Unexpected Ni(ii) and Cu(ii) polynuclear assemblies - A balance between ligand and metal ion coordination preferences

Article abstract of DOI:10.1039/c0cc00150c

Polytopic ligand design involves matching the coordination pocket composition with the metal ion coordination 'algorithm', but despite targeting [4 × 4] grids as the final outcome, metal ion preferences and ligand control can lead to widely varying complexes in the self-assembly process with Ni(ii) and Cu(ii).

Full text of DOI:10.1039/c0cc00150c

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Unexpected Ni(II) and Cu(II) polynuclear assemblies—a balance between
ligand and metal ion coordination preferencesw
Kontantin V. Shuvaev,a Santokh S. Tandon,b Louise N. Dawea and Laurence K. Thompson*a
Received 26th February 2010, Accepted 7th May 2010
First published as an Advance Article on the web 24th May 2010
DOI: 10.1039/c0cc00150c
Polytopic ligand design involves matching the coordination
pocket composition with the metal ion coordination ‘algorithm’,
but despite targeting [4 ꢀ 4] grids as the final outcome, metal ion
preferences and ligand control can lead to widely varying
complexes in the self-assembly process with Ni(II) and Cu(II).
[4 ꢀ 4] square grids have also been produced with L5,17 and
a comparable tetratopic poly-pyrimidine ligand.18
No examples of Ni16 square grids have yet been reported,
and with L1 the only product obtained is the incomplete spiral
trinuclear complex [Ni3(L1)3(Na)0.15](NO3)6.15 (1), with the
ligands adopting an exo–keto conformation. The Ni(II) ions
have N6 coordination spheres, and only three of the four N6
pockets are occupied, with the fourth partially occupied
by sodium (Fig. S1; ESIw).19,20 This site has inappropriate
dimensions to accommodate the fourth Ni(II) ion. We now
report the isomeric ligand L2, which also produces a spiral
complex, [Ni4(L2)3](ClO4)2ꢁ22H2O (2)z, (Fig. 1), similar to 1,
with the three ligands in their exo–keto form (C–O distances
1.25–1.27 A). However, in this case, all four six-coordinate N6
sites are occupied by metal ions. The central pair of nickel(II)
ions is bridged by three (pyridazine) N2 groups, and the
peripheral pairs of nickel(II) ions are bridged by open chain
diazines. Ni–N distances fall in the range 2.03–2.12 A,
with Ni–Ni distances of 3.68 A for the open chain pairs and
3.62 A for the pyridazine bridged pair. The open chain
Ni–N–N–Ni torsional angles (43.71 ave.) are rather small,
but typical for such triple bridged complexes.21 The apparent
preference of Ni(II) for the N6 coordination spheres with both
L1 and L2, rather than typical m-O bridged arrangements,
appears to be a function of the higher CFSE (crystal field
stabilization energy) demands of Ni(II) compared with Mn(II)
and Cu(II).
Strategies for the convergent self-assembly of 2-dimensional
[n ꢀ n] polymetallic grids rely on the appropriate encoding of
ligand coordination information, to match the ‘coordination
algorithm’ of the metal ion. Ditopic picolinic hydrazone
ligands (Chart S1, ESIw) readily form heteroleptic m-O bridged
square tetranuclear [2 ꢀ 2] grid complexes [M4(m-L)4(L0)4]
(anion)4 (L0 = coordinated anion or solvent) with Mn(II),
Co(II), Ni(II), Cu(II), and Zn(II).1–3 Related tritopic ligands
(Chart S1, ESIw) form homoleptic m-O bridged square nona-
nuclear [3 ꢀ 3] grid complexes [M9(m-L)6](anion)6 with Mn(II),
Cu(II) and Zn(II), but with Ni(II) no examples have yet been
produced.4–7 [2 ꢀ 2] Grids have also been produced with
ditopic pyridazine, pyrimidine and phenolic based ligands
(Cu(I), Cu(II), Co(II), and Zn(II)), and a [3 ꢀ 3] Ag(I) grid with
a tritopic pyridazine ligand.8–12 Tetratopic hydrazone ligands
have been created, based on dinucleating pyridazine and
pyrimidine subunits (L1, L2, L4–L6; Chart 1). L1 has
produced examples of Mn(II)16 and Cu(II)16 heteroleptic
square
4
ꢀ
[2
ꢀ
2] m-O bridged grids exhibiting
intramolecular antiferromagnetic exchange.13–16 Pb(II)16
Variable temperature magnetic data for 2 (Fig. S2; ESIw)
show a maximum in wM indicating intra-molecular anti-
ferromagnetic exchange. Data fitting to a linear exchange
model with a single J value was unsuccessful, but with two
different J values (J1, J2) for the open chain N2 and pyridazine
bridges, respectively (Hex = ꢂJ1{S1ꢁS2 + S3ꢁS4} ꢂ J2{S2ꢁS3}),
a much better fit was obtained.y The solid line in Fig. S2
(ESIw) was calculated for gav. = 2.12, J1 = ꢂ9.0 cmꢂ1, J2 =
ꢂ32 cmꢂ1, TIP (temperature independent paramagnetism) =
P
350 ꢀ 10ꢂ6 cm3 molꢂ1 (102R = 9.4; R = [ (wobs. ꢂ wcalc.)2/
P
wobs.
]
2 1/2). The J2 value (pyridazine bridge) is consistent with
Chart 1
a Department of Chemistry, Memorial University, St. John’s, NL,
A1B 3X7, Canada. E-mail: lk.thompson@mun.ca;
Fax: +1 709-737-3702; Tel: +1 709-737-8750
b Department of Chemistry, Kent State University at Salem, Salem,
Ohio 44440, USA
w Electronic supplementary information (ESI) available: Preparation
of ligands and complexes, eqn S1, Fig. S1–S3, and Charts S1 and S2.
CCDC 775196–775198. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0cc00150c
Fig. 1 Structure of the cation in [Ni4(L2)3](ClO4)2ꢁ22H2O (2) (blue = N,
red = O, and black = C).
ꢃc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 4755–4757 | 4755

View Article Online
values obtained for dinuclear Ni(II) complexes bridged by two
pyridazine groups (J E ꢂ30 cmꢂ1),21–23 while the much
smaller |J1| value is typical of NN diazine bridged systems
with small torsional angles.21
In previous reports the related amidrazone ligand L3 was
shown to produce the comparable linear, spiral tetranuclear
complexes [Cu4(L3)3](BF4)8 (3)24 and [Mn4(L3)3](ClO4)8 (4),14
with MN6 coordination spheres. 4 exhibited both antiferro-
magnetic (pyridazine) and ferromagnetic (open diazine)
exchange. The linear spiral structure is clearly a comfortable
arrangement for a six-coordinate metal ion based on the
proximity of the three contiguous N2 groups in this type of
ligand. Ni(II) complexes with this ligand have so far not been
produced.
Fig. 3 Variable temperature magnetic data for 5 (see text for fitted
parameters).
antiferromagnetic exchange, but with a combination of
disparate J values. There are a number of orbitally orthogonal
Cu–Cu connections in the cluster, associated with the orientations
of the copper ion Jahn–Teller axes, which will not propagate
antiferromagnetic exchange. The core coordination frame-
work (Fig. S3, ESIw) shows just the non-orthogonal magnetic
linkages, and allows the exchange model to be simplified to the
sum of two tetranuclear, one dinuclear and a mononuclear
subunit (Cu1–Cu2–Cu3–Cu4, Cu5–Cu6–Cu7–Cu8, Cu9–Cu10
and Cu11). Two different J values were included, for the
pyridazine/OH (J1) and open diazine (J2) bridges, because
of their general individual similarities. |J1| would be expected
to be c|J2| because of the additional OH bridge and large
Cu–OH–Cu angles (vide supra). Fitting to the corresponding
exchange model (eqn S1, ESIw) gave gav. = 2.12(1), J1 =
ꢂ690(7) cmꢂ1, J2 = ꢂ21(1) cmꢂ1, TIP = 500 ꢀ 10ꢂ6 cm3 molꢂ1
(102R = 2.5) (solid line in Fig. 3).
L4 has bipy end-pieces, creating four contiguous
potentially tridentate pockets. Reaction of L4 with Cu(ClO4)2/
CH3COONa
produced
dark
brown
crystals
of
[(L4)3Cu11(OH)2(CH3COO)4(ClO4)](ClO4)3Na(OH)(H2O)55 (5)z.
The structure of the undeca-nuclear cation is shown in Fig. 2,
revealing an expanded super-triangular motif, with three
ligands spanning the sides of the triangle, and pairs of Cu(II)
ions at the vertices, with the remaining copper ions arranged
along just two of the sides. The ligands adopt exo–keto
conformations, and bind to the corner Cu(II) ions via three
nitrogen atoms (Chart S2, ESIw), creating a strong bipy-like
planar donor array. The fourth N atom comes from the
amidazone nitrogen of the intersecting ligand, which creates
two essentially planar, roughly parallel CuN4 subunits, where
the Cu–Cu axial separations are quite short (3.13–3.23 A). The
pyridazine rings fall on the sides of the super-triangle, and
bridge two Cu(II) ions in two cases, with accompanying
exogenous OH bridges (Cu–OH–Cu bridge angles 122.71,
121.91). However only one Cu(II) ion is bound on the third
side (Cu10), which appears to result from a significant twist in
the ligand backbone (N31–C–C–N33 torsional angle 122.31;
Fig. 2), preventing coordination of the last copper ion
expected in the putative Cu12 structure. A perchlorate ion
(Cl1, Fig. 2) is held within the triangle cavity, associated
axially with Cu2 (Cu2–O 2.7 A). Examination of several
crystalline samples of the complex reveals the same unit cell,
suggesting sample uniformity, in agreement with elemental
analysis.
The demonstrated ability of L5 to produce a Pb(II)16 square
4 ꢀ [2 ꢀ 2] grid17 suggests that L6 would behave similarly.
Reaction of Ni(NO3)2 with L6 produced dark red crystals of
[Ni16(L62ꢂ)8(H2O)15(NO3)](NO3)15(H2O)17 (6)z, which was
shown to be a square 4 ꢀ [2 ꢀ 2] heteroleptic grid complex.
Several crystalline samples (same unit cell) were examined
structurally, but all were found to diffract rather weakly.
Despite a less than satisfactory refinement,z the main fragment
was clearly revealed, indicating the successful synthesis of the
expected grid. A structural representation is given in Fig. 4,
showing the four [2 ꢀ 2] m-O bridged Ni4 square corner
subunits, connected by the pyrimidines in the expected grid
arrangement. Specific comments on dimensions cannot be
made with accuracy, but in general they are comparable with
those observed in the [2 ꢀ 2] m-O bridged Ni4 grids.1 The end
The magnetic properties of 5 show a drop in moment
as temperature is lowered (Fig. 3), with an unusual
change in slope in the 100–300 K range, signalling overall
Fig. 2 Structure of the cation in [(L4)3Cu11(OH)2(CH3COO)4(ClO4)]
(ClO4)3Na(OH)(H2O)55 (5).
Fig.
(NO3)15(H2O)17 (6).
4
Structure of the cation in [Ni16(L62ꢂ)8(H2O)15(NO3)]
ꢃc
This journal is The Royal Society of Chemistry 2010
4756 | Chem. Commun., 2010, 46, 4755–4757

View Article Online
ꢀ
92H179Cl4N36O88Cu11Na, M = 4061.42, P1, a = 18.023(7) A,
C
b
= 20.901(6) A, c = 24.334(7) A, a = 67.954(10)1, b =
78.882(12)1, g = 86.105(14)1, V = 8337(5) A3, T = 135(1) K,
Z = 2, F(000) = 4170, m(Mo-Ka) = 15.48 cmꢂ1, 58 641 reflections,
32 789 unique (Rint = 0.0642), R1 = 0.0735, wR2 = 0.2273.
Crystal data for [Ni16(L62ꢂ)8(H2O)15(NO3)](NO3)15(H2O)17 (6):
ꢀ
C144H176N96O96, M = 5726.76, P1, a = 19.483(6) A, b = 24.701(8) A,
c = 26.510(9) A, a = 111.723(6)1, b = 94.468(6)1, g = 97.249(7)1,
V = 11 649(6) A3, T = 135(1) K, Z = 2, F(000) = 5856, m(Mo-Ka) =
=
13.72 cmꢂ1, 90 389 reflections, 39 271 unique (Rint = 0.0662), R1
0.1299, wR2 = 0.3785.
Fig. 5 Variable temperature magnetic data for 6 scaled to Ni4
y Magnetic data fitting was carried out using MAGMUN4.1;
http://www. ucs.mun.ca/Blthomp/magmun.html. Software developed
by Dr Z. Xu, with algorithms provided by Prof. Dr O. Waldmann
(Univ. of Freiburg).
(see text for fitted parameters).
hydrazone groups lead to coordinative unsaturation, and extra
ligands, including fifteen water molecules and one nitrate, are
coordinated at these peripheral sites.
1 C. J. Matthews, K. Avery, Z. Xu, L. K. Thompson, L. Zhao,
D. O. Miller, K. Biradha, K. Poirier, M. J. Zaworotko, C. Wilson,
A. E. Goeta and J. A. K. Howard, Inorg. Chem., 1999, 38,
5266–5276.
2 L. K. Thompson, C. J. Matthews, L. Zhao, Z. Xu, D. O. Miller,
C. Wilson, M. A. Leech, J. A. K. Howard, S. L. Heath,
A. G. Whittaker and R. E. P. Winpenny, J. Solid State Chem.,
2001, 159, 308–320.
3 L. N. Dawe, T. S. M. Abedin, T. L. Kelly, L. K. Thompson,
D. O. Miller, L. Zhao, C. Wilson, M. A. Leech and J. A. K.
Howard, J. Mater. Chem., 2006, 16, 2645–2659.
4 V. A. Milway, S. M. T. Abedin, V. Niel, T. L. Kelly, L. N. Dawe,
S. K. Dey, D. W. Thompson, D. O. Miller, M. S. Alam, P. Muller
¨
and L. K. Thompson, Dalton Trans., 2006, 2835–2851.
5 L. N. Dawe, K. V. Shuvaev and L. K. Thompson, Inorg. Chem.,
2009, 48, 3323–3341.
6 L. K. Thompson, L. Zhao, Z. Xu, D. O. Miller and W. M. Reiff,
Inorg. Chem., 2003, 42, 128–139.
7 L. N. Dawe, K. V. Shuvaev and L. K. Thompson, Chem. Soc. Rev.,
2009, 38, 2334.
8 M.-T. Youinou, N. Rahmouni, J. Fischer and J. A. Osborn,
Angew. Chem., Int. Ed. Engl., 1992, 31, 733.
Magnetic data for 6 show a maximum in w at 35 K (Fig. 5)
indicating intramolecular antiferromagnetic exchange. Since
the corner Ni(II)4 subunits should exhibit much stronger
internal exchange than would be expected via the pyrimidine
bridges, a model based just on the [2 ꢀ 2] corner fragments was
used (Hex = ꢂJ{S1ꢁS2 + S2ꢁS3 + S3ꢁS4 + S1ꢁS4}).
An excellent fit (solid line in Fig. 5, scaled to Ni4 subunits)
gave gav. = 2.15(1), J = ꢂ17.7(3) cmꢂ1, TIP = 700 ꢀ
10ꢂ6 cm3 molꢂ1, r = 0.07, y = 0 K (102R = 0.50; R =
P
P
[
(wobs. ꢂ wcalc.)2/ wobs.
]
2 1/2) (r = fraction paramagnetic
impurity, y = Weiss correction). The J value is consistent
with the Ni4 [2 ꢀ 2] square poap (Chart S1, ESIw) grids,1 and
the zero y value indicates that the pyrimidine bridge is not a
significant contributor to overall exchange.
L1 forms self-assembled [4 ꢀ 4] grid structures with Mn(II)
and Cu(II) successfully, but for Ni(II) the coordination ‘space’
is clearly more critical, and only chains occur with this type of
ligand. CFSE appears to play an important role, and also large
site distortions appear to discourage coordination. The
successful synthesis of the Ni16 [4 ꢀ 4] grid 6 results from
the creation of donor groupings giving the Ni(II) ion a more
comfortable coordination ‘space’, similar to the situation in
the well documented Ni4 [2 ꢀ 2] square hydrazone (poap)
based grids.1 Adding extra peripheral pyridine rings in the
case of L4 creates a tetratopic ligand with four potentially
tridentate pockets, but the strong field nature of the ‘bipy’ like
endpieces dominates the coordination process, leading to
an unexpected, novel Cu(II)11 super-triangle. Efforts are
underway to expand this class of ligand, and in particular to
examine the coordination chemistry of L4 and L6 further with
other metal ions, in order to shed more light on the subtle
balances which exist between ligand design and the metal
coordination ‘algorithm’.
9 G. S. Hanan, D. Volkmer, U. S. Schubert, J.-M. Lehn, G. Baum
and D. Fenske, Angew. Chem., Int. Ed. Engl., 1997, 36, 1842.
10 J. Rojo, J.-M. Lehn, G. Baum, D. Fenske, O. Waldmann and
P. Muller, Eur. J. Inorg. Chem., 1999, 517.
¨
11 M. Barboiu, M. Ruben, G. Blasen, N. Kyritsakas, E. Chacko,
M. Dutta, O. Radekovich, K. Lenton, D. J. R. Brook and
J.-M. Lehn, Eur. J. Inorg. Chem., 2006, 784.
12 P. N. W. Baxter, J.-M. Lehn, J. Fischer and M.-T. Youinou,
Angew. Chem., Int. Ed. Engl., 1994, 33, 2284.
13 L. N. Dawe, K. V. Shuvaev and L. K. Thompson, Inorg. Chem.,
2009, 48, 3323.
14 S. K. Dey, T. S. M. Abedin, L. N. Dawe, S. S. Tandon,
J. L. Collins, L. K. Thompson, A. V. Postnikov, M. S. Alam
and P. Muller, Inorg. Chem., 2007, 46, 7767.
¨
15 L. N. Dawe and L. K. Thompson, Angew. Chem., Int. Ed., 2007,
46, 7440.
16 S. K. Dey, L. K. Thompson and L. N. Dawe, Chem. Commun.,
2006, 4967.
17 S. T. Onions, A. M. Frankin, P. N. Horton, M. B. Hursthouse and
C. J. Matthews, Chem. Commun., 2003, 2864.
18 M. Barboiu, G. Vaughan, R. Graff and J.-M. Lehn, J. Am. Chem.
Soc., 2003, 125, 10257.
19 L. K. Thompson, C. J. Matthews, L. Zhao, C. Wilson,
M. A. Leech and J. A. K. Howard, Dalton Trans., 2001, 2258.
20 K. V. Shuvaev, T. S. M. Abedin, C. A. McClary, L. N. Dawe,
J. L. Collins and L. K. Thompson, Dalton Trans., 2009, 2926.
21 Z. Xu, L. K. Thompson, D. A. Black, C. Ralph, D. O. Miller,
M. A. Leech and J. A. K. Howard, Dalton Trans., 2001, 2042.
22 L. Rosenberg, L. K. Thompson, E. J. Gabe and F. L. Lee, Dalton
Trans., 1986, 625.
Funding from the Natural Sciences and Engineering
Research Council of Canada (NSERC) is acknowledged.
Notes and references
z Crystal data for [Ni4(L2)3](ClO4)2ꢁ7.5H2O (2): C54H57Cl2N30O21.5Ni4,
M = 1776.04, C2/c, a = 41.051(9) A, b = 9.569(2) A, c = 19.109(4) A,
b = 115.296(3)1, V = 6787(3) A3, T = 135(1) K, Z = 4, F(000) =
3636, m(Mo-Ka) = 12.72 cmꢂ1, 14 603 reflections, 6979 unique
23 A. Escuer, R. Vicente, B. Mernari, A. El Gueddi and M. Perrot,
Inorg. Chem., 1997, 36, 2511.
(Rint
=
0.0504), R1
=
0.0907, wR2
=
0.2352. Crystal data
24 C. J. Matthews, S. T. Onions, G. Morata, L. J. Davis, S. L. Heath
and D. J. Price, Angew. Chem., Int. Ed., 2003, 42, 3166.
for [(L4)3Cu11(OH)2(CH3COO)4(ClO4)](ClO4)3Na(OH)(H2O)55 (5):
ꢃc
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 4755–4757 | 4757