通讯作者地址: Tao, J (通讯作者),Xiamen Univ, Coll Chem & Chem Engn, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China  
地址: 
1. Xiamen Univ, Coll Chem & Chem Engn, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China 
2. Xiamen Univ, Coll Chem & Chem Engn, Dept Chem, Xiamen 361005, Peoples R China  
电子邮件地址: taojun@xmu.edu.cnTwo 3D coordination polymers, [Co-24(OH)(12)(SO4)(12)(ip)(6)(DMSO)(18)(H2O)(6)]center dot(DMSO)(6)-(EtOH)(6)(H2O)(36) (1.guests, ip = isophthalate) and [Ni-24(OH)(12)(SO4)(12)(ip)(6)(DMSO)(12)(H2O)(12)]center dot(DMSO)(6)-(EtOH)(6)(H2O)(20) (2.guests), constructed with nanosized tetraicosanuclear Co-II and Ni-II wheels are solvothermally synthesized. Both complexes show intra- and interwheel dominant antiferromagnetic interactions.NNSF of China  90922012 
20971106 
21021061  
Specialized Research Fund for the Doctoral Program of Higher Education  2011012111001

Jia Li

Jun Tao

Lan-Sun Zheng

Rong-Bin Huang

李佳

郑兰荪

陶军

黄荣彬

Inorganic Chemistry

Xiamen University Institutional Repository

Magnetic Nanosized {MII24}-Wheel-Based (M = Co, Ni) CoordinationPolymersJia Li, Jun Tao,* Rong-Bin Huang, and Lan-Sun ZhengState Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and ChemicalEngineering, Xiamen University, Xiamen 361005, People's Republic of China*S Supporting InformationABSTRACT: Two 3D coordination polymers,[Co24(OH)12(SO4)12(ip)6(DMSO)18(H2O)6]·(DMSO)6-(EtOH)6(H2O)36 (1·guests, ip = isophthalate) and[Ni24(OH)12(SO4)12(ip)6(DMSO)12(H2O)12]·(DMSO)6-(EtOH)6(H2O)20 (2·guests), constructed with nanosizedtetraicosanuclear CoII and NiII wheels are solvothermallysynthesized. Both complexes show intra- and interwheeldominant antiferromagnetic interactions.High-nuclearity clusters have attracted much attentionbecause of their intriguing structures and fascinatingchemical and physical properties. If possessing large-spinground states and easy-axis magnetic anisotropy, they canbehave as single-molecule magnets that link the microscopicand macroscopic worlds as well as quantum and classicalsystems.1 On the other hand, when acting as structural and/orfunctional building units and being assembled into 1D−3Dnetworks, they can endow such networks with expectedtopological structures and physical properties.2 Among thehigh-nuclearity clusters, molecular magnetic wheels are ofparticular importance not only because they usually possessinherent structural beauty but also because they represent idealmodel systems for the studies of 1D magnetism, spinfrustration, magnetic anisotropy, and quantum effects.3 Up tonow, several homometallic discrete compounds composed ofNi24,4 Fe18,5 Co24,6 Cu16,7 Mn84,8 and Mo1769 wheels have beenreported. The formation of these wheels, although seeminglyserendipitous, reveals a prevalent feature that the metal ions arebridged by oxo, hydroxyl, and/or alkoxy groups produced viahydrolysis and alcoholysis reactions of metal salts in thepresence of supporting organic ligands (except Mo176), whichhints that such wheels can be assembled into coordinationpolymers if the supporting organic ligands are polytopic.However, coordination polymers with molecular wheel buildingunits are unexpectedly rare. To our knowledge, only two wheel-based coordination polymers, Ti8O8(OH)4(tp)6 (tp = tereph-thalate) and Be12(OH)12(BTB)6 (BTB = 1,3,5-benzenetriben-zoate), were recently reported.10 As part of our interest in high-nuclearity clusters of paramagnetic ions and metal-cluster-basedcoordination polymers, we report herein two new complexes,[Co24(OH)12(SO4)12(ip)6(DMSO)18(H2O)6]·(DMSO)6-(EtOH)6(H2O)36 (1·guests) and [Ni24(OH)12(SO4)12-(ip)6(DMSO)12(H2O)12] ·(DMSO)6(EtOH)6(H2O)20(2·guests); both are 3D coordination polymers constructedwith nanosized tetraicosanuclear metal-ion wheel units.The formation of the two wheel units apparently involves thehydrolysis of CoII and NiII ions under solvothermal conditions(Supporting Information) assisted by sulfate ions, ip ligands,and even solvent molecules. It is possible that sulfate ionhereinto plays a more important role in the hydrolysis of CoIIand NiII ions and in the formation of wheel structural unitsbecause its relatively strong coordination ability compared withperchlorate, nitrate, or hydrogen phosphate ion, whose CoIIand NiII salts, however, could not give wheel structures underthe same reaction conditions.Both complexes crystallize in the trigonal space group R3 ̅ andare composed of nanosized MII24 wheels with diameter of ∼2.0nm (Figure 1a). The solvent molecules could not be located inthe structures; their amounts are determined by elementalanalysis. The MII24 wheel lies on a crystallographic 3-fold axisand an inversion center, with the asymmetric unit containingfour distinct MII ions, one ip2− ligand, and two μ3-OH− and twoη1:η1:η2:μ3-SO42− groups (Figure 1b,c). Besides, three DMSOmolecules, of which two serve as μ bridges, and one watermolecule are also coordinated to CoII ions in 1, while in 2, themolecule that is η1-DMSO in 1 is here replaced with a watermolecule (O2W on Ni4 atom). The four MII ions in theasymmetric unit can be viewed as a defected cubane, M3(μ3-O5), connected to the fourth one. All MII ions lie in distortedoctahedra formed with six O atoms. In 1, the O atoms aroundthe Co1 ion derive from two ip carboxylate groups (O1 andO4A), one μ3-OH− group (O6D), and one η1-DMSO (O15)and two μ-O from two SO42− groups (O7 and O11); the Co2ion is coordinated by one O atom (O2) from an ip carboxylategroup, one μ3-OH− group (O5), two μ-O atoms (O16 andO17) from two DMSO molecules, and two μ-O atoms (O7 andO11) from two SO42− groups. The Co3 ion does notcoordinate to the ip ligand, whose coordination sphere isformed by O atoms from two μ3-OH− groups (O5 and O6),two SO42− groups (O10C and O12C), one μ-DMSO (O16),and one water molecule (O1W), while the Co4 ion iscoordinated by one ip carboxylate group (O3B), two μ3-OH−groups (O5 and O6), one μ-DMSO (O17), and two SO42−groups (O8C and O13). The average bond lengths for Co1,Co2, Co3, and Co4 are 2.089, 2.103, 2.095, and 2.112 Å,respectively. In 2, the average Ni−O bond distances are 2.067,2.052, 2.064, and 2.056 Å for Ni1, Ni2, Ni3, and Ni4,respectively. The anions or ligands in the wheels coordinate indiverse modes, showing M−O bond lengths in a sequence ofReceived: March 4, 2012Published: May 24, 2012Communicationpubs.acs.org/IC© 2012 American Chemical Society 5988 dx.doi.org/10.1021/ic300487a | Inorg. Chem. 2012, 51, 5988−5990d(μ-O,DMSO) > d(μ-O,SO42−) > d(η1-O,DMSO) > d(η1-O,SO42−) > d(μ3-OH−) > d(η1:η1:μ-O, COO−) for 1 and d(μ-O,SO42−) > d(μ-O,DMSO) > d(η1-O,DMSO) > d(η1-O,SO42−)> d(μ3-OH−) > d(η1:η1:μ-O,COO−) for 2, respectively (TableS2 in the Supporting Information).The asymmetric MII4 units are linked to their symmetry-related ones (dotted lines in Figure 1b,c) by μ3-OH− ions,η1:η1:η2:μ3-SO42− groups, and ip carboxylate groups, respec-tively, resulting in an overall MII24 wheel that consists of sixedge- and vertex-sharing {MIIO6}4 species (Figure 1a). TheMII24 wheel can be viewed as nanosized building units (Figure2a) above and below which they are capped with peripheral ipligands. Six pairs of ip ligands connect six MII24 wheels (eachpair of ip ligands is represented by a colored rectangle; Figure2b,c), with each ip ligand bound to four MII ions, resulting in3D MII24-wheel-based coordination polymers (Figures 2d andS1 in the Supporting Information), with void spaces beingoccupied by lattice DMSO, EtOH, and water molecules. Froma topological point of view, the MII24 wheel is a structural nodeand each pair of ip ligands is a linker; the frameworks of the two3D coordination polymers can then be simplified to a 3D α-polonium-type structure of 41263 topology (Figure S2 in theSupporting Information).The molar direct-current (dc) magnetic susceptibilities (perMII24 unit) of microcrystalline samples of 1·guests and 2·guestsmeasured in the temperature range 2−300 K under 0.1 Texternal field are shown in Figure 3a. The χMT value for1·guests at 300 K are 68.26 cm3 K mol−1, significantly higherthan the spin-only value expected for 24 isolated CoII ions withS = 3/2 (45.00 cm3 K mol−1; g = 2.0). It gives a realistic gCovalue of 2.46 if we assume that the ions are uncoupled; thisresult is attributed to the unquenched orbital contributions ofCoII ions in an octahedral field. Upon temperature cooling, theχMT value monotonously decreases to attain a value of 4.51 cm3K mol−1 at 2 K, which indicates dominant antiferromagneticinteractions within and between the Co24 wheels; meanwhile,spin−orbital coupling effects may also influence the overallprofile. A low-temperature M versus H plot (Figure S5 in theSupporting Information) further confirms the overall anti-ferromagnetic interactions. The χMT value for 2·guests at 300 Kis 28.43 cm3 K mol−1, slightly higher than the spin-only valueexpected for 24 isolated NiII ions with S = 1 (24.00 cm3 Kmol−1; g = 2.0) and giving a realistic gNi value of 2.18. The χMTvalue generally decreases to 22.45 cm3 K mol−1 at 20 K andthen rises sharply to reach a value of 33.62 cm3 K mol−1 at 3 K,followed by a sudden drop to 31.93 cm3 K mol−1 at 2 K. Thisprofile and the θ value (−6.6 K; Figure S4 in the SupportingInformation) indicate dominant antiferromagnetic interactionswithin the Ni24 wheel; the rise of the χMT value at lowtemperature implies that extrinsic intrawheel antiferromagneticinteractions may be the result of competitive ferro- andantiferromagnetic interactions between NiII ions that lead to aground-state spin (ST ∼ 6 corresponding to the χMT value at aminimum) and adjacent wheels ferromagnetically coupled orantiferromagnetically coupled with spin canting. The significantmagnetic ground state is further supported by the low-temperature M versus H plot (Figure S6 in the SupportingInformation), which shows a quick increase (compared with1·guests) at relatively low external fields. The value of themagnetization (12−14 μB per NiII24 unit) after this quickincrease confirms the presence of dominant antiferromagneticinteractions that are uncompensated for by ferro- andantiferromagnetic interactions within the 2 wheel.In order to elucidate the low-temperature magnetic behavior,field-dependent magnetic susceptibilities of 1·guests and2·guests at temperature range of 2−40 K have been measured.Interestingly, only 2·guests undergoes field-dependent behaviorFigure 1. Perspective view of the MII24 wheel showing edge- and vertex-sharing MIIO6 (green) and SO4 (yellow) polyhedra (a) and the asymmetricstructural units in coordination polymers 1 (b) and 2 (c), respectively. Symmetry codes: A, x − y + 2/3, x − 2/3, −z + 7/3; B, −y + 4/3, x − y − 1/3, z− 1/3; C, x − y, x − 1, −z + 2; D, y + 1, −x + y + 1, −z + 2 for 1; A, x − y + 1/3, x + 2/3, −z + 2/3; B, −y + 1/3, x − y + 2/3, z − 1/3; C, x − y + 2/3, x +1/3, −z + 1/3; D, y − 1/3, −x + y + 1/3, −z + 1/3 for 2.Figure 2. View of the wheel unit above and below which there are sixpairs of ip ligands (a). Each pair of ip ligands simplified as a coloredrectangle (b). Each wheel linking six neighbors (c). 3D structures of 1and 2 along the c axis (d).Figure 3. χMT versus T plots of 1·guests and 2·guests measured at 1kOe external field (a) and field-dependent magnetic susceptibilities of2·guests in the 2−40 K temperature range (b).Inorganic Chemistry Communicationdx.doi.org/10.1021/ic300487a | Inorg. Chem. 2012, 51, 5988−59905989(Figure 3b), whose magnetic susceptibilities increase withdecreasing external fields, which further confirms the groundstate of 2·guests and canted interwheel antiferromagneticinteractions. Because of the nonsignificant anisotropy of NiIIions, the presence of spin canting is probably due to thenoncollinear interwheel spin structure or Dzyaloshinskii−Moriya interactions.11 It should be mentioned that the field-dependent behavior of 2·guests may also be a consequence ofthe zero-field-splitting effect associated with NiII ions. On theother hand, the monotonous increases in χM upon cooling for1·guests and 2·guests indicate that they are not antiferromag-netically ordered above 2 K (Figure S7 in the SupportingInformation). Meanwhile, the nonzero values at 2 K and themonotonous increases in χM imply that the ground state of2·guests is significantly larger than that of 1·guests. To clarifythis situation, alternating-current (ac) susceptibility measure-ments were performed in zero applied dc field and 3 Oe ac fieldoscillating at 1 and 99.9 Hz, respectively (Figures S8 and S10 inthe Supporting Information). Extrapolations of the χM′T versusT plots to 0 K give values of 4.61 and 39.84 cm3 K mol−1 for1·guests and 2·guests (Figures S9 and S11 in the SupportingInformation), respectively, which agree well with the observedones for χMT at 2 K, indicating magnetic S = 1 and 7−8 groundstates for 1·guests and 2·guests, respectively. The in-phasesignals are frequency-independent (and without peaks), and noout-of-phase signals are observed down to 2 K; thus, above thistemperature, there is no magnetization relaxation.Because of the anisotropic nature of the CoII ion, it is hard tofigure out the spin topology of 1·guests and which type ofexchange pathways should dominate, but for 2·guests, thecorrelation of the observed magnetic properties with thestructure can be rationally realized. For octahedral nickel(II)complexes, dx2−y2 and dz2 are the two magnetic orbitals. Thedominant superexchange pathway between two NiII centers (inthe Ni−O−Ni species) involves dx2−y2 orbitals of NiII ions and porbitals of the bridging O atom, which results in antiferro-magnetic exchange, whose coupling integral (−J) increases asthe Ni−O−Ni bridge angle and hence the Ni···Ni distanceincreases, while dz2 orbitals interact ferromagnetically throughspace and the magnitude of exchange depends on the distancebetween the NiII centers. Thus, increases of the Ni−O−Nibridge angle and hence the Ni···Ni distance simultaneouslystrengthen antiferromagnetic coupling and weaken ferromag-netic coupling. The ferromagnetic crossover point for a Ni−O−Ni bridge angle is 96°; however, the real Ni−O−Ni bridgeangle leading to dominant antiferromagnetic interactionsusually exceeds 99°.12 As shown in Figure S12 and Table S2in the Supporting Information, the bond angles of Ni1−O−Ni4and Ni2−O−Ni3 are less than 98°, while those of Ni1−O−Ni3, Ni2−O−Ni4, and Ni3−O−Ni4 are larger than 100°.Thus, we can simply assign the exchanges between Ni1 and Ni4and between Ni2 and Ni3 to be ferromagnetic and thosebetween Ni1 and Ni2/Ni3 and between Ni4 and Ni2/Ni3 to beantiferromagnetic. The significant ground-state spin determinedby both dc and ac magnetic susceptibility data indicates thatantiferromagnetic interactions may be noncollinear.In summary, we have synthesized and characterized two 3Dcoordination polymers based on by far the largest CoII24 andNiII24 wheel-like building units. The wheels have aestheticallypleasing structure and NiII24 has a ground-state spin S ∼ 6 dueto both ferro- and antiferromagnetic interactions within theNiII24 wheel. Further evidence shows that interwheel inter-actions in the two complex frameworks are antiferromagnetic,but in 2·guests they are canted and therefore show weakferromagnetism. The two compounds show tremendouschanges in bulky magnetic properties and magnetic groundstates, implying the possibility of tuning magnetic properties byslight structure changes.■ ASSOCIATED CONTENT*S Supporting InformationExperimental details, figures, crystal data in CIF format. Thismaterial is available free of charge via the Internet at http://pubs.acs.org.■ AUTHOR INFORMATIONCorresponding Author*E-mail: taojun@xmu.edu.cn.NotesThe authors declare no competing financial interest.■ ACKNOWLEDGMENTSWe are thankful for financial support from the NNSF of China(Grants 90922012, 20971106, and 21021061) and theSpecialized Research Fund for the Doctoral Program of HigherEducation (Grant 20110121110012).■ REFERENCES(1) (a) Gatteschi, D.; Sessoli, R.; Villian, J. Molecular Nanomagnets;Oxford University Press: Oxford, U.K., 2006. (b) Murrie, M. Chem.Soc. Rev. 2010, 39, 1986.(2) (a) Murugesu, M.; Habrych, M.; Wernsdorfer, W.; Abboud, K.A.; Christou, G. J. Am. Chem. Soc. 2004, 126, 4766. (b) Bai, Y.-L.; Tao,J.; Wernsdorfer, W.; Sato, O.; Huang, R.-B.; Zheng, L.-S. J. Am. Chem.Soc. 2006, 128, 16428. (c) Bai, Y.-L.; Tao, J.; Huang, R.-B.; Zheng, L.-S. Angew. Chem., Int. Ed. 2008, 47, 5344. (d) Mohamedally, K. Chem.Soc. Rev. 2009, 38, 1353.(3) (a) Chiolero, A.; Loss, D. 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Magnetic Nanosized {M-24(II)}-Wheel-Based (M = Co, Ni) Coordination Polymers

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Magnetic Nanosized {M-24(II)}-Wheel-Based (M = Co, Ni) Coordination Polymers

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