Unprecedented (3,9)-Connected (42.6)3(46.621.89) Net Constructed by Trinuclear Mixed-Valence Cobalt Clusters Zhang,*,†
Xian-Ming Xiao-Ming Chen*,‡
Yan-Zhen
Zheng,‡
Cui-Rui
Li,†
Wei-Xiong
Zhang,‡
and
CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 5 980-983
School of Chemistry & Material Science, Shanxi Normal UniVersity, Linfen, Shanxi 041004, China, and MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen UniVersity, Guangzhou 510275, P. R. China ReceiVed January 12, 2007; ReVised Manuscript ReceiVed March 6, 2007
ABSTRACT: A solvothermal reaction of Co2O3, CoSO4, pyridine-3,5-dicarboxylic acid, and H2O2 in an aqueous MeCN solution yielded a three-dimensional coordination framework [Co3(OH)(pdc)3]‚H2O (1) (pdc ) pyridine-3,5-dicarboxylate). Compound 1 shows an unprecedented (3,9)-connected (42.6)3(46.621.89) topology in which hydroxycentered mixed-valence Co3(OH)(CO2)6 clusters act as nine-connected nodes of a tricapped trigonal prism, and pdc groups act as three-connected nodes of trigonal geometry. Introduction There is considerable current interest in the crystal engineering of coordination polymers due to their intriguing topologies1,2 and their potential applications in zeolite-like materials, ionexchange, and catalysis. Although the main goal in the field is to discover and synthesize new materials for practical applications, it would be difficult to achieve a true advance without knowledge of topologies.3 Fortunately, the classification of structures according to topological types lays the foundation of a general understanding of inorganic solids and metal coordination frameworks.4 It has been suggested that, among the numerous possible topological nets, the most important and plausible targets for designed synthesis are those with “simple, high-symmetry” structures.5 A careful search of the literature reveals that the major structural types found in coordination frameworks are based on three-, four-, or six-connected topologies in which d-block metal ions are used as nodes.1,2 Examples of coordination frameworks with local connectivity numbers larger than six are extremely rare because the construction of such systems is severely hampered by the available number of coordination sites at the metal centers and the sterically demanding nature of organic ligands.3,6,7 Generally, there are two developed routes for highly connected coordination polymers. One is based on the combination of f-block metal centers and 4,4′-bipyridine-N,N′-dioxide ligands, by which seven- and eight-connected coordination polymers have been obtained by Schro¨der and co-workers.6 The other is to replace d- or f-block ions with metal clusters as nodes because the enhanced coordination numbers and reduced steric hindrances of metal clusters are helpful to generate highly connected coordination polymers.3,7-9 In particular, by using metal clusters as nodes, 12-connected coordination polymers with face centered cubic coordination (fcu) topology have been documented recently.8,9 Surprisingly, a coordination polymer with a local connectivity number of nine has not been documented to date. We report herein the three-dimensional (3-D) mixed-valence Co(II,III) coordination framework of [Co3(OH)(pdc)3]‚H2O (1) (pdc ) pyridine-3,5-dicarboxylate) that shows unprecedented (3,9)connected (42.6)3(46.621.89) topology in which the hydroxycen* To whom correspondence should be addressed. (X.-M.Z.) E-mail:
[email protected]. Tel: code +86 20 84112074. (X.-M.C.) E-mail:
[email protected]. † Shanxi Normal University. ‡ Sun Yat-Sen University.
tered mixed-valence Co3(OH)(CO2)6 clusters act as nineconnected nodes of a tricapped trigonal prism and pdc groups act as three-connected nodes of trigonal geometry. Experimental Procedures Material and Methods. All the starting materials were purchased commercially as reagent grade and used without further purification. Elemental analyses were performed on a Perkin-Elmer 240 elemental analyzer. The FT-IR spectra were recorded from KBr pellets in the range 400-4000 cm-1 on a Nicolet 5DX spectrometer. XRPD data were recorded in a Bruker D8 ADVANCE X-ray powder diffractometer (Cu-KR, λ ) 1.5418 Å). Thermal analysis (TG) was carried out in air using SETARAM LABSYS equipment with a heating rate of 15 °C/min. The magnetic measurements were carried out with Quantum Design SQUID MPMS XL-7 instruments. The diamagnetism of the sample and sample holder were taken into account. Synthesis of [Co3(OH)(pdc)3]‚H2O (1). A mixture of Co2O3 (0.03 g, 0.18 mmol), CoSO4‚7H2O (0.09 g, 0.32 mmol), H2pdc (0.064 g, 0.39 mmol), H2O2 (30%, 0.047 g, 0.4 mmol), MeCN (4 mL), and water (2 mL) in a mole ratio of 2:3:4:4:750:1100 was sealed in a 15 mL Teflon-lined stainless container, which was heated to 150 °C and held for 4 days. After the sample was cooled to room temperature and filtered, red block crystals of 1 in 45% yield and uncharacterized pink powder were recovered. Anal. calc. for 1 C21H12Co3N3O14: C, 35.67; H, 1.71; N, 5.94. Found: C, 35.58; H, 1.74; N, 5.86. IR (KBr, cm-1): ν ) 3427s, 3127s, 2912w, 1623s, 1565m, 1405s, 1279w, 1198w, 774w, 693w. X-ray Crystallographic Study. Data were collected at 298 and 100 K on a Bruker Apex diffractometer (Mo-KR, λ ) 0.71073 Å). Lorentz polarization and absorption corrections were applied. The structures were solved with direct methods and refined with the full-matrix leastsquares technique (SHELX-97).10 Analytical expressions of neutralatom scattering factors were employed, and anomalous dispersion corrections were incorporated. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms of organic ligands were geometrically placed and refined with isotropic temperature factors. The crystallographic data are listed in Table 1; selected bond lengths and bond angles are given in Table 2.
Results and Discussion X-ray crystallography at both 298 and 100 K reveals 1 crystallizes in rhombohedral space group R3hc, and the asymmetric unit consists of crystallographically independent one Co, one µ3-oxo, half pdc, and one water molecule. The O(1) and O(1w) atoms are located on the crystallographic c-axis (namely, the 3-fold inversion axis). The Co(1) site shows an octahedral geometry, ligated by four oxygen atoms from four carboxylates
10.1021/cg070038o CCC: $37.00 © 2007 American Chemical Society Published on Web 04/07/2007
(3,9)-Connected (42.6)3(46.621.89) Net
Crystal Growth & Design, Vol. 7, No. 5, 2007 981
Table 1. Crystallographic Data for Compound 1 formula fw temp crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z Fcalc, (g cm-3) µ, (mm-1) F(000) size (mm) θ reflections Tmax /Tmin data/parameters S R1a wR2b ∆Fmax/ ∆min (e A-3) a
C21H12Co3N3O14 707.13 298(2) rhombohedral R3c 17.1609(12) 17.1609(12) 12.6734(19) 90 90 120 3232.2(6) 6 2.180 2.375 2112 0.10 × 0.08 × 0.03 2.37 to 26.96 4391/771 0.9322 and 0.7972 771/0/63 1.108 0.0489, 0.1077 0.0604, 0.1224 1.795 and -0.513
C21H12Co3N3O14 707.13 100(2) rhombohedral R3c 17.122(3) 17.122(3) 12.530(4) 90 90 120 3181.2(12) 6 2.215 2.413 2112 0.21 × 0.08 × 0.04 2.38 to 25.96 3136/694 0.9097 and 0.6312 694/0/63 1.056 0.0497, 0.1073 0.0665, 0.1149 2.092 and -0.480
R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo2)2]1/2.
Figure 1. Perspective view of a Co3(OH)(CO2)6(py)9 fragment showing each Co3(OH)(CO2)6 unit being connected to nine pyridine rings in 1.
Table 2. Bond Lengths (Å) and Angles (°) for 1 at 298 and 100 Ka Co(1)-O(2a) Co(1)-O(2b) Co(1)-O(3c) O(1)-Co(1b)
2.081(3) 2.081(3) 2.084(3) 2.1012(8)
Co(1)-O(3) Co(1)-O(1) Co(1)-N(1d) O(1)-Co(1e)
2.084(3) 2.1012(8) 2.164(5) 2.1012(8)
O(2a)-Co(1)-O(2b) 179.2(2) O(2a)-Co(1)-O(3c) 91.1(1) O(2b)-Co(1)-O(3c) 88.9(1) O(2a)-Co(1)-O(3) 88.9(1) O(2b)-Co(1)-O(3) 91.11(14) O(3c)-Co(1)-O(3) 175.4(2) O(2a)-Co(1)-O(1) 90.40(9) O(2b)-Co(1)-O(1) 90.40(9) Co(1b)-O(1)-Co(1e) 120.0 Co(1)-O(2a) 2.060(3) Co(1)-O(2b) 2.060(3) Co(1)-O(3c) 2.069(3) Co(1)-O(3) 2.069(3)
O(3c)-Co(1)-O(1) 92.31(9) O(3)-Co(1)-O(1) 92.31(9) O(2a)-Co(1)-N(1d) 89.60(9) O(2b)-Co(1)-N(1d) 89.60(9) O(3c)-Co(1)-N(1d) 87.69(9) O(3)-Co(1)-N(1d) 87.69(9) O(1)-Co(1)-N(1d) 180.0 Co(1b)-O(1)-Co(1) 120.0 Co(1)-O(1)-Co(1e) 120.0 Co(1)-O(1) 2.0836(9) Co(1)-N(1d) 2.154(5) O(1)-Co(1a) 2.0836(9) O(1)-Co(1e) 2.0836(9)
O(2a)-Co(1)-O(2b) O(2a)-Co(1)-O(3c) O(2b)-Co(1)-O(3c) O(2a)-Co(1)-O(3) O(2b)-Co(1)-O(3) O(3c)-Co(1)-O(3) O(2a)-Co(1)-O(1) O(2b)-Co(1)-O(1) O(3c)-Co(1)-O(1)
O(3)-Co(1)-O(1) O(2a)-Co(1)-N(1d) O(2b)-Co(1)-N(1d) O(3c)-Co(1)-N(1d) O(3)-Co(1)-N(1d) O(1)-Co(1)-N(1d) Co(1a)-O(1)-Co(1e) Co(1a)-O(1)-Co(1) Co(1e)-O(1)-Co(1)
178.38(18) 88.27(14) 91.64(14) 91.64(14) 88.27(14) 173.84(18) 90.81(9) 90.81(9) 93.08(9)
93.08(9) 89.19(9) 89.19(9) 86.92(9) 86.92(9) 180.0 120.0 120.0 120.0
a Symmetry codes: (a) y, x, -z + 1/2; (b) -y, x -y, z; (c) -x, -x + y, -z + 1/2; (d) -x + 1/3, -y + 2/3, -z + 2/3; (e) -x + y, -x, z.
[bond lengths at 100 K: Co(1)-O(3), 2.068(3) Å; Co(1)-O(3c), 2.068(3) Å; Co(1)-O(2a), 2.060(3); Co(1)-O(2b), 2.060(3) Å; at 298 K: Co(1)-O(3), 2.084(3) Å; Co(1)-O(3c), 2.084(3) Å; Co(1)-O(2a), 2.081(3); Co(1)-O(2b), 2.081(3) Å, one µ3oxygen [Co(1)-O(1), 2.0838(9) Å at 100 K; 2.1013(8) at 298 K], and one pyridine nigrogen [Co(1)-N(1), 2.154(5) Å at 100 K; 2.165(5) Å at 298 K]. Bond valence sum calculations11 using data at 100 K (298 K) give a value of 2.30 (2.21) for the Co atom and 1.08 (1.04) for the µ3-O atom, which in a combination with the charge balance leads to a mixed-valence Co(II,III) compound with a formula of [Co3(OH)(pdc)3]‚H2O. The molar ratio of Co(II) and Co(III) atoms in 1 is 2:1, and only one crystallographic independent Co site is suggestive of delocalization of two extra electrons among the three Co sites.
Figure 2. View of the 3-D framework of 1.
The structure of 1 can be described as an unprecedented 3-D (3,9)-connected framework, in which the hydroxycentered Co3(OH)(CO2)6 clusters act as nine-connected nodes of a tricapped trigonal prism and pyridine rings of pdc groups act as threeconnected nodes of trigonal geometry. The Co3(OH)(CO2)6 cluster has a geometry close to D3h. The µ3-O(1) and three Co atoms within the Co3(OH)(CO2)6 cluster are coplanar with a Co-O-Co angle of 120.0°. It should be noted that in the isolated [M3O(O2CR)6L3] molecules it has been found that they usually do not occupy a site with threefold crystallographic symmetry due to spin frustration.12 However, there are a few exceptions. For example, [Cr3O(O2CPh)6(py)3]ClO4‚0.5py and [Fe3O(O2CPh)6(py)3]ClO4‚py crystallize in the space group P63/m at room temperature, with the trinuclear complexes stacked on parallel threefold axes.15 A tricapped trigonal prism can be obtained if the adjacent C-C and C-Co within the Co3(OH)(CO2)6 cluster are linked together (Figure 1). Each Co3(OH)(CO2)6 cluster is connected to nine pridine rings via six C-C bonds and three Co-N bonds, and each pyridine ring is connected to three Co3(OH)(CO2)6 trimers via two C-C bonds and one Co-N bond. As shown in Figure 2 and Scheme 1, the overall structure of 1 is a 3-D (3,9)-connected framework in which pyridine rings and Co3(OH)(CO2)6 clusters act as threeand nine-connected nodes, respectively. The short Schla¨fli
982 Crystal Growth & Design, Vol. 7, No. 5, 2007 Scheme 1.
Zhang et al.
Schematic View of the 3-D (3,9)-Connected Net of 1a
Figure 3. χmT versus T curve for 1 in the temperature range 2-300 K measured under an applied field of 1 KOe. Inset: The 1/χm versus T curve.
a The tricapped trigonal prisms represent nine-connected Co (OH)(CO ) 3 2 6 units; the Y-shaped rods represent three-connected pyridine rings.
symbol for 1 is (42.6)3(46.621.89). Alternately, if Co3(OH)(CO2)6 clusters are only considered as nodes, 1 is a 12-connected uninodal SQC15 net with a Schla¨fli symbol of (318.442.56). Reticular chemistry is the basis for materials with interesting and useful properties, the core of which is to get insights into the taxonomy and nature of nets using knowledge of mathematics and crystal chemistry. A large number of 3-D high-symmetry nets have been enumerated within the RCSR, EPINET, and Topos databases.14-16 The local connectivity of 1 is reminiscent of the binary inorganic compound LaCl3 because both compounds have nine-connected nodes of a tricapped trigonal prism and three-connected nodes of a triangle. To further study the topology of 1, various (3,9)-connected binodal nets have been carefully examined in resources of RCSR, EPINET, and Topos.14-16 For (3,9)-connected binodal 3-D nets, 53 different types have been enumerated, none of which is the same as that of 1. In this case, the net in 1 represents a (3,9)-connected topology not only unobserved but also unenumerated. Possibly the most related net is LaCl3, which shows a Schla¨fli symbol of (43)3(412.615.89). The different topological types of 1 and LaCl3 are also indicated by different space groups: the former belongs to R3hc, while the latter belongs to P63/m. Thermal and Magnetic Properties. Thermogravimetric analysis (TGA) in air and under 1 atm pressure at the heating rate of 15 °C min-1 was performed on a polycrystalline sample of this material, which showed the following two clear and wellseparated weight loss steps. An initial weight loss of 4.1% occurred between the temperature range of 270-340 °C corresponds to the removal of the encapsulated water molecule (2.5% calculated). The removal of a water molecule at high temperature in 1 is in agreement with the encapsulation of the
water molecule. The second weight loss of 60.8% in the range of 370-550 °C is consistent with the removal of pdc ligands. The remaining weight of 34.5% corresponds to the percentage (35.0%) of the Co2O3 residue. The temperature dependence of the magnetic susceptibility in the temperature range 2-300 K under 1 kOe applied field was studied with a Quantum Design SQUID MPMS XL-7. The χmT value at 300 K is 10.45 cm3 K mol-1 per Co3 unit, which is significantly larger than the spin-only value (6.74 cm3 mol-1 K for one high-spin Co(III) and two high-spin Co(II) in octahedral sites) due to the orbital contribution from the octahedral CoII ions and/or minor impurities of the sample (Figure 3).17,18 Upon cooling of the sample, χmT decreases to a value of 1.13 cm3 K mol-1 at 2 K. The fit of χm-1 versus T curve in the temperature range of 21-300 K gives a Weiss constant θ ) -49.0 K and a Curie constant C ) 12.13 cm3 K mol-1. The C value corresponds to g ) 2.68, which is normal for such a mixed-valence CoII and CoIII in octahedral geometry.17 The magnetic behavior is interpreted as dominated by the antiferromagnetic intratrimer coupling because the trimers are interconnected by large pdc bridges and cannot lead to longrange magnetic ordering. It is worth noting that a minor fluctuation around 117 K is observed, which generally comes from phase transition and/or minor impurities. For oxo-centered trinuclear mixed-valence transition-metal carboxylate complexes with the formula [M3O(O2CR)6L3]‚S (M ) Fe or Mn, L ) monodentate ligand, S ) solvate molecule), phase transition associated with intramolecular electron-transfer from a valence detrapped state at high temperature to a valence-trapped state at low temperature is commonly observed, and this kind of phase transition is very sample-, ligand-, and solvate-dependent.19 Compound 1 contains oxo-centered trinuclear mixed-valence units, and thus a similar phase transition is possible in 1. However, the same space group, presence of 3-fold inversion axis, and only one distinct Co atom at both 298 and 100 K almost eliminate the possibility of this kind of phase transition. It seems that although the experimental and calculated XRPD patterns agree well, the most possible explanation for the minor fluctuation of magnetic susceptibility around 117 K results from a common minor impurity from hydro(solvo)thermal methods.20 Conclusion Assembly of hydroxyl-centered mixed-valence Co3(OH)(CO2)6 clusters generated a 3-D coordination framework that can be described as an unprecedented (3,9)-connected net with the Schla¨fli symbol of (42.6)3(46.621.89). This work further
(3,9)-Connected (42.6)3(46.621.89) Net
demonstrates that the replacement of d- or f-block ions with metal clusters as nodes is a feasible route to synthesize highly connected metal-organic frameworks. Acknowledgment. This work was financially supported by NSFC (20401011 and 20531070), FANEDD(200422), and NCET-05-0270. Supporting Information Available: Schemes of LaCl3 and sqc15, XRPD, TGA, χm versus T curve and CIF file are available free of charge via the Internet at http://pubs.acs.org.
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CG070038O
