Crystal Structure, Thermal Behavior and Vibrational Studies of a New Organic Monoarsenate

NH3(CH2)6NH3 HAsO4.2H2O

M. Belhouchet, M. Gargouri, T. Mhiri*, A. Daoud

Laboratoire de lĺEtat Solide, FacultÚ des Sciences de Sfax, UniversitÚ de Sfax, 3018 Sfax, Tunisia.

* Corresponding Autor. E-mail:

Received: 03 August 2001; revised version accepted :22 February 2002


A new tridimensional organic monoarsenate, NH3(CH2)6NH3 HAsO4.2H2O was synthesized by slow evaporation at room temperature of the system NH2(CH2)6NH2 - H3AsO4 - H2O. It crystallizes in the triclinic space group P with lattice parameters a = 11.389(2)┼, b = 12.797(3)┼, c = 10.348(2)┼, a =107.76(2)░, b = 97.18(2)░, g = 110.09(2)░, V = 1303.6(5)┼3, Z = 4, R1 = 0.045 and wR2 = 0.080 for 3217 observed reflexions. The crystal structure is characterized by the existence of [H4As4O16.2H2O]8- clusters. The [HAsO4 ]2- tetrahedra are associated in pairs through one O-H...O hydrogen bond forming [H2As2O8]4- groups which are themselves connected with two O-H...O hydrogen bonds and two water molecules building [H4As4O16.2H2O]8- clusters. Each cluster is linked with two clusters using O(W) water molecule forming infinite centrosymetric chains parallel to the c axis. These chains are related themselves with two water molecules, building three dimensional anionic layers parallel to the (100) plane. Organic dications, encapsulated between two anionic layers, are linked to [HAsO4 ]2- groups using N-H...O hydrogen bonds.

Infrared of polycrystalline sample of NH3(CH2)6NH3 HAsO4.2H2O was investigated at room temperature. An assignment of bands due to internal modes is proposed.

Keywords: Crystal structure; Organic arsenate; TG-DTA/ DSC; Vibrational study.

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