Novel K/Mn phosphate hydrates, KMn(HO)[PO] and KMn(HO)[Al(PO)]: hydrothermal synthesis and crystal chemistry.

Two novel K/Mn phosphate hydrates, namely, dipotassium trimanganese dipyrophosphate dihydrate, KMn(HO)[PO], (I), and potassium manganese dialuminium triphosphate dihydrate, KMn(HO)[Al(PO)], (II), were obtained in the form of single crystals during a single hydrothermal synthesis experiment. Their crystal structures were studied by X-ray diffraction. Both new compounds are members of the morphotropic series of phosphates with the following formulae: AM(HO)[PO], where A = K, NH, Rb or Na and M = Mn, Fe, Co or Ni, and AM(HO)[M(PO)], where A = Cs, Rb, K, NH or (HO); M = Mn, Fe, Co or Ni; and M = Al, Ga or Fe. A detailed crystal chemical analysis revealed correlations between the unit-cell parameters of the members of the series, their structural features and the sizes of the cations. It has been shown that a mixed type anionic framework is formed in (II) by aluminophosphate [(AlO)(PO)] layers, with a cationic topology similar to the Si/Al-topology of the crystal structures of feldspars. A study of the magnetic susceptibility of (II) demonstrates a paramagnetic behaviour of the compound.