Engineering the structure and magnetic properties of crystalline solids via the metal-directed self-assembly of a versatile molecular building unit

Article abstract of DOI:10.1021/ja0200241

We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide (NPBA) with the general formula [M_a(NPBA)₂A_bS_c], where M = Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺

Full text of DOI:10.1021/ja0200241

Published on Web 05/15/2002
Engineering the Structure and Magnetic Properties of
Crystalline Solids via the Metal-Directed Self-Assembly of a
Versatile Molecular Building Unit
Juan C. Noveron,* Myoung Soo Lah,† Rico E. Del Sesto, Atta M. Arif,
Joel S. Miller, and Peter J. Stang*
Contribution from the Department of Chemistry, UniVersity of Utah, 315 S. 1400 E. RM 2020,
Salt Lake City, Utah 84112-0850
Received January 4, 2002
Abstract: We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide
(NPBA) with the general formula [Ma(NPBA)2AbSc], where M ) Co2+, Ni2+, Zn2+, Mn2+, Cu2+, Ag+; A )
NO3-, OAc-; S ) MeOH, H2O; a ) 0, 1, 2; b ) 0, 1, 2, 4; and c ) 0, 2. NPBA contains structural features
that can engage in three modes of intermolecular interactions: (1) metal-ligand coordination, (2) hydrogen
bonding, and (3) π-π stacking. NPBA forms one-dimensional (1-D) chains governed by hydrogen bonding,
but when reacted with metal ions, it generates a wide variety of supramolecular scaffolds that control the
arrangement of periodic nanostructures and form 1- (2-4), 2- (5), or 3-D (6-10) solid-state networks of
hydrogen bonding and π-π stacking interactions in the crystal. Isostructural 7-9 exhibit a 2-D hydrogen
bonding network that promotes topotaxial growth of single crystals of their isostructural family and generates
crystal composites with two (11) and three (12) different components. Furthermore, 7-9 can also form
crystalline solid solutions (M,M′)(NPBA)2(NO3)2(MeOH)2 (M, M′ ) Co2+, Ni2+, or Zn2+, 13-16), where
mixtures of Co2+, Ni2+, and Zn2+ share the same crystal lattice in different proportions to allow the formation
of materials with modulated magnetic moments. Finally, we report the effects that multidimensional
noncovalent networks exert on the magnetic moments between 2 and 300 K of 1-D (4), 2-D (5), and 3-D
(7, 8, 10, and 13-16) paramagnetic networks.
Introduction
solids, the formation of predetermined molecular networks of
noncovalent interactions has been more successful than the
Designing the solid state with molecules that encode well-
defined noncovalent motifs has recently become a rapidly
growing area of research as it pursues to establish principles
that will ultimately lead to the development of new state-of-
the-art functional materials.1-6 Among the noncovalent motifs,
hydrogen bonding,2,3 metal-ligand coordination,5-7 and π-π
stacking8-11 have been employed as synthetic paradigms to
rationally design superstructures. In the design of crystalline
prediction of the crystal structure.12 Recent progress in this area
has generated examples where the design of network structures
produced crystals with (a) one-dimensional (1-D) molecular
networks composed of hydrogen bonding,13-15 metal-ligand
coordination,16-22 or a combination of these and other inter-
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* Corresponding author. E-mail: stang@chem.utah.edu.
† Visiting scholar from the College of Science and Technology, 1271
Sa-1-dong, Ansan, Kyunggi-do, 425-791 Korea.
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J. AM. CHEM. SOC. 2002, 124, 6613-6625
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A R T I C L E S
Noveron et al.
actions, referred to as hybrid interactions,23-27 (b) 2-D networks
composed either of hydrogen bonding,28-35 metal-ligand
coordination,36-43 or hybrid interactions,44-49 and (c) 3-D
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We are exploring a strategy for the design of function in solid-
state structures based on the design of molecules that use metal-
ligand coordination, hydrogen bonding, and π-π stacking
interactions as directional motifs to guide the self-assembly of
network structures. Herein we report the supramolecular chem-
istry along with its structure-property relationships of N-(4-
pyridyl)benzamide (NPBA), Figure 1, as it utilizes several types
of interactions to form crystals where the metal ions and solvent
conditions used during the self-assembly process control the
dimensional propagation of infinite hydrogen bonding and π-π
Figure 1. N-(4-Pyridyl)benzamide (NPBA).
Scheme 1. Graphic Representation of the Formation of 1-, 2-,
and 3-D Networks of Noncovalent Interactions in Crystalline Solids
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stacking interactions to produce solids with 1-, 2-, or 3-D
noncovalent networks as illustrated in Scheme 1. We show that
isostructural materials enable topotaxial as well as solid solution
crystal growth with their isostructural members and result in
crystalline heterostructures. We also demonstrate that topotaxial
growth in these structures takes place preferentially along the
direction of hydrogen bonding. Furthermore, formation of solid
solutions with different metal ions enables the preparation of
materials with modulated magnetic properties.
Experimental Section
General. Benzyl chloride, triethylamine, 4-aminopyridine, manga-
nese(II) nitrate hexahydrate, cobalt(II) nitrate hexahydrate, nickel(II)
nitrate hexahydrate, zinc(II) nitrate hydrate, manganese(II) acetate
tetrahydrate, cobalt(II) acetate tetrahydrate, copper(II) acetate hydrate,
zinc(II)acetate, and silver(I) acetate were used as received from
commercial sources (Sigma-Aldrich or Lancaster). NMR spectra were
obtained at room temperature with a Varian XL-300 spectrometer.
Magnetic susceptibility measurements were made with a Quantum
Design MPMS-5XL SQUID ac/dc magnetometer as previously de-
scribed.58 Elemental analysis was performed by Oneida Research
Service, Whitesboro, NY, and Atlantic Microlab Inc., Norcross, GA.
Single-crystal X-ray diffraction data for all the compounds were
collected on a Nonius Kappa CCD diffractometer equipped with Mo
Ka radiation (λ ) 0.71073 Å).
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Synthesis of NPBA. A solution of benzyl chloride (1.00 g, 7.12
mmol) and triethylamine (1.0 mL, 7.20 mmol) in 50 mL of chloroform
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6614 J. AM. CHEM. SOC. VOL. 124, NO. 23, 2002

Structure and Magnetic Properties of Crystalline Solids
A R T I C L E S
was prepared and chilled to 4 °C in an ice bath for 5 min. Then,
4-aminopyridine (0.669 g, 7.12 mmol) was added slowly to the cold
solution over a period of 10 min. The reaction was allowed to stir at
room temperature overnight and upon concentration a white precipitate
was obtained and identified as the product. The solid was filtered and
solution of Co-complex 7 with single crystals of Zn-complex 9 followed
by diffusion of diethyl ether for 12 h. Next, the resulting two composite
crystals were used as seeds in a freshly prepared 1.5 mM methanol-
toluene (60:40, v/v) solution of the Ni-complex 8 followed by diffusion
of diethyl ether for another 12 h.
Formation of Solid Solutions 13-16. The solid solutions of
paramagnetic mixed crystals 13-16 were prepared by mixing warm
1.5 mM methanolic solutions of mixtures of Co-complex 7 and Ni-
complex 8 in a ratio of 75:25 for 13, 50:50 for 14, 25:75 for 15, and
50:50 of Ni-complex 8 and Zn-complex 9 for 16 followed by diethyl
ether diffusion into the respective solutions for 48 h.
Crystal Structure Determination. The data collection was carried
out at 200(1) K and the range for data collection was 3.44 to 27.89° in
θ. The data were corrected for absorption using the DENZO-SMN
program.59 The structures were solved by a combination of direct
methods and heavy atom method using SIR 97.60 For the final structural
refinement SHELXL97 was used.61 All of the non-hydrogen atoms were
refined with an anisotropic displacement coefficient. Hydrogen atoms
were located and refined isotropically using SHELXL97. Pertinent
crystallographic data are listed in Table 1.
1
washed several times with cold chloroform. Yield 1.03 g (79%). H
NMR spectrum (d6-DMSO, 300 MHz) δ from TMS: 7.63 (m, 3H,
Bz), 7.78 (d, 2H, Py), 7.95 (d, 2H, o-Bz), 8.47 (d, 2H, Py), 10.60 (s,
NH). 13C NMR spectrum (d6-DMSO, 62.5 MHz): 114.70, 128.56,
129.15, 132.76, 134.96, 146.66, 150.97, 167.19.
Preparation of [Ag(NPBA)2](NO3) (2). A solution of NPBA (20
mg, 0.10 mmol) in 5 mL of methanol was added to a 5 mL methanolic
solution of silver nitrate (8.45 mg, 0.05 mmol) and the mixture was
stirred for 30 min in the dark. Diffusion of diethyl ether into the reaction
mixture for 48 h generated large colorless crystals of 2. Yield 87%.
Anal. Calcd for C24H20N5O5Ag: C 50.90, H 3.56, N 12.37. Found: C
50.39, H 3.87, N 12.94.
Preparation of Zn(NPBA)2(OAc)2 (3) and Zn2(NPBA)2(OAc)2 (6).
A solution of NPBA (20 mg, 0.10 mmol) in 5 mL of methanol was
added to a 5 mL methanolic solution of zinc(II) acetate (12.4 mg, 0.05
mmol) and allowed to stir for 12 h. Next, the solution was allowed to
evaporate slowly over a period of 48 h during which it generated 15.9
mg (55.3%; colorless needle shaped crystals) of 3 and 7.3 mg (38.6%;
colorless prismatic crystals) of 6 that were separated by hand according
to their crystal shape. Anal. Calcd for C28H26N4O6Zn (3): C 57.99, H
4.52, N 9.66. Found: C 57.39, H 4.55, N 9.66. Anal. Calcd for
C32H32N4O10Zn2 (6): C 50.35, H 4.23, N 7.34. Found: C 50.39, H
4.37, N 7.54.
Preparation of Cu(NPBA)2(OAc)2 (4). A solution of NPBA (20
mg, 0.10 mmol) in 5 mL of methanol was added to a 5 mL methanolic
solution of copper(II) acetate (12.5 mg, 0.05 mmol) and allowed to
stir for 12 h. Slow evaporation of this methanol solution generated
20.3 mg (69.2%; purple plate crystals) of 4. Anal. Calcd for C28H26N4O6-
Cu: C 58.18, H 4.53, N 9.69. Found: C 58.39, H 4.57, N 9.74.
Preparation of Co(NPBA)2(OAc)2(H2O)2 (5). A solution of NPBA
(20 mg, 0.10 mmol) in 5 mL of ethanol was added to a 5 mL ethanolic
solution of cobalt(II) acetate hexahydrate (12.5 mg, 0.05 mmol) and
allowed to stir for 12 h. Slow evaporation of the solution during 48 h
gave 26.7 mg (86.7%; pale reddish needles) of 5. Anal. Calcd for
C28H30N4O8Co: C 55.18, H 4.96, N 9.19. Found: C 55.39, H 4.87, N
9.18.
Preparation of M(NPBA)2(NO3)2(MeOH)2 (M ) Co2+ (7), Ni2+
(8), Zn2+ (9)). A solution of NPBA (20 mg, 0.10 mmol) in 5 mL of
methanol was added to a 5 mL methanolic solution of the corresponding
metal nitrate (0.05 mmol). The mixture was heated at 60 °C for 5 min
and then allowed to stand at room temperature for 24 h. During this
time, microcystals corresponding to compounds 7-9 were formed.
Yield: 7, 95%; 8, 92%; 9, 87%. Diffusion of diethyl ether into a dilute
methanolic solution of the complexes containing seed crystals of any
one of 7-9 generated large crystals. Anal. Calcd for C26H28N6O10Co
(7): C 48.5, H 4.85, N 13.75. Found: C 48.32, H 4.65, N 13.90. Anal.
Calcd for C26H28N6O10Ni (8): C 48.60, H 4.85, N 13.75. Found: C
48.50, H 4.82, N 13.70. Anal. Calcd for C26H28N6O10Zn (9): C 48.60,
H 4.85, N 13.75. Found: C 48.45, H 4.80, N 13.8.
Preparation of Mn(NPBA)2(NO3)2(H2O)2 (10). A solution of NPBA
(20 mg, 0.10 mmol) in 5 mL of ethanol was added to a 5 mL ethanol:
water (80:20) solution of manganese(II) nitrate hydrate (14.3 mg, 0.05
mmol) and allowed to stir for 1 h. Slow evaporation of the solution
during 48 h gave 30.58 mg (97%; pale yellow needles) of 10. Anal.
Calcd for C24H24N6O10Mn: C 47.10, H 3.93, N 13.73. Found: C 47.00,
H 3.97, N 13.83.
Results and Discussion
Design Principles. To explore the supramolecular trends
exhibited by molecules that can engage simultaneously in
metal-ligand coordination, hydrogen bonding, and π-π stack-
ing interactions, N-(4-pyridyl)benzamide (NPBA) was prepared
and its coordination chemistry and crystalline packing behavior
under varying conditions was investigated. NPBA consists of
three structural parts: (1) a pyridyl group that can coordinate
to a metal, (2) a carboxamide group, which can have hydrogen
bonding interactions through the amide nitrogen atom as well
as via the carbonyl oxygen atom, and (3) a phenyl group, which
can be involved in π-π stacking interactions (Figure 1). We
hypothesized that because NPBA, as a consequence of conjuga-
tion, has planar functional groups, its reactions with various
metal ions capable of forming complexes with different
coordination numbers and geometries would generate molecular
scaffolds with unique directional hydrogen bonding and π-π
stacking motifs that might direct via self-assembly well-defined
structural motifs.
In our design, the metal centers (1) assemble the ligands into
the required geometrical orientations to promote unique inter-
molecular connections and (2) pre-organize solvent and coun-
terion via coordination to assist in the formation of infinite
ensembles of hydrogen bonding interactions.
Supramolecular Patterns of Crystalline Networks 1-10.
A systematic investigation of the supramolecular structural
trends of NPBA under various reactions conditions revealed that
depending on the coordination number, geometry of the metal
ions, and the solvent, a variety of crystalline motifs (2-10) can
be generated that comprise 1-, 2-, or 3-D solid-state networks
of hydrogen bonding and π-π stacking interactions. The
hydrogen bonding networks are primarily formed via the
directional interactions of the carboxamide group of NPBA and
counterions or solvent molecules coordinated to the metal ions.
The hydrogen bonding parameters are listed in Table 2. The
(59) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(60) SIR97 (Relase 1.02); A program for automatic solution and refinement of
crystal structure; Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliteni, A. G. G., Polidori, G.; Spagna,
R.
(61) SHELX97 [Includes SHELX97, SHELXL97, CIFTAB]; Programs for
Crystal Structure Analysis (Release 97-2); Sheldrick, G. M.; University of
Go¨ttingen: Go¨ttingen, Germany, 1997.
Formation of Crystal Composites 11 and 12. The crystal composite
11 was prepared by seeding a 1.5 mM methanol-toluene (60:40, v/v)
solution of Ni-complex 8 with single crystals of Co-complex 7 followed
by diffusion of diethyl ether for 36 h. The triple crystal composite 12
was prepared by seeding a 1.5 mM methanol-toluene (60:40, v/v)
9
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A R T I C L E S
Noveron et al.
Table 1. Crystal Data and Structure Refinement
identification code
NPBA 1
Ag-complex 2
Zn-complex 3
Cu-complex 4
Co-complex 5
Zn-complex 6
empirical formula
formula weight
space group
unit cell dimens.
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
C12H10N2O
198.22
P21/c
C24H20N5O5Ag
566.32
P1h
C28H26N4O6 Zn
579.90
C2/c
C28H26 N4O6Cu
578.07
P1h
C28H30N4O8Co
609.49
P21/c
C32H32N4O10Zn2
763.36
C2/c
5.6830(2)
11.1380(3)
15.2124(6)
90
95.0784(13)
90
959.12(6)
2187
1.028
7.4427(2)
8.8081(2)
17.2876(5)
93.6327(9)
90.9294(10)
94.3935(8)
1127.45(5)
5034
17.6920(3)
10.2177(2)
15.1922(3)
90
115.4011(12)
90
2480.82(8)
2928
1.025
8.0203(2)
8.7561(3)
9.8058(3)
76.776(2)
75.4011(18)
83.5565(14)
647.63(3)
3022
15.8579(4)
5.4924(1)
16.0201(5)
90
110.4856(11)
90
1307.08(6)
2961
1.030
19.8901(3)
12.3626(3)
15.0476(3)
90
113.9569(15)
90
3381.34(12)
3847
1.003
γ (deg)
V (Å3)
independent reflcns
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1,a wR2b
1.046
1.046
0.0380, 0.0878
0.0323, 0.0659
0.0388, 0.0921
0.0459, 0.0861
0.0321, 0.0753
0.0389, 0.0816
identification code
Co-complex 7
Ni-complex 8
Zn-complex 9
Mn-complex 10
Co:Ni-composite 11
empirical formula
formula weight
space group
unit cell dimens.
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
C26H28N6O10Co
643.47
P21/c
C26H28N6O10Ni
643.25
P21/c
C26H28N6O10Zn
649.91
P21/c
C24H24N6O10Mn
611.43
P1h
C26H28N6O10Co0.5Ni0.5
643.47
P21/c
7.4471(2)
12.6393(2)
14.7616(4)
90
97.8869(14)
90
1376.31(6)
3153
1.042
7.4380(2)
12.6144(5)
14.7117(5)
90
97.618(2)
90
1368.15(8)
3122
1.031
7.4389(3)
12.6873(2)
14.7479(5)
90
97.9708(12)
90
1378.45(8)
3110
1.039
7.4848(2)
9.1264(3)
10.0961(3)
75.4420(16)
73.0274(14)
82.5842(12)
637.28(3)
2842
7.4425(3)
12.6362(5)
14.7425(8)
90
97.8068(17)
90°
1373.61(11) Å3
3162
γ (deg)
V (Å3)
independent reflcns
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1,a, wR2b
1.009
1.042
0.0337, 0.0748
0.0362, 0.0778
0.0334, 0.0764
0.0481, 0.0789
0.0337, 0.0748
a R1 ) ∑(||Fo | - |Fc ||)/∑|Fo|. b wR2 ) [∑(w(Fo - Fc )2)/∑(Fo )2]1/2, and S ) goodness-of-fit on F2 ) [∑(w(Fo - Fc )2/(n - p)]1/2, where n is the
number of reflections and p is the number of parameters refined.
2
2
2
2
2
Table 2. Hydrogen Bonds (Å and deg) in 1-10a
D−H‚‚‚A d(D‚‚‚A)
N-H(Amido)‚‚‚N(Pyridyl) 3.041(2) 142(1)
Table 3. π-π Stacking Interactions and Distances (Å) in 2-10a
(DHA)
NPBA 1
Ag-complex 2
a
a
a
a
a
b
a
a
a
b
a
a
b
a
a
b
a
a
b
a
a
a
N-H(Amido)‚‚‚O(Nitrate)
N-H(Amido)‚‚‚O(Nitrate)
N-H(Amido)‚‚‚O(Acetate) 2.916(2) 161(2)
N-H(Amido)‚‚‚O(Acetate) 2.904(3) 161(2)
2.936(2) 169(3)
3.114(3) 157(2)
Zn-complex 3
Cu-complex 4
Co-complex 5
O-H(H2O)‚‚‚O(Acetate)
N-H(Amido)‚‚‚O(Amide)
O-H(H2O)‚‚‚O(Acetate)
2.760(2) 160(2)
3.334(2) 158(2)
2.605(2) 171(2)
Zn-complex 6
Co-complex 7
N-H(Amido)‚‚‚O(Acetate) 2.908(3) 162(3)
O-H(MeOH)‚‚‚O(Nitrate)
N-H(Amido)‚‚‚O(Nitrate)
O-H(MeOH)‚‚‚O(Amide)
O-H(MeOH)‚‚‚O(Nitrate)
N-H(Amido)‚‚‚O(Nitrate)
O-H(MeOH)‚‚‚O(Amide)
O-H(MeOH)‚‚‚O(Nitrate)
N-H(Amido)‚‚‚O(Nitrate)
O-H(MeOH)‚‚‚O(Amide)
2.822(2) 135(2)
3.034(2) 155(2)
2.834(2) 144(2)
2.802(2) 137(2)
3.053(2) 153(2)
2.849(2) 142(3)
2.861(2) 130(2)
3.048(2) 154(2)
2.821(2) 148(2)
2.847(2) 121(2)
3.012(2) 163(2)
2.730(2) 172(2)
2.888(2) 160(2)
Ni-complex 8
Zn-complex 9
Mn-complex 10 O-H(H2O)‚‚‚O(Nitrate)
N-H(Amido)‚‚‚O(Nitrate)
a Am, carboxamide group; Ph, phenyl group; Py, pyridyl group.
O-H(H2O)‚‚‚O(Amide)
O-H(H2O)‚‚‚.O(Nitrate)
parameters for the five types of π-π stacking interactions are
shown collectively in Table 3.
a A, acceptor; D, donor; a, intermolecular; b, intramolecular.
One-Dimensional Solid-State Networks. To propagate non-
covalent interactions only along one direction, each unit must
have two-point interactions with two adjacent neighbors. NPBA
1 epitomizes this model. It exhibits a two-point contact per unit
that can result in 1-D hydrogen bonding networks where the
carboxamide NH moieties and the pyridyl groups from adjacent
molecular units propagate NH‚‚‚N contacts of 3.04 Å along b
π-π stacking interactions are formed between various parts of
the resonant structure of NPBA of the molecular units and are
categorized according to the extent of π-π overlap that occurs
between the aromatic groups as Types I-V, where Type I
represents only minor π-π stacking and Types II-V correspond
to increasingly larger degrees of π-π stacking. The bonding
9
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Structure and Magnetic Properties of Crystalline Solids
A R T I C L E S
Zn(II), and Cu(II) centers and obtained 2-4, derived from the
hydrates of Ag(NO3), Zn(OAc)2, and Cu(OAc)2, respectively.
These structures comprise infinite 1-D tape-like networks formed
by concomitant hydrogen bonding and π-π stacking interac-
tions. Although these structures exhibit more than two-point
contacts per unit, these interactions occur between two adjacent
neighbors, and hence, form 1-D networked solids.
trans-[Ag(NPBA)2](NO3) (2), Figure 3, lacks solvent, and
has a 1-D noncovalent network composed of two hydrogen
bonding contacts and two types of π-π stacking interaction
between the molecular units. The hydrogen bond interactions
manifested by N-H‚‚‚O contacts of 2.94 and 3.11 Å involve
the four amide N(4)H groups in two adjacent NPBA’s and the
oxygen atoms of two bridging nitrate ions (Figure 4a and Table
2). The hydrogen bonding interactions result in the formation
of a dimer that acts as a new unit that engages in two forms of
Type I π-π stacking interactions, one within the dimers
(amide-Py‚‚‚Py 3.43 Å, Figure 4b) and the other between the
dimers (amide‚‚‚Py 3.61 Å, Figure 4c), Table 3. Together, these
associations generate infinite 1-D networks of noncovalent
interactions that propagate along a.
Figure 2. Structure of 1. NPBA molecules form 1-D hydrogen bonding
networks along b.
When NPBA is reacted with zinc(II) acetate in methanol, 3
and 6 form simultaneously in 55% and 39% yields, respectively.
Zn(NPBA)2(OAc)2 (3) is tetrahedral with two monodentate
acetates (Figure 5), and has a 1-D network arising from
hydrogen bonds and π-π stacking interactions along c. The
Zn2(NPBA)2(OAc)2 (6) exhibits a 3-D noncovalent network
system that will be discussed in a later section. The noncoor-
dinating oxygen atoms O(3) of the acetate ions hydrogen bond
Figure 3. Structure of [Ag(NPBA)2](NO3), 2.
(Figure 2 and Table 2). Despite the presence of phenyl moieties
in NPBA, 1 does not exhibit π-π stacking interactions. We
examined the interactions of NPBA with metals known to form
complexes with low coordination numbers (<6) such as Ag(I),
Figure 4. [Ag(NPBA)2](NO3), 2. (a) Dimeric units of 2 (red and blue sets) propagate π-π stacking interactions along a. (b and c) Type I π-π stacking
interactions. (d) van der Waals surface of π-π stacked rows in 2 (unique colors) as viewed from b.
9
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A R T I C L E S
Noveron et al.
Figure 7. Structure of Cu(NPBA)2(OAc)2, 4.
Two-Dimensional Solid-State Networks. To propagate
noncovalent interactions in a plane to generate lamellar (2-D)
networks, each unit must make at least three point interactions
with at least three adjacent neighbors. We examined the
interactions of NPBA with metals known to form six-coordinate
complexes such as Mn(II), Co(II), and Ni(II) centers in order
to promote the coordination of solvent molecules that could
assist in the formation of more intricate noncovalent networks.
We obtained a 2-D network structure, 5, derived from the
hydrate of Co(OAc)2. This structure exhibits ten-point non-
covalent contacts between each unit and four adjacent neighbors
and such interactions propagate in 2-D to form lamellar
networks. Reactions of NPBA with the corresponding nitrate
salts of the aforementioned metal ions generated structures with
3-D noncovalent networks (7-10) and will be discussed in the
next section.
Octahedral trans-Co(NPBA)2(OAc)2(H2O)2 (5, Figure 9)
exhibit packing in which 1-D hydrogen bonded networks
propagate perpendicular to the 1-D π-π stacking networks and
collectively form 2-D noncovalent networks. The hydrogen
bonding networks are comprised of intramolecular and inter-
molecular hydrogen bonding interactions. Intramolecular hy-
drogen bond interactions occur between the O(2)H1 atoms of
the coordinated water molecules and the noncoordinating oxygen
atoms of the acetate groups O(3). Intermolecular hydrogen bond
interactions occur between the same coordinated water O(2)-
H2 and the oxygen atoms O(4) of the acetates coordinated to
Figure 5. Structure of Zn(NPBA)2(OAc)2, 3.
with the amide N(2)H groups from two adjacent zinc complexes
that are opposite to one another and have N-H‚‚‚O contacts of
2.91 Å (Figure 6a and Table 2), which propagates along c.
Additionally, there are two π-π stacking interactions between
the pyridyl groups that are already involved in hydrogen
bonding. The π-π stacking interactions of the Py‚‚‚Py moieties
(Type II) have average inter-ring contacts of 3.50 Å and also
propagate along c through the same networks formed by the
hydrogen bonds (Figure 6b,c and Table 3).
Square-planar trans-Cu(NPBA)2(OAc)2 (4, Figure 7) has a
parallel hydrogen bonding and π-π stacking system that
generates a tape-like 1-D network along a. The hydrogen
bonding interactions occur between the amide protons N(2)H
and the noncoordinating oxygen atoms O(3) of the acetates from
the next adjacent units and have N-H‚‚‚O contacts of 2.90 Å
(Figure 8a and Table 2). The π-π stacking interactions are
similar to 3 and consist of Type II π-π interactions between
the pyridyl moieties of adjacent units with average inter-ring
contacts of 3.44 Å (Figure 8b and Table 3).
Figure 6. Zn(NPBA)2(OAc)2,3. (a) Units of 3 form dimeric rows (red and blue) that propagate hydrogen bonding and π-π stacking interactions along c.
(b) Type II π-π stacking interactions. (c) van der Waals surface of 1-D noncovalent networks in 3.
9
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Structure and Magnetic Properties of Crystalline Solids
A R T I C L E S
Figure 8. Cu(NPBA)2(OAc)2, 4. (a) Units of 4 propagate hydrogen bonding and π-π stacking interactions along a. (b) Type II π-π stacking interactions.
(c) van der Waals surface of 1-D noncovalent networks (unique colors) in 4.
the two adjacent metal complexes that are positioned opposite
to one another with average O-H‚‚‚O contacts of 2.60 Å. The
other intermolecular hydrogen bond interactions are between
the amide groups N(2)H and the carbonyl groups CdO(1), also
from the same adjacent units, and have N-H‚‚‚O average
contacts of 3.33 Å. All the hydrogen bond interactions propagate
along b and form tape-like 1-D networks (Figure 10a and Table
2). Perpendicular to the hydrogen bonding networks are 1-D
π-π stacking interactions. They consist of the stacking of the
benzamido moieties of NPBA (Ph-Am‚‚‚Ph-Am, Type III)
Figure 9. Structure of Co(NPBA)2(OAc)2(H2O)2, 5.
Figure 10. Co(NPBA)2(OAc)2(H2O)2, 5. (a) 1-D hydrogen bonding network along b. (b) Type III π-π stacking. (c) 1-D Type III π-π stacking networks
(green) propagate perpendicular to hydrogen bonding networks (yellow). (d) van der Waals surfaces of 2-D sheet networks (unique colors) of concomitant
noncovalent interactions.
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A R T I C L E S
Noveron et al.
Figure 11. Structure of Zn2(NPBA)2(OAc)2, 6.
Figure 13. Structure of M(NPBA)2(NO3)2(MeOH)2, M ) Co2+ (7), Ni2+
(8), and Zn2+ (9).
with average inter-ring contacts of 3.63 Å and propagate along
the ajc diagonal (Figure 10b,c and Table 3). The π-π stacking
forms 1-D rows that do not interact with one another, but
together with the hydrogen bonding system generates 2-D sheet-
networks parallel to the acj diagonal plane, Figure 10.
stacking interactions consist of the stacking of the phenyl and
pyridyl moieties (Py‚‚‚Py 3.42 Å) from adjacent complexes that
propagate these interactions along the ajc diagonal (Figure 12a
and Table 3). These two 1-D networks interact with one another
in a zigzag fashion along b (Figure 12d), and together generate
a 3-D noncovalent interconnected solid.
Reactions of NPBA with the corresponding nitrate salts of
Co(II), Ni(II), Zn(II), and Mn(II) form 7-10, respectively, which
exhibit more intricate 3-D networks of hydrogen bonding and
π-π stacking interactions. trans-M(NPBA)2(NO3)2(MeOH)2
7-9 (Figure 13) are isostructural and interact with eight adjacent
neighbors via twelve noncovalent connections to generate 2-D
networks of hydrogen bonding that run perpendicular to another
2-D π-π stacking array. The hydrogen bonding system in these
structures is composed of intramolecular and intermolecular
interactions. Intramolecular hydrogen bonding occurs between
the coordinated methanol O(2)H and the noncoordinated oxygen
atoms O(5) of the nitrates from the same metal complex with
average O-H‚‚‚O contacts of 2.82 Å. The intermolecular
hydrogen bonds consist of interactions between the oxygen
Three-Dimensional Solid-State Networks. 3-D intercon-
nected networks require that each unit make at least four-point
interactions with at least four adjacent molecular neighbors. The
Zn2(NPBA)2(OAc)2 (6) epitomizes the simplest case. It exhibits
a 3-D network that is formed from 1-D hydrogen bonding and
π-π stacking networks that are perpendicular to one another
and comprise a basic unit that interacts with only four adjacent
neighbors via two π-π stacking and four hydrogen bonding
interactions. Complex 6 consist of a dinuclear Zn(II) complex
where each tetrahedral metal center has one NPBA, one
monodentate acetate, and two bridging acetates (Figure 11).
Intermolecular hydrogen bonds are manifested as N-H‚‚‚O
contacts of 2.91 Å between the amide groups N(2)H and one
of the noncoordinating oxygen atoms O(5) of the monodentate
acetates from the adjacent complexes and propagate in one-
dimension along c (Figure 12b and Table 2). The Type IV π-π
Figure 12. Zn2(NPBA)2(OAc)2, 6. (a) 1-D Type IV π-π stacking networks propagate in a zigzag fashion along the ajc diagonal. (b) The 1-D hydrogen
bonding network propagates in a zigzag fashion along c. (c) Type IV π-π stacking. (d) Schematic structure of 7 (red are hydrogen bonding networks and
blue are π-π stacking networks). (e) van der Waals surfaces of the 3-D noncovalent networks in 7.
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Structure and Magnetic Properties of Crystalline Solids
A R T I C L E S
Figure 14. M(NPBA)2(NO3)2(MeOH)2, M ) Co2+ (7), Ni2+ (8), and Zn2+ (9). (a) 2-D π-π stacking networks with Type III and Type V π-π stacking
interactions propagate along the ac plane and interact via hydrogen bonding with other 2-D planes along b. Inset: Schematic structure of 7-9 (blue represents
π-π stacking networks and orange represents hydrogen bonding networks). (b) Type III π-π stacking interactions (c) Type V π-π stacking interactions.
atoms O(2)H of the coordinated methanol and the carbonyl
groups CdO(1) of two adjacent units positioned opposite to
one another and have average O-H‚‚‚O contacts of 2.83 Å.
The other intermolecular hydrogen bonds are between the amide
groups N(2)H of the ligand and the noncoordinated oxygen
atoms O(5) of the nitrate ions from another set of adjacent
units, which are also opposite to one another, and have average
N-H‚‚‚O contacts of 3.04 Å. Both sets of interactions occur
Figure 15. Structure of Mn(NPBA)2(NO3)2(H2O)2, 10.
along b and propagate in two dimensions along the bc plane
(Figure 14a and Table 2). The π-π stacking networks of 7-9
comprise two types of π-π interactions, Types III and V: the
first consists of the stacking of adjacent benzamido groups and
the second stacking between the entire structure of NPBA’s of
adjacent units with average contact distances of 3.43 and 3.59
Å, respectively, (Figure 14b,c and Table 3). The π-π stacking
system propagates along 2-D sheets that are parallel to the ac
plane. Such 2-D sheets are one molecule thick and are linked
by the hydrogen bonds that propagate along b generating an
overall structure with a 3-D noncovalent network (Figure 14).
Octahedral trans-Mn(NPBA)2(NO3)2(H2O)2 (10, Figure 15)
exhibits a 3-D network also composed of hydrogen bonding
and π-π stacking interactions. Each unit interacts with 10
neighbors via 12 noncovalent interactions and forms the most
complex 3-D network of the crystalline assemblies of NPBA,
thus observed in the study. Intramolecular hydrogen bonds occur
between the coordinated water O(2)H and the noncoordinating
oxygen atoms O(5) of the nitrates with O-H‚‚‚O contacts of
2.85 Å. There are three types of intermolecular hydrogen bonds.
One type consists of O-H‚‚‚O contacts of 2.88 Å between the
oxygen atoms O(2)H1 of the coordinated water and the
noncoordinating oxygen atoms O(4) of the nitrates from two
adjacent units along a (Figure 16d and Table 2). The two other
types of intermolecular hydrogen bonds consist of O-H‚‚‚O
contacts of 2.73 Å between the oxygen atoms O(2)H2 of the
coordinated water and the carbonyl groups CdO(1) and between
the amide groups N(2)H and the noncoordinating oxygen atoms
O(5) of the nitrates with N-H‚‚‚O contacts of 3.01 Å, both of
which occur with the next adjacent units along the bc plane
(Figure 16c and Table 2). Complex 10 contains Type IV π-π
stacking interactions that arise from the stacking of phenyl and
pyridyl moieties of adjacent units with average inter-ring
contacts of 3.59 Å and propagate along the ac plane (Figure
16a,b and Table 3). The combination of the hydrogen bonding
and π-π stacking interactions in 10 generates a 3-D solid-state
network composed of a 2-D π-π stacking system overlapped
with a 3-D hydrogen bonded network.
Ligand Geometry and Supramolecular Networks. NPBA
has three planar regions, the pyridyl, the carboxamide, and the
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A R T I C L E S
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Figure 16. Mn(NPBA)2(NO3)2(H2O)2, 10. (a) 2-D π-π stacking network comprised of (b) Type IV π-π stacking interactions. (c) 2-D hydrogen bonding
networks along the bc plane. (d) 1-D hydrogen bonding networks along a. (e) van der Waals surfaces of the 3-D noncovalent networks (red are hydrogen
bonding networks and yellow are π-π stacking networks).
phenyl group. Although conjugation through the whole ligand
would make NPBA a rigid planar structure, the actual confor-
mation deviates from the planarity due to network interactions.
For example, the torsion angles Φ1 and Φ3 (Figure 1 and Table
S2, Supporting Information) vary from -34.3° to +23.2°,
depending on the intermolecular contacts. These degrees of
freedom in the ligand enable the formation of different
directional noncovalent networks, since the flexibility adjusts
to the local environment in order to promote the formation of
the noncovalent networks.
Hydrogen-Bonding Networks. NPBA can serve as both a
hydrogen bond donor and/or acceptor using the amide nitrogen
atom and the carbonyl oxygen atom of the carboxamide group,
respectively. However, in NPBA only the amide nitrogen atom
serves as hydrogen bond donor and the pyridyl nitrogen, not
the carbonyl group, is the hydrogen bond acceptor (Figure 2
and Table 2). In 2-4 and 6, the amide nitrogen atoms are the
only hydrogen bond donors and the acetates, nitrates, and the
carbonyl groups of the ligand are the hydrogen bond acceptors.
For example, in 2 the intermolecular hydrogen bond interactions
are between the amide nitrogen and the oxygen atom of the
nitrate anion (Figure 4 and Table 2). Similarly, in 3, 4, and 6
only intermolecular hydrogen bond interactions between the
amide nitrogen and the oxygen of the anionic acetate ligands
are observed (Figures 6, 8, and 12 and Table 2).
7-10. For example, in 5, the amide nitrogen and carbonyl
oxygen of the carboxamide group hydrogen bond and resemble
those observed in the â-sheets of protein structures (Figure 10
and Table 2). In 7-9, the hydrogen bonding interactions occur
between the amide-NH group and the oxygen atoms of the
nitrates along with the interactions between the methanol and
the oxygen of the carbonyl groups (Figure 14 and Table 2).
The hydrogen bonding in 10 is very similar to that in 7-9,
except that the added hydrogen bonding ability of the coordi-
nated water generates a 3-D hydrogen bonding network (Figure
16 and Table 2).
Overall, hydrogen bonding interactions between the NPBA-
bound units determine the structural motifs as the number of
hydrogen bonds is maximized. In most cases, the directional
aspect of the hydrogen bonding motifs from the scaffolds direct
the formation of the infinite networks through various directions
in the crystal structure.
π-π Stacking Networks. No π-π stacking interactions are
observed in 1, even though potentially three planar groups,
pyridyl, carboxamide, and phenyl, are present in the ligand.
Nonetheless, when the ligand binds to metal ions with various
geometries, several types of π-π stacking interactions propagate
in unique ways through the structure. In these interactions, not
only the phenyl group but also the pyridyl and the carboxamide
groups participate in the π-π stacking networks. For example,
in 7-9, all the pyridyl-carboxamide-phenyl moieties are
involved in the π-π stacking interactions, Type V (Figure 14
and Table 3), wherein all planar groups are in coplanar
conformation (i.e., Φ1,3 ∼ 0, Table S2). This type of π-π
When solvent is present, the oxygen atom of the carboxamide
group is involved in hydrogen bonding interactions with either
the amide-NH donor of the ligand or hydroxyl-OH group of
the solvent molecules. This type of network occurs in 5 and
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Structure and Magnetic Properties of Crystalline Solids
A R T I C L E S
Figure 18. Optical microscope image of the three-component crystal
composite 12.
Scheme 2. Crystal Growth Along the Direction of the Hydrogen
Bonding Networks in 7-9
Figure 17. Optical microscopy image of two-component crystal composite
11 (red, Co-complex 7; blue, Ni-complex 8).
stacking interaction is the most extensive π-π stacking possible
in these systems. Another type of π-π stacking interaction,
Type IV, is observed between the pyridyl and phenyl groups
and is present in 6 and 10 (Figures 12 and 16, respectively,
and Table 3). This type of π-π stacking interaction is similar
to Type V, except that the ligands are to some extent displaced
from each other and the stacking interaction is limited only
within the pyridyl and phenyl groups. The third type of π-π
stacking interaction, Type III, is observed between the carbox-
amide-phenyl and phenyl-carboxamide groups in 5 (Figure 10)
and 7-9 (Figure 14 and Table 3). The extent of the stacking
interaction in Type III is much smaller than that in Type V,
since only half of the ligand is involved in the stacking
interaction. The forth type of π-π stacking interaction, Type
II, consists of the stacking of only the pyridyl groups. This type
of π-π stacking was observed in 3 and 4 (Figures 6 and 8,
respectively, and Table 3). The fifth type of π-π stacking
interaction, Type I, is the weakest π-π interactions and consists
of the stacking of the amide-pyridyl moieties with the pyridyl
groups of the ligand and is observed in 2 (Figure 4 and Table
3). In all cases, except 2, π-π stacking interactions occur when
the ligands are in antiparallel orientations with one another. In
2, the π-π stacking interactions occur when the ligands are
parallel.
to grow one crystalline material on another. When single crystals
of 7, 8, or 9 are used as seed crystals in toluene:methanol
solutions of different isostructural members of their family, the
seed crystals nucleate growth of a different material on the
surfaces that coincide with b. For example, when single crystals
of Co(NPBA)2(NO3)2(MeOH)2 (7) are placed in a 1.5 mM
toluene:methanol solution of Ni(NPBA)2(NO3)2(MeOH)2 (8)
followed by vapor diffusion of diethyl ether, the results are
single crystals where 8 is grown along b in 7 (Figure 17), as
illustrated in Scheme 2. Assignment of the crystallographic
directions was based on the X-ray diffraction data from one of
the single-crystal composites, which produced structure 11
(Table 1). Particularly interesting is that the growth predomi-
nantly takes place along b in 7, which are the lattice planes
that project an array of hydrogen-bonding elements in the
assembly (Figure 14). Thus, the 2-D growth observed in 11 is
a result of the perfect lattice match, as well as the strength and
abundance of the hydrogen-bonding interactions along b in 7-9.
In a similar way, we prepared a triple component crystal
where 7, 8, and 9 formed a single crystal. Using the same
method described above, subsequent crystallization of Co-
(NPBA)2(NO3)2(MeOH)2 (7) and Ni(NPBA)2(NO3)2(MeOH)2
(8) on single crystals of Zn(NPBA)2(NO3)2(MeOH)2 (9) resulted
in the formation of a triple component crystal 12 (Figure 18).
As in 11, the single-directional topotaxial growth in 12 suggests
that the growth propagates preferentially along b.
The π-π stacking interactions generated from the scaffolds
derived from NPBA have large variations in terms of the extent
and magnitude of their interactions. Thus, the π-π stacking
motifs, due to the diversity of their interactions, can be
opportunistic noncovalent motifs that nevertheless can direct
the formation of different kinds of noncovalent network motifs.
Their importance is underlined by the fact that in 2-10, π-π
stacking interactions established infinite networks throughout
the structures.
The molecular control of the nucleation of molecules on
substrates is a rapidly growing area of research because it can
play an important role in the formation of advanced crystalline
Hydrogen Bonding Directed Topotaxy in 11 and 12. The
fact that 7-9 are isomorphous prompted the study of their ability
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A R T I C L E S
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Scheme 3. Graphic Representation of the Formation of
Crystalline Solid Solutions 13-16
films for liquid crystal switches and displays, electroluminescent
displays, and second-harmonic generation,62 as well as for
materials that can promote the nucleation of single crystals of
selected polymorphs of pharmaceuticals, a concept recently
demonstrated by Ward and co-workers.63 Currently, some of
the approaches that are being used to control the nucleation and
growth of crystals are the design of growth interfaces such as
polymers,64 Langmuir monolayers,65 organic salt crystals,66
graphite,67 organic single crystals,68 and surfaces of metastable
crystal phases.69 At present, one of the most promising of these
approaches is the epitaxial growth of molecules on crystal
surfaces, since in this case epitaxy is governed by factors which
can be known with atomic resolution such as topological
structure, lattice parameters of ledge nucleation sites, symmetry
constrains, the substrate crystal planes, and molecular composi-
tion of the aggregates.70,71 Hydrogen bonding directed epitaxial
growth of single crystals on crystal surfaces has been reported
in the literature.48,72 Crystals 11 and 12 represent new examples
where the direction of topotaxy is directed by hydrogen bonding
networks.
Figure 19. Temperature dependence of the effective magnetic moment
for (a) Cu-complex 4, (b) Co-complex 5, and (c) Mn-complex 10. Note
that the solid lines are fits discussed in the text.
Solid Solutions of 7-9. The isomorphous nature of 7-9 also
prompted the exploration of their ability to form solid solutions
of 7-9; this concept is illustrated in Scheme 3. Similar
procedures have been applied in the past for the formation of
solid solutions with mixed metals.48 Solid solutions with varying
metal compositions of Co(II), Ni(II), and Zn(II), i.e., 13 (Co:
Ni, 75:25), 14 (Co:Ni, 50:50), 15 (Co:Ni, 25:75), and 16 (Ni:
Zn, 50:50), were made. Analysis of these crystals via X-ray
powder diffraction, magnetic susceptibilities, and elemental
analysis revealed that these solid solutions are isomorphous and
may be useful for the fine-tuning of the properties of crystals,
for example, to control the conductivity, index of refraction,
and color of materials with high precision.
Figure 20. Temperature dependence of the effective magnetic moment
for (a) Co-complex 7, solid solutions (b) 13, (c) 14, and (d) 15, (e) Ni-
complex 8, and solid solution (f) 16.
Magnetic Properties of 4, 5, 7, 8, 10, and Solid Solutions
13-16. The magnetic susceptibility, ø, of 4, 5, 7, 8, 10, and
13-16 was measured between temperatures of 2 and 300 K
using a SQUID magnetometer, and plotted as µeff(T) ) [(8øT)1/2]
(Figures 19 and 20). For the 1-D Cu(NPBA)2(OAc)2 (4), the
300 K µeff is 1.86 µB, consistent with it having a g value of
2.15. The temperature-dependent magnetic properties follow
simple Curie-Weiss behavior, ø (T - θ)-1, with θ ) -0.2,
and again g ) 2.15, indicating no interactions between the Cu-
(II) metal centers. For the 2-D Co(NPBA)2(OAc)2(H2O)2 (5),
its room temperature magnetic moment of µeff is 5.06 µB, and
exceeds the expected spin-only values of 3.87 µB. The high-
temperature deviation is attributed to the Lande g-values
deviating from the typical value of 2 due to the spin-orbit
coupling, while the deviation at low temperature is attributed
to zero-field splitting (D) of the metal ions. The ø(T) was fit to
(62) For a review see: Marks, T. J.; Ratner, M. A. Angew. Chem., Int. Ed.
Engl. 1995, 34, 155.
(63) Mitchell, C. A.; Yu, L.; Ward, M. D. J. Am. Chem. Soc. 2001, 123, 10830.
(64) Damman, P.; Dosie`re, M.; Smith, P.; Wittmann, J. C. J. Am. Chem. Soc.
1993, 117, 1117.
(65) Frostman, L. M.; Ward, M. D. Langmuir 1997, 13, 330.
(66) DaCosta, V.; Le Moigne, J.; Oswald, L.; Pham, T. A.; Thierry, A.
Macromolecules 1998, 31, 1635.
(67) Last, J. A.; Hillier, A. C.; Hooks, D. E.; Maxson, J. B.; Ward, M. D. Chem.
Mater. 1998, 10, 422.
3
expressions that account for D for Co(II), eq 1 for the S ) /2
Co(II),73 where N is Avogadro’s number, and θ accounts for
weak interactions between Co(II) sites. Thus, Co(NPBA)2-
(OAc)2(H2O)2 (5) can be modeled to eq 1 with g ) 3.30, D )
10 cm-1 (14.4 K), and θ ) -2 K. The small θ value is
consistent with weak antiferromagnetic nearest neighbor spin
coupling.
(68) Carter, P. W.; Ward, M. D. J. Am. Chem. Soc. 1993, 115, 11521.
(69) Rodr´ıguez-Hornedo, N.; Lechuga-Ballesteros, D.; Wu, H.-J. Int. J. Pharm.
1992, 85, 149.
(70) For a review see: Ward, M. D. Chem. ReV. 2001, 101, 1697.
(71) Hooks, D. E.; Fritz, T.; Ward, M. D. AdV. Mater. 2001, 13, 227.
(72) E.g.: (a) Carter, P. W.; Ward, M. D. J. Am. Chem. Soc. 1994, 116, 769.
(b) Krober, J.; Codjovi, E.; Kahn, O.; Groliere, O.; Jay, C. J. Am. Chem.
Soc. 1993, 115, 9810. (c) Ohkoshi, S.; Iyoda, T.; Fujishima, A.; Hashimoto,
K.; Phys. ReV. 1997, 56, 11642. (d) Ohkoshi, S.; Fujishima, A.; Hashimoto,
K. J. Am. Chem. Soc. 1998, 120, 5349. (e) Mizuno, M.; Ohkoshi, S.;
Hashimoto, K. AdV. Mater. 2000, 12, 1955.
(73) O’Connor, C. J. Prog. Inorg. Chem. 1982, 29, 1205.
9
6624 J. AM. CHEM. SOC. VOL. 124, NO. 23, 2002

Structure and Magnetic Properties of Crystalline Solids
A R T I C L E S
2
2
magnetic behavior of the Ni:Zn mixture compared to the pure
Ni(II) complex 8; however, only slight changes in the D-value
are observed which may be attributed to slight orientation effects
within the crystal lattice.
Co/kBT
1 + 9e-2D
4(1 + e
NµB gCo
øCo
)
+
-2DCo/kBT
3k (T - θ)
)
B
3kBT
Co/kBT
4 +
(1 - e-2D
)
2
2
2NµB gCo
3kB(T - θ)
DCo
4(1 + e-2D
Conclusion
(1)
Co/kBT
Herein we reported a set of new structural scaffolds based
on metal complexes of N-(4-pyridyl)benzamide that generate
crystalline solids with 1-, 2, and 3-D networks of hydrogen
bonding and π-π stacking interactions. The dimensionality of
the noncovalent networks in structures 2-10 is determined by
the directional noncovalent motifs of the units. 1-D networks
of hydrogen bonding and π-π stacking interactions were
observed in Ag-complex 2, Zn-complex 3, and Cu-complex 4.
Co-complex 5 comprised a pair of 1-D networks of hydrogen
bonding and π-π stacking interactions that run perpendicular
to one another and form 2-D noncovalent networks. In the Zn-
complex 6, although it also comprises two 1-D networks of
hydrogen bonding and π-π stacking interactions that run
perpendicular to one another, the overall structure exhibits a
3-D noncovalent network system as the individual networks
interact with one another in a zigzag fashion along the third
dimension of space. Co-complex 7, Ni-complex 8, and Zn-
complexe 9 are isostructural and generate 3-D noncovalent
network structures. They comprise a 2-D π-π stacking system
that forms sheets with arrays of hydrogen bonding groups
oriented orthogonally and which ultimately join the sheets
together to form a 3-D solid network. Due to their isomorphous
nature, topotaxial growth of single crystals of any member (7-
9) enables the growth of mixed single crystals, 11 and 12, as
well solid solutions 13-16. Mn-complex 10 exhibits a 3-D
noncovalent network composed of 3-D hydrogen bonding
systems that overlaps with a 2-D π-π stacking system in a
very similar way as 7-9. The temperature-dependent magnetic
moment measurements of paramagnetic assemblies 4, 5, 7, 8,
and 10 and the solid solutions 13-16 were obtained between 2
and 300 K. They indicated that minor interactions are observed
for the assemblies that exhibit higher dimensional networks of
noncovalent interactions, namely 5, 7, 8, and 13-16.
)
In the 3-D Co(NPBA)2(NO3)2(MeOH)2 (7), with a similar µeff
) 5.08 µB, the temperature-dependent magnetic behavior can
be modeled with eq 1 as well but with values of g ) 3.30, D
) 30 cm-1 (43 K), and θ ) -6 K, indicating similar
antiferromagnetic interactions to those present in Co(NPBA)2-
(OAc)2(H2O)2 (5), but with slight variances at lower tempera-
tures due to a greater D. A similar behavior is observed for the
isostructural Ni(NPBA)2(NO3)2(MeOH)2 (8), which has a 300
K µeff ) 3.12 µB and is best modeled with eq 2 for the S ) 1
Ni(II) center with g ) 2.20, D ) 18 cm-1 (26 K), and θ ) 2
K. For Co-complex 7 and Ni-complex 8, the small θ values are
consistent with a weak antiferromagnetic and ferromagnetic,
respectively, nearest neighbor spin coupling. The manganese
containing 3-D 10, which has a 300 K µeff ) 5.88 µB, follows
simple Curie-Weiss behavior with θ ) -0.1 K, and exhibits
a g value of 1.99. In this case, despite the extensive intermo-
lecular interactions present in 10, the magnetic properties appear
to be more dependent on metal-metal distances than the number
of interactions between the metal complexes.
2
2
Ni/kBT
2e-D
NµB gNi
øNi
)
+
-DNi/kBT
3k (T - θ)
1 + 2e
B
2kBT
Ni/kBT
(1 - e-D
)
2
2
2NµB gNi DNi
3kB(T - θ)
(2)
1 + 2e-D
Ni/kBT
Solid solutions 13-15 with a [CoyNi1-y(NPBA)2(NO3)2-
(MeOH)2] composition exhibit magnetic properties in relation
of the proportion of their metal content, with little perturbation
of the interactions between metal centers. The magnetic proper-
ties of these materials can be best fit with a linear combination
of eq 1 and 2, i.e., eq 3, where y is the fraction of Co(II) ions
in the sample (Figure 20).
Acknowledgment. We thank Dr. Lesley Sieburth for her
assistance with the photographic work of the crystal composites.
Financial support by the National Institute of Health (Grant No.
5R01GM57052), the National Science Foundation (Grant Nos.
CHE-9818472 and CHE-9320478), the U.S. Department of
Energy (Grant No. DE FG 03-93ER45504), and the NIH
Research Supplement for Dr. Juan C. Noveron are gratefully
acknowledged. Dedicated to the memory of Professor Donald
J. Cram for his pioneering contributions in supramolecular
chemistry.
øtotal ) (y)øCo + (1 - y)øNi
(3)
The Co:Ni samples with 3:1, 1:1, and 1:3 ratios could be
modeled with gCo ) 3.35 ( 0.05, gNi ) 2.20, DCo ) 20 ( 5
cm-1, and DNi ) 8 ( 2 cm-1. The same θ value of -2 K was
used in eq 1 and 2, thus becoming an average value of Ni-Ni,
Ni-Co, and Co-Co interactions in the solids, which again
shows weak magnetic coupling between metal centers within
the structure. Likewise, solid solution 16 that contains the Ni-
complex 8 and Zn-complex 9 at a 1:1 ratio can also be modeled
to exactly one-half of eq 2, with gNi ) 2.20, DNi ) 14 cm-1
(26 K), and θ ) 2 K, as S ) 0 Zn(II) does not contribute to the
magnetic behavior. There is little difference in the overall
Supporting Information Available: Tables of bond lengths
(Å) and angles (deg) around the metal ions and conformation
angles Φ1, Φ2, and Φ3 of NPBA (PDF) and additional
crystallographic data for 1-11 (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
JA0200241
9
J. AM. CHEM. SOC. VOL. 124, NO. 23, 2002 6625