Interest in platinum-chain complexes arose from their unusual oxidation states and physical properties. Despite their compositional diversity, isolation of crystalline chains has remained challenging. Here we report a simple crystallization technique that yields a series of dimer-based 1D platinum chains. The colour of the Pt2+ compounds can be switched between yellow, orange and blue. Spontaneous oxidation in air is used to form black Pt 2.33+ needles. The loss of one electron per double salt results in a metallic dz 2 state, as supported by quantum chemical calculations, and displays conductivity of 11 S cm-1 at room temperature. This behaviour may open up a new avenue for controllable platinum chemistry.