Synthesis and Structural Study of Copper(II) Diarsenates

BaMgAs2O7 and BaCoAs2O7 – synthesis, crystal structures and twinning of two new barium diarsenates

“…Single-crystal studies showed that, in fact, non-merohedric twinning was observable as distinctly split reflection spots; the extent of splitting in BaCuAs 2 O 7 was, however, much larger than that in the title compounds. The crystal structure of BaCuAs 2 O 7 was studied independently [18,19] on crystals synthesized by flux methods and under hydrothermal conditions (similar to that used during the present investigation), but none of these authors mentioned any twinning or any problems caused by it.…”

“…4 [16] and a small number of Ba-and Sr-M 2+ -diarsenates (see Table 7 for a comparative compilation of the crystal data). The only M(1) 2+ M(2) 2+ As 2 O 7 diarsenate known so far to crystallize in a different space group is CaCuAs 2 O 7 (space group P2 1 /c [19,20]). …”

“…The space-group symmetry of both title compounds was confirmed as P2 1 /n based on the extinction rules. Their crystal structures were refined starting from the atomic coordinates given for BaCuAs 2 O 7 [19]. Although the structure models appeared to be crystal-chemically correct for both compounds, the refinements initially converged unsatisfactorily (the obtained R(F)-values were ∼10% for BaMgAs 2 O 7 , and ∼25% for BaCoAs 2 O 7 ).…”

“…Prior to our study, the crystal structures of only five diarsenates (pyroarsenates) M(1) 2+ M(2) 2+ As 2 O 7 and a few M(1) 1+ M(2) 3+ As 2 O 7 compounds were reported. Four of the first ones are isotypic with the title compounds and crystallize in space group P2 1 /n: PbCuAs 2 O 7 [16], SrCoAs 2 O 7 [17], BaCuAs 2 O 7 [18,19], and SrCuAs 2 O 7 [19]. Worthy to note is the five-coordinated M(2) position.…”

“…Worthy to note is the five-coordinated M(2) position. CaCuAs 2 O 7 has the same space-group symmetry; however, for the reduced cell the space group setting is P2 1 /c and the structural features are different [19,20].…”