The reaction of tin(iv) iodide with phosphines: Formation of new halotin anions

Article abstract of DOI:10.1039/b917722a

The reaction of SnI₄ with each of a primary, secondary and tertiary phosphine has been investigated and in none of the cases are simple adducts formed. With Cy₃P, [Cy₃PI]⁺ salts of both [SnI₃]^-

Full text of DOI:10.1039/b917722a

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www.rsc.org/dalton | Dalton Transactions
The reaction of tin(IV) iodide with phosphines: formation of new halotin
anions†
Leonardo Apostolico,a Gabriele Kociok-Ko¨hn,a Kieran C. Molloy,*a Christopher S. Blackman,b
Claire J. Carmaltb and Ivan P. Parkinb
Received 28th August 2009, Accepted 8th October 2009
First published as an Advance Article on the web 2nd November 2009
DOI: 10.1039/b917722a
The reaction of SnI4 with each of a primary, secondary and tertiary phosphine has been investigated
and in none of the cases are simple adducts formed. With Cy3P, [Cy3PI]+ salts of both [SnI3]- (1) and
[SnI5]- (2) are isolated arising from reactions involving both reduction at tin and halogen transfer. With
the secondary and primary amines Ph2PH and CyPH2, respectively, additional HI elimination reactions
occur and the salts [Ph2PH2]+ [Sn3I12]6- (3), [Ph2PH2]+ [SnI6]2- (4) and [CyPH3]+ [SnI4]2- (5) have been
6
2
2
isolated. Compounds 1–5 have been characterised crystallographically.
phosphine adducts remains open to doubt. Of the SnX4 species,
although having the lowest Lewis acidity, SnI4, with the smallest
E◦ for any of the Sn(II)/Sn(IV) redox couples, offers the most
fertile ground for unpredictable chemistry. Furthermore, there
is now a growing body of data on the structures of polymeric
iodostannate anions involving Sn(II) because of their interesting
electronic properties.13
In this paper we report on a crystallographic study of the
reactions between phosphines (Cy3P, Ph2PH, CyPH2) and SnI4, in
which a complex mix of adduct formation, halogen transfer and
redox chemistry is operative which has led to the characterisation
of a variety of novel iodostannate anions of both tin oxidation
states.
Introduction
We have an ongoing interest in the deposition of metal phosphide
thin films, from both single-1,2 and dual-source3–13 precursors. This
has renewed our interest in phosphine adducts of metal halides,
as these are often used as CVD precursors e.g. TiCl4·2PCyH2,3 or
are potential intermediates in dual-source deposition experiments
involving separate phosphine and metal halide sources. Our work
2
on phosphine “adducts” of GeX4 has, along with the work of
Godfrey4 and Du Mont,5,6 shown that halogen transfer/redox
reactions, in which [GeX3]-[R3PX]+ are produced, are also likely
alternatives to adduct formation. Moreover, while the reaction of
Ph3As with SnCl4 forms a 2 : 1 adduct, the analogous reaction
involving SnBr4 affords the species (Ph3As)SnBr4·AsPh3, in which
one Lewis base is coordinated directly to tin while the other
forms a weak interaction with the axially-bound bromine.7 This
“1 : 1 + 1” formulation is a likely intermediate in the halogen
transfer reactions seen to be common in reactions between
phosphines and germanium halides.
Experimental
General procedures
Elemental analyses were performed using an Exeter Analytical CE
440 analyser. 1H, 13C, 31P and 119Sn NMR spectra were recorded on
a Bruker Avance 300 MHz FT-NMR spectrometer, using saturated
solutions at room temperature. Phosphines were of commercial
origin (Strem) and were used without further purification.
Our interest in the deposition of tin phosphide films8
has prompted us to re-examine the reaction chemistry be-
tween tin halides and phosphines, particularly primary and
secondary phosphines as these offer a clean route for the
elimination of hydrogen halide from any adduct, which in
turn facilitates deposition of halogen-free films. Although a
body of older work exists which reports the synthesis and
spectroscopic characterisation of phosphine adducts of tin
halides,19–23 only four compounds of this type have been crys-
tallographically authenticated as containing a P:→Sn link-
Reaction of SnI4 and Cy3P (1 : 1). A Schlenk tube, filled with
argon, was charged with CH2Cl2 (20 ml) and SnI4 (0.89 g,
1.4 mmol). The mixture produced a clear yellow solution. This
solution was added dropwise to Cy3P (0.4 g, 1.4 mmol) to give
a clear red solution. The mixture was kept under argon and left
stirring for two hours; the solution was analysed by 31P NMR
(72.9 s, Cy3PI+; 25.6 s, SnI4·PCy3). Crystals which grew in the
NMR tube were identified as [Cy3PI]+[SnI3]- (1). The solvent was
then removed from the reaction mixture under reduced pressure to
yield a black solid. The solid was redissolved in THF from which
deep red crystals of [Cy3PI]+[SnI5]- (2) formed. Microanalysis:
Found (calc.) for C18H33PI6Sn (2): C = 18.4 (18.6)%, H = 2.95
(2.84)%. 31P NMR [d (ppm), CDCl3]: 72.9 ppm [s, Cy3PI+].
Subsequent crystal crops proved to be SnI4.
age [SnCl4·2PEt3,9 SnI4·2PPrn ,10 SnCl4·dppe,11 SnCl4·2dppm12
3
(dppe = Ph2PCH2CH2PPh2; dppm = Ph2PCH2PPh2)]. In view of
earlier work on analogous germanium systems in which halogen
transfer, rather than adduct formation, occurs, the structural
authenticity of many of the compounds previously regarded as tin–
aDepartment of Chemistry, University of Bath, Claverton Down, Bath, UK
BA2 7AY
bDepartment of Chemistry, Christopher Ingold laboratories, University
College London, 20 Gordon Street, London, UK WC1H 0AJ
Reaction of SnI4 and Ph2PH (1 : 1). A clear yellow solution
was made by adding SnI4 (0.41 g, 0.65 mmol) to CH2Cl2 (20 ml).
† CCDC reference numbers 741171–741175. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b917722a
10486 | Dalton Trans., 2009, 10486–10494
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Ph2PH (0.11 ml, 0.65 mmol) was syringed into the mixture, kept
under constant argon flow and with stirring, producing a yellow
precipitate and a light orange solution. The mixture was left to
stir for 3 hours. The yellow solid and the light orange solution
were separated by filtration, though both show similar 31P NMR
spectra: [d (ppm), CDCl3]: 40.6, -35.4 ppm. Both orange and
yellow crystals grew from the NMR sample of the filtrate which
Compound 2 crystallises with three independent cations and
anions in the asymmetric unit due to a 1 : 1 disorder in one ring of
one of the PCy3 groups. For 3, one phenyl group was found to be
disordered in the ratio 70 : 30, with potential disorder in two other
groups. However, due to a weak nature of this dataset this latter
disorder could not be resolved. 4 crystallises with two CH2Cl2
molecules of solvation.
were identified by X-ray crystallography as [Ph2PH2]+ [Sn3I12]6-
6
(3) and [Ph2PH2]+ [SnI6]2- (4), respectively. Microanalytical data
2
Results and discussion
for the yellow precipitate corresponds to 4: Found (calc.) for
Reaction with Cy3P
C24H24I6P2Sn: C 22.2 (22.9)%, H 1.79 (1.93)%.
SnI4 and Cy3P react in CH2Cl2 to produce a clear red solution,
whose 31P NMR spectrum showed singlets at d = 72.9 and
25.6 ppm which are not due to Cy3P (d = 10.6 ppm). Crystals that
grew in the NMR tube were identified as the salt [Cy3PI]+[SnI3]-
(1). The solvent was removed from the reaction mixture under
reduced pressure leaving a black solid, which was redissolved
in THF; this solution generated a singlet 31P NMR spectrum
(d = 72.9 ppm) from which crystals found to be the related salt
[Cy3PI]+[SnI5]- (2) were isolated. From this evidence, it is most
likely that the resonance at 72.9 ppm in the 31P NMR belongs
to the iodophosphonium ion, [Cy3PI]+ common to both 1 and
2, while that at 25.6 ppm is tentatively assigned to the adduct
SnI4·PCy3.
Reaction of SnI4 and CyPH2 (1 : 1). CyPH2 (0.1 ml, 0.75 mmol)
was syringed dropwise into a solution of SnI4 (0.47 g, 0.75 mmol) in
CH2Cl2 (10 ml) under an argon atmosphere, with stirring. As soon
as the first drops of phosphine had been added, a yellow precipitate
formed. The mixture was left stirring for 30 minutes. The solid was
then separated from the solution by filtration and left to dry under
vacuum. Crystals of [CyPH3]+ [SnI4]2- (5) were obtained from the
2
NMR sample and were identified solely by X-ray crystallography.
Microanalysis of the yellow precipitate: Found: C 19.8%; H 2.6%;
for comparison, calc. for 5: C 16.7, H 3.29%. 31P NMR [d (ppm),
CDCl3]: -111.2 ppm [CyPH2], 36.2 ppm. 119Sn NMR [d (ppm),
CDCl3]: -1610 ppm.
The formation of both identifiable products involves halogen
transfer, resulting in oxidation at phosphorus and reduction at tin,
a result which is consistent with reports on analogous reactions of
Ge(IV) halides with tertiary phosphines.2,4–6 A plausible reaction
sequence involves SnI4 and Cy3P initially forming the adduct
SnI4·PCy3 which undergoes halogen transfer to form its isomer
[Cy3PI]+[SnI3]- (1). The latter then reacts further, possibly via
nucleophilic attack of [SnI3]- on SnI4 as the solution becomes more
concentrated on solvent evaporation, resulting in iodide transfer
between the metal centres.
Crystal structures†
Experimental details relating to the single-crystal X-ray crystal-
lographic studies are summarised in Table 1. For all structures,
data were collected on a Nonius Kappa CCD diffractometer at
˚
150(2) K using Mo Ka radiation (l = 0.71073 A). Structure
solution followed by full-matrix least squares refinement were
performed using the WinGX-1.70 suite of programmes.14 Absorp-
tion corrections were applied in all cases, and, for 1, a correction
for extinction. Hydrogens attached to phosphorus were included
at calculated positions throughout, and refined using the riding
model.
The structure of 1 is shown in Fig. 1. Tin shows a coordination
number of three (trigonal pyramid) with the I–Sn–I bond angles
Table 1 Crystallographic data for 1–5
1
2
3
4
5
Empirical formula
Crystal system
Space group
C18H33I4PSn
Monoclinic
P21/n
C18H33I6PSn
Monoclinic
P21
C72H72I12P6Sn3
Monoclinic
C2/c
C26H28Cl4I6P2Sn
Monoclinic
P21/n
C12H28I4P2Sn
Orthorhombic
Pbca
˚
a/A
10.928(5)
13.013(5)
18.512(5)
101.258(5)
2581.9(17)
4
2.333
5.836
1672
0.55 ¥ 0.50 ¥ 0.40
3.07–30.08
22 566
7359 (0.0719)
6835
0.0977, 0.0612
1.129
12.1215(1)
17.3964(1)
21.9965(2)
103.533(1)
4509.63(6)
6
2.564
7.069
3144
0.25 ¥ 0.08 ¥ 0.08
3.54–30.03
92 742
26 218 (0.0919)
18 523
0.5655, 0.2547
0.967
65.6481(5)
12.1063(1)
23.3971(2)
104.324(4)
18016.9(3)
8
2.213
5.081
11 040
0.20 ¥ 0.10 ¥ 0.08
3.58–27.52
100 805
20 252 (0.1165)
12 410
0.6667, 0.4083
0.984
8.1060(2)
14.9990(4)
16.3210(5)
92.224(1)
1982.84(9)
2
2.386
5.683
1300
0.08 ¥ 0.05 ¥ 0.05
2.99–27.46
37 593
4531 (0.1419)
2741
0.7566, 0.6684
0.953
9.0343(2)
8.7669(2)
28.6850(8)
˚
b/A
˚
c/A
b/◦
V/A
3
˚
2271.88(10)
4
2.516
6.691
1568
0.25 ¥ 0.20 ¥ 0.08
3.54–27.51
27 736
2572 (0.0991)
2138
0.5853, 0.2027
1.076
Z
r
calc/mg m-3
m(Mo Ka)/mm-1
F(000)
Crystal size/mm
Theta range/◦
Reflections collected
Independent reflns [R(int)]
Reflect’s obs (>2s)
Max., min. transmission
Goodness-of-fit
Final R indices [I > 2s(I)]
R indices (all data)
Largest diff. peak and hole
Flack parameter
0.0459, 0.1202
0.0494, 0.1229
2.012, -2.562
0.0470, 0.0935
0.0845, 0.1047
1.567, -1.924
0.01(2)
0.0528, 0.0907
0.1129, 0.1071
1.047, -1.437
0.0425, 0.0740
0.1017, 0.0869
1.131, -1.514
0.0361, 0.0858
0.0498, 0.0926
0.914, -1.269
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Fig. 1 The asymmetric unit of 1 showing the labelling scheme used;
thermal ellipsoids are at the 50% probability level. Selected metri-
cal data: P–I(1) 2.4010(13), Sn–I(2) 2.8620(13), Sn–I(3) 2.8457(12),
˚
Sn–I(4) 2.8577(9) A; I(2)–Sn–I(4) 97.44(2), I(2)–Sn–I(3) 97.352(19),
I(3)–Sn–I(4) 97.472(17), I(1)–P–C(1) 107.32(15), I(1)–P–C(7) 107.32(15),
I(1)–P–C(13) 106.89(14), C(1)–P–C(7) 115.97(19), C(1)–P–C(13) 109.2(2),
C(7)–P–C(13) 109.7(2)◦. Hydrogen atoms have been omitted for clarity.
Fig. 2 One anion/cation pair of three in the asymmetric unit of
2, showing the labelling scheme used; thermal ellipsoids are at the
50% probability level. Selected metrical data: Sn(1)–I(1) 2.7339(8),
Sn(1)–I(2) 2.7426(8), Sn(1)–I(3) 2.8743(7), Sn(1)–I(4) 2.7269(9),
ranging from 97.44(2) to 97.472(17)◦ and Sn–I distances from
˚
Sn(1)–I(5) 2.8271(7), P(1)–I(16) 2.3915(19) A; I(1)–Sn(1)–I(2) 120.84(3),
˚
I(1)–Sn(1)–I(3) 87.97(2), I(1)–Sn(1)–I(4) 118.00(3), I(1)–Sn(1)–I(5)
2.8457(12) to 2.8620(13) A. The geometry about the phosphorus
91.83(2),
I(2)–Sn(1)–I(3)
87.92(2),
I(2)–Sn(1)–I(4)
121.05(3),
atom is a distorted tetrahedron, with bond angles involving iodine
[106.89(14)–107.32(15)◦] narrower than those without [109.2(2)–
I(2)–Sn(1)–I(5) 89.99(2), I(3)–Sn(1)–I(4) 90.66(3), I(3)–Sn(1)–I(5)
177.43(3), I(4)–Sn(1)–I(5) 91.70(3), C(1)–P(1)–I(16) 111.6(2), C(1)–
P(1)–C(7) 111.5(4), C(1)–P(1)–C(13) 113.8(3), C(7)–P(1)–I(16) 104.5(3),
C(7)–P(1)–C(¢3) 108.6(3), C(13)–P(1)–I(16) 106.2(2)◦. Hydrogen atoms
have been omitted for clarity.
◦
˚
115.97(19) ]. The P–I distance is 2.4010(13) A, similar to that
in the related cation [Ph3PI]+ [2.38(1) A], but shorter than in
15
˚
16
t
17
both the adduct Ph3P·I2 and the neutral P(V) species Bu3PI2
˚
[2.481(4) and 2.461(2) A, respectively]. To our knowledge this
is the first reported structure of an isolated [SnI3]- anion, the
closest intermolecular Sn ◊ ◊ ◊ I interaction being I(3) ◊ ◊ ◊ Sn(1¢)
cations. In both these examples, the tin atoms are part of the chains
of vertex-sharing SnI6 octahedra and are in an oxidation state of
+2. Square-pyramidal SnI5 fragments are seen as part of extended
networks in [H3N(CH2)7NH3]8[CH3NH3]2[SnIVSnII12I46]13–18 and
[PrN(C2H4)3NPr][Sn4I12].20 Thus, 2 represents the first example
of a SnI5 anion containing Sn(IV), the first isolated [SnI5] anion
of either oxidation state and the first SnI5 moiety that adopts a
trigonal bipyramidal structure.
˚
4.824 A (symmetry operation 1/2 - x, y - 1/2, 3/2 - z).
Other examples reported involve aggregation of this anion into
dimers e.g. [Ph4P]2[Sn2I6],18 sheets e.g. [Me3N(CH2)2NMe3][Sn2I6]
or chains e.g. [Fe(dmf)6][SnI3]2, [Me4N][SnI3],19 [Pr4N][SnI3],18
[PrN(C2H4)3NPr][Sn4I12].20
In the Sn(IV) iodostannate [SnI5]- (2), the geometry at tin is
close to a perfect trigonal bipyramid (Fig. 2), with both equatorial
[118.00(31), 121.05(3), 120.84(3)◦] and axial bonds [177.43(3)◦]
close to ideal values. The axial Sn–I bonds [Sn(1)–I(3) 2.8743(7),
Reaction with Ph2PH
˚
Sn(1)–I(5) 2.8271(7) A] are longer than the equatorial ones [Sn(1)–
SnI4 has been reacted with Ph2PH in CH2Cl2. The solution, left
stirring for 3 hours under argon, produced a yellow precipitate
soon after the phosphine had been added. The yellow solid and
the light orange solution were separated by filtration. Both the
solid and the solution have similar 31P NMR spectra (CDCl3),
though both spectra are of low resolution, probably because of
the limited amount of dissolved material remaining in solution
and the low solubility of the precipitate. There are signals in
the 31P NMR at d = 40.6 and -35.4 ppm, the former being
a singlet which implies cleavage of the P–H bond. The signal
˚
I(1) 2.7339(8), Sn(1)–I(2) 2.7426(8), Sn(1)–I(4) 2.7269(9) A], as
expected. The geometry about the phosphorus atom is again a dis-
torted tetrahedron as in 1, with the narrower bond angles generally
involving iodine [104.5(3)–111.6(2)◦]. However, the distinction is
less clear cut for 2 and the range of C–P–C angles [108.6(3)–
113.8(7)◦] overlaps that for angles I–P–C. The P–I distance is
2.3915(19) A, shorter than the one found in 1.
2 is the first report of an isolated SnI5 species. Exclud-
ing the extended lattices formed by purely inorganic systems
˚
1
(e.g. In3SnI5), only three compounds incorporating SnI5 units
at -35.4 ppm is weak and could only be resolved under { H}
have been reported. Two of these,21,22 [SnI5] [NH2C(I) NH2]3
decoupling, but could correspond to Ph2PH (-41.1 ppm)23 or a
related P(III) species such as Ph2PSnI3 (see below). Both orange
and yellow crystals grew on standing from the NMR sample of the
3-
=
3-
=
=
and [SnI5] [NH2C(I) NH2]2(NH2CH NH2), are related to
the layered organic–inorganic perovskites of general formula
[NH2C(I) NH2]2(CH3NH3)mSnmI3m+2, which consists of m ori-
filtrate and have been identified as the salts [Ph2PH2]+ [Sn3I12]6- (3,
=
6
ented CH3NH3SnI3 perovskite sheets, separated by a layer of
orange) and [Ph2PH2]+ [SnI6]2- (4, yellow). Microanalysis of the
2
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Table 2 Selected geometrical data for 3
˚
Bond lengths/A
I(1)–Sn(1)
I(2)–Sn(1)
I(3)–Sn(1)
I(4)–Sn(1)
I(5)–Sn(1)
I(6)–Sn(1)
3.1755(7)
3.1446(7)
3.3195(7)
3.1336(7)
3.1836(8)
3.1258(7)
I(4)–Sn(2)
I(5)–Sn(2)
I(6)–Sn(2)
I(7)–Sn(2)
I(8)–Sn(2)
I(9)–Sn(2)
3.5755(7)
3.2680(8)
3.2785(7)
3.1024(7)
3.1871(8)
2.9232(7)
I(1)–Sn(3)
I(2)–Sn(3)
I(3)–Sn(3)
I(10)–Sn(3)
I(11)–Sn(3)
I(12)–Sn(3)
3.3492(7)
3.4797(7)
3.4976(7)
3.0186(7)
3.0100(7)
3.0380(7)
Bond angles/◦
I(6)–Sn(1)–I(4)
I(4)–Sn(1)–I(2)
I(4)–Sn(1)–I(1)
I(6)–Sn(1)–I(5)
I(2)–Sn(1)–I(5)
I(6)–Sn(1)–I(3)
I(2)–Sn(1)–I(3)
I(5)–Sn(1)–I(3)
I(6)–Sn(1)–I(2)
I(6)–Sn(1)–I(1)
I(2)–Sn(1)–I(1)
I(4)–Sn(1)–I(5)
I(1)–Sn(1)–I(5)
I(4)–Sn(1)–I(3)
I(1)–Sn(1)–I(3)
Sn(1)–I(1)–Sn(3)
Sn(1)–I(2)–Sn(3)
88.753(19)
91.395(19)
87.880(18)
85.812(19)
175.08(2)
96.458(19)
90.557(19)
94.273(19)
92.708(19)
176.18(2)
89.175(19)
83.884(19)
92.037(19)
174.34(2)
86.840(18)
78.936(17)
77.390(17)
I(9)–Sn(2)–I(8)
I(9)–Sn(2)–I(5)
I(8)–Sn(2)–I(5)
I(7)–Sn(2)–I(6)
I(5)–Sn(2)–I(6)
I(7)–Sn(2)–I(4)
I(5)–Sn(2)–I(4)
I(9)–Sn(2)–I(7)
I(7)–Sn(2)–I(8)
I(7)–Sn(2)–I(5)
I(9)–Sn(2)–I(6)
I(8)–Sn(2)–I(6)
I(9)–Sn(2)–I(4)
I(8)–Sn(2)–I(4)
I(6)–Sn(2)–I(4)
Sn(1)–I(3)–Sn(3)
Sn(1)–I(4)–Sn(2)
91.36(2)
90.12(2)
I(11)–Sn(3)–I(10)
I(10)–Sn(3)–I(12)
I(10)–Sn(3)–I(1)
I(11)–Sn(3)–I(2)
I(12)–Sn(3)–I(2)
I(11)–Sn(3)–I(3)
I(12)–Sn(3)–I(3)
I(2)–Sn(3)–I(3)
I(11)–Sn(3)–I(12)
I(11)–Sn(3)–I(1)
I(12)–Sn(3)–I(1)
I(10)–Sn(3)–I(2)
I(1)–Sn(3)–I(2)
I(10)–Sn(3)–I(3)
I(1)–Sn(3)–I(3)
Sn(1)–I(5)–Sn(2)
Sn(1)–I(6)–Sn(2)
89.62(2)
93.86(2)
175.14(2)
170.33(2)
82.018(19)
92.103(18)
76.049(17)
91.98(2)
92.84(2)
91.733(19)
95.39(2)
93.232(19)
165.69(2)
102.129(18)
79.261(17)
74.941(16)
77.585(17)
87.514(18)
168.83(2)
96.663(19)
90.864(19)
97.207(19)
82.372(17)
92.98(2)
89.217(18)
177.41(2)
95.319(19)
81.014(16)
168.88(2)
81.385(17)
81.628(18)
82.335(18)
Table 3 Hydrogen bond data for 3–5
yellow precipitate suggests it is predominantly 4 (Found, calc. for
C24H24P2I6Sn: C 22.2 (23.0), H 1.79 (1.93)%).
D–H ◊ ◊ ◊ A/◦
˚
˚
D–H ◊ ◊ ◊ A
D ◊ ◊ ◊ A/A
A ◊ ◊ ◊ H/A
A sequence of reactions which is consistent with these ob-
servations is as follows. Formation of a 1 : 1 adduct takes place
initially which rapidly eliminates HI leaving Ph2PSnI3. The latter
dissociates to SnI2 and Ph2PI, giving rise to the 31P singlet at
40.6 ppm (lit., neat: 39 ppm).24 Combinations of HI, Ph2PH and
either SnI2 or SnI4 then give rise to the crystals of 3 and 4 observed.
Compound 3 is only the second example of the isolated [Sn3I12]6-
3
P(1)–H(1A) ◊ ◊ ◊ I(4)
P(1)–H(1B) ◊ ◊ ◊ I(7)
P(2)–H(2A) ◊ ◊ ◊ I(4)
P(2)–H(2B) ◊ ◊ ◊ I(10)
P(3)–H(3A) ◊ ◊ ◊ I(12)
P(3)–H(3B) ◊ ◊ ◊ I(3)
P(4)–H(4B) ◊ ◊ ◊ I(8)
P(4)–H(4A) ◊ ◊ ◊ I(7)
P(5)–H(5A) ◊ ◊ ◊ I(3)
P(5)–H(5B) ◊ ◊ ◊ I(9)
P(6)–H(6B) ◊ ◊ ◊ I(1)
P(6)–H(6B) ◊ ◊ ◊ I(10)
P(6)–H(6B) ◊ ◊ ◊ I(1)
P(6)–H(6B) ◊ ◊ ◊ I(11)
P–H(1A) ◊ ◊ ◊ I(1)
4.170(2)
3.981(2)
4.046(2)
3.989(2)
4.139(2)
4.212(2)
4.334(2)
4.051(2)
4.119(2)
4.169(3)
3.584(2)
3.761(2)
3.584(2)
4.204(2)
3.964(2)
4.147(2)
3.768(2)
4.154(2)
4.147(2)
3.768(2)
3.593(2)
3.593(2)
3.593(2)
2.98
2.82
2.72
2.76
2.99
2.96
3.02
2.94
145.7
142.4
163.5
149.6
140.9
152.5
161.4
138.1
158.3
156.9
99.0
anion (Fig. 3; Table 2), the other being [Co(en)3]2+4[Sn3I12]6-[I]-
2
2.82
2.88
3.11
reported in 2007.25 Like its predecessor, the anion in 3 is made up
of three face-sharing SnI6 moieties, each of which shows a distorted
octahedral geometry about the tin atom [trans-I–Sn–I: 165.69(2)–
177.41(2)◦; cis-I–Sn–I: 76.049(17)–97.207(19)◦]. The terminal
3.27
3.11
100.3
99.0
2.88
163.1
121.32
143.40
133.41
135.41
140.40
107.24
90.53
84.78
86.47
˚
Sn–I bonds, ranging from 2.9232(7)–3.1871(8) A, are generally
4
5
3.083
3.464
2.984
3.074
3.008
3.134
3.314
3.452
3.411
shorter than the bridging ones, which range from 3.1258(7)–
P–H(1A) ◊ ◊ ◊ I(2)
˚
P–H(1A) ◊ ◊ ◊ I(3)
3.5755(7) A. The hydrogen atoms bonded to the phosphorus
P–H(1B) ◊ ◊ ◊ I(1)
atoms are in calculated positions; it is assumed that each of
the six phosphorus atoms is P(V) and brings a positive charge
to counterbalance the six negative charges of the anion. The
geometry at the phosphorus atom is tetrahedral, e.g. C(61)–P(6)–
C(67) 112.3(4)◦.
P–H(1B) ◊ ◊ ◊ I(2)
P–H(1B) ◊ ◊ ◊ I(3)
P(1)–H(1A) ◊ ◊ ◊ I(2)
P(1)–H(1B) ◊ ◊ ◊ I(2)
P(1)–H(1C) ◊ ◊ ◊ I(2)
The lattice of 3 is held together by a network of weak hydrogen
bonds involving the P–H groups and the iodine atoms (Fig. 4;
Table 3). The hydrogens attached to P(2) and P(5) each bridge
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Fig. 3 The asymmetric unit of 3 showing the labelling scheme used; thermal ellipsoids are at the 50% probability level. Selected metrical data are given
in Table 2. Hydrogen atoms have been omitted for clarity.
Fig. 4 The lattice structure of 3.
a
bridging/terminal pair of iodines [I(4)/I(10); I(3)/I(9)],
Compound 4 was obtained as a few crystals from an NMR
sample of the reaction filtrate and has only been analysed by X-ray
crystallography (Fig. 5). The tin(IV) atom, which is on an inversion
center, adopts a near perfect octahedral geometry [I(1)–Sn–
I(1¢) 180.0, I(2)–Sn–I(2¢) 180.0, I(3)–Sn–I(3¢) 180.0, other angles
89.132(13)–90.868(13)◦]. The Sn–I bonds vary from 2.8442(5) to
and along with a trifurcated set of hydrogen bonds between
P(6) and I(1)/I(10)/I(11), similar to that seen in 4, hold
the three [Sn3I12] units together; a further weaker pair of
bifurcated hydrogen bonds between P(6) and I(1)/I(10) adds
to this support. Individual [Sn3I12] anions are linked into
chains via hydrogen bonds involving P(1) and P(3) which
bridge I(4)/I(7) and I(3)/I(12) pairs of halogens, while P(4)
bridges I(7) and I(8) to form a link between parallel chains so
generated.
˚
2.8706(4) A, which are similar to the axial Sn–I bonds in 2 but
notably longer than the equatorial bonds in the same anion.
The trend is consistent with the increase in coordination number
at tin between 2 and 4. The phosphorus atom in 4 shows a
10490 | Dalton Trans., 2009, 10486–10494
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Fig. 5 The asymmetric unit of 4 showing the labelling scheme used; thermal ellipsoids are at the 50% probability level. Selected metrical data, for
one of three molecules in the asymmetric unit: Sn–I(1) 2.8599(5), Sn–I(2) 2.8442(5), Sn–I(3) 2.8706(4), I(1)–Sn–I(2) 90.524(13), I(1)–Sn–I(3) 90.072(13),
I(1)–Sn–I(2¢) 89.476(14), I(1)–Sn–I(3¢) 89.928(13), I(2)–Sn–I(3) 90.868(13), I(2)–Sn–I(3¢) 89.132(13), C(7)–P–C(1) 113.1(4). Two molecules of CH2Cl2
which co-crystallise have been omitted for clarity, as have the hydrogen atoms. Symmetry transformation used to generate equivalent atoms: 1 - x, 1 - y,
1 - z.
distorted tetrahedral geometry [C(1)–P–C(7) 113.1(4)◦], but is
unexceptional. The [Ph2PH2]+ cation is, however, instrumental in
lattice construction (as it is in 3) via a network of weak P–H ◊ ◊ ◊ I
hydrogen bonds (Table 3). Each hydrogen forms a trifurcated
H-bond with three iodines, hydrogens capping four of the eight
triangular faces of the SnI6 octahedron [Fig. 6(a)] generating a
chain of hydrogen-bonded anion–cation pairs propagating along
a [Fig. 6(b)].
most likely corresponding to uncoordinated phosphine (d =
-111.5 ppm), and 36.2 ppm. This latter shift is similar to that
found in 31P NMR of the precipitate from the reaction of GeCl4
and CyPH2 (triplet, 24.5 ppm) which we tentatively assigned
to CyPH2:→GeCl2. Furthermore, from a solution containing
this species we obtained crystals of [CyPH3]+[GeCl3]-, from the
reaction of CyPH2:→GeCl2 with HCl in situ.2 Since we have
crystallised [CyPH3]+ [SnI4]2- (5; see below) from the NMR
2
Compound 4 appears to be the first fully characterized example
of the [SnI6]2- anion, though the structures of M2SnI6 (M = Rb, Cs)
have been partially described26 and SnI6 moieties are a common
structural feature of other systems e.g. lattice association of [SnI3]-
(see above).18,20
sample of the CyPH2/SnI4 reaction precipitate, this suggests that
CyPH2:→SnI2 or CyPH2:→SnI4 may well be part of the initial
precipitate. 119Sn NMR shows a weak singlet at -1610 ppm which is
not SnI4, for which we find a 119Sn NMR signal at d = -1720 ppm in
CDCl3.
Highly sensitive yellow crystals have been obtained from
the NMR sample containing a solution of the above yellow
precipitate. X-Ray diffraction studies show that the crystals are
Reaction with CyPH2
the result of a redox reaction that produces [CyPH3]+ [SnI4]2-
Adduct formation using CyPH2 has also been attempted with
SnI4 as the Lewis acid. As soon as the phosphine had been
injected dropwise into a solution of tin(IV) iodide in CH2Cl2,
a yellow precipitate formed. The mixture was left to stir under
an atmosphere of argon for 30 minutes and then the precipitate
separated from the solution by cannula filtration. On drying the
solid appeared yellow with some red/brown discolouration in
parts. These darker features could be removed by washing with
CH2Cl2, but returned on drying the remaining solid. Thus, this
precipitate appears to be a mixture and sensitive to the presence
(or absence) of solvent, in which the brown colouration may
be due to molecular iodine. Spectral data on this reaction are
2
(5). This is similar in outcome to that observed by us from
the reaction of GeCl4 and CyPH2, which, from a complex
series of reactions, afforded [CyPH3]+[GeCl3]-.2 The appearance
of 5 as one component of the reaction probably originates
from a similar sequence to that described for 3, 4 above i.e.
adduct formation (CyH2P:→SnI4) from which HI is eliminated
leaving Cy(H)PSnI3 which dissociates to Cy(H)PI and SnI2; HI,
CyPH2 and SnI2 combine to give 5, which crystallizes from the
mixture.
The structure of 5 is shown in Fig. 7. The tin atoms, which
lie on an inversion center, show a geometry that is slightly
distorted from the ideal octahedral coordination. All the trans-
I–Sn–I angles are 180◦ by symmetry, while the cis-I–Sn–I lie in the
range 86.111(10)–93.889(10)◦; these values are similar to those
1
31
inconclusive. The yellow solid was analyzed by { H} P and
119Sn NMR (CDCl3), though low solubility precluded 31P NMR
which would allow the number of attached hydrogens to be
ascertained. The 31P NMR shows two signals, at d = -111.2,
reported for [SnI4]2-[C4H9NH3]+ .27 The Sn–I bonds [3.1186(4),
2
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Fig. 6 The network of P–H ◊ ◊ ◊ I hydrogen bonds, (a) capping four triangular faces of the SnI6 octahedron and (b) showing chain propagation along a.
˚
is part of a family of layered perovskites that can be derived
by terminating the three dimensional cubic perovskite structure
along different crystal faces. These have formulae (cat)n+1SnnI3n+1
where n relates to the number of layers within the structure;
all the known cations to date are based on quaternary am-
monium salts, thus 5 makes a novel addition to this family.
Moreover, these layered materials have been shown to demonstrate
transitions from semiconducting to metallic behaviour similar
to the copper oxide perovskites.28,29 The angle Sn–I–Sn at the
bridging iodine [160.945(13)◦], though non-linear is higher than
usually observed in single-layered perovskites systems such as
[SnI4]2-[C6F5C2H4NH3]+ [151.23(6)◦], [SnI4]2-[C6H5C2H4NH3]+
3.1186(4), 3.2012(4) A], are notably longer than in any of 1, 2 or
˚
4 (ca. 2.8 A), all of which contain discrete anions; the elongation
compared to the structurally similar [SnI6]2- is striking. Since the
octahedral coordination about tin is a result of intermolecular
association, it is perhaps not surprising that the Sn–I bond lengths
are more comparable with those in 3 [terminal Sn–I: 2.9232(7)–
˚
˚
3.1871(8) A; bridging Sn–I: 3.1260(7)–3.5754(7) A], though the
overall consistency of the data for 5 reflect a much stronger degree
of molecular association.
The lattice structure of 5 consists of single SnI42- infinite sheets,
generating an anionic network of corner-shared MI6 octahedra,
separated by layers of [CyPH3]+ cations. This structural type
2
2
10492 | Dalton Trans., 2009, 10486–10494
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Conclusions
Reaction of SnI4 with the primary, secondary and tertiary
phosphines Cy3P, Ph2PH and CyPH2 does not afford isolable
adducts but ionic products which result from a complex series of
reactions, including redox chemistry, namely [Cy3PI]+[SnI3]- and
[Cy3PI]+[SnI5]-, [Ph2PH2]+ [SnI6]2- and [Ph2PH2]+ [Sn3I12]6-, and
2
6
[CyPH3]+ [SnI4]2-, respectively. The initial formation of a P:→Sn
2
adduct is a likely first step in these reactions, which also seem
to involve HI elimination (except with Cy3P) and SnI4 → SnI2
reduction.
Fig. 7 The asymmetric unit of 5 showing the labelling scheme used;
thermal ellipsoids are at the 50% probability level. Selected metrical
data: Sn–I(1) 3.1186(4), Sn–I(1a) 3.1186(4), Sn–I(2) 3.2012(4), Sn–I(2a)
Acknowledgements
We thank the EPSRC for financial support.
b
c
a
˚
3.2012(4), Sn–I(2 ) 3.1812(4), Sn–I(2 ) 3.1812(4) A; I(1)–Sn–I(1 ) 180.0,
I(2)–Sn–I(2a) 180.0, I(2b)–Sn–I(2c) 180.0, I(1)–Sn–I(2) 86.111(10),
I(1)–Sn–I(2a) 93.889(10), I(1)–Sn–I(2b) 89.561(10), I(1)–Sn–I(2c)
90.439(10), I(2)–Sn–I(2b) 92.213(3), I(2)–Sn–I(2c) 87.787(3), Sn–I(2)–Snd
160.946(13)◦. Symmetry transformation used to generate equivalent
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10494 | Dalton Trans., 2009, 10486–10494
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©