Six- and eight-coordinate thio- and seleno-ether complexes of NbF 5 and some comparisons with NbCl5 and NbBr5 adducts

Article abstract of DOI:10.1039/b916336k

The reaction of RS(CH₂)₂SR (R = Me, Et or ⁱPr) with NbF₅ produces [NbF₄{RS(CH ₂)₂SR}₂][NbF₆] which contain distorted eight-coordinate (dodecahedral) cations

Full text of DOI:10.1039/b916336k

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Six- and eight-coordinate thio- and seleno-ether complexes of NbF5 and some
comparisons with NbCl5 and NbBr5 adducts†
Marek Jura,a William Levason,*a Raju Ratnani,‡b Gillian Reida and Michael Webstera
Received 10th August 2009, Accepted 7th October 2009
First published as an Advance Article on the web 16th November 2009
DOI: 10.1039/b916336k
The reaction of RS(CH2)2SR (R = Me, Et or iPr) with NbF5 produces [NbF4{RS(CH2)2SR}2][NbF6]
which contain distorted eight-coordinate (dodecahedral) cations and octahedral anions, whereas
RSe(CH2)2SeR (R = Me or Bun) form six-coordinate [(NbF5)2(m-RSe(CH2)2SeR)]. Et2S and Me2Se (L)
also form six-coordinate [NbF5(L)], but Me2S forms both [NbF5(Me2S)] and an eight-coordinate cation
in [NbF4(Me2S)4][NbF6]. MeS(CH2)2SMe forms eight-coordinate cations in [NbX4{MeS(CH2)2SMe}2]-
[NbX6] (X = Cl or Br), but other complexes of the heavier halides including [NbX5(L)] and
[(NbX5)2(m-L–L)] (L–L = RSe(CH2)2SeR; o-C6H4(CH2SMe)2 and o-C6H4(CH2SeMe)2) contain
six-coordinate niobium. The very unstable [NbCl5(Me2Te)] was characterised spectroscopically, but all
other attempts to form telluroether complexes resulted in decomposition, and NbI5 was reduced even
by thioethers. The complexes have been characterised by multinuclear NMR (1H, 19F, 93Nb, 77Se or
125Te), IR and UV/visible spectroscopy, and X-ray crystal structures are reported for
[NbF4{RS(CH2)2SR}2][NbF6] (R = Me, iPr), [NbF4(Me2S)4][NbF6], [NbCl5(Me2Se)], [NbBr5(Me2S)],
[(NbCl5)2{o-C6H4(CH2SMe)2}] and [(NbCl5)2{MeSe(CH2)2SeMe}]. All the complexes are very
moisture sensitive and the fluoride complexes decompose slowly with fluorination of the neutral ligand.
have been described.16 With the exception of [(NbCl5)2([14]aneS4)]
Introduction
([14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane), none of these
Complexes of soft neutral thioether or selenoether ligands with
have been structurally characterised. Here we describe systematic
hard oxophilic early transition metals in their highest oxidation
studies of the reactions of NbF5 with a range of chalcogenoether
states are relatively uncommon, and metal fluoride complexes
ligands and selected comparator data on NbCl5 and NbBr5
are very rare.1,2 We have reported dithioether and diselenoether
adducts, focusing particularly on structural and multinuclear
adducts of MoO2X2 (X = Cl or Br),3 WO2X2,4 MCl4 (M = Ti, Zr
NMR results. In a communication17 we have described the
or Hf),5,6 VOX3 (X = F or Cl (thioethers only)),7 and VCl4,7,8 all of
structural characterisation of two sulfonium salts obtained as by-
products from the reactions of NbF5 with o-C6H4(CH2SMe)2 and
[9]aneS3 (1,4,7-trithiacyclononane).
which are extremely readily hydrolysed. Some of these complexes
are single-source CVD precursors for metal dichalcogenide films.6,8
In the case of niobium(V), the simplest six-coordinate adducts
[NbX5(R2S)] (X = F, Cl or Br; R = Me or Et) were prepared by
Fairbrother and co-workers by direct reaction of NbX5 with R2S
Experimental
in the absence of a solvent and identified using a combination of
vapour pressure measurements and microanalysis.9,10 These, and
the Me2Se analogues, were also examined by Merbach and co-
workers, and solution UV-visible and 1H NMR spectra reported,
although in many cases these were from complexes generated in
situ.11–13 Subsequently, detailed 1H NMR studies revealed that lig-
and exchange proceeds by an associative mechanism, in contrast to
ether analogues, which react by a dissociative mechanism.14 There
is very little information on dithioether complexes,15 although
a small number of thiacrown complexes [(thiacrown)(NbCl5)x]
Infrared spectra were recorded as Nujol mulls between CsI plates
using a Perkin-Elmer 983G or Spectrum 100 spectrometers over
1
the range 4000–200 cm-1. H NMR spectra were recorded from
1
CDCl3 solutions using a Bruker AV300 spectrometer. 19F{ H},
1
1
77Se{ H}, 125Te{ H} and 93Nb NMR spectra were recorded using
a Bruker DPX400 spectrometer and are referenced to external
CFCl3, neat Me2Se, neat Me2Te and [Et4N][NbCl6] in MeCN
respectively. UV/visible spectra were recorded from solid samples
diluted with BaSO4 using the diffuse reflectance attachment of
a Perkin-Elmer Lambda 19 spectrometer. Microanalyses on new
complexes were undertaken by Medac Ltd, except for some of
the fluoride complexes which decomposed at room temperature in
a few hours (see Discussion section), which precluded obtaining
microanalytical data. Preparations were undertaken using stan-
dard Schlenk and glove-box techniques under a N2 atmosphere.
Solvents were dried by distillation from CaH2 (CH2Cl2) or
Na/benzophenone ketyl (hexane and diethyl ether). Anhydrous
NbX5 (X = F, Cl, Br or I) were obtained from Aldrich, Apollo
or Strem and used as received. The ligands R2S (R = Me or
aSchool of Chemistry, University of Southampton, Southampton, UK SO17
1BJ
bDepartment of Pure and Applied Chemistry, M. D. S. University, Ajmer,
305009, India
† Electronic supplementary information (ESI) available: Additional ex-
perimental and spectroscopic data for [NbX5L] complexes, and crystallo-
graphic data and ORTEPs for [NbBr5(Me2S)] and [NbCl5(Me2Se)]. CCDC
reference numbers 723266–723272. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b916336k
‡ Deceased 5th June 2009.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 883–891 | 883
©

View Article Online
Et) and Me2Se were obtained from Aldrich or Strem and stored
d 1.39 (br) [6H] Me, 2.91 (br) [4H] CH2, 3.33 (s) [4H] CH2. UV/vis
i
over molecular sieves. Me2Te, RS(CH2)2SR (R = Me, Et or Pr),
(d.r.)/cm-1: 27750.
n
RSe(CH2)2SeR (R = Me or Bu), o-C6H4(CH2EMe)2 (E = S or
i
[NbF4{ PrS(CH2)2SiPr}2][NbF6]
Se) and MeTe(CH2)3TeMe were made by literature methods,18–21
and stored over molecular sieves.
NbF5 (0.37 g, 2.0 mmol) was suspended in anhydrous CH2Cl2
i
(20 mL) and a solution of PrS(CH2)2SiPr (0.36 g, 2.0 mmol) in
[NbF5(Me2S)]
CH2Cl2 (4 mL) added with stirring. A clear colourless solution
formed rapidly, which was stirred for 30 min and then concentrated
in vacuo to ~5 mL. Refrigeration for 1 week produced large, clear
crystals, which were filtered off and dried in vacuo. Yield: 0.45 g,
63%. Required for C16H36F10Nb2S4·CH2Cl2 (817.4): C, 25.0; H,
4.7. Found: C, 25.0; H, 4.9% 1H NMR (CDCl3, 295 K): d 1.31 (d)
J = 6 Hz, [12H] Me, 3.05 (s) [4H] CH2, 3.52 (m) [2H] CH. UV/vis
(d.r.)/cm-1: 27700.
Powdered NbF5 (0.38 g, 2.0 mmol) was added to neat Me2S
(10 mL) with stirring, when the solid initially dissolved to give a
yellow solution, and then over a period of ca. 30 min precipitated
as a white powder. This was filtered off and dried in vacuo. Yield:
0.40 g, 80%. Required for C2H6F5NbS (250.0): C, 9.6; H, 2.4.
1
Found: C, 9.3; H, 3.0%. H NMR (CDCl3, 295 K): d 2.36 (s).
UV/vis (d.r.)/cm-1: 27800, 38000.
[(NbF5)2{MeSe(CH2)2SeMe}]
[NbF5(Et2S)]
Colourless oil made as described.9 1H NMR (CDCl3, 295 K): d
NbF5 (0.37 g, 2.0 mmol) was suspended in anhydrous CH2Cl2
(20 mL) at 273 K, and a solution of MeSe(CH2)2SeMe (0.22 g,
1.0 mmol) in CH2Cl2 (4 mL) added with stirring. After 5 min the
colourless solution was concentrated in vacuo to ca. 5 mL, and
the white solid produced filtered off and dried in vacuo. The solid
slowly turns brown at ambient temperatures. 1H NMR (CD2Cl2,
295 K): d 2.54 (s) [6H] Me, 3.5 (s) [4H] CH2. UV/vis (d.r.)/cm-1:
28500, 33800.
1.40 (t) [3H], 2.95 (q) [2H]. UV/vis (d.r.)/cm-1: 26000, 38400.
[NbF4(Me2S)4][NbF6]
NbF5 (0.38 g, 2.0 mmol) was suspended in CH2Cl2 (10 mL)
and Me2S (0.36 g, 6.0 mmol) syringed in with stirring to give a
colourless solution. This was refrigerated for 5 days (-18 ◦C), when
colourless crystals separated. These were filtered off from the cold
solution and dried in a stream of nitrogen. Yield: 0.35 g, 56%. The
crystals lose Me2S and crumble a little above room temperature
or in vacuo, which prevented reproducible microanalyses being
n
[(NbF5)2{ BuSe(CH2)2SenBu}]
NbF5 (0.37 g, 2.0 mmol) was suspended in anhydrous CH2Cl2
n
(20 mL) at 273 K, and a solution of BuSe(CH2)2SenBu (0.46 g,
1
obtained. H NMR (CDCl3, 295 K): d 2.28 (s); (220 K) d 2.40.
UV/vis (d.r.)/cm-1: 27500.
1.0 mmol) in CH2Cl2 (4 mL) added with stirring. After 5 min the
pale yellow solution was concentrated in vacuo to leave a clear
yellow oil, which was washed with hexane (5 mL), the hexane
removed by cannula, and the oil dried in vacuo. The oil turns dark
in a few hours at room temperature. The solution stability is poor,
solutions becoming red in about 30 min at room temperature
[NbF5(Me2Se)]
NbF5 (0.19 g, 1.0 mmol) was suspended in CH2Cl2 (10 mL) and
Me2Se (0.11 g, 1.0 mmol) syringed in with stirring to give a
colourless solution. After 10 min the solvent was removed in vacuo
to give a fawn solid, which was washed with hexane, filtered off and
dried. Yield: 0.27 g, 90%. The solid darkens slowly in the dry-box,
and solutions decompose in several hours, turning first brown and
then green–black. Decomposition is slower in a freezer. 1H NMR
(CDCl3, 295 K): d 2.76 (s). UV/vis (d.r.)/cm-1: 23000, 33800.
1
although reaction is much slower at 243 K. H NMR (CD2Cl2,
295 K): d 1.0 (t) [6H] Me, 1.45 (m) [4H] CH2, 1.9 (m) [4H] CH2,
3.40 (m) [4H] CH2, 3.50 (s) [4H] CH2.
[NbCl4{MeS(CH2)2SMe}2][NbCl6]
NbCl5 (0.39 g, 1.5 mmol) was suspended in anhydrous CH2Cl2
(20 mL) and a solution of MeS(CH2)2SMe (0.24 g, 2.0 mmol) in
CH2Cl2 (8 mL) added with stirring. The NbCl5 dissolved to give
a deep yellow solution which rapidly precipitated a deep yellow
powder. The mixture was stirred for 3 h, then concentrated in vacuo
to ~10 mL, and the deep yellow powder filtered off and dried in
vacuo. Yield: 0.52 g, 88%. Required for C8H20Cl10Nb2S4 (784.8): C,
12.3; H, 2.6. Found: C, 12.6; H, 2.8%. 1H NMR (CD2Cl2, 295 K):
d 2.46 (s) [6H] Me, 3.13 (s) [4H] CH2. UV/vis (d.r.)/cm-1: 21200
(sh), 25600, 34800.
[NbF4{MeS(CH2)2SMe}2][NbF6]
NbF5 (0.37 g, 2.0 mmol) was suspended in anhydrous CH2Cl2
(20 mL) and a solution of MeS(CH2)2SMe (0.245 g, 2.0 mmol)
in CH2Cl2 (4 mL) added with stirring. A clear colourless solution
formed rapidly, which was stirred for 30 min and then concentrated
in vacuo to ~10 mL. Refrigeration for one week produced
colourless crystals, which were filtered off and dried in vacuo. Yield:
0.45 g, 73%. Required for C8H20F10Nb2S4 (620.3): C, 15.5; H, 3.3.
Found: C, 15.0; H, 3.1%. 1H NMR (CDCl3, 295 K): d 2.25 (s) [6H]
Me, 3.03 (s) [4H] CH2. UV/vis (d.r.)/cm-1: 27700.
[NbBr4{MeS(CH2)2SMe}2][NbBr6]
This was made similarly to the chloride analogue above as a red–
brown solid. Yield: 73%. Required for C8H20Br10Nb2S4 (1229.4):
C, 7.8; H, 1.6. Found: C, 7.7; H, 1.7%. 1H NMR (CD2Cl2, 295 K):
d 2.34 (s) [6H] Me, 3.13 (s) [4H] CH2. UV/vis (d.r.)/cm-1: 19600
(sh), 23800, 26600, 34500.
[NbF4{EtS(CH2)2SEt}2][NbF6]
This was made similarly to [NbF4{MeS(CH2)2SMe}2][NbF6], as a
white powder. Yield: 65%. Required for C12H28F10Nb2S4 (676.4):
C, 21.3; H, 4.2. Found: C, 21.2; H, 3.6%. 1H NMR (CDCl3, 295 K):
884 | Dalton Trans., 2010, 39, 883–891
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
n
[(NbCl5)2{o-C6H4(CH2SMe)2}]
[(NbCl5)2{ BuSe(CH2)2SenBu}]
NbCl5 (0.49 g, 2.0 mmol) was suspended in anhydrous CH2Cl2
(20 mL) and a solution of o-C6H4(CH2SMe)2 (0.18 g, 1.0 mmol)
in CH2Cl2 (8 mL) added with stirring. The NbCl5 dissolved to
give a deep orange–yellow solution which was stirred for 3 h, then
concentrated in vacuo to ~ 10 mL, and the orange–yellow powder
filtered off and dried in vacuo. Yield: 0.52 g, 70%. Required for
C10H14Cl10Nb2S2 (738.7): C, 16.3; H, 1.9. Found: C, 16.0; H, 2.3%.
1H NMR (CDCl3, 295 K): 2.46 (s) [6H] Me, 4.34 (s) [4H] CH2,
7.34–7.43 (m) [4H] C6H4. UV/vis (d.r.)/cm-1: 25600, 34100.
This was made similarly to the diselenahexane complex as a red
wax. Yield: 80%. 1H NMR (CDCl3, 295 K): d 1.0 (t) [3H] Me, 1.45
(m) [2H] CH2, 1.9 (m) [2H] CH2, 3.2–3.5 (br) [4H] CH2. UV/Vis
(d.r.)/cm-1: 23500, 28700 (sh), 33000.
X-Ray crystallography
A summary of details of the crystallographic data collection and
refinement are given in Table 1. Crystals of the fluoride complexes
were obtained by refrigerating the synthesis solutions (see above),
other crystals were grown by refrigerating the filtrates from the
syntheses for several days at -18 ◦C. Data collection used a
Nonius Kappa CCD diffractometer fitted with monochromated
[(NbBr5)2{o-C6H4(CH2SMe)2}]
This was made similarly to the chloride analogue above us-
ing NbBr5. Orange–red powder. Yield: 40%. Required for
C10H14Br10Nb2S2 (1183.2): C, 10.1; H, 1.1. Found: C, 9.4; H, 0.9%.
1H NMR (CDCl3, 295 K): d 2.48 (s) [6H] Me, 4.36 (s) [4H] CH2,
7.38–7.43 (m) [4H] C6H4. UV/vis (d.r.)/cm-1: 22700 (sh), 25000,
32800.
˚
Mo-Ka X-radiation (l = 0.71073 A) and with the crystals
held at 120 K in a nitrogen gas stream. Structure solution
and refinement were straightforward,22–24 with H atoms being
placed in calculated positions using the default C–H distance. For
[(NbCl5)2{o-C6H4(CH2SMe)2}] the crystals examined were twins,
but for the data reported the diffractometer software enabled
satisfactory indexing of the major component.
[(NbCl5)2{o-C6H4(CH2SeMe)2}]
NbCl5 (0.39 g, 1.5 mmol) was suspended in anhydrous CH2Cl2
(20 mL) and a solution of o-C6H4(CH2SeMe)2 (0.21 g, 0.72 mmol)
in CH2Cl2 (8 mL) added with stirring. The NbCl5 dissolved to give
a deep orange solution which was stirred for 3 h, then concentrated
in vacuo to ~10 mL, and the orange powder filtered off and dried in
vacuo. Yield: 0.47 g, 78%. Required for C10H14Cl10Nb2Se2 (832.5):
C, 14.4; H, 1.7. Found: C, 13.7; H, 1.6%. 1H NMR (CDCl3, 295 K):
d 2.38 (s) [6H] Me, 4.36 (s) [4H] CH2, 7.25–7.39 (m) [4H] C6H4.
UV/vis (d.r.)/cm-1: 24400, 32800.
Results and discussion
[NbF5(R2E)] (R2E = Me2S, Et2S, Me2Se) and
[NbF4(Me2S)4][NbF6]
Reactions are shown in Scheme 1.
[(NbBr5)2{o-C6H4(CH2SeMe)2}]
This was made similarly to the chloride analogue above us-
ing NbBr5. Orange-red powder. Yield: 72%. Required for
C10H14Br10Nb2Se2 (1277.0): C, 9.4; H, 1.1. Found: C, 9.4; H, 1.0%.
1H NMR (CDCl3, 295 K): d 2.43 (br, s) [6H] Me, 4.26 (br, s) [4H]
CH2, 7.28–7.42 (m) [4H] C6H4. UV/vis (d.r.)/cm-1: 21750 (sh),
24800, 30030.
Scheme 1 Reactions of NbF5 with thio- and seleno-ethers.
The fluoride systems are extremely sensitive to moisture, and
syntheses and measurements must be conducted under rigorously
anhydrous conditions. Some of the complexes decompose in a
few days even in sealed tubes in a freezer, turning green or
brown as discussed below, and hence all measurements were
made on freshly prepared complexes. The reaction of Et2S with
NbF5 either in CH2Cl2 solution, or using neat Et2S as solvent,
followed by removal of volatiles in vacuo, left [NbF5(Et2S)]9 as
a colourless oil which solidified on cooling in an ice-bath. The
IR spectrum (Table 2) shows three n(NbF) modes as expected
for a C4v geometry. The solid-state UV/visible spectrum shows
the transitions p(R2S) → Nb at 26000 and 38400 cm-1, which
disagrees with the reported solution spectrum which quoted only
a 38000 cm-1 band.13 The p(R2S) → Nb transitions are similar
in energy to those in complexes of the heavier halides, whilst the
p(F) → Nb CT bands which are expected in the far-UV region
were not observed. In CH2Cl2 solution at 295 K, the 19F NMR
spectrum is a broad singlet (Table 2), indicating a dynamic system,
probably reversible thioether ligand dissociation. On cooling the
[(NbCl5)2{MeSe(CH2)2SeMe}]
NbCl5 (0.39 g, 1.5 mmol) was suspended in anhydrous CH2Cl2
(20 mL) and a solution of MeSe(CH2)2SeMe (0.16 g, 0.74 mmol)
in CH2Cl2 (8 mL) added with stirring. The NbCl5 dissolved to give
a deep-orange solution which was stirred for 3 h, then concentrated
in vacuo to ~10 mL, and the deep orange powder filtered off and
dried in vacuo. Yield: 0.43 g, 76%. Required for C4H10Cl10Nb2Se2
(756.4): C, 6.3; H, 1.3. Found: C, 6.1; H, 1.3%. 1H NMR (CDCl3,
295 K): d 2.46 (s) [6H] Me, 3.3 (s) [4H] CH2. UV/vis (d.r.)/cm-1:
23500, 27700 (sh), 32800.
[(NbBr5)2{MeSe(CH2)2SeMe}]
This was made similarly to the chloride analogue above. Deep
red–brown powder. Yield: 70%. Required for C4H10Br10Nb2Se2
(1200.9): C, 4.0; H, 0.8. Found: C, 3.8; H, 0.9%. 1H NMR (CD2Cl2,
223 K): d 2.2 (s) [6H] Me, 3.3 (s) [4H] CH2. UV/vis (d.r.)/cm-1:
21750 (sh), 25250, 31250.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 883–891 | 885
©

View Article Online
Table 1 Crystal data and structure refinement detailsa
i
[NbF4{MeS(CH2)2SMe}2]- [NbF4{ PrS(CH2)2SiPr}2]- [(NbCl5)2{o-
[(NbCl5)2{MeSe-
Compound
[NbF4(Me2S)4][NbF6] [NbF6]
[NbF6]
C6H4(CH2SMe)2}] (CH2)2SeMe}]
Formula
M
C8H24F10Nb2S4
624.33
Tetragonal
P4/ncc (130)
12.283(5)
12.283(5)
13.860(4)
90
C8H20F10Nb2S4
620.30
Monoclinic
C16H36F10Nb2S4
732.51
C10H14Cl10Nb2S2
738.65
C4H10Cl10Nb2Se2
756.36
Crystal system
Space group (no.)
Triclinic
Orthorhombic
Pnc2 (30)
10.3087(5)
22.4368(15)
10.3102(5)
90
90
90
2384.7(2)
4
2.252
Monoclinic
P21/n (14)
6.9033(15)
13.020(4)
11.111(3)
90
98.812(15)
90
986.9(5)
2
¯
Cc (9)
P1 (2)
˚
a/A
14.0661(10)
26.321(2)
10.7327(10)
90
101.252(5)
90
3897.3(5)
8
1.685
2432
23913
0.037
8152
10.2850(10)
11.6895(15)
13.5404(15)
115.206(7)
90.596(10)
110.136(10)
1359.1(3)
2
1.223
736
27957
0.058
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
U/A
Z
90
90
3
˚
2091.0(12)
4
1.571
1232
14628
0.150
1196
m(Mo-Ka)/mm-1
F(000)
6.184
708
17501
0.103
1432
15435
0.060
4956
Total number reflections
Rint
Unique reflections
6180
2267
No. of parameters, restraints 58, 0
442, 2
0.035, 0.081
0.039, 0.084
300, 0
0.047, 0.102
0.066, 0.113
218, 4
0.052, 0.113
0.058, 0.116
83, 0
0.060, 0.096
0.105, 0.112
R1, wR2 [I > 2s(I)]b
R1, wR2 (all data)
0.069, 0.124
0.103, 0.135
ꢀ
ꢀ
ꢀ
ꢀ
◦
a
2
4 1/2
Common items: T = 120 K; l(Mo-Ka) = 0.71073 A; q(max) = 27.5 . b R1 = ꢀFo| - |Fcꢀ/ |Fo|; wR2 = [ w(Fo - Fc2)2/ wFo
]
.
˚
Table 2 Selected spectroscopic data for [NbF5(R2E)], [NbF4(Me2S)4][NbF6] and [NbF4{R2E(CH2)2ER2}2][NbF6]
1
Compound
IR n(Nb–F)/cm-1 (Nujol)
d(93Nb)a,b
d(19F{ H})a,c
[NbF5(Et2S)]
662s, 641m, 600s
-1476 (7000) (295 K)
-1509 (7000) (295 K)
-1440 (6000) (295 K)
150.5 (br) (295 K)
146.0 [F], 134.4 [4F] (253 K)
143.2 (295 K)
144.2 (200 K)
141.6 (br) (295 K)
144.4 [F], 119.4 [4F] (253 K)
136.3 (br) (295 K)
119.5 (s) [4F], 102.5 (s) [6F]
223 K; 119.5 (s) [4F] 102.5
(10 lines) [6F] (200 K)
135.8, 105.2 (295 K)
132.8 (s) [4F], 103.8 (10 lines)
[6F] (230 K)
117.9 (sh), 111.5 (295 K)
114.6 (s) [4F], 104.5 (10 lines)
[6F] (243 K)
115.0, 104.0 (295 K)
112.5 (s) [4F], 103.8 (10 lines)
[6F] (243 K)
145.0 (br) (295 K)
144.0 (220 K)
[NbF5(Me2Se)]d
[NbF5(Me2S)]
[NbF4(Me2S)4][NbF6]
662s, 641m, 600s
640sh, 614vs (br), 594s
678sh, 610s, 552m
-1460, -1553 (295 K)
-1555 (7 lines, J = 335 Hz) (220 K)
i
[NbF4{ PrS(CH2)2SiPr}2][NbF6]
655sh, 615s (br), 599s, 565sh
640sh, 610vs, 599s, 570s
-1540 (295 K)
-1551 (7 lines, J = 335 Hz) (220 K)
[NbF4{MeS(CH2)2SMe}2][NbF6]
[NbF4{EtS(CH2)2SEt}2][NbF6]
[(NbF5)2{MeSe(CH2)2SeMe}]f
-1543 (295 K)
-1552 (7 lines, J = 335 Hz) (243 K)
645sh, 615s (br), 598s, 570sh
-1550 (295 K)
-1554 (7 lines, J = 335 Hz) (243 K)
n.o.e
650sh, 620vbr, s
650sh, 610s (vbr)
n
[(NbF5)2{ BuSe(CH2)2SenBu}]g
n.o.
146.5 (br) (295 K)
144.0 137.0 (sh) (200 K)
-
a In anhydrous CH2Cl2. b Relative to [NbCl6] in MeCN d 0, W in Hz in parenthesis. c Relative to CFCl3. d d(77Se) = +247.2 (relative to neat external
exhibits d(77Se) = 212).
1
2
Me2Se). e n.o = Not observed. d(77Se) = +265 at 295 K, (MeSe(CH2)2SeMe exhibits d(77Se) = 121). d(77Se) = +330 at 243 K, (nBuSe(CH2)2SenBu
f
g
solution the resonance splits, and at low temperatures the spectrum
contains a broad resonance at d 146.0 [F] and a sharper feature
at d 134.4 [4F], consistent with the C4v geometry expected; the
behaviour is reversible with temperature. The 93Nb spectrum§
is a broad feature at d -1476, although neither Nb–F nor
F–F couplings were resolved. The NbF5/Me2S system is more
complicated. When excess Me2S is distilled onto powdered NbF5
at 77 K, and the mixture allowed to warm slowly, reaction occurs
on melting to give a clear solution, which on further stirring
deposits the white solid, [NbF5(Me2S)]. Mixing the reagents at
ambient temperature results in a vigorous reaction, but gives
the same product. The solid state spectroscopic properties are
similar to the Et2S analogue (Table 2). However, when NbF5
reacts with excess Me2S in rigorously anhydrous CH2Cl2 solution,
§
93Nb, 100% abundance, I = 9/2, N = 24.44 MHz, Q = -0.2 ¥ 10-28 m2,
Dc = 2740 is one of the more sensitive nuclei and, despite the medium size
quadrupole moment, is readily observed in many systems.25
886 | Dalton Trans., 2010, 39, 883–891
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
19F{ H} NMR spectrum at 295 K is a broad singlet at d 136.3,
but on cooling this splits and by 240 K resolves into a relatively
sharp singlet at d 119.5 and a broad feature at d 102.5, the latter
developing the characteristic ten-line pattern of [NbF6]-, with
1JNbF = 335 Hz, on further cooling.27 The behaviour is reversible
with temperature and clearly indicates a rapidly exchanging system
at ambient temperatures. The 93Nb NMR spectrum at 295 K shows
a broad feature at d -1460 (W1/2 = 5000 Hz) and a sharper feature
at d -1556 (W1/2 = 2500 Hz), which are assigned to the cation and
anion respectively. On cooling, the higher frequency resonance
broadens and disappears below ~240 K, but the anion resonance
remains and the expected septet coupling to 19F is resolved.
Studies28 of NbF5 solutions in donor solvents including dmso, dmf
and pyridine (L) showed the characteristic resonance of [NbF6]-,
tentatively attributed to the formation of [NbF4L4][NbF6], but no
resonances for the cations were observed, explained as due to fast
relaxation (due to the lower symmetry) or exchange. Addition
of a small excess of Me2S to a solution of [NbF4(Me2S)4][NbF6]
in CH2Cl2 sharpens the cation resonance in the 93Nb spectrum,
but causes no change in the chemical shift, and the behaviour
on cooling is essentially unchanged. On storing in sealed tubes
(-18 ◦C) over several months the solid slowly becomes green, and
1
◦
˚
Table 3 Bond lengths (A) and angles ( ) for [NbF4(Me2S)4][NbF6]
Nb1–F1
S1–C1
Nb2–F2
Nb2–F3
1.899(4)
1.801(8)
1.869(9)
1.873(5)
Nb1–S1
S1–C2
Nb2–F4
2.724(2)
1.800(7)
1.901(8)
F1–Nb1–F1b
F1–Nb1–F1a
F1–Nb1–F1c
F1–Nb1–S1
F1–Nb1–S1c
C1–S1–C2
145.1(2)
S1–Nb1–S1b
S1–Nb1–S1a
S1–Nb1–S1c
F1a–Nb1–S1
F1b–Nb1–S1
Nb1–S1–C
67.67(8)
143.48(8)
125.19(8)
139.91(13)
79.81(13)
103.6(3), 105.5(3)
89.977(7)
89.8(2)
100.6(2)
71.27(13)
74.51(12)
101.5(4)
91.14(16)
88.86(16)
F2–Nb2–F3
F3–Nb2–F4
F3–Nb2–F3d
Symmetry operations: a = 1/2 - x, 3/2 - y, z; b = y - 1/2, 1/2 + x, 1/2 -
z; c = 1 - y, 1 - x, 1/2 - z; d = 1/2 - y, x, z.
a colourless solution forms, which on refrigeration for a few days,
deposited colourless crystals. The crystals crumble and lose Me2S
on drying in vacuo, but although they are extremely moisture
sensitive and difficult to handle, a satisfactory X-ray data set was
collected that identified the compound as [NbF4(Me2S)4][NbF6].
The structure (Fig. 1, Table 3) reveals an octahedral anion
and a dodecahedral cation. The dodecahedral (bisdisphenoid)
cation shows interpenetrating flattened NbF4 and elongated NbS4
tetrahedra, the crystallographic symmetry requiring only one
1
19F and H show new resonances, including ones assignable to
MeSCH2F,29 F- (and [SiF5]- from attack on the glass) consistent
with fluorination of the thioether and reduction of the niobium.
Similar decomposition occurs in a few days in CH2Cl2 solution at
room temperature.
˚
˚
Nb–F (1.899(4) A) and one Nb–S (2.724(2) A) distance in the
cation. The former is only slightly longer than the average Nb–F
distance in the associated [NbF6] anion (1.869(9)–1.901(8) A).
-
˚
Colourless [NbF5(Me2Se)] is formed from NbF5 and Me2Se in
CH2Cl2 solution, and appears to be the only product even with ex-
cess selenoether. In contrast to the dialkyl sulfide complexes which
can be stored in a glove-box for many weeks, the [NbF5(Me2Se)]
begins to darken within a few hours at room temperature, and
more slowly in a freezer, turning brown and then green, indicative
of a redox reaction. Examination of decomposed samples by 77Se
and 19F NMR spectroscopy showed a number of new resonances
(some unassigned), including ones attributable to [NbF6]- and
Eight-coordination is well known in niobium(V) chemistry,26
examples with sulfur-donor ligands including a range of dithio-
carbamates, [Nb(S2CNR2)4]+ the disulfides [NbCl4(RSSR)2]+, and
there are Nb(IV) complexes, [NbCl4(dithioether)2], although the
present complexes are the first Nb(V) examples with dithioether
or diselenoethers. In anhydrous CD2Cl2 solution at 295 K, the 1H
NMR spectrum shows a sharp singlet at d 2.28 which remains
sharp down to 190 K although the chemical shift drifts to higher
frequency on cooling the solution, reaching d 2.40 at 200 K. The
1
Me2SeF2 [d(Se) = 789 (t) JSeF = 645 Hz; d(F) = -69]29,30 again
consistent with fluorination of the chalcogenoether. Spectroscopic
data on the freshly prepared material (Table 2) are mostly similar to
those of the dialkyl sulfide adducts, but although the broad singlet
19F NMR resonance observed at room temperature sharpens on
cooling the solution, even at 200 K only a singlet is observed,
suggesting exchange processes remain significant, and indicating
weaker binding of the Me2Se compared to R2S.
[NbF4{RS(CH2)2SR}2][NbF6] (R = Me, Et or iPr)
In rigorously anhydrous CH2Cl2 solution, NbF5 and the three
1,2-dithioethanes produce colourless solutions, which deposit
i
colourless (R = Me or Et) or slightly yellow (R = Pr) crystals
on refrigeration. The crystals are extremely moisture sensitive
and decompose instantly in air, and also deteriorate slowly
in the glove-box, although they are more stable in a freezer.
X-Ray crystal structures of two examples were obtained and
both reveal distorted dodecahedral cations and octahedral anions.
The [NbF4{MeS(CH2)2SMe}2][NbF6] (Table 4, Fig. 2) contains
two chelating dithioethers in the DL configuration with chelate
angles ∠S–Nb–S of 74.2 to 75.2◦ and Nb–S distances 2.697(2)–
Fig. 1 Structure of the cation in [NbF4(Me2S)4][NbF6] showing the atom
numbering scheme. Ellipsoids are drawn at the 50% probability level and
H atoms are omitted for clarity. The Nb1 is positioned on a 4a site of
symmetry 222 (D2). Symmetry operations: a = 1/2 - x, 3/2 - y, z; b = y -
1/2, 1/2 + x, 1/2 - z; c = 1 - y, 1 - x, 1/2 - z.
˚
2.725(2) A, similar to the Me2S complex above. The NbF4 unit
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 883–891 | 887
©

View Article Online
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for [NbF4{MeS(CH2)2-
SMe}2][NbF6]
Nb1–F1
Nb1–F2
Nb1–S1
Nb1–S2
Nb2–F5
Nb2–F6
Nb2–S5
Nb2–S6
Nb3–F
1.912(3)
1.893(3)
2.7176(13)
2.7105(14)
1.916(3)
1.897(4)
2.7138(15)
2.7252(16)
Nb1–F3
Nb1–F4
Nb1–S3
Nb1–S4
Nb2–F7
Nb2–F8
Nb2–S7
Nb2–S8
1.911(3)
1.889(3)
2.7205(14)
2.7039(14)
1.901(3)
1.875(4)
2.6970(15)
2.7212(14)
1.875(4)–1.893(4)
1.843(5)–1.887(4) Nb4–F
F1–Nb1–F3 144.63(13)
F2–Nb1–F4 144.54(13)
F5–Nb2–F7 145.08(13)
F6–Nb2–F8 144.54(17)
S1–Nb1–S2
S3–Nb1–S4
74.74(4)
75.07(4)
S5–Nb2–S6
S7–Nb2–S8
75.21(5)
74.21(4)
i
Fig. 3 Structure of the cation in [NbF4{ PrS(CH2)2SiPr}2][NbF6] showing
the atom numbering scheme. Ellipsoids are drawn at the 50% probability
level and H atoms are omitted for clarity.
the chelating ligands generate a substantial electric field gradient
which promotes fast quadrupolar relaxation of the niobium, and
the resulting line-broadening accounts for the absence of the cation
resonance. The NMR spectra of all the fluoride complexes suggest
that exchangeprocesses are occurringat ambient temperatures, but
these slow on cooling. We have briefly described elsewhere17 the
synthesis and structure of [{NbF4(o-C6H4(CH2SMe)2)}n][Nb2F11]n
which also contains an eight-coordinate Nb(V) cation but the
dithioethers are bridging to form a polymeric chain.
Fig. 2 Structure of the cations in [NbF4{MeS(CH2)2SMe}2][NbF6]
showing the atom numbering scheme. Ellipsoids are drawn at the 50%
probability level and H atoms are omitted for clarity. There are two
crystallographically distinct cations with different conformations of the
bidentate S ligand; (a) Nb1 centred cation, (b) Nb2 centred cation.
[(NbF5)2{RSe(CH2)2SeR}] (R = Me or nBu)
The reaction of NbF5 with diselenoethers including
RSe(CH2)2SeR (R = Me or nBu) in a 2 : 1 molar ratio in
anhydrous CH2Cl2 solution at 295 K initially gives clear
pale-yellow solutions, but these slowly darken. The reactions,
conducted at 273 K, followed by rapid removal of the solvent,
gave a yellow viscous oil for nBuSe(CH2)2SenBu and a fawn
powder for MeSe(CH2)2SeMe both of which darken slowly at
ambient temperatures due to decomposition. They are formulated
as [(NbF5)2{m-RSe(CH2)2SeR}] on the basis of the spectroscopic
data (their instability precludes accurate microanalytical
measurements). Excess diselenoether (e.g. reaction in a 1 : 1
molar ratio) causes rapid reduction of the niobium with the
formation of dark-red solutions. The low-temperature 1H and
77Se NMR spectra, which exhibit singlet d(Me) and d(Se)
resonances, are consistent with the formulation of [NbF5{m-
MeSe(CH2)2SeMe}NbF5] for the former complex (analogous to
the structurally characterised chloride complex reported below).
˚
is a flattened tetrahedron with Nb–F 1.875(4)–1.916(3) A. The
two cations in the asymmetric unit are not the same as can be
seen in Fig. 2(a) and 2(b). In Fig. 2(a) with the Nb1 centred
cation the stereochemistry at S1–S4 is SSSS, whereas in Fig. 2(b)
for the Nb2 cation the stereochemistry at S5–S8 is SSRR. In
[NbF4{ PrS(CH2)2SiPr}2][NbF6] (Table 5, Fig. 3) the chelating
i
dithioethers are both in the meso form, but the dimensions are
otherwise very similar. In solution at 295 K the 19F NMR spectra
show two broad features (Table 2) which, on cooling the solutions,
become a sharper singlet at higher frequency, and at lower
frequency the characteristic ten-line pattern of [NbF6]-. In contrast
to the spectrum of [NbF4(Me2S)4][NbF6] discussed above, the
93Nb spectra of the dithioether complexes show only the [NbF6]-
resonance. It seems likely that the added distortions produced by
◦
i
˚
Table 5 Selected bond lengths (A) and angles ( ) for [NbF4{ PrS(CH2)2-
1
The 19F{ H} spectrum at room temperature is a broad singlet
SiPr}2][NbF6]
which sharpens on cooling, but even at 200 K does not show clear
splitting expected for the square pyramidal pentafluoride unit,
suggesting exchange processes are still present. Notably no
93Nb resonance was observed even at low temperatures (fast
relaxation), although in the decomposed (red–brown) samples
[NbF6]- is clearly present. The reaction of NbF5 with Me2Te
or MeTe(CH2)3TeMe in anhydrous CH2Cl2, instantly gave
insoluble brown–black tarry materials which were not pursued.
Nb1–F1
Nb1–F2
Nb1–S1
Nb1–S2
Nb2–F
1.904(2)
1.905(2)
2.7424(11)
2.7357(12)
1.877(4)–1.888(3) Nb3–F
Nb1–F3
Nb1–F4
Nb1–S3
Nb1–S4
1.897(2)
1.913(2)
2.7030(11)
2.7336(12)
1.881(3)–1.885(3)
F1–Nb1–F2 143.70(10)
F3–Nb1–F4 144.48(10)
S1–Nb1–S2
S3–Nb1–S4
74.14(3)
75.07(4)
888 | Dalton Trans., 2010, 39, 883–891
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
◦
˚
Selenoethers and especially telluroethers are softer ligands than
thioethers,2 and the inability of telluroethers to form stable
complexes with a very hard Lewis acid like NbF5 is therefore not
unexpected. They are also much stronger reducing agents, and
the dark coloured materials produced are no doubt the result of
reduction of the niobium, accompanying oxidative fluorination
of the ligands.
Table 6 Selected bond lengths (A) and angles ( ) for [(NbCl5)2{o-
C6H4(CH2SMe)2}]
Nb1–Cl1
Nb1–Cl3
Nb1–Cl5
2.275(2)
2.323(2)
2.303(2)
Nb1–Cl2
Nb1–Cl4
Nb1–S1
2.320(2)
2.3067(15)
2.7043(19)
Cl1–Nb1–Cl2
Cl1–Nb1–Cl3
Cl1–Nb1–Cl4
Cl1–Nb1–Cl5
Cl2–Nb1–S1
Cl3–Nb1–S1
98.11(9)
96.97(8)
96.76(8)
97.77(8)
79.18(7)
78.06(7)
Cl2–Nb1–Cl3
Cl2–Nb1–Cl5
Cl4–Nb1–Cl3
Cl4–Nb1–Cl5
Cl4–Nb1–S1
Cl5–Nb1–S1
89.16(9)
89.55(10)
88.68(7)
88.80(7)
85.98(6)
87.25(7)
[NbX5(R2E)] (X = Cl or Br, R2E = Me2S, Et2S, Me2Se; X = Cl,
R2E = Me2Te)
Reactions are shown in Scheme 2.
Table 7 Selected bond lengths (A) and angles (◦) for
[(NbCl5)2{MeSe(CH2)2SeMe}]
˚
Nb1–Cl1
Nb1–Cl3
Nb1–Cl5
2.280(2)
2.319(2)
2.334(2)
Nb1–Cl2
Nb1–Cl4
Nb1–Se1
2.318(2)
2.330(2)
2.8155(12)
Cl1–Nb1–Cl2
Cl1–Nb1–Cl3
Cl1–Nb1–Cl4
Cl1–Nb1–Cl5
Cl2–Nb1–Se1
Cl3–Nb1–Se1
96.54(9)
98.54(9)
98.18(9)
96.76(9)
80.76(7)
85.42(6)
Cl2–Nb1–Cl3
Cl2–Nb1–Cl5
Cl3–Nb1–Cl4
Cl4–Nb1–Cl5
Cl4–Nb1–Se1
Cl5–Nb1–Se1
89.05(9)
89.76(9)
88.53(9)
88.76(9)
84.58(6)
79.32(6)
Scheme 2 Reactions of NbX5 (X = Cl or Br) with thio- and seleno-ethers.
These complexes were made to provide comparative NMR and
X-ray data by direct combination of the constituents in anhy-
drous CH2Cl2 (see ESI†). All are very moisture-sensitive solids,
ranging in colour from yellow [NbCl5(Me2S)] through dark red
[NbBr5(Me2Se)], to purple [NbCl5(Me2Te)], and are easily soluble
in anhydrous CH2Cl2.10–14 The purple [NbCl5(Me2Te)] decomposes
rapidly in solution and the solid becomes sticky in a few hours,
turning dark green, clearly due to reduction of the niobium.
All spectroscopic measurements were made on freshly prepared
samples. Attempts to isolate [NbBr5(Me2Te)] were unsuccessful,
and reaction of NbI5 with Me2S gave a green–black paramagnetic
product which was not studied further. Spectroscopic data and
the crystal structures of [NbBr5(Me2S)] and [NbCl5(Me2Se)] are
described in the ESI.†
[(NbX5)2(L–L)] and [NbX4{MeS(CH2)2SMe}2][NbX6] (X = Cl or
Br, L–L = RSe(CH2)2SeR or o-C6H4(CH2EMe)2 (E = S or Se))
Fig. 4 Structure of [(NbCl5)2{o-C6H4(CH2SMe)2}] showing the atom
numbering scheme. Ellipsoids are drawn at the 50% probability level and
H atoms are omitted for clarity. The molecule has two-fold symmetry.
Symmetry operation: a = 2 - x, -y, z.
The reactions of NbX5 (X = Cl or Br) with the dithio-
and diselenoethers, RSe(CH2)2SeR (R = Me or nBu), or
o-C6H4(CH2EMe)2 (E = S or Se) gave complexes of composi-
tion [(NbX5)2(L–L)], irrespective of the NbX5 : L–L ratio used.
Uniquely within this series, MeS(CH2)2SMe gave complexes with
a 1 : 1 stoichiometry (see below). The reaction of NbCl5 with
found in [NbX5(R2E)], but the crystal structures serve to identify
the molecular unit present. The complexes with alkane-backbones
are very poorly soluble in chlorocarbon solvents which hindered
solution measurements, but the xylyl-backboned ligands have
better solubility and solution NMR data are given in Table 8.
The chloro-complexes show broad 93Nb NMR resonances at
ambient temperatures, but for [(NbBr5)2{o-C6H4(CH2EMe)2}] it
was necessary to cool the solutions to ~273 K to observe the
93Nb resonance, indicative of dissociation/exchange in solution at
◦
the ditelluroether MeTe(CH2)3TeMe in CH2Cl2 solution at 0 C,
initially gave a very dark solution, but this paled to dull khaki in
less than one min, and deposited a khaki powder. The UV/visible
spectrum of the latter has the lowest charge transfer band
at ~27000 cm-1, clearly indicating a lower niobium oxidation
state. The [(NbX5)2(L–L)] are ligand-bridged dimers, demon-
strated by the structures of [(NbCl5)2{o-C6H4(CH2SMe)2}] and
[(NbCl5)2{MeSe(CH2)2SeMe}] (Tables 6 and 7, Fig. 4 and 5). The
selenium compound is centrosymmetric and the sulfur compound
has a two-fold rotation axis which bisects the ligand backbone.
The patterns of bond lengths and angles largely replicate those
1
ambient temperatures. The 77Se{ H} NMR spectra of [(NbX5)2{o-
C6H4(CH2SeMe)2}] show large, high frequency shifts from the
“free” ligand values (Table 8). 93Nb NMR resonances were
obtained for the poorly soluble [(NbX5)2{MeSe(CH2)2SeMe}],
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 883–891 | 889
©

View Article Online
Table 8 Selected spectroscopic data for bidentate ligand complexes of NbX5 (X = Cl or Br) at 295 K unless otherwise stated
Compound
d(93Nb)a,b
d(77Se)d
n(Nb–X)/cm-1 (Nujol)
[(NbCl5)2{o-C6H4(CH2SMe)2}]
[(NbBr5)2{o-C6H4(CH2SMe)2}]
[(NbCl5)2{o-C6H4(CH2SeMe)2}]
[(NbBr5)2{o-C6H4(CH2SeMe)2}]
[NbCl4{MeS(CH2)2SMe} ][NbCl6]
[NbBr4{MeS(CH2)2SMe}22][NbBr6]
[(NbCl5)2{MeSe(CH2)2SeMe}]
[(NbBr5)2{MeSe(CH2)2SeMe}]
+80.5 (6000)
380sh, 365br, 346sh
281s, 254s
361br, 346s
+746 (12000) (273 K)h
+96 (4000)
+247
+228
—
+775 (5000) (243 K)h
+3 (vs), +150 (vbr)
+722
+97 (poorly soluble)
+750 (poorly soluble)
+95 (5000)
280s, 250s
333vs, 310sh, 280shi
257m, 248sh, 232vsj
359br, 334s
—
n.o.
n.o.
+284
294m, 233s
367s, 335s
n
[(NbCl5)2{ BuSe(CH2)2SenBu}]
Footnotes as in Table 2. h No resonance at 295 K. i Raman: 360vs, 312vs cm-1. j Raman: 250m (sh), 214vs cm-1.
Conclusions
This study has shown that the soft s-donor thioether ligands
readily form complexes with the hard Lewis acid NbF5, and that
the ligand steric demands influence significantly the coordination
numbers obtained. Thus, eight-coordination is achieved by ligands
with small steric demands, whereas bulkier thioethers form only
six-coordinate complexes. Eight-coordination is also found with
NbX5 (X = Cl or Br) and MeS(CH2)2SMe, but other thioethers
form only six-coordinate [NbX5(L)] or [(NbX5)2(m-L–L)], and
selenoether adducts with all three halides are six-coordinate. The
complexes of NbX5 (X = Cl or Br) appear stable indefinitely if
protected from moisture, but the fluorides decompose readily even
in the solid state via fluorination of the neutral ligand. The solution
spectroscopic data suggest that the heavier halides form more
stable complexes with thio- and especially seleno-ether ligands,
but the isolation of the eight-coordinate fluoride complexes is
remarkable, given the modest donor power of neutral soft sulfur
ligands.
Fig. 5 Structure of the centrosymmetric [(NbCl5)2{MeSe(CH2)2SeMe}]
showing the atom numbering scheme. Ellipsoids are drawn at the 50%
probability level and H atoms are omitted for clarity. Symmetry operation:
a = 1 - x, 1 - y, 1 - z.
but the solubility was too poor to observe 77Se resonances.
Solutions exposed briefly to air develop the 93Nb NMR resonances
of the corresponding [NbX6]- anions,25 consistent with ready
hydrolysis.
In contrast, MeS(CH2)2SMe gave 1 : 1 complexes with NbX5
(irrespective of the ratio of reactants used) which are insoluble in
chlorocarbons. The IR spectrum of the NbCl5 adduct shows a very
strong band at 333 cm-1 and the Raman spectrum has an intense
band at 360 cm-1, which correspond respectively to the t1u and a1g
vibrations of [NbCl6]-, and there are corresponding vibrations in
the bromide at 232 and 214 cm-1 due to [NbBr6]-.31 This leads to the
formulation [NbX4{MeS(CH2)2SMe}2][NbX6], analogous to the
fluoride complexes (above), with other Nb–X vibrations (Table 8)
being due to the (assumed) dodecahedral cation. The complexes
are insoluble in CH2Cl2, but dissolve in a mixture of CH2Cl2–
10% MeCN, from which solutions 93Nb NMR spectra identify
the [NbX6]- anions (Table 8). The chloride-complex also exhibits
a very broad resonance at d +150 which is tentatively ascribed
to the dodecahedral cation, but no corresponding resonance
was found in the bromide complex, possibly due to greater
dissociation, although line broadening by the quadrupolar nucleus
in a more asymmetric field gradient is also likely. Attempts to
obtain crystals of [NbX4{MeS(CH2)2SMe}2][NbX6] failed due to
very poor solubility, but the constitution is not in doubt from the
vibrational spectra and by analogy with the fluoride analogues.
The failure of the other dithio- and diseleno-ethers to form
compounds of this type may be due to slightly weaker donor
power and increasing steric bulk, disfavouring the eight-coordinate
cations.
Acknowledgements
We thank EPSRC for support and the Royal Society of Chemistry
for a Journals Grant (R. R.).
References
1 W. Levason and G. Reid, J. Chem. Res., 2002, 467; W. Levason, and G.
Reid, in Handbook of Chalcogen Chemistry ed. F. Devillanova, Royal
Society of Chemistry, 2006, p. 81.
2 W. Levason, S. D. Orchard and G. Reid, Coord. Chem. Rev., 2002, 225,
159.
3 M. D. Brown, M. B. Hursthouse, W. Levason, R. Ratnani and G. Reid,
Dalton Trans., 2004, 2487.
4 M. F. Davis, W. Levason, M. E. Light, R. Ratnani, G. Reid, K. Saraswat
and M. Webster, Eur. J. Inorg. Chem., 2007, 1903.
5 (a) R. Hart, W. Levason, B. Patel and G. Reid, J. Chem. Soc., Dalton
Trans., 2002, 3153; (b) W. Levason, B. Patel, G. Reid, V.-A. Tolhurst
and M. Webster, J. Chem. Soc., Dalton Trans., 2000, 3001.
6 S. D. Reid, A. L. Hector, W. Levason, G. Reid, B. J. Waller and M.
Webster, Dalton Trans., 2007, 4769.
7 (a) A. L. Hector, W. Levason, A. J. Middleton, G. Reid and M. Webster,
Eur. J. Inorg. Chem., 2007, 3655; (b) M. F. Davis, W. Levason, J.
Paterson, G. Reid and M. Webster, Eur. J. Inorg. Chem., 2008, 802.
8 A. L. Hector, M. Jura, W. Levason, S. D. Reid and G. Reid,
New J. Chem., 2009, 33, 641.
9 F. Fairbrother, K. H. Grundy and A. Thompson, J. Chem. Soc., 1965,
765.
10 F. Fairbrother and J. F. Nixon, J. Chem. Soc., 1962, 150.
11 A. Merbach and J. C. Bunzli, Helv. Chim. Acta, 1972, 55, 580.
890 | Dalton Trans., 2010, 39, 883–891
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
12 R. Good and A. E. Merbach, Helv. Chim. Acta, 1974, 57, 1192.
13 M. Valloton and A. E. Merbach, Helv. Chim. Acta, 1975, 58, 2272.
14 (a) R. Good and A. E. Merbach, Inorg. Chem., 1975, 14, 1030; (b) H.
Vanni and A. E. Merbach, Inorg. Chem., 1979, 18, 2758.
15 J. D. Wilkins, J. Inorg. Nucl. Chem., 1975, 37, 2095.
16 (a) R. E. DeSimone and M. D. Glick, J. Am. Chem. Soc., 1975, 97, 942;
(b) R. E. DeSimone and T. M. Tighe, J. Inorg. Nucl. Chem., 1976, 38,
1623.
22 G. M. Sheldrick, SHELXS-97, Program for crystal structure solution,
University of Go¨ttingen, Germany, 1997.
23 G. M. Sheldrick, SHELXS-97, Program for crystal structure refinement,
University of Go¨ttingen, Germany, 1997.
24 H. D. Flack, Acta Crystallogr., Sect. A: Found. Crystallogr., 1983, 39,
876.
25 D. Rehder, in Transition Metal NMR, ed. P. S. Pregosin, Elsevier, NY,
1991.
17 M. Jura, W. Levason, G. Reid and M. Webster, Dalton Trans., 2009,
26 T. Waters, A. G. Wedd, M. Ziolek and I. Nowak, in Comprehensive
Coordination Chemistry II, ed. J. A. McCleverty and T. J. Meyer,
Elsevier, Oxford, 2004, vol. 4, p. 241; J. B. Hamilton and R. E. McCarley,
Inorg. Chem., 1970, 9, 1339; P. J. McKarns, M. J. Heeg and C. H. Winter,
Inorg. Chem., 1998, 37, 4743.
27 K. J. Packer and E. L. Muetterties, J. Am. Chem. Soc., 1963, 85, 3035.
28 K. C. Moss, J. Chem. Soc. A, 1970, 1224.
29 A. M. Forster and A. J. Downs, Polyhedron, 1985, 4, 1625.
30 T. M. Klapo¨tke, B. Krumm and M. Scherr, Inorg. Chem., 2008, 47,
4712.
7610.
18 F. R. Hartley, S. G. Murray, W. Levason, H. E. Soutter and C. A.
McAuliffe, Inorg. Chim. Acta, 1979, 35, 265.
19 D. J. Gulliver, E. G. Hope, W. Levason, S. G. Murray, D. M. Potter and
G. L. Marshall, J. Chem. Soc., Perkin Trans. 2, 1984, 429.
20 (a) T. Kemmitt, E. G. Hope and W. Levason, Organometallics, 1988, 7,
78; (b) N. Kuhn, P. Faupel and E. Zauder, J. Organomet. Chem., 1986,
302, C4.
21 W. Levason, M. Nirwan, R. Ratnani, G. Reid, N. Tsoureas and M.
Webster, Dalton Trans., 2007, 439.
31 I. R. Beattie, T. R. Gilson and G. A. Ozin, J. Chem. Soc. A, 1968, 2765.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 883–891 | 891
©