Download Metal-directed self-assembly has been widely used to design and to

Metal-directed self-assembly has been widely used to design and to construct finite1 and
infinite2-9 networks that have many potential applications in magnetics, optics, catalysis,
molecular recognition and separations. The vast majority of reported compounds are
metal-organic networks, with little having been reported with metal-organometallic
networks (MOMNs).10 In previous chapters, it was shown that QMTC can be used as a
bidentate spacer, with the two quinone oxygen atoms coordinated to metal ions (see
Figure 12-1).
In the self-assembly of divalent metal ions, QMTCs and organic spacers, the
geometry at the metal ion nodes (octahedral or tetrahedral) can be controlled by
changing the solvent. Supramolecular isomers containing QMTC can be selectively
synthesized by controlling the concentration of the metal ions. One- and twodimensional MOMNs can be extended to two- and three-dimensional MOMNs by
introducing bidentate organic spacers. The introduction of methyl groups at the
benzoquinone ring was found to greatly influence the manner in which the quinone
oxygen lone pairs bind to the metal nodes. Significantly, these simple changes are easily
understood and, therefore, may find general utility in the rational design of
supramolecular coordination networks.
In this chapter, a prescription is given for the construction of MOMNs containing
semiquinone and quinone “antennae”, wherein only one quinone oxygen atom in
QMTC or (5-semiquinone)Mn(CO)3 is bonded to the metal node in the absence of any
“guests”. One can anticipate that these MOMNs have potential for - stacking,11-13
sensing, or metal-binding functions. The Packing diagrams of these MOMNs
demonstrate the formation of three-dimensional and two-dimensional networks via -
interactions and hydrogen-bonding interactions.14
12.2 Experimental
General. For a description of techniques, reagents and instrumentation used,
the reader is referred to Chapter 2, sections 2.1 – 2.3. Standard materials were purchased
from commercial sources and used without further purification. [(6-hydroquinone)
Mn(CO)3]BF4 ([3-1]BF4) and (5-semiquinone)Mn(CO)3 (3-2) were prepared as
previously described in Chapter 3. 1H NMR spectra were recorded on Bruker 300
instruments.
12.2.1 [Mn(QMTC)2(SQMTC)2]n (MOMN 12-1)
The neutral complex (5-semiquinone)Mn(CO)3 (15 mg, 0.06 mmol) and a
quarter equivalent of Mn(NO3)2·4H2O (3.7 mg, 0.015mmol) were heated in MeOH (0.6
mL) at 80 C. After 5 days, crystals of MOMN 12-1 suitable for X-ray studies were
obtained in 58 % yield. IR (KBr) CO 2039 (s), 2026 (s), 1999 (m), 1977 (s), 1966 (s),
1946 (s), 1562 (m), 1522 (w), 1512 (m) cm-1. (DMSO) CO 2030 (s), 1997 (s, sh), 1957
(s), 1941 (s), 1919 (s). Elemental analysis calcd (%), C36H18Mn5O20: C 41.37, H 1.74;
found: C 41.21, H 1.65.
The crystal was a yellow prism mounted on a glass fiber with epoxy cement. Xray data collection was carried out using a Bruker single-crystal diffractometer equipped
with an APEX CCD area detector and controlled by SMART version 5 software. Data
reduction was carried out by SAINT version 6 and absorption corrections were applied
by SADABS version 2. The compound crystallizes in a monoclinic cell that contains
four equivalents of the independent unit. The structure was determined by direct
methods and refined on F squared by use of programs in the SHELXTL version 5
package. Most hydrogen atoms appeared in a difference map, including one on
semiquinone oxygen atom; they were inserted in ideal positions, riding on the atoms to
which they are attached.
12.2.2 [Cd2(QMTC)4(MeOH)4]n (MOMN 12-2)
The neutral complex (5-semiquinone)Mn(CO)314 (15 mg, 0.06 mmol) and a
half equivalent of Cd(NO3)2 were heated in MeOH (0.6 mL) at 80 C in the absence of
light. After four days, crystals of MOMN 12-2 suitable for X-ray studies were obtained
in 86 % yield. IR (KBr) CO 2024 (s), 1946 (br, s), 1555 (m), 1508 (s) cm-1. (DMSO)
CO 1997 (s), 1918 (s, br). 1H NMR (CD3OD)  4.80 (very br, protons in QMTC).
Elemental analysis calcd (%), C40H32Mn4Cd2O24: C 35.82, H 2.40; found: C 35.69, H
2.29.
MOMN 12-2 also was obtained by using Cd(OAc)2 instead of Cd(NO3)2.
X-ray data collection was carried out using a Bruker single-crystal diffractometer
equipped with an APEX CCD area detector and controlled by SMART version 5
software. Data reduction was carried out by SAINT version 6 and absorption
corrections were applied by SADABS version 2. The structure was determined by direct
methods and refined on F squared by use of programs in the SHELXTL version 5
package. Most hydrogen atoms appeared in a difference map; they were inserted in ideal
positions, riding on the atoms to which they are attached.
12.3 Results and Discussion
The reaction of (5-semiquinone)Mn(CO)3 with a quarter equivalent of
Mn(NO3)2 was found to afford the novel one-dimensional metal-organometallic network
MOMN 1, which contains novel semiquinone manganese tricarbonyl (SQMTC), rather
like antennae. The X-ray structure of 1 is shown in figure 1. The central manganese
metal is coordinated by six oxygen atoms where four QMTC organometalloligands
serve as pairwise spacers to construct one-dimensional zig-zag frame and two SQMTC
organometalloligands form act as functional (Scheme 12-1). The novel feature of the
structure is the presence of SQMTC units that interact with one manganese metal to
form pendent moieties rather like antennae.
HO
+
O
heat
MeOH
1/4 Mn(NO3)2
MOMN 12-1
- 1/2 HNO3
Mn(CO)3
Scheme 12-1. Schematic representation of the semiquinone antennae MOMN 12-1.
Mn(CO)3
(OC)3Mn
Mn(CO)3
HO
O
O
Mn(CO)3(OC)3Mn
O
(OC)3Mn
O
O
O
O
O
Mn(CO)(OC)
3
3Mn
O
O
OH
M
O
O
M
O
Mn(CO)3
O
OH
HO
(OC)3Mn
O
O
O
HO
Mn(CO)3
O
Mn(CO)3(OC)3Mn
O
M
O
O
M
O
O
HO
OH
Mn(CO)3
(OC)3Mn
MOMN 12-1
The crystal study reveals that the Mn node adopts a slightly distorted octahedral
geometry with four quinone oxygen atoms (two O2 and two O10) and two semiquinone
oxygen atoms (two O1). Four QMTCs act as bidentate ligands to connect two Mn nodes
and two SQMTCs work as monodentate ligands, so one side of the SQMTCs remain
free and unbonded to the metal ion. These SQMTCs are expected to act as additional
binding sites to metal ions and/or to act as a detector for -molecules via - interaction
through the semiquinone rings.
Figure 12-2. Crystal structure of MOMN 12-1 with thermal ellipsoids at the 50%
probability level. All hydrogen atoms except H6b and metal-carbonyl moieties are
omitted for clarify.
Table 12-1 summarizes selected bond distances and angles for MOMN 12-1.
The bond distances from the manganese atom to the quinone oxygen atoms is 2.18 Å
for Mn1-O2 and 2.12 Å for Mn1-O10. These values are slightly shorter than that of
Mn1-O1 (semiquinone oxygen atom) at 2.26 Å. As would be expected, the bond
distance of C10-O6 is much longer than those of other C-Os (see Table 12-1).
The IR spectrum of MOMN 12-1 (Figure 12-9) shows CO bands at 2039, 2026,
1999, 1977, 1966 and 1946 cm-1 and is more complicated than those of other MOMNs.
This is due to the presence of both QMTC and SQMTC. The IR spectrum in DMSO
solvent also shows CO bands at 2030, 1957 and 1941 cm-1 from SQMTC and 1997 and
1919 cm-1 from QMTC (Figure 12-8). Both QMTC and SQMTC roughly adopt a boat
conformation with phenolic carbons bent out of the diene plane and, as would be
expected, the distance Mn2-C4 (2.22 Å) is shorter than that from manganese to oxygen
bearing quinone carbon atoms (average 2.37 Å).
Figure 12-3 shows the zig-zag network along the c axis with Mn1-Mn1-Mn1
angle of 97.37° and with Mn1-Mn1 distance of 8.23 Å. As shown in Figure 12-3a, the
semiquinone antennae, SQMTC, repeats along the c-axis with an interval of 12.36 Å at
four edges of the one-dimensional frame. A space filling representation (Figure 12-4)
illustrates that MOMN 12-1 has a nanowire structure with dimension of about 1 by 1
nm.
The most interesting feature in MOMN 12-1 is the well ordered interaction
between one-dimensional networks via - stacking and hydrogen bonding interactions.
Figure 12-5a clearly shows - interactions through semiquinone rings. The distance
between the semiquinone rings is only 3.24 Å, which is consistent with - interaction.
This interaction is not the only one to hold together two 1D networks. There is also an
inter-network hydrogen bonding interaction. As mentioned above, SQMTCs are located
at four corners, therefore, each 1D network interacts with four neighboring networks
through - interactions and hydrogen bonding interactions, resulting in the threedimensional network (see Figure 12-5c).
Figure 12-3. Stick representation of the one-dimensional MOMN 12-1: (a) side view
and (b) top view (Magenta = Mn2+, Gray = QMTC, Yellow = SQMTC). Note that that
Mn2+ and QMTC form a 1D zig-zag frame, with SQMTCs positioned at the corners. All
hydrogen atoms are omitted for clarity.
Figure 12-4. Space-filling representation of MOMN 12-1.
Figure 12-5. Space-filling and stick representation of MOMN 12-1: (a) side view and
(b) top view (Magenta = Mn, Red = oxygen, Gray = carbon, White = hydrogen) (c)
formation of the three-dimensional network. The - interactions through the SQMTC
“antenna” result in the three-dimensional network shown.
The reaction of (5-semiquinone)Mn(CO)3 and a half equivalent of Cd(NO3)2
generated the novel one-dimensional quinone antennae MOMN 12-2. The main onedimensional frame consists of QMTC and dicadmium SBUs, with quinone complexes
riding on the main 1-D frame (Scheme 12-2).
HO
1/2 Cd(NO3)2
+
O
heat, dark
MeOH
MOMN 12-2
- HNO3
Mn(CO)3
Scheme 12-2. Schematic representation of the semiquinone antennae MOMN 12-2.
O
O
(CO)3Mn
(CO)3Mn
O
O
L
O
O
L
O
L
L
Cd
O
O
Mn(CO)3
Mn(CO)3
O
O
O
L
Cd
Cd
O
Mn(CO)3
Mn(CO)3
Mn(CO)3
L
L
O
O
O
O
Cd
O
L
Mn(CO)3
Mn(CO)3
Mn(CO)3
O
O
MOMN
12-2
(L =MeOH)
Figure 12-6 shows a crystal structure of MOMN 12-2. The network is based on
dicadmium SBUs that are held in place by two quinone molecules that bridge the
cadmium atoms by coordination from the same oxygen atom (O6) (Figure 12-6). The
resultant assembly constitutes an organometallic cluster that functions as a SBU that
connects to other SBUs via the QMTC pairwise spacers.
Figure 12-6. Crystal structure of MOMN 12-2 with thermal ellipsoids at the 50%
probability level. All hydrogen atoms are omitted for clarify.
The dicadmium cluster consists of two slightly distorted octahedra of oxygen
atoms around each Cd center. Two types of QMTC exist in MOMN 12-2, one
connecting each dicadmium SBU and another that bridges dicadmium unit (Figure 126). In both types of QMTC organometalloligand, the benzoquinone units adopt a boat
conformation with the quinone carbons bent out of the diene plane by about 12.8 for
QMTC spacer and by 8.0 for QMTC antennae, so that the overall structure is best
described as 4-quinone in both QMTC types. As would be expected, the bond distance
from cadmium (Cd1) to bridged quinone oxygen atom (O6) (average 2.29 Å) is longer
than those to the non-bridged oxygen atoms (average 2.21 Å).
Figure 12-7. Ball and stick representation of MOMN 12-2: (a) side view and (b) top
view (Magenta = Cd, Gray = unbridged QMTC, Yellow = bridged QMTC). Top view
clearly shows - interactions through the bridged QMTC “antennae” resulting in a
two-dimensional network. All hydrogen atoms groups are omitted for clarity.
As stated above, the metal centers in each dicadmium unit are bridged by two
oxygen atoms from two QMTC molecules, with a Cd-Cd distance of 3.62 Å. The
remaining eight coordination sites in each dicadmium cluster are completed by four
quinone oxygen atoms and four MeOH. Each dicadmium unit is separated by 8.47 Å
from adjacent ones by QMTC pairwise spacers. This pattern produces a onedimensional linear network (Figure 12-7a).
Figure 12-7a shows how the network is propagated along the c-axis. Quinone
antennae repeat along the c-axis every 12.03 Å. Interactions through quinone rings are
shown in Figure 12-7b. As with the semiquinone antennae, quinone antennae can be
used for - stacking or metal-binding functions. QMTC antennae are located at two
opposite sites. Therefore, each 1D network interacts with two neighboring networks
through - interactions, resulting in a two-dimensional network (Figure 12-7b). The IR
spectrum of MOMN 12-2 shows CO bands at 2024 and 1946 cm-1 (Figure 12-9) and a
broad QMTC signal in the 1H NMR is present at 4.80 ppm (Figure 12-10).
MOMN 12-1 and MOMN 12-2 were obtained by using metal nitrate instead of
metal acetate. We expected that the reaction of semiquinone and cobalt nitrate would
give a network similar to MOMN 12-1. However, the product consisted of MOMN 9-2
and MOMN 10-2 were generated from this reaction. Crystals of MOMN 9-2 and
MOMN 10-2 were easily separated because they have significantly different color and
shape, tetrahedral bipyramid with deep purple color for the former and irregular shape
with light red color for the latter.
HO
O
+
1/2 Co(NO3)2
heat, dark
MeOH
- HNO3
MOMN 10-2
& MOMN 9-2
Mn(CO)3
Table 12-1. Selected bond distances (Å) and angles (deg) for MOMN 12-1 and 12-2.
_____________________________________________________________________
MOMN 12-1
MOMN
________________________________________________________________
12-2
Mn(1)-O(1)
Mn(1)-O(2)
2.261(2)
Cd(1)-O(1)
2.175(5)
2.1788(16) Cd(1)-O(2)
2.237(5)
Mn(1)-O(10)
2.118(2)
Cd(1)-O(6)
2.262(4)
O(1)-C(1)
1.283(4)
Cd(1)-O(11)
2.258(5)
O(6)-C(4)
1.348(4)
Cd(1)-O(12)
2.295(5)
O(2)-C(10)
1.2739
Cd(1)-O(6)#1
2.318(4)
O(10)-C(13)
1.277(4)
C(1)-O(1)
1.287(8)
C(1)-Mn(2)
2.373(3)
C(4)-O(2)
1.273(8)
C(2)-Mn(2)
2.189(4)
C(10)-O(6)
1.314(8)
C(3)-Mn(2)
2.166(3)
C(13)-O(7)
1.264(8)
C(4)-Mn(2)
2.230(4)
Mn(1)-C(1)
2.331(7)
C(5)-Mn(2)
2.178(4)
Mn(1)-C(2)
2.160(7)
C(6)-Mn(2)
2.203(4)
Mn(1)-C(3)
2.192(8)
C(10)-Mn(3)
2.3834(16) Mn(1)-C(4)
2.387(7)
C(11)-Mn(3)
2.1874(16) Mn(1)-C(5)
2.173(8)
C(12)-Mn(3)
2.175(4)
Mn(1)-C(6)
2.167(7)
C(13)-Mn(3)
2.342(4)
Mn(2)-C(10)
2.291(7)
C(14)-Mn(3)
2.165(4)
Mn(2)-C(11)
2.163(7)
C(15)-Mn(3)
2.164(4)
Mn(2)-C(12)
2.180(7)
Mn(2)-C(13)
2.377(7)
Mn(2)-C(14)
2.192(7)
Mn(2)-C(15)
2.175(7)
O(10)#1-Mn(1)-O(2)
95.45(8)
O(1)-Cd(1)-O(2)
90.5(2)
O(10)#2-Mn(1)-O(2)
90.72(8)
O(1)-Cd(1)-O(11)
83.4(2)
O(2)#3-Mn(1)-O(2)
88.69(9)
O(2)-Cd(1)-O(11)
94.9(2)
O(2)-Mn(1)-O(1)#3
94.67(7)
O(2)-Cd(1)-O(6)
97.87(18)
O(10)#1-Mn(1)-O(1)
89.41(9)
O(11)-Cd(1)-O(6)
85.72(18)
O(10)#2-Mn(1)-O(1)
84.10(9)
O(1)-Cd(1)-O(12)
95.9(2)
O(2)#3-Mn(1)-O(1)
94.67(7)
O(2)-Cd(1)-O(12)
83.5(2)
O(1)#3-Mn(1)-O(1)
82.42(12)
O(6)-Cd(1)-O(12)
95.21(19)
O(1)-Cd(1)-O(6)#1
98.71(17)
O(11)-Cd(1)-O(6)#1
97.9(2)
O(6)-Cd(1)-O(6)#1
75.43(17)
O(12)-Cd(1)-O(6)#1
83.82(18)
______________________________________________________________________
In conclusion, semiquinone and quinone antennae MOMNs, which have great potential
for - stacking or metal-binding functions, were generated by using metal nitrates and
a 5-semiquinone complex. Packing diagrams of these MOMNs demonstrated the
formation of the three- and two-dimensional networks via - and hydrogen-bonding
interactions.