Preparation and crystal structures of two forms of trans-[CuCl2{N(H)SPh2}2]; an unusual example of square planar/pseudo-tetrahedral isomerism in a neutral copper(II) complex

Article abstract of DOI:10.1039/a704276k

At ambient temperatures, in acetonitrile, 5,5-diphenylsulfimide reacted with CuCl₂ (molar ratio 2:1) to give trans-[CuCl₂{N(H)SPh₂}₂]; depending upon the crystallisation technique this can be isolated as either blue (perfect square-planar geometry) or green (pseudo-tetrahedral) crystals which do not interconvert in the solid state.

Full text of DOI:10.1039/a704276k

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Preparation and crystal structures of two forms of trans-
[CuCl2{N(H)SPh2}2]; an unusual example of square planar/pseudo-
tetrahedral isomerism in a neutral copper(II) complex
Paul F. Kelly,* Alexandra M. Z. Slawin and Kevin W. Waring
Department of Chemistry, Loughborough University, Loughborough, Leics., UK LE11 3TU
analyse as a straightforward 2:1 complex (Found: C, 53.6; H,
At ambient temperatures, in acetonitrile, S,S-diphenylsulfimide
reacted with CuCl2 (molar ratio 2:1) to give trans-[CuCl2-
{N(H)SPh2}2]; depending upon the crystallisation technique
this can be isolated as either blue (perfect square-planar
geometry) or green (pseudo-tetrahedral) crystals which do not
interconvert in the solid state.
3.8; N 5.1. Calc. for C24H22CuCl2N2S2: C, 53.7; H, 4.1; N, 5.2%).
X-Ray crystallography reveals these to have a trans arrange-
ment of the ligands with the sulfimides bound, as expected, by
their nitrogen atoms (Fig. 1).‡ The overall geometry about the
copper is square planar, with no discernable axial inter-
molecular interactions up to 6 Å from the copper. Such inter-
actions are probably precluded by the fact that the two sets of
phenyl rings are arranged roughly perpendicular to the
CuCl2N2 plane, providing a steric barrier to any axial close
approaches.
If a variation upon the above crystallisation procedure is per-
formed whereby the 1a that initially precipitates in acetonitrile
is filtered off and the remaining solution treated with diethyl
ether and cooled in a freezer, a combination of blue crystals of
1a and green crystalline material 1b is generated. Our initial
assumption was that the latter would prove to be the cis
analogue of 1a; in fact X-ray crystallography reveals it to again
be a trans arrangement but now with a pseudo-tetrahedral
geometry about the copper (Fig. 2). The level of distortion from
The ability of some complexes of the late transition metals,
in particular copper and nickel, to exhibit variable isomerism
between square planar and tetrahedral (or pseudo-tetrahedral)
geometries is well known.1 For example, many salts of [CuCl4]2Ϫ
exhibit thermochromic effects due to such structural changes
while a number of nickel() complexes (typically those involving
phosphine ligands) can exist in the two respective forms (or
even, in some cases, exhibit both geometries within the same
unit cell). What appears to be a much rarer scenario, however, is
isomerism such as this occurring for neutral copper() species.
Indeed, we have yet to confirm the occurrence of any such
example in the literature. We have, however, isolated an example
of just such a complex during investigations into the co-
ordination chemistry of S,S-diphenylsulfimide, N(H)SPh2 I.
Our interest in the co-ordination chemistry of compound I
stems from our general investigations into the interaction of
sulfur–nitrogen chain species with transition-metal centres.
During such work we have tended to concentrate upon long-
chain species such as (Me3SiNSNSNSNSiMe3), which can act
as a source of a range of S᎐N ligands via reaction with simple
platinum-group complexes.2 While the latter is amongst the
longest S᎐N chain species that may be isolated as a discrete
molecule, I is clearly a good example of the shortest such chain.
Interest in its chemistry is dominated by its use in organic
chemistry as, for example, a source of aziridines.3 In contrast,
its co-ordination chemistry is very much underdeveloped, with
a recently reported uranium species being the only metal com-
plex so far noted.4 We have been able to show that in fact I
readily co-ordinates to a wide range of late-transition-metal
units, including CuCl2.†
Fig. 1 Crystal structure of complex 1a. Selected bond distances (Å)
and angles (Њ): Cu᎐N(1) 1.911(8), Cu᎐Cl(1) 2.271(3), N(1)᎐S(1)
1.582(9); N(1)᎐Cu᎐Cl(1) 87.0(3), N(1)᎐Cu᎐N(1*) 180.0, Cl(1)᎐Cu᎐
Cl(1*) 180.0, Cu᎐N(1)᎐S(1) 129.0(5)
When a solution of compound I (75 mg, 0.38 mmol) in
acetonitrile (20 cm3) is slowly added to a solution of CuCl2 (25
mg, 0.19 mmol) in the same solvent (20 cm3), the expected com-
plex [CuCl2{N(H)SPh2}2] 1 forms. If the solution is reasonably
concentrated the latter spontaneously precipitates at ambient
temperatures; if this precipitate is redissolved by heating, a
small amount of diethyl ether added and the solution lagged
to promote slow cooling, a good yield of 1 may be obtained as
well formed blue crystals (henceforward designated 1a) which
‡ Crystal data 5 for complex 1a. C24H22Cl2CuN2S2, M = 537.02, mono-
clinic, Space group C2/c (no. 15), a = 17.038(2), b = 8.928(5),
c = 16.234(2) Å, β = 97.537Њ, U = 2448(1) Å 3, T = 20 ЊC, Z = 4 (the
molecule possesses a crystallographic centre of symmetry), µ(Cu-
Kα) = 4.99 mmϪ1, R = 0.058 (RЈ = 0.050) for 866 observed reflections
[I > 3σ(I)].
Crystal data 5 for complex 1b. C24H22Cl2CuN2S2, M = 537.02, mono-
clinic, space group P21/a (no. 14), a = 11.443(5), b = 16.114(4),
c = 14.267(2) Å, β = 109.62(3)Њ, U = 2478(2) Å 3, T = 20 ЊC, Z = 4, µ(Cu-
Kα) = 4.93 mmϪ1, R = 0.053 (RЈ = 0.048) for 1748 observed reflections
[I > 2σ(I)]. CCDC reference number 186/645.
† For example [Co{N(H)SPh2}6]2ϩ results from the 6:1 reaction of I
with CoCl2 while [Pt{N(H)SPh2}Cl(PMe2Ph)2][BF4] can be isolated
from the reaction of I with [PtCl2(PMe2Ph)2] and [NH4][BF4]. Details
of such reactions will be published in due course.
J. Chem. Soc., Dalton Trans., 1997, Pages 2853–2854
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interconverting in solution goes, we have been able to show that
pure crystalline 1a can be redissolved and used to generate crys-
talline 1b; indeed in such situations it is common to obtain a
mixture of intergrown crystals of both forms. As for ascertain-
ing the ability of 1b to generate 1a this has been made harder to
prove by the limited amounts of the former at our disposal
(crystallisation of 1b only occurs from relatively dilute solu-
tions, precluding the isolation of much more than 5–10 mg
from any one batch). We can say, however, that slow evapor-
ation of a solution of 1b does not seem to yield any blue crys-
tals of 1a, and that the UV/VIS spectrum of such a solution
lacks a band (λmax 385 nm, εmol = 1700 molϪ1 dm3 cmϪ1) that
appears in solutions of 1a [note that an additional band at λmax
235 nm (εmol 15 000) is common to both while a broad d–d band
centred on 730 nm in 1a envelopes the area covered by a sharper
band at 620 nm in solutions of 1b]. Both these observations
leave open the possibility that 1b could be the most thermo-
dynamically stable of the two forms and that, once formed, it
cannot regenerate 1a. We hope that future work will shed more
light on this question.
Fig. 2 Crystal structure of complex 1b. Selected bond distances (Å)
and angles (Њ): Cu᎐N(1) 1.932(8), Cu᎐N(2) 1.919(8), Cu᎐Cl(1) 2.280(2),
Cu᎐Cl(2) 2.284(2), N(1)᎐S(1) 1.607(7), N(2)᎐S(2) 1.584(7);
N(1)᎐Cu᎐N(2) 157.6(3), Cl(1)᎐Cu᎐Cl(2) 153.1(1), N(1)᎐Cu᎐Cl(1)
90.5(2), N(1)᎐Cu᎐Cl(2) 96.2(2), N(2)᎐Cu᎐Cl(1) 93.8(2), N(2)᎐Cu᎐Cl(2)
89.9(2), Cu᎐N(1)᎐S(1) 122.9(4), Cu᎐N(2)᎐S(2) 125.4(4)
planar can be quantified by the N(2)᎐Cu᎐N(1) and Cl(1)᎐Cu᎐
Cl(2) angles of 157.6 and 153.1Њ respectively (the corresponding
angles both being precisely 180Њ in 1a). In other respects, how-
ever, there is minimal difference between the two structures;
thus the average Cu᎐N and S᎐N bond lengths in 1b (1.926 and
1.596 Å respectively) compare well with those in 1a (1.911 and
1.582 Å) while the angles at the nitrogens (i.e. S᎐N᎐Cu) are also
similar (125.4Њ in 1b compared to 129Њ in 1a).
In conclusion we can say that the appearance of two
such isomeric forms appears to be unprecedented for a neutral
copper(II) complex. Given that it is likely to be some feature of
I as a ligand that is inducing such effects, it follows that these
results suggest that the ligand properties of the whole family of
sulfimides deserve far more attention than they have so far been
afforded.
The difference in packing arrangements in the two cases
manifests itself in their IR spectra. Thus the ν(N᎐H) stretch in
1b is seen at 3202 cmϪ1, which is some 90 cmϪ1 lower than in 1a,
presumably reflecting the fact that the N᎐H bond is now free to
interact with Cu᎐Cl bonds of neighbouring molecules (the
closest such H ؒ ؒ ؒ Cl approach being 2.68 Å in 1b compared to
6.26 Å in 1a; both have, of course, some degree of intra-
molecular interaction, with H ؒ ؒ ؒ Cl distances of 2.65 and 2.68
Å for 1a and 1b respectively).
References
1 Comprehensive Coordination Chemistry, ed. G. Wilkinson, Pergamon
Press, Oxford, 1987, vol. 5.
2 P. F. Kelly, A. M. Z. Slawin and A. Soriano-Rama, J. Chem. Soc.,
Dalton Trans., 1996, 53.
3 T. L. Gilchrist and C. J. Moody, Chem. Rev., 1977, 77, 409.
4 R. E. Cramer, K. A. N. S. Ariyaratne and J. W. Gilje, Z. Anorg. Allg.
Chem., 1995, 621, 1856.
5 TEXSAN, Crystal Structure Analysis Package, Molecular Structure
Corporation, Houston, TX, 1985, 1992.
The two forms of complex 1 do not interconvert in the solid
state at room temperature and melt at effectively the same
temperature (157 ЊC) decomposing in the process. As far as
Received 18th June 1997; Communication 7/04276K
2854
J. Chem. Soc., Dalton Trans., 1997, Pages 2853–2854