Spectroscopic and crystallographic characterisation of cadmium complexes incorporating a bidentate phosphine ligand

Article abstract of DOI:10.1039/a703378h

The 1 : 1 stoichiometric addition of the bidentate phosphine ligand 2,2-dimethyl-2-sila-1,3-bis(diphenylphosphino)-propane (L²) to a range of cadmium(II) salts produced a series of moisture-sensitive complexes of general formula [CdX₂(L²)] (X = Cl 1, Br, I, SCN or NO₃). These complexes have been investigated by vibrational and multinuclear (³¹P and ¹¹³Cd) NMR spectroscopy and by X-ray crystallography. Complex 1 crystallises in the orthorhombic space group P2₁2₁2₁, with a = 9.2862(10), b = 15.386(2), c = 20.724(3) A, U = 2960.9(6) A³ and Z = 4. The metal centre exhibits four-co-ordinate, tetrahedral geometry, with the ligand bound in a bidentate manner. Both the solution- and solid-state cross-polarisation magic angle spinning ³¹P NMR spectra of the complexes show clearly resolved ¹¹³Cd-³¹P and ¹¹¹Cd-³¹P one bond couplings in a ¹¹³Cd: ¹¹¹Cd ratio of 1.044:1.046 as expected. Vibrational spectroscopy indicates that each complex is mononuclear, with no evidence for bridging species; [Cd(NO₃)₂(L²)] features monodentate nitrate groups. The addition of 2 equivalents of the ligand to cadmium perchlorate yields a complex which has been established as [Cd(L₂)₂][ClO₄]₂ by spectroscopic and conductance studies.

Full text of DOI:10.1039/a703378h

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Spectroscopic and crystallographic characterisation of cadmium
complexes incorporating a bidentate phosphine ligand
Paul R. Meehan, George Ferguson, Ram P. Shakya and Elmer C. Alyea *
Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario,
Canada N1G 2W1
The 1:1 stoichiometric addition of the bidentate phosphine ligand 2,2-dimethyl-2-sila-1,3-bis(diphenylphosphino)-
propane (L2) to a range of cadmium() salts produced a series of moisture-sensitive complexes of general formula
[CdX2(L2)] (X = Cl 1, Br, I, SCN or NO3). These complexes have been investigated by vibrational and multinuclear
(31P and 113Cd) NMR spectroscopy and by X-ray crystallography. Complex 1 crystallises in the orthorhombic
space group P212121, with a = 9.2862(10), b = 15.386(2), c = 20.724(3) Å, U = 2960.9(6) Å3 and Z = 4. The metal
centre exhibits four-co-ordinate, tetrahedral geometry, with the ligand bound in a bidentate manner. Both the
solution- and solid-state cross-polarisation magic angle spinning 31P NMR spectra of the complexes show clearly
resolved 113Cd᎐31P and 111Cd᎐31P one bond couplings in a 113Cd :111Cd ratio of 1.044:1.046 as expected.
Vibrational spectroscopy indicates that each complex is mononuclear, with no evidence for bridging species;
[Cd(NO3)2(L2)] features monodentate nitrate groups. The addition of 2 equivalents of the ligand to cadmium
perchlorate yields a complex which has been established as [Cd(L2)2][ClO4]2 by spectroscopic and conductance
studies.
The complex [Cd(dmpe){TeSi(SiMe3)3}2]1 [dmpe = 1,2-bis-
Cl
P
Cl
P
Ph
Ph
Cd
Ph
Ph
(dimethylphosphino)ethane] is the only structurally character-
ised cadmium species incorporating a bidentate ditertiary
phosphine ligand reported to date. Wymore and Bailar 2
reported the preparation of [CdBr2(depe)] [depe = 1,2-
bis(diethylphosphino)ethane] via the addition of water to
a dimethylformamide (dmf) solution of [(CdBr2)3(depe)2];
addition of CdBr2 regenerated the starting material. Cadmium
halide complexes with dppe [1,2-bis(diphenylphosphino)ethane]
and dppb [1,4-bis(diphenylphosphino)butane] were shown 3 to
be four-co-ordinate, monomeric moieties, characterised by
vibrational spectroscopy.4
The general insolubility of metal complexes of ditertiary
phosphine ligands has commonly precluded their study by
multinuclear NMR spectroscopy; in order to overcome this
problem we have synthesised 5 the ligand 2,2-dimethyl-2-sila-
1,3-bis(diphenylphosphino)propane (L2). The incorporation of
a dimethyl silicon component in the ligand backbone not only
increases complex solubility but also provides an excellent
NMR spectroscopic handle.
Si
Me
Me
1
were performed on these six cadmium complexes. The 1H NMR
spectra of the 1:1 species show apparent triplets for the P᎐CH2
backbone protons. The splitting is due to two bond and four
bond virtual coupling to the two phosphorus atoms; the
appearance of a triplet is due to J(31P᎐1H) being much smaller
4
than J(31P᎐1H) and hence having a minor contribution to the
2
total coupling constant (2J ϩ 4J = 5.4–6.2 Hz). Three bond
couplings to the cadmium centres are also clearly visible, with
3J(Cd᎐H) 26.1–29.4 Hz. The coupling constants for the two
NMR-active cadmium nuclei are not clearly resolved and hence
the J(Cd᎐H) values quoted are approximate average values of
the two. The chemical shifts for the P᎐CH2 protons appear
downfield from the free ligand value (complexes δ 1.84–2.08,
free ligand 1.50), reflecting the expected increase in deshielding
upon complexation to the metal centres. The dimethylsilyl
protons appear as a singlet in each case (δ Ϫ0.29 to Ϫ0.33),
indicating the equivalence of the two methyl groups. The NMR
spectrum of the 2:1 perchlorate complex is complicated and
not clearly resolved, and coupling constants are hence not
observed.
We have recently reported the complexation of a range of
cobalt()6 and mercury()7 salts with L2, to form four-co-
ordinate, tetrahedral species of general formula [MX2(L2)]
(X = Cl, Br, I, NO3 or SCN). Cadmium is extremely amenable
to NMR spectroscopic study, as it has two isotopes of non-zero
spin, 113Cd (I = ¹) and 111Cd (I = ¹). Colton and Dakternieks8
¯
²
¯
²
studied monodentate phosphine complexes of cadmium via
low-temperature Fourier-transform NMR spectroscopic tech-
niques. The generation of analogous cadmium() salts should
thus allow characterisation by multinuclear (113Cd and 31P)
NMR and vibrational spectroscopy and engender crystal
formation for an X-ray study.
Solution-state 31P NMR spectroscopic studies reveal the
chemical environments of the phosphorus atoms; data are pre-
sented in Table 1. Chemical shift and coupling constant values
for cadmium() complexes are dependent on temperature, con-
centration, magnetic field and solvent,8 while previous studies9
have shown that for complexes of monodenate phosphines,
anion and phosphine exchange are rapid on the NMR time-
scale. The room-temperature 31P NMR spectra of the cadmium
halide and nitrate species here each show a sharp central reson-
ance for the phosphorus atoms, with clearly resolved satellites
Results and Discussion
The 1:1 stoichiometric addition of a dichloromethane solution
of L2 to a series of cadmium() salts produced a range of
moisture-sensitive complexes denoted as [CdX2(L2)] (X = Cl 1,
Br, I, NO3 or SCN). Reaction between cadmium perchlorate and
2 equivalents of the phosphine ligand yielded [Cd(L2)2][ClO4]2.
Multinuclear (1H, 31P and 113Cd) NMR spectroscopic studies
arising from J(113Cd᎐31P) and J(111Cd᎐31P) couplings. The 31
P
1
1
NMR spectrum of [Cd(NO3)2(L2)] appears in Fig. 1. The thio-
cyanate complex, however, gives a broad spectrum, with
cadmium–phosphorus coupling not readily apparent; thus it is
J. Chem. Soc., Dalton Trans., 1997, Pages 3487–3491
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Table 1 Multinuclear (31P and 113Cd) NMR spectroscopic data a for the cadmium complexes
Complex
δ31P b (ppm)
Ϫ15.5
Ϫ18.3
Ϫ25.0
Ϫ8.6
δ
113Cd c (ppm)
1J(113Cd᎐31P)d/Hz
1J(111Cd᎐31P)d/Hz
1
2
3
4
415 (t)
389 (t)
317 (t)
92 (t)
1248.5
1154.6
974.8
1756.4
1195.8
1106.3
933.8
1679.4
5
6
Ϫ10.7
Ϫ5.4
Ϫ21.0
Broad, no coupling
1111.7
Broad, no coupling
1064.3
Free L2
a
Complexes in CH2Cl2. b At 298 K, relative to external 85% H3PO4. c At 183 K, referenced to 4  Cd(NO3)2, t = triplet. d At 298 K.
Fig. 1 The 31P NMR spectrum of [Cd(NO3)2(L2)] at 298 K
clear that thiocyanate exchange occurs at room temperature:
upon cooling to 243 K, coupling to the cadmium centre
1
becomes visible [1J(113Cd᎐31P) 1435.5 and J(111Cd᎐31P) 1384.3
Hz], while at lower temperatures the insolubility of the thio-
cyanate complex precludes NMR spectroscopic study.
Both J(113Cd᎐31P) and J(111Cd᎐31P) couplings in the halide
and nitrate complexes are clearly resolved, with a 113Cd :111Cd
ratio of 1.044:1.046. This is in accordance with the gyro-
magnetic ratio calculated for the two nuclei, and remains con-
stant at variable temperature. The values of the Cd᎐P coupling
constants are comparable to those observed in related mono-
dentate phosphine complexes10 and are much smaller than those
1
1
Fig. 2 The CP-MAS solid-state 31P NMR spectrum of [Cd(NO3)2(L2)]
(SSB = spinning side band)
ligands: this is borne out by the crystal structure of 1, as dis-
cussed later.
The cross-polarisation magic angle spinning (CP-MAS)
solid-state 31P NMR spectrum of [Cd(NO3)2(L2)] is shown in
Fig. 2. An AB pattern can be clearly observed for the two
inequivalent phosphorus atoms. The non-equivalence of the
two phosphorus atoms can be explained by the distorted tetra-
hedral geometry and by crystal packing effects, as subsequently
discussed in the structural analysis. The cadmium satellites are
not fully resolved, hence the M᎐P coupling constants were
estimated by using the value of 78 Hz that is observed for
1
values noted in analogous Hg᎐L2 complexes7 {e.g. J(M᎐P) =
3684 [HgCl2(L2)], 1248 and 1196 Hz [CdCl2(L2)]}. The magni-
tudes of the chemical shifts and coupling constants in the L2
complexes here and in the monodenate phosphine analogues
vary in the order NO3 > SCN > Cl > Br > I and increase as the
temperature is decreased: this trend is readily explained by the
strengthening of the M᎐P bonds as phosphine exchange slows
upon cooling. For metals such as cadmium and mercury, in
which d orbital participation is not important, the magnitude
of the M᎐P coupling in their complexes is purely a reflection of
σ bond effects.
Although the ring contribution, ∆R , to δP cannot be accur-
ately calculated as there are no chemical shift data available for
1:2 cadmium complexes with the monodentate analogue
PPh2Pr, data for PPh2Et have been recorded.11 The co-
ordination chemical shift for [CdI2(PPh2Et)] was estimated as δ
Ϫ2.5 from the spectrum at 183 K, while the value of δ Ϫ2.8 was
noted in the L2 complex. Thus ∆R can be calculated to be Ϫ0.3
ppm, a very small upfield shift owing to the chelate ring. The
Cd᎐P coupling constants for [CdI2(PPh2Et)] were measured as
1143.3 (111Cd) and 1195.7 Hz (113Cd) at 183 K, and are hence
larger than the values observed for L2. Thus the decrease in M᎐P
coupling constants in the chelate complex is attributable to a
decrease in the valence s electron density at the metal nucleus
compared with the monodenate species. This suggests that L2
does not span the tetrahedral angle and interact as strongly
with the cadmium centre as do two monodenate phosphine
1
1
the difference between J(111Cd᎐31P) and J(113Cd᎐31P) in the
solution-state 31P NMR spectrum. The observed average coup-
ling constant is thus calculated to be 1784 Hz, with derived
individual values of 1J(111Cd᎐31P) = (1784 Ϫ 39) = 1745 and
1J(113Cd᎐31P) = (1784 ϩ 39) = 1823 Hz. This gives an expected
ratio of 1.045:1 for 113Cd :111Cd. It should be noted that the
value of 78 Hz from the solution spectrum may differ slightly
from that which would be observed in the solid state, and hence
the J values are not precise; a clear conclusion, however, is that
the larger J values observed in the solid state reflect stronger
M᎐P bonds than are present in solution. The two bond
31P᎐31P coupling through the cadmium centre can be
calculated as 211 Hz. The CP-MAS spectrum of [Cd(L2)2]-
[ClO4]2 shows a single broad resonance at δ Ϫ4.11, similar to
the value observed in solution. The Cd᎐P satellites are not
observed.
The 113Cd NMR spectroscopic studies were performed on the
halide and nitrate complexes and the results are shown in Table
1. The spectra each showed triplets with a 1:2:1 intensity,
3488
J. Chem. Soc., Dalton Trans., 1997, Pages 3487–3491

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Table 2 Selected bond lengths (Å) and angles (Њ) for complex 1
Cd᎐Cl(1)
Cd᎐Cl(2)
Cd᎐P(1)
Cd᎐P(2)
P(1)᎐C(1)
2.403(2)
2.440(2)
2.580(2)
2.553(2)
1.811(7)
P(1)᎐Cl(1)
P(1)᎐C(21)
P(2)᎐C(2)
P(2)᎐C(31)
P(2)᎐C(41)
1.815(6)
1.810(6)
1.826(6)
1.806(7)
1.806(5)
Cl(1)᎐Cd᎐Cl(2)
Cl(1)᎐Cd᎐P(1)
Cl(1)᎐Cd᎐P(2)
Cl(2)᎐Cd᎐P(1)
Cl(2)᎐Cd᎐P(2)
P(1)᎐Cd᎐P(2)
Cd᎐P(1)᎐C(1)
Cd᎐P(1)᎐C(11)
Cd᎐P(1)᎐C(21)
120.68(7)
113.05(6)
120.12(6)
102.44(7)
98.89(6)
97.94(6)
110.1(2)
113.6(2)
113.1(2)
Cd᎐P(2)᎐C(2)
Cd᎐P(2)᎐C(31) 118.0(2)
Cd᎐P(2)᎐C(41) 114.2(2)
C(1)᎐Si᎐C(2)
C(1)᎐Si᎐C(3)
C(1)᎐Si᎐C(4)
C(2)᎐Si᎐C(3)
C(2)᎐Si᎐C(4)
C(3)᎐Si᎐C(4)
104.4(2)
113.5(3)
105.3(3)
113.2(3)
104.4(3)
110.8(3)
109.1(4)
Fig. 3 The 113Cd NMR spectrum of [CdBr2(L2)] at 183 K
revealing metal co-ordination to two phosphorus atoms; the
spectrum of the bromide complex is shown in Fig. 3. The
1J(113Cd᎐31P) coupling constants were calculated and correlate
with those noted from the 31P NMR spectra. The thio-
cyanate and 1:2 perchlorate complexes were of insufficient
solubility to allow 113Cd NMR spectroscopy. The linear corre-
lation between δCd and the electronegativity of the attached
halide, and that between the chemical shift and coupling con-
stant, imply that the latter values are largely determined by σ
bond effects, as previously suggested; similar trends were
noted 8,10 for cadmium() complexes of monodentate phos-
phines.
Vibrational spectroscopic studies performed on the com-
plexes confirmed the presence of four-co-ordinate mono-
nuclear species. Assignments of ν(M᎐X) and ν(M᎐P) were
made on the basis of similar observations reported for mono-
dentate phosphine complexes.4 The halide and thiocyanate
complexes each show characteristic terminal Cd᎐X stretches in
the IR and Raman spectra, with no evidence for bridging X
groups. The thiocyanate shows clear signals assigned to ν(CN)
2080, ν(CS) 830, 790 and δ(SCN) 460 cmϪ1, and indicate co-
ordination through the S atom.
In general it is difficult to distinguish between mono- and bi-
dentate co-ordination in nitrate groups.12 However, Alyea and
co-workers13 showed that the extent of separation of the ν3
band may give some indication; values greater than 150 cmϪ1
often point towards bidentate co-ordination, while values less
than 150 cmϪ1 may infer monodenticity. In this case, ν3 appears
at 1440 and 1290 cmϪ1 and hence the separation is exactly 150
cmϪ1. However, the trend for formation of four-co-ordinate
[MX2(L2)] complexes6,7 implies that the two nitrate groups are
almost certainly bound in a monodentate fashion.
Fig. 4 A view of the crystal structure of complex 1, with thermal
ellipsoids at the 30% probability level
from tetrahedral with angles ranging from 97.94(6) [P(1)᎐
Cd᎐P(2)] to 120.68(7)Њ [Cl(1)᎐Cd᎐Cl(2)]. This can be attributed
in part to the high steric crowding about the cadmium due to
the phenyl groups. There is also evidence for an intermolecular
C(43)᎐H(43) ؒ ؒ ؒ Cl(2) interaction [H(43) ؒ ؒ ؒ Cl(2*) 2.74,
C(43) ؒ ؒ ؒ Cl(2*)3.616(11)Å,C(43)᎐H(43) ؒ ؒ ؒ Cl(2*)158Њ;Cl(2*)
at 1 Ϫ x, Ϫ¹ ϩ y, ¹ Ϫ z]. The combination of the steric effects
¯
²
¯
²
and the crystal packing thus explains the distortion from ideal-
ised tetrahedral geometry and the non-equivalence of the
phosphorus atoms in the solid state.
The ligand chelate bite angle is considerably smaller than the
values of 101.54(6) and 105.28(6)Њ in the analogous [CoBr2(L2)]6
and [HgI2(L2)]7 complexes, respectively. The six-membered
chelate ring defined by Cd, P(1), P(2), C(1), C(2) and Si adopts a
chair conformation, with torsion angles ranging from Ϫ45.6(2)
[P(2)᎐Cd᎐P(1)᎐C(1)] to Ϫ66.2(4)Њ [Cd᎐P(2)᎐C(2)᎐ Si].
In summary, the addition of 1 equivalent of L2 to
cadmium() salts produces mononuclear four-co-ordinate
tetrahedral metal species, which are of sufficient solubility to
engender multinuclear NMR spectroscopic studies.
Molar conductance measurements performed on freshly pre-
pared nitromethane solutions (10Ϫ3 ) revealed that the 1:1
complexes were all non-electrolytes. However, the perchlorate
complex showed a value of 161.1 ΩϪ1 cm2 molϪ1; this value is in
the range for a 1:2 electrolyte14 and thus confirms the assign-
ment of the complex as [Cd(L2)2][ClO4]2. Clearly this also rules
out the possibility of the formation of [Cd(L2)2][CdX4] or
[CdX(L2)2]X species.
Recrystallisation from dichloromethane afforded colourless
needle crystals of complex 1. A view of the complex is in Fig. 4,
and selected bond lengths and angles are given in Table 2.
Complex 1 contains a four-co-ordinate distorted tetrahedral
metal centre, with the ligand L2 bound in a bidentate fashion,
Cd᎐P(1) 2.580(2), Cd᎐P(2) 2.553(2) Å and P(1)᎐Cd᎐P(2)
97.94(6)Њ. The Cd᎐P bond lengths, which are significantly dif-
ferent from each other, are also considerably shorter than those
noted in [Cd(dmpe){TeSi(SiMe3)3}2] [Cd᎐P mean 2.701(5) Å],
although this may well be a reflection of the bulky silyl groups
on the latter compound. The Cd᎐Cl bond lengths differ slightly
at Cd᎐Cl(1) 2.403(2), Cd᎐Cl(2) 2.440(2) Å, but fall within the
expected range. The metal geometry is significantly distorted
Experimental
The cadmium salts were purchased from Aldrich Chemical Co.
and used as supplied. All solvents used were reagent grade and
were distilled immediately prior to use. A stock solution of L2 in
dichloromethane (1 g, 10 cm3) was prepared. The NMR spectra
were recorded on a Bruker WH-400 FT-NMR spectrometer at
400.1 (1H, ref. SiMe4), 162.0 (31P) and 88.7 MHz (113Cd). Solid-
state 31P NMR spectra were recorded on a Bruker CXP-200
using the CP-MAS technique. Infrared spectra were recorded as
Nujol mulls between CsI plates on a Perkin-Elmer 180 double-
beam spectrometer. Elemental analyses were performed by
M. H. W. Laboratories, Phoenix, AZ.
J. Chem. Soc., Dalton Trans., 1997, Pages 3487–3491
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Preparation of [CdCl2(L2)] 1
Table 3 Summary of crystal data, data collection, structure solution
and refinement details for complex 1
To a stirred solution of cadmium chloride (0.80 g, 4.40 mmol)
in ethanol (50 cm3), a dichloromethane solution of L2 (2.00 g,
4.38 mmol) was added dropwise. The white precipitate that
formed immediately was stirred for 20 min, filtered, washed
with ethanol and dry diethyl ether and dried in vacuo overnight.
Yield 2.10 g (72%), m.p. 235 ЊC (Found: C, 52.42; H, 4.70.
C28H30CdCl2P2Si requires C, 52.56; H, 4.72%). νmax/cmϪ1
(Nujol) 280vs, 255vs (Cd᎐Cl), 148w and 134w (Cd᎐P).
δH (CDCl3) 7.78–7.31 (20 H, m, 4 C6H5P), 1.84 [4 H, t, J(P᎐H)
5.4, J(Cd᎐H) 28.6 Hz, 2 CH2] and Ϫ0.29 (6 H, s, SiMe2).
Crystal data
Empirical formula
M
C28H30CdCl2P2Si
639.85
Colour, habit
Crystal size/mm
Crystal system
a/Å
Colourless, needle
0.42 × 0.18 × 0.17
Orthorhombic
9.2862(10)
15.386(2)
20.724(3)
2960.9(6)
P212121
b/Å
c/Å
U/Å3
Preparation of [CdBr2(L2)] 2
Space group
Z
4
To a stirred solution of cadmium bromide (1.10 g, 4.04 mmol)
in ethanol (50 cm3), L2 (1.85 g, 4.05 mmol) in dichloromethane
was added dropwise, yielding the immediate deposition of a
white precipitate. The reaction mixture was stirred for 30 min,
and the precipitate was filtered, washed with ethanol and dry
diethyl ether and dried in vacuo overnight. Yield 2.03 g (68%),
m.p. 245 ЊC (Found: C, 46.36; H, 4.35. C28H30Br2CdP2Si
requires C, 46.15; H, 4.15%). νmax/cmϪ1 (Nujol) 202vs, 178vs
(Cd᎐Br) and 136w (Cd᎐P). δH (CDCl3) 7.72–7.36 (20 H, m, 4
C6H5P), 1.87 [4 H, t, J(P᎐H) 5.7, J(Cd᎐H) 26.8 Hz, 2 CH2] and
Ϫ0.29 (6 H, s, SiMe2).
F(000)
1296
1.435
1.082
Dcalc/g cmϪ3
µ/mmϪ1
Data acquisitiona
T/K
θ Range/Њ
294(1)
9.8–15.0
24.91
Ϫ11 to 11; Ϫ18 to 18;
Ϫ24 to 24
1.8%
Max. θ (Њ) for reflections
hkl Range of reflectionsa
Variation in 2 standard reflections
Reflections measured
Unique reflections
5913
5172
With I > 2σ(I)
Absorption correction type
Minimum, maximum absorption correction
3151
ψ Scans
0.8038, 0.9980
Preparation of [CdI2(L2)] 3
A dichloromethane solution of L2 (2.00 g, 4.38 mmol) was
added dropwise with stirring to a solution of cadmium iodide
(1.50 g, 4.10 mmol) in ethanol (50 cm3). A white precipitate
formed immediately. After stirring for 20 min the precipitate
was filtered, washed with ethanol and dry diethyl ether and
dried in vacuo overnight. Yield 2.65 g (80%), m.p. 215 ЊC
(Found: C, 41.00; H, 3.85. C28H30CdI2P2Si requires C, 40.87; H,
3.67%). νmax/cmϪ1 (Nujol) 172s, 158s (Cd᎐I) and 134w (Cd᎐P).
δH (CDCl3) 7.79–7.27 (20 H, m, 4 C6H5P), 1.90 [4 H, t, J(P᎐H)
5.6, J(Cd᎐H) 26.1 Hz, 2 CH2] and Ϫ0.31 (6 H, s, SiMe2).
Structure solution and refinement b
Refinement
Solution method
On F 2
Direct methods
Riding
Hydrogen atom treatment
No. variables in least squares
Weights: k in w = 1/(σ2Fo2 ϩ k)
301
(0.0362P)2
[P = (Fo2 ϩ 2Fc )/3]
2
R, RЈ, S
0.043, 0.088, 0.94
Ϫ0.298, 0.501
0.001
Density range in final ∆-map/e ÅϪ3
Final shift/error ratio
Flack parameter
Ϫ0.08(4)
Preparation of [Cd(NO3)2(L2)] 4
a
Data collection on an Enraf-Nonius CAD4 diffractometer with
graphite-monochromatised Mo-Kα radiation (λ 0.71067 Å). Two
octants of data were collected, one with ϩh, ϩk, ϩl, the other with Ϫh,
Ϫk, Ϫl indices. b All calculations were done on a Silicon Graphics 4D-
35TG computer system with the NRCVAX system of programs15 for
refinement with observed data on F, or with SHELXL 9316 for refine-
ment with all data on F 2.
A stirred solution of cadmium nitrate (1.20 g, 5.08 mmol) in
ethanol (50 cm3) was treated with a dichloromethane solution
of L2 (2.00 g, 4.38 mmol) and the reaction mixture was stirred
for 4 h. The resultant white precipitate was filtered, washed with
ethanol and dry diethyl ether and dried in vacuo overnight.
Yield 2.27 g (65%), m.p. 232 ЊC (Found: C, 48.33; H, 4.37; N,
4.05. C28H30CdN2O6P2Si requires C, 48.53; H, 4.36; N, 4.04%).
νmax/cmϪ1 (Nujol) 1440s, 1290vs, 1015s, 840s, 745m, 720s (NO3)
and 140w (Cd᎐P). δH (CDCl3) 7.62–7.36 (20 H, m, 4 C6H5P),
1.96 [4 H, t, J(P᎐H) 6.2, J(Cd᎐H) 29.0 Hz, 2 CH2] and Ϫ0.33 (6
H, s, SiMe2).
50 ЊC. The white precipitate that formed immediately was fil-
tered, washed with ethanol and dry diethyl ether and dried in
vacuo overnight. Yield 2.20 g (70%), m.p. 190 ЊC (Found: C,
54.33; H, 5.36. C56H60CdCl2O8P2Si requires C, 54.93; H,
4.94%). νmax/cmϪ1 (Nujol) 1090vs (br) and 620s (ClO4).
δH (CDCl3) 7.91–7.23 (20 H, m, 4 C6H5P), 1.70–1.61 (4 H, d, 2
CH2) and Ϫ0.01 (6 H, s, SiMe2).
Preparation of [Cd(SCN)2(L2)] 5
To a stirred solution of cadmium thiocyanate (1.00 g, 4.38
mmol) in hot ethanol (50 cm3), a solution of L2 (2.00 g, 4.38
mmol) in dichloromethane was added and the reaction mixture
was stirred for 4 h. A white precipitate resulted; this was filtered,
washed with ethanol and dry diethyl ether and dried in vacuo
overnight. Yield 2.05 g (73%), m.p. 154 ЊC (Found: C, 52.49; H,
4.38; N, 4.41. C30H30CdN2P2S2Si requires C, 52.59; H, 4.41; N,
4.09%). νmax/cmϪ1 (Nujol) 2080vs (CN), 830vs, 790s (CS), 460m
(NCS), 260s (Cd᎐SCN) and 190vs (Cd᎐P). δH (CDCl3) 7.66–
7.48 (20 H, m, 4 C6H5P), 2.08 [4 H, t, J(P᎐H) 6.0, J(Cd᎐H) 29.4
Hz, 2 CH2] and Ϫ0.32 (6 H, s, SiMe2).
Crystal structure of complex 1
The slow evaporation of solvent from a dichloromethane solu-
tion of the complex yielded colourless, needle crystals of 1. A
summary of the crystal data, solution and refinement param-
eters appears in Table 3. X-Ray measurements were made on an
Enraf-Nonius CAD4 diffractometer using graphite-mono-
chromated Mo-Kα radiation. Data were collected in the range
4 р 2θ р 55Њ and corrected for Lorentz, polarisation and
absorption effects. Molecule 1 as synthesised is achiral, but it
crystallises in the chiral space group P212121. The analysis estab-
lishes the absolute structure of the crystal studied. All non-H
atoms were allowed anisotropic motion and hydrogen atoms
allowed for as riding atoms. An absorption correction was
applied, based on ψ scan data.17
Preparation of [Cd(L2)2][ClO4]2 6
Cadmium perchlorate (0.80 g, 2.57 mmol) dissolved in ethanol
(50 cm3) and a dichloromethane solution of L2 (2.35 g, 5.15
mmol) were mixed in a 1:2 molar ratio and stirred for 2 h at
3490
J. Chem. Soc., Dalton Trans., 1997, Pages 3487–3491

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Acknowledgements
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11 B. E. Mann, Inorg. Nucl. Chem. Lett., 1971, 7, 595.
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E. C. A. and G. F. would like to thank National Science and
Engineering Research Council (Canada) for research grants.
13 P. H. Merrell, E. C. Alyea and L. Ecott, Inorg. Chim. Acta, 1982,
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14 W. J. Geary, Coord. Chem. Rev., 1971, 7, 81.
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16 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993.
17 A. C. T. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr.,
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Received 16th May 1997; Paper 7/03378H
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