CRYSTAL GROWTH & DESIGN
New Inorganic-Organic Hybrid Supramolecular Architectures Generated from 2,5-Bis(3-pyridyl)-3,4-diaza-2,4-hexadiene
2005 VOL. 5, NO. 3 1005-1011
En-Qing Gao,*,† Ai-Ling Cheng,† Yan-Xia Xu,† Chun-Hua Yan,‡ and Ming-Yuan He† Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, China, and State Key Lab of Rare Earth Materials Chemistry and Applications & PKU-HKU Joint Lab in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China Received October 7, 2004;
Revised Manuscript Received January 6, 2005
ABSTRACT: Two new metal coordination polymers with interesting supramolecular architectures, [Mn(H2O)4(L1)]n(ClO4)2n‚2nL1 (1) and [Ag(L1)(NO3)]n (2) [L1 ) 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene], have been synthesized and characterized structurally. Complex 1 exhibits a novel supramolecular layer architecture sustained by the concurrence of coordination bonds, hydrogen bonds, and π-π stacking interactions: the Mn(II) ions are coordinated by water molecules and the bridging µ2-L1 ligands to yield one-dimensional (1D) zigzag [Mn(H2O)4(L1)]n coordination chains; the free L1 ligands are hydrogen bonded to half of the coordinated water molecules and form π-π stacking triads with the bridging ligands, generating three-strand supramolecular ribbons; and the perchlorate ions form hydrogen bonds with the remaining coordinated water molecules, interlinking the ribbons into an unusual tripledecked supramolecular layer. In complex 2, each Ag(I) ion is tetracoordinated by two µ2-L1 and two µ2-nitrate ligands. The µ2-L1 ligands connect the metal ions into infinite 1D helix-like AgL1 chains, and the µ2-nitrate ions interlink the chains into undulate coordination layers. C-H‚‚‚O weak hydrogen bonds exist between neighboring layers in 2. Introduction In the past decade, the design, construction, and elucidation of multidimensional supramolecular solidstate architectures have attracted considerable attention in the context of crystal engineering and supramolecular chemistry.1-3 The drives arise not only from the pragmatic perspective to obtain new technologically relevant materials, but also from the scientists’ natural interest to reveal the intriguing beauty and diversity of the architectures that can be assembled and to understand the laws of physics determining the assembly processes. The useful tools in crystal engineering have been weak noncovalent interactions such as hydrogen bonding and π-π stacking for organic architectures,1,4 and metal-ligand coordination bonds for inorganic-organic hybrid coordination networks,3 and at the meeting point, the interplay of coordination bonds with noncovalent interactions has also been employed to construct new inorganic-organic architectures.2,5 In the last case, the noncovalent interactions may serve as the forces interlinking discrete or low-dimensional coordination motifs (and other components) into higherdimensional architectures or as additional forces sustaining the coordination networks. The most widely used organic bridging ligands for coordination polymers have been those containing two or more pyridyl (especially 4-pyridyl) groups separated by various spacers, rigid or flexible, such as 4,4bipyridine and 1,2-bis(4′-pyridyl)ethane/ethene/ethyne, from which a rich variety of one- (1D), two- (2D), and * To whom correspondence should be addressed. Fax: +86-2162233424. E-mail:
[email protected]. † East China Normal University. ‡ Peking University.
Scheme 1
three-dimensional (3D) metal-organic polymeric architectures have been constructed. These have been summarized by several excellent reviews,6 and a recent review by Roesky focused on bis(4-pyridyl)-derived inorganic-organic networks with high-dimensional supramolecular architectures sustained by the interplay of coordination, hydrogen bonding, and π-π stacking interactions.7 Recently, zur Loye and co-workers reported two ditopic Schiff-base ligands containing terminal 3-pyridyl groups (Scheme 1: L1 ) 2,5-bis(3pyridyl)-3,4-diaza-2,4-hexadiene; L2 ) 1,4-bis(3-pyridyl)2,3-diaza-1,3-butadiene).8 The specific geometric features of these ligands, mainly the off-axis coordination orientation of the 3-pyridyl rings and the flexibility of the zigzag -(R)CdN-NdC(R)- central moiety, have allowed the authors to obtain new Co(II) and Cd(II) coordination polymers with interesting structures difficult to achieve by other bis(pyridyl) derivatives:8 L1 forms 1D doublebridged [M(NO3)2(L1)2]n coordination chains interlinked by C-H‚‚‚O hydrogen bonds into 2D layers, while L2 forms unusual 2D or 3D coordination networks dependent upon solvent systems. The studies on the ligands have thus far been limited to Co(II) and Cd(II) systems. Considering the flexibility and other interesting features of such ligands, we conducted the investigation with other metal ions, in hopes of obtaining new metalorganic architectures. Here we report the synthesis and crystal structure of two new complexes of L1, [Mn(H2O)4(L1)]n(ClO4)2n‚2nL1 (1) and [Ag(L1)(NO3)]n (2). It turned
10.1021/cg049659x CCC: $30.25 © 2005 American Chemical Society Published on Web 03/15/2005
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out that the L1 ligand in these complexes adopts different conformations from that in the known Co(II) and Cd(II) complexes, resulting in new and interesting supramolecular structures. Complex 1 exhibits an unusual triple-decked supramolecular layer architecture in which 1D [Mn(H2O)4(L1)]n coordination chains interact with free L1 ligands and perchlorate ions via hydrogen bonding and π-π stacking, while complex 2 contains undulate coordination layers in which 1D helixlike AgL1 chains are cross-linked by nitrate ions. Experimental Section Materials and Synthesis. All the starting chemicals were of A. R. grade and used as received. The L1 ligand was prepared according to the literature method.8 CAUTION! Although not encountered in our experiments, metal perchlorates are potentially explosive. They should be handled with care. [Mn(H2O)4(L1)]n(ClO4)2n‚2nL1 (1). A methanol solution (4 mL) of Mn(ClO4)2‚6H2O (0.20 mmol) was mixed under stirring with the solution (6 mL) of the L1 ligand (0.40 mmol) in the same solvent. The resulting clear solution was allowed to evaporate slowly at room temperature for three weeks, affording yellow crystals, which were collected by filtration, washed with methanol and ether successively, and dried in air. Yield: 74% (based on the ligand). When the starting Mn/L1 molar ratio was changed to 1:3, which corresponds to the stoichiometry of 1, the same compound was obtained. Anal. Calcd for C42H50Cl2MnN12O12: C 48.47, H 4.84, N 16.15; Found: C 48.40, H 4.68, N 16.55%. Main IR (cm-1): 3409m, 1614s, 1421s, 1371s, 1306m, 1200m, 1121vs, 1034s, 931m, 825m, 707m. [Ag(L1)(NO3)]n (2). This compound was initially prepared as a polycrystalline yellow product, which precipitated immediately upon mixing the methanol solutions of L1 and AgNO3 (1:1 mole ratio), Yield: 89%. The reaction in acetonitrile gave similar results. Crystals of the compound were obtained by slow diffusion in a H-shaped tube: A dichloromethane solution (4 mL) of L1 (0.2 mmol) and an acetonitrile solution (3 mL) of AgNO3 (0.2 mmol) were respectively added into the two sides of the H-shaped tube, and then about 5 mL of acetonitrile was carefully added so that the bridge of the tube was filled. Slow diffusion between the two solutions afforded yellow crystals of 2 within 2 weeks. Anal. Calcd for C14H14AgN5O3: C 41.20, H 3.46, N 17.16; Found: C 41.46, H 3.34, N 17.33%. Main IR (cm-1): 1612s, 1422m, 1353s, 1318vs, 1196m, 823m, 701m. Physical Measurements. Elemental analyses (C, H, N) were performed on an Elementar Vario EL analyzer. IR spectra were recorded on a Nicolet Magna-IR 750 spectrometer equipped with a Nic-Plan microscope. Crystallographic Studies. Diffraction intensity data of the single crystals were collected at 293 K on a Nonius KappaCCD diffractometer equipped with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). Empirical absorption corrections were applied using the Sortav program.9 All structures were solved by the direct method and refined by the full-matrix least-squares method on F2 with anisotropic thermal for all non-hydrogen atoms.10 Hydrogen atoms attached to carbon atoms were placed geometrically at calculated positions and refined using the riding model, and the hydrogen atoms of water molecules were located from the difference maps and refined with isotropic thermal parameters. Pertinent crystallographic data and structure refinement parameters are summarized in Table 1.
Gao et al. Table 1. Summary of Crystallographic Data for the Complexes formula fw crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Dcalcd, g cm-3 µ, mm-1 R [I > 2σ(I)] GOF
1
2
C42H50Cl2MnN12O12 1040.78 triclinic P1 h 8.9231(2) 11.2023(2) 12.7643(2) 101.4771(11) 97.0069(9) 98.7719(9) 1220.39(4) 1 1.416 0.452 0.0474 1.027
C14H14AgN5O3 408.17 monoclinic P2/c 6.24770(10) 8.4165(2) 15.0632(4) 101.7797(11) 775.40(3) 2 1.748 1.322 0.0277 1.097
cm-1, due to the ν(O-H) absorptions of water molecules. The strong absorption at 1614 cm-1 is attributable to the ν(CdN) vibration of the ligand, and the very strong absorptions at 1121 and 1034 cm-1 indicate the presence of the perchlorate ion. X-ray analyses revealed that the structure of 1 consists of infinite 1D cationic coordination chains [Mn(H2O)4(L1)]n2n+, noncoordinated L1 ligands and perchlorate anions, and that all the above components are involved in an interesting extensive hydrogen-bonding system. A perspective view of the building blocks with the atom-labeling scheme is given in Figure 1, and selected bond distances and angles are listed in Table 1. Each manganese(II) ion resides at an inversion center and assumes a trans-octahedral coordination geometry with axial elongation, with four aqua oxygen atoms in the equatorial plane (av. Mn-O, 2.15 Å) and two pyridyl nitrogen atoms from different (crystallographically equivalent) L1 ligands at the axial positions (Mn-N, 2.31 Å). The coordinated L1 ligands, also located at inversion centers, assume a transoid but nonplanar (although rather flat) conformation: the two pyridyl rings in each ligand are strictly antiparallel to each other, and both are rotated around the respective py-C bonds by 20.5° with respect to the central -(Me)CdNNdC(Me)- portion, which is almost strictly planar (including the methyl carbons). The ligands with such a conformation serve as bridges to link the Mn(II) ions into a -Mn-L1-Mn-L1- zigzag chain along the (101) direction, the Mn‚‚‚Mn distance along the chain being 14.66 Å. With all metal ions in a chain being strictly collinear, the zigzag shape arises from the tilted disposition of the L1 ligand with respect to the M‚‚‚M line, and the tilted disposition is dictated by the specific coordination orientation of the terminal 3-pyridyl rings. The
Results and Discussion The Mn(II) Complex (1). This complex was prepared by reacting manganese perchlorate and the L1 ligand in methanol. The IR spectrum of the complex exhibits a medium broad band centered at ca. 3409
Figure 1. A perspective view of the building blocks of 1 with the atom-labeling scheme. The thermal ellipsoids were drawn at 30% possibility.
Inorganic-Organic Hybrid Supramolecular Architectures
Crystal Growth & Design, Vol. 5, No. 3, 2005 1007
Table 2. Selected Bond Lengths (Å) and Angles (°) for Complex 1a Mn1-O1 Mn1-O2 O1B-Mn1-O1 O1-Mn1-O2 O1-Mn1-O2B O2-Mn1-O2B O1-Mn1-N1 a
2.1426(16) 2.1594(17) 180.0 91.25(7) 88.75(7) 180.0 90.34(6)
Mn1-N1 N2-N2A
2.3079(16) 1.403(4)
O2-Mn1-N1 O1-Mn1-N1B O2-Mn1-N1B N1-Mn1-N1B
91.54(7) 89.66(6) 88.46(7) 180.0
Symmetry codes: A -x + 1, -y, -z + 1; B -x, -y, -z.
Table 3. Relevant Distances (Å) and Angles (°) for the Hydrogen Bonds in Complex 1a D-H‚‚‚A
d(D-H)
d(H‚‚‚A)
d(D‚‚‚A)
