The crystal structure of magnesium dicarbide

The crystal structure of MgC2 is solved from powder X-ray and neutron diffr action data. Magnesium dicarbide is synthesized from Mg powder and ethyne, with yields of up to 40 wt.% (balance: unreacted Mg and MgO). The X-ray pat tern is indexed on a tetragonal unit cell, with space group P4(2)/mnm sugge sted from systematic extinctions. The unit cell refined from the powder neu tron diffraction data has a=3.9342(7) and c=5.021(1) Angstrom and Z=2. The crystal structure contains C-2 groups, with a triple-bond length of 1.215(6 ) Angstrom, aligned in ... MgCCMgCCMg ... chains having Mg-C bond lengths o f 2.174(4) Angstrom and a weak interaction [2.510(1) A] between Mg and the triple bond of the crossing chains above and below. (C) 1999 Elsevier Scien ce S.A. All rights reserved.