Copper(I) pseudohalide complexes with 4,6-dimethylpyrimidine-2(1H)-thione and triphenylphosphane as ligands. The X-ray crystal structures of [Cu(N3)(dmpymtH)(PPh3)2] and [Cu(NCS)(dmpymtH)(PPh3)2]

Article abstract of DOI:10.1016/S0277-5387(01)00701-X

The preparation of mixed-ligand copper (I) coordination compounds containing pseudohalides (azide and thiocyanate), 4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH), and triphenylphosphane is described. The crystalline and molecular structure of [Cu(N₃)(dmpymth)(PPh₃)₂] (2) and [Cu(NCS)(dmpymtH)(PPh₃)]₂ (3) have been determined by X-ray diffraction methods. The copper atom has a tetra-coordinate CuNP₂S chromophore with distorted tetrahedral coordination in both complexes. Vibrational and ¹H, ¹³C, ³¹P NMR spectra of the complexes are discussed and related to the structures

Full text of DOI:10.1016/S0277-5387(01)00701-X

Polyhedron 20 (2001) 849–854
www.elsevier.nl/locate/poly
Copper(I) pseudohalide complexes with
4,6-dimethylpyrimidine-2(1H)-thione
and triphenylphosphane as ligands.
The X-ray crystal structures of [Cu(N3)(dmpymtH)(PPh3)2]
and [Cu(NCS)(dmpymtH)(PPh3)2]ꢀ
Sebastia˜o S. Lemos a,*, Maryene A. Camargo a, Zaira Z. Cardoso a,
Victor M. Deflon a, F. Holger Fo¨rsterling b, Adelheid Hagenbach c
a Instituto de Qu´ımica, Uni6ersidade de Bras´ılia, Bras´ılia DF-70919-970, Brazil
b Department of Chemistry, Uni6ersity of Wisconsin–Milwaukee, Milwaukee, WI 53211, USA
c Institut fu¨r Anorganische Chemie der Uni6ersita¨t Tu¨bingen, Tu¨bingen D-72076, Germany
Received 25 April 2000; accepted 5 September 2000
Abstract
The preparation of mixed-ligand copper(I) coordination compounds containing pseudohalides (azide and thiocyanate),
4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH), and triphenylphosphane is described. The crystalline and molecular structure of
[Cu(N3)(dmpymtH)(PPh3)2] (2) and [Cu(NCS)(dmpymtH)(PPh3)2] (3) have been determined by X-ray diffraction methods. The
copper atom has a tetra-coordinate CuNP2S chromophore with distorted tetrahedral coordination in both complexes. Vibrational
and 1H, 13C, 31P NMR spectra of the complexes are discussed and related to the structures. © 2001 Elsevier Science Ltd. All rights
reserved.
Keywords: Synthesis; Copper(I) complexes; Pseudohalides; Crystal structures; Dimethylpyrimidinethione; NMR spectroscopy
1. Introduction
[21,22]. The copper(I) clusters of the type [Cu(L)]n
(n=4; L=1-methyl-1,3-imidazoline-2-thiolato [23],
n=6; L=4,6-dimethylpyrimidine-2-thiolato [24]) have
been structurally characterised. Mixed-ligand copper
complexes of the general formula [CuX(PPh3)nL] (X=
halide; L=heterocyclic thione) have recently been re-
ported [6,7]. In this paper we report the synthesis and
structural characterisation of neutral mononuclear cop-
per(I) pseudohalide (N3− and NCS−) complexes con-
Heterocyclic thiones have attracted considerable at-
tention because of their relevance in biological systems.
Sulphur-containing pyrimidine nucleotides have been
isolated from hydrolysates of Escherichia coli transfer
RNA [1]. Recently, the versatility of their coordination
forms has been demonstrated in a number of com-
plexes, yielding a variety of coordination compounds
with great structural diversity: neutral S-monodentate
[2–7]; anion S-monodentate [8,9]; N,S-chelate [8,10–
15]; neutral m2-S-bridge [16]; anion m2-S- [10,17]; m2-
(S,N)- [18–20]; m3-(S,N)- [14,21,22]; m4-(S,N)-bridge
taining
4,6-dimethylpyrimidine-2(1H)-thione
and
triphenylphosphane as ligands.
2. Experimental
ꢀ This article was presented at the Second Contemporary Inorganic
Chemistry Conference (CIC-II) held at Texas A&M University, Col-
lege Station, TX, USA, on March 12–15, 2000.
* Corresponding author. Tel.: +55-61-307 2171; fax:+55-61-273
4149.
2.1. Reagents and apparatus
All reagents and solvents were of reagent grade and
were used without further purification. The compound
4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH) [25]
E-mail address: sslemos@unb.br (S.S. Lemos).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00701-X

850
S.S. Lemos et al. / Polyhedron 20 (2001) 849–854
and the complex [CuCl(PPh3)3] [26] were prepared ac-
cording to reported methods. Microanalyses (C, H, and
N) were performed in a Carlo Erba 1104 elemental
analyser. Copper was analysed by the standard com-
plexometric method [27]. IR spectra of KBr pellets were
recorded on a BOMEM Hartmann & Braun MB-FT in
the 4000–400 cm−1 region. NMR spectra of the CDCl3
solution were recorded using a Bruker AC250, DPX300
or DRX500 spectrometer. All low temperature experi-
ments were carried out with the 500 MHz instrument
using a BSV300 low temperature unit. Tetramethylsi-
lane (Me4Si) was used as chemical shift reference for 1H
and 13C and 85% H3PO4 (ext.) for 31P.
1536w, 1479m, 1434s, 1384m, 1320m, 1256m, 1237s,
1196m, 1092m, 1026w, 996w, 986w, 941w, 890w, 825w,
749s, 694s, 524m, 516s, 501m, 473w, 461m and 440w
cm−1
.
2.2.3. [Cu(NCS)(dmpymtH)(PPh3)2] (3)
To an excess of melted PPh3 (1.31g, 5 mmol),
(dmpymtH) (140.2 mg, 1 mmol) was added and mag-
netically stirred. The compound CuSCN (121.6 mg, 1
mmol) was added when the temperature reached 110°C
and it was maintained for 1 h with occasional stirring.
After cooling, dichloromethane (12 ml) was added and
the suspension filtered under reduced pressure. Hexane
(10 ml) was added and the solution was cooled to
−15°C. After 2 weeks, the yellow crystals were col-
lected by filtration, washed with hexane (2×5 ml) and
dried in a vacuum pump. Yield 80% (620 mg). m.p.\
165°C (dec.). Anal. Found: C, 65.41; H, 5.39; Cu, 7.70;
N, 4.67. Calc. for C43H38CuN3S2P2: C, 65.67; H, 5.34;
2.2. Preparation of copper(I) complexes
2.2.1. [Cu(N3)(PPh3)3] (1)
To a dichloromethane solution (50 ml) containing
[CuCl(PPh3)3] (3.77 g, 4.25 mmol) and triphenylphos-
phane PPh3 (1.11g, 4.25 mmol), a methanolic solution
(18 ml) containing sodium azide NaN3 (306 mg, 4.71
mmol) was added. The resultant suspension was mag-
netically stirred for 6 h. The suspension was filtered
under reduced pressure and hexane (15 ml) was added
to the filtrate. The solution was kept at −15°C and the
crystals were collected by filtration after a week and
washed thoroughly with hexane. Yield 85% (3.3 g).
m.p. \175°C (dec.). Anal. Found: C, 72.91; H, 4.75;
Cu, 7.06; N, 4.87. Calc. for C54H45CuN3P3: C, 72.68; H,
4.71; Cu, 7.12; N, 5.08%. NMR (298 K): 1H (250 MHz)
l 7.63–7.06 ppm (m, Ph); 13C{1H} (62.9 MHz) l 134.5,
134.1, 129.7, 128.8 ppm; 31P{1H} (101.2 MHz) l −1.87
ppm (s). IR 3050m, 2037 (wassim N3)vs, 1963w, 1584w,
1479m, 1434s, 1308w, 1277w, 1266w, 1183w, 1157w,
1092m, 1026w, 998w, 745s, 726m, 695vs, 517s, 504m,
and 441w cm−1 (IR data: vs, very strong; s, strong; m,
medium; w, weak).
1
Cu, 8.08; N, 4.87%. NMR (298 K): H (300 MHz) l
12.87 (br, NH, 1H), 7.69–7.12 (m, C6H5, 30H), 6.33 (s,
C3–H, 1H) 2.32 (s, CH3, 6H) ppm; 13C{1H} (75.4
MHz) l 179.2, 140.2, 133.7, 129.3, 128.3, 110.8, and
22.5 ppm 31P{1H} (122.5 MHz) l −1.68 ppm (s). IR:
3053m, 2042 (w NC)vs, 1617s, 1562s, 1479m, 1434s,
1226s, 1187m, 1093m, 1026w, 997w, 979w, 949w, 890w,
832w, 798w, 745s, 695s, 513s, 505m, 494m, 462w and
442w cm−1
.
3. Results and discussion
3.1. Synthesis of copper(I) complexes
Complex 1 was obtained in high yield (85%) in the
presence of PPh3, otherwise a mixture would result
according to the following:
4[CuCl(PPh3)3]+4NaN3−ꢀꢀ2PꢀPꢀhꢁ [{Cu(N3)(PPh3)2}2]
68%
3
2.2.2. [Cu(N3)(dmpymtH)(PPh3)2] (2)
+2[Cu(N3)(PPh3)3]+4NaCl
To a suspension of [Cu(N3)(PPh3)3] (892.4 mg, 1
mmol) in dichloromethane (20 ml), dmpymtH (140.2
mg, 1 mmol) was added slowly. The yellow suspension
was magnetically stirred for 1 h and then filtered under
reduced pressure. Hexane (15 ml) was added to the
filtrate and it was kept at −15°C in a stopped flask.
After 2 weeks, the yellow crystals were recovered by
filtration, washed thoroughly with hexane and dried
using a vacuum pump. Yield 330 mg (43%), m.p.\130
°C (dec.). Anal. Found: C, 64.97; H, 4.86; Cu, 8.17; N,
9.09. Calc. for C42H38CuN5P2S: C, 65.48; H, 4.97; Cu,
8.25; N, 9.09%. NMR (298 K): 1H (300 MHz) l
7.42–7.20 (m, C6H5, 30H), 6.23 (br, C3–H, 1H) 2.17
(br, CH3, 6H) ppm; 13C{1H} (75.4 MHz) l 164.07,
134.7, 133.7, 129.2, 128.3 and 22.4 ppm; 31P{1H} (121.5
MHz) l 0.17 (s) and −2.52 (s) ppm. IR: 3328w,
3053m, 2583–2547w, 2034 (wassim N3)vs, 1621s, 1577vs,
32%
The analogue complex [Cu(SCN)(PPh3)3] could not be
obtained as described above; instead, only [{Cu-
(PPh3)2}2(m2-SCN)2] [28] was isolated.
The synthesis of 3 in melted PPh3 proved to be an
efficient one-pot preparation according to the equation
below:
CuSCN+dmpymtH+2PPh3
“[Cu(NCS)(dmpymtH)(PPh3)2]
3.2. Crystal structures of [Cu(N3)(dmpymtH)(PPh3)2]
(2) and [Cu(NCS)(dmpymtH)(PPh3)2] (3)
Suitable crystals were obtained from dichloro-
methane/hexane solutions of 2 and 3 at −15°C, as
described above. The molecules with labels for the

S.S. Lemos et al. / Polyhedron 20 (2001) 849–854
851
Fig. 2. ORTEP plot [37] of two neighbouring molecules in the crystal
structure of [Cu(NCS)(dmpymtH)(PPh3)2] (3). Except H(2), all other
hydrogen atoms are not shown for reasons of clarity. The hydrogen
bond N(2)–H(2)···N(3) is denoted by a dashed line.
Fig. 1. ORTEP plot [37] of [Cu(N3)(dmpymtH)(PPh3)2] (2) with the
atom numbering. Thermal ellipsoids are scaled at 50%. Except H(2),
all other hydrogen atoms are not shown for reasons of clarity. The
hydrogen bond N(2)–H(2)···N(3) is denoted by a dashed line.
Table 1
Crystal data and structure refinement for 2 and 3
2
3
Empirical formula
Crystal system
Space group
C
42H38CuN5P2S
C43H38CuN3P2S2
monoclinic
P21/c
monoclinic
P21/c
Temperature (°C)
Unit cell parameters
−60
−60
,
a (A)
9.8291(6)
15.1388(17)
12.9769(5)
20.1351(7)
94.467(5)
3943.6(5)
,
b (A)
17.7041(11)
22.3169(18)
101.416(8)
3806.7(5)
4
,
c (A)
i (°)
V (A )
3
,
Z
4
Diffractometer
Wavelength, u (A)
Crystal size (mm)
Method/q range (°)
Completeness to 2q (%)
Index ranges (h, k, l)
Collected reflections
Enraf–Nonius CAD4
1.54184, Cu Ka
0.20×0.15×0.10
ꢀ-scans/5–65
94.1
−1“10, 0“20, −26“26
7572
6333/0.0432
4395
Enraf–Nonius CAD4
1.54184, Cu Ka
0.65×0.25×0.20
ꢀ–scans/5–65
92.1
−1“17, 0“15, −20“23
7246
6492/0.0276
5965
,
a
Unique reflections/Rint
Observed data [I\2|(I)]
Absorption correction
Min./max. transmission
Extinction coefficient
Structure refinement
Hydrogen treatment
Refined parameters
Weighting scheme
„-scans [31]
0.73600/0.94223
not refined
„-scans [31]
0.88588/0.95646
0.00111(7)
full-matrix least-squares on F2
Fourier-map
612
full-matrix least-squares on F2
Fourier-map
613
w=1/[|2(F2o)+(0.0662P)2+2.926P],
w=1/[|2(F2o)+(0.0528P)2+2.0032P],
P=(maxF2o+2F2c)/3
P=(maxF2o+2F2c)/3
Structure factors [I\2|(I)] b
Goodness-of-fit, S
R1=0.0481, wR2=0.1172
1.020
R1=0.0340, wR2=0.0932
1.062
c
Programs used
HELENA, PLATON [31]; SHELXS-97 [32];
SHELXL-97 [33]
HELENA, PLATON [31]; SHELXS-97 [32];
SHELXL-97 [33]
a Rintꢀ(ꢀꢁFo2−Fo2(mean)ꢁ)/(ꢀ F2o).
b R1ꢀ(ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ)/(ꢀꢁFoꢁ), wR2ꢀꢂ(ꢀ w(F2o−Fc2)2/(ꢀ w(F2o)2)
c GooF: Sꢀꢂ(ꢀ w(Fo2−F2c)2/(n−p), n=no. of reflections, p=no. of parameters

852
S.S. Lemos et al. / Polyhedron 20 (2001) 849–854
main atoms are shown in Figs. 1 and 2, respectively.
Parameters and conditions to the structure determina-
tion are given in Table 1. In both complexes a distorted
tetrahedral coordination for the central copper atom is
attained by two phosphorus atoms from triphenylphos-
other hand, the Cu–S(1) distances in both complexes
,
,
are nearly identical (2.372 A in 2 and 2.371 A in 3) and
are in accord with the Cu–S distances of 2.374 and
,
2.352 A found in [CuCl(pySH)(PPh3)2] (pySH pyridine-
2-thione) [2] and [CuBr(pymtH)(PPh3)2] (pymtH pyrim-
idine-2-thione) [6], respectively.
phane,
a
sulphur atom from the monodentate
As in 2, also in 3 the shortest C–N and C–C
distances in the coordinated dmpymtH are C(2)–N(1)
and C(3)–C(4), so that they can best be represented by
the following resonance structure.
dmpymtH and a nitrogen atom from the pseudohalide,
azide in 2 and isothiocyanate in 3.
The main bond distances and angles are given in
Table 2. Most values are similar in both complexes and
can be considered normal. Major differences are ob-
served for the angles P–Cu–S, that show a greater
distortion from the ideal tetrahedral values in 2 than in
3 (discussed below) as well as for the Cu–N distances.
,
The distance Cu–N(3)=2.100 A in 2 is appreciably
,
longer than the mean value of 2.012 A for copper
Intramolecular hydrogen bonds are observed be-
tween the atoms N(2) and N(3) in the complexes 2 and
,
s-azido complexes [29], where the distance of 2.046 A
in 3 is in good agreement with the mean value of 2.045
,
3 with N(2)···N(3) distances of 2.786 and 2.932 A and
,
A for copper isothiocyanato complexes [29]. On the
N(2)–H(2)···N(3) angles of 175 and 168°, respectively.
The stronger hydrogen bond in 2 than in 3 is in
agreement with the NMR studies.
Table 2
a
,
Selected bond lengths (A) and bond angles (°) for 2 and 3
Due to the hydrogen bond between N(2) and N(3),
the atoms N(3), Cu, S(1), C(1) and N(2) are coplanar in
3 (Rms deviation 0.0753 A) with a dihedral angle of
2
3
,
2,4(1)° to the dmpymtH ring. The same is not observed
in 2, which shows greater distortion from the tetrahe-
dral coordination as a result of an intramolecular p-
type stacking interaction between the dmpymtH ring
and the phenyl ring bound through the carbon atom
C(221) to the phosphorus atom P(2) (Fig. 1). The angle
between both involved planar rings is 7.0(3)° and the
closest interatomic distance is N(2)···C(222)=3.367(6)
Bond lengths
Cu–P(1)
Cu–P(2)
Cu–S(1)
Cu–N(3)
2.2658(11)
2.2799(11)
2.3723(12)
2.100(4)
2.2968(6)
2.3112(6)
2.3709(6)
2.0457(18)
N(3)–N(4)
N(3)–C(33)
N(4)–N(5)
C(33)–S(33)
S(1)–C(1)
C(1)–N(1)
C(1)–N(2)
C(2)–N(1)
C(4)–N(2)
C(2)–C(3)
C(3)–C(4)
N(2)–H(2)
H(2)···N(3)
N(2)···N(3)
1.192(5)
1.162(3)
1.176(6)
1.620(2)
1.695(2)
1.353(3)
1.363(3)
1.334(3)
1.357(3)
1.390(4)
1.354(4)
0.86(3)
1.701(4)
1.347(5)
1.358(5)
1.331(5)
1.355(5)
1.387(6)
1.359(6)
0.92(5)
,
A.
The greater distortion due to the intramolecular p
interaction in 2 in comparison with 3 can be seen in the
decrease of the angle P(2)–Cu–S(1) (99.86° in 2 and
103.57° in 3) and in the resulting increase of the angle
P(1)–Cu–S(1) (114.90° in 2 and 109.36° in 3). Inter-
molecular p-type stacking interactions are also observed
between the dmpymtH rings from two neighbour com-
plex molecules. In this case the interaction occurs in
both complexes 2 and 3. Fig. 2 shows the interaction
between two molecules of 3. The closest interatomic
distances between the two parallel dmpymtH rings are
1.87(5)
2.786(5)
2.08(3)
2.932(3)
Bond angles
N(3)–Cu–P(1)
N(3)–Cu–P(2)
P(1)–Cu–P(2)
N(3)–Cu–S(1)
P(1)–Cu–S(1)
P(2)–Cu–S(1)
N(1)–C(1)–S(1)
N(2)–C(1)–S(1)
Cu–S(1)–C(1)
Cu–N(3)–N(4)
Cu–N(3)–C(33)
N(3)–N(4)–N(5)
N(3)–C(33)–S(33)
N(2)–H(2)···N(3)
103.64(10)
107.89(12)
124.96(4)
103.82(11)
114.90(4)
99.86(4)
120.9(3)
119.9(3)
107.46(15)
129.5(3)
107.34(5)
105.08(6)
122.61(2)
108.16(5)
109.36(2)
103.57(2)
120.68(16)
120.18(16)
112.20(7)
,
N(1)···C(4)%=3.319(5)
A in 2 and C(1)···C(3)%=
,
3.522(3) A in 3. While 3 shows a p–p-type of interac-
tion, in 2 a p–p–p–p-type of stacking interaction is
assumed. Such a stacking interaction has been reported
for similar systems, for example, in crystal structures of
dicopper(I) complexes of 2,2%-bipyrimidine and diphos-
phane ligands [30].
163.77(17)
177.3(5)
175(5)
178.86(19)
168(3)
3.3. Infrared spectra
a Figures in parentheses indicate the estimated standard deviation
in the least significant digit.
Complex 1 shows a strong absorption band at 2037
cm−1 due to w(N−3 ) while the reported dinuclear com-

S.S. Lemos et al. / Polyhedron 20 (2001) 849–854
853
observed. Furthermore, two distinct signals are ob-
served for C-2 and C-4 at 208 K, whereas rapid ex-
change between the two is observed at higher
temperatures. On the other hand, minimal change with
temperature is observed for H-3, C-3 and C-1, suggest-
ing fast tautomerization according to Scheme 1.
The tautomerization may involve a zwitterionic form
of the type b (below) as has been demonstrated in
pyridinethione complexes [2]. This interpretation is fur-
ther supported by the fact that the NH proton signal,
which exhibits a sharp singlet at 208 K, broadens
beyond recognition upon raising the temperature.
In the case of complex 2, however, the situation
appears to be more complex. Two sets of signals (4:1)
are observed for all protons and carbons of the
dmpymtH ligand at 208 K (Fig. 3). This observation
can be interpreted as a mixture of two respective iso-
mers, 2a and 2c, as depicted below:
Scheme 1.
plex [{Cu(PPh3)2}2(m2-N3)2] shows two bands at 2053
and 2002 cm−1 [34,35]. While 2 presents a strong band
at 2034 cm−1, w(N3−); 3 shows a strong band at 2042
cm−1, w(NC). The compound 4,6-dimethylpyrimidine-
2(1H)-thione presents a rather complicated spectrum in
the range 3200–2500 cm−1 where C–H and N–H
stretching vibrations occur. The bands in the range
2900–2500 cm−1 may be combination bands or may
correspond to strongly hydrogen bonded NH groups as
has been observed for 2-mercaptopyrimidine [36].
Those bands, although weaker, are still present on both
2 and 3.
3.4. NMR spectroscopy
The 1H and 13C NMR spectra of 3 in CDCl3 solution
at low temperature (208 K) are consistent with a static
structure as found in the crystal structure, exhibiting
two carbon and proton signals for the non-equivalent
methyl groups of the dmpymtH ligand. Upon raising
the temperature to 253 K these signals coalesce to one,
and at room temperature only one set of signals is
Fig. 3. Variable-temperature 1H NMR spectra of 2 showing the methyl and H-3 regions of the spectrum. Two processes are taking place. As the
temperature is lowered, an intermolecular process is frozen out at around 273 K, resulting in a mixture of 2a and 2c with a ratio around 4:1.
Further lowering of the temperature also slows down the amine proton tautomerization, resulting in the split of the methyl signal. Similar behavior
is observed for the corresponding 13C signals. In the case of complex 3, only isomer a is present and just the tautomerization process is observed.

854
S.S. Lemos et al. / Polyhedron 20 (2001) 849–854
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4. Supplementary material
Crystallographic data (excluding structure factors)
for the structural analysis have been deposited with the
Cambridge Crystallographic Data Centre, CCDC nos.
142294 for 2 and 142295 for 3. Copies of this informa-
tion may be obtained from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1233-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Variable-temperature spectra referring to complex 3
were included to aid the reviewer’s analysis.
Acknowledgements
The authors would like to thank Professor Dr
Joachim Stra¨hle for the use of laboratory facilities at
the Institut fu¨r Anorganische Chemie der Universita¨t
Tu¨bingen, Germany. This work was supported in part
by a grant from CNPq 42.0114/97-1 (SSL) for copper
complexes studies.
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