Extraordinarily Short Pb-Pb Bonds in the New Binary Intermetallic Ti 6Pb 4.8

Ti₆Pb_4.8 is accessible via reactions in a Pb flux starting from the elements in evacuated silica tubes at 680°C. Larger single crystals can be obtained by adding traces of iodine to promote crystal growth. At higher temperatures, Ti₆Pb_4.8 decomposes into Ti₄Pb and Pb. Ti₆Pb_4.8 crystallizes in the hexagonal α-Ti₆Sn₅ type, space group P6₃/mmc, with the lattice dimensions a=939.23(8) and c=579.01(5) pm for Ti₆Pb_4.824(7) (Z=2). While the structure is dominated by the heteronuclear Ti-Pb bonds, linear Ti and Pb chains run parallel to the c axis with interatomic distances being equidistant by symmetry c/2=289.5 pm). This results in a Pb-Pb distance being much shorter than a Pb-Pb single bond (typically 310 pm). Longer homonuclear distances of about 315 pm (Ti-Ti) and between 357 and 374 pm (Pb-Pb) occur perpendicular to the chain direction. All these interactions have bonding character, as the LMTO calculations of Ti₆Pb_4.8 reveal.