Metal‐Halide–Melem Compounds Based on M₆‐, M₉‐ and M₁₂‐Clusters

Abstract

The polymerization of melamine is known to lead to the formation of melam and melem with increasing temperature. Solid‐state reactions of metal halides with melem (2,6,10‐triamino‐s‐heptazine, C6N7(NH2)3) in the vicinity of 500 °C have resulted in the formation of a number of melem adducts that are structurally characterized. The isotypic series M6X12(melem)4 is represented by compounds with M = Ca, X = Br (1), M = Sr, X = Br (2), I (3); M = Ba, X = I (4); and M = Pb, X = Br (5). A special feature in the crystal structures of these compounds is the presence of M6‐metal halide clusters. M9‐ and M12‐metal cluster appear as face‐sharing double‐clusters in (Pb9Br19)2(Pb1.5Br2)2(melem)3(6) and as triple‐clusters in (Pb12Br25)4(Pb1.67Br2)3(melem)4(7). All compounds are characterized by single‐crystal and powder X‐ray diffraction, and further validated by infrared (IR) spectroscopy and 207Pb and 79/81Br NMR studies on (5). Photoluminescence studies on compound (6) reveal emission at 430 nm while the emission of (5) is completely quenched.