Versatile ligands for the construction of layered metal-containing networks

Article abstract of DOI:10.1071/CH08440

The synthetic opportunities furnished by organic synthesis and the inherent structure-directing possibilities of coordination complexes have been combined in the assembly of a series of layered metal-containing hybrid materials. The supramolecular assembly relies on self-complementary non-covalent interactions, and in five of the six structures presented herein, N-H...O=C hydrogen bonds between acetamide moieties on neighbouring ligands provide the primary structure-direction tool as intended. The distances between metal ions are controlled by ligand...ligand hydrogen bonds and reside within a narrow and tuneable range. The following crystal structures are reported: [Cu(4-(3-pyridyl)-1-acetamidobenzene)₂(1,1,1,5,5,5-hexafluoro-2,4- pentanedione)₂] 1; [Cu(4-(acetamidomethyl)pyridine) ₂(1,1,1,5,5,5-hexafluoro-2,4-pentanedione)₂] ·2CH₂Cl₂ 2; [Cu(3-acetamidopyridine) ₂(1,1,1,5,5,5-hexafluoro-2,4-pentanedione)₂] 3; [Ni(3-acetamidopyridine)₂(1,3-diphenyl-1,3-propanedione) ₂]·2CH₂Cl₂ 4; [Ni(3-acetamidopyridine) ₂(1,3-diphenyl-1,3-propanedione)₂] 5; and [Co(2-acetamidopyridine)₂(1,3-diphenyl-1,3-propanedione) ₂]·2CH₂Cl₂ 6.

Full text of DOI:10.1071/CH08440

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2009, 62, 899–908
Versatile Ligands for the Construction of Layered
Metal-Containing Networks
Christer B. Aakeröy,A,C Izhar Hussain,B Safiyyah Forbes,A and John DesperA
ADepartment of Chemistry, Kansas State University, Manhattan, KS 66506, USA.
BDepartment of Pharmacy, COMSATS Institute of InformationTechnology, Abbottabad 22060, Pakistan.
CCorresponding author. Email: aakeroy@ksu.edu
The synthetic opportunities furnished by organic synthesis and the inherent structure-directing possibilities of coor-
dination complexes have been combined in the assembly of a series of layered metal-containing hybrid materials.
The supramolecular assembly relies on self-complementary non-covalent interactions, and in five of the six structures
presented herein, N–H· · ·O=C hydrogen bonds between acetamide moieties on neighbouring ligands provide the pri-
mary structure-direction tool as intended. The distances between metal ions are controlled by ligand· · ·ligand hydrogen
bonds and reside within a narrow and tuneable range. The following crystal structures are reported: [Cu(4-(3-pyridyl)-
1-acetamidobenzene)2(1,1,1,5,5,5-hexafluoro-2,4-pentanedione)2] 1; [Cu(4-(acetamidomethyl)pyridine)2(1,1,1,5,5,5-
hexafluoro-2,4-pentanedione)2]·2CH2Cl2 2; [Cu(3-acetamidopyridine)2(1,1,1,5,5,5-hexafluoro-2,4-pentanedione)2] 3;
[Ni(3-acetamidopyridine)2(1,3-diphenyl-1,3-propanedione)2]·2CH2Cl2 4; [Ni(3-acetamidopyridine)2(1,3-diphenyl-1,3-
propanedione)2] 5; and [Co(2-acetamidopyridine)2(1,3-diphenyl-1,3-propanedione)2]·2CH2Cl2 6.
Manuscript received: 15 October 2008.
Final version: 14 February 2009.
O
Introduction
C
H
N
Many strategies based on coordinate-covalent bonds have been
employed in the synthesis of hybrid materials containing net-
works with predictable connectivity and dimensionality, typi-
cally through the use of bridging ligands such as 4,4ꢀ-bipyridine,
dicarboxylates, bis(amides), bis(lactams), and bis(pyridones).[1]
At the same time, the strength and directionality of hydro-
gen bonds have offered supramolecular pathways towards the
directed assembly of extended organic networks and multicom-
ponent supermolecules.[2] Although both strategies have enjoyed
considerable success, much less work has been carried out on the
assembly of metal-containing networks using a combination of
metal–ligand and hydrogen-bond interactions.[3] This approach
may in some cases have certain advantages, as it combines the
strength of the coordinate-covalent bond with the flexibility of
the softer hydrogen-bond interactions, which can offer a self-
correcting assembly process, and desirable physical properties
such as enhanced solubility in a range of organic solvents.[4] An
important role in this approach is played by versatile bifunc-
tional ligands that contain both metal-coordinating sites and
functionalitiesthatprovideopportunitiesfororganizingcomplex
molecules into infinite architectures through supramolecular
chemistry and non-covalent interactions.
We are currently assembling a library of reliable ligands
that can be employed in the construction of coordination net-
works with controllable metrics with a view to preparing porous
solids with well-defined and accessible channels. In the present
study, wehavetakenadvantageoftherobustself-complementary
hydrogen-bonding capability of the amide functionality (as a
result of strong N–H· · ·O=C hydrogen bonds), and the reli-
able metal-coordinating ability of pyridine.[5] More specifi-
cally, we have employed a series of acetamido(pyridine)-based
H
CH3
N
CH3
CH2
C
O
N
N
I
II
H
O
N
CH3
C
O
C
N
N
H
CH3
N
III
IV
Scheme 1.
compounds as such species are also present in several biolog-
ically relevant systems.[6] The four ligands I–IV (Scheme 1)
used in the present work contain an acetamido group attached
at different positions on a pyridine ring. Although complexes of
some amidopyridine derivatives have previously been reported,
such efforts have primarily involved the formation of 1-D and
2-D coordination networks, by the interaction of metal ions with
double-ended bis(amidopyridine) ligands.[7]
Systematic structural studies of organic salts and co-crystals
have demonstrated that the structural behaviour and pattern
preference of the N–H moiety depend on the position of
© CSIRO 2009
10.1071/CH08440
0004-9425/09/080899

900
C. B. Aakeröy et al.
O(27)
C(26)
C(21)
C(25)
C(24)
C(28)
C(14)
C(27)
C(15)
C(16)
N(21)
C(13)
C(12)
C(22)
C(23)
F(51C)
C(51) C(52)
F(51A)
F(55B)
C(55A)
F(55A)
N(11)
C(54)
O(52)
O(64)
F(65B)
O(62)
C(62)
Cu(1)
F(61A)
C(65)
F(65A)
N(31)
C(32)
C(33)
F(61C)
F(61B)
C(43)
C(36)
C(35)
O(47)
C(42)
C(44)
C(45)
C(34)
C(48)
C(41)
C(47)
N(41)
C(46)
Fig. 1. Molecular geometry of 1.
Fig. 2. Two-dimensional layer in the structure of 1 generated by symmetry-related N–H· · ·O hydrogen bonds.
the acetamido group with respect to the heterocyclic nitro-
gen atom.[8] A search of the Cambridge Structural Database
(CSD) shows that a catemeric N–H· · ·O=C is unlikely to form
if the acetamido group is positioned ortho to a pyridine nitro-
gen atom (2-acetamidopyridines). However, if the acetamido
group is located either meta or para to a pyridine nitrogen atom
(3- and 4-acetamidopyridines), then the most likely structural
outcome is a self-complementary N–H· · ·O=C (amide–amide)
motif. In order to exploit the latter synthon, we decided to focus
on 3- and 4-substituted acetamidopyridines as our bifunctional
ligands in an attempt to construct metal-containing 1-D and
2-D architectures (although one example of a structure with an
ortho-substituted ligand is also included).
A complication that may arise when utilizing hydrogen bonds
as the primary synthetic tool of hybrid materials is poten-
tial interference from counterions that often accompany the
metal ions. Many common anions such as chloride, nitrate,
and sulfate are powerful hydrogen-bond acceptors that can
readily disrupt the intended intermolecular ligand–ligand hydro-
gen bonds. Therefore, in order to avoid or at least minimize
this potential problem, we opted to use charge-neutral metal–
ligand complexes as building blocks,[9] such as copper(ii)
1,1,1,5,5,5-hexafluoro-2,4-pentanedione [Cu(hfac)2], cobalt(ii)
1,3-diphenyl-1,3-propanedione [Co(DBM)2], and nickel(ii) 1,3-
diphenyl-1,3-propanedione [Ni(DBM)2]. An additional advan-
tage of using two chelating ligands is that the coordination
chemistry is easier to control (especially in the case of the
notoriously unpredictable CuII ion).Acetylacetonate (acac)-type
ligands typically coordinate to M(ii) metal ions in a square-
planar arrangement, thus leaving the two axial sites open for
coordination to a suitable ligand, which can subsequently be used
for constructing the desired structural motif. The primary goal
of the current particular project is to employ the C=O· · ·H–N
amide catemer as a synthetic vehicle for organizing coordination
complexes into extended architectures and to begin to map out its
limits and limitations as a supramolecular synthon. In the present
study, we allowed ligands I–IV to react with a series of acac-
based CuII, NiII, and CoII complexes, and we obtained crystals
suitable for single-crystal X-ray diffraction in six cases reported
here:[Cu(4-(3-pyridyl)-1-acetamidobenzene)2(hfac)2]1;[Cu(4-
(acetamidomethyl)pyridine)2(hfac)2]·2CH2Cl2 2;[Cu(3-aceta-
midopyridine)2(hfac)2] 3; [Ni(3-acetamidopyridine)2(DBM)2]·
2CH2Cl2 4; [Ni(3-acetamidopyridine)2(DBM)2] 5; [Co(2-
(acetamidopyridine)2(DBM)2]·2CH2Cl2 6.

Versatile Ligands for Building Metal-Containing Networks
901
(a)
the bite of the chelate ring. The benzene rings of 4-(3-pyridyl)-
1-acetamidobenzene molecules are slightly twisted (∼30◦) with
respect to the plane of pyridine (py) rings and the amide groups
in the complex are arranged in a trans-fashion with respect to
the N(py)–Cu–N(py) axis (Fig. 1).
O(38) C(38)
C(39)
N(37)
C(37)
The N–H groups on both ligands engage in N–H· · ·O hydro-
gen bonds with a C=O moiety from a ligand on a neigh-
bouring complex, (N21· · ·O47, 3.153(4) Å and (N41· · ·O27,
3.075(4) Å), producing an infinite 2-D layer (Fig. 2).
C(35)
C(36)
F(61C)
C(34)
F(61B)
F(61A)
C(61A)
O(62)
C(33)
N(31)
Cu(2)
The crystal structure of 2 contains two crystallographically
independent 4+2 copper(ii) ions as well as two molecules of
methylene chloride. One of the two copper ions is positioned
on an inversion centre, with four oxygen atoms, from two O,Oꢀ-
chelating hexafluoro-2,4-pentanedionato anions occupying the
four equatorial coordination sites, with cis angles of 85◦ and
95◦, with the smaller angle being associated with the bite of the
chelate. The Cu–O bond lengths are 1.988(5) and 2.331(5) Å,
respectively, and the two 4-(acetamidomethyl)pyridine lig-
ands are occupying the axial sites through their pyridine
nitrogen atoms with a Cu–N bond distance of 1.981(6) Å
(Fig. 3a).
C(32)
C(65B)
F(65C)
C(65A)
O(64A)
F(65B)
O(64)
F(65A)
N(31A)
O(62A)
C(61B)
N(37A)
O(38A)
The geometry around the second copper(ii) ion in the crystal
structure of 2 can also be described as having a 4+2 coordi-
nation; see Fig. 3b. Again the two O,Oꢀ-chelating hexafluoro-
2,4-pentanedionato anions are occupying the four equatorial
coordination sites, with cis angles of 85◦, 89◦, 92◦, and 95◦,
with the two short angles being associated with the bite of the
chelate. The two 4-(acetamidomethyl)pyridine ligands are occu-
pying the axial sites through their pyridine nitrogen atoms at an
N–Cu–N angle of 176◦. The four different Cu–O bond lengths
fall in the range 2.050(6)–2.193(6) Å and the two Cu–N bond
distances are 1.971(7) and 2.012(6) Å, respectively.
As was the case with the structure of 1, the amide groups
in neighbouring complex ions are interlinked through N–
H· · ·O hydrogen bonds (N17· · ·O38, 2.806(8) Å, N27· · ·O18,
2.848(9) Å and N37· · ·O28, 2.858(9) Å) to produce infinite 2-D
sheets; see Fig. 4.
The central motif in the crystal structure of 3 is a 4+2 hexaco-
ordinated copper(ii) complex where the metal ion is located on
an inversion centre. The two chelating 1,1,1,5,5,5-hexafluoro-
2,4-pentanedionato anions occupy the equatorial plane, whereas
the two 3-acetamidopyridine molecules complete the complex
ion by coordinating through their pyridine nitrogen atoms with
a Cu–N distance of 2.007(3) Å (Fig. 5).
The pyridine rings of two amide ligands are coplanar and the
amide groups in the complex are oriented trans with respect to
theN–M(ii)–Naxis.Thechelateringsformedbytheanionicacac
ligands have cis angles of 87◦ and 93◦, with the short angle, as
expected, being associated with the bite of the chelate ring. The
N–H group of one amide ligand and the C=O group on a pyridyl
ligand on an adjacent complex engage in self-complementary N–
H· · ·O hydrogen bonds, N13· · ·O21, 2.791(4) Å. As the metal
ion is located on an inversion centre, there are two symmetry-
related N–H· · ·O=C catemers, leading to an infinite 2-D sheet
structure; see Fig. 6.
(b)
C(19)
O(18)
C(18)
N(17)
C(17)
C(14)
F(41A)
F(41B)
C(13)
C(12)
N(11)
Cu(1)
C(15)
C(41A)
F(45C)
F(45B)
C(16)
O(42)
C(45A)
F(41C)
O(44)
N(21)
C(22)
C(23)
O(54)
F(55A)
F(45A)
O(52)
F(55C)
C(26)
C(25)
F(51A)
F(51B)
F(55B)
C(24)
C(27)
C(51)
N(27)
C(28)
F(51C)
C(29)
O(28)
Fig. 3. Molecular geometries of the two unique complexes in 2.
Results
The crystal structure of 1 contains the expected six-coordinated
copper(ii) complex. The geometry at the CuII centre is a 4+2
coordination, resulting from two O,Oꢀ-chelating hexafluoro-2,4-
pentanedionato ions and two 4-(3-pyridyl)-1-acetamidobenzene
ligands coordinated through their pyridine nitrogen atoms,
in trans positions, with Cu–N distances of 2.021(3) and
2.022(3) Å, respectively. The two axial pyridine rings are copla-
nar. The chelate rings formed by the 1,1,1,5,5,5-hexafluoro-
2,4-pentanedionato ligands are planar with cis angles ranging
between 88◦ and 92◦, with the acute angles being associated with
The crystal structure of 4 shows that each nickel(ii) ion
is coordinated by two unique 1,3-diphenyl-1,3-propanedionato
ions and two 3-acetamidopyridine molecules with two additional
methylene chloride molecules present in the lattice. The chelate
rings have cis angles ranging from 87◦ to 92◦ and in contrast
to 1–3, the acute angles in this complex are associated with the
non-biting sides. The two 3-acetamidopyridine molecules are
occupying the trans positions with Ni–N distances of 2.095(2)

902
C. B. Aakeröy et al.
Fig. 4. Two-dimensional layer in the structure of 2 generated by N–H· · ·O hydrogen bonds.
O(21)
Pyridine-based ligands on adjacent complex ions form
intermolecular N–H· · ·O=C hydrogen bonds, N13· · ·O17,
2.9696(18) Å, resulting in a 2-D sheet structure (Fig. 10).
The crystal structure of 6 contains a 4+2 cobalt(ii) complex
as well as two molecules of methylene chloride. Each metal
complex is located on a crystallographic inversion centre with
an octahedral geometry constructed from two chelating anions
and two 2-acetamidopyridine molecules (Fig. 11).
C(22)
C(21)
N(13)
C(14)
C(13)
C(15)
C(16)
N(11)
C(12)
The chelate rings are almost planar with cis angles of 90.6◦
and 90.4◦ but two phenyl groups on each 1,3-diphenyl-1,3-
propanedionato ion are slightly twisted with respect to each
other. The two trans-2-acetamidopyridine molecules are coor-
dinated to the central metal(ii) ion with Co–N distances of
2.2332(9) Å. In contrast to previous cases 1–5, the N–H group of
each amide ligand is involved in intracomplex N–H· · ·O hydro-
gen bonding with an oxygen atom from the nearest acac ligand,
N12· · ·O23, 2.8984(13) Å. As the most prominent hydrogen-
bond donors in the compound, the N–H moieties, are occupied
with intramolecular interactions, there are no other structure-
directing complementary intermolecular interactions that can
connect discrete metal complexes into specific and recognizable
networks.
F(35B)
O(34)
C(34)
Cu(1)
O(32)
C(32)
F(35C)
F(31B)
C(33)
C(35A)
F(35A)
C(31A)
F(31A)
F(31C)
Fig. 5. Molecular geometry and thermal ellipsoids (50%) for the complex
ion in 3.
Discussion
Single-crystal X-ray analysis of 1–6 has demonstrated
that the self-complementary N–H· · ·O=C intermolecular
ligand· · ·ligand hydrogen-bond interaction is present as long as
the N–H donor is not forced into an intramolecular interaction as
a result of ortho-substitution of the pyridyl backbone. The O,Oꢀ-
chelating anions employed in the present study, hexafluoro-2,4-
pentanedionate and 1,3-diphenyl-1,3-propanedionate, occupy
the four equatorial sites around the metal(ii) ions, and when
the amide moiety is located so close to the equatorial plane, the
N–H group is essentially pre-organized for an intramolecular N–
H· · ·O interaction (as seen in the structure of 6). However, if the
N–H moiety is given the structural freedom (as is the case with
the meta- and para-substituted pyridine-based ligands) to select
a hydrogen-bond acceptor, the carbonyl moiety is the preferred
interaction site in each case 1–5. The nature of the metal ion
and 2.108(2) Å, respectively, and the two amide groups are
oriented in a trans manner (Fig. 7).
Again, ligands on adjacent complex ions form two
intermolecular N–H· · ·O=C hydrogen bonds, N23· · ·O17,
2.967(3) Å and N13· · ·O27, 2.819(3) Å, respectively resulting
in a 2-D sheet structure, (Fig. 8).
The crystal structure determination of 5 shows that each
nickel(ii) ion is coordinated by two unique 1,3-diphenyl-1,3-
propanedionato ions and two 3-acetamidopyridine molecules in
a 4+2 manner, but this time there is no solvent present in the
lattice (these crystals were grown from acetonitrile, whereas 4
wasobtained from CH2Cl2).The two symmetry-related axial lig-
ands display Ni–N(py) distances of 2.1188(12) Å and the amide
groups are again arranged in a trans fashion (Fig. 9).

Versatile Ligands for Building Metal-Containing Networks
903
Fig. 6. Two-dimensional layer in the structure of 3 generated by symmetry-related N–H· · ·O hydrogen bonds.
for possibly disruptive counterions, which undoubtedly facili-
tates the supramolecular synthetic strategy. The importance of
using chelating ligands for controlling the coordination geome-
try, and thereby also the structural role of the complex ion itself,
is illustrated by a previously reported crystal structure of a five-
coordinate CuII complex comprising two 4-acetamidopyridine,
two acetate ions and a water molecule in the first coordination
sphere; in this case the amide· · ·amide hydrogen bond is dis-
rupted by the water molecule, and the result is a complex 3-D
architecture.[10]
It is interesting to note that 1–5 form layered structures as dic-
tated by the ligand· · ·ligand hydrogen bonds; however, as soon
as the intermolecular interaction is prevented (as in 6, when the
amide is now in the ortho-position), the layers are no longer
present.
Furthermore, in all the layered structures, the metal· · ·metal
distances are in the 9–11-Å range as a result of the 1-D amide
α-network. The second dimension of the layer unit cell varies
more because the size of the ligand shows greater variation
(Fig. 12).
Even though the five layered structures 1–5 display very sim-
ilar structural chemistry, the crystallographic symmetry varies
between them (layers are related by either translation, inversion,
or by a glide plane).
O(17)
C(18)
C(17)
C(14)
N(11)
N(13)
C(15)
C(16)
C(13)
C(12)
C(63)
C(61)
C(71)
C(81)
O(63)
O(33)
C(82)
O(61)
O(31)
Ni(1)
C(72)
C(52)
C(51)
C(31)
C(33)
C(41)
C(32)
N(21)
C(42)
C(26)
C(25)
C(22)
C(23)
N(23)
C(27)
C(24)
C(28)
O(27)
The self-complementary acetamido moiety has also been
previously utilized in the preparation of a series of silver(i)-
containing 2-D architectures,[11] and it is clear that this par-
ticular supramolecular synthon is robust enough to organize
relatively large complex ions into desired extended net-
works. Some 50 crystal structures containing silver(i) ions
and acetamido-substituted pyridyl-based ligands were found
in the CSD database and approximately half of those con-
tained extended networks assembled via self-complementary
N–H· · ·O=C hydrogen bonds. In most of the structures that
Fig. 7. Molecular geometry and thermal ellipsoids (50%) for the complex
ion in 4 (solvent molecules not shown).
does not affect the resulting structure notably because in each
case, the metal ion is ‘strapped into’ a fixed geometry dictated
by the two anionic chelating ligands. All six complex ions have
a 4+2 coordination with the two chelating ligands located in
the equatorial plane. The charge balance that results when com-
bining MII ions with two acac ligands also removes the need

904
C. B. Aakeröy et al.
Fig. 8. Two-dimensional layer in the crystal structure of 4 generated by two unique N–H· · ·O hydrogen bonds.
coordinating pyridyl nitrogen atom in order to avoid a bis(N,O)
chelating mode or an intramolecular N–H· · ·O hydrogen bond if
an acac-based ligand (a strong hydrogen-bond acceptor) is used
as a way of controlling coordination geometry and charge of the
complex ion. We are currently exploring how amide· · ·amide
hydrogen bonds can be utilized for the construction of 3-D archi-
tectures with accessible cavities with controllable size and shape.
O(21A)
O(23A)
Ni(1)
N(11)
Experimental
O(17A)
N(13A)
C(18)
C(12)
All chemicals were purchased from Aldrich and used without
further purification. Melting points were determined on a Fisher-
Johns melting point apparatus and are uncorrected.
N(13)
C(17)
N(11A)
O(21)
C(13)
C(14)
C(32)
O(23)
C(23)
C(16)
C(15)
C(21)
O(17)
Synthesis of Ligands
C(42A)
Synthesis of 4-(Bromo)acetamidobenzene
C(33)
C(34)
C(31)
C(36)
C(41A)
C(46A)
Acetic anhydride (5 mL) was added dropwise to
4-bromoaniline (5.16 g; 30 mmol) and the mixture was heated
under reflux for 30 min. The excess acetic anhydride and
acetic acid produced during the reaction were removed on a
rotary evaporator, and the precipitates thus obtained on cooling
were recrystallized from methanol. Yield 70%. Mp 173–174◦C.
νmax(KBr)/cm−1 3293m (ν(NH)), 1669vs (ν(C=O)), 1534vs
(ν(amide II)). δH (400 MHz, CDCl3) 7.41 (br s, 4H), 7.34 (s, 1H),
2.17 (s, 3H).
C(43A)
C(44A)
C(22)
C(35)
C(45A)
Fig. 9. Molecular geometry and thermal ellipsoids (50%) for the complex
ion in 5.
did not contain an N–H· · ·O=C synthon, the N–H moiety was
instead engaged in charge-assisted hydrogen bonds with a strong
hydrogen-bond acceptor such as a nitrate or sulfate ion. The
relative positions of the hydrogen-bonding site with respect to
the pyridyl nitrogen atom is also of considerable importance,
because in the absence of more strongly chelating ligands (such
as acac), 2-acetamidopyridine acts as a bis(N,O)chelator that
prevents any structure-directing intermolecular N–H· · ·O=C
hydrogen bonds from forming.[12] For the N-oxide analogue of
2-acetamidpyridine, a seven-membered chelate is not formed,
however, and instead the ligand is binding to the metal ion only
through the N-oxide moiety.[13]
In the structures of 1–6, the central metal complex is
charge-neutral, which removes the need for counterions, which
emphasizes the importance of minimizing the number of struc-
turally competing factors if a desired supramolecular goal is to
be attained in a reasonable yield. Furthermore, an amide moi-
ety should be placed either meta or para with respect to the
Synthesis of 4-(3-Pyridyl)-acetamidobenzene, I
(Scheme 1)
Amixtureof4-bromo-1-acetamidobenzene(2.14 g, 10 mmol),
3-pyridylboronic acid (1.58 g, 10.33 mmol), sodium carbonate
(0.700 g, 6.6 mmol), and trans-dichlorobis(triphenylphosphine)
palladium(ii) (0.180 g; 0.25 mmol) was weighed in a round-
bottom flask and acetonitrile (35 mL) and water (35 mL) were
added to it. After passing through nitrogen for 10 min, the solu-
tion was heated at 80◦C under a nitrogen atmosphere. The
reaction was monitored by TLC and on completion (24 h) was
allowed to cool to room temperature. The solution was then
diluted with 150 mL of ethyl acetate, and washed with water
(3 × 100 mL), followed by saturated aqueous sodium chloride
solution (2 × 100 mL). The organic layer was separated and
dried over magnesium sulfate. After removing the solvent on
a rotary evaporator, the residue was chromatographed on silica

Versatile Ligands for Building Metal-Containing Networks
905
Fig. 10. Two-dimensional layer in the crystal structure of 5 generated by symmetry-related N–H· · ·O hydrogen bonds.
(ν(NH)), 1677vs (ν(C=O)), 1535, 1524vs (ν(amide II)). (Calc.:
C 47.93, H 2.90, N 6.21%. Found: C 47.7, H 3.1, N 6.0.)
C(14)
Synthesis of [Cu(4-(acetamidomethyl)pyridine)2
(1,1,1,5,5,5-hexafluoro-2,4-pentanedione)2]·
2CH2Cl2 2
C(15)
C(16)
C(13)
C(12)
O(17)
N(12)
C(17)
C(18)
4-(Acetamidomethyl)pyridine (0.030 g, 0.20 mmol) was dis-
solved in cold methylene chloride (10 mL) and was added to the
solution of Cu(hfac)2(0.049 g, 0.10 mmol) in methylene chloride
(15 mL). The resulting solution was transferred to a screw-cap
vial and allowed to stand at room temperature. Green needles
appeared over 3 days’ time. νmax(KBr)/cm−1 3297m (ν(NH)),
1662vs (ν(C=O)), 1547, 1525vs (ν(amide II)). (Calc.: C 35.48,
H 2.76, N 5.91%. Found: C 35.3, H 2.8, N 5.7.)
N(11)
C(33)
C(32)
C(31)
O(21)
C(21)
Co(1)
O(23)
C(23)
C(41)
C(34)
C(35)
C(22)
C(42)
C(43)
C(36)
C(46)
Synthesis of [Cu(3-acetamidopyridine)2(1,1,1,5,5,5-
hexafluoro-2,4-pentanedione)2] 3
C(45)
C(44)
A hot solution of Cu(hfac)2 (0.049 g, 0.10 mmol) in
methylene chloride (10 mL) was added to a solution of 3-
acetamidopyridine (0.027 g, 0.20 mmol) also in methylene chlo-
ride (15 mL). The resulting solution was brought to the boil and
then left to cool overnight. The following day, green crystals had
formed. νmax(KBr)/cm−1 3268m (ν(NH)), 1684vs (ν(C=O)),
1546, 1525vs (ν(amide II)). (Calc.: C 38.44, H 2.42, N 7.47%.
Found: C 38.7, H 2.5, N 7.3.)
Fig. 11. Molecular geometry and thermal ellipsoids (50%) for the complex
ion in 6.
with hexane/ethyl acetate.The product was recrystallized as light
yellow plates from ethyl acetate. Yield 64%. Mp 186–188◦C.
νmax(KBr)/cm−1 3254m (ν(NH)), 1687vs (ν(C=O)), 1532vs
(ν(amide II)). δH (400 MHz, CDCl3) 8.84 (d, J 1.56, 1H), 8.59
(dd, J 2, 1H), 7.85 (t, J 4, 1H), 7.88 (t, J 2.6, 1H), 7.63 (m, 2H),
7.56 (m, 2H), 7.52 (br s, 1H), 2.22 (s, 3H).
Synthesis of [Ni(3-acetamidopyridine)2(1,3-diphenyl-
1,3-propanedione)2]·2CH2Cl2 4
A solution of 3-acetamidopyridine (0.027 g, 0.20 mmol) in
methylene chloride (15 mL) was added to a solution of nickel(ii)
DBM (0.048 g, 0.10 mmol) in 10 mL of methylene chloride. The
mixture was heated for 5 min to reduce the volume to 7 mL and
then allowed to stand in a screw-cap vial at room temperature
until green crystals appeared. νmax(KBr)/cm−1 3301m (ν(NH)),
1673vs (ν(C=O)), 1550, 1520vs (ν(amide II)). (Calc.: C 58.32,
H 4.47, N 5.91%. Found: C 58.5, H 4.6, N 5.6.)
Synthesis of 4-(acetamidomethyl)pyridine II,[14] 3-aceta-
midopyridine III,[15] and 2-acetamidopyridine IV were carried
out by previously reported methods.[8]
Synthesis of Metal Complexes
Synthesis of [Cu(4-(3-pyridyl)-1-acetamidobenzene)2
(1,1,1,5,5,5-hexafluoro-2,4-pentanedione)2] 1
Synthesis of [Ni(3-acetamidopyridine)2(1,3-diphenyl-
1,3-propanedione)2] 5
4-(3-Pyridyl)-1-acetamidobenzene (0.042 g, 0.20 mmol) was
dissolved in hot methylene chloride (10 mL) and mixed with
the hot solution of Cu(hfac)2 (0.049 g, 0.10 mmol) in methy-
lene chloride (15 mL). The resulting solution was boiled in a
screw-cap vial several times and allowed to stand. The green
prisms formed over a period of 7 days. νmax(KBr)/cm−1 3337m
3-Acetamidopyridine (0.03 g, 0.22 mmol) was dissolved in
acetonitrile (5 mL) and mixed with a solution of NiII DBM
(0.049 g, 0.10 mmol) in acetonitrile (5 mL). The solution was
heated for 10 min and then allowed to stand in a screw-cap vial at

906
C. B. Aakeröy et al.
18.268
10.376
10.376
18.268
Fig. 12. Metal· · ·metal distances within the layer in the crystal structure of 1. The metal ions are separated by 10.4 Å along the amide link, and
by over 18 Å in the plane but perpendicular to this direction.
room temperature. The green plates were formed over 4 weeks’
time. νmax(KBr)/cm−1 3306m (ν(NH)), 1684(ν(C=O)), 1548,
1525vs (ν(amide II)). (Calc.: C 67.97, H 4.93, N 7.21%. Found:
C 67.8, H 5.1, N 7.2.)
Compound 1: Attempted absorption correction did not
improve fit statistics and the uncorrected dataset was used for
structure refinement. The complex sits on a general position.
One of the four –CF3 groups was disordered. All non-hydrogen
atoms were given anisotropic thermal parameters. All hydrogen
atoms were included in calculated positions and allowed to ride.
Compound 2: Data were corrected for absorption using
SADABS. The asymmetric unit contains five species: a complete
copper(ii) complex on a general position, a half-complex (sit-
ting on an inversion centre), and three ordered dichloromethane
molecules. Five of the six –CF3 groups were disordered. Four
were modelled with two species, and the fifth was modelled with
three species. Geometry of all –CF3 fragments was restrained
to be similar to the first fragment (C41A, F41A-F41C) by the
SAME command. The geometry of the first fragment (C41A,
etc.) was idealized to tetrahedral by using DFIX restraints on
the C–F bond distances and F–F distances. Thermal parame-
ters for the set of three fluorine atoms on each species having
occupancy <50% were constrained with EADP commands. The
fluorine atoms having occupancy >60% were given isotropic
thermal parameters (anisotropic refinement of other fluorine
atoms was unstable). All hydrogen atoms were included in
calculated positions and were allowed to ride.
Compound 3: Data were corrected for absorption using
SADABS. The complex sits on a crystallographic inversion cen-
tre. Both –CF3 groups were disordered: they were both modelled
as a triplet of species. For each triplet, site occupancy was
restrained to 1.0 with individual occupancy free variables and
a SUMP command; the major species (>75% occupancy) was
refined with anisotropic fluorine atoms; the two minor species
(<15% occupancy each) were refined with isotropic thermal
parameters. Geometry of the six independent –CF3 fragments
was restrained using SAME commands. All hydrogen atoms
were included in calculated positions and were allowed to ride.
Compound 4: Data were corrected for absorption using
SADABS. The asymmetric unit contains three species: a nickel
complex, an ordered dichloromethane solvent molecule, and a
disordered dichloromethane solvent molecule. Geometry of all
three dichloromethane fragments was restrained with SAME
commands.All non-hydrogen atoms were given anisotropic ther-
malparameters.Thermalparametersforthetwo(closelylocated)
disordered dichloromethane species were pairwise constrained
Synthesis of [Co(2-acetamidopyridine)2(1,3-diphenyl-
1,3-propanedione)2]·2CH2Cl2 6
2-Acetamidopyridine (0.027 g, 0.20 mmol) was dissolved
in methylene chloride (10 mL) and mixed with a solution of
cobalt(ii) DBM (0.048 g, 0.10 mmol) in methylene chloride
(12 mL).The solution was boiled and stored at room temperature
in a screw-cap vial. The dark orange prisms were formed over
3 weeks. νmax(KBr)/cm−1 3295m (ν(NH)), 1704vs (ν(C=O)),
1545, 1521vs (ν(amide II)). (Calc.: C 58.31, H 4.47, N 5.91%.
Found: C 58.2, H 4.6, N 5.8.)
X-Ray Crystallography
X-ray data were collected on a Bruker SMART 1000 four-
circlechargecoupleddevice(CCD)diffractometer(1–4), Bruker
Kappa APEX II (5), or Bruker SMART APEX CCD diffracto-
meter (6) using, in each case, a fine-focus molybdenum Kα tube.
Data were collected using SMART (1–4)[16] or APEX2 (5 and
6)[17] software. Initial cell constants were found by small widely
separated ‘matrix’runs. Generally, an entire hemisphere of recip-
rocal space was collected regardless of Laué symmetry. Scan
speed and scan width were chosen based on scattering power
and peak rocking curves.
Unit cell constants and orientation matrix were improved
by least-squares refinement of reflections thresholded from
the entire dataset. Integration was performed with SAINT,[18]
using this improved unit cell as a starting point. Precise unit
cell constants were calculated in SAINT from the final merged
dataset. Lorenz and polarization corrections were applied. Laué
symmetry, space group, and unit cell contents were found with
XPREP.
Data were reduced with SHELXTL.[19] The structures were
solved in all cases by direct methods without incident. In gen-
eral, hydrogen atoms were assigned to idealized positions and
were allowed to ride. Where possible, the coordinates of the
amide hydrogen atoms were allowed to be refined. Heavy atoms
were refined with anisotropic thermal parameters. Absorption
correction was performed with SADABS where possible.

Versatile Ligands for Building Metal-Containing Networks
907

908
C. B. Aakeröy et al.
using EADP commands. The position of the two amide protons
(H13 and H23) was allowed to be refined; all other hydrogen
atoms were included in calculated positions and allowed to ride.
Compound 5: Data were corrected for absorption using
SADABS. The position of the amide proton was allowed to be
refined; all other hydrogen atoms were included in calculated
positions and allowed to ride.
Compound 6: Data were corrected for absorption using
SADABS. The position of the amide proton was allowed to be
refined; all other hydrogen atoms were included in calculated
positions and allowed to ride. Table 1 provides crystallographic
data for 1–6. CCDC-697901–697906 contain the supplemen-
tary crystallographic data for the present paper. These data can
be obtained free of charge fromThe Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data-request/cif.
(b) E. R. Strieter, D. G. Blackmond, S. L. Buchwald, J. Am. Chem.
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Acknowledgements
We are grateful for financial support from NSF (CHE-0316479) and the
ACS-PRF#46011-AC1.
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