Superconductivity in Ba_2Sn_3Sb_6 and SrSn_3Sb_4
  Resistivity and ac magnetic susceptibility measurements on Ba2Sn3Sb6 and SrSn3Sb4 indicate that these Zintl compounds display a transition to a superconducting phase at Tc = 3.9 K. The Meissner effect was observed for Ba2Sn3Sb6 under an applied field of 25 Oe. The signatures for superconductivity, such as high and low velocity conduction electrons and lone pairs, are present for both of these compounds. 
Laura Deakin, Robert Lam, Frank Marsiglio, and Arthur Mar