The present invention is directed to crystalline solids having an empirical formula of M2A2X, wherein M is at least one Group IIIB, IVB, VB, or VIB metal, preferably Cr, Hf, Sc, Ti, Mo, Nb, Ta, V, Zr, or a combination thereof; wherein A is Al, Ga, Ge, In, Pb, or Sn, or a combination thereof; and each X is CxNy, where x + y = 1. In some particular embodiments, the crystalline composition has a unit cell stoichiometry of Mo2Ga2C.