Cu(II) assisted self-sorting towards pseudorotaxane formation

Article abstract of DOI:10.1039/c1cc10472a

A new triamino macrocycle shows Cu(II) templated self-sorting of a pseudorotaxane out of sixteen such possibilities from the mixture of nine components of a tridentate, four bidentate ligands and four transition metal ions.

Full text of DOI:10.1039/c1cc10472a

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2011, 47, 6272–6274
www.rsc.org/chemcomm
COMMUNICATION
Cu(II) assisted self-sorting towards pseudorotaxane formationw
Subrata Saha, I. Ravikumar and Pradyut Ghosh*
Received 24th January 2011, Accepted 27th January 2011
DOI: 10.1039/c1cc10472a
A new triamino macrocycle shows Cu(II) templated self-sorting
of a pseudorotaxane out of sixteen such possibilities from the
mixture of nine components of a tridentate, four bidentate
ligands and four transition metal ions.
base with three –NH of L1 and the second CH3CN occupies
the apical position of the distorted square pyramid. The
equatorial CH3CN is bound to the metal ion more strongly
[Cu1–N7, 1.980(12) A] compared to the apical one [Cu1–N6,
2.232 (12) A]. These coordinated solvent molecules could
easily be replaced by other monodentate or bidentate ligands.
In this context we have chosen four bidentate ligands,
1,10-phenanthroline (L2), 2,9-dimethyl-1,10-phenanthroline
(L3) 2,20-bipyridine (L4) and 6,60-dimethylbipyridine (L5), for
syntheses of Cu2+ templated ternary complexes possibly via
pseudorotaxane formation. Complexes 2–5 were isolated in
solid form upon reaction of L1, Cu2+ and L2/L3/L4/L5
respectively in a methanol/CH2Cl2 binary mixture. The electro-
spray ionisation mass spectrum (ESI-MS) of complexes 2–5
support the formulation of [Cu(L1)(X)(ClO4)]+, X = L2, L3,
L4 and L5 for complexes 2–5, respectively (Fig. 2).
One of the most important aspects of self-assembly is the
formation of interpenetrated molecules like rotaxanes, pseudo-
rotaxanes, catenanes etc. for their potential applications in the
area of molecular devices.1–5 Self-assembly and self-sorting of
more than two components demands selectivity.6–10 It is
challenging to develop an artificial set of molecules which
can generate a self-assembled structure from a complex mix-
ture of multiple components.11 In a proof-of-concept experi-
ment, we have demonstrated that a newly synthesized triamino
macrocycle (L1) and Cu2+ selectively form a pseudorotaxane
with 1,10-phenanthroline (L2) over 2,9-dimethyl-1,10-phenan-
throline (L3) 2,20-bipyridine (L4), and 6,60-dimethylbipyridine
(L5) whereas the combination of L1 and L2 selectively bind
with Cu2+ over Co2+, Ni2+, Zn2+. Further, we show selective
formation of the pseudorotaxane from a mixture of L1–L5 and
Co2+, Cu2+, Ni2+, Zn2+. To the best of our knowledge this
represents the first example of Cu(II) assisted self-sorting
towards the formation of a pseudorotaxane from a mixture
of multiple components.
Solution state UV/Vis experiments were carried out to
follow the formation of ternary complexes among L1, Cu2+
and each one of L1–L5 (Fig. 16S, ESIw). For these four
combinations UV/Vis spectra showed broad absorption bands
at 670, 632, 665 and 634 nm upon addition of 1 : 1 : 1 of
equimolar solution of L1, Cu2+ and L2/L3/L4/L5 solution,
respectively. In all four complexes red shifted absorption
spectra are obtained compared to the absorption band at
620 nm for (1 : 1) L1 and Cu2+ under the same experimental
conditions. Observed red shifts of the d–d bands in these
complexes are in good agreement with the ligand field
strengths. Additionally the X-band EPR spectraw in acetonitrile
solution of all the complexes show very similar patterns with
gJ > g> indicating dx2–y2 ground states with distorted square
A new macrocycle, L1 (Fig. 1a) having a tridentate amine
chelating binding site and two amide functionalities was
synthesized in good yield (ESIw). The UV/Vis spectrum of
L1 with Cu2+ (1 : 1 complex) in methanol shows a distin-
guishable absorption band at 620 nm (e = 127 Mꢀ1 cmꢀ1
)
corresponds to the d–d transition and titration of L1 with
Cu2+ shows 1 : 1 binding in solution (Fig. 11Sw). Crystals of
the Cu2+ complex of L1 (1) suitable for single crystal X-ray
study were obtained by slow evaporation of an acetonitrile
(CH3CN) solution of L1 and Cu(ClO4)2ꢁ6(H2O). Detailed
structural analysis of 1 reveals that Cu2+ is in penta coordina-
tion with the three –NH groups of L1 and two nitrogen atoms
from CH3CN (Fig. 1b and c).z The coordination geometry
around copper(II) is distorted square pyramidal (t = 0.2).12
The N-atom of one of the two CH3CN completes the square
Department of Inorganic Chemistry, Indian Association for the
Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata
700 023, India. E-mail: icpg@iacs.res.in
w Electronic supplementary information (ESI) available: Experimental
details. CCDC 783143 (1) and 783144 (2). For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c1cc10472a
Fig. 1 (a) L1, (b) single crystal X-ray structure of 1 and (c) distorted
square pyramidal representation of Cu centre. H atoms in 1 are
omitted for clarity.
c
6272 Chem. Commun., 2011, 47, 6272–6274
This journal is The Royal Society of Chemistry 2011

View Article Online
Scheme 2 Sixteen possible ternary complexes of L1 with all other
components (L2–L5) and Co2+, Ni2+, Cu2+ and Zn2+
.
Fig. 2 ESI mass spectra of complexes 2–5.
formation of ternary complex 2 out of these seven possible
ternary complexes.
pyramidal geometry. All of these results suggest threading of
bidentate ligands in the cavity of L1 to form ternary complexes
When an equimolar solution of L2, L3, L4, L5 in a methanol/
CH2Cl2 binary mixture was added to an equimolar mixture
of L1, Co2+, Ni2+, Cu2+ and Zn2+ and stirred at RT, a blue
precipitate developed after 4 h. ESI-MS of the collected
precipitate shows a peak corresponding to [Cu(L1)(L2)(ClO4)]+
of the ternary complex 2 whereas no peaks corresponding to
other possible ternary complexes involving macrocycle L1 are
observed (Fig. 17S)w. It is important to mention that in the
mixtures as many as 16 ternary complexes are possible with L1
(Scheme 2). Thus L1 selectively picks up Cu2+ and L2 from the
mixture to form the ternary complex 2.
of Cu2+
.
To investigate the selective formation of a ternary complex
we carried out complexation studies of equimolar amounts of
L1 and Cu2+ in a methanol/CH2Cl2 binary mixture in the
presence of all bidentate ligands, L2–L5 (each at same molar
amounts to that of L1) following path a (Scheme 1). The blue
solid was isolated and characterized by ESI-MS as well as UV/
Vis spectroscopic studies. Both studies support the formation
of complex 2 from the mixtures. Thus this result reveals the
preferential formation of ternary complex 2 from the mixture
of six components. We performed another experiment to
understand the selectivity toward Cu2+ by L1 and L2 over
transition metal ions with common stable oxidation numbers
(Co2+, Ni2+, Cu2+, Zn2+) following path b (Scheme 1).
Equimolar amounts of L1, L2 and all four metal ions were
stirred for 4 h in a methanol/CH2Cl2 binary mixture at room
temperature; the precipitate was characterized by UV/Vis,
ESI-MS and energy dispersion X-ray (EDX) studies. The
EDX spectrum (Fig. 27S)w shows only the presence of copper
ions, and no peaks for other metal ions. Further spectroscopic
studies confirm the formation of complex 2 in pure form.
Considering paths a and b in Scheme 1, formation of a number
of ternary complexes is possible which is shown in
Scheme 2Sw. Thus our studies clearly show the selective
Solution state selective formation of [Cu(L1)(L2)(ClO4)]+ is
established by ESI-MS analysis of clear solutions obtained from
all combinations described in the above three precipitate isolation
processes by using low concentrations of ligands and metal ions
in methanol. In all three cases, ESI-MS of the resulting clear
solutions showed selective formation of the ternary complex that
corresponds to [L1ꢁL2ꢁCuꢁClO4]+ (Fig. 18S–20S)w.
The above studies show selective formation of ternary
complex 2 from mixtures of different components. Thus we
have carried out detailed studies on the formation of 2 in the
solution and solid states. The UV/Vis titration of an equimolar
mixture of L1, L2 with Cu2+ shows 1 : 1 : 1 ternary complexation
(Fig. 28S)w. We also carried out ternary complexation studies
in a step-wise manner. First we titrated L1 with Cu2+ which
showed 1 : 1 complex formation (as shown in Fig. 11S)w; then we
titrated the complex with L2 in methanol as shown in Fig. 3.
Fig. 3 UV/Vis titration profile of L1 + Cu2+ (5 ꢂ 10ꢀ3 M) with
aliquots of L2 (5 ꢂ 10ꢀ3 M) in methanol. Selected UV-Vis spectra are
shown for clarity whereas sigmoidal fits show more points.
Scheme 1 Selective formation of one ternary complex from mixtures
of analogous third components by path (a) and (b).
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6272–6274 6273

View Article Online
crystal X-ray facility at the department of Inorganic
Chemistry, IACS.
Notes and references
z Crystallographic data for: 1: C34 H42 Cl2 Cu N7 O13, M = 889.17,
monoclinic, space group P2(1)/c , a = 9.328(2), b = 29.816(6),
c = 15.503(3) A, b = 109.638(10), V = 4061.0(14) Aꢀ3, rcalcd
=
1.454 g cmꢀ3, Z = 4, rcal = 1.454 g cmꢀ3, Z = 4, l = 0.71073 A, T =
100(2) K, 14 451 reflections, 2890 independent (Rint = 0.1059), and
1667 observed reflections [I Z 2s(I)], 516 refined parameters, R =
0.0609, wR2 = 0.1123. Crystallographic data for: 2: C42H45Cl2-
CuN7O14, M = 991.17, monoclinic, space group P2(1)/c, a =
11.7929(9), b = 11.6986(9), c = 32.650(2) A, b = 97.443(2), V =
4466.4(6) A3, rcal = 1.474 g cmꢀ3, Z = 4, l = 0.71073 A, T = 100(2)
K, 38 647 reflections, 7219 independent (Rint = 0.0363), and 5446
observed reflections [I Z 2s(I)], 589 refined parameters, R = 0.0591,
wR2 = 0.1660.
Fig. 4 (a) Single crystal X-ray structure of 2 with disordered
diethylene triamine moieties in two positions. One set of disordered
diethylene triamine is shown whereas H atoms and counter anions
along with lattice water molecules are omitted for clarity. (b) Space-
filling model of (a).
1 (a) J. J. Gassensmith, J. M. Baumes and B. D. Smith, Chem.
Commun., 2009, 6329; (b) Z. Niu and H. W. Gibson, Chem.
Rev., 2009, 109, 6024; (c) G. Wenz, B.-H. Han and A. Mueller,
Chem. Rev., 2006, 106, 782; (d) F. Huang and H. W. Gibson,
Prog. Polym. Sci., 2005, 30, 982; (e) J.-P. Collin, V. Heitz and
J.-P. Sauvage, Top. Curr. Chem., 2005, 262, 26; (f) T. Takata,
N. Kihara and Y. Furusho, Adv. Polym. Sci., 2004, 171, 1;
As a result the absorption band of the Cu2+–L1 complex at
620 nm shifted to 670 nm, indicating the complexation of L2
with Cu2+-L1 complex possibly via a threading mechanism to
form a pseudorotaxane that supports 1 : 1 : 1 complexation of
(g) C. Dietrich-Buchecker and J.
A
P Sauvage, Catenanes,
Rotaxanes and Knots. Journey Through the World of
L1 : L2 : Cu2+
.
Molecular Topology, Wiley-VCH, Weinheim, Germany, 1999;
(h) D. B. Amabilino and J. F. Stoddart, Chem. Rev., 1995, 95,
2725; (i) G. Schill, Catenanes, Rotaxanes and Knots, Academic
Press, New York, 1971.
2 (a) J. D. Crowley, S. M. Goldup, A.-L. Lee, D. A. Leigh and
R. T. McBurney, Chem. Soc. Rev., 2009, 38, 1530; (b) M. S. Vickers
and P. D. Beer, Chem. Soc. Rev., 2007, 36, 211; (c) R. Jager and
Single crystals of complex 2 suitable for X-ray analysis were
obtained upon slow evaporation of acetonitrile solutions at
RT. The single crystal X-ray structure of 2 shows involvement
of L1, L2, and Cu2+ in the complex (Fig. 4) and confirms the
coordination geometry where three of its coordination site are
attached to –NH of L1 and the other two are coordinated with
nitrogen centers of L2.z It is important to mention that L2 is
coordinated to the metal center to satisfy the coordination
number via threading of L1. This confirms the formation of a
Cu2+ templated pseudorotaxane assembly from L1 and L2.
Other than coordination number and geometry, the driving
force for threading in complex 2 could be p–p stacking
between the two phenyl rings of L1 and arene moiety of the
L2 which is evident from the distance between Cg1ꢁ ꢁ ꢁCg3
(Cg1: centroid of ring C11–C15 and Cg3: centroid of ring
C34–C49), and Cg2ꢁ ꢁ ꢁCg3 (Cg2: centroid of ring C22–C27)
are 3.568 A and 3.567 A, respectively (Fig. 4a).
F. Vogtle, Angew. Chem., Int. Ed. Engl., 1997, 36, 930.
¨
3 (a) S. M. Goldup, D. A. Leigh, T. Long, P. R. McGonigal,
M. D. Symes and J. Wu, J. Am. Chem. Soc., 2009, 131, 15924;
(b) J. A. Wisner, P. D. Beer, N. G. Berry and B. Tomapatanaget,
Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 4983.
4 J.-P. Collin, C. O. Dietrich-Buchecker, P. Gavina, M. C. Jiminez-
Molero and J.-P. Sauvage, Acc. Chem. Res., 2001, 34, 477.
5 (a) V. Balzani, A. Credi and M. Venturi, Molecular Devices and
Machines—Concepts and Perspectives for the Nanoworld, Wiley-
VCH,Weinheim, 2008; (b) M. S. Vickers and P. D. Beer, Chem.
Soc. Rev., 2007, 36, 211; (c) T. Hoshino, M. Miyauchi,
Y. Kawaguchi, H. Yamaguchi and A. Harada, J. Am. Chem.
Soc., 2000, 122, 9876.
6 (a) S. Ulrich and J.-M. Lehn, J. Am. Chem. Soc., 2009, 131, 5546;
(b) M. Barboiu, F. Dumitru, Y.-M. Legrand, E. Petit and A. van
der Lee, Chem. Commun., 2009, 2192.
7 (a) Y. Rudzevich, V. Rudzevich, F. Klautzsch, C. A. Schalley and
V. Bohmer, Angew. Chem., Int. Ed., 2009, 48, 3867;
(b) S. J. Rowan, D. G. Hamilton, P. A. Brady and J. K.
M. Sanders, J. Am. Chem. Soc., 1997, 119, 2578.
8 (a) D. Schultz and J. R. Nitschke, Proc. Natl. Acad. Sci., U. S. A.,
2005, 102, 4763; (b) B. H. Northrop, Y. R. Zheng, K. W. Chi and
P. J. Stang, Acc. Chem. Res., 2009, 42, 1554.
Thus, selective formation of 2 could be attributed to the
suitable coordination sites and geometry of Cu2+ in the cavity
of L1 over other metal ions whereas preferences of L2 over
other bidentate ligands L3–L5 could be due to the resultant of
the steric effect as well as p–p stacking interactions.
In summary, we have demonstrated a copper(II) templated
co-ordination driven by self-sorting of a pseudorotaxane by a
new triamino macrocycle and phenanthroline. This proof-of-
concept strategy of selective formation of one complex from a
common pool of other subcomponents could be extended in
the area of self-sorting of complex mixtures in general. Selec-
tive formation of threaded complexes has an immense utility in
the construction of new interlocked systems like rotaxanes and
catenanes towards the development of metal driven molecular
machines.
9 (a) S. Liu, C. Ruspic, P. Mukhopadhyay, S. Chakrabarti,
P. Zavalij and L. Isaacs, J. Am. Chem. Soc., 2005, 127, 15959;
(b) D. Schultz and J. R. Nitschke, Angew. Chem., Int. Ed., 2006, 45,
2453.
10 (a) K. Parimal, E. H. Witlicki and A. H. Flood, Angew. Chem., Int.
Ed., 2010, 49, 4628; (b) K. Ghosh, H.-B. Yang, B. H. Northrop,
M. M. Lyndon, Y.-R. Zheng, D. C. Muddiman and P. J. Stang,
J. Am. Chem. Soc., 2008, 130, 5320; (c) W. Jiang, A. Schafer,
P. C. Mohr and C. A. Schalley, J. Am. Chem. Soc., 2010, 132, 2309.
11 (a) W. Jiang, H. D. F. Winkler and C. A. Schalley, J. Am. Chem.
Soc., 2008, 130, 13852; (b) K. Mahata and M. Schmittel, J. Am.
Chem. Soc., 2009, 131, 16544; (c) W. Jiang and C. A. Schalley,
Proc. Natl. Acad. Sci. U. S. A., 2009, 106, 10425; (d) M. Schmittel
and K. Mahata, Chem. Commun., 2010, 46, 4163.
SS acknowledges CSIR for a JRF. PG gratefully thanks
DST for financial support. X-ray diffraction of complexes 1
and 2 was performed in the DST funded National single
12 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and
G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349.
c
6274 Chem. Commun., 2011, 47, 6272–6274
This journal is The Royal Society of Chemistry 2011