Control of self-assembly through the influence of terminal hydroxymethyl groups on the metal coordination of pyrimidine?hydrazone CU(ii) complexes

Article abstract of DOI:10.1021/ic100384e

The synthesis and characterization of 6-hydroxymethylpyridine-2- carboxaldehyde (2-methyl-pyrimidine-4,6-diyl)bis(1-methylhydrazone) (1) is reported. Ligand 1 was designed as a ditopic pyrimidine?hydrazone molecular strand with hydroxymethyl groups attached to the terminal pyridine rings. Coordination of 1 with Cu(ClO₄)₂·6H₂O or Cu(SO₃CF₃)₂·4H₂O in a 1:2 molar ratio resulted in the dinuclear Cu(II) complexes [Cu₂1(CH ₃CN)₄](ClO₄)₄·CH ₃CN (4) and [Cu₂1(SO₃CF₃) ₂(CH₃CN)₂](SO₃CF₃) ₂·CH₃CN (5) · X-ray crystallography and ¹H NMR NOESY experiments showed that 1 adopted a horseshoe shape with both pyrimidine?hydrazone (pym?hyz) bonds in a transoid conformation, while 4 and 5 were linear in shape, with both pym?hyz bonds in a cisoid conformation. Coordination of 1 with Cu(ClO₄)₂·6H₂O or Cu(SO₃CF₃)₂·4H₂O in a 1:1 molar ratio resulted in three different bent complexes, [Cu(1H)(ClO ₄)₂](ClO₄) (6), [Cu(1H)(CH₃CN)] (ClO₄)₃·0.5H₂O (7), and [Cu1(SO ₃CF₃)]₂(SO₃CF₃) ₂·CH₃CN (8), where the pym?hyz bond of the occupied coordination site adopted a cisoid conformation, while the pym?hyz bond of the unoccupied site retained a transoid conformation. Both 6 and 7 showed protonation of the pyridine nitrogen donor in the empty coordination site; complex 8, however, was not protonated. A variety of Cu(II) coordination geometries were seen in structures 4 to 8, including distorted octahedral, trigonal bipyramidal, and square pyramidal geometries. Coordination of the hydroxymethyl arm in the mononuclear Cu(II) complexes 6, 7, and 8 appeared to inhibit the formation of a [2 × 2] grid by blocking further access to the Cu(II) coordination sphere. In addition, the terminal hydroxymethyl groups contributed to the supramolecular structures of the complexes through coordination to the Cu(II) ions and hydrogen bonding.

Full text of DOI:10.1021/ic100384e

Inorg. Chem. 2010, 49, 5923–5934 5923
DOI: 10.1021/ic100384e
Control of Self-Assembly through the Influence of Terminal Hydroxymethyl Groups
on the Metal Coordination of Pyrimidine-Hydrazone Cu(II) Complexes
Daniel J. Hutchinson, Lyall R. Hanton,* and Stephen C. Moratti
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
Received February 25, 2010
The synthesis and characterization of 6-hydroxymethylpyridine-2-carboxaldehyde (2-methyl-pyrimidine-4,6-diyl)bis(1-
methylhydrazone) (1) is reported. Ligand 1 was designed as a ditopic pyrimidine-hydrazone molecular strand
with hydroxymethyl groups attached to the terminal pyridine rings. Coordination of 1 with Cu(ClO4)2 6H2O
or Cu(SO3CF3)2 4H2O in a 1:2 molar ratio resulted in the dinuclear Cu(II) complexes [Cu21(CH3CN)4]-
3
3
1
(ClO4)4 CH3CN (4) and [Cu21(SO3CF3)2(CH3CN)2](SO3CF3)2 CH3CN (5). X-ray crystallography and H NMR
NOESY experiments showed that 1 adopted a horseshoe shape with both pyrimidine-hydrazone (pym-hyz) bonds
in a transoid conformation, while 4 and 5 were linear in shape, with both pym-hyz bonds in a cisoid conformation.
Coordination of 1 with Cu(ClO4)2 6H2O or Cu(SO3CF3)2 4H2O in a 1:1 molar ratio resulted in three different
bent complexes, [Cu(1H)(ClO4)2](ClO4) (6), [Cu(1H)(CH3CN)](ClO4)3 0.5H2O (7), and [Cu1(SO3CF3)]2-
(SO3CF3)2 CH3CN (8), where the pym-hyz bond of the occupied coordination site adopted a cisoid conformation,
while the pym-hyz bond of the unoccupied site retained a transoid conformation. Both 6 and 7 showed protonation of
the pyridine nitrogen donor in the empty coordination site; complex 8, however, was not protonated. A variety of Cu(II)
coordination geometries were seen in structures 4 to 8, including distorted octahedral, trigonal bipyramidal, and square
pyramidal geometries. Coordination of the hydroxymethyl arm in the mononuclear Cu(II) complexes 6, 7, and 8
appeared to inhibit the formation of a [2 ꢀ 2] grid by blocking further access to the Cu(II) coordination sphere. In
addition, the terminal hydroxymethyl groups contributed to the supramolecular structures of the complexes through
coordination to the Cu(II) ions and hydrogen bonding.
3
3
3
3
3
3
Introduction
has been observed when using metal salts of Pb(II),5 Ag(I),7
Zn(II),8 and Hg(II)9,10 in polar solvents such as CH3CN and
CH3NO2, resulting in linear, grid, and double helical com-
plexes. Previous studies have shown that this dynamic pro-
cess is reversible and that the volume change associated with
it is significant.5
The key to applying these dynamic molecular systems is
their incorporation into devices such as polymer gel actua-
tors, which have potential applications in the fields of bio-
medical science,11 robotics,12 and microfluidics.13 Our first pym-
hyz ligand (1) has been designed with terminal 6-hydroxy-
methyl-2-pyridinecarboxaldehyde rings, which have the
Supramolecular systems that undergo dynamic structural
changes induced by external stimuli are intriguing as they
have potential applications as components in nanoscale
mechanical devices.1-3 The pyrimidine-hydrazone (pym-
hyz) motif is of interest due to the dynamic structural change
of pym-hyz molecular strands from a helical shape to a
linear arrangement upon coordination of suitable metal
ions.4-6 Coordination causes the pym-hyz-pym linkage
to rotate from the preferred transoid conformation to a cisoid
conformation, which creates a tridentate coordination site
for the incoming metal ion (Figure 1). This structural change
*To whom correspondence should be addressed. Phone: (þ64) 3-479-
7918. Fax: (þ64) 3-479-7906. E-mail: lhanton@chemistry.otago.ac.nz.
(1) Schneider, H.-J.; Strongin, R. M. Acc. Chem. Res. 2009, 42(10), 1489–
1500.
(2) Balzani, V.; Credi, A.; Raymo, F. M.; Stoddart, J. F. Angew. Chem.,
Int. Ed. 2000, 39, 3348–3391.
(3) Ulrich, S.; Buhler, E.; Lehn, J.-M. New J. Chem. 2009, 33, 271–292.
(4) Schmitt, J.-L.; Stadler, A.-M.; Kyritsakas, N.; Lehn, J.-M. Helv.
Chim. Acta 2003, 86, 1598–1624.
(8) Barboiu, M.; Ruben, M.; Blasen, G.; Kyritsakas, N.; Chacko, E.;
Dutta, M.; Radekovich, O.; Lenton, K.; Brook, D. J. R.; Lehn, J.-M. Eur. J.
Inorg. Chem. 2006, 784–792.
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nen, J.; Rissanen, K.; Allouche, L.; Lehn, J.-M. Z. Anorg. Allg. Chem. 2007,
633, 2435–2444.
(10) Ramirez, J.; Stadler, A.-M. Z. Anorg. Allg. Chem. 2009, 635, 1348–
1351.
(5) Schmitt, J.-L.; Lehn, J.-M. Helv. Chim. Acta 2003, 86, 3417–3426.
(6) Stadler, A.-M.; Kyritsakas, N.; Graff, R.; Lehn, J.-M. Chem.;Eur. J.
2006, 12, 4503–4522.
(7) Stadler, A.-M.; Kyritsakas, N.; Vaughan, G.; Lehn, J.-M. Chem.;
Eur. J. 2006, 13, 59–68.
(11) Lyon, L. A.; Meng, Z.; Singh, N; Sorrell, C. D.; St. John, A. Chem.
Soc. Rev. 2009, 38, 865–874.
(12) Mirfakhrai, T.; Madden, J. D. W.; Baughman, R. H. Mater. Today
2007, 10, 30–38.
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r
2010 American Chemical Society
Published on Web 05/28/2010
pubs.acs.org/IC

5924 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hutchinson et al.
Figure 1. Reversible rotation of the pym-hyz bond from transoid to cisoid conformation, induced by the addition of metal ions. While the uncoordinated
pym-hyz unit acts as a helicity codon, the coordinated pym-hyz þ Mnþ unit imposes a linear shape on the molecular strand.
potential to allow the ligand to be assimilated into larger
systems through chemical manipulation of the terminal OH
functional groups. While this functionality has been added
ultimately to allow incorporation of the ligand strands into
molecular devices, the way in which the hydroxymethyl sub-
stituents affect the metal coordination chemistry of the pym-
hyz strands needs first to be explored. The terminal 6-hydro-
xymethylpyridine motif may have a direct effect on the self-
assembly reaction between the ligand strand and the metal
ions by forming a chelate ring with the metal ion through
coordination of the Npy and O donors.14-16 It may also alter
the supramolecular chemistry of a complex, due to the ability
of the OH group to act as both a hydrogen bonding acceptor
and donor.17,18 These attributes have led to the frequent use
of the 6-hydroxymethylpyridine motif with Cu(II) ions to create
self-assembled supramolecular architectures through a combi-
nation of metal coordination and hydrogen bonding.19-21
An extensive family of pym-hyz (and isomorphically
equivalent pym-py) ligands has been reported with different
substituents on the ternary hydrazone N atoms, the 2 position
of the pyrimidine ring, and the terminal pyridine rings.4-6
These modifications have been made to tune the redox22 and
magnetic23 properties of the pym-hyz complexes, alter the
solid state structure of the self-assembled complexes,6 pro-
duce functionalized grids which may be used as sensors,24
and produce extended 1D and 2D grid assemblies through
self-assembly reactions.25,26 However, few examples exist
where the pym-hyz strands have been decorated with OH
functional groups,6 particularly at the terminal pyridine rings
where they can influence the metal-directed self-assembly
process.
Herein, we report the preliminary metal coordination
studies of this new pym-hyz ligand with Cu(ClO4)2 6H2O
3
and Cu(SO3CF3)2 4H2O in CH3CN. The addition of each of
3
the Cu(II) salts to 1 in a 2:1 molar ratio resulted in a linear
complex with Cu(II) ions occupying both of the pym-
hyz-py coordination pockets of 1. In both of the dicopper
complexes, only one of the terminal hydroxymethyl groups
was coordinated to a Cu(II) ion. When the Cu(II) salts were
added to 1 in a 1:1 molar ratio, the conformational change of
the pym-hyz linkage from transoid to cisoid was localized to
only the occupied pym-hyz-py pocket, while the vacant
coordination pocket retained a horseshoe-like shape. Two
different solid state structures with differing Cu(II) coordina-
tion spheres were obtained from reacting 1 with Cu(ClO4)2 in
a 1:1 molar ratio. In both complexes, the pyridine nitrogen
donor of the empty coordination pocket was protonated,
while the hydroxymethyl group of the occupied site was
bound to the Cu(II) ion. Coordination of the hydroxymethyl
arm in these mononuclear Cu(II) complexes appeared to
inhibit the formation of a [2 ꢀ 2] grid by blocking further
access to the Cu(II) coordination sphere.
Experimental Section
(14) Winter, S.; Seichter, W.; Weber, E. Z. Anorg. Allg. Chem. 2004, 630,
General. All chemicals were used as received without further
purification. The precursor 4,6-bis(1-methylhydrazino)-2-
methylpyrimidine (2) was prepared from 4,6-dichloro-2-methyl-
pyrimidine and methyl hydrazine.27 Activated manganese(IV)
dioxide (MnO2) and 2,6-bis(hydroxymethyl)pyridine were obtained
434–442.
(15) Yilmaz, V. T.; Guney, S.; Andac, O.; Harrison, W. T. A. Polyhedron
2002, 21, 2393–2402.
ꢀ
ꢀ
ꢀ
(16) Maroszova, J.; Stachova, P.; Vaskova, Z.; Valigura, D.; Koman, M.
Acta Crystrallogr., Sect. E: Struct. Rep. Online 2006, E62, m109–m110.
ꢀ
(17) Lah, N.; Leban, I.; Clerac, R. Eur. J. Inorg. Chem. 2006, 4888–4894.
from Merck and Acros Organic, respectively. Cu(ClO4)2 6H2O
3
(18) Lavalette, A.; Tuna, F.; Clarkson, G.; Alcock, N. W.; Hannon, M. J.
Chem. Commun. 2003, 2666–2667.
(19) Telfer, S. G.; Parker, N. D.; Kuroda, R.; Harada, T.; Lefebvre, J.;
Leznoff, D. B. Inorg. Chem. 2008, 47(1), 209–218.
(20) Moncol, J.; Mudra, M.; Lonnecke, P.; Koman, M.; Melnik, M.
J. Coord. Chem. 2004, 57(12), 1065–1078.
(21) Gupta, A. K.; Kim, J. Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 2003, C59, m262–m264.
(22) Ruben, M.; Breuning, E.; Barboiu, M.; Gisselbrecht, J.-P.; Lehn, J.-
M. Chem.;Eur. J. 2003, 9(1), 291–299.
(23) Cao, X.-Y.; Harrowfield, J.; Nitschke, J.; Ramirez, J.; Stadler,
A.-M.; Kyritsakas-Gruber, N.; Madalan, A.; Rissanen, K.; Russo, L.;
Vaughan, G.; Lehn, J.-M. Eur. J. Inorg. Chem. 2007, 2944–2965.
(24) Tielmann, P.; Marchal, A.; Lehn, J.-M. Tetrahedron Lett. 2005, 46,
6349–6353.
(25) Breuning, E.; Ziener, U.; Lehn, J.-M.; Wegelius, E.; Rissanen, K.
Eur. J. Inorg. Chem. 2001, 1515–1521.
was acquired from Aldrich, while Cu(SO3CF3)2 4H2O was
3
prepared by the treatment of CuCO3 with HSO3CF3. All sol-
vents were used as received and were of LR grade or above. The
petroleum ether used was the 40-60 variety.
€
Column chromatography was performed using silica gel
(10% hydrated v/v). Microanalyses were carried out in the
Campbell Microanalytical Laboratory, University of Otago. All
measured microanalysis results had an uncertainty of (0.4%. 1H
and 13C NMR spectra and two-dimensional (gCOSY, NOSEY,
€
(26) Ruben, M.; Ziener, U.; Lehn, J.-M.; Ksenofontov, V.; Gutlich, P.;
Vaughan, G. B. M. Chem.;Eur. J. 2005, 11, 94–100.
(27) Hutchinson, D. J.; Hanton, L. R.; Moratti, S. C. Acta Crystallogr.,
Sect. E: Struct. Rep. Online 2009, E65(7), o1546.

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 5925
HSQC, gHMBC) spectra were collected on a 500 MHz Varian
UNITY INOVA spectrometer at 298 or 348 K. Spectra were
collected in CDCl3 or d6-DMSO and were referenced to the
internal solvent signal. Chemical shifts are reported in δ units
(ppm). Electrospray Mass Spectrometry (ESMS) was carried
out on a Bruker microTOFQ instrument (Bruker Daltronics,
Bremen, Germany). Samples were introduced using direct infu-
sion into an ESI source in the positive mode. Sampling was
averaged for 2 min over a m/z range of 50 to 3000 amu. The mass
was calibrated using an external calibrant of sodium formate
clusters, 15 calibrations points from 90 to 1050 amu, using a
quadratic plus HPC line fit. ESMS spectra were processed using
the Compass software (version 1.3, Bruker Daltronics,
Bremen, Germany). UV-vis spectra were recorded on an
Agilent 8453 spectrophotometer against a CH3CN back-
ground using quartz cells with a 1 cm path length. Infrared
(IR) spectra were recorded on a Perkin-Elmer Spectrum BX
FT-IR system using KBr discs.
C-H str), 1712 (s, CdO str), 1601 (s), 1580 (m), 1450 (s), 1338
(s), 1317 (s), 1211 (m), 1114 (s), 1048 (s), 1001 (s).
Complexes. Cu21(ClO4)4. Cu(ClO4)2 6H2O (40.0 mg, 0.108
mmol) was dissolved in CH3CN (2 mL) and added to 1 (21.8 mg,
0.052 mmol), resulting in the partial dissolution of 1 and the
formation of a green solution. This mixture was stirred and
heated until all the solid had dissolved. Diethyl ether was slowly
diffused into this solution, resulting in the formation of green
crystals. These crystals were filtered and dried in vacuo to yield
Cu21(ClO4)4 as a green solid (15.7 mg, 32%). Anal. Found: C,
3
26.00; H, 3.04; N, 11.13. Calcd for C21H24N8O18Cl4Cu2 2H2O: C,
3
25.70; H, 2.88; N, 11.42. ESMS m/z Found: 443.1894. Calcd
for C21H24N8O2Naþ: 443.1914. UV-vis (CH3CN), λmax(ε)/nm
(L mol-1 cm-1): 691 (251). Selected IR (KBr), ν/cm-1: 3455 (m,
br, O-H str), 3062 (w, C-H str), 1630 (s), 1604 (s), 1589 (s), 1561
(s), 1498 (m), 1431 (m), 1386 (w), 1292 (m, C-O str), 1273 (m),
1158 (s), 1092 (s, br). Green crystals suitable for X-ray determina-
tion were grown by slow diffusion of diethyl ether into a CH3CN
solution of Cu21(ClO4)4.
Caution! Although no problems were encountered in this work,
transition metal perchlorates are potentially explosive. They
should be prepared in small amounts and handled with care.
Syntheses. 6-Hydroxymethylpyridine-2-carboxaldehyde(2-
methyl-pyrimidine-4,6-diyl)bis(1-methylhydrazone) (1). A solu-
tion of 2 (1.002 g, 5.50 mmol) and 6-hydroxymethyl-2-pyridi-
necarboxaldehyde (3) (1.627 g, 11.9 mmol) in EtOH (100 mL)
was refluxed for 5 h under an inert atmosphere of N2. Over
the course of the reaction, a white solid precipitated out of the
reaction solution. The reaction mixture was filtered, and the
solid was washed with EtOH and dried in vacuo to give 1 as a
white solid (2.138 g, 92%). Mp: 268-270 °C (decomp.). Anal.
Found: C, 60.04; H, 5.71; N, 26.40. Calcd for C21H24N8O2: C,
59.99; H, 5.75; N, 26.64. 1H NMR (500 MHz, DMSO-d6),
δ/ppm: 7.96 (2H, t, J = 7.7 Hz, H12), 7.88 (2H, d, J = 7.2 Hz,
H11), 7.87 (2H, s, H9), 7.65 (1H, s, H5), 7.28 (2H, d, J=7.5 Hz,
H13), 5.37 (2H, t, J = 5.8 Hz, OH), 4.63 (4H, d, J = 5.8 Hz,
H15), 3.65 (6H, s, H8), 2.47 (3H, s, H7). 13C NMR (500 MHz,
DMSO-d6), δ/ppm: 165.44 (C2), 162.45 (C4, C6), 161.75 (C14),
153.21 (C10), 137.41 (C9), 136.87 (C12), 119.57 (C13), 116.92
Cu21(SO3CF3)4. Cu21(SO3CF3)4 was prepared as descri-
bed for Cu21(ClO4)4 but using Cu(SO3CF3)2 4H2O (31.0 mg,
3
0.0715 mmol) and 1 (10.7 mg, 0.0254 mmol) in CH3CN (2 mL),
which gave a green solution from which green crystals were
obtained (26.2 mg, 90%). Anal. Found: C, 25.99; H, 2.39; N,
9.99. Calcd for C25H24N8O14F12S4Cu2: C, 26.25; H, 2.11; N,
9.80. ESMS m/z Found: 482.1214, 844.9536, 994.9112. Calcd for
C21H23N8O2Cuþ: 482.1234. Calcd for C21H23N8O2Cuþ2-
(SO3CF3)2þ: 844.9576. Calcd for C21H24N8O2Cu2(SO3CF3)3
:
994.9153. UV-vis (CH3CN), λmax(ε)/nm(L mol-1 cm-1): 699
(222). Selected IR (KBr), ν/cm-1: 3445 (m, br, OH str), 3129 (w,
CH str), 3061 (w, CH str), 1636 (m), 1622 (m,), 1603 (s), 1586 (s),
1558 (s), 1502(w), 1459 (w), 1428 (w), 1386 (w), 1260 (s, C-O
str), 1177 (s), 1155 (s), 1059 (m), 1032 (s). Green crystals suitable
for X-ray determination were grown by slow diffusion of diethyl
ether into a CH3CN solution of Cu21(SO3CF3)4.
Cu(1H)(ClO4)3. Cu(1H)(ClO4)3 was prepared as descri-
bed for Cu21(ClO4)4 but using Cu(ClO4)2 6H2O (73.0 mg,
3
0.197 mmol) and 1 (62.2 mg, 0.148 mmol) in CH3CN (10 mL),
which gave a green solution from which green crystals were
obtained (87.1 mg, 75%). Anal. Found: C, 32.20; H, 3.22; N,
(C11), 84.74 (C5), 64.06 (C15), 29.30 (C8), 25.79 (C7). ESMS
þ
m/z Found: 421.2134, 443.1929. Calcd for C21H25N8O2
:
421.2095. Calcd for C21H24N8O2Naþ: 443.1914. Selected IR
(KBr) ν/cm-1: 3366 (m, br), 3236 (m, br, OH str), 2919 (m,
C-H str), 1592 (s), 1561 (s, CdN str), 1489 (s), 1453 (s), 1412
(m), 1395 (s), 1265 (m), 1212 (m), 1165 (s), 1095 (m), 1038 (s).
Crystals suitable for X-ray determination were grown from a
DMSO solution of 1.
14.30. Calcd for C21H25N8O14Cl3Cu 0.5CH3CN: C, 32.87; H,
3
3.32; N, 14.81. ESMS m/z Found: 482.1245. Calcd for C21H23-
N8O2Cuþ: 482.1234. UV-vis (CH3CN), λmax(ε)/nm (L mol-1
cm-1): 657 (171). Selected IR (KBr), ν/cm-1: 3462 (m, br, O-H
str), 3068 (m, CH str), 2931 (m, CH str), 1653 (m), 1616 (m), 1598
(s), 1558 (s), 1485 (m), 1455 (m), 1432 (m), 1406 (m), 1302 (m,
C-O str), 1163 (m), 1089 (s, br), 1057 (s). Green crystals of
differing morphology suitable for X-ray determination were
grown by slow diffusion of diethyl ether into a CH3CN solution
of Cu(1H)(ClO4)2.
Preparation of 6-Hydroxymethyl-2-pyridinecarboxaldehyde
(3). The following method was modified from Artali et al.28
MnO2 (15.94 g, 183 mmol) was added slowly to a stirring solu-
tion of 2,6-bis(hydroxymethyl)pyridine (10.12 g, 72.7 mmol) in
CHCl3 (200 mL). The mixture was stirred and refluxed for 3 h, at
which point more MnO2 (12.71 g, 146 mmol) was added, and the
reflux resumed for a further 3 h. After cooling, the mixture was
filtered through Celite, and the black inorganic salts were
washed with CH3OH. The combined filtrate and washings were
concentrated by rotary evaporation and the resulting oily
residue subjected to column chromatography with an ethyl
acetate/petroleum ether gradient (30 to 70%), giving the pro-
duct as a white solid (5.049 g, 51%). Mp: 68-70 °C (lit. 66-
69 °C29) Anal. Found: C, 60.59; H, 5.23; N, 10.07. Calcd for
Cu1(SO3CF3)2. Cu1(SO3CF3)2 was prepared as described for
Cu21(ClO4)4 but using Cu(SO3CF3)2 4H2O (21.1 mg, 0.0486
3
mmol) and 1 (18.4 mg, 0.0437 mmol) in CH3CN (4 mL), which
gave a green solution from which green crystals were obtained
(7.80 mg, 22%). Anal. Found: C, 34.52; H, 3.22; N, 13.89. Calcd
for C23H24N8O8F6S2Cu H2O: C, 34.52; H, 3.28; N, 14.00.
3
ESMS m/z Found: 482.1199. Calcd for C21H23N8O2Cuþ:
482.1234. UV-vis (CH3CN) λmax(ε)/nm (L mol-1 cm-1): 679
(170). Selected IR (KBr) ν/cm-1: 3364 (m, br, OH str), 3055 (w,
CH str), 1615 (m), 1597 (s), 1567 (s), 1547 (s), 1494 (m), 1461 (m),
1461 (m), 1424 (m), 1398 (m), 1364 (w), 1274 (s), 1249 (s), 1169
(m), 1116 (m), 1053 (m), 1030 (s). Green crystals suitable for
X-ray determination were grown by slow diffusion of diethyl
ether into a CH3CN solution of Cu1(SO3CF3)2.
1
C7H7NO2: C, 61.31; H, 5.14; N, 10.21. H NMR (500 MHz,
CDCl3), δ/ppm: 10.09 (1H, s, CHO), 7.88 (2H, m, H3py, H5py),
7.52 (1H, m, H4py), 4.88 (2H, s, CH2). Selected IR (KBr),
ν/cm-1: 3134 (s, br, O-H str), 2847 (m, C-H str), 2718 (m,
X-Ray Crystallography. Details of the crystallographic data
collection and refinement parameters are given in Table 1. X-ray
diffraction data were collected on a Bruker APEX II CCD
diffractometer, with graphite monochromated Mo KR (λ =
(28) Artali, R.; Botta, M.; Cavallotti, C.; Giovenzana, G. B.; Palmisano,
G.; Sisti, M. Org. Biomol. Chem. 2007, 5, 2441–2447.
(29) Okuyama, Y.; Nakano, K.; Kabuto, C.; Nozawa, E.; Takahashiu,
K.; Hongo, H. Heterocycles 2002, 58, 457–460.
˚
0.71073 A) radiation at 90 K in a nitrogen gas stream. Intensities

5926 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hutchinson et al.
Table 1. Crystallographic Data
[Cu21(CH3CN)4]
(ClO4) CH3CN (4)
[Cu21(SO3CF3)2(CH3CN)2]
(SO3CF3)2 CH3CN (5)
[Cu(1H)(ClO4)2](ClO4)
(6)
1
3
3
formula
fw
C21H24N8O2
420.48
triclinic
P1
7.2289(17)
10.044(2)
15.247(4)
96.133(12)
96.304(13)
108.676(13)
1030.5(4)
2
90(2)
0.093
10055
3830 (0.0276)
0.0535
0.1850
C31H39Cl4Cu2N13O18
1150.63
triclinic
P1
10.4995(7)
13.3286(8)
17.5470(11)
80.749(3)
76.047(4)
78.554(3)
2319.2(3)
2
90(2)
1.233
21557
8147 (0.0407)
0.0614
0.1513
C31H33Cu2F12N11O14S4
1267.00
triclinic
C21H25Cl3CuN8O14
783.38
monoclinic
P2(1)/c
11.1743(9)
12.5567(11)
20.6999(19)
90.000
102.655(4)
90.000
2833.7(4)
4
90(2)
1.141
37579
4976 (0.0348)
0.0318
0.0796
cryst syst
space group
P1
˚
a/A
13.1415(19)
13.909(2)
15.291(3)
96.715(7)
106.583(7)
115.590(7)
2320.9(7)
2
90(2)
1.220
27415
7996 (0.0405)
0.0604
0.1714
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
V/A
Z
T/K
μ/mm-1
reflns collected
unique reflns (Rint
R1 indices [I > 2σ(I)]
wR2 (all data)
goodness-of-fit
)
1.027
1.043
1.065
1.078
[Cu(1H)(CH3CN)] (ClO4)3 0.5H2O (7)
[Cu1(SO3CF3)]2(SO3CF3)2 CH3CN (8)
3
3
formula
fw
C23H28Cl3CuN9O14.50
832.43
triclinic
P1
9.5283(13)
11.2257(15)
16.279(3)
79.320(9)
84.008(10)
73.075(8)
1634.6(5)
2
90(2)
0.996
22579
5987 (0.0429)
0.0480
0.1417
C48H49Cu2F12N17O16S4
1603.36
triclinic
cryst syst
space group
P1
˚
a/A
14.2625(9)
16.2630(11)
16.7874(12)
104.770(4)
103.449(5)
94.037(4)
3627.0(4)
2
90(2)
0.802
22581
10641 (0.0346)
0.0807
0.1951
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
V/A
Z
T/K
μ/mm-1
reflns collected
unique reflns (Rint
R1 indices [I > 2σ(I)]
wR2 (all data)
goodness-of-fit
)
1.044
1.99
were corrected for Lorentz polarization effects,30 and a multiscan
absorption correction31 was applied. The structures were solved
by direct methods (SHELXS32 or SIR-9733) and refined on F2
using all data by full-matrix least-squares procedures (SHELXL
9734). All calculations were performed using the WinGX inter-
face.35 Detailedanalysesoftheextendedstructurewere carriedout
using PLATON36 and MERCURY37 (version 1.4.1). X-ray data
were deposited with the Cambridge Crystallographic Data Center
CCDC-773524-CCDC-773529. These data can be obtained free
of charge from the Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
Some of the crystal structures contained disordered compo-
nents. One of the ClO4 counterions in [Cu21(CH3CN)4]-
-
(ClO4)4 CH3CN (4) showed translational disorder over two
3
sites, with site occupancy factors of 0.68 and 0.32. One of the
coordinated ClO4 ions in [Cu(1H)(ClO4)2](ClO4) (6) showed
-
rotational disorder about a 3-fold axis with site occupancy
factors of 0.83 and 0.17. One of the ClO4 counterions in
[Cu(1H)(CH3CN)](ClO4)3 0.5H2O (7) showed translational
-
3
disorder over two sites with site occupancy factors of 0.50 and
0.50. Complex 7 also contained a H2O molecule that was only
present half the time. The H atoms on this H2O molecule
-
were not located. One of the SO3CF3 counterions in [Cu1-
(SO3CF3)]2(SO3CF3)2 CH3CN (8) was disordered over two
3
(30) SAINT Software Reference Manual; Bruker AXS: Madison; WI, 1998.
(31) Sheldrick, G. M. SADABS, Program for Absorption Correction;
sites with site occupancy factors of 0.66 and 0.34. The ADP
values and bond distances seen in both parts of the disordered
SO3CF3- counterion were restrained using the EADP and DFIX
commands, respectively. Additionally, there appeared to be a
chain of disordered CH3CN molecules in 8 which could not be
modeled. The SQUEEZE option of PLATON36 was therefore
employed to remove them from the structure. The number of
electrons located was 101 per unit cell, and this was assigned to 4.5
CH3CN molecules of solvent.
€
€
University of Gottingen: Gottingen, Germany, 1996.
(32) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990,
A46(6), 467–473.
(33) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115–119.
(34) Sheldrick, G. M. SHELXL-97, Program for the Solution of Crystal
€
€
Structures; University of Gottingen: Gottingen, Germany, 1997.
(35) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
(36) Spek, A. L. Acta Crystallogr., Sect A: Found. Crystallogr. 1990,
46, C34.
Results and Discussion
(37) (a) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.;
Shields, G. P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl. Crystallogr.
2006, 39, 453–457. (b) Bruno, I. J.; Cole, J. C.; Edgington, P. R.; Kessler, M. K.;
Macrae, C. F.; McCabe, P.; Pearson, J.; Taylor, R. Acta Crystallogr., Sect. B:
Struct. Sci. 2002, B58, 389–397.
The ligand (1) was designed with terminal hydroxymethyl
groups so that it could be incorporated into a larger mole-
cular structure. The 4,6-bis(1-methylhydrazino)pyrimidine

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 5927
Scheme 1.a
a Showing NMR numbering.
precursor (2) was prepared by the treatment of 4,6-dichloro-
2-methylpyrimidine with methyl hydrazine.4 The structure of
2 in solution and in the solid state has been described
elsewhere.27 The arm component, 6-hydroxymethyl-2-pyri-
dinecarboxaldehyde (3), was synthesized through activated
MnO2 oxidation of one of the alcohol groups of commer-
cially available 2,6-bis(hydroxymethyl)pyridine.28 Chroma-
tography with silica gel (10% hydrated v/v) and a gradient of
ethyl acetate/petroleum ether (30 to 70%) as the eluant was
found to be the most efficient means of purifying 3. It was
also discovered that any unreacted 2,6-bis(hydroxymethyl)-
pyridine could be recovered from the chromatography col-
umn by eluting it with iso-propanol.
(C8, C13, and C14) and N1py and N8py atoms were
arranged on the outside of the horseshoe, while the ter-
nary Nhyz atoms (N2hyz and N7hyz) pointed inward.
Conjugation between the pyrimidine ring and hydrazone
bonds resulted in the majority of 1 lying in the mean plane
of the central pyrimidine ring (C9, C10, C11, C12, N4,
N5). The terminal pyridine rings were twisted with respect
to this plane in such a way that both the N1py and N8py
(py=pyridine) atoms occupied the same side of the mean
plane. The angles between the mean plane and the plane
of the N1py and N8py containing pyridine rings were 7.74°
and 8.04°, respectively. The hydroxymethyl arm on the
pyridine ring containing N1py lay in the mean plane, while
the corresponding group on the pyridine ring containing
N8py was twisted out of this plane by 83.76°.
Synthesis and Structure of 1. Ligand 1 was produced in
high yield by a condensation reaction of 2 and 3 in a 1:2
molar ratio (Scheme 1). No workup was needed as 1
precipitated out of the solution as a pure white solid. The
ligand was found to be only sparingly soluble in pyridine,
Molecules of 1 were organized into centrosymmetic-
stepped dimers through self-complementary H-bonding
interactions between the hydroxymethyl arms (Figure 2).
1
CHCl3, DMSO, and DMF at 50 °C. H and 13C NMR
The O1-H O2A distance was 1.970(2) A (correspon-
˚
3 3 3
˚
ding to an O1 O2A separation of 2.707(2) A). This
spectra of 1 were collected from a dilute DMSO-d6
solution at elevated temperatures. The 1H NOE correla-
tion between the proton of the pyrimidine ring (H5) and
the H11 protons of the terminal pyridine rings, combined
with the lack of any correlation between the methyl
protons on the ternary Nhyz atom (H8) and H5, showed
that 1 adopted a folded shape in solution, with both the
pym-hyz bonds in a transoid conformation (Scheme 1).
3 3 3
arrangement of the two horseshoe ligands created a shape
which was reminiscent of a macrocycle. These cyclic
dimers were linked together through self-complementary
H-bonding between O2-H N8B at a distance of 1.901(2)
3 3 3
˚
A [corresponding to an O2 N8B separation of 2.720(2)
3 3 3
˚
A], which formed a 1D chain in the diagonal [1 1 0] direction.
These chains were arranged into a 2D sheet through two
types of π-π stacking interactions involving alternating
The IR spectrum showed a broad peak at 3236 cm-1
,
corresponding to the OH stretching mode, and a strong
peak at 1561 cm-1, which was attributed to the stretching
mode of the newly formed imine bond. The ESMS
spectrum showed a base peak at m/z 421.2134 corre-
sponding to the molecular ion [1 þ H]þ. The microana-
lysis results were consistent with the predicted formula
for 1.
pyridine rings [centroid-to-centroid distances: N8py
˚
N8py = 3.7065(15) and N8py N1py = 3.8682(15) A]. An
3 3 3
3 3 3
additional π-stacking interaction between interdigitated
pyrimidine rings of adjacent sheets extended the struc-
ture into three dimensions [centroid-to-centroid distance:
3.7277(14) A].
Synthesis and Structures of Complexes. The Cu(II)
salts, Cu(ClO4)2 6H2O or Cu(CF3SO3)2 4H2O, were
˚
X-Ray Structure of C21H24N8O2, 1. The low solubility
of 1 in most organic solvents made obtaining X-ray-
quality crystals difficult. Crystals of suitable quality were
eventually obtained from a dilute DMSO solution of 1
which was left standing for over two months. Ligand 1
crystallized in the triclinic space group P1. The asym-
metric unit contained one complete ligand molecule
folded in a horseshoe conformation, with both pym-hyz
bonds (C9pym-N3hyz and C11pym-N6hyz) in a transoid
conformation (Figure 2). The distance across the horse-
shoe, from the centroid of one of the terminal pyridine
3
3
dissolved in CH3CN and added to 1 in either a 2:1 or
1:1 molar ratio. While 1 was not soluble in CH3CN, the
addition of the metal salt, with agitation and heat,
resulted in dissolution of 1 upon complexation to form
a clear green solution of the desired complex. UV-vis
spectroscopy was performed on these solutions; there-
after the complexes were crystallized by the slow diffusion
of diethyl ether. These crystals were used for single-crystal
X-ray analysis. Additional solid material was produced in
a similar fashion and was filtered and dried in vacuo, then
analyzed by microanalysis, ESMS, and IR spectroscopy.
˚
rings to the other, was 6.73 A. The three methyl groups

5928 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hutchinson et al.
Figure 2. (Top) View of 1 (crystallographic numbering). Thermal ellipsoids drawn at the 50% probability level. (Bottom) View showing the assembly of
1 into a 1D chain of dimers, along the [1 1 0] direction, through H-bonding (symmetry codes, A: 2 - x, 1 - y, 2 - z; B: 1 þ x, -1 þ y, z).
Cu21(ClO4)4. The UV-vis spectrum of the solution
showed a single broad peak at 691 nm. The microanaly-
tical result of the dried crystals was consistent with the
formula Cu21(ClO4)4 2H2O. The complex fragmented
3
and lost Cu(II) ions during ESMS, resulting in a base
peak at m/z 443.18942 which was consistent with the ion
[1 þ Na]þ. IR spectroscopy showed that coordination of
the Cu(II) ions increased the frequency of the OH stretch-
ing mode to 3455 cm-1. Four of the pym and py stretching
modes and the CdN stretching mode occurred between
1630 and 1561 cm-1
.
X-Ray Structure of [Cu21(CH3CN)4](ClO4)4 CH3CN,
3
4. Complex 4 crystallized in the triclinic space group P1,
with one [Cu21(CH3CN)4]4þ cation, four ClO4- counter-
ions, and a CH3CN of crystallization in the asymmetric
unit. The complex had a slightly bowed linear shape, with
both pym-hyz linkages in a cisoid conformation. The
centroid-to-centroid distance between the terminal pyr-
Figure 3. View of the [Cu21(CH3CN)4]4þ cation showing the coordina-
tion environments about the Cu(II) ions (crystallographic numbering).
Thermal ellipsoids drawn at the 50% probability level.
cules. Cu1 had a six coordinate, tetragonally distorted
octahedral geometry, with elongated Cu-N bonds to the
out-of-plane CH3CN ligands.38 Cu2 was present in a five
coordinate environment with a τ5 parameter of 0.605,
which was consistent with a distorted trigonal bipyramid
geometry.39 The axial sites were occupied by the N5pym and
N8py donors, while the two CH3CN molecules and the
N7hyz donor occupied the three equatorial sites (Figure 3).
The distance from the Cu(II) ions and the mean plane
through the central pyrimidine ring (C9, C10, C11, C12,
˚
idine rings of 4 was 12.59 A, which was almost twice the
length measured in the free ligand. A Cu(II) ion was
bound to each of the pym-hyz-py coordination sites.
The Cu1 ion was bound to the three N donors, and the
hydroxymethyl O donor of the pym-hyz-py coordina-
tion site, while Cu2 was only bound to the three N donors
of the pym-hyz-py coordination site, and not to the
hydroxymethyl O donor. The coordination sphere of
each Cu(II) ion was completed by two CH3CN mole-
˚
˚
N4, N5) was 0.193 A for Cu1 and 0.064 A for Cu2,
(38) Hathaway, B. J. Comprehensive Coordination Chemistry; Pergamon:
Oxford, U. K., 1987; Vol. 5.
(39) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 7, 1349–1356.

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 5929
Figure 4. View of two [Cu21(CH3CN)]4þ cations arranged into an offset
dimer through H-bonding interactions. The ClO4 counteranion
H-bonded to O2 is also shown (symmetry codes, A: 1 - x, 1 - y, 1 - z).
-
Figure 5. View of the [Cu21(SO3CF3)2(CH3CN)2]2þ cation showing the
coordination environment about the Cu(II) ions (crystallographic
numbering). Thermal ellipsoids drawn at the 50% probability level.
respectively. The complex was slightly bowed out of the
mean plane, such that the terminal pyridine rings both
resided on the same side of the mean plane as the two
Cu(II) ions. The angle between the plane of the pyridine
ring containing N1 and the mean plane was 4.77°, while
for the pyridine ring containing N8, this angle was 4.56°.
The complex was arranged into discrete offset dimers
by self-complementary H-bonding between O1 and O2 of
the N9 and N10 donors of the two bound CH3CN
molecules were bound in the equatorial positions. The
O2 donor was not bound to Cu2 and was instead orien-
tated away from Cu2 (Figure 5).
Most of the ligand backbone lay in the mean plane of
the central pyrimidine ring. A slight twist to the complex
meant that the N1py and N8py containing pyridine rings
projected out from either side of the mean plane by angles
of 3.53° and 4.57°, respectively. Cu1 and Cu2 sat above
and below the mean plane through the central pyrimidine
the hydroxymethyl arms (Figure 4). The O1-H O2A
3 3 3
3 3 3
˚
distance was 1.844(3) A [corresponding to an O1 O2A
˚
distance of 2.633(5) A]. Additionally, one of the free
-
˚
ClO4 anions was weakly H-bonded to O2 with an
˚
ring by 0.096 and 0.092 A, respectively. The only notice-
able intermolecular contact was a H bond between O2
O2-H O22 distance of 2.425(8) A [corresponding to
3 3 3
-
˚
an O2 O22 distance of 3.125(9) A].
3 3 3
and a symmetry generated SO3CF3 counterion. The
˚
Cu21(SO3CF3)4. The UV-vis spectrum showed a sin-
gle broad peak at 699 nm. Dark green crystals were grown
by the slow diffusion of diethyl ether into a CH3CN
solution of the complex. The microanalytical results for
the dried crystals were consistent with the complex formula
Cu21(SO3CF3)4. ESMS showed peaks at m/z 844.9536 and
944.9112, which were assigned to the molecular fragments
[Cu2(1-H)(SO3CF3)2]þ and [Cu21(SO3CF3)3]þ, respec-
tively. The IR spectrum showed the OH stretching
mode at 3445 cm-1. There were five peaks between 1636
and 1558 cm-1, due to the pym, py, and CdN stretching
modes.
O2-H O41 distance was 2.482(4) A [corresponding
3 3 3
˚
to a O2 O41 distance of 2.896(6) A.
3 3 3
Cu(1H)(ClO4)3. The UV-vis spectrum showed a single
broad peak at 657 nm. Dark green needle-shaped crystals
were obtained by the slow diffusion of diethyl ether into
this solution. Closer inspection revealed that there were
two different morphologies of green crystals growing
from the one solution. Single-crystal X-ray structural
analysis was successfully performed on a crystal of each
morphology, yielding the structural solutions [Cu(1H)-
(ClO4)2](ClO4) (6) and [Cu(1H)(CH3CN)](ClO4)3 0.5H2O
3
(7). The N8py donor was protonated in both isomers. The
microanalytical result from additional solid material was
consistent with the formula Cu1H(ClO4)3 0.5CH3CN. The
X-Ray Structure of [Cu21(SO3CF3)2(CH3CN)2](SO3-
CF3)2 CH3CN, 5. Complex 5 crystallized in the triclinic
3
3
space group P1 with one [Cu21(SO3CF3)2(CH3CN)2]2þ
cation, two SO3CF3 counterions, and a CH3CN of
ESMS spectrum of the dried material showed a peak at m/z
482.1245, corresponding to the ion fragment C21H23-
N8O2Cuþ. The IR spectrum obtained showed the O-H
stretching mode at 3462 cm-1 and four pym, py, and
-
crystallization in the asymmetric unit. The ligand back-
bone had a slightly bowed linear shape, similar to complex
4, with a length between the terminal pyridine ring cen-
CdN stretching modes between 1653 and 1558 cm-1
.
˚
troids of 12.67 A. Both pym-hyz bonds adopted a cisoid
X-Ray Structure of [Cu(1H)(ClO4)2](ClO4), 6. Com-
plex 6 crystallized in the monoclinic space group P21/c
with one [Cu(1H)(ClO4)2]þ cation and one ClO4- coun-
terion in the asymmetric unit. The complex had an asym-
metric bent shape, as the pym-hyz bond of the coordina-
conformation, and there was a Cu(II) ion bound to each of
the two pym-hyz-py coordination sites. Cu1 was present
in an elongated tetragonal octahedral geometry38 with the
O1, N1py, N2hyz, and N4pym donors of the pym-hyz-py
coordination pocket in equatorial positions and the O11
and O21 donors of two different SO3CF3- anions in axial
positions. The Cu2 coordination sphere of 5 closely re-
sembled that of Cu2 in 4. Cu2 was present in a five
coordinate distorted trigonal bipyramidal geometry with
a τ5 parameter of 0.574.39 The N5pym and N8py donors
were present in the axial sites, while the N7hyz donor and
tion pocket occupied with the Cu(II) ion (C9pym-N3hyz
)
had a cisoid arrangement, while the pym-hyz bond of the
uncoordinated pym-hyz-py site (C11pym-N6hyz) main-
tained a transoid conformation. As a result, the O1 to
C9pym half of the complex had a slightly bowed, linear
shape reminiscent of complexes 4 and 5, while the C11pym
to O2 half of the complex had a half horseshoe shape

5930 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hutchinson et al.
X-Ray Structure of [Cu(1H)(CH3CN)](ClO4)3 0.5H2O,
3
7. Complex 7 crystallized in the triclinic space group P1
with one [Cu(1H)(CH3CN)]3þ cation, three ClO4- coun-
terions, and a disordered H2O of crystallization in the
asymmetric unit. Complex 7 had a similar asymmetric
bent shape to 6. The Cu(II) ion in 7 was coordinated to the
O1, N1py, N2py, and N4pym donors of one of the
pym-hyz-py sites on 1. It was also coordinated to a
CH3CN molecule, giving the Cu(II) ion a five-coordinate,
pseudosquare pyramidal geometry, with a τ5 parameter
of 0.048.39 The Cu(II) ion was raised slightly above the
˚
mean plane of the central pyrimidine ring by 0.108 A. As
in 6, the coordination of the Cu(II) ion held the N2hyz
-
C9pym bond in its cisoid conformation and gave the O1 to
C9pym half of the ligand a slightly bowed, linear shape.
This half of the ligand also curved away from the mean
plane of the central pyrimidine ring such that the N1py
containing pyridine ring resided at an angle of 4.32° above
the mean plane. The C11pym-C21 half of 7 closely
resembled that of 6. It had the same half horseshoe shape,
and N8py was similarly orientated toward the middle of
the molecule and was protonated. The plane of the N8py
containing pyridine ring was tilted to a greater extent in 7
as its plane intersected the mean plane through the central
pyrimidine ring at an angle of 17.34°. In contrast to 6, the
hydroxymethyl O2 donor in 7 pointed away from the
vacant pym-hyz-py coordination pocket (Figure 8).
The distance between the centroids of the terminal pyr-
Figure 6. View of the [Cu(1H)(ClO4)2]þ cation showing the coordina-
tion environment about the Cu(II) ion and the cisoid N3hyz-C9pym and
transoid C11pym-N6hyz bonds (crystallographic numbering). Thermal
ellipsoids drawn at the 50% probability level.
similar to that of the structure of uncoordinated 1 (Figure 6).
The centroid-to-centroid distance between the terminal pyr-
˚
idine rings was 12.11 A.
The Cu(II) ion adopted a tetragonally distorted octahe-
dral geometry,38 with the donors O1, N1py, N2hyz, and
N4pym arranged in equatorial positions and the O23 and
O32 donors from two different ClO4- anions in axial co-
ordination sites (Figure6). The Cu(II) ionwas raisedoutof
˚
˚
the mean plane of the central pyrimidine ring by 0.105 A.
idine rings was 12.30 A, which was slightly longer than
that of 6.
The hydrogen on N8 was involved in a bifurcated H
bond with O24 on the ClO4- counterion, which sat above
the vacant pym-hyz-py coordination pocket, and a
disordered H2O (O3) molecule, which resided below the
The ligand backbone had a slight curve, such that the
terminal pyridine rings pointed away from the mean plane
of thecentralpyrimidine ring atanglesof5.88° fortheN1py
ring and 9.52° for the N8py ring. In addition, the N8py
containing pyridine ring was tilted with respect to the rest
of the molecule such that its plane intersected the mean
plane of the central pyrimidine ring at an angle of 9.52°.
The N8py and O2 donors were orientated towardthe center
of the vacant pym-hyz-py coordination pocket, and the
N8py donor was protonated.
empty pocket. The N8-H O24 distance was 2.697(4)
3 3 3
˚
A [corresponding to a N8 O24 distance of 3.064(5) A],
˚
3 3 3
˚
while the N8-H O3 distance was 2.172(7) A [corres-
3 3 3
˚
ponding to a N8 O3 distance of 2.949(8) A]. That same
ClO4 counterion was also H-bonded to O2A on a
3 3 3
-
The resultant positive charge on N8py was balanced by
neighboring [Cu(1H)(CH3CN)]3þ cation through O23,
-
˚
a third ClO4 counterion which bridged neighboring
with an O2A-H O23 distance of 2.233(4) A [cor-
3 3 3
[Cu(1H)(ClO4)2]þ cations through H-bonding between
O14 on the ClO4- counterion and the O1 and O2 termi-
nal OH arms on the neighboring cations. The O1-
˚
responding to an O2A O23 distance of 2.785(5) A]
- 3 3 3
(Figure 9). The ClO4 counterion containing Cl1 was
held in an unusual position beneath the Cu1-O1 coordi-
nation bond by a H bond between O13 and O1-H and a
H
O14 and O2A-H O14 distances were 2.048(2)
3 3 3
3 3 3
˚
and 2.502(2) A, respectively, [corresponding to O1
weak interaction between O12 and Cu1 (Figure 9). The
˚
3 3 3
O14 and O2A O14 distances of 2.799(2) and 2.819(3)
3 3 3
O1-H O13 distance was 2.208(4) A [corresponding to
3 3 3
˚
˚
an O1 O13 distance of 2.662(5) A], while the
A, respectively]. In addition, an intramolecular H bond
3 3 3
existed between O1 and O24 of the ClO4- bound to Cu1,
O12 Cu1 distance was 2.845(4) A. A search of O3Cl-
˚
3 3 3
˚
with an O1-H O24 distance of 2.474(2) A [cor-
O-Cu(II) bond distances in the Cambridge Stuctural
3 3 3
Database (CSD version 5.29)40 revealed that this O12
˚
responding to an O1 O24 distance of 2.977(3) A].
3 3 3
3 3 3
-
˚
Cu1 distance is above the upper quartile (2.73 A) of all
reported bond lengths (923 bond distances in 663 com-
O2A was also H-bonded to O13 on the bridging ClO4
˚
counterion, with an O2A-H O13 distance of 2.819(3) A
3 3 3
3 3 3
˚
[corresponding to an O2A O13 distance of 3.289(2) A].
˚
plexes, range from 1.91 to 3.58 A). Therefore, the O12
Cu1 distance was too long to be considered a bond,
but the unusual clamp-like positioning of the ClO4
3 3 3
Molecules of 6 were arranged through H-bonding with
the bridging ClO4- counterion into propeller-shaped 1D
chains, with an angle of 36.62° between the central pyri-
midine mean planes of neighboring molecules (Figure 7).
These chains ran along the c axis and were organized
into pairs through self-complementary offset face-to-face
π-π stacking interactions, which existed between the
central pyrimidine and the N8py containing pyridine rings
-
counterion over the Cu1-O1 bond suggested some
weak interaction was present between Cu1 and O12.
The other ClO4 counterion, which contained Cl3, was
-
(40) Allen, F. H.; Davies, J. E.; Galloy, J. J.; Johnson, O.; Kennard, O.;
Macrae, C. F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J. M.; Watson, D. G.
J. Chem. Inf. Comput. Sci. 1991, 31, 187–204.
˚
[centroid-to-centroid distance of 3.697(2) A]

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 5931
Figure 7. (Top) View of the arrangement of the [Cu(1H)(ClO4)2]þ cations into a 1D chain through bifurcated H-bonding between the hydroxymethyl
groups (O1 and O2) on neighboring cations with the ClO4- counteranion (O13 and O14). The intramolecular H bond between O24 on the ClO4- anion
bound to Cu1 and O1-H can be seen also (symmetry codes, A: x, 3/2 - y, 1/2 þ z). (Bottom) View of the one-dimensional chain along the c direction
showing the propeller shape created by the 36.62° angle between the planes of alternating cations.
structural solution. The microanalytical result of the
dried crystals was consistent with the complex formula
Cu1(SO3CF3)2. The IR spectrum showed the OH stretch-
ing peak at 3364 cm-1, and five peaks between 1615 and
1494 cm-1 due to various pym, py, and CdN stretching
modes.
X-Ray Structure of [Cu1(SO3CF3)]2(SO3CF3)2 CH3CN
3
8. Complex 8 crystallized in the triclinic space group P1
with two [Cu1(SO3CF3)]þ cationic units, two SO3CF3
-
counterions, and a CH3CN molecule of crystallization in
the asymmetric unit. There were also 4.5 disordered
CH3CN molecules in the unit cell; however, these were
removedfrom the structure with theSQUEEZE procedure,
as they could not be modeled effectively. Both of the
[Cu1(SO3CF3)]þ cations had a bent shape similar to that
of complexes 6 and 7, with one Cu(II) ion bound in one of
the pym-hyz-py coordination pockets in each cation. As
seen in 6 and 7, the pym-hyz bond of the occupied
coordination site adopted a cisoid conformation, while
Figure 8. View of the [Cu(1H)(CH3CN)]3þ cation showing the coordi-
the pym-hyz bond of the unoccupied site maintained a
nation environment about the Cu(II) ion and the cisoid N3hyz-C9pym and
transoid conformation. The two cations were stacked on
transoid C11pym-N6hyz bonds (crystallographic numbering). Thermal
top of each other in an off-center head-to-toe fashion. They
were arranged almost parallel to each other, with an angle
of 2.51° between the mean planes through their central
pyrimidine rings (C9, C10, C11, C12, N4, N5 and C30, C31,
C32, C33, N13, N14). Each cation was paired head-to-toe
with its symmetry generated centrosymmetic twin through
a coordination bond between the Cu(II) ion and the
hydroxymethyl O donor of the unoccupied coordination
site on the symmetry related cation (Cu1-O2A and Cu2-
O4A, Figure 10). As a result, complex 8 existed as a pair
of crystallographically distinct centrosymmetric dimers
(Figure 11).
ellipsoids drawn at the 50% probability level.
disordered over two sites, so possible H bonds were not
described.
Cu1(SO3CF3)2. The UV-vis spectrum showed a single
broad peak at 679 nm. Crystals were extremely hard to
grow. After many attempts, a batch of single crystals
suitable for X-ray determination were obtained through
the slow diffusion of diethyl ether into the complex
solution. The data from the first three X-ray experiments
were not of high enough quality to yield a stable structural
solution. For the fourth experiment, data were collected
on the crystal over 48 h, and the structure (described
below) was able to be refined successfully. Each of the
four crystals used gave the same cell, space group, and
The coordination spheres of Cu1 and Cu2 were very
similar, with only minor differences in bond lengths
and angles. Cu1 was present in a tetragonally distorted

5932 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hutchinson et al.
2þ
Figure 11. View of the two [Cu1(SO3CF3)]2
cationic dimers
H-bonded together through O2-H O12 and O4-H O22. Also
3 3 3
3 3 3
shown is the CH3CN molecule of crystallization, which is H-bonded to
O3-H (symmetry codes, A: 1 - x, 1 - y, 1 - z; B: -x, 1 - y, 1 - z).
Figure 9. (Top) View of two neighboring [Cu(1H)(CH3CN)]3þ cations
joined by self-complementary H-bonding between O2-H and O23 of one
of the ClO4- counterions. Also shown is the bifuricated H bond between
N8-H and O24 and O3 (symmetry codes, A: -x, 1 - y, 1 - z). (Bottom)
view of the Cl1 containing ClO4- positioned along the Cu1-O1 coordi-
nation bond due to a H bond between O1-H and O13 and a weak inter-
action between Cu1 and O12.
Cu2 were occupied by O11 of a SO3CF3- anion and O4A
of a symmetry generated [Cu1(SO3CF3)]þ cation. Cu1 sat
˚
0.262 A below the mean plane of the central pyrimidine
ring of its cation (C9, C10, C11, C12, N4, N5), while Cu2
˚
sat 0.238 A above the mean plane of the central pyrimi-
dine ring of its cation (C30, C31, C32, C33, N12, N13).
Both of the distinct [Cu1(SO3CF3)]þ cations had a
bowed shape, such that their terminal pyrimidine rings
were curved away from the mean plane of the cation. For
the cation that contained Cu1, the angles between the
planes of the N1 and N8 containing pyridine rings and the
mean plane of the cation were 6.92 and 2.78°, respectively.
For the cation that contained Cu2, the angles between the
planes of the N9 and N16 containing pyridine rings and
the mean plane of the cation were 9.06 and 1.12°, respec-
tively. Unlike 6 or 7, the N donors of the unoccupied
coordination sites were not protonated in either cation of
complex 8. The N8py and N16py donors were facing out
from the ligand backbone of each cation, whereas in both
6 and 7, the N8py donor was orientated toward the inside
of the complex. Interestingly, the N8py and N16py were
not involved in any significant intramolecular or inter-
molecular interactions
Figure 10. View
of
the
two
crystallographically
distinct
[Cu1(SO3CF3)]þ cation units of the asymmetric unit showing the coordi-
nation environment about the Cu(II) ion and the cisoid N3hyz-C9pym and
N11hyz-C30pym bonds and the transoid C11pym-N6hyz and C32pym
-
N14hyz bonds (crystallographic numbering). Thermal ellipsoids drawn at
the 50% probability level (symmetry codes, A: 1 - x, 1 - y, 1 - z; B: -x,
1 - y, 1 - z).
2þ
The two crystallographically distinct [Cu1(SO3CF3)]2
dimers were held together in a head-to-toe fashion by a
pair of H bonds between the SO3CF3- anion coordinated
to the Cu(II) ion of one dimer with the hydroxymethyl
arm of the unoccupied coordination site of the other
dimer (Figure 11). The O2-H O12 and O4-H O22
octahedral environment, with O1, N1py, N2hyz, and
N4pym occupying the equatorial coordination sites and
O21 of a SO3CF3- anion occupying one of the axial sites.
The other axial position was occupied by the hydroxy-
methyl O2A donor of a symmetry generated [Cu1-
(SO3CF3)]þ cation. Cu2 was also present in a distorted
octahedral environment, bound to the hydroxymethyl O
and three N donors of a pym-hyz-py coordination
pocket of the other cation of the asymmetric unit. Simi-
larly to Cu1, the axial sites of the coordination sphere of
3 3 3
3 3 3
˚
distances were 2.105(7) and 2.307(8) A, respectively
[corresponding to O2 O12 and O4 O22 distances
3 3 3
3 3 3
˚
of 2.843(7) and 2.798(8) A, respectively]. The pairing of
the dimers through H-bonding resulted in an infinite 1D
chain of cations running along the a axis (Figure 11). No
π-π stacking interactions were present between the
[Cu1(SO3CF3)]22þ dimers. The only other intermolecular

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 5933
interaction was a H bond between the CH3CN mole-
cule and O3, which had a O3-H N17 distance of
This is in contrast to previous studies where the reaction
of larger metals such as Pb(II), Zn(II), Hg(II), and Ag(I)
with pym-hyz strands on a 1:1 metal/ligand ratio re-
sulted in [2 ꢀ 2] grid5,9,10 and double helical7 structures.
Examples of pym-hyz strands forming grids with Cu(II)
ions are rarer,23 despite the fact that Cu(II) is commonly
used in the self-assembly of [2 ꢀ 2] grids due to its flexible
coordination sphere and its small crystal field stabilization
energy (CFSE) which does not inhibit grid formation.38,48,49
However, the coordination number of Cu(II) is typically
restricted to 4, 5, or 6, and the addition of the hydro-
xymethyl arm makes the coordination pocket on 1 tetra-
dentate, leaving only the axial coordination sites on
Cu(II) available. In this way the terminal 6-hydroxy-
methyl substituent exerted control over the self-assembly
of the mononuclear complexes 6, 7, and 8.48-50 Ligand 1
could still potentially be used to synthesize grids with
larger metals such as Pb(II), which can support coordina-
tion numbers above six.51 Additionally, the half extended
complexes 6, 7, and 8 could possibly be utilized as inter-
mediate structures in the stepwise assembly of heterome-
tallic grids,52-54 if the hydroxymethyl arm could be
displaced from the Cu(II) ion. This seemed feasible as 4
and 5 showed that the hydroxymethyl arm was not always
coordinated to the Cu(II) ion.
3 3 3
˚
1.846(11) A [corresponding to a O3 N17 distance of
3 3 3
˚
2.639(11) A].
Comparison of the Ligand and Its Metal Complexes
Electronic Spectroscopy. In all cases, the d-d transi-
tions of the Cu(II) complexes were represented by a
single, broad, featureless peak in the UV-visible spectra,
making assignment of the Cu(II) stereochemistry dif-
ficult.38,41 Interpretation of the UV-visible spectra for
the dinuclear linear complexes, Cu21(ClO4)4 and Cu21-
(SO3CF3)4, was complicated further as their solid state
structures (4 and 5, respectively) both included one Cu(II)
ion in a tetragonally distorted octahedral geometry, while
the other Cu(II) ion adopted a distorted trigonal bipyr-
amidal geometry. The λmax values of 691 and 699 nm that
were observed for the two complexes, respectively, were
typical of Cu(II) in a trigonal bipyramidal environ-
ment;38,42 however, they were still within the wide range
of values seen for tetragonally distorted octahedral
CuNxLy chromophores.38,41,43-46 The mononuclear
Cu1(SO3CF3)2 complex showed a single broad peak at
679 nm, which also tentatively suggested an elongated
tetragonally distorted Cu(II) stereochemistry. The mono-
nuclear Cu(1H)(ClO4)2 complex yielded two isomeric
solid state structures, 6 and 7, which contained a Cu(II)
ion in a elongated tetragonal octahedral geometry and a
distorted square pyramidal geometry, respectively. The
peak at 657 nm was typical for Cu(II) in a distorted square
pyramidal environment,41,47 but it also fell within the
wide range of values for tetragonally distorted octahedral
Cu(II) geometries. Thus, the stereochemistries of the
Cu(II) ion in solution could not be ascertained.
Complexes 4 to 8 exhibited a range of Cu(II) geome-
tries, including elongated tetragonal octahedral, distorted
trigonal bipyramidal, and distorted square pyramidal.
Interestingly, the two Cu(II) ions in both 4 and 5 had
different geometries, despite the coordination pockets
they occupied being equivalent. In both 4 and 5, one of
the Cu(II) ions was present in a elongated tetragonal octa-
hedral geometry and bound to the hydroxymethyl OH
donor while the other Cu(II) ion was not bound to the O
donor and adopted a distorted trigonal bipyramidal
geometry. Additionally, in 5, the tetragonally distorted
octahedral Cu(II) ion was bound to two SO3CF3- anions,
whereas the distorted trigonal bipyramidal Cu(II) was
bound to two solvent molecules instead. The Cu(II) ions
present in complexes 6, 7, and 8 were all bound to a
hydroxymethyl O donor. As expected, SO3CF3- proved to
be a stronger coordinating anion than ClO4-, with 5 and
X-Ray Crystallography. X-ray crystallography con-
firmed that coordination of Cu(II) ions caused the
pym-hyz bonds of 1 to rotate from a transoid to a cisoid
conformation. In its free state, 1 was a horseshoe-shaped
˚
ligand with a distance of 6.73 A between the centroids of
its terminal pyridine rings. This distance increased sig-
˚
nificantly to 12.59 and 12.67 A upon coordination with a
two molar equivalence of Cu(II) ions to make the linear
dinuclear complexes 4 and 5, respectively. These lengths
were similar in magnitude to those of other dinuclear
pym-hyz complexes which contained Pb(II) and Zn(II)
ions.5 Complexes 6, 7, and 8 on the other hand only
contained one Cu(II) ion per ligand and consequently
only the pym-hyz bond of the occupied coordination site
was in a cisoid conformation, while the pym-hyz bond of
the empty coordination site retained a transoid shape.
-
8 showing coordination between SO3CF3 and Cu(II).
Complex 6 was the only one containing ClO4 anions
-
coordinated to Cu(II), while in 4 and 7 the coordination
geometries of the Cu(II) ions were completed by CH3CN
solvent molecules instead. The use of Cu(ClO4)2 6H2O
also led to the protonation of the N8py donor of the empty
3
coordination site in complexes 6 and 7. Complex 8, which
was synthesized using Cu(SO3CF3)2 4H2O was not pro-
3
tonated, and the N8py and N16py donor atoms of the
empty coordination sites were not involved in any sig-
nificant intra- or intermolecular interactions.
(41) Hathaway, B. J. J. Chem. Soc., Dalton Trans. 1972, 1196–1199.
(42) Murakami, T.; Takei, T.; Ishikawa, Y. Polyhedron 1996, 16(1),
89–93.
(43) Comba, P.; Lang, C.; Lopez de Laorden, C.; Muruganantham, A.;
Rajaraman, G.; Wadepohl, H.; Zajaczkowski, M. Chem.;Eur. J. 2008, 14,
5313–5328.
(44) Murakami, T.; Hatakeyama, S.; Igarashi, S.; Yukawa, Y. Inorg.
Chim. Acta 2000, 310, 96–102.
(45) Comba, P.; Hauser, A.; Kerscher, M.; Pritzkow, H. Angew. Chem.,
Int. Ed. Engl. 2003, 42, 4536–4540.
(48) Dawe, L. N.; Shuvaev, K. V.; Thompson, L. K. Chem. Soc. Rev.
2009, 38, 2334–2359.
(49) Dawe, L. N.; Thompson, L. K. Dalton Trans. 2008, 3610–3618.
(50) Hausmann, J.; Brooker, S. Chem. Commun. 2004, 1530–1531.
(51) Harrowfield, J. Helv. Chim. Acta 2005, 88, 2430–2432.
(52) Bassani, D. M.; Lehn, J.-M.; Fromm, K.; Fenske, D. Angew. Chem.,
Int. Ed. Engl. 1998, 37(17), 2364–2367.
€
(46) Belousoff, M. J.; Tjioe, L.; Graham, B.; Spiccia, L. Inorg. Chem.
2008, 47, 8641–8651.
(53) Uppadine, L. H.; Gisselbrecht, J.-P.; Kyritsakas, N.; Nattinen, K.;
Rissanen, K.; Lehn, J.-M. Chem.;Eur. J. 2005, 11, 2549–2565.
(54) Uppadine, L. H.; Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 2004, 43,
240–243.
ꢀ
(47) Kruszynski, R.; Kuznik, B.; Bartczak, T. J.; Czakis-Sulikowska, D.
J. Coord. Chem. 2005, 58, 165–173.

5934 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hutchinson et al.
The terminal hydroxymethyl groups were involved in a
variety of hydrogen bonding interactions which gave rise
to supramolecular structures such as dimers (4 and 7) and
1D chains (6 and 8). Additionally, the orientation of the
pyridine ring in the empty pym-hyz-py coordination
site in complexes 6, 7, and 8 was influenced by the
interactions of the hydroxymethyl O donor atom of that
site. In complexes 6 and 7, the pyridine ring was rotated
such that the N8py donor atom pointed in toward the
central pyrimidine ring of the complex as a result of the
ClO4- and SO3CF3- complexes, respectively. Coordination
of the hydroxymethyl arm inhibited the formation of a [2 ꢀ 2]
grid when 1 was reacted with the Cu(II) salts in a 1:1 molar
ratio, resulting in bent complexes, where only one of the
coordination sites was occupied with a Cu(II) ion and the
other site was left empty. In this way, the hydroxymethyl
functional groups of the terminal pyridine rings controlled
the outcome of the self-assembly between ligand 1 and the
Cu(II) ions.
The Cu(II) ions in the complexes showed a variety of
coordination geometries, and all the complexes showed some
coordination between the terminal OH groups and the Cu(II)
ions. Various H-bonding interactions resulted from the OH
groups, which created different supramolecular patterns such
as dimers and 1D chains. It is envisioned that the terminal
OH groups provide a route to incorporating pyrimidi-
ne-hydrazone molecular strands into larger molecules, so
that their metal-induced, dynamic structural change could be
applied to nanoscale mechanical devices.
-
terminal OH group being H-bonded to a ClO4 anion
located near the empty site. In complex 8, the pyridine
ring of the empty site retained the conformation seen in
the free ligand, with the pyridine N donor on the outside
of the ligand, due to the OH group being coordinated to a
symmetry related Cu(II) ion.
Conclusion
The synthesis of ligand 1 shows that hydroxymethyl
groups can be added to the terminal ends of an otherwise
chemically inert pym-hyz strand to extend its versatility.
Structural analysis revealed that coordination of 1 with
Cu(ClO4)2 6H2O and Cu(SO3CF3)2 4H2O on a 1:2 molar
Acknowledgment. We thank the Department of Chem-
istry, University of Otago and the New Economic Re-
search Fund of the Foundation for Research, Science and
Technology (NERF Grant No UOO-X0808) for finan-
cial support.
3
3
ratio resulted in an expansion from the horseshoe-shaped free
ligand to linear dicopper complexes. This uncoiling action,
brought about by the rotation of the pym-hyz bonds from a
transoid to cisoid conformation, resulted in an increase in the
Supporting Information Available: X-ray data in CIF format
and selected bond length and angle data. This material is
available free of charge via the Internet at http://pubs.acs.org.
˚
˚
length of the ligand from 6.73 A to 12.59 and 12.67 A for the