Synthesis and characterisation of palladium(II) iodo complexes containing water soluble phosphine ligands. Crystal structures of [PdI2(PTA-H)2][PtI3(PTA)]2 · 2H2O and trans-[PdI2(PTA)2]

The aqueous solution behaviour of the equilibrium related cis-[PdCl2(PTA)2] and [PdCl(PTA)3]Cl complexes has been investigated in the presence of acid and iodide ions. Several of the resulting species were identified and a reaction scheme accounting for identified complexes is proposed. The crystal structures of trans-[PdI2(PTA-H)2][PdI3(PTA)]2 · 2H2O (1) (PTA-H+ = protonated form of PTA) and trans-[PdI2(PTA)2] (2) are reported. The geometry around the Pd(II) metal centre in 1 (for both the cation and anion) and 2 is distorted square planar. The PTA ligands occupy a trans orientation in the cation of 1 and in complex 2. Compound 1 represents a rare example of a Pd(II) system wherein the cation:anion pair, in a 1:2 ratio, are both coordination complexes. It is the first d8 Ni-triad square planar complex containing only one PTA ligand and only the second platinum group metal complex. For the cation in 1, the bond distances and angles are Pd(1)–P(1) = 2.2864(16) Å, Pd(1)–I(1) = 2.6216(7) Å, P(1)–Pd(1)–P(1)′ = 180.00(7)° and P(1)–Pd(1)–I(1) = 87.62(4)°, while in the anion the bond distances are Pd(2)–P(2) = 2.2377(15) Å, Pd(2)–I(4) = 2.5961(13) Å, Pd(2)–I(2) = 2.6328(13) Å, Pd(2)–I(3) = 2.6513(8) Å, while the angles are P(2)–Pd(2)–I(4) = 90.00(5)°, P(2)–Pd(2)–I(2) = 89.69(5)°, I(4)–Pd(2)–I(2) = 179.57(2)°, P(2)–Pd(2)–I(3) = 175.19(4)°, I(4)–Pd(2)–I(3) = 90.29(4)° and I(2)–Pd(2)–I(3) = 90.05(4)°. Bond distances and angles of the coordination polyhedron in 2 are Pd–P = 2.327(3) Å, Pd–I = 2.5916(10) Å, P–Pd–I = 89.13(7)° and P–Pd–P = 180.00(13)°. The average effective- and Tolman cone angles for the two ligands, calculated from the crystallographic data, are 115° and 117° for PTA and PTA-H, respectively.