I was wondering why the melting point of $\ce{TiCl4}$ was below that of $\ce{TiCl3}$

The melting point of the former is $\ce{-25 Celsius}$ whereas the latter is $\ce{425 Celsius}$ .



-The high melting point of $\ce{TiCl3}$ is mainly due to the short bond length $\ce{Ti-Ti}$ , which infer a strong metallic character to these bonds between titanium ions in $\ce{TiCl3}$.

-While in $\ce{TiCl4}$, the main intermolecular forces are of van der Waals type.

  • $\begingroup$ What leads to this short bond length? Is it less shielding by Cl or greater charge, which would lead to a smaller radius per unit cell? $\endgroup$ – Andy Apr 11 '15 at 15:13
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    $\begingroup$ Most metal chlorides are polymers, wherein the chloride atoms bridge between the metals. TiCl3 (crystallographic form beta) structure consists of chains of TiCl6 octahedra that share opposite faces such that the closest Ti—Ti contact is 2.91 Å. Even, for the other crystallographic forms of TiCl3 (alpha, gamma and delta) where the distance Ti-Ti becomes bigger, the metallic character of the bond is dominant. $\endgroup$ – Yomen Atassi Apr 12 '15 at 4:52
  • $\begingroup$ Oh I see! TiCl3 has a polymer/ crystalline structure but TiCl4 has a molecular structure. That makes sense! Thank you for clarifying! $\endgroup$ – Andy Apr 12 '15 at 16:21

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