STRUCTURE AND PROPERTIES OF THE TRANSITION-METAL ZINTL COMPOUNDS A14MNPN11 (A=CA, SR, BA PN=AS, SB)

The compounds A14MnPn11 (A = Ca, Sr, Ba; Pn = As, Sb), have been synth esized by reacting the elements in stoichiometric amounts in welded Nb tubes sealed in quartz ampules at high temperature (1250-degrees-C). Single-crystal X-ray data (130 K, tetragonal, I4(1)/acd (142), Z = 8) were refined for all compounds except Ba14MnAs11: a = 16.688 (8) angst rom, c = 22.266 (9) angstrom (R = 5.82%, R(w) = 6.95%, Ca14MnSb11); a = 17.511 (4), c = 23.321 (7) angstrom, (R = 4.07%, R(w) = 3.93%, Sr14M nSb11); a = 18.394 (3), c = 24.069 (6) angstrom (R = 7.52%, R(w) = 6.9 6%, Ba14MnSb11); a = 15.754 (3), c = 21.037 (7) angstrom (R = 4.09%, R 2 = 8.82%, Ca14Mn As11); a = 16.576 (10), c = 22.167 (14) angstrom (R = 5.70%, R(w) = 4.87%, Sr14MnAs11). These compounds are isostructural to the main-group Zintl compound Ca14AlSb11. Magnetization measurement s performed on powder samples have shown that the antimony compounds a re ferromagnets with ordering temperatures of 65 (Ca), 45 (Sr), and 20 K (Ba), whereas the arsenic compounds are paramagnetic down to 5 K. T he temperature dependence of the resistivity of pressed pellets indica tes that the Sb compounds may be metallic and the As compounds are sem iconductors.