X-ray structure and properties of a dinuclear palladium(II) complex [Pd2(μ-L)4] with four adenine-based bridges in a paddle wheel-like arrangement

A unique dinuclear palladium(II) complex of the general composition [Pd2(μ-L)4]·xDMF (DMF = N,N′-dimethylformamide, x = 2 for 1a, x = 4 for 1b) was prepared by a reaction of K2[Pd(mal)2] and two molar equivalents of 2-chloro-N6-benzyl-9-isopropyladenine (HL); mal stands for the malonate dianion. The prepared complex was fully characterized by elemental analysis, molar conductivity measurements, IR, Raman and NMR spectroscopies, ESI + mass spectrometry, TG/DTA thermal studies (for 1a), and by a single crystal X-ray analysis (for 1b). The results revealed that both metal centres are bridged by four N6-deprotonated 2-chloro-N6-benzyl-9-isopropyladenine molecules (L) in a paddle wheel-like arrangement with the Pd1⋯Pd1A separation of 2.7532(4) Å. Each of the L molecules is coordinated to the Pd(II) ions through its N6 and N7 atoms. The geometry around each of the central atoms can be described as distorted square-planar formed by two N6 and two N7 atoms. The [Pd2(μ-L)4]·xDMF complex represents the first dinuclear transition metal complex with two central ions bridged by four adenine derivatives coordinated through their N6 and N7 atoms.