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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.