Fig. 1 The structure of [Cu2L2(SO4)]2ϩ, cation of (4) in the solid-state
(H atoms have been removed for clarity). Atom disorder of approx.
50% was modelled for two atoms in one of the hexyl chains, the
encapsulated sulfate anion and one tert-butyl group. Selected bond
lengths (Å) and angles (Њ): Cu(1)–O(1A) 1.901(4), Cu(1)–O(1B)
1.899(4), Cu(1)–N(2A) 2.026(5), Cu(1)–N(2B) 2.083(5), Cu(1)–O(1S)
2.165(4), Cu(2)–O(1D) 1.870(5), Cu(2)–O(1C) 1.880(5), Cu(2)–N(2D)
2.064(5), Cu(2)–N(2C) 2.066(5), Cu(2)–O(2S) 2.188(10), Cu(2)–O(2SЈ)
2.305(8); O(1A)–Cu(1)–N(2A) 91.5 (2), O(1B)–Cu(1)–N(2B) 91.3(2),
O(1C)–Cu(2)–N(2D) 91.7(2), O(1D)–Cu(2)–N(2C) 92.7(2).
Fig. 2 Molecular structure of [Cu2L2(BF4)]3ϩ, cation of (5) (H atoms
have been removed for clarity). Selected bond lengths (Å) and angles (Њ):
Cu(1)–O(1A) 1.891(5), Cu(1)–O(1B) 1.903(5), Cu(1)–N(2B) 1.993(6),
Cu(1)–N(2A) 1.993(6), Cu(2)–O(1D) 1.898(4), Cu(2)–O(1C) 1.908(4),
Cu(2)–N(2D) 2.000(5), Cu(2)–N(2C) 2.003(5); O(1A)–Cu(1)–N(2A)
94.4(2), O(1B)–Cu(1)–N(2B) 92.9(2), O(1C)–Cu(2)–N(2D) 94.0(2),
O(1D)–Cu(2)–N(2C) 93.1(2).
Each copper atom has a distorted trigonal-bipyramidal
coordination environment, with the O(phenolate)–Cu–
O(phenolate) angles approximately linear (173 and 170Њ).
The equatorial Cu–N(imine) (2.026–2.083 Å) and the some-
what longer Cu–O(sulfate) bonds (2.165 and 2.188 Å)
complete the distorted D3h symmetry (av. 119.7Њ). The
encapsulated sulfate anion occupies a cavity that can be
thought of as a cylinder with a height of 6.4 Å (Cu ؒ ؒ ؒ Cu)
and a diameter of 7.7 Å (N ؒ ؒ ؒ N) giving an approximate
volume of 300 Å3.
The ligand architecture is similar in the related tricationic
tetrafluoroborate complex¶ [Cu2L2(BF4)]3ϩ of (5), but the
Ϫ
encapsulated BF4 is not coordinated to the copper atoms
2Ϫ
which have tetrahedrally distorted “planar” trans-N2O2
Ϫ
donor sets (Fig. 2). The encapsulated BF4 anion forms
H-bonds with the alkyl ammonium protons, but these are
weaker (N ؒ ؒ ؒ F = 2.890–3.579 Å) than in the sulfate complex
as would be expected. The volume of the “cylindrical” cavity is
larger (330 Å3).
Fig. 3 Comparison of the UV/Vis spectra of the Cu() complexes 4, 5
and 6 in methanol (20 ЊC, 1 mmol).
Ϫ
Ϫ
The UV/Vis spectra of the BF4 and ClO4 complexes in
methanol (Fig. 3) are very similar, in accordance with the solid
state structure of [Cu2L2(BF4)]3ϩ which suggests only a very
weak interaction of the anion with the copper centres. There
are small but significant differences in the spectrum of the
Notes and references
† Prepared by an adaption of the method of Fenton and coworkers.9
‡ Satisfactory C, H, N, analysis was obtained for [Cu2L2(SO4)]SO4
4 (expected: C, 63.3; H, 7.0; N, 6.7. Found: C, 63.2; H, 7.0; N, 6.7%),
[Cu2L2(BF4)](BF4)3ؒ2H2O 5ؒ2H2O (expected: C, 56.8; H, 6.5; N, 6.0.
Found: C, 57.0; H, 6.2; N, 5.8%) and [Cu2L2(ClO4)](ClO4)3ؒ2H2O
6ؒ2H2O (expected: C, 55.3; H, 6.3; N, 5.8. Found: C, 55.3; H, 6.0; N,
5.4%).
§ Diffusion of diisopropyl ether vapours into a saturated methanol
solution of 4 produced green plate crystals suitable for X-ray diffrac-
tion. The structure was solved by Patterson methods (DIRDIF)10 and
refined against F 2 (SHELXL-97).11 Crystal data for 4: C88H116N8O-
12Cu2S2, M = 1669.1, orthorhombic, space group Pbca, a = 16.980(3),
b = 25.614(5), c = 48.948(10) Å, V = 21289(7) Å3, Z = 8, Dc = 1.042 g
cmϪ3, µ(Mo-Kα) = 0.491 mmϪ1, 18770 unique reflections measured
(Rint = 0.0735), 1008 parameters, 39 restraint, largest difference peak
1.00 e ÅϪ3, final R1[I > 4σ(I)] = 0.102, ωR2 = 0.320, goodness of fit on
F 2 = 1.008. Diffuse solvent was treated in the manner described by
Van der Sluis and Spek.12 CCDC reference number 191879.
2Ϫ
SO4 complex consistent with a pertubation of the charge
transfer bands of the copper centres by coordinated SO42Ϫ. This
imples that the 2 : 2 : 1 assemblies of Cu : L : anion are
maintained in solution. Further evidence for the stability of
the assemblies is obtained from FAB mass spectrometry results.
For 4 there are peaks due to the parent ion, [Cu2L2(SO4)]SO4
and for the parent ion less one sulfate. No peaks are seen for the
parent less two sulfate ions, because major fragmentation
results once the central stabilising sulfate is lost from the
assembly.
The coordination chemistry of the “strapped” systems
described above confirms the effectiveness of using ligand
zwitterions to complex metal salts. The ease of synthesis
of such systems from commercial precursors using Mannich
reactions offers the possibility of tuning the selectivity of
anion-complexation by varying the geometry and functionality
of the strap and exploiting the templating role of the metal
cations in the salicylaldimato sites.
¶ Diffusion of diethyl ether vapours into a saturated methanol solution
of 5 produced brown block crystals suitable for X-ray diffraction.
Crystal data for 5ؒ1.5(CH3OH)ؒ1.5(CH3CH2OCH2CH3)ؒ0.625H2O:
C88H116N8O4Cu2B4F16ؒ1.5(CH3OH)ؒ1.5(CH3CH2OCH2CH3)ؒ0.625H2O,
¯
M = 1990.4, triclinic, space group P1, a = 13.636(3), b = 18.598(4),
J. Chem. Soc., Dalton Trans., 2002, 3928–3930
3929