Isostructural, "clamshell"-like, neutral dimeric pyrophosphato complexes of general formula [M(bipy)]2(μ-P2O 7) [M = PdII (1) or PtII (2)] were synthesized and studied through single-crystal X-ray diffraction, IR, 31P 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 (Na4P2O7) in water. Compound 2 was prepared through two different routes. The first involved the reaction of the PtIV precursor Na2PtCl6, bipy, and Na4P2O7 in water, followed by reduction in DMF. The second involved the reaction of the PtII precursor K 2PtCl4, bipy, and Na4P2O7 in water. Both complexes crystallize in the monoclinic chiral space group Cc as hexahydrates, 1 · 6H2O (1a, yellow crystals) and 2 · 6H2O (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 · 3.5H2O (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. 31P 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=PO3]+ (Pα) and O=PO3 (Pβ) 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 d8-d8 interaction was present in 1 and 2. © 2011 American Chemical Society.
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|Titolo:||Isostructural PdII and PtII pyrophosphato complexes: Polymorphism and unusual bond character in d8-d8 systems|
|Data di pubblicazione:||2011|
|Appare nelle tipologie:||1.1 Articolo in rivista|