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

Abstract

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.