Synthesis, crystallographic, and theoretical investigation of fac-[Re I(salen)(CO)3(S)] complexes, salen = monocharged bidentate Schiff-base and S = pyridine, CH3OH

Article abstract of DOI:10.1080/00958972.2010.538050

Two rhenium(I) complexes of the form fac-[Re(L-L′)(CO) ₃(S)] were synthesized (L-L′ = N-O salen-type bidentate ligand, S = coordinating methanol or pyridine) and the crystal structures of fac-[tricarbonylmethanol-(2-(3-methylbutyliminomethyl)phenolato)rhenium(I)] and fac-[tricarbonyl-(2-(3-methylbutyliminomethyl)phenolato)pyridinerhenium(I)] are reported. The influence of the coordinating neutral monodentate ligand in these fac-[tricarbonyl(N,O-salen)rhenium(I)] complexes was investigated both in solid state and at theoretical level using X-ray diffraction, IR, NMR, and DFT calculations.

Full text of DOI:10.1080/00958972.2010.538050

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Synthesis, crystallographic, and
theoretical investigation of fac-
[ReI(salen)(CO)3(S)] complexes,
salenꢀ=ꢀmonocharged bidentate Schiff-
base and Sꢀ=ꢀpyridine, CH3OH
Alice Brink a , Hendrik G. Visser a & Andreas Roodt a
a Department of Chemistry, University of the Free State, PO Box
339, Bloemfontein 9300, South Africa
Available online: 07 Dec 2010
To cite this article: Alice Brink, Hendrik G. Visser & Andreas Roodt (2011): Synthesis,
crystallographic, and theoretical investigation of fac-[ReI(salen)(CO)3(S)] complexes,
salenꢀ=ꢀmonocharged bidentate Schiff-base and Sꢀ=ꢀpyridine, CH3OH, Journal of Coordination
Chemistry, 64:1, 122-133
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Journal of Coordination Chemistry
Vol. 64, No. 1, 10 January 2011, 122–133
Synthesis, crystallographic, and theoretical investigation of
fac-[ReI(salen)(CO)3(S)] complexes, salen ^ monocharged
bidentate Schiff-base and S ^ pyridine, CH3OH
ALICE BRINK, HENDRIK G. VISSER* and ANDREAS ROODT*
Department of Chemistry, University of the Free State,
PO Box 339, Bloemfontein 9300, South Africa
(Received 14 August 2010; in final form 1 October 2010)
Two rhenium(I) complexes of the form fac-[Re(L–L0)(CO)3(S)] were synthesized (L–L0 ¼ N–O
salen-type bidentate ligand, S ¼ coordinating methanol or pyridine) and the crystal structures
of fac-[tricarbonylmethanol-(2-(3-methylbutyliminomethyl)phenolato)rhenium(I)] and fac-
[tricarbonyl-(2-(3-methylbutyliminomethyl)phenolato)pyridinerhenium(I)] are reported. The
influence of the coordinating neutral monodentate ligand in these fac-[tricarbonyl(N,O-
salen)rhenium(I)] complexes was investigated both in solid state and at theoretical level using
X-ray diffraction, IR, NMR, and DFT calculations.
Keywords: Rhenium; Salen; N–O bidentate ligand; Crystal structure
1. Introduction
Interest in rhenium and technetium complexes bearing the fac-MðCOÞþ3 entity
(M ¼ Tc(I), Re(I)) as potential diagnostic and therapeutic radiotracers in the treatment
of cancer has increased tremendously [1–4] due to the fact that the fac-[M(CO)3]þ core
is inert while the water molecules bound to it are quite labile [5]. It therefore comes as
no surprise that several promising compounds have been synthesised over the past few
years using these tri-carbonyl synthons [6–10].
One approach to the design of potential radiopharmaceuticals is the so-called mixed
ligand [2 þ 1] approach proposed by Mundwiler et al. [11]. This approach offers a
variety of options to the designer, since the bidentate ligand could be used as a chelator
with a directing ligand attached to it, while the third labile position on the rhenium
metal center is occupied by another ligand, which simply acts as a ‘‘blocker’’ to
nucleophilic attack from other biomolecules in vivo. Another option is that the third
position is occupied by a directing ligand while the bidentate ligand simply offers
stability in terms of chelation.
Fundamental chemical knowledge of the fac-tricarbonylrhenium(I) complexes
will afford more effective design of complexes to be used as radiopharmaceuticals.
*Corresponding authors. Email: visserhg@ufs.ac.za; roodta@ufs.ac.za
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2010.538050

fac-[ReI(salen)(CO)3(S)]
123
This knowledge includes stability evaluations, formation kinetics, and the development
of new synthetic pathways. A few limitations must however be considered when
designing experimental procedures for radiopharmaceuticals for routine clinical
application. The restrictions require the synthetic procedures to occur in one step,
a high purity yield, ideal biomolecule concentration, and the experimental time
dependent on the half-life of the radionuclide. An important limitation which must also
be kept in mind is that any preparation is performed in saline solution (0.9% NaCl
in water or buffer) [5]. Therefore, the majority of fac-MðCOÞþ3 complexes synthesized to
date has focused on water as solvent, although the study of these complexes in various
solvents have led to interesting spectroscopic and photochemical results [12–14].
Our interest is to investigate the possible use of Schiff-base ligands in the [2 þ 1]
approach, since coordination chemistry of Schiff-bases has received much interest due
to their ability to form stable complexes with most transition metals [15]. These
compounds display potential as ligands and are generally prepared by condensation
of primary amines with a carbonyl precursor [16]. The versatility of Schiff-bases,
in particular salicylaldiminates, allows for mono- and bi-valent bidentate ligands with
varying electronic and steric effects afforded by the substituent on the nitrogen atom
[17, 18]. Moreover, the introduction of a biological active amine onto a relatively small
backbone holds great promise. However, all our efforts to synthesize fac-[Re(CO)3
(salen)X]nꢀ complexes (X ¼ H2O, Brꢀ, py) from aqueous medium proved to be
extremely difficult since these reactions almost always formed oily products and gave
low yields. This led us to use methanol as an alternative solvent (scheme 1). As a result,
Scheme 1. General reaction scheme of [Re(L–L0)(CO)3(S)] synthesis (L–L0 ¼ mono-anionic bidentate ligand,
Py ¼ pyridine, S ¼ coordinating ligand).

124
A. Brink et al.
we propose here a new synthetic route for the synthesis of mixed ligand complexes of
rhenium tricarbonyls. The crystal structures of fac-[tricarbonylmethanol-(2-(3-
methylbutyliminomethyl)phenolato)rhenium(I)] 2, and fac-[tricarbonyl-(2-(3-methylbu-
tyl-iminomethyl)phenolato)pyridinerhenium(I)] 3, are included as part of this study.
This is the first published crystal structure of a complex of fac-[Re(CO)3(L–
L0)(CH3OH)]nꢀ
.
2. Experimental
2.1. Materials and general procedures
All reagents used for synthesis and characterization were of analytical grade, purchased
from Sigma-Aldrich, unless otherwise stated. Reagents were used as received, without
purification. Rhenium pentacarbonyl bromide was purchased from Strem Chemicals,
Newburyport, US. fac-[NEt4]2[ReBr3(CO)3] (ReAA) was synthesized as described by
1
Alberto et al. [19]. 13C- and H FT-NMR spectra of the rhenium compounds were
recorded at 150.96 and 600.28 MHz, respectively, on a Bruker AXS 600 MHz at 25ꢁC
in CD3OD (3.31 ppm) and C3H6O (2.05 ppm); chemical shifts are reported in ppm.
Infrared spectra were recorded on a Bruker Tensor 27 Standard System spectro-
photometer with a laser range of 4000–370 cmꢀ1, equipped with a temperature cell
regulator, accurate within 0.3ꢁC. Solid samples were analyzed as KBr pellets and liquid
samples in methanol solution in an NaCl liquid cell. All data were recorded at room
temperature. UV-Vis spectra were collected on a Varian Cary 50 Conc UV-Visible
Spectrophotometer, equipped with a Julabo F12-mV temperature cell regulator
(accurate within 0.1ꢁC) in a 1.000 ꢂ 0.001 cm quartz cuvette cell. Computational
calculation results were obtained using the GAUSSIAN-03W [20] software package.
DFT calculations were done at the B3LYP [21] level of theory with the 6–31Gþþ(d,p)
[22, 23] basis set for the main group elements and LanL2Dz for rhenium, using the
High Performance Computing Facility of the University of the Free State. Optimized
structures were verified as minima through frequency analysis. Graphical representa-
tions of overlays of selected complexes are obtained with Hyperchem 7.52 [24].
2.2. Synthesis of salen-3MeBu (1)
The ligand 2-(3-methylbutyliminomethyl)phenol (salen-3MeBu) was synthesized
according to the method previously reported [25]. Salicylaldehyde (1.40 g, 11.5 mmol)
was dissolved in 30 mL methanol, to which 3 g of anhydrous MgSO4 was added, and
3-methylbutylamine (14.0 mmol, 1.00 g, 11.5 mmol) dissolved in methanol (10 mL) was
then added dropwise to this mixture. The reaction was heated to 80ꢁ and refluxed for
3 h. MgSO4 was filtered off and solvent removed under reduced pressure to yield the
yellow oil product (Yield: 1.61 g, 73.5%). 1H-NMR (600 MHz, acetone-d6) ꢀ 8.53 (s, 1H,
HC¼N), 7.37 (m, 1H, Ar), 7.31 (m, 1H, Ar), 6.87 (m, 2H, Ar), 3.65 (dt, 2H, J ¼ 7.2,
1.3 Hz), 1.72 (m, 1H), 1.58 (q, 2H, J ¼ 7.2 Hz), 0.96 (d, 6H, J ¼ 6.5 Hz). 13C-NMR
(600 MHz, acetone-d6) ꢀ 165.43 (C1), 161.25, 131.90, 131.41, 119.10, 118.32, 116.50
(Ar), 57.28, 39.82, 25.69, 21.86 (C24, C25).

fac-[ReI(salen)(CO)3(S)]
125
2.3. Synthesis of [Re(salen-3MeBu)(CO)3(HOCH3)] (2)
Salen-3MeBu (0.0169 g, 8.84 ꢃ 10ꢀ5 mol) dissolved in methanol (5 mL) was added to
ReAA (0.0623 g, 8.09 ꢃ 10ꢀ5 mol) in methanol (5 mL). The reaction was stirred for
24 h at room temperature. A yellow, micro-crystalline product was obtained upon
evaporation of the solvent. Yellow crystals suitable for X-ray diffraction were obtained
by slow evaporation of solvent (Yield: 0.024 g, 38%). IR (KBr, cmꢀ1): v(CO) 2001.4 (vs),
1876.5 (vs). UV-Vis (nm; L molꢀ1 cmꢀ1): ꢁmax ¼ 382.9, " ¼ 1.311 ꢃ 103. 1H-NMR
(600 MHz, acetone-d6) ꢀ 8.22 (s, 1H, HC¼N), 7.15 (m, 2H, Ar), 6.65 (d, 1H, Ar,
J ¼ 8.5 Hz), 6.42 (m, 1H, Ar), 1.68 (m, 5H), 0.99 (d, 3H, J ¼ 6.5 Hz), 0.93 (d, 3H,
J ¼ 6.5 Hz). 13C-NMR (600 MHz, acetone-d6) ꢀ 166.78 (C1), 166.24, 136.23, 134.54,
122.77, 121.53, 113.92 (Ar), 69.14, 41.99, 26.54, 23.12, 22.64.
2.4. Synthesis of [Re(salen-3MeBu)(CO)3(NC5H5)] (3)
Salen-3MeBu (0.027 g, 1.43 ꢃ 10ꢀ4 mol) dissolved in methanol (5 mL) was added to a
methanol (10 mL) solution of ReAA (0.1 g, 1.30 ꢃ 10ꢀ4 mol). The reaction was stirred
for 6 h at 25ꢁC before addition of pyridine (0.015 g, 1.95 ꢃ 10ꢀ4 mol), in 5 mL methanol,
followed by a further 12 h stirring. The pale yellow precipitate was filtered and dried.
Crystals suitable for X-ray diffraction were obtained from slow evaporation of the
filtrate (Yield: 0.0152 g, 22%). The addition of pyridine to a methanol solution of 2,
after stirring for 4–6 h and allowing solvent evaporation, also yielded 3. IR (KBr,
cmꢀ1): v(CO) 2013.6 (vs), 1904.8 (w), and 1878.4 (vs). UV-Vis (nm; L molꢀ1 cmꢀ1):
ꢁmax ¼ 389.0, " ¼ 2.038 ꢃ 103. 1H-NMR (600 MHz, acetone-d6) ꢀ 8.69 (m, 2H, Ar), 8.33
(s, 1H, HC¼N), 8.03 (tt, 1H, Ar, J ¼ 7.8, 3.2, 1.6 Hz), 7.55 (m, 2H, Ar), 7.27 (m, 1H,
Ar), 7.14 (dd, 1H, Ar, J ¼ 7.8, 1.8 Hz), 6.79 (d, 1H, Ar, J ¼ 8.5 Hz) 6.50 (m, 1H, Ar),
4.23–4.04 (m, 2H) 1.62 (m, 1H), 1.80–1.57 (m, 2H), 0.94 (d, 3H, J ¼ 6.5 Hz), 0.91 (d, 3H,
J ¼ 6.5 Hz). 13C-NMR (600 MHz, acetone-d6) ꢀ 166.75 (C1), 165.41, 152.05, 139.28,
135.46, 134.64, 125.92, 122.09, 120.58, 114.53 (Ar), 68.08, 40.83, 25.71, 22.03, 21.61.
2.5. Structure analysis and refinement
Diffraction data for 2 were collected on a Bruker ApexII 4K CCD diffractometer using
˚
Mo-Kꢂ (0.71073 A) and !-scans at 100(2) K. All reflections were merged and integrated
with SAINT-PLUS [26] and corrected for Lorentz, polarization, and absorption effects
using SADABS [27]. The data for 3 were collected on an Oxford Diffraction Xcalibur 3
˚
Crysalis CCD system [28] using Mo-Kꢂ (0.71073 A) and !-scans at 100(2) K. Intensity
data were extracted and integrated using Crysalis RED [29]. Both structures were
solved by the heavy atom method and refined through full-matrix least-squares cycles
using SHELX-97 [30] as part of the WinGX [31] package with Æ(||Fo| ꢀ |Fc||)2 being
minimized. All non-H atoms were refined with anisotropic displacement parameters,
while hydrogens were constrained to parent atom sites using a riding model [aromatic
˚
˚
C–H ¼ 0.95 A {Uiso(H) ¼ 1.2 Ueq}; aliphatic C–H ¼ 0.98 A {Uiso(H) ¼ 1.5 Ueq}]. The
graphics were obtained with the Visual Crystal Structure Information System software
DIAMOND [32]; crystallographic details are summarized in table 1. Selected bond
lengths and angles of 2 and 3 are listed in tables 2 and 3. Distances and angles involving
selected hydrogen-bonding interactions of 2 are given in table 4. Figures 1–3 represent

126
A. Brink et al.
Table 1. General X-ray crystallographic data and refinement parameters for [Re(salen-3-MeBu)(CO)3(S)]
(S ¼ coordinating ligand).
Compound
2
3
Empirical formula
Formula weight
Temperature (K)
ReNO5C16H20
492.53
100(2)
0.71069
Monoclinic
C2/c
ReN2O4C20 H21
539.60
100(2)
0.71073
Monoclinic
P21/c
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimensions (A, )
ꢁ
˚
a
b
c
ꢂ
ꢃ
ꢄ
19.3075(8)
13.8078(6)
13.7882(6)
90.0
110.299(2)
90.0
3447.6(3), 8
1.898
7.072
12.9051(4)
8.6642(3)
18.6961(5)
90.0
105.279(3)
90.0
2016.57(11), 4
1.777
6.052
3
˚
Volume (A ), Z
Calculated density (g cmꢀ1
)
Absorption coefficient (mmꢀ1
F(000)
Crystal color
)
1904
Yellow
1048
Yellow
Crystal morphology
Crystal size (mm3)
ꢅ range for data collection (ꢁ)
Completeness
Cuboid
0.34 ꢃ 0.10 ꢃ 0.08
Cuboid
0.36 ꢃ 0.20 ꢃ 0.15
1.85–27.99
100.0%
2.26–28.00
99.7%
Index ranges
h ¼ ꢀ25 to 23
k ¼ ꢀ18 to 16
l ¼ ꢀ18 to 17
20559
4179 [R(int) ¼ 0.0412]
Full-matrix least-squares on F2
4179/3/221
h ¼ ꢀ17 to 15
k ¼ ꢀ11 to 11
l ¼ ꢀ14 to 24
15447
4867 [R(int) ¼ 0.0226]
Full-matrix least-squares on F2
4867/0/244
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I 4 2ꢆ(I)]
1.047
0.983
R1 ¼ 0.0379, wR2 ¼ 0.0699
R1 ¼ 0.0496, wR2 ¼ 0.0741
1.889 and ꢀ2.784
R1 ¼ 0.0208, wR2 ¼ 0.0455
R1 ¼ 0.0331, wR2 ¼ 0.0500
0.787 and ꢀ0.761
R indices (all data)ꢀ3
˚
ꢇmax and ꢇmin (e A
)
ꢁ
˚
Table 2. Selected interatomic bond lengths (A) and angles ( ) for 2.
Re(1)–O(1)
2.117(4)
2.148(7)
2.219(16)
1.900(6)
1.902(6)
1.891(8)
2.179(4)
1.152(7)
1.165(7)
O(03)–C(03)
O(04)–C(04)
C(1)–N(1A)
C(1)–N(1B)
O(1)–C(12)
1.139(8)
1.406(9)
1.346(11)
1.212(18)
1.331(7)
1.447(9)
1.402(8)
1.469(10)
1.540(30)
Re(1)–N(1A)
Re(1)–N(1B)
Re(1)–C(01)
Re(1)–C(02)
Re(1)–C(03)
Re(1)–O(04)
O(01)–C(01)
O(02)–C(02)
C(1)–C(11)
C(11)–C(12)
N(1A)–C(21A)
N(1B)–C(21B)
O(1)–Re(1)–N(1A)
O(1)–Re(1)–N(1B)
C(01)–Re(1)–C(02)
C(03)–Re(1)–C(01)
C(03)–Re(1)–C(02)
C(03)–Re(1)–O(1)
C(01)–Re(1)–O(1)
C(02)–Re(1)–O(1)
O(1)–C(12)–C(1)–N(1A)
84.0(2)
83.5(4)
86.4(3)
87.6(3)
88.3(3)
95.5(2)
93.4(2)
176.2(2)
3.4(6)
C(12)–O(1)–Re(1)
C(01)–Re(1)–N(1A)
C(01)–Re(1)–N(1B)
C(04)–O(04)–Re(1)
N(1A)–Re(1)–O(04)
C(03)–Re(1)–O(04)
O(1)–Re(1)–O(04)
127.4(3)
172.0(3)
170.3(4)
124.5(4)
76.4(2)
175.1(2)
80.78(14)
O(1)–C(12)–C(1)–N(1B)
32.1(9)

fac-[ReI(salen)(CO)3(S)]
127
ꢁ
˚
Table 3. Selected interatomic bond lengths (A) and angles ( ) for 3.
Re(1)–O(1)
Re(1)–N(1)
Re(1)–N(2)
Re(1)–C(01)
Re(1)–C(02)
Re(1)–C(03)
N(1)–C(1)
2.1075(19)
2.172(2)
2.213(3)
1.919(3)
1.901(3)
1.917(4)
1.290(4)
1.482(4)
O(01)–C(01)
O(02)–C(02)
O(03)–C(03)
N(2)–C(31)
C(11)–C(1)
O(1)–C(12)
C(11)–C(12)
C(21)–C(22)
1.152(3)
1.156(3)
1.146(4)
1.340(4)
1.433(4)
1.305(3)
1.416(4)
1.517(4)
N(1)–C(21)
O(1)–Re(1)–N(1)
O(1)–Re(1)–N(2)
N(1)–Re(1)–N(2)
C(02)–Re(1)–C(03)
C(02)–Re(1)–C(01)
C(03)–Re(1)–C(01)
O(1)–C(12)–C(1)–N(1)
86.35(8)
81.42(9)
84.27(9)
90.51(13)
88.07(13)
90.04(13)
3.01(2)
N(1)–C(1)–C(11)
C(1)–N(1)–Re(1)
128.8(3)
124.9(2)
C(02)–Re(1)–O(1)
C(03)–Re(1)–O(1)
C(01)–Re(1)–O(1)
C(21)–N(1)–Re(1)
C(1)–N(1)–C(21)–C(22)
175.50(12)
93.90(10)
91.07(10)
119.32(17)
102.3(3)
Table 4. Hydrogen bonds for 2 (A and ꢁ).
˚
D–H ꢄ ꢄ ꢄ A
d(D–H)
d(H ꢄ ꢄ ꢄ A)
d(D ꢄ ꢄ ꢄ A)
ff(DHA)
O(04)–H(04) ꢄ ꢄ ꢄ O(1)#1
C(1)–H(1) ꢄ ꢄ ꢄ O(03)#2
C(13)–H(13) ꢄ ꢄ ꢄ O(01)#3
0.84
0.95
0.95
1.85
2.51
2.48
2.578(5)
3.125(11)
3.317(8)
143.4
122.4
146.8
Symmetry transformations used to generate equivalent atoms: #1: ꢀx þ 1, y, ꢀz þ 3/2; #2: x þ 1/2,
ꢀy þ 3/2,ꢀz þ 1; #3: ꢀx þ 1,ꢀy þ 1,ꢀz þ 1.
Figure 1. Molecular diagram of 2 showing atom numbering scheme and displacement ellipsoids (50%
probability). H-atoms omitted for clarity.

128
A. Brink et al.
Figure 2. Molecular diagram showing the disorder on the 3-MeBu tail of 2.
Figure 3 Molecular diagram of 3 showing atom numbering scheme and displacement ellipsoids (50%
probability). H-atoms omitted for clarity.
the atom numbering schemes for 2 and 3, with ellipsoids drawn at 50% probability and
hydrogens omitted for clarity.
3. Results and discussion
[Re(salen-3MeBu)(CO)3(HOCH3)] (2) and [Re(salen-3MeBu)(CO)3(NC5H5)] (3) were
synthesized from methanol and single crystals of good enough quality for X-ray data
diffraction analysis were obtained. The decision to use methanol as solvent in the
synthesis of Re(I)-tricarbonyl complexes with salen ligands proved to be successful
for several reasons. First, it was possible to obtain crystallographically pure materials

fac-[ReI(salen)(CO)3(S)]
129
from methanol as opposed to the impure oils obtained from water. All our attempts
to recrystallize these complexes from the water were unsuccessful and addition of a
range of organic solvents in an attempt to induce crystallization of these products
yielded poor results. In terms of the [2 þ 1] approach, we illustrate here that methanol
is easily substituted to yield a pure product in satisfactory yield. This certainly
creates yet another exciting prospect for the development of a radiopharmaceutical
kit using the [2 þ 1] approach with these ligand systems. The low yields obtained
for 2 and 3 are based on recrystallized products. Yields before recrystallization
exceed 80%.
IR spectra of 2 and 3 show strong symmetric and asymmetric bands due to ꢈCO at
2001.4, 1876.5 and 2013.6, 1904.8, 1878.4 cmꢀ1, respectively, compared to the ReAA
carbonyl bands at 1999.4 and 1867.1 cmꢀ1. The increase in ꢈCO stretching frequency
from 2 to 3 indicates lower electron density present on Re(I) for 3 [33–36].
1
All H-NMR spectra exhibit a strong peak at approximately 8 ppm for the imine
proton. The effect of increasing electron density is seen in the stepwise upfield shift
for 1 (ꢀ 8.53), 3 (ꢀ 8.33), and 2 (ꢀ 8.22). The aromatic protons for 1 and 2 appear at
7.37–6.87 ppm and 7.15–6.42 ppm, respectively. The aromatic protons for 3 including
those of pyridine appear at 8.69–6.50 ppm. The methine, methylene, and methyl protons
1
for 1, 2, and 3 appear at 3.65–0.96, 1.68–0.93, and 4.23–0.91 ppm. H-NMR spectra
for 2 and 3 both indicate rotamers for the 3-MeBu tail. 13C-NMR data are consistent
with 1H-NMR data. The imine carbon (C1) peak appears at 165.43, 166.78, and
166.75 ppm for 1, 2, and 3. The aromatic carbons appear at 161.25 to 116.50 ppm (1),
166.24–113.92 ppm (2), and 165.41–114.53 ppm (3). Carbons assigned to the 3-MeBu
tail appear at 57.28–21.86 ppm (1), 69.14–22.64 ppm (2), and 68.08–21.61 ppm (3).
The crystal structure determinations of 2 (figure 1) and 3 (figure 3) show interesting
results. The 3-methyl-butyl substituent is severely disordered over two positions
(67–33%) in 2 (figure 2). There are no disorders observed for 3. All bond distances
and angles fall within the expected range for both these complexes. A few classical
hydrogen-bonding interactions are observed for 2 (table 4). Both structures are
stabilized by weak inter- and intra-molecular hydrogen-bonding interactions.
The octahedron around rhenium(I) is more severely disordered for 2 than for 3. In 2,
the bidentate salen bite angle at rhenium is 84.0(2)ꢁ (O1–Re–N1A) results in large
deviations from octahedral geometry, best illustrated by the C03–Re–N1A angle of
100(2)ꢁ, and the N1A–Re–O04 angle of 76.4(2)ꢁ. To our knowledge, this is the first
published crystal structure of a fac-ReðCOÞþ3 complex with a methanol in one of the
positions trans to a carbonyl. Zobi et al. [37] reported a fac-TcðCOÞþ3 complex
containing a coordinated methanol with a Tc–OH–CH3 bond angle of 128.7(3)ꢁ and a
˚
Tc–OH bond distance of 2.177(3) A. The bond distance of the rhenium to O04 (table 2),
˚
the methanol oxygen, was calculated as 2.182(4) A, slightly longer than that found for
Re–OH2 bonds [38, 39] where bond distances to the water oxygen range between
˚
2.153(3) A and 2.170(5) A.
˚
Bond distances of the bidentate N and O ligand to rhenium are 2.148(7) and
˚
2.117(4) A, respectively, and compare well with other N,O ligand-to-metal bond
˚
˚
distances which are in the range 2.162–2.186 A for Re–N and 2.099–2.184 A for Re–O
[11, 38, 40]. The bite angle formed by the salen ligand, and rhenium(I) in 3 is 86.35(8)ꢁ,
more than two degrees larger than that found for 2. As a result, less distortion of the
octahedron around rhenium in 3 is observed (table 3). Here, the C01–Re–N1 bond
angle is only 92.80(10)ꢁ. The angle formed by the nitrogen of coordinated pyridine,

130
A. Brink et al.
Figure 4. DFT optimized structure of 1. H-atoms omitted for clarity.
Figure 5. DFT optimized structures of (a) 2 and (b) 3. H-atoms omitted for clarity.
rhenium, and nitrogen of the bidentate ligand is 84.27(9)ꢁ, also closer to ideal
octahedral geometry than what was observed for the similar angle formed between the
˚
bidentate ligand, rhenium, and methanol in 2. The Re–N2 bond distance is 2.213(3) A
and compares well with similar complexes [40, 41] where bond distances between 2.203
˚
and 2.230 A were observed. The bonds formed between the N and O donors of the
˚
bidentate ligand in 3 of 2.172(2) and 2.1075(19) A, respectively, are very similar to
similar bonds in 2. These observations, together with the fact that no classical
hydrogen-bonding interactions were observed for 3, lead us to believe that the more
severe distortion of the octahedron in 2 is due to hydrogen bonding. This assumption is
further supported by the fact that the methanol is involved in a strong hydrogen bond
0
0
˚
with O1 of the Re molecule (ꢀx þ 1, y, ꢀz þ 3/2; D–A ¼ 2.578(5) A).
Calculations are increasingly being used to understand the behavior of metal ions in
coordination and organometallic chemistry [42–44]. To compare the factors which
determine the crystal structures in the solid state, theoretical structures for 1–3 (figures 4
and 5a,b) were optimized and verified to be a global minimum through frequency
calculations. Overlay diagrams of the theoretical molecules with their experimental
solid state counterparts are shown in figure 6(a) and (b). The structure of 1 (figure 4)
was calculated even though the crystal structure could not be obtained, in order to
observe any geometrical trends within these three compounds. The solid state structure
of 2 shows good correlation with the DFT optimized structure (figure 6a), with an RMS
˚
overlay value of only 0.21 A (excluding the disordered part of the 3-MeBu group).

fac-[ReI(salen)(CO)3(S)]
131
˚
Figure 6. (a) Overlay of the DFT optimized and crystal structures of 2 (RMS value ¼ 0.21 A). (b) Overlay of
˚
the DFT optimized and crystal structures of 3 (RMS value ¼ 1.61 A). Overlay fits exclude the 3-MeBu group
and all hydrogens. The blue structures denote the DFT optimized complexes, while the black structures
indicate the solid state structures.
Table 5. Comparison of selectedꢁ ligand geometrical parameters of the crystal structures of 1–3 with their
˚
DFT optimized counterparts (A, ).
a
1DFT
2Crystal
2DFT
3Crystal
3DFT
N(1)–C(1)
N(1)–C(21)
N(1)–O(1)
C(1)–C(11)
O(1)–C(12)
1.281
1.455
2.6321
1.456
1.341
1.346(11)
1.469(10)
2.854(10)
1.447(9)
1.331(7)
1.316
1.499
2.874
1.448
1.347
1.290(4)
1.482(4)
2.929(3)
1.433(4)
1.305(3)
1.318
1.498
2.918
1.444
1.335
C(11)–C(1)–N(1)
O(1)–C(12)–C(11)
C(1)–N(1)–C(21)
N(1)–C(21)–C(22)
O(1)–C(12)–C(1)–N(1)
122.8
128.0(7)
128.9
128.8(3)
125.2(3)
115.8(2)
112.2(2)
3.1(2)
129.4
121.8
119.5
110.9
122.7(5)
115.7(7)
112.2(7)
3.4(6)
122.2
115.4
112.2
8.2
123.3
115.1
112.4
4.5
0.11
aIndicates bond distances and angles to the principal fraction of disorder of 2.
Table 6. Comparison of selected coordination polyhedral geometrical parameters of the
crystal structures of 2 and 3 with their DFT optimized counterparts (A, ꢁ).
˚
a
2Crystal
2DFT
3Crystal
3DFT
Re(1)–O(1)
Re(1)–N(1)
2.117(4)
2.148(7)
1.900(6)
1.902(6)
1.891(8)
2.179(4)
1.139(8)
1.152(7)
1.406(9)
2.118
2.185
1.930
1.907
1.901
2.243
1.189
1.188
1.470
2.108(2)
2.172(2)
1.919(3)
1.901(3)
1.917(4)
2.213(3)
1.146(4)
1.152(3)
–
2.120
2.188
1.932
1.905
1.922
2.245
1.187
1.186
–
Re(1)–C(01)
Re(1)–C(02)
Re(1)–C(03)
Re(1)–O(04)/N(2)
C(03)–O(03)
C(01)–O(01)
O(04)–C(04)
O(1)–Re(1)–N(1)
84.0(2)
124.5(4)
76.4(2)
86.4(3)
122.2(5)
3.4(6)
83.8
127.4
83.9
89.9
125.6
8.2
86.35(8)
–
84.27(9)
88.07(13)
124.9(2)
3.1(2)
85.3
–
86.1
89.9
125.5
4.5
Re(1)–O(04)–C(04)
N(1)–Re(1)–O(04)/N(2)
C(01)–Re(1)–C(02)
Re(1)–N(1)–C(1)
O(1)–C(12)–C(1)–N(1)
aIndicates bond distances and angles to the principal fraction of disorder of 2.

132
A. Brink et al.
The DFT optimized structure of 3, on the other hand, has a much poorer correlation
˚
with its crystallographic counterpart (RMS ¼ 1.61 A; figure 6b). The pyridine ring
rotation and the salen backbone of the crystal structure show significant deviation from
the DFT optimized structure. Angles and distances are compared in tables 5 and 6, and
quite good agreement exists. Even though the conformations in the crystal and DFT
optimized structures are similar, some deviations between the corresponding DFT/solid
state structures are clear. These differences between the crystallographic data and the
corresponding DFT optimized structures illustrate the net impact of packing effects and
intermolecular bonds on the geometrical parameters of the solid state structures.
4. Conclusions
Rhenium salen tricarbonyl complexes were synthesized and crystals suitable for X-ray
diffraction were obtained. The coordination of methanol to the rhenium metal center
was established as the first example of a rhenium complex of this type reported and
discussed. The spectroscopic data indicated the effects of various neutral monodentate
ligands have on the rhenium metal center. A theoretical study on the compounds was
presented and compared with the corresponding solid state structures.
Supplementary material
Crystallographic data for the structures are available free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk or Email: data_
request@ccdc.cam.ac.uk as CCDC 801586 anf 801587.
Acknowledgments
Financial assistance from the University of the Free State is gratefully acknowledged.
We thank Prof. Ola Wendt from the University of Lund, Sweden for the use of their
Oxford X-ray diffractometer. We also express our gratitude toward SASOL, the South
African National Research Foundation (SA-NRF/THRIP), PETLabs Pharmaceuticals,
the University of the Free State Strategic Academic Initiative (Advanced Biomolecular
Cluster), and the Swedish International Development Cooperation Agency (SIDA) for
the financial support for this project. Part of this material is based on the work
supported by the SA-NRF/THRIP under grant number GUN 2068915. Opinions,
findings, conclusions, or recommendations expressed in this material are those of the
authors and do not necessarily reflect the views of the SA-NRF.
References
[1] R. Alberto, R. Schibli, A.P. Schubiger, U. Abram, T.A. Kaden. Polyhedron, 15, 1079 (1996).
[2] U. Abram, S. Abram, R. Alberto, R. Schibli. Inorg. Chim. Acta, 248, 193 (1996).
[3] R. Alberto, W.A. Herrmann, P. Kiprof, F. Baumgartner. Inorg. Chem., 31, 895 (1992).
¨
[4] H.H.K. Castro, C.E. Hissink, H.J.H. Teuben, W. Vaalburg, K. Panek. Recl. Trav. Chim. Pays-Bas, 111,
105 (1992).

fac-[ReI(salen)(CO)3(S)]
133
[5] R. Alberto, R. Schibli, R. Waibel, U. Abram, A.P. Schubiger. Coord. Chem. Rev., 192, 901 (1999).
[6] A. Egli, R. Alberto, R. Schibli, A.O. Schaffland, U. Abram, S. Abram, T.A. Kaden, P.A. Schubiger.
J. Labelled Compounds Radiopharm., 37, 443 (1997).
[7] R. Alberto, R. Schibli, U. Abram, A. Egli, F.F. Knapp, P.A. Schubiger. Radiochim. Acta, 79, 99 (1997).
[8] R. Schibli, R. Alberto, U. Abram, S. Abram, A. Egli, P.A. Schubiger, T.A. Kaden. Inorg. Chem., 37,
3509 (1998).
[9] R. Alberto, A. Egli, R. Schibli, U. Abram, T.A. Kaden, A.O. Schaffland, R. Schwarzbath,
P.A. Schubiger. Q. J. Nucl. Med., 42, 9 (1998).
[10] R. Alberto, R. Schibli, A. Egli, P.A. Schubiger, W.A. Herrmann, G. Artus, U. Abram, T.A. Kaden.
J. Organomet. Chem., 493, 119 (1995).
[11] S. Mundwiler, M. Kundig, K. Ortner, R. Alberto. Dalton Trans., 1320 (2004).
¨
[12] R. Alberto, A. Egli, U. Abram, K. Hegetschweiler, V. Gramlich, P.A. Schubiger. J. Chem. Soc., Dalton
Trans., 2815 (1994).
[13] D.H. Gibson, B.A. Sleadd, X. Yin. Organometallics, 17, 2689 (1998).
[14] R. Czerwieniec, A. Kapturkiewicz, R. Anulewicz-Ostrowska, J. Nowacki. J. Chem. Soc., Dalton Trans.,
2756 (2001).
[15] G.J.J. Steyn, A. Roodt, I.A. Poletaeva, Y.S. Varshavsky. J. Organomet. Chem., 536/7, 197 (1997).
[16] R. Hernandez-Molina, A. Merderos. In Comprehensive Coordination Chemistry II, J.A. McCleverty,
´
T.J. Meyer (Eds.), Vol. 1, pp. 411–446, Elsevier, Oxford (2003).
[17] T. Sasamori, T. Matsumoto, N. Takeda, N. Tokitoh. Organometallics, 26, 3621 (2007).
´
[18] E. Tozzo, S. Romera, M.P. dos Santos, M. Muraro, R.H. de A. Santos, L.M. Lia
˜
o, L. Vizotto,
E.R. Dockal. J. Mol. Struct., 876, 110 (2008).
[19] R. Alberto, R. Schibli, P.A. Schubiger. Polyhedron, 15, 1079 (1996).
[20] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery
Jr, T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci,
M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.
Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma,
G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain,
O. Farkas, D.K. Malick, A.D. Rabuck, F. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G.
Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,
R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe,
P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople. GAUSSIAN-03, Revision
C.01, Gaussian, Inc., Wallingford, CT (2004).
[21] A.D. Becke. J. Chem. Phys., 98, 5648 (2003).
[22] P.C. Hariharan, J.A. Pople. Theor. Chim. Acta, 28, 213 (1973).
[23] M.M. Francl, W.J. Petro, W.J. Hehre, J.S. Binkley, M.S. Gordon, D.J. DeFree, J.A. Pople. J. Chem.
Phys., 77, 3654 (1982).
[24] HyperchemTM Release 7.52, Windows Molecular Modeling System, Hypercube, Inc. (2002).
[25] A. Brink, A. Roodt, H.G. Visser. Acta Cryst., E65, o3175 (2009).
[26] Bruker SAINT-PLUS (including XPREP). Version 7.12, Bruker AXS Inc., Madison, WI (2004).
[27] Bruker SADABS. Version 2004/1. Bruker AXS Inc., Madison, WI (1998).
[28] Crysalis CCD. Oxford Diffraction Ltd., Abingdon, Oxfordshire, UK (2005).
[29] Crysalis RED. Oxford Diffraction Ltd., Abingdon, Oxfordshire, UK (2005).
[30] G.M. Sheldrick. Acta Cryst., A64, 112 (2008).
[31] L.J. Farrugia. J. Appl. Cryst., 32, 837 (1999).
[32] K. Brandenburg, H. Putz. DIAMOND. Release 3.0e. Crystal Impact GbR, Postfach 1251, D-53002,
Bonn, Germany (2004).
[33] G.J.J. Steyn, A. Roodt, J.G. Leipoldt. Inorg. Chem., 31, 3477 (1992).
[34] S. Otto, A. Roodt. Inorg. Chim. Acta, 357, 1 (2004).
[35] A. Roodt, S. Otto, G. Steyl. Coord. Chem. Rev., 245, 125 (2003).
[36] A. Brink, H.G. Visser, A. Roodt, G. Steyl. Dalton Trans., 1246 (2010).
[37] F. Zobi, B. Spingler, T. Fox, R. Alberto. Inorg. Chem., 42, 2818 (2003).
[38] M. Schutte, H.G. Visser. Acta Cryst., E64, m1226 (2008).
[39] M. Schutte, H.G. Visser, A. Roodt. Acta Cryst., E64, m1610 (2008).
[40] R. Czerwieniec, A. Kapturkiewicz, R. Anulewicz-Ostrowska, J. Nowacki. J. Chem. Soc., Dalton Trans.,
2756 (2001).
[41] R. Czerwieniec, A. Kapturkiewicz, R. Anulewicz-Ostrowska, J. Nowacki. J. Chem Soc., Dalton Trans.,
3434 (2002).
[42] R.D. Adams, B. Captain, C.B. Hollandsworth, M. Johansson, J.L. Smith Jr. Organometallics, 25, 3848
(2006).
[43] K.P. Gable, A. AbuBaker, K. Zientara, A.M. Wainwright. Organometallics, 18, 173 (1999).
[44] D.V. Partyka, N. Deligonul, M.P. Washington, T.G. Gray. Organometallics, 28, 5837 (2009).