  We employ the chemical fragment formalism to perform a targeted
superconductor search in the Nb-Ru-B system, yielding the orthorhombic
metal-rich boride NbRuB, which displays BCS-like superconductivity with a Tc =
3.1 K. NbRuB is derived from the chemical fragments Nb3B2 + Ru3B, in which the
Nb3B2 fragment contains B-B dimers and the Ru3B fragment contains isolated B
atoms. A charge transfer occurs between the fragments. The results indicate
that the fragment formalism is a useful chemical tool for the design of new
intermetallic superconductors much the same way as the charge reservoir concept
has been a useful chemical tool for the design of new copper oxide
superconductors.
