Crystal structure of (1-hydroxy-1-phosphono-pentyl)-phosphonic acid dimethyl ammonium salt, C~7~H~21~NO~7~P~2~, and of (1,8- dihydroxy- 1,8,8-tris-phosphono-octyl)-phosphonic acid bis-dimethylammonium salt tetra-hydrate, C~12~H~36~N~2~O~14~P~4~ · 4H~2~O, evidence for trapped alcaline species by bisphosphonic and tetraphosphonic acids in the crystalline state
