Crystal data and nuclear quadrupole resonance spectra of tetra-arsenic triselenide

Abstract

Tetra-arsenic triselenide, As₄Se₃, has been synthesized and isolated in two polymorphs of which α-As₄Se₃ is isostructural with α-As₄Se₃. It is orthorhombic, space group Pnma, with Z= 4, in a unit cell of dimensions a= 9.46(2), b= 7.97(2), c= 10.47 (2)Å. The ⁷⁵As n.q.r. spectrum at 77 K shows three resonances with intensities 1 : 2 : 1 at 60.78 and 61.07 MHz due to the basal As and at 68.97 due to the apical As of the As₄Se₃ molecule. The polymorph β-As₄Se₃ is monoclinic, space group C2/c or Cc, with Z= 16 in a unit cell of dimensions a= 25.62(5), b= 6.52(2), c= 23.01(5)Å, β= 126.6 ± 0.5°. Its n.q.r. spectrum at 77 K shows a number of incompletely resolved lines between 57.5 and 61.0 MHz and between 69.5 and 71.5 MHz, associated with basal and apical As atoms of the As₄Se₃ molecule.