The Crystal Structure of (NH4)2Cr2O7. With a Discussion of the Relation between Bond Number and Interatomic Distances.

Synthesis Methods For Ce(CrO4)2 · χH2O And Crystal Structures Of K2CrSO7, (NH4)2Cr2O7 And Na2Cr2O7 · 2H2O

“…The twin volume ratio was refined to 0.505(4)/0.495 (4). There are two potassium cations and one chromatosulfato, CrSO 7 2− , anion in the asymmetric unit. The CrSO 7 2− ion, consisting of one chromate tetrahedron sharing one oxygen atom with one sulfate tetrahedron, has a pseudo syn-C 2v conformation with eclipsed oxygen atoms ( Fig.…”

“…Sporadic cases of hydrated dichromates have been structurally characterized until now: the sodium dichromate tetrahydrate [14], three modifications of lithium dichromate dihydrate [15] and the sodium dichromate dihydrate [16]. Only three structures with pyrosulfate anions were known [17] until recently when Ståhl et al [18] There is evidence for the existence of a "chromo sulfate" anion [19], but no structures of compounds containing CrSO 7 2− ions have been reported until now. Here we present the crystal structure of K 2 CrSO 7 and the redetermination of the structures of (NH 4 New and quick methods to synthesize compounds 1 and 2, giving high yields, are described in the experimental section.…”

“…Three polymorphic forms for potassium dichromate [11] and four modifications for rubidium dichromate [12] have been reported. One crystal structure of ammonium dichromate has been published [7,13]. Sporadic cases of hydrated dichromates have been structurally characterized until now: the sodium dichromate tetrahydrate [14], three modifications of lithium dichromate dihydrate [15] and the sodium dichromate dihydrate [16].…”

“…Solving the crystal structure of (NH 4 ) 2 Cr 2 O 7 , Byström and Wilhelmi [7] made the first structure determination of a compound with the stoichiometric formula A 2 M 2 O 7 , where A is a large cation and M is a small atom with high formal oxidation state. These structures contain M 2 O 7 units consisting of two corner sharing MO 4 tetrahedra.…”

Bond-valence summation for borates

“…R(v) and R(1) designate radii that correspond to the values of the bond valence given between parentheses. By- Wilhelmi (1951), followed by Evans (1960), modified equation (1) to make it applicable to V-O bonds. For our purpose, which is to obtain the bond valence of a B-O bond in terms of its length, we add, to each member of (1), the oxygen radius Ro that will make RB + Ro equal to the B-O bond length L.…”