Axial-ligand and metal-metal trans influences in binuclear platinum(III) complexes. Crystal structures and spectroscopic properties of K4[Pt2(P2O5H2)4(SCN)2].cntdot.2H2O, K4[Pt2(P2O5H2)4(NO2)2].cntdot.2KNO2.cntdot.2H2O, and K4[Pt2(P2O5H2)4(C3H3N2)2].cntdot.7H2O

The crystal structures of K4[Pt2(pop)4(SCN)2]·2H 2O (1), K4[Pt2(pop)4(NO2) 2]·2KNO2-2H2O (2), and K4[Pt2(pop)4(Im)2]·7H 2O (3) have been determined (pop = diphosphite, P2O5H2; ImH = imidazole). Compound 1: space group P1, with a = 9.509 (7) Å, b = 9.494 (5) Å, c = 9.957 (5) Å, α = 117.19 (4)°, β = 110.88 (4)°, γ = 94.18 (4)°, V = 716.4 (6) Å3, and Z = 1. Compound 2: space group C2/c, a = 16.545 (3) Å, b = 18.091 (7) Å, c = 10.653 (2) Å, β = 92.80°, V = 3185 (1) Å3, Z = 4. Compound 3: space group C2/c, a = 19.419 (8) Å, b = 10.843 (4) Å, c = 16.480 (8) Å, β = 98.29 (3)°, V = 3434 (2) Å3, Z = 4. The Pt-Pt bond lengths in [Pt2(pop)4(XY)]4- complexes vary in the order XY = CH3I [2.782 (1) Å] > (SCN)2 [2.760 (1) Å] > (NO2)2 [2.754 (1) Å] > (Im)2 [2.745 (1) Å] > Cl2 [2.695 (1) Å], a trend that parallels the known trans-influence series for these ligands. The axial platinum-ligand bonds are much longer than normal, revealing that the metal-metal bond also exerts a strong trans influence. With the exception of [Pt2(pop)4(Im)2]4- [E(σ → σ*), 250 nm], increasing E (σ → σ*) values [345 nm, CH3I; 282 nm, Cl2] correlate in a qualitative fashion with decreasing Pt-Pt bond distances.