Coordination chemistry of α-ω-bis(pyridylimine) ligands containing flexible linkers with copper(I)

Article abstract of DOI:10.1002/ejic.201101414

Copper(I) complexes of a series of six potentially tetradentate bis(pyridylimine) ligands were prepared, where the pyridylimine groups were separated by different linking units [in L1, CH₂CH₂CH ₂(SiMe₂O)₂₀SiMe₂CH ₂CH₂CH₂; in L2, CH₂CH ₂CH₂SiMe₂OSiMe₂CH₂CH ₂CH₂; in L3, CH₂CH₂; in L4, CH ₂(CH₂)₄CH₂; in L5, CH ₂(CH₂)₇CH₂; in L6, CH ₂CH₂CH₂OCH₂CH₂OCH ₂CH₂OCH₂CH₂CH₂]. The solubilities of L1, L2 and [Cu(L2)](PF₆) in supercritical carbon dioxide were determined. The coordination chemistry of L1-L2 with Cu^I was studied by UV/Vis, multinuclear NMR and IR spectroscopy, MALDI-TOF and ESI mass spectrometries and elemental analysis. These data suggested that [1+1] complexes had formed. Dicopper complexes of L3-L6 were prepared for comparison, and [Cu₂(L5)₂](PF₆)₂ characterized by single-crystal X-ray diffraction analysis. Close methylene C-H...π interactions are observed within the structure. PGSE NMR spectroscopy was used to determine the hydrodynamic radii of the species in solution and comparison of these data with computational models for the complexes was made. Freezing point depression measurements afforded molecular weights for solution-state species in agreement with the formulations proposed via NMR and mass spectrometric data. There is no evidence to support linear metallopolymer formation but data suggest that [2+2] and [1+1] metallomacrocyles were formed, with siloxane linking groups encouraging the formation of [1+1] species. Solid-state NMR spectroscopic data on [Cu(L1)](PF₆) indicate the presence of two different environments for the PF₆^- anions.

Full text of DOI:10.1002/ejic.201101414

FULL PAPER
DOI: 10.1002/ejic.201101414
Coordination Chemistry of α-ω-Bis(pyridylimine) Ligands Containing Flexible
Linkers with Copper(I)
Zhenzhong Hu,[a] Celine M. Schneider,[a,b] Christina N. Price,[a] Whitney M. Pye,[a]
Louise N. Dawe,[a,c] and Francesca M. Kerton*[a]
Keywords: Supramolecular chemistry / Copper / N ligands / Coordination modes / Supercritical carbon dioxide
Copper(I) complexes of a series of six potentially tetradentate
bis(pyridylimine) ligands were prepared, where the pyr-
idylimine groups were separated by different linking units
[in L1, CH2CH2CH2(SiMe2O)20SiMe2CH2CH2CH2; in L2,
CH2CH2CH2SiMe2OSiMe2CH2CH2CH2; in L3, CH2CH2; in
L4, CH2(CH2)4CH2; in L5, CH2(CH2)7CH2; in L6,
CH2CH2CH2OCH2CH2OCH2CH2OCH2CH2CH2]. The solu-
bilities of L1, L2 and [Cu(L2)](PF6) in supercritical carbon di-
oxide were determined. The coordination chemistry of L1–L2
with CuI was studied by UV/Vis, multinuclear NMR and IR
spectroscopy, MALDI-TOF and ESI mass spectrometries and
elemental analysis. These data suggested that [1+1] com-
plexes had formed. Dicopper complexes of L3–L6 were pre-
pared for comparison, and [Cu2(L5)2](PF6)2 characterized by
single-crystal X-ray diffraction analysis. Close methylene C–
H···π interactions are observed within the structure. PGSE
NMR spectroscopy was used to determine the hydrodynamic
radii of the species in solution and comparison of these data
with computational models for the complexes was made.
Freezing point depression measurements afforded molecular
weights for solution-state species in agreement with the for-
mulations proposed via NMR and mass spectrometric data.
There is no evidence to support linear metallopolymer forma-
tion but data suggest that [2+2] and [1+1] metallomacrocyles
were formed, with siloxane linking groups encouraging the
formation of [1+1] species. Solid-state NMR spectroscopic
data on [Cu(L1)](PF6) indicate the presence of two different
–
environments for the PF6 anions.
water oxidation,[3] and have also been used extensively in
olefin dimerization, oligomerization and polymerization ca-
talysis.[4] We have recently used such ligands in catalytic aer-
obic oxidation reactions of alcohols.[5] Therefore, we de-
cided to study their coordination chemistry in more detail
to better understand catalytic reactions employing them
and possible intermediates that might form.
Introduction
A number of research groups, including our own, have
previously used mono end-capped polydimethylsiloxane
(PDMS) in green chemistry and other applications,[1] in-
cluding the preparation of CO2-philic molecules with po-
tential uses in green catalysis.[1a,1e,1f] Difunctional PDMS,
containing ligating groups at either end of a PDMS chain,
has been explored to a lesser extent in the field of coordina-
tion chemistry and catalysis. In such a situation, the ligands
could bind to metal centres in a number of ways, Figure 1.
Tritopic ligands separated by short PDMS chains have been
used by Lehn and co-workers to prepare metal-containing
extended polymers that can be processed into films with
potential sensor applications.[2] Pyridylimine-based ligands
have recently found applications in the field of catalytic
[a] Department of Chemistry, Memorial University of
Newfoundland,
St. John’s, NL, A1B 3X7, Canada
Fax: +1-709-864-3702
E-mail: fkerton@mun.ca
[b] NMR Laboratory, Centre for Chemical Analysis, Research and
Training, Memorial University of Newfoundland,
St. John’s, NL, A1B 3X7, Canada
[c] X-ray Crystallography Laboratory, Centre for Chemical
Analysis, Research and Training, Memorial University of
Newfoundland,
St. John’s, NL, A1B 3X7, Canada
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101414.
Figure 1. Schematic representation of possible binding modes for
bridging/linked ligands.
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F. M. Kerton et al.
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bilities of L1 and L2 in scCO2 were assessed. L2 was mis-
cible in liquid CO2 at room temperature. Cloud point data
for L1 over the temperature range 60–100 °C were mea-
sured, Figure 3. Copper complexes of these ligands were
prepared, see below, and their solubility in scCO2 gauged.
Significantly higher temperatures and pressures were
needed to dissolve [Cu(L2)](PF6) compared with the unco-
ordinated parent ligand L2, presumably due to the ionic
nature of the metal complex. Unfortunately, [Cu(L1)](PF6)
was insoluble in CO2 at all temperatures and pressures
studied (25–120 °C, 4000–7500 psi).
Results and Discussion
The coordination chemistry of L1–L6, Figure 2, with
copper(I) is described below. L3 has been widely studied
by others,[6] and was included in this work for comparative
purposes.
Figure 2. Ligands used in this study.
Preliminary Studies Using L1
Figure 3. Cloud point data for L1 and [Cu(L2)](PF6), measure-
As we had previously worked with PDMS-derived li-
gands,[1a] we studied the chemistry of L1 first. The poly-
meric starting material PDMS-NH2 and L1 were charac-
ments made using a SFT phase monitor II.
1
terized using H NMR, 13C{1H} NMR, FT-IR, MALDI-
Initial investigations into the coordination chemistry of
TOF mass spectrometric (MS) data and elemental analyses. L1 were performed via UV/Vis spectroscopy, Figure 4. The
GPC analysis confirmed that no polymer degradation or spectra of [Cu(CH3CN)4](PF6) and L1 show no ab-
coupling occurred during the synthesis of L1 as its retention sorbances in the visible region. However, a MLCT band
volume was nearly identical to PDMS-NH2. The number was seen to grow in intensity relative to an increase in con-
of dimethylsiloxane repeat units (n) was determined using centration of copper(I) ions. This band reached a maximum
end-group analysis of the 1H NMR spectrum and elemental intensity (λ = 465 nm, ε = 21000 Lmol–1 cm–1) when there
analysis to be 20. It should be noted that increased relax- was one copper(I) ion per each L1 corresponding to a [1+1]
ation times were used to obtain spectra where resonances complex forming where each copper ion is surrounded by
could be integrated with greater accuracy. However, MS two chelating pyridylimine groups. This initial titration was
analysis revealed that L1 had Mw 1567, Mn 1317 and a performed in air but all further coordination chemistry ex-
resulting polydispersity of 1.19. This corresponds to n = 16, periments were performed under strictly air- and moisture-
but this low value could be a result of poor signal-to-noise free conditions to avoid oxidation of the copper ion. The
ratio in the high mass region of the spectrum. Overall, the reaction was then performed on a synthetic scale and the
spectrum had a similar appearance to that of its coordina- resulting solid characterized using FT-IR, NMR, MALDI-
tion complex (see below and Supporting Information) in TOF MS, GPC and elemental analyses. These data support
that the peak separations (74 mass units), their intensities the self-assembly of a [1+1] metallocyclopolymeric com-
and isotope patterns are typical for monodisperse PDMS plex, [Cu(L1)](PF6). The GPC chromatogram (using refrac-
chains.[7] Such monodisperse chains will have a narrow tive index detection) contained a single, inverted peak at a
polydispersity (between 1.1 and 1.5), where polydispersity retention volume nearly identical to L1 and PDMS-NH2.
is the ratio of Mw/Mn (Mw = weight average molecular Due to the inversion of this peak (it appeared below the
weight and gives greater statistical weighting to heavier mo- baseline of a control run as opposed to above it), mass data
lecules, Mn = number average molecular weight and gives could not be obtained through conventional calibration
greater statistical weighting to lighter molecules). When against polystyrene standards. However, in contrast to pre-
polydispersity is 1.0, all of the polymer chains will be of viously characterized [1+1] metallocyclopolymers,[8] MS
exactly the same weight and length.
analyses show no evidence for larger [2+2] or other species.
In our previous studies, monodentate PDMS-derived li- MALDI-TOF MS data, Table 1, revealed that the [Cu-
gands and their Pd complexes were found to be soluble in (L1)]+ cations had Mw 1710, Mn 1382 and a polydispersity
supercritical carbon dioxide (scCO2).[1a] Therefore, the solu- of 1.24. Modeling of ESI MS data also supported this for-
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Copper Complexes Containing Flexible Linkers
mulation. On comparing the Mn values of the complex ion MLCT band at 475 nm (ε = 16 000 Lmol–1 cm–1). The fre-
with the free ligand L1, a difference of 65 mass units is quency of this absorbance is similar to that reported for
obtained that is close to the molecular weight of Cu. Also, the known dicopper(I) helicate complexes of L3,[10] but the
inspection of individual peaks within the mass spectrum molar extinction coefficient for the MLCT of the L1 and
showed an isotopic match corresponding to the presence of L2 complexes is much greater. The presence and energy of
one copper atom and not two per polymer chain. However, the MLCT band is in good agreement with the calculated
at this stage, we could not overlook the possibility of either energies of the frontier orbitals for [Cu(L2)](PF6) (Support-
a gas-phase rearrangement/fragmentation within the mass ing Information). FT-IR data for our complexes are similar
spectrometer or the possibility of equilibration to yield the to structurally verified copper(I) and nickel(II) complexes
[1+1] complex from larger [n+n] species in solution during of bidentate and tetradentate pyridylimine ligands.[6g,6j,11]
chromatographic analysis. We were intrigued by these re- However, both the electronic and vibrational spectroscopic
1
sults because, as far as we are aware, there are very few data would be alike for [1+1] and [2+2] species. H and 13C
examples of [1+1] metallocycles,[8–9] and if the ligands are solution NMR spectroscopic data for [Cu(L1)](PF6) and
separated by flexible, long bridging groups, there is a ten- [Cu(L2)](PF6) show the expected number of resonances,
dency for mixtures to form.
which are moderately shifted compared to the free ligands.
1H-1H coupling observable for the pyridyl protons in the
free ligand was not observed in the complexes presumably
due to the fluxionality of coordinate covalent bonds in solu-
tion leading to signal broadening. Through parallels with
known copper(I) pyridylimine complexes,[6a,6i,12] processes
including inter- and intramolecular ligand exchange
through twisting at the metal or ligand dissociation are
thought to occur. Oxidation of the copper centre might also
be the cause of signal broadening in these NMR spectra.
However, EPR spectra of these samples were silent and gave
no indication of the presence of copper(II).
Discussion of Mass Spectrometric Data for Copper(I)
Complexes of L1–L6
Figure 4. UV/Vis spectra for the titration of L1 with [Cu(CH3CN)4]-
(PF6) in CH2Cl2; Cu = [Cu(CH3CN)4](PF6) only, L1 = L1 only,
molar equiv. of Cu with respect to L1 from 0.2 to 1.0.
L3–L6 were prepared and their reactions with
[Cu(CH3CN)4](PF6) investigated in order to obtain greater
insight into the chemistry of L1 and L2. L4 has been ex-
plored to some extent previously,[13] and L3 studied exten-
sively by other chemists.[6] [Cu2(L3)2](PF6)2 and [Cu2(L3)2]-
(ClO4)2 have been structurally characterized.[6i,6j] The cen-
tral dicopper(I) helicate cation was determined to be 13.7 Å
in diameter. A [1L + 2Cu] complex, [Cu2(L3)(PPh3)2I2], has
also been structurally characterized.[6f] An extensive study
of copper complexes of L3 and related ligands has been
performed by Fabbrizzi and co-workers involving spectroe-
lectrochemistry and mass spectrometric monitoring of the
assembly and disassembly of the copper helicates.[10] They
propose the formation of [CuI(L)]+ complexes upon re-
duction of the analogous copper(II) ion and prior to the
self-assembly of the typical copper(I) bimetallic bis(ligand)
helicates. The lifetimes of the intermediate [CuI(L)]+ species
were assessed to be less than 20 ms, however, their presence
in this cycle shows that the formation of such complexes is
not thermodynamically barred rather that there is a kinetic
Table 1. Comparison of mass data for complexes of L1, L2 and
L5.[a]
Complexes
Theoretical
Mw from freezing Mw from MS
Mw
point depression
[Cu(L1)]+
[Cu(L2)]+
1895.5[b]
1740
540[c]
980
Mw 1710
Mn 1382 (MALDI)
489.3 (MALDI)
489.2 (ESI)
489.2
[Cu2(L5)2]2+ 798.3
943.3(MALDI)
–
[a] Data obtained for PF6– species unless otherwise indicated, (PF6
= 145.0 gmol–1). [b] Exact mass value, [Cu2(L1)2]2+ Mw = 3791. [c]
BF4 complex (BF4 = 86.8 gmol–1).
–
–
Preliminary Studies Using L2 as a Low Molecular Weight
Model of L1
Due to the scarcity of well-characterized [1+1] com- preference for the helicate structures with these particular
plexes,[8–9] we undertook the synthesis of a low molecular ligands.
weight analog using L2. Spectral data for the resulting com-
In 1984, van Koten and co-workers reported extensive
pound agreed with the formulation [Cu(L2)](PF6). For ex- NMR studies on the dynamic behavior and solution-state
ample, the mass spectrum (positive mode) contained a sin- structures of pyridylimine complexes of AgI and CuI includ-
gle peak at an m/z and isotope match corresponding to [Cu ing [Cu2(L3)2](O3SCF3)2,[6a,12] using 1H, natural-abundance
+ L2]+, Table 1. Furthermore, UV/Vis analysis showed a INEPT 15N and INEPT 109Ag NMR experiments. Where
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F. M. Kerton et al.
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present the nature of the bridging C2 chain between the fusion coefficients of solution-state species and in turn this
pyridylimine ligands was determined to be the major influ- data can be used to obtain molecular sizes.[15] In the ab-
ence on intramolecular fluxional processes.[6a] FD mass sence of structural data, and for comparison with NMR
spectra for the complexes in that study confirmed the for- spectroscopic data, MMFF- and semi-empirical PM3-cal-
mation of dimetallic dications including [Cu2(L3)2]2+. More culations were performed using SPARTAN ’08 software to
recently, ESI mass spectra for [CuII(L3)](CF3SO3)2 showed obtain approximate radii for the compounds in their geom-
a peak at m/z 450 corresponding to {[Cu(L3)]CF3SO3}+ etry optimized equilibrium [1+1] and [2+2] forms (Figure 5
and for [CuI2(L3)2](ClO4)2 showed a peak at m/z 701 corre- and Table 1). The relative stability of the two complexes was
sponding to {[Cu2(L3)2]ClO4}+.[10] In ESI experiments per- determined to be very similar and therefore, no conclusions
formed in our laboratory, the mass spectrum for the cop- regarding a thermodynamic preference for either form
per(I) complex of L3 contained a peak at m/z 747 corre- could be made.
sponding to {[Cu2(L3)2]PF6}+. However, even with the
The hydrodynamic radii, rH, of the [CunLn]n+ species in
fragmentor voltage set to low, all coordination compounds solution were determined from the sample diffusion coeffi-
reported in this paper afforded spectra containing 100% in- cients, D, Table 2, once a proper model (spherical model,
tensity peaks which could be assigned to [Cu + L]+ on the ellipsoidal-prolate or ellipsoidal-oblate model) and equa-
basis of m/z and isotope patterns. It should be noted that tion had been chosen. Data from these diffusion studies,
[Cu2(L)2]2+ species would appear at the same m/z positions alongside computational studies, clearly suggest that L1
as [Cu + L]+ ions but would possess significantly different and L2 form [1+1] metal-ligand complexes. For
isotope patterns. It should also be noted that care was taken [Cu(L1)](PF6), the experimentally determined radius from
to avoid oxidation of the copper(I) complexes in this study PGSE data was 13.7Ϯ0.1 Å, which is much closer to the
and therefore, the peaks in the mass spectra are not from computationally modeled radius of the [1+1] complex
copper(II) species. Furthermore, EPR spectra were silent (12.3 Å) than the [2+2] species (24.0 Å). The radius ex-
strongly suggesting that copper(II) was not present. For L2, tracted from NMR spectroscopic data for copper(I) com-
L4–6, ESI mass spectra showed no peaks that could be as- plexes with L3 or L5 showed reasonable agreement with
signed to bimetallic species. Mass spectra for the polymeric that derived from X-ray diffraction data for the [2+2] spe-
ligand L1 and its copper complex were discussed above. cies. For example, in solution [Cu2(L3)2](PF6)2 was deter-
These data were obtained using a MALDI-TOF mass spec- mined to have a radius of 7.9Ϯ0.1 Å from NMR spectro-
trometer. Therefore, we studied the complexes of L2–L6
using this method. Using this type of ionization, bimetallic
ions were observed for L4–L6. The molecular ion region of
the mass spectra and theoretical isotope patterns for
{[Cu2(L)2]PF6}+ (L = L4, L5 or L6) are available in Sup-
porting Information. Numerous MS spectra of L1–L2 com-
plexes were obtained but none showed evidence of bimetal-
lic species. These results highlight that, if numerous related
coordination complexes (monometallic, bimetallic, trime-
tallic etc.) could potentially be formed, it would be advis-
able to perform as broad a range of mass spectrometric ex-
periments as possible to confirm initial results and data ob-
tained using one technique.
Due to the range of different gas phase ions observed
through mass spectrometry, freezing point depression ex-
periments were performed in order to get solution phase
values for comparison. Data from DMSO solutions of com-
plexes are presented in Table 1 and show reasonable agree-
ment with mass spectrometric-derived formulations.
PGSE NMR Studies of Copper(I) Complexes of L1–L6
In order to confirm the formation of the unusual large-
sized [1+1] metallocyclic species [Cu(L1)](PF6) in solution,
other analytical methods were pursued. Recently, Constable
and co-workers have shown that Pulse-field gradient spin-
Figure 5. Molecular models of [Cun(L1)n](PF6)n (n = 1 and 2) and
echo (PGSE) NMR spectroscopy is a valuable technique to
[Cu2(L6)2](PF6)2, obtained using SPARTAN ’08 software [ground
use in determining the size and, therefore, the major species
state equilibrium geometry, semi-empirical (restricted Hartree–
Fock) PM3 calculation from an initial geometry obtained via
in solution for [ConLn][PF6]3n metallomacrocyles.[14] PGSE
diffusion NMR spectroscopy can be used to obtain dif- MMFF calculation].
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Copper Complexes Containing Flexible Linkers
Table 2. Measured solution viscosity (η) and solution diffusion coefficients (D), calculated hydrodynamic radii, rH, for copper coordination
compounds and computationally modeled or known radii for [1+1] and [2+2] species.
Complexes
η
D
rH
[Å]
[1+1][a]
[Å]
[2+2][a]
[Å]
[10–3 kgs–1 m–1]
[10–9 m2 s–1]
[Cu(L1)](PF6)
0.70
0.41
0.29
0.28
0.35
0.38
0.54Ϯ0.06
2.50Ϯ0.12
3.44Ϯ0.21
2.94Ϯ0.06
1.96Ϯ0.07
1.18Ϯ0.02
13.7Ϯ0.1
4.1Ϯ0.2
4.0Ϯ0.5
7.9Ϯ0.1
9.6Ϯ0.4
14.8Ϯ0.3
12.3
6.4
6.4
4.8
5.1
5.6
24.0
10.5
10.5
6.8[b]
9.9
10.5,
10.6[c]
10.4
[Cu(L2)](PF6)
[Cu2(L2)2](BF4)2
[Cu2(L3)2](PF6)2
[Cu2(L4)2](PF6)2
[Cu2(L5)2](PF6)2
[Cu2(L6)2](PF6)2
0.34
2.06Ϯ0.25
9.7Ϯ1.1
6.4
[a] Unless otherwise indicated, approximate radii for the compounds in their geometry optimized equilibrium forms obtained through
MMFF- and semi-empirical PM3-calculations using SPARTAN ’08 software. [b] The radius for [Cu2(L3)2]2+ in the solid-state from
crystallographic data reported in ref.[6i] [c] The radius of [Cu2(L5)2]2+ in the solid-state from crystallographic data reported herein.
scopic data and in the solid-state it has been shown to have metallopolymer, as by analogy to Lehn and Chow’s results
a radius of 6.8 Å. Also, hydrodynamic radii data and com- an elastomeric polymer would be expected due to the flexi-
putational studies clearly suggest that L4 and L6 form bi- ble nature of the PDMS linking group.[2]
metallic dicationic complexes in solution. Furthermore, the
Extensive efforts were made to grow and isolate crystals
NMR-derived radii for the copper complexes with all li- of the complexes reported herein. One sample of [Cu2(L5)2]-
gands showed good agreement with the formulation deter- (PF6)2 upon storage at –20 °C in a methanol solution for
mined from mass spectrometric evidence, Table 1 and Exp. over one year afforded brown crystals amenable to single-
Section.
crystal X-ray diffraction analysis. The asymmetric unit con-
tained two independent half complexes and two half-occu-
pancy methanol molecules. Closer inspection of the coordi-
nation environment around copper reveals that Cu1–N2 is
significantly shorter [1.770(7) Å; Figure 6] than the other
Cu–N bond lengths [1.979(6)–2.068(8) Å]. The second mo-
lecule in the dimer contains typical Cu–N bond lengths for
copper-imine and copper-pyridine interactions (Figure 7).
This X-ray determined structure confirms the dimetallic na-
ture of the L5 species formed, which was proposed through
mass spectrometric, PGSE NMR and freezing point de-
pression data. Furthermore, the radius of the complex is in
good agreement with that determined through PM3-calcu-
lations, Table 1.
X-ray Diffraction Data
Unfortunately to date, we have been unable to obtain
single crystals of our model complex, [Cu(L2)](PF6), to un-
ambiguously confirm the cyclic [1+1] nature of the silox-
ane-containing complexes in the solid-state. However, over
the course of our studies, we noticed that during solvent
evaporation from solutions of [Cu(L1)](PF6) dark-coloured
seed crystals formed on the surface of the glassware. Upon
further inspection under a microscope, these crystalline do-
mains became more visible, especially under cross-polarized
light (Supporting Information). At room temperature, pow-
der X-ray diffraction analysis of [Cu(L1)](PF6) showed two
intense, sharp peaks at a constant Bragg angle 2θ of 0.42°
and 1.44°. These correspond to d-spacings of 210.1 Å and
61.3 Å. Both are significantly longer than the predicted dia-
meter of the metallocyclopolymer, which is calculated to be
24.6 Å for a [1+1] complex and 48.0 Å for a bimetallic [2+2]
complex. Therefore, bimolecular (or greater) aggregration
must exist within the crystalline phase. Recently, Gloe and
co-workers reported the remarkable self-assembly of three
hexametallic copper(II) meso-helicates, [CuL(SO4)]6·24H2O
where L is a linked bis-pyridylimine ligand, that were circu-
lar in shape.[16] The self-assembly was controlled by the co-
ordination of sulfate ions with the copper(II) centres. The
diameter of these structures in the solid-state was deter-
mined to be 31–32 Å by single-crystal X-ray diffraction
analysis. At this stage, a multimetallic structure similar to
these cannot be ruled out for the L1 complex in the solid-
state. Although, in solution and in the gas phase [1+1] spe-
cies dominate, as discussed earlier. However, the crystalline
Figure 6. 30% probability ellipsoid representation of one of the two
bimetallic moieties, {Cu2(L5)2} (H-atoms omitted for clarity). Sym-
metry codes: (i) x, y, z (ii) x, 1.25 – y, 1.25 – z. Selected bond lengths
[Å] and bond angles [°]: Cu1–N2 1.770(7); Cu1–N3 1.983(7); Cu1–
N4 2.062(8); Cu1–N1 2.069(8); Cu2–N7 1.979(6); Cu2–N6
1.990(7); Cu2–N5 2.047(8); Cu2–N8 2.054(7) N2–Cu1–N3
140.9(3); N2–Cu1–N4 113.0(3); N3–Cu1–N4 80.9(3); N2–Cu1–N1
83.6(3); N3–Cu1–N1 119.2(3); N4–Cu1–N1 125.1(3); N7–Cu2–N6
140.6(3); N7–Cu2–N5 118.0(3); N6–Cu2–N5 82.1(3); N7–Cu2–N8
nature of the complex does rule out a supramolecular linear 82.2(3); N6–Cu2–N8 112.2(3); N5–Cu2–N8 129.4(3).
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F. M. Kerton et al.
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cell; that is, two methanol molecules are contained in each
void, consistent with the maximum number of expected
methanol molecules based on their volume in the liquid
phase (ca. 67.2 Å3).
Solid-State NMR Studies
In an attempt to confirm the presence of cyclic species
in the solid-state, MAS NMR experiments were performed
[Cu(L1)](PF6) and [Cu(L2)](PF6), Figure 9. As a baseline
for comparison, data was also obtained for [Cu(CH3CN)4]-
(PF6), see Supporting Information. The 19F NMR spec-
trum in solution exhibits a doublet at δ = –75 ppm, JP,F
=
711 Hz with a relaxation time T2* of 72.0 ms. In the solid-
state, the signal shifts to higher frequency, –67 ppm, JP,F
remains unchanged and T2* decreases to 2.0 ms. T2* relax-
ation times are a reflection of the mobility (or tumbling) of
the nucleus. Therefore, values in solution are typically much
larger than solid-state values. The solid-state 31P NMR
spectrum of [Cu(CH3CN)4](PF6) exhibits a sept at δ =
–142 ppm, JP,F = 709 Hz and T2* of 5.2 ms. This frequency
and coupling constant is typical for a non-constrained
hexafluorophosphate anion in the solid-state.[17] 19F NMR
spectra of [Cu(L1)](PF6) and [Cu(L2)](PF6) in solution dis-
play the expected doublet resonance (Supporting Infor-
mation), but in the solid state [Cu(L1)](PF6) is significantly
different to the other species studied. The relaxation time
for the 31P environment is significantly shorter for the L1
complex (0.34 ms) compared with the L2 complex (1.26 ms)
and [Cu(CH3CN)4](PF6) (5.2 ms). This leads to significant
broadening of the resonances for the L1 species. The dra-
matically shorter T2* and T2 values suggest that the anions
are held in a much more rigid environment in the cyclopoly-
mer complex. Furthermore, for [Cu(L1)](PF6) the broad
Figure 7. Dimer unit, [Cu2(L5)2]2, showing close methylene C–H···π
interactions (30% probability ellipsoids); disordered carbon-chain
–
atoms, PF6 ions and lattice solvent CH3OH omitted for clarity.
Each dimer [Figure 7; symmetry related atoms generated
by (x, 1.25 – y, 1.25 – z)] is generated by the intersection of
one twofold proper rotation axis and one twofold screw
axis, with one molecule aligned lengthwise with the b axis,
and the other with the c axis. Very close intermolecular
methylene C–H···π interactions are present, with C11–
H11B···Cg1 3.07 Å and C31–H31B···Cg2 2.94 Å [where
Cg1 and Cg2 are the centroids of the rings formed by (N8,
C38-C42) and (N1, C1–C5), respectively; these are indi-
cated by dashed lines in Figure 7]. Such C–H···π interac-
tions may in part be the cause of the different formulation
observed for copper complexes of the siloxane-derived li-
gands, as the –OSiMe2– linkers would not facilitate this
phenomenon. The unit cell contains 16 solvent accessible
volumes (each measuring 181–182 Å3) that run parallel to
the c-axis, centered with average x and y positions given by
(nx/8, my/8) (where n and m = 1, 3, 5, 7; these lie on twofold
proper rotation axes), occupied by disordered methanol
molecules (Figure 8; solvent and H-atoms omitted for clar-
ity). The model contains 32 methanol molecules per unit
Figure 9. Solid-state NMR spectra for (a) [Cu(L1)](PF6), 19F-
NMR δ = –65 (v. br.) (deconvoluted as two environments) δ = –67
(F1 35%), –60 (F2 65%), 31P-NMR: δ = –139 (v. br.), JF-P
=
Figure 8. Packed unit cell, viewed down the c axis. H-atoms, disor-
dered carbon-chain atoms, PF6 ions and lattice solvent CH3OH
omitted for clarity.
685 Hz, T2 = 0.46 ms, T2* = 0.34 ms; (b) [Cu(L2)](PF6), 19F-NMR
δ = –70 (br.), 31P-NMR δ = –141 (sept), JF-P = 711 Hz, T2
2.81 ms, T2* = 1.26 ms (*: spinning side bands).
=
–
1778
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1773–1782

Copper Complexes Containing Flexible Linkers
19F resonance, –65 ppm, can be modeled as two 19F envi-
ronments, –67 and –60 ppm, with occupancies of 35% and
65% respectively. These unusual differences in NMR spec-
troscopic data could be interpreted in a number of ways.
We tentatively propose that in [Cu(L1)](PF6) some of the
anions are held within cyclic or cage structures like a metal
ion within a crown ether and therefore, have restricted mo-
tion compared with the small molecule L2 analog where the
anion cannot fit inside the macrocycle or cage. Hydrolysis
eter. Chemical shifts were reported in ppm using the residual pro-
tons of the deuterated free CDCl3 or tetramethylsilane as an in-
ternal reference. Tetramethylsilane-free deuterated solvents were
used in the collection of NMR spectra for all siloxane containing
species. For polymeric samples in solution, delays were increased
to allow complete relaxation of all protons and to obtain more
accurate integration. For L1, L2 and their copper complexes,
MALDI-TOF mass spectroscopic data were obtained using an Ap-
plied Biosystems Voyager mass spectrometer. Dithranol was used
as the matrix. For copper complexes of L2, L4–L6, mass spectro-
of the PF6– anion or oxidation of the copper ion were ruled scopic data were obtained using an ABI QSTAR XL (Applied
Biosystems/MDS Scies, Foster City, USA) hybrid quadrupole TOF
MS/MS system equipped with an oMALDI 2 ion source. Dihy-
droxybenzoic acid (DHB) was used as the matrix. Also, for copper
complexes of L1–L6, ESI-MS spectra were recorded using direct
injection into an Agilent 1100 LC/MSD (G1946A) instrument in
ESI mode (solvent: acetonitrile, concentration: 1 mg/mL). The cap-
illary voltage of the instrument was 3000 V and the fragmentor
voltage was varied through low, medium and high settings for all
samples. X-ray Powder Diffraction data were obtained on a Rigaku
Ru-200 12 kW Automated Powder Diffractometer. Polarized
microphotos were obtained using a Leica DM 2500 microscope. A
Bruker TENSOR 27 spectrometer was used to record FT-IR spec-
tra. Gel permeation chromatographs (GPC) were obtained using a
Viscotek VE 2001 instrument equipped with RI detector using the
following condition: column type: Poly[Analytik]n, PAS-106M-H,
8.0 mm (ID)ϫ300 mm (L); flow rate: 1.0 mL/min; solvent: chloro-
benzene. UV/Vis spectra were recorded using an Ocean Optics UV/
Vis spectrometer. TGA spectra were measured by Universal V4.5A
TA instrument. Solubility studies on ligands and complexes in su-
percritical carbon dioxide were performed using a Supercritical
Fluids Technologies Phase Monitor II (SFT PM II). Freezing point
depression measurements were obtained using a LabQuest data ac-
quisition unit, a temperature probe and solutions of the copper
complexes in DMSO (HPLC grade). Homogeneous solutions were
prepared by heating the metal complexes in DMSO at 36 °C over-
night and measurements made while slowly cooling the solutions
in an ice salt bath. Using benzophenone as a standard, Kf (the
molal freezing point constant) for DMSO was determined to be
4.20 K mol–1 kg. EPR experiments were performed on a Mag-
nettech benchtop EPR spectrometer MiniScope MS100.
out as the reasons for the signal broadening and the pres-
ence of two environments in the 19F MAS NMR spectrum,
because (i) if the same sample is dissolved and solution
NMR spectroscopic data is obtained a single environment
is observed, and (ii) ESI MS showed no evidence of PF6
hydrolysis or copper oxidation (z = 2 ions should be evident
–
if oxidation occurred). Also, EPR spectra were silent.
Conclusions
In summary, we have found that chelating pyridylimine
ligands separated by a low molecular weight dimethylsilox-
ane or polymeric PDMS group can form [1+1] metall-
ocycles. We tentatively propose that this is due to their in-
ability to undergo C–H···π interactions due to their in-
creased steric demand compared with –(CH2)n– and
–(CH2O)n– bridging units. Some of the siloxane-derived
compounds are soluble in scCO2. PGSE NMR spec-
troscopy was useful in ascertaining the size of these and
related complexes in solution and in confirming the forma-
tion of [1+1] or [2+2] species suggested from mass spectro-
metric data. For L5, crystals were grown and X-ray diffrac-
tion analysis confirmed its [2+2] nature. The extended
structure of this complex exhibited interesting packing in
the solid-state. Solid-state 19F NMR spectroscopic data for
the polymeric metallocycle (L1 complex) suggests two envi-
ronments exist for the hexafluorophosphate anion. We pro-
pose that the anion could reside both inside and outside a
cycle or cavity, which is feasible given the size and resulting
cavity in the proposed [1+1] species.
Computational Studies: Molecular model structures were obtained
using SPARTAN ’08 software [ground state equilibrium geome-
tries, semi-empirical (restricted Hartree–Fock) PM3 calculations
from initial geometries obtained via MMFF calculations]. Using
SPARTAN ’06 software, a higher level calculation was performed
on [Cu(L2)]PF6 (a restricted hybrid HF-DFT SCF calculation per-
formed using Pulay DIIS + Geometric Direct Minimization,
Method: RB3LYP, Basis set: 6-31G(D). Images representing the
frontier orbitals in this molecule are presented in the Supporting
Information.
Experimental Section
General Information: All reactions were carried out under dry nitro-
gen using standard Schlenk-line techniques. THF was dried and
distilled from sodium benzophenone ketyl, whilst CH2Cl2 was dried
and distilled from CaH2. 2-Pyridinecarbaldehyde, tetrakis(aceto-
nitrile)copper(I) hexafluorophosphate and other reagents unless
specified were purchased from Aldrich and used as received.
PDMS-NH2 [H2N(CH2)3(SiMe2O)20SiMe2(CH2)3NH2] and 1,3-
Bis(aminopropyl)tetramethyldisiloxane were purchased from Gel-
est. The ligands L1–L6 were prepared as described previously.[5]
Elemental analyses were performed by Canadian Microanalytical
Service Ltd. (Delta, BC). 1H-NMR spectra were acquired on a
Bruker AVANCE 500 MHz spectrometer. 13C{1H}-, 19F- and 31P-
NMR spectra were acquired on a Bruker AVANCE 300 MHz spec-
trometer. 19F-NMR and 31P-NMR solid-state (and some solution)
spectra were acquired on a Bruker AVANCE II 600 MHz spectrom-
Crystallographic Procedures: A crystal of [Cu2(L5)2](PF6)2·CH3OH
was mounted on a low temperature diffraction loop and measured
on a Rigaku Saturn CCD area detector with graphite monochro-
mated Mo-Kα radiation (Table 3). The structure was solved by di-
rect methods[19a] and expanded using Fourier techniques.[19b] Neu-
tral atom scattering factors were taken from Cromer and Waber.[19c]
[19d]
Anomalous dispersion effects were included in Fcalc
;
the values
for ΔfЈ and ΔfЈЈ were those of Creagh and McAuley[19e] The values
for the mass attenuation coefficients are those of Creagh and Hub-
bell.[19f] All calculations were performed using CrystalStruc-
ture[19g,19h] except for refinement, which was performed using
SHELXL-97.[19a] All non-hydrogen atoms were refined anisotropi-
Eur. J. Inorg. Chem. 2012, 1773–1782
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1779

F. M. Kerton et al.
FULL PAPER
cally, however, DFIX and SIMU restraints were used to model the
disordered chain [PART 1 C30-C32 and corresponding protons,
0.448(12) occupancy, PART 2 C30A-C32A and corresponding pro-
tons, 0.552(12) occupancy]. All H-atoms were introduced in calcu-
lated positions and refined on a riding model.
NMR (75 MHz, CDCl3, 298 K): δ = 161.3, 150.7, 148.7, 138.5,
128.0, 127.2, 63.6, 24.9, 15.3, 0.4 ppm. 19F NMR (565 MHz, solid
state, 298 K): δ = –70 (br.) ppm. 31P NMR (243 MHz, solid state,
298 K): δ = –141 (sept, JF-P = 711 Hz) ppm. IR (KBr): ν = 2954,
˜
1594, 1443, 1265, 1058, 843, 772, 734, 703 cm–1. MALDI-TOF MS
(matrix: dithranol or dihydroxybenzoic acid): m/z 489.3 [L2 + Cu+].
ESI MS (CH3CN): m/z 489.2 (100) [L2 + Cu+]; found C 41.22, H
5.29, N 8.54. C22H34N4OSi2CuPF6 requires C 41.60, H 5.40, N
8.82%.
Table 3. Summary of crystal data for {[Cu2(L5)2](PF6)2}2.
Compound reference
Chemical formula
Formula mass
Crystal system
a /Å
b /Å
c /Å
[Cu2(L5)2](PF6)2·CH3OH
C43H60Cu2F12N8OP2
1122.02
orthorhombic
20.339(5)
40.0583(10)
51.004(12)
90.00
[Cu(L2)]BF4: 1H NMR (500 MHz, CDCl3, 298 K): δ = 8.59 (s, 2
H), 8.39 (s, 2 H), 8.01 (s, 2 H), 7.87 (s, 2 H), 7.58 (s, 2 H), 3.84 (s,
4 H), 1.81 (s, 4 H), 0.41 (s, 4 H), 0.03 (s, 12 H) ppm. 13C{1H}NMR
(75 MHz, CDCl3, 298 K): δ = 161.3, 150.7, 148.7, 138.5, 128.0,
127.2, 77.6, 77.2, 76.7, 63.6, 24.9, 15.3, 0.4 ppm. MALDI-TOF MS
(matrix: dihydroxybenzoic acid): m/z 489.3 [L2 + Cu+]. ESI MS
(CH3CN): m/z 489.2 (100) [L2 + Cu+]; found C 45.97, H 5.87, N
9.48. C22H34N4OSi2CuBF4 requires C 45.79, H 5.94, N 9.71%.
α /°
β /°
γ /°
90.00
90.00
41555(14)
163(2)
Fddd
Unit cell volume /Å3
Temperature /K
Space group
Z
[Cu2(L4)2](PF6)2: 1H NMR (500 MHz, CD3CN, 298 K): δ = 8.58
(s, 2 H), 8.37 (s, 2 H), 8.07 (s, 2 H), 7.81 (s, 2 H), 7.62 (s, 2 H),
3.73 (s, 4 H), 1.57 (s, 2 H), 1.19 (s, 2 H) ppm. 13C{1H} NMR
(75 MHz, [D6]acetone, 298 K): δ = 162.6, 151.8, 150.0, 139.5, 129.1,
127.8, 60.4, 31.8, 27.4 ppm. 19F NMR (282 MHz, [D6]acetone,
298 K): δ = –73.00 (d, JF-P = 708 Hz) ppm. 31P NMR (122 MHz,
[D6]acetone, 298 K): δ = –144.1 (sept, JF-P = 708 Hz) ppm. IR
32
Radiation type
Absorption coefficient, μ /mm–1
Reflections measured
Independent reflections
Rint
Final R1 [IϾ2σ(I)]
Final wR(F2) (all data)
GOF on F2
Mo-Kα
0.964
73518
7695
0.0558
0.1117
0.3282
1.149
(KBr): ν = 2928, 2857, 1592, 1441, 1302, 1254, 1157, 828, 770 cm–1.
˜
MALDI-TOF MS (matrix: dihydroxybenzoic acid): m/z 859.2 [2L4
+ 2Cu + PF6]+. ESI MS (CH3CN): m/z 357.4 (100) [L4 + Cu]+;
found C 42.71, H 4.35, N 10.97. C18H22N4CuPF6 requires C 42.99,
H 4.41, N 11.14%.
CCDC-857548 (for copper complex of L5) contains the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[Cu2(L5)2](PF6)2: 1H NMR (500 MHz, [D6]acetone, 298 K): δ =
8.91 (s, 2 H), 8.62 (s, 2 H), 8.23 (s, 2 H), 8.07 (s, 2 H), 7.78 (s, 2
H), 3.91 (s, 4 H), 1.71 (s, 4 H), 1.48–0.78 (m, 10 H) ppm. 13C{1H}
NMR (75 MHz, [D6]acetone, 298 K): δ = 162.5, 151.9, 150.1, 139.5,
129.2, 127.9, 60.7, 31.8, 27.7 ppm. 19F NMR (282 MHz, [D6]ace-
tone, 298 K): δ = –72.33 (d, JF-P = 708 Hz) ppm. 31P NMR
(122 MHz, [D6]acetone, 298 K): δ = –144.1 (sept, JF-P = 708 Hz)
General Procedure for Preparation of CuI Complexes:
[Cu(L1)](PF6), [Cu(L2)](PF6), [Cu(L2)](BF4), [Cu2(L3)2](PF6)2,
[Cu2(L4)2](PF6)2, [Cu2(L5)2](PF6)2, [Cu2(L6)2](PF6)2.
ppm. IR (KBr): ν = 2925, 2854, 1592, 1466, 1441, 1302, 1218, 1154,
˜
For [Cu(L1)]PF6: Tetrakis(acetonitrile)copper(I) hexafluorophos-
phate (0.744 g, 2.00 mmol) was added to a Schlenk flask containing
THF (50 mL). This mixture was left to stir until all of the copper
salt had dissolved. L1 (3.64 g, ca. 2.0 mmol) was dissolved in THF
(5 mL) and transferred to the flask containing the copper salt via
cannula. The dark red solution was stirred at room temperature for
24 h. The solvent was removed under vacuum and the product was
isolated as a dark red-brown sticky solid; yield 52%.
830, 771 cm–1. MALDI-TOF MS (matrix: dihydroxybenzoic acid):
m/z 943.3 [2L5 + 2Cu + PF6]+. ESI MS (CH3CN): m/z 399.5 (100)
[L5 + Cu]+; found C 45.84, H 5.07, N 10.59. C21H28N4CuPF6 re-
quires C 46.28, H 5.18, N 10.28%.
[Cu2(L6)2](PF6)2: 1H NMR (500 MHz, CD3CN, 298 K): δ = 8.66
(s, 2 H), 8.46 (s, 2 H), 8.09 (s, 2 H), 7.88 (s, 2 H), 7.66 (s, 2 H),
3.89 (s, 4 H), 3.43 (s, 8 H), 3.37 (s, 4 H), 1.85 (s, 4 H ppm.) 13C{1H}
NMR (75 MHz, CD3CN, 298 K): δ = 162.5, 151.9, 150.0, 139.3,
129.1, 127.7, 71.4, 70.5, 68.5, 57.6, 31.7 ppm. 19F NMR (282 MHz,
CD3CN, 298 K): δ = –72.71 (d, JF–P = 707 Hz) ppm. 31P NMR
(243 MHz, CD3CN, 298 K): δ = –144.5 (sept, JF–P = 707 Hz) ppm.
For the remaining complexes, reactions were performed in CH2Cl2
and stirred at room temperature for 12 h. [Cu(L2)]PF6, [Cu(L2)]-
BF4, [Cu2(L3)2](PF6)2, [Cu2(L4)2](PF6)2 and [Cu2(L5)2](PF6)2, were
isolated as dark red-brown powders; yields 83–88%. [Cu2(L6)2]-
(PF6)2 was isolated as a dark brown powder; yield 90%.
IR (KBr): ν = 2862, 1592, 1466, 1444, 1301, 1260, 1099, 828, 771
˜
cm–1. MALDI-TOF MS (matrix: dihydroxybenzoic acid): m/z
1067.3 [2L6 + 2Cu + PF6]+. ESI-MS (CH3CN): m/z 461.4 (100)
[L6 + Cu]+; found C 43.75, H 4.81, N 9.07. C22H30N4O3CuPF6
requires C 43.53, H 4.98, N 9.23%.
[Cu(L1)]PF6: 1H NMR (500 MHz, CDCl3, 298 K): δ = 8.61 (s, 2
H), 8.44 (s, 2 H), 8.01 (s, 2 H), 7.89 (s, 2 H), 7.58 (s, 2 H), 3.80 (s,
4 H), 1.67 (s, 4 H), 0.53 (s, 4 H), –0.05 to +0.08 (br., 126 H) ppm.
19F NMR (565 MHz, solid state, 298 K): δ = –61, –67 ppm. 31P
NMR (243 MHz, solid state, 298 K): δ = –140 (v.br.) ppm. IR
PGSE NMR Spectroscopy: Diffusion NMR measurements were
performed on a Bruker Avance II 600 NMR spectrometer equipped
with a 5-mm TXI probe and a z-gradient coil with a maximum
strength of 5.35 Gcm–1 at 298 K. Samples were run in CDCl3 and
in CD3CN. The 90° pulse lengths were determined for each sample.
A standard 2D sequence with stimulated echo and spoil gradient
(STEGP) was used. A gradient recovery delay of 2 ms was used
and the relaxation delay was set at 10 s. The gradient strength was
calibrated by using the self-diffusion coefficient of residual HOD
(KBr): ν = 2963, 2359, 1592, 1437, 1301, 1258, 1017, 835, 793, 705,
˜
668 cm–1. MS (MALDI-TOF, matrix: dithranol): Mw = 1710, Mn
= 1382, polydispersity 1.24; found C 35.10, H 7.01, N 2.91.
C60H148N4O20Si21CuPF6 requires C 35.25, H 7.30, N 2.74%.
[Cu(L2)]PF6: 1H NMR (500 MHz, CDCl3, 298 K): δ = 8.59 (s, 2
H), 8.38 (s, 2 H), 8.01 (s, 2 H), 7.88 (s, 2 H), 7.59 (s, 2 H), 3.84 (s,
4 H), 1.81 (s, 4 H), 0.42 (s, 4 H), 0.02 (s, 12 H) ppm. 13C{1H}
1780
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1773–1782

Copper Complexes Containing Flexible Linkers
in D2O (1.9 10–9 m2 s–1). For each experiment, the gradient strength
was increased from 2–95% in 32 equally spaced steps with 16 scans
per increment. Values of d (gradient pulse length) and D (diffusion
time) were optimized on the sample HU-1 (coordination complex
of L1) to give an intensity of between 5 and 10% of the initial
intensity at 95% gradient strength and were set to 1.5 ms and
100 ms respectively for all subsequent samples.
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[4]
The solvent peak was used as an internal standard to measure the
viscosity of each sample. To that end, the diffusion coefficient of
the pure solvent (CDCl3 and CD3CN) was first measured. This
diffusion coefficient D0 corresponds to the known viscosity η0 of
the pure solvent according to the Stokes–Einstein Equation (1).
[5]
[6]
(1)
Therefore for the solvent peak the diffusion coefficient in solution,
Dsol, is afforded by Equation (2).
(2)
Consequently the viscosity of each solution is obtained from Equa-
tion (3).
(3)
[7]
The numerical coefficient B has been shown to vary from 2 to
6π,[18] and can be calculated from the pure solvent diffusion coeffi-
cient too.
[8]
[9]
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3587.
The data were plotted using MestReNova as Peak area vs. Q =
g2δ2G2(Δ – δ/3) and the diffusion coefficient (D) was extracted by
fitting a mono exponential function [I = I0 exp(–D*Q)] with the
data analysis component of the software.
Supporting Information (see footnote on the first page of this arti-
cle): Geometry optimized structure and frontier orbitals of
[Cu(L2)](PF6), mass spectra of [Cun(L)n](PF6)n complexes, UV/Vis
spectrum of [Cu(L2)](PF6), IR spectra of PDMS-NH2, L1 and
[Cu(L1)](PF6), further 19F and 31P NMR spectroscopic data, and
details of diffusion studies.
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Acknowledgments
We gratefully acknowledge financial support from Natural Sciences
and Engineering Research Council of Canada (Discovery Grant
and Undergraduate Student Research Award), the Canada Foun-
dation for Innovation, the Provincial Government of Newfound-
land and Labrador and Memorial University. We thank Prof. Erika
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Received: December 19, 2011
Published Online: February 28, 2012
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