A process for producing a solid ligand-modified poly oxo-hydroxy metal ion material comprising metal ions, ligands and oxo or hydroxy groups, wherein: M represents one or more metal ions selected from Ag 2+, Al 3+, Au 3+, Be 2+, Ca 2+, Co 2+, Cr 3+, Cu 2+, Eu 3+, Fe 3+, Mg 2+, Mn 2+, Ni 2+, Sr 2+, V 5+, Zn 2+ and Zr 2+, L represents one or more ligands which comprise a ligand selected from a carboxylic acid, maltol, ethyl maltol, vanillin, bicarbonate, sulphate, phosphate, silicate, borate, molybdate, selenate, tryptophan, glutamine, proline, valine, histidine, folate, ascorbate, pyridoxine, niacin, adipate, acetate, glutarate, dimethyl glutarate, pimelate, succinate, benzoate and propionate, and wherein the material has a polymeric structure in which the ligands are non-stoichiometrically substituted for the oxo or hydroxy groups and are distributed within the solid phase structure of the metal oxo-hydroxy material and so that the substitution of the oxo or hydroxy groups by the ligands is substantially random; wherein at least some of the ligand integrates into the solid phase so that it displays formal M-L bonding that can be detected by physical analytical techniques and the gross solid ligand-modified poly oxo-hydroxy metal ion material has one or more reproducible physico-chemical properties, the process comprising: (a) mixing the metal ions M and the ligands L at a first pH at which the components are soluble; (b) changing the pH to a second pH to cause a solid precipitate of the solid ligand-modified poly oxo-hydroxy metal ion material to be formed; and (c) separating, and optionally drying, the solid ligand-modified poly oxo-hydroxy metal ion material produced in step (b). M represents one or more metal ions selected from Ag 2+, Al 3+, Au 3+, Be 2+, Ca 2+, Co 2+, Cr 3+, Cu 2+, Eu 3+, Fe 3+, Mg 2+, Mn 2+, Ni 2+, Sr 2+, V 5+, Zn 2+ and Zr 2+, L represents one or more ligands which comprise a ligand selected from a carboxylic acid, maltol, ethyl maltol, vanillin, bicarbonate, sulphate, phosphate, silicate, borate, molybdate, selenate, tryptophan, glutamine, proline, valine, histidine, folate, ascorbate, pyridoxine, niacin, adipate, acetate, glutarate, dimethyl glutarate, pimelate, succinate, benzoate and propionate, and wherein the material has a polymeric structure in which the ligands are non-stoichiometrically substituted for the oxo or hydroxy groups and are distributed within the solid phase structure of the metal oxo-hydroxy material and so that the substitution of the oxo or hydroxy groups by the ligands is substantially random; wherein at least some of the ligand integrates into the solid phase so that it displays formal M-L bonding that can be detected by physical analytical techniques and the gross solid ligand-modified poly oxo-hydroxy metal ion material has one or more reproducible physico-chemical properties, the process comprising: (a) mixing the metal ions M and the ligands L at a first pH at which the components are soluble; (b) changing the pH to a second pH to cause a solid precipitate of the solid ligand-modified poly oxo-hydroxy metal ion material to be formed; and (c) separating, and optionally drying, the solid ligand-modified poly oxo-hydroxy metal ion material produced in step (b). (a) mixing the metal ions M and the ligands L at a first pH at which the components are soluble; (b) changing the pH to a second pH to cause a solid precipitate of the solid ligand-modified poly oxo-hydroxy metal ion material to be formed; and (c) separating, and optionally drying, the solid ligand-modified poly oxo-hydroxy metal ion material produced in step (b).