SYNTHESIS, CRYSTAL-STRUCTURE, AND MAGNETIC-PROPERTIES OF NH4CUPO4-CENTER-DOT-H2O

In tdi's paper is described the synthesis and characterization of a ne w layered phosphate, NH4CuPO4H2O, and its magnetic properties. Its cry stal Structure has been solved at room temperature. It crystallizes in the P2(1)/a monoclinic space group; with; a= 7.3907(8), b =7.5191(6), c =8.651(1) Angstrom, beta=94.54(1)degrees and Z=4. The compound; pre sents a layered;; structure, with copper phosphate sheets linked by NH 4+ cations. These layers are parallel to the (001) plane and are inter connected by hydrogen bonds with the NH4+ cations. The layers are form ed by centrosymmetric dimers of CuO5 edge-sharing distorted square pyr amids; crosslinked by corner-sharing phosphate tetrahedra. Each copper (n) cation is bonded to three phosphate oxygens and one water molecule forming the base of the square pyramid, and a-symmetry related phosph ate oxygen in the axial position. The crystal structure of NH4CuPO4 . H2O is related to the layered dittmarite (NH4MgPO4 . H2O) type structu re. However, in the dittmarite family there are MO6 octahedra separate d by the phosphate groups. The title compound is the first one related to the dittmarite 1 family which exhibits layers-formed by centrosymm etric Cu2O8 dimers crosslinked by phosphate tetrahedra. The IR data of this layered phosphate are in good agreement with-the-symmetry observ ed in the phase. EPR data and magnetic studies show the existence of a ntiferromagnetic interactions and the presence of predominant short ra nge interactions. In spite of the layered structure exhibited by the c ompound, the magnetic study indicates that the magnetic behaviour is c onsistent with a dimeric structure with a J/k value of 4.93 K.A 2D ord ering, as exhibited by other related compounds, may be reached at temp eratures lower than 1.8 K.