Magnesium Phosphate (Mg3 PO4 2): Structure, Properties

The magnesium phosphate is a term that is used to refer to a family of inorganic compounds formed by magnesium, alkaline earth metal and the oxoanion phosphate. The simplest magnesium phosphate has the chemical formula Mg3 PO4 2. The formula indicates that for every two anions PO43– there are three Mg cations2+ interacting with these. Likewise, these compounds can be described as magnesium salts derived from orthophosphoric acid (H3PO4). In other words, the magnesium "coalesces" between the phosphate anions, regardless of their inorganic or organic presentation (MgO, Mg (NO3)2, MgCl2, Mg (OH)2, etc.).

Forms of magnesium phosphate and the neutrality of its charges
Magnesium phosphates are derived from the substitution of H protons3PO4. When orthophosphoric acid loses a proton, it remains as the dihydrogen phosphate ion, H2PO4–. Next, when the acid loses two protons, the hydrogen phosphate ion, HPO, remains42–. Now how do you neutralize these two negative charges? Like Mg2+ it only needs two negative charges to neutralize itself, it interacts with a single HPO ion42–. In this way, magnesium acid phosphate is obtained: MgHPO4. Finally, when all the protons are lost, the phosphate anion PO remains.43–. This requires three Mg cations2+ and from another phosphate to assemble into a crystalline solid. The mathematical equation 2 (-3) + 3 (+2) = 0 helps to understand these stoichiometric ratios for magnesium and phosphate. As a result of these interactions, tribasic magnesium phosphate is produced: Mg3 PO4 2.

However, it is only an image that rather demonstrates the tetrahedral geometry of phosphates. So, the crystal structure involves phosphate tetrahedra and magnesium spheres. In the case of Mg3 PO4 2 anhydrous, the ions adopt a rhombohedral structure, in which the Mg2+ it is coordinated with six O atoms. Right in the center of the structure, the octahedron formed by the six red spheres around the bluish sphere can be located. Likewise, these crystalline structures are capable of accepting water molecules, forming magnesium phosphate hydrates.
This is because they form hydrogen bonds with phosphate ions (HOH-O-PO33–). Furthermore, each phosphate ion is capable of accepting up to four hydrogen bonds; that is, four molecules of water. Like Mg3 PO4 2 it has two phosphates, it can accept eight molecules of water (which happens with the mineral bobierrite). In turn, these water molecules can form hydrogen bonds with others or interact with the positive centers of Mg.2+.