Maciej Grzywa

Crystal structure of potassium and ammonium tetraperoxovanadates (V)

Powder diffraction measurements are fast, and sample preparation does not require time consuming manipulations what is very important for toxic, unstable or explosive samples. In addition, very good results can be also obtained at structure solution level by nowadays methods. Unfortunately, structure solution results can sometimes be biased towards assumed structure models in most popular nowadays ‘direct space search procedures’. However, in typical applications crystal structure studies can be performed using ‘ab initio’ methods. Using this approach the crystal structures of two very unstable tetraperoxovanadates (V) — (NH4)3[V(O2)4] and K3[V(O2)4] — have been ab initio solved from powder diffraction data by direct methods. The two ammonium and potassium salts are isotypic with lattice parameters: a = 6.9769(5), c = 8.211(1) and a = 6.6861(4), c = 7.708(2) Å, V = 399.68(7) Å3 and 344.6(6) Å3, respectively. The space group is I-42m (No. 121) with Z = 2 for both compounds.

Crystal structure of potassium tetraperoxomolybdate (VI) K 2 [Mo(O 2 ) 4 ]

Potassium tetraperoxomolybdate (VI) K 2 [Mo(O 2 ) 4 ] was prepared, and its X-ray powder diffraction pattern was recorded at low temperature (258 K). The unit cell parameters were refined to a =10.7891(2) A, α =64.925(3)°, space group R −3 c (167), Z =6. The compound is isostructural with potassium tetraperoxotungstate (VI) K 2 [W(O 2 ) 4 ] (Stomberg, 1988). The sample of K 2 [Mo(O 2 ) 4 ] was characterized by analytical investigations, and the results of crystal structure refinement by Rietveld method are presented; final R P and R W P are 9.79% and 12.37%, respectively.

X-ray powder diffraction investigations of phenol derivatives

The X-ray powder diffraction patterns of three phenol derivatives—2-chlorophenol, 2,6-dichloro-4-nitrophenol, and 2,6-dichloro-phenoloindophenol tetrahydrate—were collected and the lattice parameters of these compounds were determined. The measurement for 2-chlorophenol was carried out at 250 K in a low-temperature chamber; this compound crystallizes in hexagonal system with a=1.59602(8) nm, c=0.59761(7) nm, space group P6 or P6 3 /m. Investigated at room temperature, 2,6-dichloro-4-nitrophenol and 2,6-dichloro-phenoloindophenol tetrahydrate crystallize in the triclinic system with the unit cell parameters refined to a=0.8169(2) nm, b=1.6637(6) nm, c=0.7440(1) nm, α=96.6(3)°, β=116.19(2)°, γ=78.68°, and space group P-1(2), and a=0.7792(3) nm, b=1.2795(4) nm, c=0.7256(3) nm, α=91.17(5)°, β=96.93(4)°, γ=85.41(3)°, and space group P-1(2), respectively.