The synthesis, spectroscopic investigation, crystal and molecular structure of the [ReBrCl2(SbPh3)3] complex

Article abstract of DOI:10.1016/S1387-7003(03)00120-5

The [ReBrCl₂(SbPh₃)₃] complex has been obtained in the reaction of [Bu₄^tN]₂[ReBr₃Cl₂(NO)] with an excess of triphenylstibine. The halide ions and stibine molecules of [ReBrCl₂(SbPh₃)₃] are arranged in a meridional fashion. The substitution reactions of the nitrosyl ligand are very rare so the formation of the [ReBrCl₂(SbPh₃)₃] compound in this reaction is particularly interesting.

Full text of DOI:10.1016/S1387-7003(03)00120-5

Inorganic Chemistry Communications 6 (2003)859–863
www.elsevier.com/locate/inoche
The synthesis, spectroscopic investigation, crystal and
molecular structure of the [ReBrCl2(SbPh3)3] complex
a
a,
b
B. Machura , J.O. Dzißegielewski *, J. Kusz
Department of Inorganic and Radiation Chemistry, Institute of Chemistry, University of Silesia, 9th Szkolna St., Katowice 40-006 Poland
a
b
Institute of Physics, University of Silesia, 4th Uniwersytecka St., Katowice 40-006 Poland
Received 28 February 2003; accepted 20 March 2003
Abstract
The [ReBrCl2(SbPh3)3] complex has been obtained in the reaction of [But4N]2[ReBr3Cl2(NO)] with an excess of triphenylstibine.
The halide ions and stibine molecules of [ReBrCl2(SbPh3)3] are arranged in a meridional fashion. The substitution reactions of the
nitrosyl ligand are very rare so the formation of the [ReBrCl2(SbPh3)3] compound in this reaction is particularly interesting.
Ó 2003 Elsevier Science B.V. All rights reserved.
Keywords: Rhenium(III); Stibine; Nitrosyl complexes; X-ray structure
1. Introduction
Now we are extending our studies to the examination
of the reaction of [Bu4t N]2[ReBr3Cl2(NO)] with triphe-
nylstibine. The formation of the [ReBrCl2(SbPh3)3]
compound in this reaction is particularly interesting
since substitution reactions of the nitrosyl ligand are
very rare observed [19–21]. Here, we present the syn-
thesis, spectroscopic and structural characterisation of
the [ReBrCl2(SbPh3)3] complex.
The widespread contemporary interest in the coor-
dination chemistry of rhenium is motivated by the
perspective of replacing technetium-99m with rhenium-
186/188 for use as a diagnostic or radiotherapeutic agent
[1–5]. Due to key role of nitric oxide in human cardio-
vascular and nervous systems and in immune response
to pathogen invasion [6–9] the rhenium nitrosyl com-
plexes are of special importance.
2. Experimental
Previously, weinvestigatedthereactivity of[ReOX3L2]
compounds(X ¼ ClandBr,L ¼ PPh3 andAsPh3)towards
gaseous nitric oxide and the reactions of [But4N]2[ReX5
(NO)] with an excess of triphenylphosphine and triph-
enylarsine [10–18]. The [ReOX3L2] complexes react with
NO to give various products, depending on the reaction
conditions: [ReX3(NO)(OPPh3)2], [ReX3(NO)(PPh3)2],
[ReX2(NO)2(PPh3)2], [ReBr3(NO)(MeCN)(PPh3)], [Re-
Cl3(NO)(PPh3)(OPPh3)], [ReCl4(PPh3)2], [ReBr3(NO)(dppe)]
[ReBr4(dppe)], [ReX3(NO)(OAsPh3)2], [ReCl4(OAsPh3)2]
and [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2]. The reactions
of [But4N]2[ReX5(NO)] with PPh3 and AsPh3 lead to
[ReBr3(NO)(PPh3)2], [ReCl3(NO)(PPh3)2], [ReBr3(NO)
(AsPh3)2] and [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2], re-
spectively.
Triphenylstibine, triphenylphosphine and NH4ReO4
were purchased from Aldrich Chemical Co. and used
without further purification. The [ReO(OEt)Cl2(PPh3)2]
complex was synthesised according to the litera-
ture method [22]. Gaseous NO, obtained in the reac-
tion: 2NaNO2+3H2SO4+FeSO4 !2NO+2NaHSO4 +Fe2
(SO4)3 þ 2H2O, was purified by passing through the
washers with concentrated KOH solution and over solid
NaOH. The reaction was performed under argon
atmosphere.
2.1. Synthesis of [NBu4]2[ReBr3Cl2(NO)]
The [But4N]2[ReBr3Cl2(NO)] complex was obtained
according to the modified synthesis of Giusto and co-
workers [23]. [ReO(OEt)Cl2(PPh3)2] (1.5 g, 1.8 mmol)
* Corresponding author. Tel.: +48-32-258-2441; fax: +32-259-9978.
E-mail address: jod@tc3.ich.us.edu.pl (J.O. Dzißegielewski).
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1387-7003(03)00120-5

860
B. Machura et al. / Inorganic Chemistry Communications 6 (2003) 859–863
was added to a solution of [But4N]Br (3.30 g, 10 mmol)
in ethanol (60 cm3). Nitrogen oxide was bubbled under
reflux for 3 h. The reaction solution was evaporated to
the volume of 10 cm3 and green precipitate of
[But4N]2[ReBr3Cl2(NO)] was formed by an addition of
60 cm3 of diethylether and after overnight it was filtered
off. The product was washed with cold ether and dried in
vacuo. The yield 25%.
IR (KBr, cmÀ1)3049 (m), 2999(w)1736 (s), 1481 (br,
m), 1438 (sh), 1381 (m), 1261 (w), 1155 (m), 1119 (w),
1093 (w), 1029 (w), 882 (m) 803 (m), 748 (w), 725 (m),
695 (m), 545 (m), 534 (m).
Table 1
Crystal data and structure refinement for [ReBrCl2(SbPh3)3]
Empirical formula
Formula weight
Temperature
C54H45Sb3BrCl2Re
1396.16
293(2)K
ꢀ
0.71073 A
Wavelength
Crystal system
Space group
Unit cell dimensions
Orthorhombic
P212121
ꢀ
ꢀ
a ¼ 13:410ð3Þ A; a ¼ 90°
b ¼ 16:215ð3Þ A; b ¼ 90°
ꢀ
c ¼ 22:683ð5Þ A; c ¼ 90°
3
ꢀ
4932.3(18) A
Volume
Z
4
3
Density (calculated)1.880 M g/m
Absorption coefficient
F ð000Þ
5.025 mmÀ1
2664
Anal. Found: C, 14.48; H, 2.77; N, 6.35. Calc. for
C8H18N3OBr3Cl2Re: C, 14.36; H, 2.71; N, 6.28.
Crystal size
0.32Â0.26Â0.21 mm
1.54–25.06°
À2 6 h 6 15
0 6 k 6 19
h range for data collection
Index ranges
2.2. Synthesis of [ReBrCl2(SbPh3)3]
A mixture of [But4N]2[ReBr3Cl2(NO)] (1 g, 1.5 mmol)
À2 6 l 6 27
3
Reflections collected
6210
and SbPh3 (5.3 g, 15 mmol)in ethanol (50 cm )was
Independent reflections
Max. and min. transmission
Completeness to 2h
5912 ðRint ¼ 0:0331Þ
0.4184 and 0.2962
99.9%
refluxed for 12 h. The formed yellow-green precipitate
was filtered and washed with ether. X-ray quality crys-
tals were obtained by recrystallization from a mixture of
chloroform and ethanol. Yield 65%.
IR (KBr, cmÀ1) 3052 (m), 2898 (w), 1480 (s), 1431 (s),
1332 (w), 1303 (w), 1264 (w), 1186 (w), 1158 (w), 1067
(s), 1020 (m) 998 (w), 728 (s), 692 (s), 658 (w), 451 (s).
Found: C, 46.32; H, 3.23. Calc. for C54H45Sb3BrCl2
Re: C, 46.45; H, 3.25.
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices ½I > 2rðIÞꢀ
5912/0/551
1.131
R1 ¼ 0:0504
wR2 ¼ 0:1013
R1 ¼ 0:0760
wR2 ¼ 0:1134
)0.024(13)
R indices (all data)
Absolute structure parameter
Largest diff. peak and hole
À3
ꢀ
1.435 and )0.877 e A
2.3. Physical measurements
equal 1.2 times the value of equivalent temperature factor
of the parent carbon atom. SHELXL97 [25] and SHEL-
XTL [26] programs were used for all the calculations.
UV–VIS spectra were recorded on a spectropho-
tometer Lab Alliance UV–VIS 8500 in the range 800–
220 nm in deoxygenated dichloromethane solution. IR
spectra were recorded as KBr pellets with a Nicolet
Magna 560 spectrophotometer in the spectral range
4000–400 cmÀ1. Elemental analyses (C H N)were per-
formed on a Perkin–Elmer CHN-2400 analyzer. Mag-
netic susceptibilities were measured at 296 K by the
Faraday method.
3. Results and discussion
The reactions of [But4N]2[ReX5(NO)] (X ¼ Cl or Br)
with an excess of PPh3 and AsPh3 in ethanol produced
[ReCl3(NO)(PPh3)2], [ReBr3(NO)(PPh3)2], [ReBr3(NO)
(AsPh3)2] and [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2]
complexes, respectively [15,17,18]. The [ReX3(NO)
(EPh3)2] complexes (E ¼ P or As)have pseudooctahedral
geometry with trans-phosphine or arsine ligands, merid-
ional halide ligands and a linear nitrosyl group. The ni-
trosyl stretching frequencies in [ReX3(NO)(EPh3)2]
compounds are nearly independent of E, it depends only
on X ligands: 1776 cmÀ1 for [ReBr3(NO)(PPh3)2], 1773
cmÀ1 for [ReBr3(NO)(AsPh3)2], 1734 cmÀ1 for [Re-
Cl3(NO)(PPh3)2] and 1738 cmÀ1 for [ReCl3(NO)
(PPh3)2][ReCl4(AsPh3)2]. The lower values of mNO for
chloro-compounds than for the corresponding bromo-
complexes is in accordance with the greater p-acceptor
character of bromo ion than chloro one.
2.4. Crystal structures determination and refinement
The X-ray intensity data were collected with graphite
ꢀ
monochromated Mo-Ka radiation (k ¼ 0:71073 A)at
room temperature on a Kuma Diffraction KM4 diffrac-
tometer and processed with Omnibus-BLP data pro-
cessing program [24]. Details concerning crystal data and
refinement are given in Table 1. Lorentz polarization,
empirical absorption corrections were applied. The
structures were solved by means of the Patterson and
Fourier methods. All the non-hydrogen atoms were re-
fined anisotropically using full-matrix, least-squares
technique. The hydrogen atoms of the phenyl rings were
treated as ‘‘riding’’ on their parent carbon atoms [d(C–
The nitrosyl [ReBrCl2(NO)(SbPh3)2] complex has not
been isolated in the reaction of mer,trans-[But4N]2
ꢀ
H) ¼ 0.96 A] and assigned isotropic temperature factors

B. Machura et al. / Inorganic Chemistry Communications 6 (2003) 859–863
861
[ReBr3Cl2(NO)] with triphenylstibine in ethanol but the
formation of the nitrosyl has been confirmed by moni-
toring of the reaction via IR spectroscopy. However, the
presence of mNO at much lower frequencies (1680 cmÀ1
)
suggests the different ligandsÕ arrangement around the
rhenium center in the stibine nitrosyl in comparison with
phosphine and arsine [ReX3(NO)(EPh3)2] complexes. It
is most likely that the stibine ligands are in cis-geometry
and the nitosyl group occupies the trans-position to
SbPh3 molecule. The cis-arrangement of SbPh3 mole-
cules in [ReCl(CO)3(SbPh3)2] was confirmed by a crystal
structure determination [27]. The PPh3 molecules of the
analogous [ReCl(CO)3(PPh3)2] carbonyl are in trans-
geometry [28]. It is known that the increase of M–E and
E–C bond lengths in the order P>As>Sb leads to the
decrease of the EPh3 cone angles [29]. The smaller size of
SbPh3 in comparison with PPh3 and AsPh3 can be used
to explain the cis-arrangement of SbPh3 molecules in
[ReCl(CO)3(SbPh3)2] and the formation of [ReBrCl2
(SbPh3)3] in the reaction of [But4N]2 [ReBr3Cl2(NO)]
with SbPh3. The Re–E and E–C bond lengths and C–E–
C angles (E ¼ P or As)for selected rhenium complexes
are summarised in Table 2.
Fig. 1.
ꢀ
(SbPh3)2] [30] [Re–Sb: 2.711(8)and 2.710(8) A] and
[ReCl(CO)3(SbPh3)2] [27] [Re–Sb: 2.726(1)and 2.729(2)
The [ReBrCl2(SbPh3)3] complex crystallises in the
orthorhombic space group P212121 and its structure
consists of discrete and well-separated monomers. Fig. 1
shows the molecular structure of this compound and the
selected bond lengths and angles for [ReBrCl2(SbPh3)3]
are summarized in Table 3. The two groups of ligands of
[ReBrCl2(SbPh3)3] (halide ions and stibine molecules)
are arranged in a meridional fashion. Due to steric re-
pulsion of three bulky SbPh3 molecules the octahedral
Re geometry shows the expected angular distortions.
The angles between cis-ligands vary between 85.12(6)°
and 96.00(10)°, while the trans-angles are between
170.00(4)° and 178.13(16)°. The conformations of [Re-
BrCl2(SbPh3)3] molecules are stabilised by two C–
Hꢁ ꢁ ꢁCl weak intramolecular hydrogen bonds [31]:
C(14)–H(14A)ꢁ ꢁ ꢁCl(2)with D ꢁ ꢁ ꢁA distance equal 3.56(2)
ꢀ
A] being the closet chemical examples and showing a
little longer Re–Sb bond lengths to the present com-
pound [Re–Sb: 2.6694(13), 2.6830(13) and 2.6942(14)
ꢀ
A]. In solid SbPh3 the C–Sb–C angles range from
95.1(3)° to 98.0(3)° with an average of 96.3° [32],
whereas in the complex reported here the values are
larger than in free ligand; 94.1–103.1(7)°, 99.1° (av).
This is most likely due to the large Sb–C bond lengths,
ꢀ
ranging from 2.104(14)to 2.180(18) A with an average
ꢀ
of 2.134 A, making it possible for the phenyl rings to be
compressed a little more than what is encountered for
analogous phosphine and arsine ligands. A significant
difference between Re–Cl(1)and Re–Cl(1)in the title
complex must be a consequence of crystal packing. The
Re–Br distance of [ReBrCl2(SbPh3)3] is considerable
longer than Re–Br bond lengths in the mer,trans-
[ReBr3(NO)L2] compounds (L ¼ PPh3 and AsPh3)
[15,17,18] but comparable with the Re–Br distance trans
to CO ligand in [ReBr2(NO)(CO)(PPh3)2]ꢁNO [16].
A notable trans-influence of triphenylstibine ligand is
ꢀ
A and D–Hꢁ ꢁ ꢁA angle – 153.3°; C(8)–H(8A)ꢁ ꢁ ꢁCl(1)
ꢀ
with Dꢁ ꢁ ꢁA distance equal 3.52 (2) A and D–Hꢁ ꢁ ꢁA
angle – 152.9°.
There are very few Re–Sb distances reported in the
Cambridge structural database with [ReCl2(NO)2
Table 2
The Re–E and E–C bond lengths and C–E–C angles (E ¼ P, As or Sb)for selected rhenium complexes
Complex
Re–E bond length
ꢀ
(average, [A])
E–C bond length
ꢀ
(average, [A])
C–E–C angle
(average, [°])
Reference
[Re(NO)Cl3(PPh3)2]
[Re(NO)Br3(PPh3)2]
[Re(NO)Cl3(AsPh3)2]
[Re(NO)Br3(AsPh3)2]
[ReCl(CO)3(SbPh3)]
[ReCl2(NO)2(SbPh3)2]
2.530
2.540
2.612
2.595
2.728
2.711
1.822
1.822
1.942
1.935
2.137
2.114
104.3
104.3
103.4
103.7
100.1
102.5
[15]
[17]
[18]
[18]
[27]
[30]

862
B. Machura et al. / Inorganic Chemistry Communications 6 (2003) 859–863
Table 3
Table 4
Band positions, molar absorption coefficients and assignments for
[ReBrCl2(SbPh3)3]
ꢀ
Selected bond lengths [A] and angles [°] for [ReBrCl2(SbPh3)3]
Bond lengths
Angles
Band position [cmÀ1
]
e
Assignment
Re(1)–Br(1)
Re(1)–Cl(1)
Re(1)–Cl(2)
2.5962(19)
2.466(5)
2.407(7)
Cl(2)–Re(1)–Cl(1)
Cl(2)–Re(1)–Br(1)
Cl(1)–Re(1)–Br(1)
Cl(2)–Re(1)–Sb(1)
Cl(1)–Re(1)–Sb(1)
Br(1)–Re(1)–Sb(1)
Cl(2)–Re(1)–Sb(2)
Cl(1)–Re(1)–Sb(2)
Br(1)–Re(1)–Sb(2)
Sb(1)–Re(1)–Sb(2)
Cl(2)–Re(1)–Sb(3)
Cl(1)–Re(1)–Sb(3)
Br(1)–Re(1)–Sb(3)
Sb(1)–Re(1)–Sb(3)
Sb(2)–Re(1)–Sb(3)
C(1)–Sb(1)–C(7)
178.13(16)
87.27(14)
91.06(11)
85.66(13)
96.00(10)
172.91(7)
90.60(14)
88.44(10)
85.83(6)
93.66(4)
93.20(14)
87.50(10)
85.12(6)
95.85(4)
170.00(4)
100.9(7)
98.4(7)
1
23,450
26,300
34,980
44,030
45,500
790
680
3T1 ! T2
1
3T1 ! A1
3
Re(1)–Sb(1) 2.6694(13)
Re(1)–Sb(2) 2.6830(13)
Re(1)–Sb(3) 2.6942(14)
14,000
20,625
17,425
3T1 ! E; p ! pꢂRe–Sb
C6H5
3
3T1 ! T2; pb
6H5
! 5dSb
p ! pꢂC
Sb(1)–C(1)
Sb(1)–C(7)
2.121(17)
2.152(17)
e ¼ molar absorption coefficient [dm3 molÀ1 cmÀ1].
Sb(1)–C(13) 2.180(18)
Sb(2)–C(19) 2.119(16)
Sb(2)–C(25) 2.130(18)
Sb(2)–C(31) 2.132(14)
Sb(3)–C(37) 2.132(16)
Sb(3)–C(43) 2.134(18)
Sb(3)–C(49) 2.104(14)
terms 1T2 and 1A1 with 3T1 causes, in some degree,
singlet–singlet character of the intercombination tran-
sitions. The central ion of Re(III)has the following
electron configuration (dxy)2(dxz)1(dyz)1. Re–Sb bond in
ꢀ
trans-position towards Re–Br is ca. 0.023 A shorter in
comparison with the other Re–Sb bonds. This fact
confirms formation of p(Re–Sb)bond with participation
of donor electrons from dxz and dyz orbitals of the rhe-
nium atom. Obviously, the electrons occupying dxy or-
bital of the central atom also participate in Re–Sb bonds
formation, but the number of donor electrons per one
Sb atom, lower by half, results in longer Re–Sb bonds in
trans-position. High degree of covalence of the complex
is confirmed by values of Dq ¼ 3498 cmÀ1, B ¼ 440 cmÀ1
and C ¼ 1758 cmÀ1. Significantly lower molar extinction
coefficient of the band connected with pbC H ! 5dSb
C(1)–Sb(1)–C(13)
C(7)–Sb(1)–C(13)
C(1)–Sb(1)–Re(1)
C(7)–Sb(1)–Re(1)
C(13)–Sb(1)–Re(1)
C(19)–Sb(2)–C(25)
C(19)–Sb(2)–C(31)
C(25)–Sb(2)–C(31)
C(19)–Sb(2)–Re(1)
C(25)–Sb(2)–Re(1)
C(31)–Sb(2)–Re(1)
C(43)–Sb(3)–C(49)
C(43)–Sb(3)–C(37)
C(49)–Sb(3)–C(37)
C(43)–Sb(3)–Re(1)
C(49)–Sb(3)–Re(1)
C(37)–Sb(3)–Re(1)
99.3(7)
115.8(4)
123.4(5)
115.0(5)
103.1(7)
94.1(7)
99.6(7)
119.4(4)
117.2(5)
119.4(4)
101.3(7)
99.2(6)
6
5
transition, compared with an analogous electron trans-
fer towards 3dP, also confirms the participation of 5dSb
acceptor orbitals in the formation of p(Re–Sb)bond. It
lowers the probability of pbC H ! 5dSb transition.
95.7(7)
117.2(4)
116.5(4)
122.8(5)
6
5
observed in mer-[OsBr3(SbPh3)3] [33], in which the
ꢀ
Os–Br trans to SbPh3 [2.522(2) A] is considerable longer
Supplementary data
ꢀ
than the others 2.507(2)and 2.508(2) A.
Supplementary data of [ReBrCl2(SbPh3)3] complex
are available from the CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK on request, quoting the deposition
number 205379.
The complex [ReBrCl2(SbPh3)3] shows room tem-
perature magnetic moment of 1.5 BM. This value is
characteristic of mononuclear complexes with low-spin
rhenium(III)(d 4)ions in O h field [34], and arises because
of the large spin–orbit coupling [35]. Magnetic moment
corresponding with two unpaired electrons may be
achieved only at very low temperature, because it is a
condition favoring the triplet state.
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