Syntheses, structures and multinuclear NMR (45Sc, 89Y, 31P) studies of Ph3PO, Ph2MePO and Me3PO complexes of scandium and yttrium nitrates

Article abstract of DOI:10.1039/b001669l

The reactions of the tertiary phosphine oxides Ph₃PO, Ph₂MePO or Me₃PO with hydrated yttrium(in) nitrate in ethanol gave the complexes [Y(R₃PO)₂(EtOH)(NO₃)₃] (R₃PO = Ph₃PO or Ph₂MePO), [Y(Me₃PO)₂(H2O)(NO₃)₃], [Y(R₃PO)₃(NO₃)₃] (R₂PO = Ph₁PO, Ph₂MePO or Me3PO), and [Y(Ph₃PO)₄(NO₃)₂]NO₃. The species [Y(R₃PO)₄(NO₃)₂]NO₃ (R₃PO = Ph₂MePO or Me3PO) were formed from [Y(R₃PO)₃(NO₃)₃] and an excess of R₃PO in CH₂C1₂ solution and identified spectroscopically, but have not been isolated as solids. Corresponding reactions of hydrated scandium(m) nitrate produced [Sc(Ph₃PO)_a(NO₃)₃], [Sc(Ph₂MePO)₃(NO₃)₃], [Sc(Ph₂MePO)₄(NO₃)₂]NO₃, [Sc(Me₃PO)₂(EtOH)(NO₃)₃], and [Sc(Me₃PO)₆][NO₃]3. All complexes were characterised by elemental analysis, IR and ¹H NMR spectroscopy and conductance measurements. Variable temperature ⁸⁹Y, ⁴⁵Sc and ³¹P-{¹H} NMR spectroscopies have been used to identify species present in solution, and probe the interconversions. ³¹P-{¹H} NMR studies show that exchange with added R₃PO in solution is slow on the NMR timescale. Crystal structures were determined for [Y(Ph₃PO)₂(EtOH)(NO₃)₃] and [Y(R₃PO)₃(NO₃)₃] (R₃PO = Ph₃PO,: Ph₂MePO or Me₃PO: all contain 9-co-ordinate Y with symmetrically co-ordinated bidentate nitrate groups. Structures of the 8-co-ordinate [Sc(Ph₃PO)₂(NO₃)₃] and Sc(Ph₂MePO)₄(NO₃)JNO₃ are also described. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b001669l

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89
31
Syntheses, structures and multinuclear NMR (45Sc, Y, P)
studies of Ph3PO, Ph2MePO and Me3PO complexes of scandium
and yttrium nitrates
Lucy Deakin, William Levason, Michael C. Popham, Gillian Reid and Michael Webster
Department of Chemistry, University of Southampton, Southampton, UK SO17 1BJ
Received 1st March 2000, Accepted 15th May 2000
Published on the Web 27th June 2000
The reactions of the tertiary phosphine oxides Ph3PO, Ph2MePO or Me3PO with hydrated yttrium() nitrate in
ethanol gave the complexes [Y(R3PO)2(EtOH)(NO3)3] (R3PO = Ph3PO or Ph2MePO), [Y(Me3PO)2(H2O)(NO3)3],
[Y(R3PO)3(NO3)3] (R3PO = Ph3PO, Ph2MePO or Me3PO), and [Y(Ph3PO)4(NO3)2]NO3. The species [Y(R3PO)4-
(NO3)2]NO3 (R3PO = Ph2MePO or Me3PO) were formed from [Y(R3PO)3(NO3)3] and an excess of R3PO in CH2Cl2
solution and identified spectroscopically, but have not been isolated as solids. Corresponding reactions of hydrated
scandium() nitrate produced [Sc(Ph3PO)2(NO3)3], [Sc(Ph2MePO)3(NO3)3], [Sc(Ph2MePO)4(NO3)2]NO3, [Sc(Me3-
PO)2(EtOH)(NO3)3], and [Sc(Me3PO)6][NO3]3. All complexes were characterised by elemental analysis, IR and 1H
NMR spectroscopy and conductance measurements. Variable temperature 89Y, 45Sc and 31P-{1H} NMR spectro-
scopies have been used to identify species present in solution, and probe the interconversions. 31P-{1H} NMR studies
show that exchange with added R3PO in solution is slow on the NMR timescale. Crystal structures were determined
for [Y(Ph3PO)2(EtOH)(NO3)3] and [Y(R3PO)3(NO3)3] (R3PO = Ph3PO, Ph2MePO or Me3PO): all contain
9-co-ordinate Y with symmetrically co-ordinated bidentate nitrate groups. Structures of the 8-co-ordinate
[Sc(Ph3PO)2(NO3)3] and [Sc(Ph2MePO)4(NO3)2]NO3 are also described.
The co-ordination chemistries of scandium and yttrium have
received much less study than that of most d-block elements, in
part because the only accessible oxidation state in solution, the
d0 MIII, lacks both magnetic and d–d UV-visible spectroscopic
probes. However both metals are suitable for NMR studies,
being monoisotopic (45Sc and 89Y) and diamagnetic in the
metal() oxidation state. Scandium-45 is quadrupolar (I = 7/2)
but with only a moderate quadrupole moment Ϫ0.22 × 10Ϫ28
m2, and is one of the most sensitive nuclei in the periodic table
(Dc (receptivity relative to 13C) = 1700), whilst 89Y has I = 1/2
and moderate sensitivity (Dc = 0.67), but has a low absolute
frequency (Ξ = 4.92 MHz) and very long relaxation times.1 Here
we report the synthesis and multinuclear NMR studies of some
phosphine oxide complexes of scandium and yttrium nitrates,
and crystal structures of representative examples. Since the first
detailed study by Cousins and Hart2 in the late 1960s, phos-
phine oxides have been popular ligands for complexing with
trivalent lanthanide metals,3 although much less is known about
yttrium or scandium complexes, and none of the latter has been
structurally characterised.2,4–6
Ph2MePO (Aldrich), Me3PO (ALFA), Sc(NO3)3ؒ5H2O (Strem)
and Y(NO3)3ؒ6H2O (Aldrich) were used as received.
Synthesis
The syntheses generally followed similar methods, with the
ratio of reagents and the temperature the main variants.
Representative preparations are given below, and for the other
complexes only differences are noted.
[Y(Ph3PO)3(NO3)3]. Yttrium nitrate hexahydrate (0.38 g,
1.0 mmol) and Ph3PO (1.11 g, 4.0 mmol) were dissolved
separately in warm (60 ЊC) ethanol (10 cm3), the solutions
mixed and stirred for 1 h. The solution was evaporated to
ca. 10 cm3 and refrigerated overnight. The white solid was
filtered off and dried in vacuo. Yield 0.93 g, 91% (Found: C,
58.1; H, 3.7; N, 3.7. Calc. for C54H45N3O12P3Y: C, 58.4; H, 4.1;
N, 3.8%). IR (cmϪ1) (Nujol mull): 1500w, 1437m, 1311w, 1187w,
1168s (PO), 1154s (PO), 1121m, 1092m, 1031w, 815m, 745s,
725m and 690w. 31P-{1H} NMR (300 K, CH2Cl2): δ 36.5 and
33.9. 89Y NMR (300 K): not observed. Λm (CH2Cl2, 10Ϫ3 mol
dmϪ3) = 13 ohmϪ1 cm2 molϪ1.
Experimental
Physical measurements were made as described previously.7
Conductivities were measured in anhydrous CH2Cl2 or MeNO2
from 10Ϫ3 mol dmϪ3 solutions of the complexes on a Pye 1700
Conductance bridge. NMR spectra were recorded on a Bruker
AM360 in 10 mm o.d. tubes from CH2Cl2–10% CDCl3 solu-
tions. 31P-{1H} NMR spectra at 145.5 MHz were referenced to
external 85% H3PO4. 89Y NMR spectra were recorded at 17.65
MHz with a sweep width of 25 kHz from solutions containing
TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) as a relaxation
agent and with a 2 s pulse delay. A 2 mol dmϪ3 solution of
YCl3 at pH 1 (added HCl) was used as zero reference.8 45Sc
NMR spectra were recorded at 87.5 MHz using a solution of
0.1 mol dmϪ3 Sc(NO3)3 at pH 1 as zero reference.1,8 Ph3PO and
[Y(Ph2MePO)3(NO3)3]. Made similarly 74% (Found: C, 50.2;
H, 4.1; N, 4.5. Calc. for C39H39N3O12P3Y: C, 50.7; H, 4.3;
N, 4.6%). IR (cmϪ1) (Nujol mull): 1500w (sh), 1450m, 1306w,
1300w (sh), 1172w (sh), 1150s (PO), 1126s, 1105m, 1035m,
895w, 883w, 781m, 745m, 716w, 696w and 668m. 31P-{1H}
NMR (300 K, CH2Cl2): δ 36.6. 89Y NMR (300 K): δ Ϫ22br. 1H
2
NMR (300 K, CDCl3): δ 7.2–7.7m, 1.95d, JPH 13.5 Hz. Λm
(CH2Cl2, 10Ϫ3 mol dmϪ3) = 4.5 ohmϪ1 cm2 molϪ1.
[Y(Me3PO)3(NO3)3]. Made similarly 33% (Found: C, 19.1;
H, 4.8; N, 7.5. Calc. for C9H27N3O12P3Y: C, 19.6; H, 4.9; N,
7.6%). IR (cmϪ1) (Nujol mull): 1308m, 1171 (sh), 1146s (PO),
1120 (sh), 1036m, 949s, 863m, 819w, 390m and 365w. 31P-{1H}
DOI: 10.1039/b001669l
J. Chem. Soc., Dalton Trans., 2000, 2439–2447
This journal is © The Royal Society of Chemistry 2000
2439

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NMR (300 K, CH2Cl2): δ 48.3. 89Y NMR (300 K): δ Ϫ17.0s.
1H NMR (300 K, CDCl3): δ 1.65d, 2JPH 13.6 Hz.
45Sc NMR (300 K, CH2Cl2): δ Ϫ3.5 (W1/2 = 500) and Ϫ33 (W1/2
1
2
10000 Hz). H NMR (300 K, CDCl3): δ 2.10d, JPH = 12 Hz.
Λm (10Ϫ3 mol dmϪ3 CH2Cl2) = 8 ohmϪ1 cm2 molϪ1
.
[Y(Ph3PO)2(EtOH)(NO3)3]. Yttrium nitrate hexahydrate
(0.38 g, 1.0 mmol) and Ph3PO (0.28 g, 1.0 mmol) were dissolved
in boiling ethanol (15 cm3). After 15 min the solution was
cooled and refrigerated overnight to give a white solid, which
was filtered off and dried in vacuo. Yield 0.46 g, 53% (Found: C,
52.3; H, 4.1; N, 4.5. Calc. for C38H36N3O12P2Y: C, 52.0; H, 4.1;
N, 4.8%). IR (cmϪ1) (Nujol mull): 3300 (br) s, 1500w, 1314m,
1171s (PO), 1155s (PO), 1120m, 1039m, 1032 (sh), 816w,
692m and 539s. 31P-{1H} NMR (300 K, CH2Cl2): δ 37.0. 89Y
[Sc(Ph2MePO)3(NO3)3].
A
boiling solution of Sc-
(NO3)3ؒ5H2O (0.23 g, 1.0 mmol) in absolute ethanol (20 cm3)
was treated with a solution of Ph2MePO (0.43 g, 2.0 mmol)
in absolute ethanol (10 cm3). The solution was concentrated to
ca. 5 cm3, cooled and refrigerated for 24 h. A sticky solid
deposited, the supernatent liquid was decanted off, the solid
washed with ice-cold diethyl ether (5 cm3), and dried in vacuo.
Yield 0.25 g, 28% (Found: C, 53.2; H, 4.4; N, 4.6. Calc. for
C39H39N3O12P3Sc: C, 53.3; H, 4.5; N, 4.8%). IR (cmϪ1) (Nujol
mull): 1590w, 1302s, 1153s (PO), 1090w, 1025w, 971w, 890m,
814w, 777m, 692m, 502s, 422w, 400w and 287m. 31P-{1H} NMR
(300 K, CH2Cl2): δ 39.5. 45Sc NMR (300 K, CH2Cl2): δ Ϫ4.0
(W1/2 = 350 Hz). 1H NMR (CDCl3): δ 2.10d, 2JPH = 12 Hz.
1
NMR (300 K): not observed. H NMR (d6-acetone, 300 K):
δ 7.1–7.6m, 3.56 (q, J = 7) and 1.11 (t, J = 7 Hz). Λm (CH2Cl2,
10Ϫ3 mol dmϪ3) = 10.0 ohmϪ1 cm2 molϪ1
.
[Y(Ph2MePO)2(EtOH)(NO3)3]. Made similarly 33% (Found:
C, 46.4; H, 4.0; N, 4.8. Calc. for C28H32N3O12P2Y: C, 44.6;
H, 4.3; N, 5.6%) see text. IR (cmϪ1) (Nujol mull): 3300 (br),
1591w, 1300 (br) s, 1181 (sh), 1155s (PO), 1126m, 1109m,
1073w, 998w, 969w, 893m, 881m, 816m, 779w, 741s, 693s,
513m, 504s and 398w. 31P{1H} NMR (300 K, CH2Cl2): δ 37.7.
89Y NMR (300 K) not observed. 1H NMR (d6-acetone,
[Sc(Me3PO)2(EtOH)(NO3)3]. A boiling solution of Sc-
(NO3)3ؒ5H2O (0.346 g, 1.5 mmol) in ethanol (20 cm3) was added
to a boiling ethanol (10 cm3) solution of Me3PO (0.139 g,
1.5 mmol). The solution was evaporated in vacuo to dryness,
redissolved in the minimum volume of alcohol and refrigerated
overnight. A sticky solid formed which was discarded and
the mother liquor allowed to evaporate to produce colourless
crystals, which were filtered off and dried in vacuo. Yield 0.05 g,
10% (Found: C, 20.4; H, 5.1; N, 9.6. Calc. for C8H24N3O12P2Sc:
C, 20.8; H, 5.6; N, 9.1%). IR (cmϪ1) (Nujol mull): 3200 (br),
1312m, 1152s (PO), 1112m, 1026w, 956m, 866w, 815w, 534w,
485w, 430w, 372w and 327w. 31P-{1H} NMR (300 K, CH2Cl2):
δ 54.8. 45Sc NMR (300 K, CH2Cl2): δ Ϫ2.5 (W1/2 = 600 Hz).
1H NMR (300 K, CDCl3): δ 0.9 (t, J = 7), 1.6 (d, 2JPH = 10) and
3.6 (q, J = 7 Hz).
2
300 K): δ 7.6–7.9m, 3.60 (q, J = 7), 2.05 (d, JPH = 14) and
1.15 (t, J = 7 Hz). Λm (CH2Cl2, 10Ϫ3 mol dmϪ3) = 7.5 ohmϪ1 cm2
molϪ1
.
[Y(Me3PO)2(H2O)(NO3)3]. Prepared by boiling Y(NO3)3ؒ
6H2O and Me3PO in a 1:1 mol ratio in ethanol, similar to the
preparation of the ethanol complexes, 36% (Found: C, 14.5; H,
3.9; N, 8.7. Calc. for C6H20N3O12P2Y: C, 15.1; H, 4.2; N, 8.7%).
IR (cmϪ1) (Nujol mull): 3400 (br) s, 1650m, 1297s, 1160 (sh)
(PO), 1140s (PO), 1083m, 1034m, 951s, 866m, 816m, 745m, 605
(br), 391m, 371m and 333w. 31P{1H} NMR (300 K, CH2Cl2):
δ 50.5. 89Y NMR (300 K) not observed. 1H NMR (d6-acetone,
300 K): δ 1.45d, 2JPH = 13.6 Hz.
[Sc(Me3PO)6][NO3]3. A solution of Sc(NO3)3ؒ5H2O (0.23 g,
1.0 mmol) in ice-cold ethanol (20 cm3) was added to a solution
of Me3PO (0.53 g, 6.0 mmol) in ethanol (10 cm3) and the
mixture shaken. A white precipitate formed immediately, the
solution was refrigerated for 24 h, filtered and the solid dried
in vacuo. Yield 0.43 g, 57% (Found: C, 26.9; H, 6.6; N, 5.2. Calc.
[Y(Ph3PO)4(NO3)2]NO3. A solution of Ph3PO (0.84 g,
3.0 mmol) in ice-cold ethanol (15 cm3) was added to yttrium
nitrate hexahydrate (0.175 g, 0.50 mmol) in ethanol (5 cm3) at
0 ЊC. The white product was filtered off after 1 h and dried in
vacuo. Yield 0.35 g, 51% (Found: C, 62.0; H, 4.0; N, 3.2. Calc.
for C72H60N3O13P4Y: C, 62.3; H, 4.3; N, 3.0%). IR (cmϪ1) (Nujol
mull): 1520w, 1298m, 1154s (PO), 1121s, 1091m, 1031w, 997w,
971w, 830w, 816w, 742m, 692m, 542s, 416w and 308w. 31P-{1H}
NMR (300 K, CH2Cl2): δ 36.5, 33.3 and 26.0. 89Y NMR (300 K):
not observed. Λm (CH2Cl2, 10Ϫ3 mol dmϪ3) = 14.5 ohmϪ1 cm2
for C18H54N3O15P6Sc: C, 27.6; H, 6.9; N, 5.4%). IR (cmϪ1
)
(Nujol mull): 1361m, 1298m, 1156 (sh), 1104vs (PO), 958s,
891w, 870s, 834s, 760m, 681w, 423m, 371m, 363m and 350w.
31P-{1H} NMR (300 K, MeNO2): δ 64.7, 62.0 (sh) and 43.0.
45Sc NMR (300 K, MeNO2): δ 11.4 (W1/2 = 450) and 5.0 (W1/2
=
1
2
180 Hz). H NMR (300 K, CD3NO2): δ 2.6 (d, JPH = 13) and
2.4 (d, 2JPH = 13 Hz). ΛM (10Ϫ3 mol dmϪ3 MeNO2) = 157 ohmϪ1
molϪ1
.
cm2 molϪ1
.
[Sc(Ph3PO)2(NO3)3]. A boiling solution of Sc(NO3)3ؒ5H2O
(0.23 g, 1.0 mmol) in absolute ethanol (20 cm3) was treated with
a solution of Ph3PO (0.83 g, 3.0 mmol) in absolute ethanol
(10 cm3). The solution was concentrated to ca. 15 cm3, cooled
and refrigerated for 24 h. White crystals separated and were
filtered off, rinsed with cold ethanol (5 cm3), and dried in vacuo.
Yield 0.26 g, 33% (Found: C, 54.5; H, 4.0; N, 5.1. Calc. for
C36H30N3O11P2Sc: C, 54.9; H, 3.8; N, 5.3%). IR (cmϪ1) (Nujol
mull): 1562, 1437, 1299, 1282, 1167 (PO), 1140, 1123, 1009,
808, 747, 725, 692 and 542. 31P-{1H} NMR (300 K, CH2Cl2):
δ 37.7. 45Sc NMR (300 K, CH2Cl2): δ Ϫ7.5 (W1/2 = 900 Hz). Λm
Crystallography
Diffraction data were recorded using either a Rigaku AFC7S
or a Nonius CCD diffractometer both fitted with Mo-Kα
radiation (λ = 0.71073 Å) and graphite monochromator. Unless
stated otherwise data were collected on the former diffrac-
tometer with the sample at 150 K. The crystals studied scattered
weakly as judged by I/σ(I) and the area detector diffractometer
was used for the smaller crystals. Data processing was per-
formed using the TEXSAN package9 for AFC7S data and
structure refinement was carried out using either TEXSAN or
SHELXL 97.10 Trial structures were obtained from SHELXS
8611 unless stated otherwise. Crystallographic data are reported
in Table 1 and brief comments about each structure deter-
mination are given below. A number of the crystals appeared of
high quality by microscopic examination but disappointingly
gave structures of moderate quality.
(CH2Cl2, 10Ϫ3 mol dmϪ3) = 2 ohmϪ1 cm2 molϪ1
.
[Sc(Ph2MePO)4(NO3)2]NO3. Prepared similarly from Sc-
(NO3)3ؒ5H2O (1 mmol) and Ph2MePO (4 mmol) in absolute
ethanol, 60% (Found: C, 56.9; H, 5.0; N, 3.7. Calc. for
C52H52N3O13P4Sc: C, 57.0; H, 4.7; N, 3.8%). IR (cmϪ1) (Nujol
mull): 1591w, 1299m, 1153s (PO), 1125m, 1108m, 1073m,
1037w, 996w, 889s, 831w, 818w, 811s, 744s, 694s, 507s, 479m,
453m, 425w, 400w and 277m. 31P-{1H} NMR (CH2Cl2): (300 K)
δ 38.5 (W1/2 = 700 Hz); (220 K) δ 39.6vw, 38.7s and 29.2vw.
[Y(Ph3PO)2(EtOH)(NO3)3]. Crystals were grown by slow
evaporation of an EtOH solution of complex and data
collected on the CCD diffractometer at 150 K. The structure
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J. Chem. Soc., Dalton Trans., 2000, 2439–2447

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was solved using DIRDIF12 and the data refined9 on F with
isotropic atomic displacement parameters (adps) for C and N
atoms due to the small amount of ‘observed’ data. Hydrogen
atoms were placed in calculated positions for phenyl groups
only.
largest peaks in the residual electron density are close to Cl
atoms.
CCDC reference number 186/1991.
See http://www.rsc.org/suppdata/dt/b0/b001669l/ for crystal-
lographic files in .cif format.
[Y(Ph3PO)3(NO3)3]ؒxCH2Cl2
and
[Y(Ph3PO)3(NO3)3].
Colourless plate-like crystals of the dichloromethane solvate
were grown by vapour diffusion of Et2O into a CH2Cl2 solution
of the compound with the crystallising cell held in a freezer.
At a later stage of refinement, solvate CH2Cl2 molecules
were apparent and included in the model with a refined popu-
lation. Although correlation was not a problem between the
atom population parameters and the isotropic adp values
of the solvate atoms, refinement tended to drift and the adps
were eventually fixed for the final refinement. The H atoms
were included in the model in calculated positions (d(C–H) =
0.95 Å) and significantly improved the fit to the data. Refine-
ment on F2 was carried out using SHELXL 9710 with aniso-
tropic (Y, P, O, N) and isotropic (C, H, Cl) atoms. A
non-solvated form of the crystals was obtained in later experi-
ments using the same crystallising solvents. During refine-
ment one phenyl ring became an odd shape and was treated as a
rigid group. The weaker data, poorer R value and refinement
difficulty led us to concentrate on the structure of the solvated
crystal.
Results and discussion
Yttrium complexes
The complexes were made straightforwardly by reaction of
hydrated yttrium() nitrate with the phosphine oxide in
ethanol. Although, as shown by the 31P NMR studies described
below, many solutions contain a mixture of complexes, pure
samples of a single complex usually crystallise from the solu-
tions with the reagents in the ratios described. The reaction of
Y(NO3)3ؒ6H2O with Ph3PO in a 1:1 or 1:2 mole ratio in boiling
ethanol produced [Y(Ph3PO)2(EtOH)(NO3)3], whilst from a
1:4 ratio the product was the tris(phosphine oxide) complex
[Y(Ph3PO)3(NO3)3]. Finally, reaction of a 1:6 ratio in ice-cold
ethanol produced Y(Ph3PO)4(NO3)3. For Ph2MePO, reaction
with Y(NO3)3ؒ6H2O in boiling ethanol in a 3:1 ratio gave
[Y(Ph2MePO)3(NO3)3], whilst a 1:1 ratio gave poor yields of
[Y(Ph2MePO)2(EtOH)(NO3)3]. The latter always seems to be
contaminated with some (<10%) [Y(Ph2MePO)3(NO3)3], and
an analytically pure sample has not been obtained despite
many attempts, although the spectroscopic identification of the
ethanol complex is clear (Experimental section). The 89Y NMR
data (below) show that solutions of [Y(Ph2MePO)3(NO3)3]
in CH2Cl2 containing an excess of Ph2MePO are essentially
completely converted into Y(Ph2MePO)4(NO3)3, but concen-
tration of such solutions, or reaction of Y(NO3)3ؒ6H2O with
Ph2MePO in a 1:6 ratio in ethanol, resulted only in isolation of
the tris(phosphine oxide) complex. The [Y(Me3PO)3(NO3)3]
was easily formed from the constituents in a 3:1 ratio in hot
ethanol, but from a 1:1 ratio in boiling ethanol the product
was [Y(Me3PO)2(H2O)(NO3)3] rather than the expected ethanol
complex. Although NMR studies showed that mixtures of
Y(NO3)3ؒ6H2O and Me3PO with 1:≥6 in ethanol or CH2Cl2
contained a tetrakis(phosphine oxide) complex (cf. the Ph2-
MePO system), on concentration these solutions deposited
crystals of [Y(Me3PO)3(NO3)3]. Treatment of Ph3PS with
yttrium nitrate under similar conditions in EtOH gave no
evidence for complex formation.
All the complexes are poorly soluble in alcohols, the 3:1 and
4:1 complexes are easily soluble in CH2Cl2, the 2:1 complexes
less so, which made it difficult to obtain 89Y NMR spectra of
the latter. The mull IR spectra are complex (Experimental
section), but the ν(PO) vibrations are easily identified by their
high intensities, and in all cases are 20–50 cmϪ1 to lower
wavenumbers of the vibrations of the “free” ligand (Me3PO
1161, Ph2MePO 1172, Ph3PO 1195 cmϪ1) showing that all
the phosphine oxides are co-ordinated to the yttrium. The
IR spectrum of Y(Ph3PO)4(NO3)3 is very similar to that15
of [Lu(Ph3PO)4(NO3)2]NO3 (which contains 8-co-ordinate
lutetium and bidentate nitrato-groups) and in particular shows
a weak band at 830 cmϪ1, absent for the other yttrium com-
plexes, which may be assigned as ν2 of an ionic NO3Ϫ, indicating
a [Y(Ph3PO)4(NO3)2]NO3 constitution. Distinction of mono-
and bi-dentate co-ordinated nitrate groups by IR spectroscopy
is notoriously difficult16 and has not been attempted. However
crystal structures have been determined for [Y(R3PO)3(NO3)3]
(R3 = Me3, Ph2Me or Ph3) and [Y(Ph3PO)2(EtOH)(NO3)3].
Unfortunately all attempts to grow crystals of Y(Ph3PO)4-
(NO3)3 failed; it separates as a powder from the synthesis, and
attempts to grow crystals using the pre-isolated complex from
a variety of solvents produced crystals of [Y(Ph3PO)3(NO3)3].
The crystal structure of [Y(Ph3PO)2(EtOH)(NO3)3] is shown
in Fig. 1 and selected bond lengths and angles are given in Table
2. As with all the structures reported here, the co-ordinated
[Y(Ph2MePO)3(NO3)3]. Small colourless needle crystals were
grown as above. Nonius CCD data recorded at 150 K, with
SORTAV13 absorption correction applied. Full-matrix least-
squares refinement on F was carried out in TEXSAN. A
number of plausible H atoms appeared in the Fourier difference
synthesis and all were introduced in calculated positions
(d(C–H) = 0.95 Å). All the non-H atoms were treated as aniso-
tropic and there was no evidence for solvate molecules.
[Y(Me3PO)3(NO3)3]. A few large crystals were grown as
above and in view of the rather weak data noted for other
samples a larger than usual crystal was selected. During refine-
ment some C atoms went non-positive definite on anisotropic
refinement and all C atoms were retained with isotropic adp
values in the model and no H atoms were included. The space
¯
group P1 (no. 2) with Z = 4 caused some concern but the Niggli
cell did not indicate any missed symmetry and although the
coordinates of the two Y atoms of the asymmmetric unit look
to be related this did not appear to extend to the other atoms
and thus no smaller cell with Z = 2 was identified.
[Sc(Ph3PO)2(NO3)3]. The crystal used was isolated from the
preparation of the compound. Attempts were also made to
grow crystals by vapour diffusion using the procedure in the
preceding section, but these experiments tended to give clusters
of very small crystals. From the trial Sc and P atoms, sub-
sequent structure factor-Fourier calculations identified the
remaining non-H atoms. There was no evidence for solvate
molecules and later electron-density maps showed evidence
for some of the phenyl H atoms. All H atoms were introduced
into the model in calculated positions (d(C–H) = 0.95 Å)
and full-matrix least-squares refinement10 was carried out on
F2. The absolute configuration of the selected crystal was
established (Flack parameter14 0.01(9)).
[Sc(Ph2MePO)4(NO3)2]NO3ؒxCH2Cl2. Crystals were grown
from CH2Cl2 solution by vapour diffusion of light petroleum
(bp 40–60 ЊC). The solvate CH2Cl2 became apparent in later
electron-density maps but gave rather large U values. Accor-
dingly the population of CH2Cl2 was adjusted to get Cl atom
adp values similar to those of Sc and P atoms. Phenyl H atoms
were added in calculated positions (d(C–H) = 0.95 Å) and full-
matrix least-squares refinement10 was carried out on F2. The
J. Chem. Soc., Dalton Trans., 2000, 2439–2447
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Fig. 1 The structure of [Y(Ph3PO)2(EtOH)(NO3)3] showing the atom
labelling scheme. Thermal ellipsoids are drawn at the 40% probability
level and H atoms omitted for clarity.
Fig. 3 The co-ordination polyhedron around Y in [Y(Ph2MePO)3-
(NO3)3]. Details as in Fig. 1.
Fig. 2 The co-ordination polyhedron around Y in [Y(Ph3PO)3(NO3)3]ؒ
xCH2Cl2. Details as in Fig. 1.
Fig. 4 The structure of [Y(Me3PO)3(NO3)3] showing the atom label-
ling scheme for the molecule centred on Y(1). Thermal ellipsoids
are drawn at the 40% probability level. The second molecule in the
asymmetric unit is very similar.
nitrate groups bond in the bidentate symmetrical mode, one of
the several modes of co-ordination of this anion.17 As has been
recognised before,18 the geometry shows that the co-ordinated
O atoms (Oc) have longer N–O distances than the unco-
ordinated or “free” N–O and the Oc–N–Oc angles to
Me3PO adduct (both molecules). This is most easily seen from
the figures and the (P)O–Y–O(P) angles (Table 2). The Y–O(P)
and Y–O(N) distances are insensitive to the compound with the
latter ca. 0.2 Å longer. The M–O–P angle in complexes of R3PO
is very variable and the values in these four compounds range
from 140 to 170Њ with the hint in the data that the larger angles
correlate with more phenyl substituents (Y–O–P (av.): Me3PO,
146; Ph2MePO, 156; Ph3PO, 166Њ). The non-solvated form of
[Y(Ph3PO)3(NO3)3] has the same stereochemistry as that of the
CH2Cl2 solvate with similar bond lengths and angles.
Ϫ
be smaller than the idealised 120Њ of the isolated NO3 anion.
The Y atom is nine-co-ordinate, but if the NO3 group is con-
ceptually replaced by a monatomic ligand the molecule can be
described as mer-(pseudo)-octahedral with cis Ph3PO ligands.
The corresponding compounds of Ce,15 Eu,18 Nd19 and Sm20
are probably isomorphous judged by cell dimensions and space
group. The structures of [Y(R3PO)3(NO3)3] (R3 = Ph3, Ph2Me
or Me3) have also been determined, the first as both the
dichloromethane solvate and non-solvated forms (see Figs. 2, 3
and 4 and Table 2). All are based on nine-co-ordinate Y with
the symmetrical bidentate NO3 ligand. They are based on
a (pseudo-)octahedral metal atom when regarding NO3 as a
monatomic ligand with the mer arrangement for Ph3PO and
Ph2MePO and, unexpectedly, the fac arrangement for the
31P-{1H} and 89Y NMR studies. 89Y is among the more dif-
ficult nuclei to observe,1,21 a consequence of its low resonance
frequency (Ξ = 4.92 MHz) and very long T1 values. Our spectra
were obtained from CH2Cl2 solutions containing 1–2 mg of
2442
J. Chem. Soc., Dalton Trans., 2000, 2439–2447

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Fig. 5 The 89Y NMR spectrum at 200 K of [Y(Ph3PO)3(NO3)3] in
CH2Cl2–10%CDCl3 with 2 mg TEMPO. 2000 scans, 25 kHz sweep
width and 2 s pulse delay.
TEMPO as a relaxation agent and with a pulse delay of 2 s.
From concentrated solutions 89Y resonances were typically
observed after 2000–3000 scans. The NMR data obtained at
300 K are given in the Experimental section, but in a number
of cases 89Y resonances were observed only from cooled solu-
tions, and low temperatures were necessary to resolve spin–spin
couplings. The high resolution data are listed in Table 3, the
temperatures quoted being those at which couplings were well
resolved.
The 31P-{1H} NMR spectrum of [Y(Ph3PO)2(EtOH)(NO3)3]
at 300 K is a singlet at δ 37.0, and we did not observe an 89Y
resonance from this solution. On cooling to 200 K the phos-
phorus resonance was a poorly resolved doublet, but more
importantly an 89Y resonance at δ Ϫ35.8 showed a clear triplet
2
structure with J(31P–89Y) = 11 Hz. Solutions of [Y(Ph3PO)3-
(NO3)3] at 300 K consistently showed two phosphorus reson-
ances at δ 36.5 and 33.9. The possibility that these reflected
inequivalent phosphine oxides (a “T” shaped arrangement of
the ligands is present in the solid) was ruled out by their relative
intensities which were nearer 1.5:1 than the expected 2:1,
moreover the relative intensities varied slightly with dilution
of the solution. Addition of Ph3PO to the solution at 300 K
showed three resonances δ 26.0 (Ph3PO), 33.9, and 36.5,
showing slow exchange with “free” ligand on the 31P NMR
timescale, but notably with the δ 36.5 resonance now relatively
much more intense than that at δ 33.9. On cooling the solution
to 200 K both resonances of the co-ordinated phosphine oxides
exhibited doublet couplings (Table 3). At 200 K an 89Y NMR
spectrum was obtained from the initial solution which revealed
two resonances of approximately equal intensity, a quartet at
δ Ϫ35.7 and a quintet at δ Ϫ2.0 (Fig. 5), demonstrating that
in solution [Y(Ph3PO)3(NO3)3] exists as a mixture of [Y(Ph3-
PO)3(NO3)3] and [Y(Ph3PO)4(NO3)2]NO3.† Addition of an
excess of Ph3PO (>10 fold) to this solution results in the dis-
appearance of the δ(31P) of 33.9 and δ(89Y) of Ϫ35.7 resonances
showing that the equilibrium is easily shifted in favour of the
tetrakis(phosphine oxide) complex. As would be expected,
NMR studies of solutions of [Y(Ph3PO)4(NO3)2]NO3 reveal
very similar data to those of the tris(phosphine oxide) complex
with an extra resonance in the 31P-{1H} spectrum due to free
Ph3PO at δ 26.0. Support for the presence of [Y(Ph3PO)4-
(NO3)2]NO3 in CH2Cl2 solutions of both the 3:1 and 4:1
complexes comes from the molar conductances which are
significantly higher (Λm ca. 13–14 ohmϪ1 cm2 molϪ1) than those
expected for non-electrolytes, and which increase on addition
of Ph3PO, approaching that of 1:1 electrolytes with an excess
of Ph3PO (Λm ca. 22 ohmϪ1 cm2 molϪ1).22
In contrast to the Ph3PO complex, the 300 K 31P-{1H} NMR
spectrum of [Y(Ph2MePO)3(NO3)3] in CH2Cl2 shows only a
single resonance, and at 200 K this resolves into a doublet,
whilst a quartet 89Y resonance is observed (Table 3). Thus
we conclude that unlike the Ph3PO complex, the Ph2MePO
† Mass balance requires at least one other yttrium species is formed,
but none was detected in the 89Y spectrum.
J. Chem. Soc., Dalton Trans., 2000, 2439–2447
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Table 2 Selected bond lengths (Å) and angles (Њ) for [Y(Ph3PO)2(EtOH)(NO3)3] and [Y(R3PO)3(NO3)3] (R3 = Ph3, Me3 or Ph2Me)
(a) [Y(Ph3PO)2(EtOH)(NO3)3]
Y(1)–O(1)
Y(1)–O(2)
Y(1)–O(N)
2.25(2)
2.27(1)
2.39(2)–2.47(1)
1.22(2)–1.33(2)
O(1)–P(1)
O(2)–P(2)
Y(1)–O(12)
N–Ofa
1.50(2)
1.50(1)
2.40(2)
1.25(2), 1.20(2), 1.21(2)
a
N–Oc
O(1)–Y(1)–O(2)
O(1)–Y(1)–O(12)
O(2)–Y(1)–O(12)
89.2(6)
149.8(6)
79.8(5)
52.1(5)–52.9(6)
Y(1)–O(1)–P(1)
Y(1)–O(2)–P(2)
Oc–N–Oc
170(1)
164(1)
113(2)–115(2)
b
Oc–Y(1)–Oc
(b) [Y(Ph3PO)3(NO3)3]ؒxCH2Cl2
Y(1)–O(1)
Y(1)–O(2)
Y(1)–O(3)
Y(1)–O(N)
2.269(5)
2.284(5)
2.283(5)
2.403(5)–2.506(5)
1.254(8)–1.271(8)
O(1)–P(1)
O(2)–P(2)
O(3)–P(3)
P–C
1.503(5)
1.484(5)
1.498(5)
1.789(7)–1.807(8)
1.215(8), 1.235(8), 1.220(8)
a
a
N–Oc
N–Of
O(1)–Y(1)–O(2)
O(1)–Y(1)–O(3)
O(2)–Y(1)–O(3)
Oc–N–Oc
83.4(2)
86.2(2)
149.5(2)
116.0(7)–116.7(6)
Y(1)–O(1)–P(1)
Y(1)–O(2)–P(2)
Y(1)–O(3)–P(3)
156.8(3)
173.7(3)
162.6(3)
51.5(2)–52.1(2)
b
Oc–Y(1)–Oc
(c) [Y(Ph2MePO)3(NO3)3]
Y(1)–O(1)
Y(1)–O(2)
Y(1)–O(3)
Y(1)–O(N)
2.258(3)
2.248(4)
2.252(4)
2.413(4)–2.491(4)
1.255(6)–1.279(5)
O(1)–P(1)
O(2)–P(2)
O(3)–P(3)
P–C
1.510(3)
1.513(4)
1.494(4)
1.773(6)–1.815(7)
1.221(6), 1.232(5), 1.209(6)
a
a
N–Oc
N–Of
O(1)–Y(1)–O(2)
O(1)–Y(1)–O(3)
O(2)–Y(1)–O(3)
Oc–N–Oc
84.1(1)
84.2(1)
153.5(1)
115.8(5)–116.4(6)
Y(1)–O(1)–P(1)
Y(1)–O(2)–P(2)
Y(1)–O(3)–P(3)
154.3(3)
157.9(2)
157.3(3)
50.9(1)–52.4(1)
b
Oc–Y(1)–Oc
(d) [Y(Me3PO)3(NO3)3]
Y(1)–O(1)
Y(1)–O(2)
Y(1)–O(3)
Y(1)–O(N)
2.281(7)
2.279(7)
2.262(7)
2.441(7)–2.520(8)
1.495(7)–1.521(7)
1.26(1)–1.30(1)
Y(2)–O(4)
Y(2)–O(5)
Y(2)–O(6)
Y(2)–O(N)
2.270(6)
2.251(7)
2.258(7)
2.463(8)–2.525(7)
P(n)–O(n) (n = 1–6)
a
a
N–Oc
N–Of
1.21(1)–1.25(1)
O(1)–Y(1)–O(2)
O(1)–Y(1)–O(3)
O(2)–Y(1)–O(3)
Y(1)–O(1)–P(1)
Y(1)–O(2)–P(2)
Y(1)–O(3)–P(3)
Oc–N–Oc
86.0(2)
82.9(2)
84.3(2)
149.9(4)
140.2(4)
147.0(4)
115(1)–119(1)
O(4)–Y(2)–O(5)
O(4)–Y(2)–O(6)
O(5)–Y(2)–O(6)
Y(2)–O(4)–P(4)
Y(2)–O(5)–P(5)
Y(2)–O(6)–P(6)
82.5(2)
86.8(3)
86.1(2)
149.3(4)
147.8(4)
144.5(4)
51.2(2)–52.5(2)
b
Oc–Y–Oc
a Oc and Of refer to co-ordinated and ‘free’ O respectively of NO3. b The Oc–Y–Oc angle refers to co-ordination by one NO3 group.
Table 3 Multinuclear NMR dataa
Complex
δ (31P-{1H})
δ(89Y/45Sc)
2J(31P–89Y)/Hz
T/K
[Y(Ph3PO)3(NO3)3]
33.3 (d)
35.7 (d)
37.0 (d)
36.6 (d)
37.7 (d)
38.3 (d)
48.3 (d)
52.0d
Ϫ35.7 (quartet)
Ϫ2.0 (quintet)
Ϫ35.8 (triplet)
Ϫ26.2 (quartet)
Ϫ37.6 (triplet)
ϩ6.0 (quintet)
Ϫ17.7 (quartet)
Ϫ0.3 (quintet)
Ϫ12.0 (triplet)
Ϫ7.5
Ϫ4.0
Ϫ36.0 (br)
Ϫ2.5
ϩ5.0
ϩ11.5
9
12
11
10
8
10
6
240
240
200
220
200
200
200
200
200
300
300
240
300
300
300
[Y(Ph3PO)4(NO3)2]NO3
[Y(Ph3PO)2(EtOH)(NO3)3]
[Y(Ph2MePO)3(NO3)3]
[Y(Ph2MePO)2(EtOH)(NO3)3]
“Y(Ph2MePO)4(NO3)3”b
[Y(Me3PO)3(NO3)3]
“Y(Me3PO)4(NO3)3”c
8
≈12
[Y(Me3PO)2(H2O)(NO3)3]
[Sc(Ph3PO)2(NO3)3]
[Sc(Ph2MePO)3(NO3)3]
[Sc(Ph2MePO)4(NO3)2]NO3
[Sc(MePO)2(EtOH)(NO3)3]
51.0d
37.7
39.5
38.7
54.8
62.0 (octet)
64.7
—
—
—
—
20 f
—
e
[Sc(Me3PO)6][NO3]3
“[Sc(Me3PO)5(NO3)][NO3]2”g
a At temperature stated in CH2Cl2–CDCl3 solutions resonances are singlets unless indicated otherwise, d = doublet. b In situ from [Y(Ph2-
MePO)3(NO3)3] and an excess of Ph2MePO (see text). c In situ from [Y(Me3PO)3(NO3)3] and an excess of Me3PO. d Ill defined coupling. e In
MeNO2–CD3NO2 solution containing an excess of Me3PO. f 2J(45Sc–31P). g In situ from [Sc(Me3PO)6][NO3]3 in MeNO2–CD3NO2 (see text).
2444
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Table 4 Selected bond lengths (Å) and angles (Њ) for [Sc(Ph3PO)2(NO3)3] and [Sc(Ph2MePO)4(NO3)2]NO3ؒxCH2Cl2
(a) [Sc(Ph3PO)2(NO3)3]
Sc–O(1)
Sc–O(2)
Sc–O(N)
2.068(7)
2.047(7)
2.205(8)–2.311(7)
1.264(12)–1.280(11)
O(1)–P(1)
O(2)–P(2)
P–C
1.497(8)
1.513(7)
1.77(1)–1.81(1)
1.208(11)–1.216(12)
a
a
N–Oc
N–Of
O(1)–Sc–O(2)
Sc–O(1)–P(1)
Oc–N–Oc
90.7(3)
165.1(5)
112.0(10)–114.4(9)
Sc–O(2)–P(2)
Oc–Sc–Oc
178.5(5)
55.2(3)–57.1(3)
b
(b) [Sc(Ph2MePO)4(NO3)2]NO3ؒxCH2Cl2
Sc–O(1)
Sc–O(2)
Sc–O(3)
Sc–O(4)
Sc–O(N)
2.099(6)
2.097(6)
2.090(6)
2.088(6)
2.311(6)–2.425(6)
1.257(9)–1.277(9)
O(1)–P(1)
O(2)–P(2)
O(3)–P(3)
O(4)–P(4)
P–C
1.493(6)
1.505(6)
1.502(6)
1.504(6)
1.782(9)–1.822(9)
1.214(9), 1.219(9)
a
a
N–Oc
N–Of
O(1)–Sc–O(2)
O(1)–Sc–O(4)
O(2)–Sc–O(3)
O(3)–Sc–O(4)
Oc–N–Oc
93.8(2)
91.7(2)
93.5(2)
92.2(2)
Sc–O(1)–P(1)
Sc–O(2)–P(2)
Sc–O(3)–P(3)
Sc–O(4)–P(4)
162.7(4)
159.6(4)
161.3(4)
162.4(4)
b
114.4(7), 116.5(7)
Oc–Sc–Oc
54.8(2), 53.3(2)
a Oc and Of refer to co-ordinated and ‘free’ O respectively of NO3. b The Oc–Sc–Oc angle refers to co-ordination by one NO3 group.
complex does not disproportionate in solution. Moreover,
the phosphine oxides are equivalent according to NMR, which
contrasts with the “T” shape arrangement in the solid, and
presumably indicates fluxionality in solution. Although it was
not possible to isolate a [Y(Ph2MePO)4(NO3)2]NO3 complex,
addition of an excess of Ph2MePO to CH2Cl2 solutions of
[Y(Ph2MePO)3(NO3)3] produces essentially complete con-
version into the tetrakis complex, identified (Table 3) by a
quintet at δ 6.0 in the 89Y NMR spectrum. The Me3PO com-
plexes generally behave similarly to the Ph2MePO analogues
in solution, including formation of [Y(Me3PO)4(NO3)2]NO3 in
the presence of an excess of ligand (Table 3). All the Y–R3PO
complexes show slow exchange (on the phosphorus NMR
timescale) with added R3PO at ambient temperatures, which
contrasts with the lanthanum systems where exchange is fast
at 300 K, but slows at <ca. 240 K.15
Scandium complexes
The scandium nitrate–R3PO systems are simpler than the
yttrium ones showing a more limited range of stoichiometries.
The reaction of Sc(NO3)3ؒ5H2O with Ph3PO in ethanol,
irrespective of the ratio of reagents, gave colourless crystals of
[Sc(Ph3PO)2(NO3)3]. In contrast, a ≥4:1 molar ratio of Ph2Me-
Fig. 6 The co-ordination polyhedron around Sc in [Sc(Ph3PO)2-
(NO3)3] showing the atom labelling scheme. Phenyl C atoms not bonded
to P have been omitted for clarity. Thermal ellipsoids are drawn at the
50% probability level and H atoms omitted.
PO:Sc(NO3)3ؒ5H2O in ethanol gave [Sc(Ph2MePO)4(NO3)2]-
NO3. A 1:1 or 2:1 molar ratio in ethanol produced [Sc(Ph2-
MePO)3(NO3)3] which was very soluble and difficult to isolate,
tending to separate as an oily product on concentration of the
solution. The species has not been obtained as a crystalline
solid, but in solution in CH2Cl2 it has a conductance well below
that of a 1:1 electrolyte, whilst the IR spectrum of the solid
shows no evidence for ionic nitrate. It is not possible on the
basis of the available data to distinguish between 9-co-ordinate
[Sc(Ph2MePO)3(η2-NO3)3] or 8-co-ordinate [Sc(Ph2MePO)3-
(η2-NO3)2(η1-NO3)] structures, and whereas 9-co-ordination is
very rare for the small scandium ion,23 it may be possible here
given the small bite of η2-NO3 groups. The Me3PO–Sc(NO3)3
system proved to be significantly different, in that reaction of a
large excess (6–10 fold) of ligand with Sc(NO3)3ؒ5H2O in cold
ethanol gave white [Sc(Me3PO)6][NO3]3. The IR spectrum (CsI
disc) is rather simple and, in addition to phosphine oxide bands,
shows moderate intensity peaks at 1361, 1298 and 834 cmϪ1
which are assigned to ionic nitrate groups,16 and there was no
evidence of co-ordinated nitrate groups. The complex is
insoluble in chlorocarbons, acetone and cold ethanol, but is
soluble in nitromethane in which it has a molar conductance of
157 ohmϪ1 cm2 molϪ1 which is in the range expected for 2:1
electrolytes, and on addition of Me3PO the conductance rises to
250 ohmϪ1 cm2 molϪ1, typical of a 3:1 electrolyte.22 It dissolves
with some decomposition in cold dmf, and in boiling ethanol
it decomposes mainly to [Sc(Me3PO)2(EtOH)(NO3)3] and Me3-
PO identified by in situ 31P and 45Sc NMR studies. The [Sc(Me3-
PO)2(EtOH)(NO3)3] was isolated with difficulty in very poor
yield from solutions of Sc(NO3)3ؒ5H2O and Me3PO in a 1:1
ratio in ethanol.
The crystal structures of [Sc(Ph3PO)2(NO3)3] and [Sc(Ph2-
MePO)4(NO3)2]NO3ؒxCH2Cl2 have been determined and are
shown in Figs. 6 and 7 with selected bond lengths and angles in
Table 4. In both structures the Sc atom is eight-co-ordinate
with the co-ordinated NO3 group bonded in the symmetrical
bidentate mode. With a monodentate group conceptually
J. Chem. Soc., Dalton Trans., 2000, 2439–2447
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Fig. 8 The 31P-{1H} NMR resonance of [Sc(Me3PO)6]3ϩ in MeNO2
solutions of [Sc(Me3PO)6][NO3]3 containing an excess of Me3PO.
(Fig. 8) due to coupling to 45Sc (I = 7/2). The 45Sc NMR of the
initial solution contained a broad feature at δ 11.8 (W1/2 = 450
Hz) and a sharp weaker feature at δ 5.0 (W1/2 ca. 150 Hz). In
the presence of an excess of Me3PO only a single resonance at
δ 5.0 (W1/2 180 Hz) was observed, but unlike the corresponding
31P resonance this showed no resolved 45Sc–31P coupling. The
species which shows resolved 45Sc coupling on the 31P NMR
resonance (Fig. 8) must be [Sc(Me3PO)6]3ϩ, where the regular
Oh symmetry slows the quadrupolar relaxation rate. This is also
supported by the conductance data showing a 3:1 electrolyte is
present. In the absence of an excess of Me3PO, the complex
partially decomposes to a lower symmetry cation [Sc(Me3-
PO)5(NO3)][NO3]2 (which is likely to be fluxional) and Me3PO,
consistent with the lower conductance and the NMR data
described above.
Fig. 7 The structure of the cation in [Sc(Ph2MePO)4(NO3)2]NO3ؒ
xCH2Cl2 showing the atom labelling scheme. Thermal ellipsoids are
drawn at the 40% probability level and H atoms omitted for clarity.
replacing NO3 the two structures are described as a trigonal
bipyramid (with axial and equatorial Ph3PO) and an octa-
hedron (with trans NO3 groups). Similar changes in NO3
geometry are observed as were seen in the yttrium compounds
above and the difference in Sc–O(P) and Sc–O(N) is again
similar but with smaller values for both due to the smaller
radius of Sc.
The δ(31P) of 54.8 and δ(45Sc) of Ϫ2.5 of [Sc(Me3PO)2(EtOH)-
(NO3)3] in CH2Cl2 seem unexceptional. As noted above, in situ
31P-{1H} and 45Sc NMR studies of Sc(NO3)3–Me3PO mixtures
with 1:1–1:4 ratios in ethanol show [Sc(Me3PO)2(EtOH)-
(NO3)3] (and sometimes Me3PO δ(31P) 43.0) as the only major
constituents, and similar spectra were obtained from solutions
of [Sc(Me3PO)6][NO3]3 dissolved in hot ethanol.
31P-{1H} and 45Sc NMR Studies. In contrast to 89Y, the 45Sc
NMR spectra were easily observed even at ambient tem-
peratures, but in only one case 31P–45Sc coupling was resolved,
its absence for the other complexes no doubt due to the fast
quadrupolar relaxation resulting from the low symmetry
environments of the scandium nuclei. The 31P-{1H} NMR
spectrum of [Sc(Ph3PO)2(NO3)3] in CH2Cl2 was a singlet at
δ 37.7 and was unchanged on cooling the solution to 200 K.
The 31P-{1H} resonance and the scandium resonance at δ Ϫ7.5
(W1/2 = 900 Hz) were unaffected by the addition of an excess
of Ph3PO showing both that exchange with ligand was slow
on the NMR timescales and that no other complex formed.
The NMR data on [Sc(Ph2MePO)3(NO3)3] are also simple;
δ(31P) = 39.5, δ(45Sc) Ϫ4.0 (W1/2 350 Hz) (Table 3). In contrast
the 31P-{1H} NMR spectrum of [Sc(Ph2MePO)4(NO3)2]NO3 at
300 K (CH2Cl2) is a broad (W1/2 700 Hz) peak at δ 38.5, which
on cooling sharpens rapidly to give at 250 K a major peak at
δ 38.7 (tetrakis complex) and weaker peaks at δ 39.5 (tris)
and 29.2 (Ph2MePO). The 45Sc NMR spectrum at 300 K shows
partially overlapping resonances at ca. δ Ϫ4 and Ϫ33 which
broaden into one asymmetric feature on cooling, presumably a
result of the scandium quadrupole. Addition of an excess of
Ph2MePO to the solution at 300 K results in an increase in the
relative intensity of the lower frequency resonance, but in con-
trast to the yttrium systems it does not appear to be possible
completely to suppress the tris complex by adding an excess of
phosphine oxide.
Conclusion
The multinuclear NMR studies have revealed a range of
complexes are present in M(NO3)3–R3PO systems, which show
subtle variations with M, R3PO and the reaction conditions.
Although the complexes are not undergoing fast exchange with
free R3PO on the NMR timescale, all are labile and interconvert
easily in solution, the fast equilibria probably accounting
for the fact that single species crystallise from most solutions.
The NMR data do not reflect the inequivalent R3PO environ-
ments identified in the crystalline solids, consistent with
fluxionality at the high co-ordination number metal centres in
solution.
Acknowledgements
We thank EPSRC for a studentship (M. C. P.) and Professor
M. B. Hursthouse for access to the Nonius CCD diffractometer.
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The 31P-{1H} NMR spectrum obtained from [Sc(Me3-
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MeNO2, mp 244 K). On addition of a 10 fold excess of Me3PO
the co-ordinated phosphine oxide resonance shifted to δ 62.0
and under higher resolution was seen to be an eight line pattern
2446
J. Chem. Soc., Dalton Trans., 2000, 2439–2447

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