2836
nitrate in the IR spectra of the two cobalt complexes (Co(Cy3PO)2
(NO3)2 and Co(Ph3PO)2(NO3)2); m3 occurs as two strong bands
centred on 1284 and 1484 cmÀ1 in the spectrum of Co(Cy3PO)2
(NO3)2, very similar to those at 1282 cmÀ1 and a split band (1490,
There is no pattern in \X–Co–X or \X–Co–O, but in all three
series, \O–Co–O increases as the halogen becomes heavier. This
may be a genuine trend reflecting a greater cone angle of the larger
halogens, as simple estimates of the cone angles 2h of the halogens
(based on h = radius XÀ/Co–X distance) do indicate a slight increase
in the order ClÀ (146.2°), BrÀ (149.2°) and IÀ (155.6°). This calcula-
tion relies on the use of the ionic radii of the halide ions in six-coor-
dination [16].
1482 cmÀ1
compounds
)
in the spectrum of Co(Ph3PO)2(NO3)2. In both
m
1 lies at ca. 1010 cmÀ1
.
3.4. Electronic spectra of [Co(R3PO)2X2] complexes
Overall in these families it is clear that there is relatively little
variation in bond length for similar complexes, but that bond an-
gles can vary substantially, in the solid state. This in turn may
mean that the potential energy well has relatively steep sides with
respect to stretching along the Co–O and Co–X coordinates, but
shallow sides with respect to deformation.
The electronic spectra can be found in the Supporting Informa-
tion. The spectrum of 1 in chloroform is typical of tetrahedrally
coordinated Co2+; having a maximum ꢀ667 nm with
e value of
450, significantly higher than the value for octahedral coordina-
tion, due to the 4A2 ? 4T1(P) transition with splitting due to either
spin-orbit coupling effects or to doublet state transitions [15]. Sim-
ilar spectra are obtained from the other tetrahedral Co(R3PO)2X2
complexes in chloroform. On dissolution of these tetrahedral com-
plexes in ethanol, the absorptions due to the tetrahedral species re-
main, but with substantially reduced extinction coefficients and
extra absorptions in the ‘‘octahedral region’’ ꢀ500 nm can often
be seen, notably in the spectra of 1 and 2. We ascribe this to addi-
tional coordination of solvent ethanol, leading to complexes of the
type Co(R3PO)2X2(EtOH)2. Similarly in the spectrum of 8 in ethanol,
the peaks at 641 and 601 nm may be associated with a tetrahedral
species and those at 524 and 480 nm with an octahedral species.
Thus an ethanolic solution of 5 has absorptions at 668, 639(sh);
624(sh); 583(sh) and 526 nm, in both the ‘‘octahedral’’ and ‘‘tetra-
hedral’’ regions. The absorptions in the spectrum of 4 in chloroform
have very low extinction coefficients for a tetrahedral complex.
When the chloroform solution was prepared, a significant amount
of pale violet coloured insoluble material remained; this is proba-
bly an insoluble chloride bridged polymer with an octahedral
geometry about the cobalt, which presumably crystallizes from
the tetrahedral form in chloroform solution.
Acknowledgements
We thank the EPSRC for studentships to S.S. and for a Senior Re-
search Fellowship to P.R.R. We are also grateful to Professor J.C.
Anderson of University College, London for arranging for analyses
to be carried out, and for running mass spectra.
Appendix A. Supplementary data
CCDC 834053–834061 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2011.08.005.
The spectrum of 9 in ethanol is typical of octahedral coordi-
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