Black shiny platelets of Bi₈Pt₅I₃ and Bi₁₆Pt₁₁I₆ were crystallized from melts of the metals and BiI₃. Despite very similar compositions and close peritectics, a protocol for targeted synthesis could be developed based on differences of the decomposition pressures. Bi₈Pt₅I₃ has a monoclinic crystal structure [space group C2/m; a = 1850.7(2) pm, b = 391.46(3) pm, c = 1340.5(1) pm, β = 113.28(1)°], in which corrugated intermetallic layers alternate with monolayers of non-coordinating iodide ions. The platinum atoms are in square, trigonal-prismatic, or capped trigonal-prismatic coordination by bismuth atoms. Additional covalent bonding between platinum atoms defines flat stripes of five atoms width inside the intermetallic layer. Bi₁₆Pt₁₁I₆ crystallizes in the acentric tetragonal space group P42₁2 with a = 1386.6(1) pm and c = 924.5(1) pm. Corresponding to the higher transition-metal content, the covalent network of platinum atoms is two-dimensional. The node connectivity in the network is three or four; the total coordination number of all platinum atoms is ten. Single layers of iodide ions separate the intermetallic layers. Two-thirds of the iodide ions are coordinating bismuth atoms that protrude from the intermetallic layer, forming [BiI₄] squares. Temperature-dependent electrical resistivity and magnetic susceptibility measurements on polycrystalline powders indicate that Bi₈Pt₅I₃ and Bi₁₆Pt₁₁I₆ are diamagnetic metals. The calculated electronic band structures confirm pseudo two-dimensional metallic character only for Bi₈Pt₅I₃.