Copper(I) coordination chemistry of (Pyridylmethyl)amide ligands

Article abstract of DOI:10.1021/ic0612810

Copper(I) chloro complexes were synthesized with a family of ligands, HL^R [HL^R = N-(2-pyridylmethyl)acetamide, R = null; 2-phenyl-N-(2-pyridylmethyl)acetamide, R = Ph; 2,2-dimethyl-N-(2-pyridylmethyl) propionamide, R = Me₃; 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide, R = Ph₃)]. Five complexes were synthesized from the respective ligand and cuprous chloride: [Cu(HL)Cl]_n (1), [Cu₂(HL) ₄Cl₂] (2), [Cu₂(HL^Ph) ₂(CH₃CN)₂Cl₂] (3), [Cu ₂(HL^Ph3)₂Cl₂] (4), and [Cu(HL ^Me3)₂Cl] (5). X-ray crystal structures reveal that for all complexes the ligands coordinate to the Cu in a monodentate fashion, and inter- or intramolecular hydrogen-bonding interactions formed between the amide NH group and either amide C=O or chloro groups stabilize these complexes in the solid state and strongly influence the structures formed. Complexes 1-5 display a range of structural motifs, depending on the size of the ligand substituent groups, hydrogen bonding, and the stoichiometry of the starting materials, including a one-dimensional coordination polymer chain (1) and binuclear (2-4) or mononuclear (5) structures.

Full text of DOI:10.1021/ic0612810

Inorg. Chem. 2006, 45, 9416−9422
Copper(I) Coordination Chemistry of (Pyridylmethyl)amide Ligands
Lei Yang and Robert P. Houser*
Department of Chemistry and Biochemistry, UniVersity of Oklahoma, 620 Parrington OVal,
Norman, Oklahoma 73019
Received July 11, 2006
Copper(I) chloro complexes were synthesized with a family of ligands, HLR [HLR
null; 2-phenyl-N-(2-pyridylmethyl)acetamide, R Ph; 2,2-dimethyl-N-(2-pyridylmethyl)propionamide, R
2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide, R
)
N-(2-pyridylmethyl)acetamide,
Me3;
R
)
)
)
)
Ph3)]. Five complexes were synthesized from the respective
ligand and cuprous chloride: [Cu(HL)Cl]n (1), [Cu2(HL)4Cl2] (2), [Cu2(HLPh)2(CH3CN)2Cl2] (3), [Cu2(HLPh )2Cl2] (4),
3
and [Cu(HLMe )2Cl] (5). X-ray crystal structures reveal that for all complexes the ligands coordinate to the Cu in a
3
monodentate fashion, and inter- or intramolecular hydrogen-bonding interactions formed between the amide NH
group and either amide C
the structures formed. Complexes 1
substituent groups, hydrogen bonding, and the stoichiometry of the starting materials, including a one-dimensional
coordination polymer chain (1) and binuclear (2 4) or mononuclear (5) structures.
dO or chloro groups stabilize these complexes in the solid state and strongly influence
−5 display a range of structural motifs, depending on the size of the ligand
−
Introduction
coordination modes, including the anionic amidate
form1,2,4-6,8-11 and the neutral amide form.3-6,8,11 While we
are particularly interested in examples of CuII complexes with
polydentate amide ligands,1,4-6,8,10 numerous other transition-
metal pyridyl amide or pyridyl amidate complexes have also
been reported.2,3,9,11 Among the various reported transition-
metal complexes with pyridyl amide ligands, several have
been specifically used as biomimetic models,5,9 while others
have produced interesting supramolecular and/or polymeric
structures.3,10,11 Only a few examples of pyridyl amide ligands
coordinated to CuI ions have been reported.12
Pyridyl amide ligands have garnered interest because of
their biomimetic potential and their variable ligation modes.1-11
These ligands have been shown to bind in a wide variety of
* To whom correspondence should be addressed. E-mail: houser@
ou.edu.
(1) (a) Rowland, J. M.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.
2000, 39, 5326-5332. (b) Toscano, P. J.; Fordon, K. J.; Macherone,
D.; Liu, S.; Zubieta, J. Polyhedron 1990, 9, 2375-2383. (c) Lee, B.
W.; Min, K. S.; Doh, M. K. Inorg. Chem. Commun. 2002, 5, 163-
165. (d) Tounsi, N.; Dupont, L.; Mohamadou, A.; Cadiou, C.;
Aplincourt, M.; Plantier-Royon, R.; Massicot, F.; Portella, C. New J.
Chem. 2004, 28, 785-792.
In our laboratory, a variety of pyridyl amide ligands have
been designed and synthesized to explore their complexation
properties.5-8 It was established that the protonation or
deprotonation of the amide N can control the coordination
geometry of the metal center and the stability of complexes
formed. In addition, the substituent groups attached to the
amide also play an important role in the formation of
different shapes and spatial orientations of the complex
structure formed.6,8 Recently, we employed a series of
(pyridylmethyl)amide ligands (HLR; R ) H, Me3, Ph, and
Ph3) with different substituent groups on the amide.6 These
(2) (a) Toscano, P. J.; Belsky, K. A.; Hsieh, T.-C.; Nicholson, T.; Zubieta,
J. Polyhedron 1991, 10, 977-991. (b) Toscano, P. J.; Belsky, K. A.;
Engelhardt, L. M.; Fordon, K. J.; White, A. H. Inorg. Chem. 1990,
29, 1357-1359. (c) Gao, D. Z.; Lin, H. K.; Zhu, S. R. Acta
Crystallogr. E 2005, 61, M2359-M2361. (d) Cati, D. S.; Stoeckli-
Evans, H. Acta Crystallogr. E 2004, 60, M174-M176.
(3) (a) Uemura, K.; Kitagawa, S.; Kondo, M.; Fukui, K.; Kitaura, R.;
Chang, H.-C.; Mizutani, T. Chem.sEur. J. 2002, 8, 3587-3600. (b)
Uemura, K.; Kitagawa, S.; Fukui, K.; Saito, K. J. Am. Chem. Soc.
2004, 126, 3817-3828.
(4) (a) Nonoyama, M. Inorg. Chim. Acta 1975, 13, 5-10. (b) Nonoyama,
M.; Tomita, S.; Yamasaki, K. Inorg. Chim. Acta 1975, 12, 33-37.
(5) Klein, E. L.; Khan, M. A.; Houser, R. P. Inorg. Chem. 2004, 43, 7272-
7274.
(6) Pal Chaudhuri, U.; Whiteaker, L. R.; Yang, L.; Houser, R. P. Dalton
Trans. 2006, 1902-1908.
(7) Michels, J. T.; O’Malley, B. G.; Klein, E. L.; Yang, L.; Grohmann,
A.; Houser, R. P. Acta Crystallogr. E 2005, 61, O3834-O3836.
(8) Mondal, A.; Li, Y.; Khan, M. A.; Ross, J. H.; Houser, R. P. Inorg.
Chem. 2004, 43, 7075-7082.
(9) (a) Harrop, T. C.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.
2005, 44, 9527-9533. (b) Zhu, S. R.; Brennessel, W. W.; Harrison,
R. G.; Que, L. Inorg. Chim. Acta 2002, 337, 32-38.
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Chem. 2004, 43, 1021-1030. (b) Hausmann, J.; Jameson, G. B.;
Brooker, S. Chem. Commun. 2003, 2992-2993.
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9416 Inorganic Chemistry, Vol. 45, No. 23, 2006
10.1021/ic0612810 CCC: $33.50
© 2006 American Chemical Society
Published on Web 10/11/2006

CuI Coordination Chemistry of (Pyridylmethyl)amide Ligands
The solution was filtered through Celite, and the diffusion of Et2O
into filtrate leads to the formation of light-yellow crystals (0.015
g, 82.2% yield). Anal. Calcd for C32H34Cl2Cu2N6O2: C, 52.46; H,
4.68; N, 11.47. Found: C, 51.94; H, 4.48; N, 10.46. NMR (300
MHz, DMSO-d6): δ 2.92 (t, 3H), 3.95 (s, 2H), 4.87 (s, 2H), 7.65-
7.76 (m, 8H), 8.27 (t, 1H), 9.16 (s, 1H). FTIR (KBr): 3265, 3607,
2918, 1669, 1652, 1599, 1568, 1475, 1438, 1410, 1359, 1325, 1311,
ligands have exhibited very interesting coordination proper-
ties that lead to novel Cu clusters. A highly symmetrical
copper hydroxide tennis ball cluster, [Cu8L8(OH)4]4+, was
characterized by X-ray crystallography, electron paramag-
netic resonance, electronic absorption spectra, and magne-
tism.8 The increasing steric effect and electron-donating or
-withdrawing property from substituent groups, R, led to the
formation of different Cu clusters [Cu4(LPh)4(OH)2]2+, [Cu2-
(HLMe )2(OMe)2] , and [Cu2(HL )2(OMe)2] with lower
nuclearity.6 While the CuII chemistry of our ligands has been
thoroughly investigated, the CuI chemistry remains un-
explored. Herein, we report the synthesis and detailed
structural properties of five CuI complexes synthesized from
CuCl and HLR.
1250, 1173, 1152, 1027, 764, 743, 728, 695, 624, 490 cm-1
.
Ph3
[Cu2(HLPh )2Cl2] (4). A solution of HL (0.378 g, 1 mmol) in
dichloromethane (2 mL) was added to a stirred solution of CuCl
(0.0496 g, 0.5 mmol) in acetonitrile (2 mL). The reaction was stirred
for 7 h, during which the color changed to light yellow. The solution
was filtered, and diffusion of diethyl ether into the filtrate produced
colorless crystals suitable for crystallographic characterization
(0.273 g, 51.1% yield). Anal. Calcd for C26H22ClCuN2O: C, 65.40;
3
4+
Ph3
4+
3
1
H, 4.64; N, 5.87. Found: C, 65.51; H, 4.67; N, 5.94. H NMR
(300 MHz, CD2Cl2): δ 2.02 (s, 3H), 4.75 (d, 2H), 6.99 (s, 1H),
7.32-7.35 (m, 15H), 7.75 (t, 1H), 8.54 (s, 1H). FTIR (KBr): 3450,
3214, 3056, 3022, 1661, 1599, 1571, 1491, 1439, 1362, 1319, 1252,
1236, 1224, 1187, 1151, 1102, 1084, 1050, 1033, 1000, 931, 910,
894, 846, 772, 762, 742, 700, 670, 638, 616, 596, 549, 531, 521
Experimental Section
General Procedures. All reagents were purchased from com-
mercial suppliers and used as received without further purification,
unless otherwise stated. Ligands N-(2-pyridylmethyl)acetamide
(HL), 2,2-dimethyl-N-(2-pyridylmethyl)propionamide (HLMe ),
cm-1
.
3
2-phenyl-N-(2-pyridylmethyl)acetamide (HLPh), and 2,2,2-triphenyl-
3
[Cu(HLMe )2Cl] (5). A solution of HL (0.192 g, 1 mmol) in
acetone (2 mL) was added to a stirred slurry of CuCl (0.0496 g,
0.5 mmol) in acetone (2 mL). The reaction was stirred for 1.5 h,
during which the color changed to light yellow. The solution was
filtered, and diffusion of diethyl ether into the filtrate produced
light-yellow crystals suitable for crystallographic characterization
(0.179 g, 74.0% yield). Anal. Calcd for C22H32ClCuN4O2: C, 54.65;
Me3
N-(2-pyridylmethyl)acetamide (HLPh ) were synthesized according
3
to procedures previously reported.6,8 All solvents were dried under
nitrogen using standard methods and distilled before use, and all
CuI complexes were synthesized under nitrogen in a glovebox.
Fourier transform (FTIR) spectra were collected on a Nexus 470
FTIR spectrometer using the KBr pellet technique. 1H NMR spectra
were recorded on a Varian 300-MHz spectrometer using a deuter-
ated solvent as the internal standard. Elemental analyses were
carried out by Atlantic Microlabs, Norcross, GA.
1
H, 6.67; N, 11.59. Found: C, 54.54; H, 6.75; N, 11.49. H NMR
(300 MHz, CD3COCD3): δ 1.20-1.29 (m, 9H), 4.67 (d, 2H), 7.42
(s, 1H), 7.45 (s, 1H), 7.78 (s, 1H), 7.94 (t, 1H), 8.72 (s, 1H). FTIR
(KBr): 3298, 3079, 2961, 1678, 1644, 1605, 1559, 1514, 1478,
1442, 1397, 1365, 1354, 1298, 1255, 1203, 1160, 1104, 1057, 1009,
[Cu(HL)Cl]n (1). A solution of HL (0.15 g, 1 mmol) in
acetonitrile (3 mL) was added to a stirred solution of CuCl (0.0989
g, 1 mmol) in acetonitrile (3 mL). The reaction was stirred for 1.5
h, during which the color changed to light yellow. The solution
was filtered, and diffusion of diethyl ether into the filtrate produced
crystals suitable for crystallographic characterization (0.169 g,
68.0% yield). Anal. Calcd for C8H10ClCuN2O: C, 38.56; H, 4.05;
N, 11.24. Found: C, 38.59; H, 3.98; N, 11.18. 1H NMR (300 MHz,
DMSO): δ 1.94 (s, 3H), 4.42 (s, 2H), 7.12 (s, 1H), 7.39 (s, 2H),
7.83 (t, 1H), 8.58 (s, 1H). FTIR (KBr): 3295, 3069, 1644, 1604,
1569, 1550, 1477, 1439, 1411, 1373, 1357, 1290, 1235, 1156, 1116,
944, 886, 860, 793, 760, 719, 642, 622, 585, 530, 466 cm-1
.
X-ray Crystal Structure Determination. Single crystals of 1-5
were obtained by vapor diffusion of Et2O into solutions of the
complex. Data for 1-5 were collected on a Bruker Apex CCD
area detector diffractometer with graphite-monochromated Mo KR
(λ ) 0.710 73 Å) radiation. The diffraction data from complex 3
had serious twinning problems, and a large amount of overlapping
data from twinning were omitted. Only the raw structure was
determined because of the incompleteness of the data. For
complexes 1, 2, 4, and 5, cell parameters were determined from a
nonlinear least-squares fit of the data. The data of these four
complexes were corrected for absorption by the semiempirical
method. The structures were solved by direct methods by use of
the SHELXTL program and refined by full-matrix least squares on
F 2 by use of all reflections.13 H atom positions were initially
determined by geometry and refined by a riding model. Non-H
atoms were refined with anisotropic displacement parameters.
Crystal data for 1, 2, 4, and 5 are summarized in Table 1.
1086, 1032, 774, 719, 685, 613, 585, 497, 459 cm-1
.
[Cu2(HL)4Cl2] (2). A solution of HL (0.30 g, 2 mmol) in
acetonitrile (4 mL) was added to a stirred solution of CuCl (0.0989
g, 1 mmol) in acetonitrile (3 mL). The reaction was stirred for 5.5
h, during which the color changed to yellow. The solution was
filtered, and diffusion of diethyl ether into the filtrate produced
yellow crystals suitable for crystallographic characterization (0.284
g, 71.1% yield). Anal. Calcd for C32H40Cl2Cu2N8O4: C, 48.12; H,
5.05; N, 14.03. Found: C, 48.05; H, 5.11; N, 14.09. 1H NMR (300
MHz, CD3CN): δ 2.02 (s, 3H), 4.48 (d, 2H), 7.12 (s, 1H), 7.34 (s,
1H), 7.42 (s, 1H), 7.80 (t, 1H), 8.54 (s, 1H). FTIR (KBr): 3352,
3292, 3067, 1678, 1644, 1601, 1550, 1512, 1478, 1439, 1409, 1398,
1370, 1354, 1294, 1279, 1231, 1156, 1037, 1012, 850, 779, 760,
Results and Discussion
There are three donor atoms in the (pyridylmethyl)amide
ligands, HLR, namely, one N donor atom from the pyridyl
ring and N and O donor atoms from the amide group.
Previously, we observed that the coordination modes of our
ligands are tunable by deprotonation of the amide N-H
727, 682, 595, 547, 498 cm-1
.
[Cu2(HLPh)2(CH3CN)2Cl2] (3). A solution of CuCl (0.0495 g,
0.5 mmol) in acetonitrile (1 mL) was added to a stirred solution of
HLPh (0.113 g, 0.5 mmol) in acetonitrile (2 mL). The resulting light-
yellow suspension was stirred for 4 h, and then the solvent was
removed under reduced pressure. The light-yellow powder was
washed with 2 mL of Et2O and dissolved in acetonitrile (2 mL).
(13) (a) Sheldrick, G. M. Gaussian, version 6.10; Bruker AXS Inc.:
Madison, WI, 2000. (b) International Tables for Crystallography;;
Hahn, T., Ed.; Kluwer: Boston, 1995; Vol. C.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9417

Yang and Houser
Table 1. Summary of Crystal Data and Refinement Parameters for Complexes 1, 2, 4, and 5
1
2
4
5
formula
fw
temp (K)
space group
a (Å)
C8H10ClCuN2O
249.17
113(2)
P212121
4.8153(4)
13.7892(11)
14.0641(11)
90
C32H40Cl2Cu2N8O4
798.70
87(2)
C52H44Cl2Cu2N4O2
954.89
87(2)
C22H32ClCuN4O2
483.51
100(2)
P2/c
11.162(3)
7.3381(16)
15.441(3)
90
107.754(5)
90
2
1204.5(5)
1.333
1.042
P21/c
P1h
13.738(6)
9.126(4)
15.083(6)
90
113.643(7)
90
8.9143(16)
9.5821(16)
13.346(2)
83.872(5)
80.222(5)
72.218(5)
1
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
Z
90
90
4
2
V (Å3)
933.84(13)
1.772
2.582
0.0179
0.0475
0.972
1732.3(13)
1.531
1.431
0.0221
0.0617
1.023
1067.9(3)
1.485
1.169
0.0295
0.0855
F
calcd (g/cm3)
µ (mm-1
)
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
GOF on F 2
0.0300
0.0799
1.001
1.003
Scheme 1. Syntheses and Structures of Complexes 1-5
group to form an amidate.5,6,8 If HLR remains neutral, the
pyridyl N atom and carbonyl O atom chelate to the same
Cu atom to form a stable seven-membered ring. A mono-
nuclear species in which one Cu atom is coordinated
symmetrically by two ligands forms in the absence of a
bridging ligand,8 and binuclear species will form with two
µ2-methoxide bridging ligands.6 On the other hand, if the
ligand is deprotonated by a base, a bidentate bridging
coordination mode is observed. In the octa- and tetranuclear
Cu clusters previously synthesized in our laboratory,6,8 ligand
All five CuI complexes were synthesized in degassed
organic solvents by the reaction of cuprous chloride with
the respective ligand, summarized in Scheme 1. While 1-5
are stable in the solid state when stored under nitrogen,
solutions of 1-5 decompose when exposed to open air,
producing uncharacterized green precipitates within hours.
In these five complexes, the ligand HLR displays a new
monodentate coordination mode that has not been observed
in previous examples of complexes synthesized with these
ligands in our laboratory.5,6,8 The amide group does not
coordinate, and only the N atom from the pyridyl group
coordinates to the Cu ion. One possible reason for this is
that the electron donor properties of the Cl ion decrease the
effective charge on the Cu ion, and the Cu ion is “softer” in
the hard and soft acids and bases sense, making coordination
L
R- (R ) null and Ph) not only chelates to one Cu through
the pyridyl and amidate N atoms but also bridges to another
Cu through the amido O atom. In this paper, the synthesis,
characterization, and structures of five new CuI complexes
coordinated by HLR (R ) null, Ph, Ph3, Me3) are presented.
9418 Inorganic Chemistry, Vol. 45, No. 23, 2006

CuI Coordination Chemistry of (Pyridylmethyl)amide Ligands
by the “hard” O donor less favorable.14 Stoichiometry is
another factor of complex conformation, which is illustrated
in the syntheses of complexes 1 and 2. Increasing from 1 to
2 equiv of HL relative to CuCl leads to structural differences
between one-dimensional chains in 1 and binuclear chloro-
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) of
Complexes 1, 2, 4, and 5
Complex 1
Cu1-N1
Cu1-Cl1
1.9835(13)
2.2246(4)
Cu1-Cl1A
Cl1-Cu1A
2.3997(4)
2.3997(4)
bridged molecular Cu species in 2. Likewise, HLMe combines
3
N1-Cu1-Cl1
N1-Cu1-Cl1A
140.63(4)
107.25(4)
Cl1-Cu1-Cl1A
Cu1-Cl1-Cu1A
110.592(14)
90.309(14)
with CuCl to form a 2:1 ligand-to-metal complex. However,
our efforts to synthesize 2:1 ligand-to-metal adducts with
Complex 2
Me3
HLPh and HLPh or a 1:1 ligand-to-metal complex with HL
Cu1-N1
Cu1-N3
2.0547(15)
2.0351(13)
Cu1-Cl1
Cu1-Cl1A
2.4001(9)
2.4762(9)
3
were not successful, perhaps attributable to steric effects of
the substituent groups on the amide.
N3-Cu1-N1
N3-Cu1-Cl1
N1-Cu1-Cl1
Cu1-Cl1-Cu1A
121.48(5)
114.14(4)
103.13(4)
68.99(3)
N3-Cu1-Cl1A
N1-Cu1-Cl1A
Cl1-Cu1-Cl1A
105.22(4)
101.07(3)
111.00(3)
When ligand HL is deprotonated by triethylamine, octa-
nuclear CuII clusters were isolated,8 which prompted us to
investigate the reaction between ligand HLR and CuCl in
the presence of a base. However, although the mixture of 1
equiv of HLR and 1 equiv of triethylamine reacts with CuCl
to give a yellow solution, disproportionation quickly occurs.
The substituent group on the amide is an important factor to
the disproportionation rate: the larger the substituent group,
the slower the disproportionation rate. Specific kinetic
parameters and further characterization of the resultant CuII
species from disproportionation are currently under inves-
tigation.
Complex 4
Cu1-N1
Cu1-Cl1A
1.9553(16)
2.2765(6)
Cu1-Cl1
2.2878(6)
N1-Cu1-Cl1A
N1-Cu1-Cl1
129.65(5)
123.95(5)
Cl1A -Cu1-Cl1
Cu1A -Cl1-Cu1
106.023(19)
73.976(19)
Complex 5
Cu1-N1B
Cu1-N1A
1.9509(15)
1.9509(15)
Cu1-Cl1
2.3060(9)
107.44(4)
N1B-Cu1-N1A
N1B-Cu1-Cl1
145.12(9)
107.44(4)
N1A-Cu1-Cl1
Complexes of cuprous chloride with unidentate N donor
ligands have been reported.15,16 However, to our knowledge,
the monodentate coordination of multidentate ligands to
copper(I) chloride adducts has not been previously observed.
Crystal data for 1, 2, 4, and 5 are presented in Table 1, and
selected bond distances and angles are presented in Table 2.
Compound 1. The reaction of 1 equiv of HL with 1 equiv
of CuCl leads to the formation of one-dimensional chains
of 1, possessing a novel right-handed helical structure (Figure
1). The CuI atom is coordinated by one pyridyl N atom and
two Cl anions with Cu-Cl distances of 2.2246(4) and
2.3997(4) Å, respectively. The CuI atom in 1 displays trigonal
geometry, and the Cu ion and the three ligand atoms nearly
fall in the same plane as the pyridyl ring. The mean deviation
of the Cu, Cl, and pyridyl ring atoms from this least-squares
plane is 0.0284 Å. The N atom from the pyridyl group
coordinates to the Cu ion with a Cu-N distance of 1.9835-
(13) Å. Interestingly, the two Cl atoms do not bridge to the
same Cu ion to form a simple binuclear complex but bind
to two separate Cu-HL units, with a Cu1-Cl1-Cu1A angle
of 90.309(14)° and a Cu‚‚‚Cu distance of 3.281 Å. Addition-
ally, instead of forming a linear or zigzag chain structure,
the ∼98.9° angle between the trigonal planes of N1A-
Cu1A-Cl1A-Cl1 and N1-Cu1-Cl1-Cl1B forces the
central Cu-Cl units to roll around an axis and extend to
form a one-dimensional right-handed helical chain in the
direction of the crystallographic a axis. The vertical distance
between two adjacent units is 4.815 Å (Figure 1b). The view
looking down the helical axis clearly shows the formation
of a 1.392 × 2.072 Å parallelogram channel (Figure 1c).
An important aspect of the one-dimensional structure of
complex 1 is that it has two peripheral hydrogen-bonded
chains on either side of the helical channel (Figure 1a). To
our knowledge, this distinct supramolecular structural feature
has not been reported for copper(I) halide compounds. The
amide group of the ligand is not involved in coordination
and sticks out from the central helical structure. The N-H
and CdO groups sit in the same plane with a mean deviation
of 0.019 Å for all atoms, and they are oriented toward each
other so that one N-H‚‚‚O hydrogen bond forms between
adjoining amide groups with an N‚‚‚O distance of 2.8559-
(17) Å and an N-H‚‚‚O angle of 161.4°. Molecules of HL
in 1 are arranged along the crystallographic a axis on both
sides of the helical channel, which results in the formation
of two one-dimensional zigzag hydrogen-bonded chains that
are also nearly parallel with the central helical axis and helps
to stabilize the right-handed helical structure. Despite the
monodentate coordination mode of HL, hydrogen bonding
between amide groups in 1 allows the unique helical
coordination polymer with dual parallel hydrogen-bonded
chains to form.
By far, the most common structures for one-dimensional
copper(I) halide complexes include zigzag chains, double-
stranded ladders, and hexagonal grid chains.17 There are two
examples of helical chains: [Cu2(µ-Br)2(µ-TMT-TTF)]∞
(TMT-TTF ) tetrakis(methylthio)tetrathiafulvalene) and [Cu-
(µ-Cl)(µ-2,5-dimethylpyrazine-N,N′)]∞.18 However, the trigo-
nal coordination geometry of the Cu center formed by one
(14) Murugesan, T.; Sarode, P. R.; Gopalakrishnan, J.; Rao, C. N. R. J.
Chem. Soc., Dalton Trans. 1980, 837-839.
(15) (a) Dyason, J. C.; Engelhardt, L. M.; Healy, P. C.; Pakawatchai, C.;
White, A. H. Inorg. Chem. 1985, 24, 1950-1957. (b) Engelhardt, L.
M.; Healy, P. C.; Kildea, J. D.; White, A. H. Aust. J. Chem. 1989, 42,
107-113.
(17) (a) Caulton, K. G.; Davies, G.; Holt, E. M. Polyhedron 1990, 9, 2319-
2351. (b) Li, G.; Shi, Z.; Liu, X.; Dai, Z.; Feng, S. Inorg. Chem. 2004,
43, 6884-6886.
(16) Dyason, J. C.; Healy, P. C.; Pakawatchai, C.; Patrick, V. A.; White,
A. H. Inorg. Chem. 1985, 24, 1957-1960.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9419

Yang and Houser
Figure 1. (a) X-ray crystal structure of 1. All H atoms except for those
on the amide groups have been omitted for clarity, with thermal ellipsoids
at the 50% probability level. (b) Central helical structure of complex 1. (c)
Top view of the parallelogram channel.
Figure 2. X-ray crystal structure (top) and hydrogen bonding (bottom)
for 2 with thermal ellipsoids at the 50% probability level.
N atom and two Cl atoms in 1 is different from the distorted
tetrahedral geometry of the two examples. Additionally, the
one-dimensional chains in 1, which lack any interchain
hydrogen bonding, are different from the two-dimensional
sheets or three-dimensional networks arranged between
helical chains in the two published examples.
Compound 2. The reaction of 2 equiv of HL and 1 equiv
of CuCl gives complex 2, which is a binuclear CuI complex.
Disposed about a crystallographic inversion center, complex
2 displays a bis(µ-chloro)-bridged planar Cu2Cl2 diamond
core structure. Each CuI atom is coordinated by two pyridyl
N atoms in HL. The Cu-Npy distances in 2 [2.0547(15) and
2.0351(13) Å] are longer than those in 1, which may be a
consequence of the steric effects between two HL ligands
coordinated to the same Cu center. The Cu atoms are bridged
by two Cl ions, leading to the formation of a distorted
tetrahedral geometry at each CuI center (Figure 2). Because
of the second Cl bridge, the Cu‚‚‚Cu distance in 2 [2.7625-
(12) Å] is much shorter than the corresponding distance in
1 (3.281 Å). Similar Cl2-bridged Cu2 complexes supported
by bis-pyridines,19 amidines,20 and aromatic amines21 have
been reported. Although 2’s average Cu-Cl (2.438 Å) and
Cu-N (2.045 Å) bond distances are comparable with values
observed in other Cu2Cl2 examples with diamond core
Although X-ray crystallography indicated right-handed
helical chains in the solid state, circular dichroism (CD)
spectra of solutions of 1 in CH3CN or CH2Cl2 did not
produce any CD signal, indicating the absence of chirality
in solution. One explanation for the absence of a CD signal
is that solvation breaks the two hydrogen-bonded chains,
resulting in the loss of interaction among repeating Cu-HL
units and the loss of the helical structure. In coordinating
solvents such as CH3CN, it is likely that the one-dimensional
polymer chains of 1 break into monomers. Another likely
explanation is that 1 crystallized to form a racemic mixture
of crystals, from which we happened to select one with the
right-handed helical structure. Dissolving roughly equal
quantities of left- and right-handed crystals would result in
a solution with no net CD signal.
(19) (a) Healy, P. C.; Kildea, J. D.; Skelton, B. W.; Waters, A. F.; White,
A. H. Acta Crystallogr. C 1991, 47, 1721-1723. (b) Hiller, W. Acta
Crystallogr. C 1986, 42, 149-150.
(20) Oakley, S. H.; Soria, D. B.; Coles, M. P.; Hitchcock, P. B. Dalton
Trans. 2004, 537-546.
(18) (a) Munakata, M.; Kurodasowa, T.; Maekawa, M.; Hirota, A.;
Kitagawa, S. Inorg. Chem. 1995, 34, 2705-2710. (b) Nather, C.;
Greve, J.; Jess, I. Solid State Sci. 2002, 4, 813-820.
(21) Gustafsson, B.; Hakansson, M.; Jagner, S. Inorg. Chim. Acta 2003,
350, 209-214.
9420 Inorganic Chemistry, Vol. 45, No. 23, 2006

CuI Coordination Chemistry of (Pyridylmethyl)amide Ligands
structures, the smaller Cu-Cl-Cu bond angle [68.99(3)°]
and the larger Cl-Cu-Cl bond angle [111.00(3)°] in 2 lead
to a Cu‚‚‚Cu distance that is distinctly shorter than those of
reported examples, having Cu‚‚‚Cu distances ranging from
2.997(1) to 3.150(2) Å.19,21,22 This structural difference could
be a consequence of the more distorted tetrahedral geometry
in 2, due to the repulsion between the amide groups of two
ligands in the same Cu center.
Two types of intermolecular hydrogen bonds are observed
in the packing structure of complex 2 (Figure 2, bottom).
Hydrogen bonds between amide N-H and chloro bridging
atoms connect the ligands on one dimer to adjacent dimers
via N-H‚‚‚Cl hydrogen bonds, with an N‚‚‚Cl distance of
3.4430(16) Å and an N-H‚‚‚Cl angle of 160.7(19)°. A
second type of hydrogen bond between the amide N-H
groups on one dimer and the CdO groups on adjacent
dimers, with an N‚‚‚Cl distance of 2.9239(18) Å and an
N-H‚‚‚Cl angle of 159.5(17)°, completes the hydrogen
bonding in 2. These hydrogen bonds extend to form a three-
dimensional network in 2 that stabilizes the solid-state
structure.
Figure 3. X-ray crystal structure of 4 with thermal ellipsoids at the 50%
probability level. All H atoms except for those on the amide groups have
been omitted for clarity.
Compound 3. Single-crystal X-ray diffraction analysis of
complex 3, which was synthesized by the reaction of 1 equiv
of HLPh and 1 equiv of CuCl in CH3CN, reveals a bis(µ-
chloro)-bridged diamond core binuclear Cu structure similar
to that of complex 2. Unfortunately, the diffraction data for
complex 3 had serious twinning problems, and a large
amount of the overlapping data from twinning were omitted;
hence, the incomplete data for 3 make its structure unpub-
lishable. However, the raw structure of complex 3 along with
its corroborating analytical data reveal a stoichiometry of
ligand-to-Cu of 1:1, which is different from that of complex
2. This is likely caused by the bulkier phenyl substituent
group in HLPh compared to HL. Each Cu center possesses a
distorted tetrahedral geometry, and two Cl atoms bridge the
two Cu centers. Although the N2Cl2 coordination environ-
ment of each Cu atom in complex 3 is the same as that in
complex 2, the fourth position in 3 is occupied by a CH3CN
solvent molecule, which is attributed to the steric effect from
the benzyl group of ligand HLPh. This effect prevents the
coordination of the second HLPh ligand to the Cu center.
Although the X-ray data suggest the existence of hydrogen-
bonding interactions involving the amide groups, the poor
quality of the X-ray data precludes further discussion of the
hydrogen bonding and packing structure.
Figure 4. X-ray crystal structure and hydrogen bonding for 5 with thermal
ellipsoids at the 50% probability level. All H atoms except for those on the
amide groups have been omitted for clarity.
shorter than that in 2. The average Cu-N and Cu-Cl
distances are typical for CuI complexes (see Table 2). The
bond distances in 4 are slightly shorter than the Cu-N and
Cu-Cl bonds of complex 2, which is a consequence of the
decreased coordination number of the Cu ions in 4. Further-
more, the amide groups are oriented such that each amide
H atom forms intramolecular hydrogen bonds with the
bridged Cl ions, having an N‚‚‚Cl distance of 3.5445(16) Å
and an N-H‚‚‚Cl angle of 132.7°. The hydrogen bonding
in 4 is distinct from the others discussed so far, in that they
possess intermolecular hydrogen bonding while 4 contains
only intramolecular hydrogen bonding. This difference in
hydrogen bonding is most likely a consequence of the much
Compound 4. The reaction of 2 equiv of HLPh with 1
3
greater steric bulk of the HLPh ligand compared to the others,
3
equiv of CuCl leads to the formation of complex 4. This
complex has the same bis(µ-chloro)-bridged planar Cu2Cl2
diamond core as complexes 2 and 3, but the Cu ion exhibits
trigonal coordination geometry with only one Npy atom from
which would prevent molecules of 4 from getting close
enough to form intermolecular hydrogen bonds.
Compound 5. The reaction of 2 equiv of HLMe and 1
3
equiv of CuCl leads to the formation of complex 5. In
contrast to complexes 1-4, complex 5 exists as a discrete
HLPh and two Cl ions in each Cu ion’s coordination sphere
3
(Figure 3). The bulky triphenyl group in HLPh prevents
3
mononuclear species bearing two HLMe ligands and one Cl
3
access of a second ligand or solvent molecule to each Cu
(Figure 4). A trigonal geometry is adopted in complex 5,
with the two Npy donors and one terminal Cl ion. The Cu
atom lies 0.0097 Å out of the N1A-N1B-Cl1 plane,
indicating near-planarity of the Cu and coordinating ligand
atoms. The tert-butyl group decreases the flexibility of the
ion, even when the reaction stoichiometry of HLPh and CuCl
3
is 2:1. The Cu‚‚‚Cu distance of 2.746 Å in 4 is 0.017 Å
(22) Lu, J.; Crisci, G.; Niu, T. Y.; Jacobson, A. J. Inorg. Chem. 1997, 36,
5140-5141.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9421

Yang and Houser
amide group, and the steric effect between the two adjacent
the strong coordinating abilities of Cl, coupled with the
weaker coordinating ability of the neutral amide group. For
ligand HL, one-dimensional chains (1) or a dinuclear
complex (2) can be synthesized by changing the stoichiom-
etry of the reactants. The substituent group R on the amide
of HLR also influences the metal center geometry of these
complexes. The steric effect of the R group, which increases
in the order of H < Ph < Me3 < Ph3, contributes to the
variety of structures observed, ranging from one-dimensional
polymeric chains (1) to binuclear (2-4) to mononuclear (5).
Finally, hydrogen bonding plays a significant role in
determining not only the molecular structures of 1-5 but
also the intermolecular hydrogen bonds of the network
structuressor lack thereofsthat are formed in these com-
plexes.
HLMe ligands may prevent the formation of a tetrahedral
3
geometry around the Cu center by denying access to a second
Cl ion. There is only one example of a monomeric neutral
chlorocopper(I) complex with pseudo-trigonal-planar coor-
dination.16 The Cu-Cl distance of 2.3060(9) Å in 5 is
comparable to those of complexes 1, 2, and previous
examples,19,21,22 but the Cu-Npy distances are shorter. The
Cu-Cl bond is parallel with the crystallographic b axis, and
this molecule exhibits a 2-fold rotational axis along the Cu-
Cl bond. Both N-Cu-Cl bond angles are 107.44(4)°, which
is consistent with the 2-fold symmetry of the molecule. Each
Cl ligand forms two hydrogen bonds with the amide N-H
groups from an adjacent molecule. The hydrogen bonds in
4 and 5 are similar because both involve N-H‚‚‚Cl hydrogen
bonds and no N-H‚‚‚O hydrogen bonds. These intermo-
lecular N-H‚‚‚Cl hydrogen bonds, with N‚‚‚Cl distances of
3.1884(18) Å and N-H‚‚‚Cl angles of 151(2)°, extend to
form a one-dimensional chain that helps to stabilize the solid-
state structure of complex 5 (Figure 4).
Acknowledgment. This work was supported by the
National Science Foundation (Grant CHE-0094079) and the
Herman Frasch Foundation. We thank Dr. Masood Khan for
the X-ray data collection of complex 1 and Dr. Douglas
Powell for assistance with the refinement of the X-ray
structures of complexes 2-5. Finally, we thank the NSF
(Grant CHE-0130835) and University of Oklahoma for the
purchase of a CCD-equipped X-ray diffractometer.
Conclusions
The CuI coordination chemistry of a set of (pyridylmethyl)-
amide ligands has been investigated. All of the ligands, each
with different substituent groups on the amide (HLR; R )
null, Ph, Ph3, Me3), exhibit similar monodentate coordination
modes when combined with CuCl to form CuI complexes.
This preference for a monodentate, rather than a bidentate
or tridentate, coordination mode is likely a consequence of
Supporting Information Available: X-ray structural informa-
tion for 1, 2, 4, and 5 (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
IC0612810
9422 Inorganic Chemistry, Vol. 45, No. 23, 2006