Coordination chemistry of platinum and palladium in the solid-state: synthesis of imidazole and pyrazole complexes.

Solid-state reactions of palladium(II) and platinum(II) chloride complexes with imidazole (Him) and pyrazole (Hpz) or their hydrochloride salts are shown to produce metal complex salts and coordination compounds. Thus, K2[MCl4] or MCl2 can be ground with imidazolium chloride ([H2im]Cl) to produce the salts [H2im]2[MCl4] (M = Pd, 1; Pt, 5), which can then be dehydrochlorinated in the solid state to produce the coordination compounds trans-[PdCl2(Him)2] 3 or cis-[PtCl2(Him)2] 6. The complex cis-[PdCl2(Him)2] 2 is produced when Pd(OAc)2 is ground with [H2im]Cl. Reaction of platinum chloride reagents with imidazole (Him) also produces cis-[PtCl2(Him)2] 6, but reaction of imidazole with analogous palladium chloride reagents first produces [Pd(Him)4]Cl24 which then slowly converts to trans-[PdCl2(Him)2] 3. Grinding pyrazolium chloride with K2[MCl4] produces [H2pz]2[MCl4] (M = Pd, 7; Pt, 10), which may also be dehydrochlorinated in the solid state to produce the coordination compounds trans-[PdCl2(Hpz)2] 8 or cis-[PtCl2(Hpz)2] 11. Grinding K2[PdCl4] or PdCl2 with pyrazole gives [Pd(Hpz)4]Cl29, which is then slowly converted into trans-[PdCl2(Hpz)2] 8. Grinding PtCl2 with Hpz generates [Pt(Hpz)4]Cl212, but using K2PtCl4 as the metal source does not generate the same product. The single-crystal structures of 8, a new polymorph of 11 and [H2pz]2[PtCl6]·2H2O (isolated as a decomposition product) are reported for the first time, and the structures of 5 and 10 have been solved ab ibitio from XRPD data.