An Obscured or Nonexistent Binary Intermetallic, Co7Pr17, Its Existent Neighbor Co2Pr5, and Two New Ternaries in the System Co/Sn/Pr, CoSn3Pr1-x, and Co2-xSn7Pr3

Four compounds are reported in this study. Co7Pr17 (10, cP96, P2(1)3, a = 13.4147(8) angstrom, Z = 4), either nonexistent or obscured in the Co/Pr phase diagram, has been obtained from a PrBr3 flux. With 29.2 mol % Co, it is close to Co2Pr5 (28.6 mol % Co, 2, C2Mn5 type of structure, mC28, C2/c, a = 16.5471(7) angstrom, b = 6.5107(3) angstrom, c = 7.1067(3) angstrom, beta = 96.230(3)degrees, Z = 4), existent in the Co/Pr phase diagram, produced by arc-melting of a stoichiometric mixture of the metals. The addition of the reactive metal tin to Co/Pr mixtures yielded two new ternary polar intermetallics, CoSn3Pr1-x (x = 0.04, 11, RuSn3La type, cP40, Pm(3) over barn, a = 9.587(3) angstrom, Z = 8) and Co2-xSn7Pr3 (x = 0.78, 12, Ni2-xSn7-yCe3 type, oC24, Cmmm, a = 4.5043(4) angstrom, b = 27.227(2) angstrom, c = 4.5444(3) angstrom, Z = 2). Electronic structure calculations reveal extensive heteroatomic Co-Pr interactions in the binaries with little homoatomic contributions. With tin as the third component in the ternaries, heteroatomic Co-Sn and Sn-Pr bonding interactions are dominant, following the sequence of coordination spheres around Co.