The growth of hexagonal boron nitride (h-BN) on a Pt(111) surface by decomposition of B-trichloroborazine (ClBNH)(3) leads to two different sets of domain structures as indicated by low-energy electron diffraction (LEED). In addition to a domain structure, for which the top, hcp, and fcc sites of the substrate lattice are occupied by the BN lattice, there is a new type of domain structure with B and N alternatingly occupying the top and bridge sites of the Pt(111) substrate, a structural motif which has not been observed so far. The new domain structures are a result of the precursor chemistry (B-trichloroborazine vs borazine) as well as the lattice mismatch of the substrate [Pt(111) vs h-BN; mismatch similar to 11%].