Anionic and neutral metal-4,4¢-bipyridine networks. Synthesis, structures and thermal properties of one- and three-dimensional coordination polymers constructed by metal salts and 4,4�-bipyridine Ming-Liang Tong and Xiao-Ming Chen* School of Chemistry and Chemical Engineering, Zhongshan University, Guangzhou 510275, P. R. China. E-mail: cescxm@zsu.edu.cn Received 13th December 1999, Accepted 19th January 2000, Published 24th January 2000 Two compounds, [Zn3(4,4�-bipy)3(H2O)6(SO4)4](4,4�-H2bipy)·10H2O (1) and [Cu(4,4�-bipy)(H2O)3(SO4)]·2H2O (2) (4,4�- bipy = 4,4�-bipyridine), were obtained from the reactions of different metal salts and 4,4�-bipy under weak acidic conditions. Compound 1 is the first anionic 3D coordination network constructed by 4,4�-bipy in which each structural unit consists of three Zn(II) atoms with the formula [Zn3(4,4�-bipy)3(H2O)6(SO4)4]2–. Two Zn(II) atoms are linked by a 4,4�-bipy units to form linear [4,4�-bipy-Zn(1)-4,4�-bipy-Zn(2)]¥ chains, the third Zn(II) atom is also connected by 4,4�-bipy unit and forms another type of linear [Zn(3)-4,4�-bipy]¥ chains; both types of chains are interlinked covalently by m2-sulfate bridges, resulting in a 3D coordination network of novel topology. The large cationic [4,4�-H2bipy]2+ molecules as well as lattice water molecules occupy the channels.Compound 2 comprises 1D linear coordination chains. The adjacent chains are each arranged in a cross-like fashion at the midpoints of the 4,4�-bipy ligands, resulting in a 3D supramolecular array. 2O)3(SO4)]·2H2O (2).Introduction The synthesis of coordination polymers with large channels or cavities has been rapidly expanding due to their intriguing structural diversity and potential functions as microporous solids for molecular adsorption, ion exchange, and heterogeneous catalysis.1–3 The construction of such cavities mainly surrounded by aromatic edges is very attractive since the shape, size and function of the cavity may be designable based on the different oxidation states, the coordination preference of the metal ions, the types of ligands and solvents, and the molar ratio of the metal ions and the ligands. On the other hand, the design of supramolecular architectures is also interesting in the field of host–guest chemistry.1c A number of the infinite frameworks well meet the requirements, because these hosts are relatively rigid and contain large cavities, and the van der Waals surfaces and electrostatic potential surfaces of the host and guest may be complementary.4 Although a wide range of infinite 2- and 3D coordination frameworks, including diamondoid,5,3b honeycomb,5a,6 square or rectangular grid,7 T-shaped,3c,8 ladder,9 brick wall,7a,9a molecular bilayers10 and octahedral11 frameworks, have already been generated with simple, linear spacers such as 4,4�-bipyridine (4,4�-bipy) and pyrazine, to the best of our knowledge, these frameworks are all neutral or cationic, no anionic framework constructed with 4,4�-bipy has been reported up to date.We have recently reported a series of non-interpenetrating open-frameworks with variable cavities or channels, in which the rod-like rigid spacers such as 4,4�-bipy, pyrazine and the related species are chosen as building blocks.12 We report herein the preparation, crystal structures and thermal properties of an anionic 3D coordination framework and one neutral 1D coordination polymeric architecture constructed by metal salts with 4,4�-bipy, namely [Zn3(4,4�-bipy)3(H2O)6(SO4)4](4,4�-H2bipy)·10H2O (1) and [Cu(4,4�-bipy)(H CrystEngComm, 2000, 1 Experimental All reagents were commercially available and used as received. The C, H and N microanalyses were carried out with a Perkin-Elmer 240 elemental analyzer.The FTIR spectra were recorded from KBr pellets in the range 4000– 400 cm–1 on a Nicolet 5DX spectrometer.Thermogravimetric data were collected on a Perkin-Elmer TGS-2 analyzer in flowing nitrogen at a heating rate of 10 °C min–1. Synthesis of [Zn3(4,4�-bipy)3(H2O)6(SO4)4](4,4�-H2bipy) ·10H2O (1). To a solution of ZnSO4·7H2O (0.287 g, 1.0 mmol) in 4 : 1 (v/v) MeOH/H2O (10 cm3), a solution of 4,4�-bipy (0.156 g, 1.0 mmol) in MeOH (5 cm3) was slowly added with stirring for 20 min at 60 ºC. The solution was adjusted to pH » 4.5 by addition of dilute H2SO4 solution. Colourless block crystals were deposited within two weeks in 86% yield based on 4,4�-bipy (calc. for C40H66N8O32S4Zn3: C 32.13, H 4.45, N 7.49; found: C 32.04, H 4.36, N 7.42). IR data (cm–1): 3444s, 3050w, 1609vs, 1560w, 1539w, 1489m, 1419s, 1356w, 1321w, 1215m, 1117vs, 1068s, 1011m, 983w, 857w, 807s, 723w, 646m, 617vs, 575w, 484w.Synthesis of [Cu(4,4�-bipy)(H2O)3(SO4)]·2H2O (2). To a solution of CuSO4·5H2O (0.250 g, 1.0 mmol) in 4 : 1 (v/v) MeOH/H2O (10 cm3), a solution of 4,4�-bipy (0.156 g, 1.0 mmol) in MeOH (5 cm3) was slowly added with stirring for 20 min at 60 °C. The solution was adjusted to pH » 4.5 by addition of dilute H2SO4 solution. Blue block crystals were deposited within two weeks in 72% yield (calc. for C10H18N2O9SCu: C 29.59, H 4.47, N 6.90; found: C 29.46, H 4.39, N 6.78). IR data (cm–1): 3360s, 3100s, 1658w, 1609vs, 1539m, 1489m, 1419s, 1335w, 1229m, 1159vs, 1110vs, 1068vs, 1039vs, 955s, 821s, 723m, 646m, 617m, 470m. X-Ray crystallography Diffraction intensities for the two complexes were collected at 21 °C on a Siemens R3m diffractometer using the w-scanTable 1 Crystallographic and experimental data for complexes 1 and 2 1 2 C40H66N8O32S4Zn3 C10H18N2O9SCu 1495.36 405.86 Triclinic Monoclinic P-1 Cc 11.491(2) 10.189(10) 12.094(2) 19.760(18) 12.620(3) 7.455(3) 64.15(3) 90 69.61(3) 100.36(10) 72.46(3) 90 1456.0(5) 1476(2) 1 4 1.705 22 0.71073 14.70 0.0641 0.1777 Formula Formula weight Crystal system Space group a/ Å b/ Å c/ Å a/deg b/deg g/deg V /Å3 Zrcalc /g cm–3 1.826 T /ºC 22 l (MoKa) /Å 0.71073 m (MoKa) /cm–1 16.72 R1(I > 2s (I))a 0.0419 wR2 (all data)a 0.1135 a R1 = å||Fo|–|Fc||/å|Fo|, wR2 = [åw((Fo2-Fc2)2/åw(Fo2)2]1/2, w = [s2(Fo)2 + (0.1(max(0,Fo2) + 2Fc2)/3)2]–1.Click here for full crystallographic data (CCDC no. 1350/7). technique. Lorentz-polarization and absorption corrections were applied.13 The structures were solved with direct methods and refined with full-matrix least-squares technique using the SHELXS-97 and SHELXL-97 programs, respectively.14,15 Non-hydrogen atoms were refined anisotropically. The organic hydrogen atoms were generated geometrically (C–H = 0.96 Å); the aqua hydrogen atoms were located from difference maps and refined with isotropic temperature factors. Analytical expressions of neutral-atom scattering factors were employed, and anomalous dispersion corrections were incorporated.16 The absolute structure for complex 2 has been determined with a Flack parameter of –0.0020(22).17 The crystallographic data for 1 and 2 are listed in Table 1.Drawings were produced with SHELXTL.18 Results and discussion Synthesis chemistry Three 1D coordination chains which have the same formula and coordination chains as 2, [M(4,4�-bipy) (H2O)3(SO4)]·xH2O [M = Cu(II), Co(II) and Zn(II)],19b,20,21 have been recently synthesized and structurally characterized by Zubieta et al., Jacobson et al and Kitagawa et al. Surprisingly, their lattice structures are greatly different from that of 2, these may result from the different reaction conditions. The former complexes are synthesized using hydrothermal or solution methods under weak basic conditions, whereas complexes 1 and 2 were isolated under weak acidic conditions and in the MeOH– H2O mixed solvents at room temperature. On the other hand, in contrast to the isolation of common 1D metal–4,4�- bipy coordination chains,22 the presence of large cationic [4,4�-H2bipy]2+ molecules in the reaction systems may serve as structure-directing templates in the formation of the 3D ions.12d Crystal structures [Zn3(4,4�-bipy)3(H2O)6(SO4)4](4,4�-H2bipy)·10H2O (1).Complex 1 is made up of the infinite [Zn3(4,4�- bipy)3(H2O)6(SO4)4]n2n– anionic polymer, [4,4�-H2bipy]2+ cations and lattice water molecules. An ORTEP view of the coordination environments of the metal atoms is depicted in Fig.1, in which each of three crystallographically independent Zn(II) atoms has octahedral coordination geometry, being coordinated by two 4,4�-bipy, two aqua and two sulfate groups [Zn(1)–N(1) = 2.142(5), Zn(1)– O(21) = 2.135(4), Zn(1)–O(1w) = 2.143(4) Å; Zn(2)– N(2) = 2.122(5), Zn(2)–O(11) = 2.182(4) and Zn(2)– O(2w) = 2.104(4); Zn(3)–N(3) = 2.169(5), Zn(3)– O(22) = 2.128(5) and Zn(3)–O(3w) = 2.130(6) Å]. Among the two crystallographically independent sulfate groups, one acts in the monodentate in coordination with the Zn(2) atom, while the other functions in an anti–anti bidentate mode to bridge the Zn(1) and Zn(3) atoms. Fig. 1 Coordination environments of the metal atoms in 1. Click here for a larger image. The anionic polymer exhibits a non-interpenetrated 3D coordination network. The building block in the 3D coordination network of 1 is shown in Fig.2, in which the Zn(1) and Zn(2) atoms are linked by 4,4�-bipy bridges to form linear [4,4�-bipy-Zn(1)-4,4�-bipy-Zn(2)]¥ chains (Achain); the Zn(3) atom is also linked by two 4,4�-bipy ligands to form another type of [Zn(3)-4,4�-bipy]¥ chains (B-chain). The A-chains and B-chains are joined covalently by m2-sulfate bridges with the Zn(2) atoms, resulting in a 3D non-interpenetrating coordination network with channels, as shown in Fig. 3. It should be noted that thenetwork topology in 1 is unprecedented, although some uncommon topologies have been observed in metal-4,4�- bipy coordination networks.23 The cationic [4,4�-H2bipy]2+ molecules are located in these channels, and the 4,4�- H2bipy nitrogen atoms form a pair of strong acceptor hydrogen bonds [O···N = 2.663(7) Å] with adjacent monodentate sulfate ligands.Fig. 2 The building block in 1. The 4,4�-bipy molecular rods and cationic [4,4�-H2bpy]2+ molecules are represented by bold lines and large shaded circles, respectively. The uncoordinated oxygen atoms of m2-sulfate groups, aqua ligands and monodentate sulfate groups are omitted for clarity. Click here for a larger image. (a) (b) Fig. 3 The anionic three-dimensional network of 1 viewed along the b-axis (a) and c-axis (b) directions. The 4,4�-bipy molecular rods and cationic [4,4�-H2bpy]2+ molecules are represented by bold lines and large shaded circles, respectively.Click for larger images of 3a and 3b. The Zn(2) atoms in adjacent A-chains are also interlinked by hydrogen bonds between the aqua ligands and the monodentate sulfate groups. The pyridyl rings of each 4,4�- bipy ligand are virtually coplanar with each other, only with very small dihedral angles [2.1(5)–4.2(5)°], since there are strong p–p stacking interactions among the adjacent 4,4�-bipy ligands belonging to both types of the chains and [4,4�-H2bipy]2+ counterions at a ring-to-ring distance of ca. 3.5 Å.24 The lattice water molecules are extensively hydrogen-bonded to the sulfate groups [O···O = 2.658(8)– 3.123(9) Å]. It is noteworthy that the reported frameworks constructed with 4,4�-bipy are all neutral or cationic,4–12 no framework with anionic coordination skeleton has been reported up to date.The channels of the anionic coordination network are occupied by lattice water molecules and the large cationic [4,4�-H2bipy]2+ molecules which are present for charge neutrality of the overall structure. Therefore, complex 1 constitutes the first example of an anionic coordination network constructed by 4,4�-bipy with a metal salt. On the other hand, among the reported metal-4,4�-bipy networks, only a few 3D coordination ones have been synthesized and structurally characterised, such as [Zn(4,4�-bipy)2(SiF6)]n·xDMF,11b [Cu(4,4�-bipy)Cl],3a [Cu(4,4�-bipy)1.5](NO3)·1.25H2O,3b [Cu(4,4�-bipy)2](PF6),5b [Ag(4,4�-bipy)](CF3SO3),5c [M2(4,4�- bipy)3(NO3)4] [M = Co(II), Ni(II) and Zn(II)],9e [Co2(4,4�- bipy)3(NO3)4](3C6H6,8b and [Ag(4,4�-bipy)](NO3).3c,8a Of these networks, the anions serving as bridges in construction are only seen in two examples.3a,11b Even so, the sulfate ion has recently been found to serve as bridges in construction of some 2-, or 3D metal–N,N�-bidentate spacer coordination networks.19,21,25 [Cu(4,4�-bipy)(H2O)3(SO4)]·2H2O ((2).The adjacent chains are each arranged in a cross-like fashion at the midpoints of the 4,4�-bipy ligands, resulting in a 3D supramolecular array with rhombic channels (11.12 � 11.12 Å) running along the c-axis (Fig. 4). The structure of the resulting array (Fig. 4) is predominantly directed by p–p stacking interactions between the 4,4�-bipy bridges and extensive hydrogen bonds between water molecules and the sulfate groups [O···O = 2.655(7)–2.969(8) Å].The two pyridyl rings of each 4,4�-bipy ligand are virtually coplanar with each other, only with a smaller dihedral angle 4.6(3)° which may be attributed to the p–p stacking interactions between the pyridyl rings of the adjacent chains with a face-to-face distance of ca. 3.6 Å.24 It is noteworthy that such arrangement of linear coordination polymers in 2 is different from three recently documented 1D coordination polymers26 with the analogous formula and coordination chain skeletons as 2, in which the chains in the adjacent layers are rotated by 60° to provide helical staircase networks,19b,20,21 and it is also different from another arrangement of 1D coordination chains with a similar chain skeleton to 2, in which each pair of adjacent polymeric chains is interconnected by hydrogen bonds, resulting in 2D layers.12a,12c,27 Fig.4 Top view of the 3D supramolecular arrays of 2. Click here for a larger image. -10H2O 70-121°C -3H2O -3H2O Thermogravimetric analysis Complexes 1 and 2 were heated to 800 °C in N2. The TGA results for 1 and 2 can be summarised as follows: [Zn3(4,4�-bipy)3(H2O)6(SO4)4].(4,4�-H2bipy).10H2O [Zn3(4,4�-bipy)3(H2O)6(SO4)4].(4,4�-H2bipy) 125-139 °C [Zn3(4,4�-bipy)3(H2O)3(SO4)4].(4,4�-H2bipy) 139-159 °C-[4,4�-H2bipy]2+[SO4]2- [Zn3(4,4�-bipy)3(SO4)4].(4,4�-H2bipy) °C 160-258 -4,4�-bipy [Zn3(4,4�-bipy)3(SO4)3] ZnSO4 further decomposition 260-550 °C 550 °C -2H2O [Cu(4,4�-bipy)(H Cu(4,4�-bipy)(H2O)3(SO4) 2O)3(SO4)].2H2O 70-99 °C -H2O -H2O Cu(4,4�-bipy)(H 2O)2(SO4) Cu(4,4�-bipy)(H2O)(SO4) 125-224 °C 100-123 °C -4,4�-bipy Cu(4,4�-bipy)(SO CuSO4 4) further decomposition 300 °C 400 °C Complex 1 first lost weight corresponding to ten lattice water molecules (observed 12.05%, calculated 11.73%) from 70 to 122 °C.Upon further heating, the six aqua ligands lost in two separate steps (from 125 to 139 °C and from 140 to 159 °C), which may possibly be concomitant with a decrease of the coordination number. Further weight loss corresponding to [4,4�-H2bipy]2+[SO4]2– was observed between 160 and 258 °C. All of the 4,4�-bipy ligands lost weight between 260 and 550 °C.When 1 was heated up to 800 °C, the final residue was white. The thermal decomposition behaviour of 2 is much similar to that of 1. The TGA data showed that 2 first lost weight corresponding to two lattice water molecules (observed 8.45%, calculated 8.88%) from 70 to 99 °C. Upon further heating, the three aqua ligands lost in three separate steps (from 99 to 113 °C, from 114 to 123 °C and from 124 to 225 °C), which may possibly be concomitant with a decrease of the coordination number. Further weight loss corresponding to one molecule of 4,4�-bipy was observed between 300 and 400 °C. When 2 was heated up to 800 °C, the final residue was black. Conclusions Two 1- and 3D coordination polymers assembled b coordination network. 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