Reactivity of the tetraphenyldithioimidodiphosphine-diiodine (HL·I2) adduct towards indium powder

Article abstract of DOI:10.1039/b211542e

The reaction of indium powder with the mixture (SPPh₂) ₂NH and I₂ (HL-I₂) in Et₂O at room temperature gave the indium(III) complex InLI₂ (1). The reaction occurs in two steps, the first of which leads to the formation of InI ₃ and free HL, then the subsequent reaction between these species yields compound 1, H⁺, and the anion InI₄^-. The crystal lattice of 1 is made up of neutral acentric molecules where the metal ion is bonded through two sulfur atoms to one anionic (SPPh₂) ₂N^- (L) ligand and two iodide ions. The central In ^III ion shows a slightly distorted tetrahedral coordination geometry. Density functional theory (DFT) calculations, carried out at the B3LYP level, have been used to interpret the electrochemical behaviour of 1. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b211542e

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Reactivity of the tetraphenyldithioimidodiphosphine–
diiodine (HLؒI2) adduct towards indium powder
G. Luca Abbati,b M. Carla Aragoni,a Massimiliano Arca,a F. A. Devillanova,a
Antonio C. Fabretti,b Alessandra Garau,a Francesco Isaia,*a Vito Lippolisa and G. Verania
a Dipartimento di Chimica Inorganica ed Analitica, Università di Cagliari,
S.S. 554 bivio per Sestu, I-09042 Cagliari, Italy
b INSTM and Dipartimento di Chimica, Università di Modena e Reggio Emilia,
via G. Campi 183, I-41100 Modena, Italy
Received 28th November 2002, Accepted 26th February 2003
First published as an Advance Article on the web 11th March 2003
The reaction of indium powder with the mixture (SPPh2)2NH and I2 (HLؒI2) in Et2O at room temperature gave the
indium() complex InLI2 (1). The reaction occurs in two steps, the first of which leads to the formation of InI3 and
free HL, then the subsequent reaction between these species yields compound 1, Hϩ, and the anion InI4Ϫ. The crystal
lattice of 1 is made up of neutral acentric molecules where the metal ion is bonded through two sulfur atoms to one
anionic (SPPh2)2NϪ (L) ligand and two iodide ions. The central InIII ion shows a slightly distorted tetrahedral
coordination geometry. Density functional theory (DFT) calculations, carried out at the B3LYP level, have been
used to interpret the electrochemical behaviour of 1.
In previous papers7a,b,8a we reported on the oxidation ability
Introduction
of the mixture of HL and I2 towards metal powders in a low
The chemistry of metal powder activation by CT-adducts of
polar solvent and mild reaction conditions. Sb0 is easily oxid-
halogen and interhalogen has been widely developed by McAu-
ised to ϩ3 in a single step to separate an unusual dinuclear
liffe and co-workers during the past ten years.1 Owing to the
complex [LSb(µ-S)(µ-I)2SbL].8a Similarly, the same mixture has
main use of R3EؒX2 adducts (R = alkyl, aryl; E = P, As, Sb; X2 =
I2, Br2, IBr), novel metal tertiary phosphine, arsine, and stibine
complexes were prepared. The versatility of this synthetic
successfully been used to react palladium and cobalt powders to
produce the complexes PdL2 7a and CoL2.7b
Considering these promising results and given the import-
method allows one to prepare coordination compounds having
ance of indium complexes in view of their applications in
unusual geometries, stoichiometries, and oxidation number at
organic synthesis as catalysts in trans-esterification processes,10
the metal centres. Furthermore, it points the way towards a
and the increasing interest in the recovery process of indium
safe, clean technology for the recovery of precious metals.2 In
from scrap and waste products from the electronics industry,11
this way, the metal activation reaction using I2-adducts of
polyfunctional thione donors has been carried out to produce
we report on the activation of indium powder by the mixture
HL and I2.
complexes such as [Pt(Me2Pipdt)2](I3)2 (Pipdt = N,N Ј-dimethyl-
piperazinium-2,3-dithione),2 [AuDI2]I3 (D = N,N Ј-dimethyl-
perhydrodiazepine-2,3-dithione),3 and SnI2(DЈ)2(I3)2ؒ2/3I2
(DЈ = 1,1Ј-bis(3-methyl-4-imidazolidine-2-thione).4
Results and discussion
Solid-state structure
In this context, the diiodine adducts of tetraphenyl-
dithioimidodiphosphinic acid (SPPh2)2NH (HL) represents an
interesting system for activating metal powder since it contains
Group 15 and 16 donor elements. The coordination chemistry
of HL, and more in general of some imidodiphosphinic acids
(XPR2)(YPRЈ2)NH (X, Y = O, S; R, RЈ = Me, Pri, Ph), has
already been investigated5 thoroughly and some complexes
have found application as catalysts for methanol carbonyl-
ation.6
Stable colourless crystals suitable for an X-ray study were
obtained by reaction of HL, I2 and indium powder (see
Experimental section, synthesis method a) in anhydrous diethyl
ether at room temperature. The crystal lattice is made up of
neutral acentric InLI2 (1) molecules where the metal ion is
bonded through two sulfur atoms to one anionic ligand
(SPPh2)2NϪ (L) and two iodide ions (Fig. 1). The central InIII
ion shows a slightly distorted tetrahedral coordination geom-
etry with X–In–X angles (X = I, S) in the range 102.28(3)–
115.57(3)Њ (see Table 1) and a dihedral angle between the
I(1)In(1)I(2) and S(1)In(1)S(2) planes of 83.73(2)Њ. The pro-
nounced difference observed in the mean values of the In–S and
In–I bond-lengths (2.485 and 2.682 Å, respectively) is probably
due to the arrangement of the sterically restrained S ؒ ؒ ؒ S
ligand “bite” in the metal ion coordination geometry. The In–I
distances are in fact equal, within experimental errors, to the
value of 2.64(4) Å reported as the usual InIII–I mean distance
in four-coordinated pseudo-tetrahedral complexes.12 To our
knowledge, 1 is the first example of an indium–iminobis-
(phosphinechalcogenide) complex showing a tetrahedral metal
coordination geometry. All the previously studied indium com-
plexes with such ligands in fact showed an octahedral13 or tri-
gonal bipyramidal geometry.14 In 1 the InSPNPS ring adopts
a pseudo-boat conformation where atoms S(1) and P(2)
act as “bow” and “stern”, with deviations of 0.8798(14) and
The reaction of HL with metal ions usually leads to the for-
mation of the (SPPh2)2NϪ anion (L) which has the negative
charge delocalised over the SPNPS moiety, and is capable of
coordinating a metal centre by both sulfur atoms to form six-
membered MSSP2N metallacycles. Square planar, tetrahedral,
or octahedral complexes of formula MLn (n = 2 or 3) are the
most commonly observed coordination geometries.7 In some
cases, more complicated stoichiometries have been obtained
with formation of bridges or supramolecular polymeric
structures.8,9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 5 1 5 – 1 5 1 9
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Table 1 Selected interatomic distances (Å) and angles (Њ) for complex 1
In(1)–S(1)
In(1)–I(1)
S(1)–P(1)
P(1)–N(1)
P(1)–C(7)
P(2)–C(13)
2.4841(12)
2.6769(5)
2.0452(13)
1.585(3)
1.793(4)
1.788(3)
In(1)–S(2)
In(1)–I(2)
S(2)–P(2)
P(2)–N(1)
P(1)–C(1)
P(2)–C(19)
2.4863(10)
2.6872(6)
2.0478(12)
1.578(3)
1.794(4)
1.805(3)
Fig. 2 Simplified chemical structure representations of the InPSNPS
ring in 1, 2, and 3. Bold-printed atoms act as ‘bow’ or ‘stern’ of the
pseudo-boat conformation shown by the rings.
I(1) ؒ ؒ ؒ I(2)
I(1) ؒ ؒ ؒ S(1)
I(1) ؒ ؒ ؒ S(2)
4.4781(8)
4.3677(13)
4.1284(11)
S(1) ؒ ؒ ؒ S(2)
I(2) ؒ ؒ ؒ S(2)
I(2) ؒ ؒ ؒ S(1)
4.041(2)
4.2627(11)
4.0287(13)
I(1)–In(1)–I(2)
S(1)–In(1)–I(1)
S(2)–In(1)–I(1)
P(1)–S(1)–In(1)
N(1)–P(1)–S(1)
P(2)–N(1)–P(1)
N(1)–P(1)–C(1)
C(1)–P(1)–S(1)
C(7)–P(1)–C(1)
N(1)–P(2)–C(13)
C(13)–P(2)–S(2)
C(13)–P(2)–C(19)
113.20(2)
115.57(3)
106.12(3)
98.60(5)
117.03(12)
132.7(2)
109.2(2)
108.72(13)
106.8(2)
S(1)–In(1)–S(2)
S(2)–In(1)–I(2)
S(1)–In(1)–I(2)
P(2)–S(2)–In(1)
N(1)–P(2)–S(2)
108.77(3)
110.90(3)
102.28(3)
100.00(4)
116.22(13)
bond lengths decrease [1.672(2)–1.683(2) vs. 1.578(3)–1.585(3)
Å] and the P–N–P angle is practically the same [132.7(2) vs.
132.68(14)Њ]. These values substantially confirm that the bond
geometry of the metal–(XPR2)2N fragment is insensitive to the
oxidation number and coordination environment of the
involved metal ion.7a
N(1)–P(1)–C(7)
C(7)–P(1)–S(1)
107.6(2)
107.05(14)
The 31P MAS NMR spectrum of the indium complex 1
shows two resonances at δ 36.8 and 41.3 with an approximate
intensity ratio of 1 : 1 originated from the non-equivalent P sites
of the ligand within the complex. Peaks have a line width ∆ν1/2
of ≈300 Hz, thus excluding the possibility of observing any
2J(31P, 31P) [≈25 Hz in this class of ligands]. The inequivalence
of the P sites in the ligand moiety is not found in diethyl ether
106.5(2)
105.22(12)
106.5(2)
N(1)–P(2)–C(19)
C(19)–P(2)–S(2)
112.5(2)
109.19(13)
solution, in fact the 31P spectrum of InLI2 (1.3 × 10Ϫ2 mol dmϪ3
,
25 ЊC) is a sharp singlet (δ 38.1, ∆ν1/2 = 3.5 Hz), and both δ and
∆ν1/2 are substantially unaffected in the temperature range ϩ40
to Ϫ55 ЊC, the latter being the lowest temperature for which 31
P
NMR data were available. No 115In NMR resonance was
detected with a solution of 1 in diethyl ether. Owing to the
high nuclear spin of indium, we were not able to detect any
115In NMR signal in accordance with the fact that only InIII-
containing species with high symmetry are detectable.16
IR spectroscopy agrees with structural and NMR data. The
P᎐S bonds are lengthened and the P–N bonds are shortened
᎐
compared to the ligand HL as a consequence of the electron
delocalisation associated with deprotonation/complexation.
The ν(P–S) stretching bands in the complex (566 and 523 cmϪ1
)
agree with a reduced P–S bond order compared to the free
ligand HL (689 and 650 cmϪ1).17 The νasym(PNP) (1240 cmϪ1),
which is the most sensitive band to ligand complexation, is indi-
cative of an increased bond order with respect to the free ligand
(922 cmϪ1).17
UV-Vis and NMR solution studies
Fig. 1 ORTEP27e plot of 1 showing the atom labeling scheme and
30%-probability thermal ellipsoids. Hydrogen atoms have been omitted
for clarity.
The reaction between HL, I2 and In (1 : 1.5 : 1 molar ratio; HL
= 2.22 × 10Ϫ3 mol dmϪ3, 25 ЊC) in diethyl ether differs from
those carried out with the metals Co0, Pd0, and Sb0, in that
the typical dark-red colour of the reaction mixture, due to the
immediate formation of the charge-transfer adduct bearing the
S–I–I group, rapidly disappears. In fact, on monitoring the
course of the reaction by the blue-shifted band of iodine18 at
460 nm, it appears clear that the concentration of the adduct
HLؒI2 lowers during the first hour of reaction and becomes
negligible within ninety minutes. At this stage of the reaction,
115In and 31P NMR spectroscopy show signals at δ(115In) Ϫ1020
(∆ν1/2 = 775 Hz) and δ(31P) 57.1. This strongly indicates the
formation of indium triiodide16,19 and free HL.5f In the course
of the reaction, the 31P NMR signal related to HL decreases in
intensity and the formation of a new signal at δ 38.1 is observed
at the same time. After one day the solution does not undergo
any further reaction, about 60% of the initially formed HL is
still present unreacted in the solution (Fig. 3a). The chemical
shift at δ 38.1 indicates formation of a deprotonated ligand-
containing species, according to the upfield shift of ca. 19 ppm
of the 31P NMR signal upon complexation of HL.5f Assign-
ment of this signal to the species InLI2 is confirmed by com-
parison with the spectrum of the neat compound dissolved in
Et2O showing a signal at δ 38.1.
0.756 (2) Å, respectively, from the mean In(1)P(1)N(1)S(2)
plane and dihedral angles between the named plane and
In(1)P(1)S(1) [S(2)N(1)P(2)] of 39.13(7)Њ [49.91(9)Њ]. Interest-
ingly, the conformation of the InSPNPS ring seems to be con-
trolled by the steric hindrance of the bulky (SPR2)2N ligands
(R = Ph,13,14b Pri 14a) rather than by the coordination number of
the indium ion. Despite the different coordination geometries
the rings in fact show the same overall boat conformation in 1,
InL3 (2)13a and InCl((SPPri2)2N)2 (3) (Fig. 2),14a although a
“flipping” of the InSPNPS ring is observed upon increasing the
steric requirements of the ligand molecule arrangement around
the metal ion, on passing from 1 to 2, and 3 (where N and In act
as bow/stern of the ring). Though far from being planar [devi-
ations from the mean plane 0.5537(13) Å], the geometry of
the InSPNPS moiety clearly shows a π-electron delocalisation
over the whole ring as a result of metal coordination, in a way
already observed in various metal–(XPR2)2N complexes (R =
Ph, Me, Pri; X = S, Se, O).7a,13,14 In 1 in particular, on comparing
with the free ligand HL,15 the P–S distances increase from
1.937(1)–1.950(1) to 2.0452(13)–2.0478(12) Å, while the P–N
D a l t o n T r a n s . , 2 0 0 3 , 1 5 1 5 – 1 5 1 9
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eqns. (1) and (2); in fact, it provides the way to free the metal
from 1 as InI4Ϫ species, which are easily separable as salts from
the solution of HL, which can be re-utilised.
Interestingly, it is possible to start from the caesium salt CsL,
instead of HL itself, to prepare 1 with a higher yield and a
shorter reaction time. This result is not unexpected because of
the higher nucleophilicity of L compared to HL (the calculated
NBO charges on the sulfur donor atoms of the (SPH2)2NH
model ligand HLЈ are Ϫ0.707 and Ϫ0.496 e for LЈ and HLЈ
respectively).7a,7b The 31P NMR spectrum of a mixture of CsL,
I2, and indium metal powder (1 : 1.5 : 1 molar ratio) in
anhydrous diethyl ether recorded after one day is reported in
Fig. 4. Although the reaction carried out with CsL has a higher
yield in complex 1 compared to the use of HL, one of its main
drawbacks is the formation of by-products, which were not
identified (starred peaks in Fig. 4). Moreover, a partial
hydrolysis of the monohydrate salt CsLؒH2O regenerates the
HL species.
Fig. 3 31P NMR spectra in Et2O at 25 ЊC of the reaction mixtures HL,
I2, and In at different molar ratios recorded after 7 days. Molar ratios: 1
: 1.5 : 1; 1 : 3 : 2; 1 : 4.5 : 3, for a, b, and c, respectively; HL = 2.22 × 10Ϫ3
mol dmϪ3
.
Based on these results we also synthesised complex 1 (see
Experimental section, synthesis method b) by using indium tri-
iodide and HL as reagents. We found that the yield of this
reaction is slightly lower than that based on indium powder,
moreover, we reckon that the possibility of generating indium
triiodide in situ easily (see Experimental section, synthesis
method a) is a great advantage as this compound is itself very
air-sensitive. At present the influence exerted by the mixture of
HL and I2 in the process of oxidation of the metal is still not
fully understood,7a although it is recognisable from a qualitative
experimental basis that indium powder reacts with I2 more
quickly in the presence of HL.
In order to elucidate its stoichiometry, we also monitored the
reaction by 31P NMR starting from HL, I2, and In in a 1 : 3 : 2
molar ratio (HL = 2.22 × 10Ϫ3 mol dmϪ3, 25 ЊC) in order to
obtain a higher InI3 to HL reaction molar ratio. The 31P NMR
spectrum of the mixture recorded after 7 days shows one peak
at δ 38.1 and a very small peak at δ 57.1. In this case the form-
ation of InLI2 is almost quantitative (Fig. 3b). By starting from
an HL, I2 and In 1 : 4.5 : 3 molar ratio, the only peak observable
after 7 days in the 31P NMR spectrum is that at δ 38.1 (Fig. 3c).
Interestingly for all reaction molar ratios employed, the 115In
NMR spectrum measured at the end of the reaction supports
the formation of a new indium-containing species different
Fig. 4 31P NMR spectrum in Et2O at 25 ЊC of the reaction mixture of
CsL, I2, and In (1 : 1.5 : 1 molar ratio) recorded after 1 day. The peaks
labeled with a star are due to unidentified species.
We also tried to synthesise complexes with a higher ligand
content by reacting an excess of CsL with a solution of InLI2 in
Et2O, but complex 1 remained the only isolated species.
Redox properties and theoretical calculations
The redox properties of 1 have been measured by cyclic
voltammetry in CH3CN (0.1 mol dmϪ3 in Bu4NBF4) in the
range ϩ1.6 to Ϫ1.6 V where the ligand HL is electrochemically
inactive. Two irreversible coulometrically-tested monoelec-
tronic reductions at Epc1 = Ϫ0.65 V and Epc2 = Ϫ1.2 V vs. Ag/
AgCl were observed and can be assigned to the couples InIII/InII
and InII/InI, respectively. In addition, one irreversible bi-
electronic oxidation was observed at Epa = ϩ0.51 V vs. Ag/
AgCl, due to the couple 2IϪ/I2. Interestingly, indium triiodide in
CH3CN exhibits a cyclic voltammogram similar to that of 1,
with two irreversible reduction processes at Epc1 = Ϫ0.35 V and
Epc2 = Ϫ0.85 V and one irreversible oxidation at Epa = ϩ0.98 V
vs. Ag/AgCl.
from InI3 and 1. In fact, a resonance at δ Ϫ1022 (Et2O, ∆ν1/2
=
520 Hz) is observed which indicates formation of the tetraio-
doindate anion InI4 ;
Ϫ 20,21 Raman peaks at 184w and 138vs cmϪ1
confirming the presence of this species.22
Therefore, it can be hypothesised that the reaction between
the adduct and indium powder occurs in two subsequent steps.
One leads to the formation of indium triiodide [eqn. (1)],
(1)
which is known to exist exclusively as dimer In2I6 in non-
coordinating solvents;20,21 while the other consists of the reac-
tion of this species with HL to yield the stable complex InLI2
(1) [eqn. (2)].
The non-bonding Kohn–Sham23 HOMO (Fig. 5) and the
HOMO Ϫ 1, involved in the reduction processes, have been
calculated on the model complex InLЈI2 (4) [LЈ = (SPH2)2NϪ] in
which the bulky phenyl groups have been replaced by hydrogen
atoms, and are simply formed by the combination of the two
corresponding iodine px and py atomic orbitals. The LUMO
(Fig. 5), involved in the oxidation process, is a σ* antibonding
molecular orbital with a very large contribution of the valence
shell s indium atomic orbital interacting with the pz atomic
orbitals of the four donor atoms. It should be pointed out that
the HOMO and LUMO calculated at the same level of theory
for InI3 in its dimeric form show analogous compositions.
Although the changes in the thermodynamic parameters
involved in the redox processes are neglected, the lower Kohn–
Sham LUMO eigenvalue calculated for In2I6 compared to that
calculated for 4 (εLUMO = Ϫ0.147 and Ϫ0.087 Hartree, respect-
ively) (Fig. 5) explains the easier reduction process observed for
In2I6. The nature of the LUMO implies that the reductions in
both compounds are mainly centred on the In atom (InIII/InII
(2)
Unlike the previously studied reactions of HL and I2 with
cobalt and palladium metal powders, where we were able to
identify the intermediate species CoI2ؒHL and PdI2ؒHL respect-
ively, in this case the formation of the 1 : 1 adduct InI3ؒHL was
not detected, not even by reacting indium triiodide and HL at
Ϫ40 ЊC. Moreover, the possibility of preparing InI3ؒHL by
addition of HI to a solution of InLI2 (1.3 × 10Ϫ2 mol dmϪ3
,
Et2O, 25 ЊC) was also verified. Conversely, this reaction leads to
the release of the free ligand HL, as shown by the 31P NMR
chemical shift change to 57.1 from 38.1 ppm and the formation
of the anion InI4Ϫ. The latter reaction might be very important
for an indium-recovery process from industry residues based on
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FT-Raman spectra were recorded on a Bruker FRS 100
Fourier-transform Raman spectrometer, operating with a
diode-pumped Nd:YAG exciting laser emitting at 1064 nm.
Cyclic voltammetry experiments were recorded at room tem-
perature, in anhydrous CH2Cl2 or CH3CN at a scan rate of
100 mV sϪ1, using a conventional three-electrode cell, consist-
ing of a combined working and counter platinum electrode
and a standard Ag/AgCl (in 3.5 mol dmϪ3 KCl; 0.2050 V)
reference electrode. The solution was about 1 × 10Ϫ3 mol
dmϪ3 in the complex InLI2, with Bu4NBF4 (0.1 mol dmϪ3) as
supporting electrolyte. A stream of argon was passed through
the solution prior to the scan. Data were recorded on a
computer-controlled EG&G (Princeton Applied Research)
potentiostat-galvanostat Model 273 EG&G, using Model
270 electrochemical analysis software. Ultraviolet-visible
spectra were recorded on a Varian model Cary 5 UV-Vis-NIR
spectrophotometer.
Fig. 5 Comparison of the Kohn–Sham HOMO and LUMO energies
calculated for model compound InLЈI2 [LЈ = (SPH2)2NϪ] (4) (left) and
for In2I6 (right).
Synthesis
Compounds (SPPh2)2NH (HL) and Cs(SPPh2)2N (CsL) were
prepared according to ref. 25 and 7c, respectively.
and InII/InI). Moreover, the antibonding nature of this orbital
accounts for the irreversibility of the processes. As far as oxid-
ation is concerned, the composition of the HOMOs in terms of
atomic orbitals indicates that the process regards the iodide
ions of both species (2IϪ/I2). The HOMOs’ eigenvalues (εHOMO
= Ϫ0.290 and Ϫ0.259 Hartree for In2I6 and 4, respectively)
account for the different oxidation potentials of 1 and In2I6.
InLI2 (1). Method a. A mixture of HL (0.100 g, 0.222 mmol)
and I2 (0.084 g, 0.333 mmol) in diethyl ether (200 mL) was
stirred at 25 ЊC under N2 until complete dissolution of the
reagents. Indium metal powder (100 mesh) (0.0255 g, 0.222
mmol) was added while stirring. This was continued at room
temperature for ca. 7 days. The filtered solution was allowed to
concentrate at room temperature. The very first crop of crystals
which separate from the solution were collected, washed with a
mixture of CH2Cl2 and n-hexane (1 : 5 v/v), and air dried to give
0.042 g, 0.051 mmol of 1, yield 23%.
Method b. HL (0.100 g, 0.222 mmol) in diethyl ether (50 mL)
was added to a solution of indium triiodide (0.110 g, 0.222
mmol) in diethyl ether (100 mL). The mixture was allowed to
react at 25 ЊC under N2 for ca. 7 days. The filtered solution was
allowed to concentrate at room temperature. The very first crop
of crystals which separate from the solution were collected,
washed with a mixture of CH2Cl2 and n-hexane (1 : 5 v/v), and
air dried to give 0.030 g, 0.036 mmol of 1, yield 16%. mp 230–
232 ЊC. Anal calcd for C24H20NP2S2I2In: C, 35.28; H, 2.47; N,
1.71; S, 7.85%. Found: C, 36.1; H, 2.5; N, 1.8; S, 8.0%. 31P NMR
(Et2O): δ 38.1. IR(KBr): ν(PS)/cmϪ1 566, 523; νasym(PNP)/cmϪ1
1240.
Conclusions
To sum up we have shown that the reaction between the adduct
HLؒI2 and In in Et2O clearly affords the oxidation of indium to
the ϩ3 oxidation state and its complexation to produce InLI2.
We have found that this complex readily reacts with HI to yield
Ϫ
the anion InI4 with the release of HL. These two reactions
performed in sequence may open new perspectives for the
recovery of In0 from indium-containing materials according to
Scheme 1.
X-Ray crystallography
Crystal data for complex 1. C24H20I2InNP2S2, M = 817.11,
monoclinic, a = 8.8500(6), b = 17.555(2), c = 18.649(3) Å,
β = 93.665(9), U = 2891.4(6) Å3, T = 298(2) K, space group26
P21/n (No. 14), Z = 4, µ (Mo-Kα) = 3.221 mmϪ1. 9683 reflec-
tions (9147 unique) were collected at room temperature on an
Enraf Nonius-CAD4 automatic diffractometer, and 9677 were
used in structure refinement (Rint = 0.0109). Intensities were
corrected for Lorentz-polarisation effects and empirical absorp-
tion (ψ-scan).27a The structure was solved by direct methods
Scheme 1
Experimental
Materials and instrumentation
Reagents were used as purchased from Aldrich. Diethyl ether
was distilled over LiAlH4 shortly before use. All reactions were
carried out under a dry nitrogen atmosphere.
(SIR-97)27b and refined on Fo using the SHELXL-97 pro-
2
gram27c implemented in the WINGX suite.27d All non-hydrogen
atoms were refined anisotropically while the hydrogen atoms
were treated as idealized contributors and dealt with iso-
tropically. The final value for R1 [wR2] was 0.0471 [0.1473] on
I > 2σ(I ) [all data] with GoF = 1.087 for 290 parameters and
no restraints. The maximum and minimum residual electron
density on the final ∆F map are 1.32 and Ϫ1.58 e ÅϪ3, respect-
ively. Selected interatomic distances and angles are listed in
Table 1.
31P{1H} and 115In NMR (indium-115, spin number I = 9/2,
isotopic abundance of 95.72%) spectra were recorded on a
Varian Unity 400 MHz spectrometer; chemical shift values were
referenced to an external standard of 85% H3PO4 (δ31P 0.0),
inserted as a sealed co-axial tube, and to an 0.5 mol dmϪ3 solu-
tion of InCl4Ϫ in dichloromethane (δ115In 0.0),24 respectively. All
solution NMR experiments were carried out with NMR tubes
with a PTFE valve (Aldrich). 31P NMR MAS spectra were cali-
brated indirectly through the 85% H3PO4 peak (δ 0.0). IR spec-
tra were measured as KBr (4000–400 cmϪ1) and polyethylene
pellets (400–50 cmϪ1) on a Bruker IFS 55 FT-IR spectrometer.
CCDC reference number 198787.
See http://www.rsc.org/suppdata/dt/b2/b211542e/ for crystal-
lographic data in CIF or other electronic format.
D a l t o n T r a n s . , 2 0 0 3 , 1 5 1 5 – 1 5 1 9
1518

View Article Online
10 B. C. Ranu, Eur. J. Org. Chem., 2000, 13, 2347.
Computations
11 The three major applications for indium – display devices, low
melting-point alloys and solders, and semiconductors – are expected
to grow steadily in future years to reach 250 tonnes per year by 2005.
Flue dusts and treatable residues from which indium can be
recovered is therefore expected to increase too. Source: Roskill,
Reports on Metals and Minerals, The economics of Indium, 7th
edition, published November 1999. ISBN 0862148359. http://
roskill.co.uk/indium.html (Accessed November 2002).
12 M. A. Brown and D. G. Tuck, Inorg. Chim. Acta, 1996, 247, 135.
13 (a) R. Cea-Olivares, R. A. Toscano, G. Carreón and J. Valdès-
Martinez, Monatsh. Chem., 1992, 123, 391; (b) V. García-Montalvo,
R. Cea-Olivares, D. J. Williams and G. Espinoza-Pérez, Inorg.
Chem., 1996, 35, 3948; (c) V. García-Montalvo, R. Cea-Olivares,
J. Novosad, D. J. Williams, R. A. Toscano and G. Espinoza-Pérez,
Chem. Ber., 1996, 129, 919.
Density functional calculations (DFT)23 were carried out on
the model complex 4 and on the dimeric form of InI3 using the
suite of programs Gaussian 94,28 with the hybrid Becke 3LYP
functional29 and Schafer, Horn and Ahlrichs pVDZ basis set30
for C, H, N, P, and S. For In and I atoms the LANL2DZ basis
set was used with effective core potentials (ECP)31 accounting
for 46 inner electron shells. In the case of 4, SCF convergence
was achieved by a quadratic convergence procedure (QC
option) based on the Bacskay method.32 Starting from crystal-
lographic geometrical parameters, geometry optimisations were
performed and the results were examined with the Molden 3.6
program.33 Both quantum mechanically optimised structures
were verified by normal-mode harmonic frequency analysis.
The NBO charge distribution34 was calculated for all the
examined compounds.
14 (a) K. Darwin, L. M. Gilby, P. R. Hodge and B. Piggott, Polyhedron,
1999, 18, 3729; (b) R. Cea-Olivares, R. A. Toscano, S. Hernández-
Ortega, J. Novosad and V. García-Montalvo, Eur. J. Inorg. Chem.,
1999, 1613.
15 S. Husebye and K. Maartmann-Moe, Acta Chem. Scand., Ser. A,
1983, 37, 439.
16 Because of the large quadrupole moment of the indium-115 nucleus,
the 115In NMR resonance will be observable only when the nucleus is
in a symmetrical environment, and even then typical linewidths are
250–1000 Hz. T. H. Cannon and R. E. Richards, Trans. Faraday
Soc., 1966, 62, 1378.
17 G. P. McQuillan and I. A. Oxton, Inorg. Chim. Acta, 1978, 29, 69.
18 K. F. Purcell and J. C. Kotz, Inorganic Chemistry, W. B. Saunders
Company, Philadelphia, 1977, ch. 5, pp. 209–212.
Acknowledgements
This research was financially supported by the “Regione
Autonoma della Sardegna”. We are grateful to the “Centro
Interdipartimentale Grandi Strumenti (C.I.G.S.)” of the
University of Modena and Reggio Emilia for providing X-rays
analysis equipment.
19 M. A. Malyarick and S. P. Petrosyants, Inorg. Chem., 1993, 32, 2265.
20 M. A. Brown, D. G. Tuck and E. J. Wells, Can. J. Chem., 1996, 74,
1535.
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D a l t o n T r a n s . , 2 0 0 3 , 1 5 1 5 – 1 5 1 9
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