Polysulfi des of several metals can be prepared by reaction of the metals with excess sulfur in liquid
NH 3 (group IA metals) or by heating sulfur with the molten metal sulfi de. The polysulfi de ion binds
to metals to form coordination compounds in which it is attached to the metal by both sulfur atoms
(as a so-called bidentate ligand). One example is an unusual titanium complex containing the S 5
2
ion that is produced by the following reaction (the use of to denote the bonding mode of the cyclo-pentadienyl ion is explained in Chapter 16):