New <i>M</i> <sup>+</sup>, <i>M</i> <sup>3+</sup>-arsenates – the framework structures of Ag<i>M</i> <sup>3+</sup>(HAsO<sub>4</sub>)<sub>2</sub> (<i>M</i> <sup>3+</sup> = Al, Ga) and <i>M</i> <sup>+</sup>GaAs<sub>2</sub>O<sub>7</sub> (<i>M</i> <sup>+</sup> = Na, Ag)
Acta crystallographica. Section E, Crystallographic communications