β‑Technetium Dichloride: Solid-State Modulated Structure, Electronic Structure, and Physical Properties

A second
polymorph of technetium dichloride, β-TcCl2, has
been synthesized from the reaction of Tc metal and chlorine
in a sealed tube at 450 °C. The crystallographic structure and
physical properties of β-TcCl2 have been investigated.
The structure of β-TcCl2 consists of infinite chains
of face sharing [Tc2Cl8] units; within a chain,
the TcTc vectors of two adjacent [Tc2Cl8] units are ordered in the long-range where perpendicular and/or
parallel arrangement of TcTc vectors yields a modulated structure.
Resistivity and Seebeck measurements performed on a β-TcCl2 single crystal indicate the compound to be a p-type semiconductor
while a magnetic susceptibility measurement shows technetium dichloride
to be diamagnetic. A band gap of 0.12(2) eV was determined by reflectance
spectroscopy measurements. Theoretical calculations at the density
functional level were utilized for the investigation of other possible
stable forms of TcCl2.