Diplatinum-(II) and -(III) complexes with bridging µ-diphosphonito-P,P′ or µ-methylenebis(phosphonito)-P,P′ ligands. Synthesis, structure, and nuclear magnetic resonance analysis of the ‘lantern’ complexes. Crystal structures of K4[Pt2{µ-CH2[P(O)OH]2}4]·6H2O and K4[Pt2{µ-CH2[P(O)OH]2}4Cl2]·8H2O

Abstract

The complex K₄[Pt₂{µ-CH₂[P(O)OH]₂}₄]·6H₂O {K₄[Pt₂(pcp)₄]} has been prepared by treating K₂[PtCl₄] with CH₂[PH(O)OH]₂. The structure shows a ‘lantern’ arrangement of phosphorus ligands about the two platinum(II) centres, with a Pt–Pt separation of 2.980 1(2)Å. This complex, K₄[Pt₂(pcp)₄], reacts with halogens X₂(X = Cl, Br, or I) to give diplatinum(III) complexes K₄[Pt₂(pcp)₄X₂] The structure of the dichloro complex K₄[Pt₂{µ-CH₂[P(O)OH]₂}₄Cl₂]·8H₂O shows long Pt–Cl distances of 2.442(1)Å and a short Pt–Pt separation of 2.750 0(3)Å. The complexes [Pt₂(pcp)₄X₂]^4– show X→Pt^III ligand to metal charge transfer bands at 298 (X = Cl), 326 (X = Br), 354 and 454 nm (X = I). The ³¹P-{¹H} and ¹⁹⁵Pt-{¹H} n.m.r. spectra of the complexes [Pt₂(pcp)₄]^4–, [Pt₂(pcp)₄X₂]^4–, [Pt₂(pop)₄]^4–, and [Pt₂(pop)₄X₂]^4–{X = Cl, Br, or I; pop =µ-O[P(O)OH]₂^2–} have been solved by second-order analysis of the nine-spin Pt¹⁹⁵Pt and ten-spin ¹⁹⁵Pt₂ isotopomer mixtures in the solutions. The spectra have been simulated as the [A₄][X]₂[A′₄] spin system using the program PANIC, and as the [A]₄[X]₂[A′]₄ spin system using DSYMPLOT. In the diplatinum(II) complexes ¹J(PtPt) < 1 000 Hz, but in the diplatinum(III) complexes ¹J(PtPt)≈ 7 000–11 000 Hz.