Prenucleation and coalescence of cobalt nanoclusters mediated by multivalent calixarene complexes

Article abstract of DOI:10.1039/b903954f

The formation of cobalt nanoclusters from polynuclear Co-alkyne species can be directed by multivalent calixarene ligands; thermochemical studies of Co_n-calixarenes reveal the influence of multivalency in prenucleation and postnuclear growth processes.

Full text of DOI:10.1039/b903954f

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Prenucleation and coalescence of cobalt nanoclusters mediated
by multivalent calixarene complexeswz
Jie Liu and Alexander Wei*
Received (in Austin, TX, USA) 25th February 2009, Accepted 26th May 2009
First published as an Advance Article on the web 9th June 2009
DOI: 10.1039/b903954f
The formation of cobalt nanoclusters from polynuclear
Co–alkyne species can be directed by multivalent calixarene
self-condensation into nanoclusters, but with stricter limits
on postnuclear growth relative to more reactive (and less
discriminate) monovalent precursors.
n
ligands; thermochemical studies of Co –calixarenes reveal the
influence of multivalency in prenucleation and postnuclear
growth processes.
In this communication we examine the effect of multi-
valency on the kinetics of nanoparticle growth. Co nano-
clusters are generated from Co –alkyne or Co –alkyne species,
2
4
Inorganic and organometallic precursors for metal nano-
particle synthesis tend to be simple compounds, perhaps for
using the octapropargyl ether of C1 resorcinarene (1) or
propargyl phenyl ether (PPE) as multivalent or monovalent
ligands, respectively (Scheme 1). The thermal decomposition
of metal carbonyls has been widely used in the synthesis of Co
nanoparticles, but optimization of size and shape control is
typically developed by experimenting with reaction conditions
1
practical reasons. In most cases, the chemical information
provided by supporting ligands is lost after the nucleation of
precursors into nanoclusters, and are displaced by other
surfactants or reactive species. The early loss of metal–ligand
interactions imposes some limits on our ability to influence
subsequent growth stages. For example, the metallization of
organic nanostructures such as DNA is not conformal but
proceeds stochastically with independent nucleation events
along the chain, followed by coalescence into nanowires with
9
,10
or surfactant stoichiometry.
have previously been employed in metal nanoparticle
While macrocyclic ligands
1
1
syntheses, the results have been variable and not well
correlated with nucleation or growth kinetics. To address this,
we include a thermochemical analysis of organocobalt
precursors to evaluate the effect of multivalency on thermal
activation and postnucleation growth or ripening.
2
roughnesses typically in excess of 5 nm. Metal nanostructures
have been ‘‘templated’’ within confined volumes, such as
3
those supported by inverse micelles, supramolecular gels or
Octapropargyl ether 1 was prepared from tetramethyl-
4
dendrimers, biomolecular nanocapsules, self-organized
5
2 8 4
resorcinarene and treated with Co (CO) or Co (CO)12 to
6
7
block copolymers, and polymer brushes. Most of these cases
do not distinguish nucleation from growth processes, as
nanoparticle formation is already dictated by the local metal
concentration prior to reduction or heat activation.
yield polynuclear Co–alkyne complexes 2 and 3, respectively
(Scheme 1; see ESIz for synthetic details). Addition of
Co
Co
2
8 4
(CO) or Co (CO)12 to PPE yielded the monovalent
n
–alkyne complexes 4 and 5. In the case of polynuclear
(CO) –alkyne units
In our interest to develop synthetic methods for novel
8
magnetic nanostructures, we considered whether kinetic
Co complex 2, the formation of eight Co
was confirmed by elemental analysis and X-ray crystallo-
2
6
growth processes before or after nucleation could be rationally
influenced by a ligand-directed approach. In particular,
multivalent ligands may serve as platforms for cluster
formation but hinder postnucleation growth, resulting instead
in the formation of nanoclusters by coalescence, as idealized in
Fig. 1. This strategy depends on at least two criteria: (i) the
coordinated species will readily decompose into precritical
clusters upon thermal or chemical activation (prenucleation),
and (ii) the metal–ligand interactions are sufficiently robust to
maintain coordination, such that newly formed clusters would
be stabilized by multivalent ‘‘caps.’’ These capped clusters
are expected to have lower reactivity yet are still capable of
graphyy (Fig. 2), by the disappearance of the Csp–H stretch
at 3280 cm by IR spectroscopy, and by a migration in NMR
ꢀ
1
1
2
chemical shift of the Csp–H proton from 2.47 to 5.75 ppm.
The crystal structure of hexadecanuclear complex 2 shows
all Co (CO) –alkyne units to be on the same face of the
2
6
calixarene, and amenable to the prenucleation of zerovalent
Co clusters.
In the case of polynuclear Co–calixarene complex 3,
elemental analysis indicates incomplete saturation with a mean
of 5 Co
units per molecule. IR spectroscopy indicates a strong
4
ꢀ1
band centered at 1868 cm , a signature peak for bridging CO
1
3
ligands in Co –alkyne species, as well as the absence of free
4
alkynes. This suggests that one or more Co clusters in 3 may
4
be chelated by two propargyl ligands or possibly split into
Purdue University, Department of Chemistry, West Lafayette, IN,
USA. E-mail: alexwei@purdue.edu; Fax: +1 765 4940239;
Tel: +1 765 4945257
w Dedicated to Professor Seiji Shinkai on the occasion of his 65th
birthday.
z Electronic supplementary information (ESI) available: Synthesis and
chemical characterization of 1–5, conditions for thermogravimetric
analysis and nanocluster synthesis, and particle size analyses for Fig. 5.
CCDC 722503. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b903954f
Fig. 1 (a) Multivalent metal–ligand complex; (b) prenucleation of
capped cluster; (c) coalescence into nanocluster.
4
254 | Chem. Commun., 2009, 4254–4256
This journal is ꢁc The Royal Society of Chemistry 2009

View Article Online
decarbonylation for the former below 175 1C but a greater rate
of weight loss for the latter at higher temperatures, in
1
accordance with some earlier observations. Furthermore,
7
the thermal decomposition of multivalent Co –calixarenes 2
n
and 3 (Fig. 3a and c) is retarded relative to monovalent
Co –PPE species 4 and 5 (Fig. 3b and d), requiring tempera-
n
tures above 300 1C for complete decarbonylation.z We
attribute this to differences in the stability of the surface
ligands around the nascent Co clusters: monovalent PPE is
prone to surface migration which contributes to autocatalytic
1
0b,c
decarbonylation,
whereas the multivalent calixarenes are
less mobile and present a barrier to metal polycondensation.
The effect of multivalency on the thermolysis of Co–alkyne
complexes into Co nanoclusters was first evaluated by heating
deaerated solutions of 2–5 in o-dichlorobenzene (ODCB) at a
constant atom molarity ([Co] = 28 mmol), in the presence of
oleic acid.8 These solutions were maintained at reflux (182 1C)
for at least 25 min to ensure complete consumption of the
organocobalt precursors. Thermal decomposition occurred
rapidly in all cases as indicated by the immediate blackening
of the reaction mixture, but size analysis by transmission
electron microscopy (TEM) indicated significant differences
in particle size distributions (Fig. 4). The mean diameter of the
nanoclusters generated from Co16–calixarene 2 was 4.1 nm,
Scheme 1 C1 resorcinarene octapropargyl ether 1, Co-calixarene
complexes 2 and 3, and Co–PPE complexes 4 and 5.
whereas that produced from Co –PPE 4 at the same Co
2
concentration was 6.3 nm (see ESIz for details). Similarly,
the diameter of nanoclusters from Co –calixarene 3 (n E 20)
was 6.5 nm, whereas that produced from Co –PPE 5 was
4
n
Fig. 2 X-Ray crystal structure of Co16–calixarene complex 2: (a) side
view; (b) top view. For clarity, hydrogen atoms are omitted and cobalt
atoms are enlarged. Co = violet; O = yellow.
9
.8 nm. Differences in particle size distributions from
Co –alkyne versus Co –alkyne precursors (i.e. 2 vs. 3, and
4
2
Co –alkyne units. The literature does not indicate whether Co
2
4 vs. 5) were also observed. The larger particles from Co –alkyne
4
4
carbonyl clusters can form stable complexes with multiple
1
species 3 and 5 correlate with their longer Co–C bonds and
17
more efficient thermal decomposition.
4,15
alkynes,
alkyne and diynes.
but cluster fission is known to occur with excess
1
6
Thermogravimetric analysis (TGA) of complexes 2–5
reveals significant differences with respect to thermal
stability and multivalency (Fig. 3 and ESIz). A comparison
2 4
of Co –alkyne complexes (Fig. 3a and b) with Co –alkyne
complexes (Fig. 3c and d) indicates an initially higher rate of
Fig. 4 TEM images (Philips CM-10, 80 kV) of metal nanoclusters
produced by the thermolysis of Co–alkyne complexes in ODCB, using
equal amounts of Co: (a) Co16–calixarene 2 (4.1 ꢂ 0.9 nm);
Fig. 3 TGA (relative weight loss and first derivative) of (a) Co16
calixarene 2, (b) Co –PPE 4, (c) Co –calixarene 3 (n E 20), and
d) Co –PPE 5. Weight loss corresponding to complete decarbonylation
–
2
n
(b) Co
(d) Co
2
–PPE 4 (6.5 ꢂ 1.0 nm); (c) Co20–calixarene 3 (6.3 ꢂ 1.0 nm);
–PPE 5 (9.8 ꢂ 1.6 nm). Size analysis based on a minimum of
(
4
4
represented by dashed lines.
100 particles per image; scale bar = 50 nm.
This journal is ꢁc The Royal Society of Chemistry 2009
Chem. Commun., 2009, 4254–4256 | 4255

View Article Online
H. Nir, S. Tal, Y. Eichen and T. Carell, J. Am. Chem. Soc., 2006,
1
28, 1398.
3
4
(a) M. Gobe, K. Kon-no, K. Kandori and A. Kitahara, J. Colloid
Interface Sci., 1983, 93, 293; (b) S. H. Sun and C. B. Murray,
J. Appl. Phys., 1999, 85, 4325; (c) C. Petit, A. Taleb and
M. P. Pileni, J. Phys. Chem. B, 1999, 103, 1805;
(
d) J. P. Wilcoxon, J. E. Martin and P. Provencio, Langmuir,
000, 16, 9912; (e) F. S. Diana, S.-H. Lee, P. M. Petroff and
E. J. Kramer, Nano Lett., 2003, 3, 891.
2
(a) Y. H. Niu, L. K. Yeung and R. M. Crooks, J. Am. Chem. Soc.,
2
001, 123, 6840; (b) M.-K. Kim, Y.-M. Jeon, W. S. Jeon,
H.-J. Kim, S. G. Hong, C. G. Park and K. Kim, Chem. Commun.,
001, 667; (c) Y. Wang, J. Yang, Z. Zheng, M. D. Carducci, J. Jiao
and S. Seraphin, Angew. Chem., Int. Ed., 2001, 40, 549;
d) C. S. Love, V. Chechik, D. K. Smith, K. Wilson, I. Ashworth
and C. Brennan, Chem. Commun., 2005, 1971.
(a) T. Douglas, D. P. E. Dickson, S. Betteridge, J. Charnock,
C. D. Garner and S. Mann, Science, 1995, 269, 54;
2
Fig. 5 Semilog plot of Co nanocluster sizes as a function of time,
following rapid injection of Co16–calixarene 2 (K) or Co –PPE 4 (&)
2
(
into hot ODCB ([Co] = 28 mmol). See ESIz for particle size analysis.
5
6
Rapid injection of Co–alkyne complexes into preheated
ODCB solutions containing oleic acid8 yielded Co nano-
clusters with similar size distributions as above, and provided
an opportunity to further examine the influence of ligand
multivalency on particle size. Both Co16–calixarene 2 and
(
b) H. Yoshimura, Colloids Surf., A, 2006, 282–283, 464.
(a) J. P. Spatz, T. Herzog, S. Mossmer, P. Ziemann and M. Mo
Adv. Mater., 1999, 11, 149; (b) T. Thurn-Albrecht, J. Schotter,
G. A. Kastle, N. Emley, T. Shibauchi, L. Krusin-Elbaum,
K. Guarini, C. T. Black, M. T. Tuominen and T. P. Russell, Science,
¨
ller,
¨
2
000, 290, 2126; (c) W. A. Lopes and H. M. Jaeger, Nature, 2001, 414,
35; (d) L. A. Miinea, L. B. Sessions, K. D. Ericson, D. S. Glueck and
2
Co –PPE 4 yielded Co nanoclusters within the first 2 minutes
7
R. G. Grubbs, Macromolecules, 2004, 37, 8967.
after injection, but the initial size of the former was smaller
and changed little over time, whereas the latter experienced
significant postnuclear growth (Fig. 5 and ESIz). The
essentially invariant size of nanoclusters produced from 2
implies that calixarene 1 stabilizes the Co nanoclusters against
Ostwald ripening and other postnucleation growth processes,
in accordance with the TGA analysis.
7
8
O. Azzaroni, A. A. Brown, N. Cheng, A. Wei, A. M. Jonas and
W. T. S. Huck, J. Mater. Chem., 2007, 17, 3433.
(a) S. L. Tripp, S. V. Pusztay, A. E. Ribbe and A. Wei, J. Am.
Chem. Soc., 2002, 124, 7914; (b) S. L. Tripp, R. E. Dunin-
Borkowski and A. Wei, Angew. Chem., Int. Ed., 2003, 42, 5591;
(
c) T. Kasama, R. E. Dunin-Borkowski, M. R. Scheinfein,
S. L. Tripp, J. Liu and A. Wei, Adv. Mater., 2008, 20, 4248;
d) A. Wei, S. L. Tripp, J. Liu, T. Kasama and R. E. Dunin-
Borkowski, Supramol. Chem., 2009, 21, 189.
9 (a) P. H. Hess and P. H. Parker, Jr, J. Appl. Polym. Sci., 1966, 10,
915; (b) J. R. Thomas, J. Appl. Phys., 1966, 37, 2914;
c) D. P. Dinega and M. G. Bawendi, Angew. Chem., Int. Ed.,
999, 38, 1788; (d) V. F. Puntes, K. M. Krishnan and
(
The controlled thermochemistry of the multivalent
Co–calixarene complexes suggests that their transformation
into stable nanoclusters proceeds by prenucleation into
metastable capped clusters, followed by coalescence. These
results imply that calixarene 1 can also serve as a polyvalent
ligand for Co surfaces, although further studies are needed to
fully define the metal–adsorbate structure. Our comparative
study with monovalent ligands demonstrates that multivalent
species can influence the kinetics of nanocluster growth, both
prior to and after the critical nucleation event.
1
(
1
A. P. Alivisatos, Science, 2001, 291, 2115; (e) V. F. Puntes,
D. Zanchet, C. K. Erdonmez and A. P. Alivisatos, J. Am. Chem.
Soc., 2002, 124, 12874; (f) H. Bo
R. Brinkmann, N. Matoussevitch, N. Waldo
H. Mudrow, Inorg. Chim. Acta, 2003, 350, 617.
10 (a) A. Lagunas, C. Jimeno, D. Font, L. Sola and M. A. Pericas,
`
¨
nnemann, W. Brijoux,
¨
fner, N. Palina and
`
Langmuir, 2006, 22, 3823; (b) R. M. de Silva, V. Palshin,
F. R. Fronczek, J. Hormes and C. S. S. R. Kumar, J. Phys.
Chem. C, 2007, 111, 10320; (c) R. M. de Silva, V. Palshin,
K. M. N. d. Silver, L. L. Henry and C. S. S. R. Kumar,
J. Mater. Chem., 2008, 18, 738.
1 (a) A. V. Nabok, T. Richardson, F. Davis and C. J. M. Stirling,
Langmuir, 1997, 13, 3198; (b) X.-M. Li, M. R. de Jong, K. Inoue,
S. Shinkai, J. Huskens and D. N. Reinhoudt, J. Mater. Chem., 2001,
The authors gratefully acknowledge the National Science
Foundation (CHE-0243496) for financial support, Dr Philip
Fanwick for X-ray crystallographic analysis, Dr Daniel Lee
for microanalysis, and Clancy Kadrmas for assistance with
thermogravimetric analysis.
1
11, 1919; (c) J. Liu, J. Alvarez, W. Ong, E. Roman and A. E. Kaifer,
´
Langmuir, 2001, 17, 6762; (d) J. Liu, W. Ong and A. E. Kaifer,
Langmuir, 2002, 18, 5981; (e) L. Li, X. Sun, Y. Yang, N. Guan and
F. Zhang, Chem.–Asian J., 2006, 1, 664; (f) V. Huc and K. Pelzer,
J. Colloid Interface Sci., 2008, 318, 1; (g) Y. Sun, C. G. Yan, Y. Yao,
Y. Han and M. Shen, Adv. Funct. Mater., 2008, 18, 3981.
2 B. Happ, T. Bartik, C. Zucchi, M. C. Rossi, F. Ghelfi, G. Palyi,
G. Varadi, G. Szalontai, I. T. Horvath, A. Chiesivilla and
C. Guastini, Organometallics, 1995, 14, 809.
Notes and references
y X-Ray structural analysis (CCDC 722503) was performed using
MoK radiation on a Nonius KappaCCD, equipped with a graphite
a
crystal and incident beam monochromator.
z Additional mass loss for 4 and 5 (above 300 1C) is likely associated
with PPE and its byproducts; see ref. 12 for examples.
1
8
Oleic acid is widely used as a supporting surfactant in the synthesis
1
3 G. Gervasio, R. Rossetti and P. L. Stanghellini, Organometallics,
1
of Co nanoparticles, and can assist the initial decarbonylation. The
resulting nanoparticles are presumably passivated by a mixture of
alkynes and carboxylates.
985, 4, 1612.
1
1
4 M. J. Went, Adv. Organomet. Chem., 1997, 41, 69.
5 P. Chini and B. T. Heaton, Top. Curr. Chem., Springer-Verlag,
Berlin, 1977, vol. 71, pp. 3–70.
16 (a) K. Kruerke and W. Hubel, Chem. Ber., 1961, 94, 2829;
(b) R. S. Dickson and G. R. Tailby, Aust. J. Chem., 1969, 22, 1143.
17 V. Calvo-Perez, A. Vega C, P. Cortes and E. Spodine, Inorg. Chim.
Acta, 2002, 333, 15.
1
2
Y. Xia, Y. Xiong, B. Lim and S. E. Skrabalak, Angew. Chem., Int.
Ed., 2009, 48, 60.
(a) E. Braun, Y. Eichen, U. Sivan and G. Ben-Yoseph, Nature,
1998, 391, 775; (b) K. Keren, R. S. Berman and E. Braun, Nano
Lett., 2004, 4, 323; (c) G. A. Burley, J. Gierlich, M. R. Mofid,
4
256 | Chem. Commun., 2009, 4254–4256
This journal is ꢁc The Royal Society of Chemistry 2009