Isostructural Pd^II and Pt^II Pyrophosphato Complexes: Polymorphism and Unusual Bond Character in d⁸−d⁸ Systems

Abstract

Isostructural, "clamshell"-like, neutral dimeric pyrophosphato complexes of general formula {[M(bipy)](2)(μ-P(2)O(7))} [M = Pd(II) (1) or Pt(II) (2)] were synthesized and studied through single-crystal X-ray diffraction, IR, (31)P NMR spectroscopy, and MALDI-TOF mass spectrometry. Compound 1 was synthesized through the reaction of palladium(II) acetate, 2,2'-bipyridine (bipy), and sodium pyrophosphate (Na(4)P(2)O(7)) in water. Compound 2 was prepared through two different routes. The first involved the reaction of the Pt(IV) precursor Na(2)PtCl(6), bipy, and Na(4)P(2)O(7) in water, followed by reduction in DMF. The second involved the reaction of the Pt(II) precursor K(2)PtCl(4), bipy, and Na(4)P(2)O(7) in water. Both complexes crystallize in the monoclinic chiral space group Cc as hexahydrates, 1·6H(2)O (1a, yellow crystals) and 2·6H(2)O (2a, orange crystals), and exhibit a zigzag chain-like supramolecular packing arrangement with short and long intra/intermolecular metal-metal distances [3.0366(3)/4.5401(3) Å in 1a; 3.0522(3)/4.5609(3) Å in 2a]. A second crystalline phase of the Pt species was also isolated, with formula 2·3.5H(2)O (2b, deep green crystals), characterized by a dimer-of-dimers (pseudo-tetramer) structural submotif. Green crystals of 2b could be irreversibly converted to the orange form 2a by exposure to air or water, without retention of crystallinity, while a partial, reversible crystal-to-crystal transformation occurred when 2a was dried in vacuo. (31)P NMR spectra recorded for both 1 and 2 at various pHs revealed the occurrence of a fluxional protonated/deprotonated system in solution, which was interpreted as being composed, in the protonated form, of [HO=PO(3)](+) (P(α)) and O=PO(3) (P(β)) pyrophosphate subunits. Compounds 1 and 2 exhibited two successive one-electron oxidations, mostly irreversible in nature; however, a dependence upon pH was observed for 1, with oxidation only occurring in strongly basic conditions. Density functional theory and atoms in molecules analyses showed that a d(8)-d(8) interaction was present in 1 and 2.

Acetate-Bridged Platinum(III) Complexes Derived from Cisplatin

“…The larger discrepancy between the computed and experimental Pt–Pt distance for Pt(II) is consistent with a recent observation that standard hybrid DFT functionals have difficulty in modeling weak d 8 –d 8 interactions between Pt(II) centers. 98 Otherwise, the computed platinum-ligand distances agree well with experimental values. Notably, the trans influence of the metal-metal bond in [ 2 ] 2+ and [ 3 ] 2+ is recapitulated, as revealed by the long computed platinum-halide distances.…”

Redox trends in cyclometalated palladium(ii) complexes

“…The Group I palladacycles feature metal-metal interactions and bond order of 0.10-0.15 between two palladium atoms. 27,30 Complexes 7, 8, and 9 belong to the Group II as unfolded palladacycles where no direct metal-metal interactions can be observed but the palladium atoms can influence one another in redox processes. Palladacycle 7 was synthesized from Li 2 [PdCl 4 ] treated with phpy ligand 27 (Fig.…”

Supramolecular Assembly of Diplatinum Species through Weak PtII⋅⋅⋅PtII Intermolecular Interactions: A Combined Experimental and Computational Study

“…For reasons that are still unclear, here we found that LDA (unlike GGA/hybrid functionals) seems to yield reasonable Pt···Pt intermolecular distances as already reported for aurophilic interactions [20] and for Pd II and Pt II pyrophosphato complexes. [21] In addition, we note that the equilibrium Pt···Pt distance becomes smaller when the geometrical optimisation is performed in the presence of dichloromethane as solvent with the PCM model. Given the difficulty of reproducing the experimental geometry (in particular, the Pt···Pt interaction) with DFT, we decided to use the crystallographic structure in most of our subsequent calculations.…”