As an important class of inorganic-organic hybrid materials, metal phosphonates have received increasing attentions in the past two decades owing to their potential applications in ion-exchange and absorption, catalysis, proton conductivity and optics etc. We focus on the assembly of new metal phosphonate materials with novel architectures and interesting physical and chemical properties. Particular attentions are being paid on the paramagnetic 3d and 4f systems in order to discover excellent molecule-based magnets, chiral or polar materials in order to explore new optical and multifunctional materials, and proton conductors for fuel cell applications.
1. Molecule-based magnets (分子磁体)
The search for new low- or high-dimensional molecule-based magnets has been of intense current interest due to their potential applications in the information storage, molecular spintronics and quantum computing. Of equal importance is the modulation of magnetic behavior via external stimuli. By incorporating phosphonate ligands, we have succeeded in synthesizing a number of 3d or 4f compounds that show single molecule magnet (SMM), single-chain magnet (SCM) and long-range ordering behaviors. The tuning of the magnetic behaviors by structures and external stimulus has been investigated.
The spin state of cobalt in a layered 3d-4f complex [ls-CoLa(notp)(H2O)4] •nH2O (notpH6 = 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid) may be modulated in a controllable manner by the geometrical rearrangement of Co environment via the variation of the La(III) coordination sphere. (Angew. Chem. Int. Ed. 2011, 50, 5504 –5508)
By reducing the particle size to nanoscale region, compound Co3(µ3-OH)2(BTP)2 (1) (BTP = 4-(3-bromothienyl)phosphonate, Tc = 30.5 K) can vary from a soft magnet to one of the hardest molecule-based magnets at low temperature. (Chem. Eur. J. 2012, 18, 9534 – 9542)
The first example of iridium/lanthanide phosphonates, i.e. [DyIr6(ppy)12(bpp)2(bppH)4](CF3SO3)•8H2O (1) (ppy- = 2-phenylpyridine, bpp2- = 2-pyridylphosphonate) is reported. It shows dual functions with the photoluminescence and field-induced slow magnetization relaxation originating from the Ir and Dy moieties, respectively. (Chem. Commun. 2014, 50, 8356-8359)
A layered erbium(III) phosphonate compound, [Er(notpH4)(H2O)]ClO4•3H2O, in which the Er(III) ion has a pseudo-D5h symmetry exhibits field tunable multiple magnetic relaxation process. The near-IR emission spectrum, excited at 1064 nm (Nd:YAG laser), provides a direct probe of the crystal field splitting correlated to the magnetic data. (Chem. Commun. 2014, 50, 7621-7624)
(1) S.-S. Bao, Y. Liao, Y.-H. Su, X. Liang, F.-C. Hu, Z. Sun, L.-M. Zheng,* S. Wei,* R. Alberto, Y.-Z. Li, J. Ma,* Tuning the spin state of cobalt in a Co-La heterometallic complex via controllable coordination sphere of La, Angew. Chem. Int. Ed. 2011, 50, 5504 –5508.
(2) L.-R. Guo, S.-S. Bao, B. Liu, D. Zeng, J. Zhao, J. Du, and L.-M. Zheng*, Enhanced magnetic hardness in a nanoscale metal-organic hybrid ferrimagnet, Chem. Eur. J. 2012, 18, 9534 – 9542.
(3) X.-J. Yang, M. R., S.-S. Bao, N. Hoshino, T. Akutagawa, L.-M. Zheng,* Polar metal phosphonate containing unusual 4-OH bridged double chains showing canted antiferromagnetism with large coercivity, Chem. Commun. 2014, 50, 3979-3981.
(4) D. Zeng, M. Ren, S.-S. Bao, L. Li, L.-M. Zheng,* A luminescent heptanuclear DyIr6 complex showing field-induced slow magnetization relaxation, Chem. Commun. 2014, 50, 8356-8359.
(5) M. Ren, S.-S. Bao, R. A. S. Ferreira, L.-M. Zheng,* L. D. Carlos,* A layered erbium phosphonate in pseudo-D5h symmetry exhibiting field-tunable magnetic relaxation and optical correlation, Chem. Commun. 2014, 50, 7621-7624.
(6) M. Ren, S.-S. Bao,* N. Hoshino, T. Akutagawa, B. Wang, Y.-C. Ding, S. Wei, and L.-M. Zheng*, Solvent responsive magnetic dynamics of a dinuclear dysprosium single molecule magnet, Chem. Eur. J. 2013, 19, 9619-9628.
2. Clean energy-related materials (清洁能源相关材料)
Proton-conducting materials are essential components of fuel cells and hence are very important in the field of clear energy. We aim at exploring new high-performance proton conductors based on metal phosphonates and understanding the mechanism about the proton conduction pathways.
We report that a new 2D 3d-4f phosphonate [CoLa(notpH)(H2O)6]ClO4•5H2O (CoLa-II) can undergo a phase transition above 45 °C and 93% relative humidity, resulting in [H3O][CoLa(notp)(H2O)4]ClO4•3H2O (CoLa-III). The transition is accompanied with the release of the proton from intralayer to interlayer, and thus the proton conductivity of the material is increased by 1 order of magnitude. This work opens a new route in searching for high performance proton conductors. (J. Am. Chem. Soc. 2014, 136, 9292−9295.)
S.-S. Bao, K. Otsubo, J. M. Taylor, Z. Jiang, L.-M. Zheng,* H. Kitagawa,* Enhancing Proton Conduction in 2D Co-La Coordination Frameworks by Solid State Phase Transition, J. Am. Chem. Soc. 2014, 136, 9292−9295.
3. Other functional metal phosphonates (其它功能材料)
Metal-organic frameworks (MOFs) are of intense current interest. Compared with the popular carboxylates, metal phosphonates possess relatively high thermal and chemical stabilities. However, phosphonate-based MOFs are still rare. On the other hand, metal phosphonates can be designed and synthesized for particular purpose simply by modifying the organic groups of the ligands. We are interested in assembling novel phosphonate-based MOFs, chiral or polar compounds in order to explore materials with multifunctions.
Cobalt phosphonates Co2(pbtcH)(2,2'-bpy)2(H2O) (1) and Co2(pbtcH)(phen)2(H2O) (2) (pbtcH5 is 5-phosphonatophenyl-1,2,4-tricarboxylic acid) with layer structures can experience reversible single-crystal to single-crystal (SC–SC) structural transformations upon heating. Particularly, the breathing effect is observed for 1, accompanied with the pore-opening and closing due to the re-orientation of the coordinated 2,2'-bpy molecules. (Chem. Eur. J. 2013, 19, 16394 – 16402)
A chiral layered vanadium compound (VO)3(2-cpp)2(H2O)6•H2O (2-cpp3- = 2-carboxyphenylphosphonate) is obtained with enantioexcess through symmetry breaking on crystallization. Different level of enantiomeric excess is observed. (Chem. Commun. 2012, 48, 6565–6567)
A general approach to obtain pyrodiphosphonates is achieved by reacting arylphosphonic acids with AgNO3 in CH3CN under solvothermal conditions. The process is coupled with the C-C bond cleavage of acetonitrile with the formation of novel complexes [Agn(RPO2(O)O2PR)m](CN). (Chem. Commun. 2009, 2893-2895)
1. Tao Zheng, Juan M. Clemente-Juan, Jing Ma, Lin Dong, Song-Song Bao, Jian Huang, Eugenio Coronado, Li-Min Zheng,* Breathing Effect in a Cobalt Phosphonate upon Dehydration/rehydration: A Single–crystal to Single–crystal Study, Chem. Eur. J. 2013, 19, 16394 – 16402.
2. J. Huang, S.-S. Bao, L.-S. Ling, H. Zhu, Y.-Z. Li, L. Pi, and L.-M. Zheng*, A racemic polar cobalt phosphonate with weak ferromagnetism, Chem. Eur. J. 2012, 18, 10839 – 10842.
3. X.-J. Yang, S.-S. Bao, T. Zheng and L.-M. Zheng*, An enantioenriched vanadium phosphonate generated via asymmetric chiral amplification of crystallization from achiral sources showing a single-crystal-to-single-crystal dehydration process, Chem. Commun. 2012, 48, 6565–6567.
4. L.-R. Guo, S.-S. Bao, Y.-Z. Li, L.-M. Zheng*, Ag(I)-mediated formation of pyrodiphosphonate coupled with C-C bond cleavage of acetonitrile, Chem. Commun. 2009, 2893-2895.