Th(IV) complexes with cis-ethylenebis(diphenylphosphine oxide): X-ray structures and NMR solution studies

Article abstract of DOI:10.1016/j.poly.2015.05.016

The complexation of Th(NO₃)₄ with the rigid diphosphoryl ligand cis-ethylenebis(diphenylphosphine oxide) has been investigated using X-ray crystallography, IR, NMR and CHN analysis. Three crystal polymorphs were grown out of methanol

Full text of DOI:10.1016/j.poly.2015.05.016

Polyhedron xxx (2015) xxx–xxx
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Polyhedron
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Th(IV) complexes with cis-ethylenebis(diphenylphosphine oxide): X-ray
structures and NMR solution studies
Paul T. Morse a, Richard J. Staples b, Shannon M. Biros a,
⇑
a Department of Chemistry, Grand Valley State University, 1 Campus Dr., Allendale, MI 49401, United States
b Center for Crystallographic Research, Department of Chemistry, Michigan State University, 578 S. Shaw Lane, East Lansing, MI 48824, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The complexation of Th(NO3)4 with the rigid diphosphoryl ligand cis-ethylenebis(diphenylphosphine
oxide) has been investigated using X-ray crystallography, IR, NMR and CHN analysis. Three crystal poly-
morphs were grown out of methanolic solution where the 1:3 Th(IV)–ligand complex is ten-coordinate,
and the metal is bound by three bidentate ligands and two nitrato groups. An additional metal–ligand
complex with similar geometry was also grown from the non-coordinating solvent CHCl3. Analysis of
CD3OD and CDCl3 solutions of this complex using 1H and 31P NMR reveals that ligand exchange rates
are fast on the NMR time scale in methanol-d4, and slow on the NMR time scale in chloroform-d.
Further, three additional crystal structures are reported describing the 1:1 and 1:2 Th(IV)–ligand com-
plex, the 1:3 Th(IV)–ligand complex with an extra aqua ligand, and a serendipitous 1:3 Th(IV)–ligand
structure where one ligand bears an epoxide.
Received 5 March 2015
Accepted 12 May 2015
Available online xxxx
Keywords:
Actinide
Crystal structure
NMR
Phosphine oxide
High denticity complex
Published by Elsevier Ltd.
1. Introduction
To this end, investigations into the synthesis and structure of
high-denticity Th(IV) complexes will contribute to each of the
The coordination chemistry of the actinide thorium continues
to gain attention from researchers for uses in catalysis, energy pro-
duction, and the production of new materials. Thorium is found in
small quantities in nearly all rock, soil, and water samples in the
form of 232Th, its major isotope. Additional isotopes of Th have
been identified (228Th, 230Th, 234Th), but these are mainly decay
products of other man-made radionuclides or from absorption in
nuclear reactors. 232Th has a half-life of 14 billion years and emits
diverse set of chemical areas described above. New organic ligands
could find use as sequestering agents for Th(IV) out of nuclear
waste streams, provide stereochemical control for catalytic trans-
formations, or generate new thorium containing materials with
unique properties. Interestingly, out of the over 750,000 structures
in the Cambridge Structural Database [13] only 553 contain
coordination complexes of thorium. Of these 553 reported
structures, less than 100 are greater than nine-coordinate
containing all oxygen donors. The need for additional structural
information describing the coordination geometries available to
this unique element is strong. We contribute to this area here with
radiation through
-emission to give 228Ra and ending with the stable isotope 208Pb.
Due in part to its extremely high melting point (3300 °C), ThO2
a long decay series beginning with an
a
(aka ‘‘thoria’’) has found applications in light bulb elements, lan-
tern mantles and heat-resistant ceramics [1,2]. It is a component
of spent nuclear fuel from uranium-based nuclear reactors, and
has itself been explored as an energy source [3]. There have also
been a wide variety of reports directed toward the use of Th(IV)
complexes as catalysts for chemical transformations [4]. A selec-
tion of reactions mediated by Th(IV) organometallic complexes
include: C–H and C–O bond activation [5,6], hydrosilylation of
alkenes and alkynes [7], hydroamination [7–10], aldehyde
dimerization [11], and phosphonoester hydrolysis [12].
seven new crystal structures containing Th(IV) and a rigid,
bidentate phosphine oxide ligand. The crystallographic work is
accompanied by a complete set of high resolution spectra (IR, 1H
and 31P NMR) used to characterize the isolated complex, as well
as corresponding elemental analysis (CHN) data.
2. Experimental
2.1. Materials and measurements
All chemicals (including deuterated solvents) were purchased
from Sigma–Aldrich, Fisher Scientific, Strem Chemicals, VWR or
Acros Chemicals and used without further purification. 1H, 13C
⇑
Corresponding author. Tel.: +1 616 331 8955; fax: +1 616 331 3230.
E-mail address: biross@gvsu.edu (S.M. Biros).
http://dx.doi.org/10.1016/j.poly.2015.05.016
0277-5387/Published by Elsevier Ltd.
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2
P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
and 31P NMR spectral data were recorded on a Varian Inova 400
FTNMR spectrophotometer. For 1H and 13C NMR, chemical shifts
are expressed as parts per million (d) relative to SiMe4 (TMS,
d = 0), and referenced internally with respect to the protio solvent
impurity. For 31P NMR, chemical shifts are expressed as parts per
million (d) relative to H3PO4 (d = 0). IR spectra were acquired neat
on a Jasco 4100 FT-IR. Elemental (CHN) analysis of ligand 1 was
carried out using a Perkin Elmer 2400 Series II CHNS/O Analyzer.
Elemental (CHN) analysis of the Th(IV) complex was performed
by Atlantic Microlab Inc., Norcross, GA.
2.4. Crystal structure determination and refinement
Data were collected using a Bruker CCD (charge coupled device)
based diffractometer equipped with an Oxford Cryostream
low-temperature apparatus operating at 173 K. The total number
of images was based on results from the program COSMO [16] where
redundancy was expected to be 4.0 and completeness of 100% out
to 0.83 Å. Cell parameters were retrieved using APEX II software [17]
and refined using SAINT on all observed reflections. Data reduction
was performed using the SAINT software [18], which corrects for
Lp. Scaling and absorption corrections were applied using SADABS
[19] multi-scan technique, supplied by George Sheldrick. The
structures were solved either by the direct method or the
Patterson Expansion method using the SHELXS-97 program and
refined by least squares method on F2, SHELXL-97 [20], which are
incorporated in OLEX2 [21,22]. All non-hydrogen atoms are refined
anisotropically. Hydrogens were calculated by geometrical meth-
ods and refined as a riding model. The crystals used for the diffrac-
tion study showed no decomposition during data collection.
Further crystallographic data and experimental details for struc-
tural analysis of all the complexes are summarized in Tables 2, 4
and 7, and selected bond lengths and angles with their estimated
standard deviations are given in Tables 3, 5, 6, 8 and 9. Complete
tables for each structure reported here, along with diagrams
CAUTION!!! Natural thorium (primary isotope 232Th) is a weak
a
-emitter (4.012 MeV) with a half-life of 1.41 ꢀ 1010 years; manip-
ulations and reactions should be carried out in monitored fume
hoods or in an inert atmosphere drybox in a radiation laboratory
equipped with a- and b-counting equipment.
2.2. Synthesis of ligand 1
For the preparation of ligand 1, a slightly modified procedure of
that described by Daigle and co-workers [14] was followed, and
the 31P NMR data from Gallagher et al. was used to confirm the
stereochemistry of the alkene in the final product [15]. cis-
ethylenebis(diphenylphosphine) (0.250 g, 0.631 mmol) was dis-
solved in tetrahydrofuran (2.50 mL) at 290 K. To this solution,
30% H2O2 (0.25 mL) was added drop wise with stirring over
5 min while keeping the solution chilled in an ice bath under an
inert atmosphere of nitrogen gas. The ice bath was removed
20 min after completion of the addition, and the reaction was
allowed to stir for an additional 2 h. The resultant white slurry
was placed in a crystallization dish for 24 h to facilitate solvent
evaporation. The crude product was recrystallized from boiling
benzene (125 mL) and dried under reduced pressure for 24 h to
yield cis-ethylenebis(diphenylphosphine oxide) (cis-dppeO2) 1 as
a white solid (0.178 g, 71% yield). 1H NMR (400 MHz, CDCl3): d
7.72–7.64 (m, 8H), 7.49–7.42 (m, 4H), 7.40–7.18 (m, 10H); 13C
NMR (100 MHz, CDCl3): d 143.3 (dd, JCP = 3.0, 95 Hz, Cipso), 132.7
(dd, JCP = 4.0, 110 Hz, C@C alkene), 132.0 (s, Cpara), 131.6 (dd,
JCP = 5.0, 6.0 Hz, Cmeta); 31P NMR (162 MHz, CDCl3): d 21.6 (s); 1H
NMR (400 MHz, CD3OD): d 7.71–7.63 (m, 8H), 7.62–7.49 (m, 5H),
7.52–7.32 (m, 9H); 31P NMR (162 MHz, CD3OD): d 23.2 (s);
Table 2
Crystal and structure refinement data for 2–3.
Data
Structure 2
78H66N3O15P6Th
Structure 3
Empirical formula
Formula weight
Crystal system
Space group
CCDC number
a (Å)
C
C79H66Cl4N4O18P6Th
1919.02
monoclinic
P21/n
1052127
11.956(3)
51.299(15)
16.463(5)
90.00
95.647(4)
90.00
10048(5)
4
1.268
1.743
1703.19
triclinic
ꢀ
P1
1052114
13.0917(14)
17.0276(18)
19.920(2)
87.449(1)
79.494(1)
81.881(1)
4321.5(8)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.309
1.895
l
(mmꢁ1
)
mp = 228–230 °C, IR (neat)
m = 1490, 1434 (C@C), 1173 (P@O)
cmꢁ1; Anal. Calc. for C26H22O2P2 (found): C, 72.89 (72.58); H, 5.18
Crystal size (mm)
Minimum/maximum
transmission
0.31 ꢀ 0.262 ꢀ 0.141
0.306 ꢀ 0.169 ꢀ 0.122
0.8757
0.7878
(4.89); N, 0.00 (0.03).
hkl ranges
ꢁ15 6 h 6 15,
ꢁ20 6 k 6 20,
ꢁ23 6 l 6 24
15815
13184
0.0789
ꢁ14 6 h 6 14,
ꢁ61 6 k 6 58,
ꢁ19 6 l 6 19
78368
18058
0.0793
2.3. Synthesis of 1:3 Th–ligand 1 complex
Total reflections
Unique reflections
Rint
cis-dppeO2 1 (0.100 g, 0.252 mmol) was dissolved in MeOH
(15.0 mL) at 290 K. To this solution, thorium(IV) nitrate hydrate
(0.037 g, 0.078 mmol) was added. The mixture was stirred for
24 h until it became a homogenous solution. The volatiles were
removed via rotary evaporation and dried via Schlenk line for
24 h to yield the resultant complex, Th(NO3)2-13ꢂ(NO3)2, as a white
solid (0.130 g, 95% yield). 1H NMR (400 MHz, CD3OD): d 7.92–7.72
(m, 2H), 7.71–7.35 (m, 14H), 7.27–7.15 (m, 6H); 31P NMR
(162 MHz, CD3OD): d 31.7 (s); 31P NMR (162 MHz, CDCl3): d 33.9
Parameters
R1 (all data)
910
0.0505
0.0393
0.1034
0.0981
1.335/ꢁ0.759
770
0.1158
0.0890
0.2025
0.1937
2.63/ꢁ2.01
a
a
R1 (I > 2
r
(I))
b
wR2 (all data)
b
wR2 (I > 2
Max/min residual
(e Åꢁ3
r
(I))
)
Goodness-of-fit
1.044
1.093
(GOF) on F2
(s), 31.5 (s), 21.5 (s); IR (neat)
m = 1496, 1438 (C@C), 1141 (P@O)
a
cmꢁ1; Anal. Calc. for C78H66N4O18P6Thꢂ4.5H2O (found): C, 50.74
R1
wR2 = [
=
R
j|Fo| ꢁ |Fc||/ |Foj.
R
b
R
[w(F2o ꢁ F2c)2]/
R .
[wF2o]2]1/2
(50.63); H, 4.09 (4.09); N, 3.03 (3.21).
Table 1
Infrared absorption bands (cmꢁ1) of cis-dppEO (1) and the Th(NO3)2-13ꢂ(NO3)2 complex.
Compound
m(P@O)
m(C@C)
m
(C@C)
m
(N@O)
ma(NO2)
m
s(NO2)
m(NO)
Ionic nitrate
1
1173
1141
1490
1496
1434
1438
–
–
–
1027
–
809
-
Th(NO3)2-13ꢂ(NO3)2
1437
1296
1396
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P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
3
Table 3
Omondi and co-workers [23]. In our hands, we noticed a small
amount of trans-isomer as a byproduct from the oxidation reaction.
The desired cis-isomer 1 was readily purified, however, by recrys-
tallization from hot benzene to give the product as a white powder
in good yield.
Selected bond lengths (Å) and angles (°) for structures 2 and 3.
Structure 2
Structure 3
Th1–O1
Th1–O2
Th1–O3
Th1–O4
Th1–O5
Th1–O6
Th1–O7
Th1–O8
Th1–O10
Th1–O11
O1–Th1–O2
O3–Th1–O4
O5–Th1–O6
O7–Th1–O8
O10–Th1–O11
2.441(3)
2.444(3)
2.411(3)
2.425(3)
2.394(3)
2.414(3)
2.633(3)
2.603(3)
2.558(3)
2.641(3)
70.44(10)
70.66(10)
68.94(10)
48.16(11)
48.69(9)
Th1–O1
Th1–O2
Th1–O3
Th1–O4
Th1–O5
Th1–O6
Th1–O7
Th1–O8
Th1–O10
Th1–O11
O1–Th1–O2
O3–Th1–O4
O5–Th1–O6
O7–Th1–O8
O10–Th1–O11
2.4023
2.4007
2.3857
2.4039
2.4214
2.4369
2.6310
2.5659
2.5997
2.6497
69.1
Ligand 1 was characterized using 1H, 13C and 31P NMR, as well
as IR, melting point and CHN analysis. Due to the similar electronic
environment of the vinyl and aromatic hydrogen atoms in ligand 1,
and further complicated by extensive 1H–31P coupling, the 1H NMR
spectrum of this compound is not a first order spectrum and thus
the assignment of the hydrogens to the observed signals is not
trivial. The 13C and 31P NMR spectra, however, are straightforward
to interpret with the 31P data being especially useful in the
confirmation of the cis- vs. trans- isomers as described by
Duncan and Gallagher [15].
68.5
69.6
49.0
48.3
Based on other Th(IV) structures in the literature with bidentate
ligands, we proposed that there would be room for three bidentate
ligands 1 in the first coordination sphere of the thorium center. To
this end, we prepared the 1:3 Th-1 complex by stirring three molar
Table 4
Crystal structure and refinement data for 4–5.
equivalents of ligand
1
with Th(NO3)4ꢂhydrate in methanol.
Evaporation of the volatiles under reduced pressure gave the
desired complex as an air-stable white powder in nearly quantita-
tive yield (Scheme 1). The obtained solid was characterized by CHN
analysis, IR, 1H and 31P NMR, and X-ray crystallography.
Data
Structure 4
Structure 5
Empirical formula
Formula weight
Crystal system
Space group
CCDC number
a (Å)
C80 H74N8O32P6Th2
2309.37
orthorhombic
Pbca
C78H66N2O13P6Th
1657.18
triclinic
ꢀ
P1
1052128
20.4872(3)
21.7028(3)
40.0869(5)
90
1052129
12.5057(16)
16.069(2)
22.475(3)
79.639(2)
76.497(2)
67.749(2)
4043.7(9)
2
3.2. NMR and IR studies
b (Å)
c (Å)
Confirmation of metal-complexation can be readily assessed by
the IR spectrum of the Th-1 complex (Table 1 and Supporting
Information). The phosphoryl P@O stretch of the complex is shifted
a
(°)
b (°)
90
90
c
(°)
V (Å3)
17823.8(4)
8
1.721
to lower wavenumbers from free 1 by approximately 30 cmꢁ1
,
Z
Dcalc (g cmꢁ3
)
1.361
2.021
indicating chelation of the donor oxygen atoms to the metal center.
The stretches corresponding to vinyl and aryl C@C bonds broaden,
but shift only slightly upon complexation. Further examination of
the IR spectrum provides information about the environment and
binding geometry of the nitrate counter ions present from the
Th(NO3)4 salt used in the preparation. The binding mode of inner
sphere nitrato groups can be identified as monodentate or biden-
tate based on the peak separation of relevant stretches at ꢃ1450
l
(mmꢁ1
)
12.461
Crystal size (mm)
Minimum/maximum
transmission
0.206 ꢀ 0.087 ꢀ 0.084
0.378 ꢀ 0.124 ꢀ 0.046
0.5604
0.8288
hkl ranges
ꢁ24 6 h 6 24,
ꢁ25 6 k 6 25,
ꢁ48 6 l 6 47
94,226
16,122
0.0901
1157
0.0641
0.0445
0.1126
ꢁ15 6 h 6 15,
ꢁ19 6 k 6 19,
ꢁ27 6 l 6 26
50,569
14,955
0.0656
901
0.0585
0.0426
0.0960
Total reflections
Unique reflections
Rint
(m
(N@O)) and ꢃ1300 cmꢁ1
(msymm(NO2)) [24–26]. For this
Th(NO3)2-13ꢂ(NO3)2 complex, nitrato stretches appear at 1437
and 1296 cmꢁ1 (Table 1). The peak separation of 141 cmꢁ1 strongly
suggests that at least one inner-sphere nitrate is bound to the
Th(IV) metal center in a bidentate fashion in the solid state.
Stretches for the purely ionic outer sphere nitrates can also be
identified in the IR spectrum at 1396 cmꢁ1. This analysis is further
supported by the X-ray crystal structure (vide infra).
Parameters
a
R1 (all data)
a
R1 (I > 2
r
(I))
b
wR2 (all data)
b
wR2 (I > 2
Max/min residual
(e Åꢁ3
r
(I))
0.1031
3.26/ꢁ1.16
0.0910
1.72/ꢁ0.96
)
Goodness-of-fit
1.029
1.029
(GOF) on F2
Solution studies of the Th(NO3)2-13ꢂ(NO3)2 complex were car-
ried out by 1H and 31P NMR in both CD3OD and CDCl3 solutions.
In CD3OD solution, the 1H NMR spectrum of the Th(IV) complex
showed broad signals with complicated splitting patterns similar
to the ones observed in the spectrum of free ligand 1 (Fig. 1).
Interestingly, an apparent doublet of a doublet appears downfield
centered at ꢃ7.8 ppm bearing a large coupling constant (ꢃ30 Hz)
consistent with two-bond phosphorus–hydrogen splitting. Most
likely this signal corresponds to the vinylic hydrogens, since
they are the closest to the chelating P@O groups of the ligand. It
is difficult to make conclusive signal assignments from this spec-
trum owing to the complex nature of the splitting patterns fea-
tured by free ligand 1. The 31P{H} NMR spectrum of the
Th(NO3)2-13ꢂ(NO3)2 complex displays a sole signal resonating at
a
R1
wR2 = [
=
R
j|Fo| ꢁ |Fc||/ |Foj.
R
b
R
[w(F2o ꢁ F2c)2]/
R .
[wF2o]2]1/2
depicting the thermal ellipsoids at 50%, are provided in the
Supporting Information.
3. Results and discussion
3.1. Synthesis of the ligand and 1:3 Th–ligand complex
The organic ligand involved in this study, cis-ethylenebis
(diphenylphosphine oxide) (1), was prepared following standard
procedures with stoichiometric oxidation of the starting phosphine
using hydrogen peroxide (Scheme 1). The synthesis, IR and 1H NMR
characterization of this compound was reported by Daigle and
co-workers [14], and its X-ray crystal structure determined by
30 ppm (Dd 8.5 ppm) and appearing as a sharp singlet. From the
relatively sharp and single signal observed in this 31P{H} spectrum,
we suggest that in CD3OD solution the chemical exchange process
between the ligand occurs at a rate that is fast on the NMR time
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4
P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
Table 5
3.3. Crystal structures of the complex
Selected bond lengths (Å) and angles (°) for structure 4.
3.3.1. Crystal structures of the 1:3 Th–ligand complex from MeOH and
CHCl3
1:1 Th(IV)–ligand complex
1:2 Th(IV)–ligand complex
Th1–O1
2.381(5)
Th2–O3
Th2–O4
Th2–O5
Th2–O6
Th2–O22
Th2–O23
Th2–O25
Th2–O26
2.348(5)
2.342(5)
2.377(4)
2.351(5)
2.557(6)
2.589(6)
2.573(5)
2.543(5)
2.627(5)
2.550(5)
73.63(17)
72.35(17)
48.31(18)
50.03(16)
48.80(18)
Crystals suitable for X-Ray diffraction of the Th(NO3)2-13ꢂ(NO3)2
complex were grown by slow vapor diffusion of benzene into a
concentrated solution of the complex in methanol to give structure
2. Alternatively, crystals were also obtained by the vapor diffusion
of carbon tetrachloride into a concentrated solution of the complex
in chloroform to give structure 3. Crystal structure and refinement
data for structures 2 and 3 are given in Table 2.
Th1–O2
Th1–O7
Th1–O8
Th1–O10
Th1–O11
Th1–O13
Th1–O14
Th1–O16
Th1–O17
Th1–O19
Th1–O20
O1–Th1–O2
O7–Th1–O8
O10–Th1–O11
O13–Th1–O14
O16–Th1–O17
O19–Th1–O20
2.360(5)
2.593(6)
2.643(5)
2.601(5)
2.550(5)
2.636(5)
2.619(5)
2.597(5)
2.607(6)
2.656(5)
2.618(5)
68.23(17)
48.60(17)
49.41(16)
48.44(15)
48.85(16)
47.98(16)
Th2–O28
Th2–O29
ꢀ
Complex 2 crystallized in the triclinic space group P1. The
O3–Th2–O4
O5–Th2–O6
O22–Th2–O23
O25–Th2–O26
O28–Th2–O29
asymmetric unit consists of one ten-coordinate 1:3 Th(NO3)2–
ligand complex and two outer sphere nitrate anions (Fig. 2) with
Th–O distances ranging from 2.394 to 2.641 Å. The overall metal
coordination geometry resembles a distorted bicapped square
antiprism where the bidentate nitrato groups occupy the apical
positions. Three ligands, all bidentate, are coordinated along the
equator of the Th(IV) ion. Two of these coordinated ligands are
bound nearly parallel to one another and the equator, while the
third is coordinated in a perpendicular orientation (O5 and O6).
To accommodate this orientation, the coordination of the apical
nitrato groups is tilted slightly away from O5 and O6 of the third
ligand.
Extensive pi–pi and CH–pi interactions exist both intramolecu-
larly and intermolecularly throughout the crystal lattice. One phe-
nyl ring (C74–79) is disordered and was modeled with 50%
occupancy over two positions. Both orientations of this disordered
ring engage in pi-stacking interactions with nearby phenyl rings.
One outer sphere nitrate was ordered in the matrix, however the
second nitrate ion along with, we suspect, solvent methanol or
water was disordered in a large space within the crystal lattice
(see packing diagram, Fig. 3). Attempts to model these disordered
molecules were unsuccessful. The intensity contribution of the
disordered nitrate and solvent molecules was removed using the
BYPASS procedure [27] as implemented in OLEX2 [21,22]. This
space is located at average x, y, z coordinates of [ꢁ0.537, 0.000,
ꢁ0.478], has a calculated size of 998.5 Å3, and contains approxi-
mately 170 electrons.
Table 6
Selected bond lengths (Å) and angles (°) for structure 5.
Th1–O1
Th1–O2
Th1–O3
Th1–O4
Th1–O5
Th1–O6
Th1–O7
Th1–O8
2.435(3)
2.489(3)
2.377(3)
2.411(3)
2.413(3)
2.403(3)
2.616(3)
2.585(3)
2.543(3)
2.642(3)
1.4334(7)
1.439(6)
68.86(10)
69.31(10)
71.11(11)
48.83(10)
48.95(11)
60.9(4)
Th1–O10
Th1–O11
C1–O13
C2–O13
O1–Th1–O2
O3–Th1–O4
O5–Th1–O6
O7–Th1–O8
O10–Th1–O11
C1–O13–C2
scale, and the observed broadening in the 1H NMR spectrum is
caused by the presence of the Th(IV) metal.
The coordination environment of the Th(IV) metal center in
structure 3, grown out of the non-coordinating solvent chloroform,
is very similar to that of 2 grown from methanol (Fig. 4). Complex 3
crystallized in the monoclinic space group P21/n. The asymmetric
unit consists of one ten-coordinate 1:3 Th(NO3)2–ligand complex,
two outer sphere nitrate anions, and one molecule of solvent car-
bon tetrachloride. This complex, again, is ten-coordinate with a
similar arrangement of three ligands and two nitrato groups bound
to the Th(IV) center having Th–O bond distances ranging from
2.3857 to 2.6497 Å. Extensive pi–pi stacking interactions can be
seen between adjacent molecules of the complex, as shown in
Fig. 4. One of the aromatic rings, C73–C78, was disordered over
two positions (80:20 ratio) where both orientations could partici-
pate in favorable CH–pi interactions with neighboring phenyl
rings. Due to the close packing of the aromatic groups in this struc-
ture, the two orientations of ring C73–C78 affected the position of
ring C43–C48 ever so slightly, but enough to merit the modeling of
this ring in two separate orientations as well. Since this disorder is
localized to the pendant aromatic rings and does not affect the
metal center, we show both models only in the Supporting
Information.
A different picture of the dynamics emerges when the complex
Th(NO3)2-13ꢂ(NO3)2 is dissolved in the non-coordinating solvent
CDCl3. The signals in the 1H NMR spectra are severely broadened
and, unfortunately, uninterpretable. The 31P{H} NMR spectrum
shows three sharp singlets corresponding to what, we propose,
are three different magnetic environments for the phosphorus
atoms in the ligands (Fig. 1). The signal at 21.5 ppm likely
corresponds to free, uncoordinated ligand as this chemical shift is
the same as observed for 1 alone in CDCl3. The signals at 31.5 and
33.9 ppm likely correspond to metal bound ligands in complexes of
different stoichiometry (i.e. 1:2, 1:3).
As to why different 31P{H} NMR spectra are observed for the
complex dissolved in these two different solvents, we can employ
a relatively simple explanation related to the solvent’s role in
assisting ligand dissociation. In the case of CD3OD, the solvent
likely aids in the dissociation mechanism of the ligand by occupy-
ing a metal coordination site when the ligand detaches from the
metal. This reduces the energy barrier of the dissociation process,
resulting in a time averaged signal for the ligand in both the 1H
and 31P{H} NMR spectra. Conversely, in CDCl3 there is no assistance
from the solvent in this ligand exchange mechanism and the
process slows on the 31P NMR time scale and multiple species
can be observed in solution as separated phosphorus signals. The
1H NMR spectrum is difficult to interpret because the multiple
species have overlapping signals and interfere with one another.
Two spaces, both having volumes of 1307 Å3 and containing
approximately 506 electrons, are also present in the unit cell with
average x, y, z coordinates of [ꢁ0.019, 0.000, 0.000] and [ꢁ0.209,
0.500, 0.500]. We suspect these spaces contain a mixture of
disordered chloroform and carbon tetrachloride molecules. The
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P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
5
Table 7
Crystal structure and refinement data for 6–8.
Data
Structure 6
81H80N3O19P6Th
Structure 7
Structure 8
Empirical formula
Formula weight
Crystal system
Space group
CCDC number
a (Å)
C
C80H74N3O17P6Th
1767.28
C156H138N7O36P12Th2
3522.45
1817.34
triclinic
triclinic
triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
1052130
13.3259(17)
15.634(2)
20.525(3)
84.769(2)
79.961(1)
81.617(2)
4156.2(9)
2
1052131
13.4174(15)
15.7703(18)
20.555(2)
86.993(1)
81.113(1)
84.995(1)
4277.4(8)
2
1052132
13.2034(14)
23.440(3)
26.574(3)
74.120(1)
81.997(1)
78.611(1)
7723.0(14)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢁ3
)
1.452
1.979
1.372
1.919
1.515
2.126
l
(mmꢁ1
)
Crystal size (mm)
Minimum/maximum
transmission
0.378 ꢀ 0.18 ꢀ 0.09
0.355 ꢀ 0.317 ꢀ 0.142
0.265 ꢀ 0.213 ꢀ 0.064
0.8359
0.8197
0.7562
hkl ranges
ꢁ16 6 h 6 16, ꢁ18 6 k 6 18,
ꢁ16 6 h 6 16, ꢁ19 6 k 6 19,
ꢁ14 6 h 6 16, ꢁ28 6 k 6 28,
ꢁ24 6 l 6 24
50,948
15,279
0.0446
988
ꢁ25 6 l 6 25
73,664
16,976
0.0499
968
ꢁ32 6 l 6 32
84,779
30,169
0.0671
1925
Total reflections
Unique reflections
Rint
Parameters
a
R1 (all data)
0.0549
0.0443
0.1146
0.1103
5.60/ꢁ1.18
1.074
0.0601
0.0463
0.1081
0.1032
2.60/ꢁ1.18
1.044
0.0971
0.0599
0.1269
0.1187
2.06/ꢁ3.42
1.097
a
R1 (I > 2
r
(I))
b
wR2 (all data)
b
wR2 (I > 2
Max/min residual (e Åꢁ3
Goodness-of-fit (GOF) on F2
r(I))
)
a
R1
wR2 = [
=
R
j|Fo| ꢁ |Fc||/ |Foj.
R
R
[w(F2o ꢁ F2c)2]/
R .
[wF2o]2]1/2
b
intensity contribution of these disordered solvent molecules was
removed by the BYPASS procedure [27] as implemented in OLEX2
[21,22]. Pertinent bond lengths and angles for both structures 2
and 3 are given in Table 2.
Table 8
Selected bond lengths (Å) and angles (°) for structures 6 and 7.
Structure 6
Structure 7
Th1–O1
Th1–O2
Th1–O3
Th1–O4
Th1–O5
Th1–O6
Th1–O7
Th1–O8
Th1–O10
Th1–O11
O1–Th1–O2
O3–Th1–O4
O5–Th1–O6
O7–Th1–O8
O10–Th1–O11
2.406(3)
2.413(4)
2.424(3)
2.443(4)
2.402(3)
2.404(3)
2.700(4)
2.567(3)
2.593(4)
2.638(4)
70.06(12)
69.99(12)
69.48(11)
47.96(11)
48.21(12)
Th1–O1
Th1–O2
Th1–O3
Th1–O4
Th1–O5
Th1–O6
Th1–O7
Th1–O8
Th1–O10
Th1–O11
O1–Th1–O2
O3–Th1–O4
O5–Th1–O6
O7–Th1–O8
O10–Th1–O11
2.401(3)
2.391(3)
2.440(4)
2.437(3)
2.407(4)
2.429(3)
2.663(3)
2.562(3)
2.609(4)
2.619(4)
69.96(11)
69.89(12)
70.95(11)
48.40(10)
48.68(14)
3.3.2. Crystal structure of the 1:1 and 1:2 Th–ligand complexes
To investigate other metal–ligand stoichiometries of the
Th(NO3)2-13ꢂ(NO3)2 complex, we prepared a concentrated mixture
of Th(NO3)4 hydrate and ligand 1 in methanol with a 1:1 stoichio-
metric ratio. Upon standing in the refrigerator over three days,
plate crystals formed that were suitable for analysis by X-ray
diffraction to give structure 4 (Fig. 5). This structure was solved
in the orthorhombic space group Pbca. Interestingly, both 1:1 and
1:2 Th–ligand complexes were present in the asymmetric unit
along with two ordered molecules of solvent methanol. In both
Th(IV) complexes, all ligands are bound in a bidentate manner,
and all eight nitrate counterions are bound directly to the metal
centers. The 1:1 metal–ligand complex is twelve-coordinate and
Table 9
Selected bond lengths (Å) and angles (°) for both Th(IV) complexes of structure 8.
8 (Th1)
8 (Th2)
Th1–O1
Th1–O3
Th1–O4
Th1–O5
Th1–O6
Th1–O13
Th1–O14
Th1–O16
2.428(4)
2.423(5)
2.393(5)
2.484(4)
2.401(5)
2.606(5)
2.542(5)
2.707(5)
2.561(4)
2.422(4)
70.18(15)
72.60(16)
69.21(15)
48.97(17)
47.95(15)
Th2–O7
Th2–O8
Th2–O9
Th2–O10
Th2–O11
Th2–O12
Th2–O20
Th2–O21
2.446(5)
2.397(5)
2.420(5)
2.413(5)
2.433(4)
2.386(5)
2.573(5)
2.678(5)
2.653(5)
2.589(5)
70.85(16)
70.25(17)
69.65(15)
48.66(15)
48.45(16)
Th1–O17
Th1–O19
Th2–O23
Th2–O24
O1–Th1–O19
O3–Th1–O4
O5–Th1–O6
O13–Th1–O14
O16–Th1–O17
O7–Th2–O8
O9–Th2–O10
O11–Th2–O12
O20–Th2–O21
O23–Th2–O24
Scheme 1. Synthesis of ligand 1 and the 1:3 [Th(NO3)2-13ꢂ(NO3)2] complex.
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6
P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
Fig. 1. NMR analysis: (a) 1H NMR spectrum (400 MHz) of free ligand (top) and Th(NO3)2-13ꢂ(NO3)2 complex (bottom) in CD3OD; (b and c) 31P NMR spectrum (162 MHz) of free
ligand (top) and Th(NO3)2-13ꢂ(NO3)2 complex (bottom) in CD3OD and CDCl3, respectively.
bears five bidentate nitrato groups, giving this complex an overall
ꢁ1 charge, while the 1:2 metal–ligand complex is ten-coordinate
and bears three bidentate nitrato groups resulting in an overall
+1 charge.
two nitrato groups occupy the apical positions. The third nitrato
group binds to the metal in the same orientation as the third ligand
in complexes 2 and 3, along the equator but rotated perpendicular
to the bound ligands. The apical nitrato groups are tilted slightly
away from this third nitrato group, in a similar fashion as seen in
complexes 2 and 3. Th(IV)–O bond distances range from 2.342 to
2.627 Å, slightly shorter than that observed in complexes 2 and 3
above. This decreased bond distance is likely due to the presence
of a smaller nitrato group coordinating to the metal center in the
place of organic ligand 1. Refinement and crystal structure data
for structure 4 is given in Table 4; pertinent bond lengths and
angles are listed in Table 5.
The coordination geometry of the twelve coordinate 1:1
[Th(NO3)5-1]ꢁ1 complex resembles an icosahedron. At time of
manuscript submission, twelve structures are reported in the
Cambridge Structural Database containing a 12-coordinate Th(IV)
metal. In eleven of these structures, the 12-coordinate metal is
Th(NO3)26ꢁ acting as the anionic counterpart in an ion-pair complex
[28–38]. The twelfth includes a Th(IV) metal bearing two bidentate
organic ligands and four nitrate ions [38]. Complex 4 described
here represents the third structurally unique contribution of a
12-coordinate Th(IV) structure to the CSD. Th–O bond distances
in this complex range from 2.360 to 2.656 Å, slightly longer than
the ten-coordinate 1:3 Th–ligand complex described above.
The coordination geometry of the ten-coordinate 1:2 [Th(NO3)3-1]+1
complex again resembles a distorted bicapped square antiprism.
The two ligands are bound along the equator of the metal, while
3.3.3. Serendipitous crystal structure of the 1:3 Th–ligand complex
with an epoxide
The fourth structure we describe here was a serendipitous dis-
covery from our investigations into the Th(NO3)2-13ꢂ(NO3)2 com-
plex. This structure was obtained from a concentrated solution of
the Th(NO3)2-13ꢂ(NO3)2 dissolved in methanol, but crystallized
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P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
7
Fig. 2. Coordination environment of structure 2 with (left) atom numbering scheme and phenyl rings omitted for clarity, and (right) only hydrogens omitted. Only one
orientation of the disordered phenyl ring C74–79 is shown for clarity; drawings are done at 50% thermal ellipsoids using standard CPK colors. (Color online.)
Fig. 3. Packing diagram viewed down the a-axis showing the ordered outer-sphere nitrate ions (grey sticks) and the spaces in the lattice that hold one disordered nitrate and
possibly solvent (denoted with grey dots). Viewed down this axis, pi–pi interactions can be seen between phenyl rings on adjacent metal–ligand complexes (orange and blue
sticks). This drawing is done as a stick model; one orientation of the disordered phenyl ring C74–C79 and all hydrogen atoms have been omitted for clarity. (Color online.)
with vapor diffusion of diisopropylether. In this case, structure 5
crystallized in the triclinic space group P1 as a 1:3 metal–ligand
thermal values, likely because there are no ordered hydrocarbon
structures with which to engage in pi–pi or CH–pi interactions.
The phenyl rings on the opposite side of the complex engage in
extensive intermolecular pi–pi stacking interactions with nearby
complexes. These relatively ordered rings can also be seen in
Fig. 6 denoted by a grey arrow. The range of Th–O bond lengths
was 2.377(3)–2.642(3) Å; selected bond lengths and angles are
given in Table 6.
The overall geometry of this ten-coordinate complex again
resembles a distorted bicapped square antiprism. The inner sphere
nitrato groups occupy the apical positions, and the three organic
ligands are bound along the equator of the complex. A subtle
difference is seen here, however, when compared to the parent
1:3 Th(IV)–ligand structure 2. The ligand bearing the epoxide is
bound with both oxygen atoms approximately perpendicular to
the apical nitrates. This orientation is likely stabilized by favorable
ꢀ
complex with one ligand bearing an epoxide in place of the alkene
(Fig. 6, structure and refinement details in Table 4). The asymmet-
ric unit contains one ten-coordinate Th(IV) center bearing three
ligands and two nitrato groups, each bound in a bidentate manner.
The two outer sphere nitrates were severely disordered in the
crystal lattice, perhaps along with solvent molecules, and their
electron density contribution was removed using the BYPASS
[27] procedure in Olex2 [21,22]. Two spaces were found per unit
cell with average x, y, z coordinates of [ꢁ0.500, 0.500, 0.000] and
[ꢁ0.646, 0.500, 0.500] containing approximately 99 and 148 elec-
trons, respectively. The packing diagram in Fig. 6 shows the large,
oval-shaped space located in the center of the unit cell containing
this disordered electron density. The phenyl rings of the ligands
creating the border of this oval-shaped space have relatively large
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8
P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
Fig. 4. (left) Coordination environment of structure 3 with atom numbering scheme and phenyl rings omitted for clarity. This drawing was done with 50% thermal ellipsoids
using standard CPK colors. (right) Packing diagram of complex 3 viewed down the a-axis, only one orientation of the disordered phenyl rings C73–C78 and C43–C48 are
shown for clarity. From this viewpoint the ordered outer-sphere CCl4 (light green) and nitrate ions (grey) can be seen, as well as the spaces in the lattice that hold disordered
solvent (denoted with a dark grey circle). Intramolecular pi–pi stacking interactions can also be seen. This drawing is done with a stick model; all hydrogen atoms have been
omitted for clarity. (Color online.)
Fig. 5. Coordination environment of both Th(IV) atoms in structure 4 with atom numbering scheme and phenyl rings omitted for clarity: (left) Th1 of the 1:1 complex and
(right) Th2 of the 1:2 complex. Drawings are done at 50% thermal ellipsoids using standard CPK colors. (Color online.)
Fig. 6. (left) Coordination environment of Th(IV) in structure 5 with atom numbering scheme and phenyl rings omitted for clarity. This drawing was done with 50% thermal
ellipsoids using standard CPK colors. (right) Packing diagram of complex 5 viewed down the a-axis. From this viewpoint the large spaces in the center of the unit cell, denoted
with a grey circle, can be seen that likely hold disordered nitrate ions and possibly solvent. Black arrows indicate pi-stacking interactions between adjacent complexes. This
drawing is done as a stick model and each complex is colored completely in either blue or orange, with hydrogen atoms omitted, for clarity. (Color online.)
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P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
9
Fig. 7. Packing diagrams of structures 6 and 7. (a, left) Complex 6 and (b, right) complex 7, both viewed down the a-axis. Spaces containing disordered electron density are
denoted with a grey circle; unbound nitrate ions as well as solvent water and methanol molecules are shown as light grey sticks. This drawing is done as a stick model; all
hydrogen atoms have been omitted for clarity.
Fig. 8. (left) Coordination environment of Th1 in structure 8 with atom numbering scheme and phenyl rings omitted for clarity; hydrogen bonds are shown as dashed grey
lines and atoms are depicted as 50% thermal ellipsoids. (right) Coordination environments of both Th1 and Th2 within the asymmetric unit viewed down the apical nitrates;
four phenyl rings involved in CH–pi interactions are shown with ball and stick drawings. Only hydrogen atoms involved in hydrogen bonding or CH–pi interactions are shown
(light pink); standard CPK colors are used for the rest of the atoms. (Color online.)
electrostatic interactions between the epoxide oxygen O13 and the
bound nitrato nitrogen N2 (interatomic distance = 2.811 Å). The
other two bound ligands are both tilted slightly toward the apical
positions, rather than one parallel to and one perpendicular to the
first ligand (as seen in structures 2 and 3).
As for the formation of the 1:3 Th–ligand complex bearing an
epoxide in solution, we have a few hypotheses. Our first thought
was that the metal bound ligand bearing an epoxide was a small
impurity from the preparation of ligand 1, and perhaps due to
the extra electrostatic interaction between the epoxide and metal
bound nitrato group this 1:3 metal–ligand species crystallized
out of solution selectively. However, we see no indication of this
putative ligand impurity in the 31P NMR or CHN analysis of the free
ligand.
the 1H NMR of our ligand, and the CHN analysis further attests to
the purity (P95%) of our product. Hypothesis 2: The solvent used
to crystallize this complex via vapor diffusion was diisopropyl
ether, which could have trace amounts of peroxides present in
solution. As a result of this crystal structure we tested our bottle
of iPrO2 with peroxide test strips and did not detect the presence
of peroxides in our solvent (detection limit is approximately
0.5 ppm or 1 mg peroxide/liter of solvent). We also note here that
we have not observed this epoxide-containing structure under any
other conditions than with the iPr2O vapor diffusion into a
methanolic solution of 1:3 metal–ligand complex. At this point,
we have no conclusive evidence for an explanation for the genera-
tion of this epoxide-containing structure.
We then turned our thoughts to the reported reactive ability of
Th(IV) toward activated alkenes. There have been two reports in
the literature of Th(IV) acting as a catalyst in the epoxidation of
activated alkenes in the presence of tBuOOH [39,40]. There are
two possible sources of peroxide contamination in our crystalliza-
tion experiments. Hypothesis 1: Our ligand was prepared using
hydrogen peroxide as the phosphine oxidant, and although the
product was recrystallized from benzene it could be possible that
trace amounts of hydrogen peroxide were present in this batch
of ligand. However, we see no signals corresponding to HOOH in
3.3.4. Experiments to reproduce the 1:3 complex bearing an epoxide:
three more crystal structures
In attempt to reproduce the epoxide structure, we prepared a
new methanolic solution of Th(NO3)2-13ꢂ(NO3)2 complex and set
up three crystallization experiments with varying equivalents (1,
2 and 3) of tBuOOH. Our rationale here was to try increase the
amount of epoxidation occurring in solution (if, in fact, Th(IV) or
peroxide catalysis is involved) and isolate more crystals to study.
The metal-ligand-peroxide solutions were allowed to stir for one
hour at room temperature, and crystallization was induced with
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10
P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
Fig. 9. Packing diagram of complex 8 viewed down the a-axis. From this viewpoint the spaces holding disordered nitrate ions and possibly solvent can be seen and are
denoted with a grey circle. This drawing is done as a stick model where the blue complexes contain Th1 and the orange complexes contain Th2. Outer sphere nitrate ions and
water molecules are shown as light grey sticks, and all hydrogen atoms have been omitted for clarity. (Color online.)
vapor diffusion of both benzene and iPr2O (separate experiments)
at 4 °C. From the crystals that formed in these experiments we
did not observe a complex bearing an epoxide on one or more
bound ligands. We did, however, crystallize two new polymorphs
6 and 7 of the 1:3 Th(IV)–ligand complex varying only in the
amount and location of solvent in the crystal lattice. Structure
and refinement data for structures 6 and 7 are given in Table 7,
while pertinent bond lengths and angles for these new structures
can be found in Table 8. Th(IV)–O bond lengths range from
2.413(4) to 2.700(4) Å for structure 6, and 2.391(3) to 2.663 Å for
structure 7.
As part of these experiments a crystal was also isolated with
two different Th(IV)–ligand complexes in the asymmetric unit
(structure 8, Fig. 8). This structure was solved in the triclinic space
ꢀ
group P1. In the first complex, Th1 bears two bidentate nitrato
groups, two bidentate ligands, one monodentate ligand and one
water molecule. The second complex, Th2, has a 1:3 metal–ligand
ratio and is similar in coordination geometry to the parent struc-
ture 2. The two Th(IV) complexes are packed tightly within the
asymmetric unit; multiple intermolecular CH–pi interactions are
seen between ligands on neighboring complexes. As a likely conse-
quence of this tight packing, three nitrates and two waters were
found ordered in the crystal lattice. The remaining nitrate and
likely solvent was disordered and all attempts to model this disor-
der were unsuccessful. The electron density contribution to this
disorder was removed using the BYPASS procedure to give a space
of 439.9 Å3 located at average x, y, z coordinates of [ꢁ0.651, 0.000,
0.500] containing approximately 104 electrons. Crystal structure
and refinement data for 8 is given in Table 7.
The coordination geometry of the metal center in both struc-
tures 6 and 7 is very similar to structure 2 described above, so
we have included drawings of these complexes only in the
Supplemental Information. Packing diagrams of these structures
showing their different morphologies are shown in Fig. 7. Both
structures 6 and 7 bear three bidentate ligands and two bidentate
ꢀ
nitrato groups, and were solved in the triclinic space group P1.
These new structures have similar unit cell dimensions to structure
2, however the unit cell volumes vary slightly from 4321.1 Å3 for
structure 2, to 4156.2 and 4277.4 Å3 for 6 and 7, respectively.
Structure 6 boasts one ordered outer sphere nitrate ion, three
methanol molecules and one water. The remaining outer sphere
nitrate ion, likely along with additional solvent, was severely disor-
dered. The electron contribution to this disorder, in a space of
300.7 Å3 containing 82 electrons, was removed using the BYPASS
procedure [27] as implemented in OLEX2 [21,22]. This space has
average x, y, z coordinates of [ꢁ0.500, 0.000, 0.500]. Structure 7
has one ordered outer sphere nitrate and two methanol molecules.
The remaining nitrate ion, likely along with additional solvent, was
disordered in the lattice. The electron contribution to this disorder,
in a space of 670.3 Å3 located at average x, y, z coordinates of
[ꢁ0.332, 0.500, 0.500], was also removed using the BYPASS proce-
dure. This space was calculated to contain approximately 138
electrons.
The coordination geometry of metal center Th1 is shown in
Fig. 8. The water molecule has displaced one of the oxygens from
the ligand oriented perpendicular to the equator, and the complex
retains the distorted antiprism geometry around the ten-coordi-
nate Th(IV). The water molecule is engaged in hydrogen bonds
with one bound nitrato group, one unbound nitrate, and the mon-
dentate ligand. The bond angle between this aqua oxygen and the
monodentate ligand oxygen (O19 and O1) at 70.18(15)° is the
same, within error, to the bond angle of the bound bidentate ligand
of the other Th(IV) complex in this asymmetric unit (O11 and O12)
at 69.95(15)°. Analysis of the packing diagram of structure 8
viewed down the a-axis reveals the oval shaped space occupied
by disordered nitrates and likely solvent molecules (Fig. 9). This
space is lined with non-polar aromatic rings of the ligands, result-
ing in a hydrophobic cavity occupied by polar molecules. Pertinent
bond lengths and angles for both Th–ligand complexes of structure
8 are given in Table 9.
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P.T. Morse et al. / Polyhedron xxx (2015) xxx–xxx
11
[12] R.A. Moss, H. Morales-Rojas, S. Vijayaraghavan, J. Tian, Metal-cation-mediated
hydrolysis of phosphonoformate diesters: chemoselectivity and catalysis, J.
Am. Chem. Soc. 126 (2004) 10923.
[13] F.R. Allen, The Cambridge Structural Database: a quarter of a million crystal
structures and rising, Acta Crystallogr., Sect. B 58 (2002) 380.
4. Scope and outlook
This report of seven new crystal structures adds to the current
body of Th(IV) coordination complexes within the CSD. The range
of structures solved here offers a series of ‘‘snapshots’’ of the
dynamic behavior of this Th–ligand complex in solution. These dif-
ferent structures are also observable as a mixture in solution
depending on the choice of solvent. We note here that the excep-
tional crystalline nature of this Th–ligand complex is due, we pro-
pose, to the rigid nature of the organic ligand. Extensive
intramolecular pi–pi and CH–pi interactions between pendant aro-
matic rings on adjacent complexes likely strengthen and solidify
the crystal lattice. This is a useful strategy to consider in the design
of new ligands as chelators for Th(IV) and other f-elements where
the coordination geometry of the complex is often dominated by
the ligand.
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Acknowledgements
We thank Grand Valley State University (Weldon Fund, OURS,
CSCE) for financial support of this work. We are grateful to the
NSF for student support (REU-1062944) and NMR instrumentation
(300 MHz JEOL, CCLI-0087655), as well as Pfizer, Inc. for the gener-
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diffractometers at Michigan State University were upgraded and/or
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can be obtained free of charge via http://www.ccdc.cam.ac.
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Please cite this article in press as: P.T. Morse et al., Polyhedron (2015), http://dx.doi.org/10.1016/j.poly.2015.05.016