Abstract:
The invention provides metal-phosphorus-nitrogen polymer compounds and methods for their preparation at low temperatures using readily available starting materials. One group of compounds, metal-phosphazene polymers, are comprised of repeating units of [PN] 3  rings linked to form polymers through P--X--M--X--P bonds. The linking atoms X are either NH 2  or O, and M is a metal cation. Another group of the compounds have the generic formula M a  (P 2  O 5 ) b  (NH 3 ) c  O d .eH 2  O. If the metal-phosphorus-nitrogen polymers are heated to a sufficiently high temperature to reduce the nitrogen/phosphorus ratio, additional novel solid metal phosphorus compounds of the invention are formed, many of which have a foamed, porous structure. The properties of the compounds of the invention can be varied by choice of metal and reaction conditions to create materials having useful conductive, magnetic, optical, catalytic, or ion-exchange properties.

Description:
U.S. GOVERNMENT RIGHTS TO THE INVENTION 
     the work leading to this invention was carried out with United States Government funds. Therefore, the U.S. Government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to solids, and more particularly to metal-phosphazene polymers and metal-phosphate compounds. 
     BACKGROUND OF THE INVENTION 
     Novel solid materials with desirable physical and chemical properties are constantly being sought for commercial applications. Economical, low temperature synthetic routes to new solids from readily available starting materials are of particular interest. Especially desirable attributes for novel materials are easy variability of physical and chemical properties and high thermal, storage and in-use stability. 
     One class of compounds used as starting material for new solids is the phosphazenes, compounds of the formula (NPX 2 ) n , with alternating phosphorus and nitrogen atoms. Soluble linear chlorophosphazene, [NPCl 2  ] n , is desirable as a primary source for making substituted phosphazene polymers (e.g., [NP(OR) 2  ] n ), many of which are useful as flame retardants and low-temperature elastomers. Solid hexachlorocyclotriphosphazene, [NPCl 2  ] 3 , undergoes polymerization at 200° C.-300° C. to [NPCl 2  ] n . The reaction is difficult to control because of cross-linking, air sensitivity, and the formation of insoluble gel products. The molecule [NPCl 2  ] 3  is a potential hexa-coordinating ligand and might be expected to react with metal salts to form cationic metal-bridged polymers, [(ring)P--Cl--M II  --Cl--P(ring)] n , with useful properties. However, this approach does not work well in practice because [NPCl 2  ] 3  is very water-sensitive. Reaction of [NPCl 2  ] 3  with water results in formation of hydrochloric acid (HCl) which prevents formation of the metal-bridged polymer by competing protonation. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides novel solid metal-phosphorus-nitrogen polymers which can be made at low temperatures. In one group of compounds of the invention, repeating units of phosphazene [PN] 3  rings are linked by P--X--M--X--P bonds to form a polymer. The linking atoms X are either NH 2  or O, and M is a metal cation. Another group of the compounds have the generic formula M a  (P 2  O 5 ) b  (NH 3 ) c  O d .eH 2  O. Preferably, M is Mg II , Mn II , Fe II , Co II , Ni II , Cu II , or Zn II . Compositions having Al III , Cr III , Fe III , or V IV  may also be formed. A wide range of metal-phosphorus-nitrogen polymers with various properties may thus be realized. Generally, the method of preparing the metal-bridged polymers involves reacting [NP(NH 2 ) 2  ] 3 .6NH 4  Cl with a metal salt in an aqueous environment, preferably either at room temperature or under reflux conditions, and isolating the precipitate. 
     In another aspect of the invention, the metal-phosphorus-nitrogen polymers are heated to a sufficiently high temperature to reduce the nitrogen/phosphorus ratio. The resulting solid products are novel metal-phosphorus compounds, many of which have a foamed, porous structure. 
     The compounds of the invention have a wide range of properties, making them appropriate for uses as diverse as fire retardants, lubricants, ion-exchangers, ingredients in glazes, and heterogenous catalysts. The proportions of the reactants, the choice of the reaction conditions, and the selection of the metal reactant will all influence the properties of the final product. 
     Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof and from the claims. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The starting materials for the polymers of the invention may be phosphazenes having the formula (NPX 2 ) n . For example, a phosphonitrilic halide such as (NPCl 2 ) 3  can be reacted with ammonia (NH 3 ) to provide [NP(NH 2 ) 2  ] 3 .6NH 4  Cl. The [NP(NH 2 ) 2  ] 3 .6NH 4  Cl product is an air-stable, white solid that is insoluble in cold water. The description of this reaction is given by R. A. Shaw in &#34;Phosphorus and Sulfur&#34; (1978), Vol. 4, page 101, which is incorporated herein by reference. 
     The phosphonitrilic compound [NP(NH 2 ) 2  ] 3 .6NH 4  Cl is then reacted with a metal salt in an aqueous environment to produce a metal-phosphorus-nitrogen polymer of the invention. The co-production of ammonium salts, which are only weakly acidic, permits the reaction to go to completion. As will be described in further detail below, the reaction conditions, the metal cation used, and the proportions of the initial reactants are all determinative of the molar ratios of the included elements and the specific linking atoms in the final product. 
     One class of products is composed of polymers having repeating units of metal-linked phosphazene [PN] 3  rings. The subunit of a typical metal-phosphazene polymer has the formula ##STR1## The [PN] 3  ring is linked to at least one other [PN] 3  ring through one or more (P--X) 1  --M--(X--P) 2  bonds where the phosphorus of said (P--X) 1  is a member of a first [PN] 3  subunit and the phosphorus of said (X--P) 2  is a member of a second [PN] 3  subunit and where X is either NH 2  or O and where M is a metal cation. The X substituents on the phosphazene ring not involved in metal-linked bonds are in the form NH 2  or OH. 
     If the starting materials are reacted at room temperature, the products precipitating from solution have intact phosphazene rings and retain from zero to six of the original six NH 2  groups of the precursor phosphonitrilic compound. Different products, as determined by elemental analysis, usually having different properties from those formed at room temperature, are formed from the same precursors if the reaction takes place at higher temperatures. In general, as the reaction temperature is increased from room temperature to 100° C. (reflux conditions), the nitrogen content (and, therefore, the ratio N/P) of the product polymer is decreased. 
     A different class of products, novel metal-phosphorus compounds, is produced if the products prepared in the original reaction are heated to a high temperature, e.g., about 600° C. The products of high temperature treatment have considerably reduced to no nitrogen content, and a number of them are unusual foamed, or porous, materials. 
     The descriptions and charts below give sample reaction conditions and products formed for a broad spectrum of metal systems. 
    
    
     EXAMPLE I--ROOM TEMPERATURE PROCEDURE 
     The reactants are generally the phosphonitrilic compound, e.g., [NP(NH 2 ) 2  ] 3 .6NH 4  Cl (A) and a metal salt (usually the halide, nitrate or, preferably, the sulfate hydrate) (B) and distilled water. In a typical experiment, 5.5 gm (0.01 mol) of A is treated with 0.01 mol of B in 100 mL of distilled water, and the mixture is stirred at room temperature for 24 hr. The precipitated product is filtered, washed several times with water and methanol and then air dried. No precipitate is obtained with common magnesium or nickel salt hydrates at room temperature. The colors, yields and analytical data of the precipitated solids are shown in Table I. 
     
                                           TABLE I__________________________________________________________________________Room Temperature ProductsFormula M.sub.a [(PN).sub.3 O.sub.b (OH).sub.c (NH.sub.2).sub.d ].sub.e.fH.sub.2 O                                         Solubility                                                 Solubility in 0.1N                         Anal. (%).sup.1                                  Molar Ratios                                         0.1N HCl                                                 NaOHM     Color   Yield.sup.2             a b c d e f M  P  N  N/P                                     N/M Cold                                             Hot Cold                                                     Hot__________________________________________________________________________Al(OH).sub.2 White powder         4.03             3 3 0 3 1 19                         10.9                            14.2                               11.6                                  1.8                                     2.1 Insol.                                             S. sol.                                                 Insol.                                                     Insol.FW.sup.3 708                  11.4                            13.1                               11.4Co(OH) Pink powder         0.43             3 3 0 3 1 1 41.8                            17.9                               16.6                                  2.1                                     1.7 Insol.                                             Insol.                                                 Insol.                                                     S. sol.FW.sup.3 477                  37.1                            19.5                               17.6                  blueCr    Green powder         3.00             5 5 1 0 2 35                         16.9                            17.5                               8.1                                  1.0                                     1.8 Insol.                                             Insol.                                                 Insol.                                                     Insol.FW.sup.3 1554                 16.7                            17.9                               8.1Cu    Greenish blue         1.88             2 4 0 2 1 7 28.2                            19.1                               13.4                                  1.6                                     2.2 Insol.                                             Insol.                                                 Insol.                                                     S. sol.FW.sup.3 484 powder                  26.2                            19.2                               14.4                  blueFe(OH).sub.2 Khaki powder         1.54             4 0 0 6 1 22                         21.1                            9.4                               14.2                                  3.3                                     2.7 Insol.                                             Insol.                                                 S.                                                     ChangedFW.sup.3 974                  22.9                            9.6                               12.9                  to brown                                                     ppt.Mn    Cream powder         0.16             1 1 2 3 2 14                         7.0                            24.0                               21.1                                  1.9                                     11.8                                         Insol.                                             Insol.                                                 S.                                                     ChangedFW.sup.3 773                  7.1                            24.1                               21.7                  to brown                                                     ppt.VO(OH).sub.2 Gray-green         2.60             4 0 0 6 1 36                         16.4                            7.4                               9.2                                  2.8                                     2.1 Insol.                                             S. sol.                                                 S.                                                     Sol.FW.sup.3 1283 powder                  15.9                            7.2                               9.8           bluish  reddish                                             violet  brownZn    White powder         1.64             3 3 2 2 2 10                         23.5                            24.8                               18.9                                  1.7                                     3.8 Sol.                                             Ppted                                                 Insol.                                                     Insol.FW.sup.3 782                  25.1                            23.8                               17.9          when                                             heated__________________________________________________________________________ .sup.1 Second row of each entry shows the calculated elemental percentages. .sup.2 Typical yield (gm) under standard experimental conditions. .sup.3 Calculated formula weight of product. 
    
     From the data given in Table I it can be seen that all the tested room temperature products have an N/P molar ratio ≧1.0, implying the presence of intact phosphazene rings [PN] 3 . From zero to six of the original six NH 2  groups of the phosphonitrilic compound (A) remain in the products. Only two products (those containing V and Fe) have six NH 2  groups and these products have the highest formula weights. Each phosphazene ring generally coordinates from two to four metal units. Exceptions are the products containing Mn (where one metal unit coordinates two phosphazene rings ), Cr (1.7 Cr per phosphazene ring) and Zn (1.5 Zn per phosphazene ring). The highest yields (lowest solubility) are observed for the Al and Cr products, which are M III  systems. With the notable exceptions of Co (0.33) and Mn (14), the room temperature products contain from three to nine water molecules per metal center. 
     EXAMPLE II--REFLUX PROCEDURE 
     In a typical experiment, 5.5 gm (0.01 mol) of solid compound (a) described above and 100 mL of distilled water are placed in a 250 mL round bottom flask fitted with a reflux condenser. An equimolar amount of solid metal salt (B) is added and the mixture is refluxed for two hr. After the mixture is cooled to room temperature, the precipitated solid is filtered and washed several times with water and methanol and then air-dried. The colors, yields and analytical data of the precipitated solids prepared by the reflux procedure are shown in Table II. 
     
                                           TABLE II__________________________________________________________________________Reflux Temperature ProductsFormula M.sub.a (P.sub.2 O.sub.5).sub.b (NH.sub.3).sub.c O.sub.d.eH.sub.2                                Molar Solubility in                                                Solubility in 0.1N                       Anal. (%).sup.1                                Ratios                                      HCl       NaOHM     Color  Yield.sup.2            a b c d e  M  P  N  N/P                                   N/M                                      Cold                                          Hot   Cold Hot__________________________________________________________________________Al    White  3.79            10              7 11                  15                    35 11.4                          18.8                             6.5                                0.77                                   1.1                                      Insol.                                          S. sol.                                                Sol. Sol.FW.sup.3 2317 powder                11.4                          18.3                             6.5Co    Lavender        2.72            15              5 11                  15                    0  47.1                          16.9                             8.5                                1.1                                   0.77                                      S. sol.                                          Ppted when                                                Insol.                                                     Insol.FW.sup.3 2020 powder                43.7                          15.3                             7.6      pink                                          heatedCr    Green  4.71            6 5 8 9 27 17.1                          17.7                             6.2                                0.77                                   1.3                                      Insol.                                          Insol.                                                Insol.                                                     Insol.FW.sup.3 1788 powder                17.4                          17.1                             6.3Cu    Pale blue        2.19            63              21                22                  63                    93 40.2                          13.0                             3.0                                0.52                                   0.34                                      Sol.                                          Sol. blue                                                Insol.                                                     Insol.FW.sup.3 10037 powder                40.0                          13.0                             3.1      blue           change to                                                     blackFe    Yellow-        4.40            14              4 15                  14                    65 26.8                          8.5                             6.9                                1.8                                   1.1                                      Insol.                                          Insol.                                                S.                                                     S. sol.FW.sup.3 2998 brown                 26.1                          8.3                             7.0                brown                                                     dark powder                                              brownMg    White  1.13            10              12                24                  10                    20 8.2                          26.4                             11.9                                0.96                                   2.4                                      S. sol.                                          S. sol.                                                Insol.                                                     Insol.FW.sup.3 2875 powder                8.4                          25.8                             11.7Mn    Pale pink        2.09            4 7 17                  4 17 11.6                          22.9                             12.7                                1.2                                   4.3                                      S. sol.                                          White ppt.                                                Insol.                                                     ChangedFW.sup.3 1880 powder                11.7                          23.1                             12.7         when  changed                                                     to brown                                          heated                                                to                                                     ppt.n                                                ppt.Ni    Pale green        2.02            10              7 18                  10                    32 22.4                          16.4                             9.8                                1.3                                   1.8                                      Sol.                                          Sol.  Insol.                                                     Insol.FW.sup.3 2623 powder                22.4                          16.5                             9.6V     Pale blue        2.53            43              5 16                  86                    212                       25.9                          3.6                             2.7                                1.6                                   0.37                                      Sol.                                          Sol. blue                                                S.                                                     Sol.FW.sup.3 8412 powder                26.0                          3.7                             2.7      blue           reddish                                                     brownZn    White  2.17            6 4 10                  6 11 27.6                          17.3                             9.9                                1.3                                   1.7                                      Sol.                                          Turbid                                                S.                                                     S. sol.Fw.sup.3 1424 powder                27.5                          17.4                             9.8          when                                          heated__________________________________________________________________________ .sup.1 Second row of each entry shows the calculated elemental percentages. .sup.2 Typical yield (gm) under standard experimental conditions. .sup.3 Calculated formula weight of product. 
    
     From the data presented in Table II it can be observed that precipitated products are obtained under reflux conditions with Mg and Ni salts as reactants whereas these two metals do not lead to precipitated products at room temperatures. The product N/P ratio is always lower under reflux conditions than at room temperature, indicating that a higher reaction temperature favors the hydrolysis of NH 2  substituents on the phosphazene ring. This is substantiated by lower N/M molar ratios under reflux conditions. 
     With three exceptions, the N/P ratio varies between 0.96 (Mg) and 1.8 (Fe) under reflux. In this range, the pattern of variation of N/P with metal is similar to that at room temperature. Since the intact phosphazene ring has N/P=1.0 when all the NH 2  groups have been hydrolyzed to OH groups, most of the products appear to contain intact PN rings. On this basis, those with N/P&gt;1.0 have one or two residual NH 2  groups per phosphazene ring. The notable exceptions are the products prepared from Al and Cr (N/P=0.77) and Cu (N/P=0.52). These products evidently contain hydrolyzed PN rings. The calculated formula weights under reflux are higher than at room temperature, consistent with a higher degree of hydrolysis and polymerization. This is consistent with polymerization through M-O linkages. The products under reflux conditions always contain fewer water molecules of crystallization per metal center than those obtained at room temperature. Aside from the above analytical differences, a number of the products formed under reflux conditions have different acid/base solubility properties from those products prepared from the same metal at room temperature. For example, the product obtained at reflux with aluminum is soluble in cold 0.1 M NaOH while the product obtained at room temperature is insoluble. 
     EXAMPLE III--HIGH TEMPERATURE PROCEDURE 
     A solid sample (typically 100 mg) of each precipitate obtained from the room temperature or reflux procedure is heated in air in a porcelain or glass crucible from room temperature to 600° C. in 15 min, held at 600° for 3 hr, and then allowed to cool to room temperature in the oven (typically 2 hr). The colors and analytical data for the solid products obtained on standing at room temperature are shown in Tables III and IV. 
     
                       TABLE III______________________________________High Temperature Products(prepared from room temperature products)M             Color of Product______________________________________Al            White powderCo            Blue foamed hard lumpsCr            Gray brown sof powderCu            Foamed pale-green solidFe            Off-white chalky chunksMn            Hard off-white massV             Shiny hard green-gold solidZn            Gray hard solid______________________________________ 
    
     
                       TABLE IV______________________________________High Temperature Products(prepared from reflux products)                  Anal. (%).sup.1Product      Color       FW.sup.2                            M    P    N______________________________________AlPO.sub.4   White powder                    244     21.7 20.9 0                            22.1 25.4 0CO.sub.22 (P.sub.3 O.sub.2).sub.5        Foamed blue 1921    65.6 24.2 0        solid               67.5 24.2 0Cr.sub.2 (P.sub.2 O.sub.5).sub.2 O.sub.3.13H.sub.2 O        Brown powder                    770     14.0 15.7 0                            13.5 16.1 0Cu.sub.3 (PO.sub.2).sub.3        Blue-green  381     47.0 17.1 0        powder              50.1 16.3 0Fe.sub.3 (PO.sub.4).sub.2.8H.sub.2 O        Foamed yellow                    501     33.9 12.6 0        solid               33.3 12.4 0Mg.sub.2 (PO.sub.3).sub.5        Hard white  444     11.1 33.4 0        mass                11.0 34.9 0Mn(P.sub.2 O.sub.5).sub.2 N.7H.sub.2 O        Foamed off- 479     10.7 27.8 3.1        white solid         11.5 25.9 2.9Ni.sub.3 (P.sub.2 O.sub.5).sub.2 N.4H.sub.2 O        Tan, chunky,                    546     31.6 23.0 2.9        soft solid          32.2 22.7 2.6(VO).sub.8 (PO.sub.4).sub.2 O.sub.5.9H.sub.2 O        Foamed hard 967     41.1 6.4  0        black beads         42.1 6.4  0Zn.sub.11 (PO.sub.3).sub.10        Hard gray solid                    1509    49.5 21.8 0                            47.6 20.5 0______________________________________ .sup.1 Second line in each entry shows calculated elemental analysis. .sup.2 Calculated. 
    
     As can be seen from the analytical data presented in Table IV, heating precipitates from reflux experiments at 600 ° C. for three hours gives orthophosphate products only with Al, Fe and V. All other products are unusual phosphorus-containing compounds. Only two products (Mn and Ni) contain any detectable N. The pattern of variation of the molar P/M ratio in the products is similar to that of the materials that are heated. This means that the formulas and properties of the high temperature products are set by choice of the precursors, as is illustrated further by the data presented in Tables V and VI. Of particular practical importance is the synthesis of foamed (porous) materials in several metal systems. 
     
                                           TABLE V__________________________________________________________________________Comparison of High Temperature Products from PrecursorsMade at Room and Reflux Temperatures                              Anal. (%).sup.1Material Heated Product                 Color     FW.sup.2                              M  P__________________________________________________________________________Cu.sub.63 (P.sub.2 O.sub.5).sub.21 (NH.sub.3).sub.22 O.sub.63.93H.sub.2O.sup.3         Cu.sub.2 (PO.sub.2).sub.3                 Foamed pale green                           316                              37.7                                 27.7                 solid        40.2                                 29.4Cu.sub.2 [(PN).sub.3 O.sub.4 (NH.sub.2).sub.2 ].7H.sub.2 O.sup.4           Cu.sub.3 (PO.sub.4).sub.2                 Blue-green powder                           381                              47.0                                 17.1                              50.1                                 16.3__________________________________________________________________________ .sup.1 Second line of each entry gives calculated elemental data for assigned product. .sup.2 Calculated. .sup.3 Obtained at reflux temperature (see Table II). .sup.4 Obtained at room temperature (see Table I). 
    
     
                       TABLE VI______________________________________Compariston of High Temperature Products from PrecursorsMade at Room and Reflux TemperaturesElement  Product.sup.1    Product.sup.2______________________________________Fe     Off-white chalky chunks                   Foamed yellow solidMn     Hard, off-white solid                   Foamed off-white solidV      Shiny, hard green-gold                   Foamed, hard black beads  solid______________________________________ .sup.1 Precursor made at room temperature. .sup.2 Precursor made at reflux temperature. 
    
     Products obtained at room temperature or reflux exhibit extremely weak X-ray powder patterns, indicating that they are amorphous. The main effects of treatment at 600° C. are sharpening of ν P-O  ir bands, the appearance of strong ν M-O  bands (at ca. 600 cm -1  for M II  and 1100 cm -1  for V IV ), and the appearance of sharp X-ray powder diffraction peaks, indicating crystallization. 
     The novel solids according to the invention have a wide range of uses depending on their specific properties. For example, the foamable compounds are fire resistant and are useful replacements for organic phosphazenes. Some of the materials, e.g., the high temperature Cr compound and the Ni compound prepared under reflux conditions, are slippery and can be used as lubricants. Protective or lubricant coatings can be formed from those products soluble in acid or base. The high temperature products are useful as metal containing fillers for polymers or copolymers or as metalizing agents for refractory materials. Heated samples can be pelletized, making some products suitable for conductivity and optical measurements. Others are possible supports for metal, alloy and mixed-metal oxide catalysts. 
     Treatment of a suspension of the colorless Al or Zn compounds prepared at room temperature with a molar deficit of copper(II) sulfate in water at room temperature gives a colorless solution and blue solids, the intensity of color increasing with the amount of copper (II) in the treatment solution. Thus, aluminum and zinc in the metal-phosphazene products easily can be ion-exchanged with copper (and, presumably, with other M II  ions) that form stronger bonds to the phosphazene rings than aluminum and zinc, from doping levels up to the level of complete metal replacement. This suggests useful ion-exchange applications, for example in high performance liquid chromatography, in water treatment, and in precious metal recovery from process streams. 
     Of special interest are the extensive decorative possibilities for using the compounds of the invention. For example, glazes can be prepared for porous glasses, e.g., from the vanadium compound, or metal components can be added to a ceramic body, either to the fired ceramic or to the slip as a reactive component. The product prepared from zinc at room temperature can be drawn into metallated fibers. 
     Other embodiments of the invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. It is intended that the specification and the examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.