Co-ordination behaviour of N-carboxymethylpseudoephedrine: Crystal structures of seven-co-ordinated cadmium(II) and fac-RS-octahedral copper(II) complexes

Article abstract of DOI:10.1039/a704485b

Co-ordination compounds of N-[2-hydroxy-1(R)-methyl-2(R)-phenylethyl]-N-methylglycine (N-carboxymethylpseudoephedrine, Hcpse) with copper(II), cobalt(II) and cadmium(II) have been prepared and characterised. Crystal structures of copper and cadmium comple

Full text of DOI:10.1039/a704485b

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Co-ordination behaviour of N-carboxymethylpseudoephedrine:
crystal structures of seven-co-ordinated cadmium(II) and fac-RS-
octahedral copper(II) complexes
Horacio C. López-Sandoval,a Noráh Barba-Behrens,*,†,a Sylvain Bernès,a
Norberto Farfán-García b and Herbert Höpflb
a
División de Estudios de Posgrado, Facultad de Química,
Universidad Nacional Autónoma de México, C.U., 04510, México, D.F., México
b Departamento de Química, Centro de Investigación y Estudios Avanzados del IPN,
Apdo. Postal 14-740, 07000 México, D.F., México
Co-ordination compounds of N-[2-hydroxy-1(R)-methyl-2(R)-phenylethyl]-N-methylglycine (N-carboxymethyl-
pseudoephedrine, Hcpse) with copper(), cobalt() and cadmium() have been prepared and characterised. Crystal
structures of copper and cadmium complexes were obtained. In the compound [Cu(cpse)2]ؒH2O, two cpse are
co-ordinated in a tridentate mode giving place to a fac-RS-octahedral geometry. The monomeric compound
[Cd(cpse)2(H2O)] has an uncommon seven-co-ordinate geometry with one cpse bonded in a similar arrangement
to that of the copper() compound, with an oxygen from the carboxylate group in an apical position. The second
cpse molecule is co-ordinated with all three atoms in the equatorial plane, the remaining axial position of the
distorted pentagonal bipyramid being occupied by a water molecule. As for the latter complex, the metal centre of
[Cd(cpse)Cl(H2O)]ؒH2Oؒdmso (dmso = dimethyl sulfoxide) presents a distorted pentagonal-bipyramidal geometry
where the apical positions are occupied by a water molecule and a chloride ion. The tridentate cpse ligand lies in
the equatorial plane and the co-ordination sphere is completed by a chelating carboxylic group from another cpse
ligand. Each carboxylate group of cpse is bridging two different cadmium atoms, forming a zigzag chain in a
polymeric structure.
Metal ions play a vital role in a vast number of widely differing
biological processes. Most naturally occurring metal ions are
bound to proteins. The question of the nature and extent of
metal ion–protein interaction is therefore a most important
one. It has been the subject of extensive work using amides,
amino acids and small peptides as model compounds.1–3 The
binding of metal ions may control the conformation of bio-
logical molecules and so affect their chemical and biological
properties. In this context we have been interested in the chem-
istry of co-ordination compounds derived from N-substituted
glycine ligands which may act as tridentate molecules. Many
tridentate ligands have a strong preference for facial or merid-
ional co-ordination, for example some amino acids co-ordinate
facially,4,5 while glycylglycine co-ordinates meridionally,6,7 or
both geometries could be stabilised, as in the case of imino-
diacetic acid derivatives.8–13 N-(Phosphonomethyl)glycine may
stabilise all possible geometric isomers;14 once the nitrogen is
attached to a metal atom its stereochemistry is fixed, adopt-
ing either an R or S configuration. It was found in previous
works with some pseudoephedrine [2-(methylamino)-1-phenyl-
propan-1-ol] derivatives such as phenylboronic acids15–18 and
diorganotin() oxides19 that only one molecule of the ligand
was facially co-ordinated to the Lewis acid, through the alkox-
ide, one carboxylic oxygen and the nitrogen, giving bicyclic
compounds. The co-ordination behaviour of N-[2-hydroxy-
1(R)-methyl-2(R)-phenylethyl]-N-methylglycine (N-carboxy-
methylpseudoephedrine, Hcpse) towards transition-metal ions
has not been investigated, therefore we initiated a study of its
complexing ability.
J. T. Baker. All reagents were used without further purifi-
cation.
Syntheses
N-[2-Hydroxy-1(R)-methyl-2(R)-phenylethyl]-N-methyl-
glycine (Hcpse). A mixture of (Ϫ)pseudoephedrine (5 g, 30.3
mmol), glyoxal (40% in water; 4.8 cm3, 33.3 mmol), and EtOH
(5 cm3) was stirred at 70 ЊC for 16 h. The mixture was then
evaporated in vacuo and the product recrystallised from EtOH–
acetone; yield 5.35 g (80%), m.p. 153 ЊC.20
[Cu(cpse)2]ؒH2O 1. In a test-tube, Hcpse (0.0334 g, 0.15
mmol) was dissolved in EtOH (5 cm3), and an aqueous solution
(5 cm3) of Cu(O2CMe)2ؒH2O (0.0149 g, 0.075 mmol) was added
slowly in order to obtain an interface between the two sol-
vents. After 2 d blue needles were obtained at the interface. The
crystals were filtered off, washed with methanol and dried in
vacuo; yield 0.053 g (67.3%).
[Cu(cpse)Br] 2, [Cu(cpse)(NO3)] 3 and [Co(cpse)2]ؒ2H2O 4.
All these compounds were prepared using a 2:1 Hcpse:metal
salt molar ratio. The metal salt (0.25 mmol) was dissolved in
boiling MeOH (10 cm3) and added to a hot solution of Hcpse
(0.1116 g, 0.5 mmol) in MeOH (10 cm3). The mixture was
stirred for 1 h and then set aside at room temperature until a
precipitate formed. The resulting precipitate was filtered off,
washed and dried in vacuo; yields 0.0952 g (52.1), 0.0751 g
(43.2) and 0.152 g (58.3%) for 2, 3 and 4 respectively.
[Cd(cpse)2(H2O)] 5. The metal salt Cd(O2CMe)2ؒ2H2O
(0.0765 g, 0.25 mmol) dissolved in boiling MeOH (10 cm3) was
added to a hot methanol solution (30 cm3) of Hcpse (0.1116 g,
0.5 mmol). The reaction mixture was refluxed for 3 h. The white
precipitate was filtered off, washed with methanol and dried in
vacuo. Transparent crystals of compound 5 were obtained after
2 weeks from a solution of this precipitate dissolved in dimethyl
sulfoxide (dmso); yield 0.0436 g (30.3%).
Experimental
Materials
Metal salts and solvents were obtained from E. Merck and
† E-Mail: norah@servidor.unam.mx
J. Chem. Soc., Dalton Trans., 1997, Pages 3415–3420
3415

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Table 1 Elemental analyses for Hcpse and co-ordination compounds 1–8
Analysis (%)*
Compound
Hcpse
Colour
C
H
N
Cream
63.42
8.00
6.26
(64.54)
54.22
(7.67)
6.39
(6.27)
5.40
1 [Cu(cpse)2]ؒH2O
Blue
(54.78)
39.30
(39.41)
42.55
(41.43)
54.00
(6.51)
4.12
(4.13)
4.95
(4.63)
7.05
(5.32)
3.74
(3.83)
8.09
(8.05)
4.72
2 [Cu(cpse)Br]
Blue-green
Blue-green
Pink
3 [Cu(cpse)(NO3)]
4 [Co(cpse)2]ؒ2H2O
(53.43)
50.63
(6.73)
6.08
(5.19)
4.95
5 [Cd(cpse)2(H2O)]
White
(49.95)
35.55
(34.72)
31.93
(30.75)
34.00
(6.28)
4.91
(5.41)
4.17
(4.73)
4.53
(4.85)
3.29
(2.89)
2.88
(2.98)
6.36
6 [Cd(cpse)Cl(H2O)]ؒH2Oؒdmso
7 [Cd(cpse)Br(H2O)]ؒ2H2O
8 [Cd(cpse)(NO3)(H2O)]ؒH2O
White
White
White
(33.30)
(4.65)
(6.47)
* Calculated values in parentheses.
[Cd(cpse)Cl(H2O)]ؒH2Oؒdmso 6. In
a
test-tube, Hcpse
polarisation effects. An absorption correction was not con-
sidered necessary in the case of compound 1 due to the needle
shape of the crystal, but was applied for 5 which was a very thin
plate, using 21 ψ scans with χ close to 90Њ, yielding minimum
and maximum transmission factors of 0.227 and 0.246. Com-
(0.0610 g, 0.25 mmol) was dissolved in EtOH (5 cm3), and an
aqueous solution (5 cm3) of CdCl2ؒ2.5H2O (0.0285 g, 0.125
mmol) was added slowly in order to obtain an interface
between the two solvents. After 5 d a white precipitate was
obtained in a very low yield, which was filtered off, washed with
methanol and dried in vacuo. The microcrystals were soluble in
dmso and single crystals of compound 6 were obtained after
4 months by slow evaporation of the solution.
21
putations were performed with the SHELXTL package on a
personal computer and scattering factors were taken from ref.
22. The non centrosymmetric character of the space groups was
confirmed by Wilson’s statistics yielding 〈|E 2 Ϫ 1|〉 = 0.681 for
1, 0.653 for 5 and 0.676 for 6.
[Cd(cpse)Br(H2O)]ؒ2H2O 7 and [Cd(cpse)(NO3)(H2O)]ؒH2O
8. The corresponding metal salt (0.25 mmol) was dissolved in
boiling MeOH (10 cm3) and added to a hot solution of Hcpse
(0.1116 g, 0.5 mmol) in MeOH (30 cm3). The reaction mixture
was refluxed for 2 h. The white precipitate was filtered off,
washed with methanol and dried in vacuo; yields 0.075 g (64)
and 0.0235 g (21.72%) for 7 and 8 respectively.
The structure of compound 1 was solved by direct methods
followed by subsequent Fourier-difference maps and refined by
full-matrix least squares, minimising Σ[w(Fo Ϫ Fc)2], without
restraints or constraints. Hydrogen atoms attached to carbon
atoms were included at geometrically idealised positions and
refined using a riding model with fixed isotropic U. For the two
hydroxyl groups [O(4) and O(7)] and the water molecule [O(1)],
hydrogen atoms could not be positioned from a Fourier-
difference map and were omitted. The correct absolute con-
figuration of the molecule was confirmed by refinement of a
Rogers parameter:23 η = 0.97(6).
The solution for compound 5 was derived from the interpret-
ation of the Patterson map completed and refined as for 1. The
hydrogen atoms of the water molecule O(1) and of the hydroxyl
groups O(4) and O(7) were omitted and the remaining hydrogen
atoms were treated as for 1. The correct absolute configuration
was confirmed in the same way, giving η = 0.98(15).
The molecular structure of compound 6 was resolved and
refined as for 1. The hydrogen atoms of the water molecules
O(1) and O(7) as well as for the hydroxyl group O(4) were
omitted. The absolute configuration was confirmed from refine-
ment of the Rogers parameter η = 1.2(2). The solvent molecules
were refined with isotropic thermal parameters because of lack
of data.
No significant features were observed in the last Fourier-
difference maps for compounds 1 and 5. In case of 6 the largest
residual peak (2.26 e ÅϪ3) was close to S(1) from the dmso
solvent molecule.
Physical measurements
Diffuse reflectance spectra were recorded on a Cary 5E UV/
VIS/NIR spectrophotometer over the range 250–2500 nm, IR
spectra on a Nicolet FT-IR 740 spectrophotometer using KBr
pellets in the range 4000–400 cmϪ1 and polyethylene pellets in
the range 700–70 cmϪ1 and 13C (67.80 MHz) NMR spectra on a
JEOL GSX-270 spectrometer. Magnetic susceptibility meas-
urements of powdered samples were recorded on a Johnson
Matthey balance using the Gouy method. Elemental analyses
were performed by the Microanalytical Department, University
College, London (see Table 1).
Crystallography
Suitable single crystals of [Cu(cpse)2]ؒH2O 1, [Cd(cpse)2(H2O)] 5
and [Cd(cpse)Cl(H2O)]ؒH2Oؒdmso 6 were obtained as des-
cribed previously. In the case of 6 total decomposition of the
crystal after 32 h of irradiation prevented the collection of data
at high resolution (θmax = 20Њ) and an absorption correction.
The diffraction data were collected at 293 K on a Siemens P4/
PC automatic diffractometer using graphite-monochromatised
Mo-Kα radiation (λ = 0.710 73 Å) at variable scan speed in ω
(4 to 60Њ minϪ1 for 1, 2 to 30Њ minϪ1 for 5, 3 to 60Њ minϪ1 for 6)
in the 2θ range of 4–50Њ for 1 and 5, and 3–40Њ for 6. Pertinent
crystal data and other crystallographic parameters are listed in
Table 2. The measured intensities were corrected for variation
of check reflections monitored periodically (minimum 1.00,
maximum 1.04, for 1 and 5; 0.91, 1.00 for 6) and Lorentz-
CCDC reference number 186/644.
Results and Discussion
The reaction of Hcpse with copper(), cobalt() and
cadmium() afforded two types of compounds, which are
summarised in Table 1. When using their acetate salts in the
synthesis, two cpse molecules are co-ordinated. In complexes
3416
J. Chem. Soc., Dalton Trans., 1997, Pages 3415–3420

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Table 2 Crystallographic data for compounds 1, 5 and 6
1
5
6
Formula
M
Crystal system
Space group
C24H32CuN2O6ؒH2O
526.07
Orthorhombic
P212121
C24H34CdN2O7
574.93
Monoclinic
P21
C12H18CdClNO4ؒH2Oؒ(CH3)2SO
484.27
Orthorhombic
P212121
a/Å
b/Å
c/Å
6.271(2)
13.598(3)
28.721(6)
14.717(4)
6.279(2)
15.618(4)
116.80(1)
1288.4(7)
2
1.482
592
0.89
0.8 × 0.1 × 0.02
3342
8.194(1)
12.467(1)
19.795(3)
β/Њ
U/Å3
2448.9(12)
4
1.427
1108
0.94
0.7 × 0.1 × 0.1
3369
3111
2301
308
2022.2(4)
4
1.591
984
1.34
0.4 × 0.2 × 0.1
1578
1408
1315
194
Z
Dc/Mg mϪ3
F(000)
µ(Mo-Kα)/mmϪ1
Crystal dimensions/mm
Total reflections measured
No. unique reflections
No. observed reflections [F > 4σ(F )]
No. variables
2945
2225
308
Goodness of fit
R = Σ(|Fo Ϫ Fc|)/Σ|Fo|
0.90
1.06
2.25
0.049
0.046
0.046
¹
¹
RЈ = Σ(w²|Fo Ϫ Fc|)/Σw²|Fo|
w = [σ2(F ) ϩ 0.0021F 2]Ϫ1 b w = [σ2(F ) ϩ 0.0003F 2]Ϫ1
0.059a
0.045b
0.065c
a
.
.
c w = [σ2(F ) ϩ 0.0004F 2]Ϫ1
.
Table 3 Selected bond lengths (Å) and angles (Њ) with standard
deviations in parentheses for compound 1
Cu᎐O(7)
Cu᎐O(3)
Cu᎐N(1)
O(3)᎐C(1)
O(4)᎐C(4)
N(1)᎐C(3)
C(1)᎐C(2)
C(3)᎐C(5)
O(4) ؒ ؒ ؒ O(5)*
2.379(5)
1.974(5)
2.048(6)
1.296(8)
1.434(8)
1.520(10)
1.508(10)
1.526(10)
2.626
Cu᎐O(4)
Cu᎐O(6)
Cu᎐N(2)
O(2)᎐C(1)
N(1)᎐C(2)
N(1)᎐C(6)
C(3)᎐C(4)
C(4)᎐C(7)
O(2) ؒ ؒ ؒ O(7)*
2.475(5)
1.944(5)
2.030(6)
1.216(9)
1.476(9)
1.470(10)
1.545(9)
1.530(11)
2.599
O(4)᎐Cu᎐O(7)
O(6)᎐Cu᎐O(7)
O(4)᎐Cu᎐O(6)
N(1)᎐Cu᎐N(2)
N(1)᎐Cu᎐O(4)
N(1)᎐Cu᎐O(7)
N(2)᎐Cu᎐O(4)
N(2)᎐Cu᎐O(6)
Cu᎐O(6)᎐C(13)
Cu᎐O(7)᎐C(16)
Cu᎐N(2)᎐C(14)
Cu᎐N(1)᎐C(3)
Cu᎐N(1)᎐C(6)
O(3)᎐C(1)᎐C(2)
N(1)᎐C(3)᎐C(4)
C(4)᎐C(3)᎐C(5)
175.4(2)
98.4(2)
80.1(2)
173.1(2)
79.5(2)
96.4(2)
O(3)᎐Cu᎐O(4)
O(3)᎐Cu᎐O(7)
O(3)᎐Cu᎐O(6)
N(1)᎐Cu᎐O(3)
N(1)᎐Cu᎐O(6)
N(2)᎐Cu᎐O(3)
N(2)᎐Cu᎐O(7)
Cu᎐O(3)᎐C(1)
Cu᎐O(4)᎐C(4)
Cu᎐N(1)᎐C(2)
Cu᎐N(2)᎐C(15)
Cu᎐N(2)᎐C(18)
O(6)᎐C(13)᎐C(14)
N(2)᎐C(15)᎐C(16)
C(16)᎐C(15)᎐C(17)
95.8(2)
85.7(2)
175.7(2)
83.2(2)
97.2(2)
94.8(2)
Fig. 1 Geometry and atom numbering for [Cu(cpse)2]ؒH2O 1
obtained from copper() and cadmium() chloride, bromide or
nitrate the metal ion is co-ordinated to only one cpse molecule
and to a counter ion.
107.4(2)
85.3(2)
76.8(2)
111.6(4)
101.9(4)
101.2(4)
110.1(4)
105.9(4)
116.7(6)
110.4(6)
110.6(6)
113.8(4)
109.4(4)
106.8(4)
111.9(4)
111.4(5)
116.5(6)
109.8(6)
112.8(6)
Crystal structures of compounds 1, 5 and 6
A perspective view of complex [Cu(cpse)2]ؒH2O 1, with the
labelling of the atoms is given in Fig. 1. The bond lengths and
angles are listed in Table 3. Two cpse molecules are co-
ordinated to the metal in a tridentate mode giving a bicyclic
chelate with two distorted five-membered rings, where the
nitrogen and the oxygens from the carboxylic and the alkoxide
functions are bonded to the metal ion. The compound presents
a fac-RS-octahedral geometry with the copper() ion in the
centre bonded to the six atoms in an all-trans configuration.
The carbonyl rings have distances Cu᎐O(3) and Cu᎐O(6) of
1.974(5) and 1.944(5) Å, respectively. The Cu᎐N(1) 2.048(6)
and Cu᎐N(2) 2.030(6) Å distances are very similar to those
observed in an analogous five-membered ring of a copper()
monoethyliminodiacetato complex;8 on the other hand, the
Cu᎐O bond lengths in the axial positions are different from
each other, Cu᎐O(4) 2.475(5) and Cu᎐O(7) 2.379(5) Å, due to a
Jahn–Teller effect. The two C᎐O distances in the carboxylate
group are very similar (Table 3), due to the presence of hydro-
gen bonding in the network structure between the non-co-
ordinated O(2, 5) and the H(4, 7) from neighbouring molecules,
as has been observed in other systems.5
* Intermolecular oxygen–oxygen contact for hydrogen bonds.
complexes.24–26 Selected bond lengths and angles are listed in
Table 4. The geometry can be regarded as distorted pentagonal
bipyramidal with one cpse ligand bonded to the metal ion in a
similar arrangement to that of the copper() compound, with
an oxygen from the carboxylate group in an apical position,
Cd᎐O(6) 2.301(8) Å, and the nitrogen and the alkoxide oxygen
in the equatorial plane, Cd᎐N(2) 2.448(9) and Cd᎐O(7) 2.341(5)
Å. The second cpse molecule is co-ordinated with all three
atoms in the equatorial plane, an unusual co-ordination mode
for this ligand, Cd᎐O(3) 2.368(8), Cd᎐N(1) 2.398(7) and
Cd᎐O(4) 2.534(6) Å; these distances are similar to normal
Cd᎐O and Cd᎐N bonds,24–26 with exception of Cd᎐O(4) which
is longer than expected, probably due to steric hindrance from
the methyl group of the A ring of the other ligand, as can be
appreciated from the small angle N(1)᎐Cd᎐O(4) 67.7(3)Њ, which
is substantially smaller than the corresponding one of complex
1, 79.5(2)Њ. The seventh position is occupied by a water mole-
The cadmium compound 5 has an uncommon seven-co-
ordinate geometry (Fig. 2). Up to now just a few examples for
this type of co-ordination are known, mainly in polymeric
J. Chem. Soc., Dalton Trans., 1997, Pages 3415–3420
3417

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Table 4 Selected bond lengths (Å) and angles (Њ) with standard
deviations in parentheses for compound 5
Table 5 Selected bond lengths (Å) and angles (Њ) with standard
deviations in parentheses for compound 6
Cd᎐O(1)
Cd᎐O(3)
Cd᎐O(7)
Cd᎐N(2)
O(3)᎐C(1)
O(6)᎐C(13)
N(2)᎐C(14)
N(2)᎐C(15)
C(13)᎐C(14)
2.318(8)
2.368(8)
2.341(5)
2.448(9)
1.261(14)
1.261(15)
1.471(13)
1.493(14)
1.524(17)
Cd᎐O(4)
Cd᎐O(6)
Cd᎐N(1)
O(2)᎐C(1)
O(5)᎐C(13)
N(1)᎐C(2)
N(1)᎐C(3)
C(1)᎐C(2)
O(4) ؒ ؒ ؒ O(5)*
2.534(6)
2.301(8)
2.398(7)
1.209(16)
1.228(13)
1.451(27)
1.490(9)
1.557(16)
2.606
Cd(1)᎐Cl(1)
Cd(1)᎐O(3)
Cd(1)᎐O(2A)
Cd(1)᎐N(1)
O(3)᎐C(1)
N(1)᎐C(6)
N(1)᎐C(3)
O(3)᎐Cd(1A)
2.551(4)
2.323(9)
Cd(1)᎐O(1)
Cd(1)᎐O(4)
Cd(1)᎐O(3A)
O(2)᎐C(1)
O(4)᎐C(4)
N(1)᎐C(2)
2.336(10)
2.360(10)
2.500(10)
1.259(20)
1.406(19)
1.447(20)
2.410(11)
2.410(11)
2.437(12)
1.287(18)
1.456(21)
1.522(19)
2.500(10)
O(2)᎐Cd(1A)
Cl(1)᎐Cd(1)᎐O(4)
Cl(1)᎐Cd(1)᎐O(2A)
Cl(1)᎐Cd(1)᎐O(3)
N(1)᎐Cd(1)᎐O(3)
O(3)᎐Cd(1)᎐O(2A)
Cl(1)᎐Cd(1)᎐N(1)
87.4(3)
92.9(3)
109.7(4)
69.9(4)
80.23
Cl(1)᎐Cd(1)᎐O(2A)
Cl(1)᎐Cd(1)᎐O(1)
Cl(1)᎐Cd(1)᎐O(3A)
N(1)᎐Cd(1)᎐O(4)
O(4)᎐Cd(1)᎐O(3A)
92.9(3)
169.6(3)
87.9(2)
72.7(4)
83.6(3)
O(1)᎐Cd᎐O(6)
O(1)᎐Cd᎐O(3)
N(1)᎐Cd᎐O(1)
N(1)᎐Cd᎐N(2)
N(1)᎐Cd᎐O(4)
O(3)᎐Cd᎐O(7)
172.2(3)
95.6(3)
99.3(5)
138.9(2)
67.7(3)
75.3(2)
O(1)᎐Cd᎐O(4)
O(1)᎐Cd᎐O(7)
N(2)᎐Cd᎐O(1)
N(1)᎐Cd᎐O(3)
N(1)᎐Cd᎐O(6)
N(2)᎐Cd᎐O(7)
87.8(2)
85.2(2)
100.8(4)
70.8(3)
86.6(5)
71.3(2)
92.7(3)
Symmetry operation implied by A label: ¹ ϩ x, ¹ Ϫ y, 2 Ϫ z.
¯
¯
²
²
* Intermolecular oxygen–oxygen contact for hydrogen bonds.
of 0.23 Å for O(3). The shorter distance Cd᎐O(4) and the larger
angle, N(1)᎐Cd᎐O(4) 72.7(4)Њ, when compared to those of
compound 5, indicate that there is no significant steric hin-
drance in this compound: this difference between the two
complexes can be understood as a consequence of the atom
which occupies an apical position in 5 and 6, cpse carboxylate
O(4) and a chloride ion, respectively.
The observed polymeric structure is very similar to that
reported for triaqua(malonato)cadmium(),26 where the co-
ordination sphere is comprised only of oxygen atoms. The
structure of 6 is completed with a dmso and a water solvent
molecule which form a complicated three-dimensional net-
work by weak hydrogen-bond interactions with the polymeric
system.
Fig. 2 Geometry and atom numbering for [Cd(cpse)2(H2O)] 5
Spectroscopic characterisation of compounds 1–8
Some spectral and magnetic data of the co-ordination com-
pounds of cpse are presented in Table 6. The IR spectrum of
Hcpse shows bands of the νasym and νsym stretching modes
of the carboxylic group at 1638 and 1384 cmϪ1, whereas
for compounds 1–5 these bands are shifted, presenting a
∆ν(νasym Ϫ νsym) of ≈200 cmϪ1, which is in accordance with the
inequivalence of the two C᎐O bonds in the carboxylic
group.28,29 This can be seen from the molecular structures of 1
and 5 (Tables 3 and 4; Figs. 1 and 2) where the C᎐O distance is
longer for the oxygen bonded to the metal ion while the other
presents more double-bond character. Owing to the similarity
of the IR spectra of compounds 1–5, it can be proposed that
the ligand is co-ordinated in a monomeric tridentate mode.
Additionally, the copper compound 3 showed new bands from
a co-ordinated nitrate group (1344 and 1318 cmϪ1) and the
far-IR spectrum of compound 2 has a strong band at 172 cmϪ1
assigned to ν(Cu᎐Br).30
Fig.
H2Oؒdmso 6
3
Geometry of the polymeric part of [Cd(cpse)Cl(H2O)]ؒ
The IR spectra of the cadmium() compounds 6–8 (Table 6)
showed a ∆ν of ≈160 cmϪ1, which has been observed for struc-
tures where chelation and monoatomic bridging27,29 is present,
as in compound 6, Fig. 3. In the low-frequency infrared spectra
of 6 and 7 the vibrational bands at 240 and 196 cmϪ1 were
assigned as ν(Cd᎐Cl) and ν(Cd᎐Br) respectively.30 Compound 8
presented new absorption bands due to a co-ordinated nitrate
group (Table 6).
The reflectance spectrum of the crystalline compound 1
(Fig. 4) presents a band indicative of a tetragonally distorted
octahedral geometry at 16357 cmϪ1 and the spectra of [Cu-
(cpse)Br] 2 and [Cu(cpse)(NO3)] 3 (Fig. 4) exhibit a strong band
(11848 and 12771 cmϪ1 respectively) in the region expected for a
distorted tetrahedral geometry in copper() compounds.31–38
This geometry could be stabilised by the tridentate cpse co-
ordination, as shown in copper compound 1, allowing the
cule, Cd᎐O(1) 2.318(8) Å, with a typical bond length for apical
co-ordination.24–26
As for the previous complex 5, the metal centre of 6 has a
seven-co-ordinated environment with a distorted pentagonal-
bipyramidal geometry (see Table 5). The apical positions are
occupied by a water molecule and a chloride ion, Cl᎐Cd᎐O(1)
169.6(3)Њ. As observed in 5, the tridentate cpse ligand lies in the
equatorial plane, Cd᎐O(3) 2.323(9), Cd᎐N(1) 2.437(12) and
Cd᎐O(4) 2.360(10) Å, however the co-ordination sphere is
completed by a chelated carboxylic group from another cpse
ligand, Cd᎐O(2A) 2.410(11) and Cd᎐O(3A) 2.500(10) Å. Each
carboxylate group of cpse is bridging two different cadmium
atoms, as in Cd(O2CMe)2(H2O)2,27 forming a zigzag chain
structure as depicted in Fig. 3. Atoms Cd᎐O(3)᎐N(1)᎐O(4)᎐
O(2A)᎐O(3A) all lie close to a plane with a maximum deviation
3418
J. Chem. Soc., Dalton Trans., 1997, Pages 3415–3420

View Article Online
Table 6 Spectral and magnetic data for compounds Hcpse and compounds 1–8
IR cν max/cmϪ1
UV/VISb
λmax/cmϪ1
νasym(CO2
νsym(CO2 )
∆ν
ν(M᎐X)
ν(NO3)
Ϫ
)
Ϫ
Compound
µeffa/µB
Hcpse
—
—
1638
1633
1598
1602
1384
1401
1403
1385
253
232
195
217
—
—
ν3 172
—
—
—
—
ν5 1344
ν1 1318
—
1
2
3
2.16
1.70
1.86
16357
11848
12771
4
5.19
ν1 9183
1592
1408
212
—
ν3 20325
5
6
7
8
1598
1569
1567
1565
1398
1412
1410
1401
200
157
157
164
—
—
—
—
—
—
ν3 240
ν3 196
—
—
—
ν5 1385
ν1 1312
a
25 ЊC; µB ≈ 9.27 × 10Ϫ24 J TϪ1 b Diffuse reflectance. c From KBr pellets, in the range 4000–600 cmϪ1, and polyethylene pellets, in the range 700–70
.
cmϪ1
.
Table 7 Carbon-13 NMR data for compounds Hcpse and compound
7 in (CD3)2SO
O
1
C
H2C 2
H3C
H3C
OH
6
N:
5
H
C
3
H
C
OH
4
H5C6
δ
Carbon
Hcpse
7
1
2
3
4
5
6
i
o
m
p
167.1
56.1
65.1
72.2
9.8
173.9
62.6
72.7
79.2
7.9
Fig. 4 Diffuse reflectance spectra of copper() compounds 1 (—),
2 (...) and 3 (–ؒ–)
36.9
40.7
141.4
127.4
128.4
128.2
141.8
128.1
127.8
127.6
in monomeric compounds and bidentate (chelate) with mono-
atomic bridging in polymeric complexes. Interestingly, for the
two cadmium() seven-co-ordinated compounds both co-
ordination types were observed.
fourth position to be occupied by the anion. Nevertheless, there
is a possibility that the cpse ligand may behave as a bridging
ligand using the carboxylate functionality as in complex 6 or in
3 the nitrate could be bidentate. Their magnetic moments are
as expected for a copper() ion.
Acknowledgements
H. C. L.-S. acknowledges a CONACYT scholarship. S. B. is
grateful to the UNAM for financial support and USAI for
diffractometer time.
The cobalt() compound 4 has a magnetic moment and
diffuse electronic spectrum characteristic of
a high-spin
4
octahedral geometry with the transitions ν1 T2g(F ) ←
4T1g(F ) at 9183 cmϪ1 and ν3 T1g(P) ← 4T1g(F ) at 20325 cmϪ1
.
C
4
References
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observed, although in principle two diastereomers may be
expected. Comparison of the 13C data between free Hcpse and
complex 7 shows that the C(1) from the carboxylate group is
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Received 25th June 1997; Paper 7/04485B
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J. Chem. Soc., Dalton Trans., 1997, Pages 3415–3420