New Template-Free Layered Manganese(III) Phosphate: Hydrothermal Synthesis, Ab Initio Structural Determination, and Magnetic Properties Stanislav Ferdov, †,‡,§ Armandina M. L. Lopes, §,| Zhi Lin,* ,† and Rute A. Sá Ferreira § Departments of Chemistry and Physics, CICECO, UniVersity of AVeiro, 3810-193 AVeiro, Portugal, and Department of Physics, IFIMUP, UniVersity of Porto, 4169-007 Porto, Portugal ReceiVed July 20, 2007. ReVised Manuscript ReceiVed September 25, 2007 A new template-free layered manganese(III) phosphate, Na 3 MnH(P 0.9 O 4 ) 2 , has been hydrothermally synthesized. The crystal structure was solved ab initio from powder X-ray diffraction data, and the model was confirmed using the Rietveld method. The material crystallizes in triclinic space group P1 j (No. 2) with lattice parameters a ) 5.2925(2) Å, b ) 6.9004(3) Å, c ) 5.2452(3) Å, R) 91.56(0)°,  ) 116.95(0)°, γ ) 90.5(0)°, and Z ) 1. The structure consists of [Mn(P 0.9 O 4 ) 2 ] ∞ layers composed of isolated MnO 6 octahedra connected via corner-sharing asymmetric PO 4 tetrahedra. The interconnection between the layers is assured by Na + cations, which reside in the interlayered space. The system is paramagnetic above 50 K, with an effective paramagnetic moment of 4.85(3) µ B , ascertaining the Mn 3+ valence state of the Mn ions. Antiferromagnetic short-range-order effects are observed below 26.5 K. 1. Introduction Manganese has one of the most varied oxidation states of all of the elements. Materials with Mn 3+ or Mn 4+ or both are widely used in batteries 1 and catalytic processes. 2–5 In this respect, manganese phosphates are used as catalysts for the oxidation of methyl mandelate 6 and of adonitol to ribose. 7 These materials also have useful coating characteristics and play a major role in the corrosion protection of mild steels 8 and as the intermediate layer before the final painting of automobile iron casting. 9 Finally, the electrochemical proper- ties of manganese phosphates are now proving to be of industrial interest. 10,11 Although manganese phosphates are among the most widespread of all mineral phosphates, the synthetic com- pounds with an open framework are very scarce and the chemistry of new phases in this area is emerging. The majority of the reported phases contain only Mn 2+ , 12,13 and open structures with Mn 3+ are rare. One reason is the easy reduction of Mn 3+ and/or Mn 4+ materials to Mn 2+ materials at high temperature. The other reason is the very low solubility of Mn 3+ and Mn 4+ in solution, which causes difficulties in the hydrothermal synthesis of open-structural materials with high crystallinity. 14 Furthermore, the majority of the open-framework manganese phosphates contain an organic molecule as a structure-forming unit. In this paper, we report a new example of template-free layered manganese(III) phosphate, although 2-methylpen- tamethylenediamine (MPMD) has been used in its prepara- tion. To date, MPMD is used only as a template for the preparation of crystalline mesoporous germanium oxides, 15 and here for the first time, we present the synthesis of a metal phosphate using MPMD. The present work also demonstrates a combination of laboratory powder X-ray diffraction (XRD) data, spectroscopic study, and magnetic properties for successful ab initio structural determination. 2. Experimental Section 2.1. Synthesis. A typical synthesis of Na 3 MnH(P 0.9 O 4 ) 2 is as follows. A solution of 0.47 g of NaH 2 PO 4 (Aldrich) in 8.67 g of distilled water was mixed with 13.28 g of MPMD (Du Pont). Then, 0.05 g of MnSO 4 · H 2 O (Aldrich) dissolved in 6.58 g of distilled water was added to the above solution. The resulting mixture was homogenized for 40 min and then transferred into a Teflon-lined * Author to whom correspondence should be addressed. E-mail:zlin@ua.pt. Tel: 351 234401519. Fax: 351 234370084. † Department of Chemistry, CICECO, University of Aveiro. ‡ On leave from the Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences. § Department of Physics, CICECO, University of Aveiro. | University of Porto. (1) Chabre, Y.; Pannetier, J. Prog. Solid State Chem. 1995, 23, 1. (2) Krishnan, V. V.; Suib, S. L. J. Catal. 1999, 184, 305. (3) Wang, J.-Y.; Xia, G.; Yin, Y.-G.; Suib, S. L.; O’Young, C. L. O. J. Catal. 1998, 176, 321. (4) Xia, G. G.; Yin, Y. G.; Willis, W. S.; Wang, J. Y.; Suib, S. L. J. Catal. 1999, 185, 91. (5) Luo, J.; Zhang, Q.; Huang, A.; Suib, S. L. Microporous Mesoporous Mater. 2000, 35–36, 209. (6) Malkani, R. K.; Suresh, K. S.; Bakore, G. V. J. Indian Chem. Soc. 1978, 55 (3), 215. (7) Fadnis, A. G.; Kulshrestha, S. K. React. Kinet. Catal. Lett. 1982, 19 (3–4), 267. (8) Talaat El-Mallah, A.; Hassib, A. M.; Farid, S. M. Met. Finish. 1988, 86 (4), 29. (9) Li, G.-Y.; Lian, J.-S.; Niu, L.-Y.; Jiang, Z.-H. ISIJ Int. 2005, 45 (9), 1326. (10) Takuaki, O.; Yoji, T.; Yoshio, U. Jpn. Kokai Tokkyo Koho 2006, 13. (11) Ojczyk, W.; Marzec, J.; Swierczek, K.; Molenda, J. Diffus. Defect Data. Pt. A 2005, 237–240, 1299. (12) Daidouh, A.; Martinez, J. L.; Pico, C.; Veiga, M. L. J. Solid State Chem. 1999, 144, 169. (13) Escobal, J.; Mesa, J. L.; Pizarro, J. L.; Lezama, L.; Olazcuaga, R.; Rojo, T. J. Mater. Chem. 1999, 9, 2691. (14) Tong, W.; Xia, G.-G.; Tian, Z.-R.; Liu, J.; Cai, J.; Suib, S. L.; Hanson, J. C. Chem. Mater. 2002, 14 (2), 615. (15) Zou, X.; Conradsson, T.; Klingstedt, M.; Dadachov, M. S.; O’Keeffe, M. Nature 2005, 437, 716. 6025 Chem. Mater. 2007, 19, 6025–6029 10.1021/cm701951w CCC: $37.00  2007 American Chemical Society Published on Web 10/31/2007