Manganese (IV) compounds are well known and are used in a variety of oxidation reactions. For example, manganese dioxide (MnO.sub.2) has been used in the manufacture of chlorine gas from hydrogen chloride and the oxidation of aniline to hydroquinone. See "Chemistry of the Elements", N. N. Woodward and A. Earnnshaw, Pergammon Press, Oxford, pp 1219-20 (1984). A molecular manganese-oxo cluster is involved in the oxidation of water to oxygen in the photosynthesis process used by plants. See Yachandra et.al., Science, 260, 675-679 (1993). Because manganese has stable oxidation states of +4, +3 and +2, manganese oxides can be used in batteries.
Manganese oxides can have layered structures or three-dimensional microporous structures. S. Bark et al., Electrochimica Acta, 36, 1595-1603 (1991), P. LeGoff et al., Mat. Res. Bull., 31, 63-75 (1996), P. Strobel et al., Mat. Res. Bull., 28, 93-100 (1993), Y. Shen et al., Science, 260, 511-515 (1993). Finally, the ion-exchange properties of manganese oxide compositions have been reported by Q. Feng et al. in Chem. Mater., 7, 148-153 and 1722-1727 (1995).
In addition to manganese oxide compounds, there are reports of manganese phosphate molecular complexes containing Mn(IV). For example, Weighardt et al. have reported the synthesis of a trimeric manganese (IV) phosphate complex. Weighardt et al., Chem. Comm., 1145 (1988). A Mn(IV) dimer having the formula [(bpy)(H.sub.2 PO.sub.4)Mn.sup.+4 (.mu.-O).sub.2 (.mu.-HPO.sub.4)Mn.sup.+4 (bpy)]*H.sub.2 O where bpy=bipyridine has been reported by J. Sarneski et al., Inorg. Chem., 30, 2833-35 (1991). M. Jaky has disclosed dilute manganese (IV) phosphate solutions which were used for the oxidation of various organic substrates. Polyhedron, 12, 1271 (1993). Finally, there are a number of examples of Mn(III)-containing phosphates that have been prepared by hydrothermal synthesis, e.g., KMn.sub.2 O(PO.sub.4)(HPO.sub.4), Lightfoot et. al., J. Solid State Chem., 73, 325-329, (1988), and NH.sub.4 Mn.sub.2 O(PO.sub.4)(HPO.sub.4), Lightfoot et. al., J. Solid State Chem., 78, 17-22, (1989).
In contrast to these references, applicants have synthesized crystalline manganese phosphate compounds which contain Mn(IV) and which have an extended network. By extended network is meant that the defining Mn--P--O structural unit of the material repeats itself into at least two adjacent unit cells without termination of bonding, i.e., the material is not molecular. See "Structural Inorganic Chemistry, Fifth Edition," A. F. Wells, Clarendon Press, Oxford, pp. 11-15, (1984). The network can be one-dimensional (a linear chain), two-dimensional (layered) or three-dimensional. The three dimensional network may or may not be a microporous network. There is no mention of a manganese(IV)-containing phosphate material with an extended network. By Mn(IV)-containing phosphate, it is meant that the average oxidation state of Mn is greater than 3.0 but less than or equal to 4.0, indicating the presence of some Mn(IV). These compositions are prepared by employing large excesses of phosphate to avoid the precipitation of insoluble Mn(IV) oxides, and through careful control of the pH and the use of mild reaction conditions. Further, applicant has also synthesized metallo manganese phosphates where a portion of the manganese is replaced by a metal such as iron (III), aluminum, gallium, etc. This new family of compounds are useful in several hydrocarbon conversion processes such as oxidative dehydrogenation of alkanes and oxidative coupling of methane to higher hydrocarbons.