Synthesis and crystal structure of dinuclear cyclopalladated 1,2- and 1,3-bridged squarato complexes

Two new dinuclear Pd(II) cyclometalated complexes of formula [L2Pd2(μ-1,2-sq)(C5H11N)2] (1) and [L2Pd2(μ-1,3-sq)(C5H11N)2]·2[(C5H12N)BF4] (1a) [HL=2,6-dimethylazobenzene], have been synthetized from a reaction of the mononuclear [LPd(acetone)2][BF4] with the piperidinium salt of squaric acid, [C5H12N]2[sq]. The single crystal X-ray analysis of complexes 1 and 1a shows that the sq ligand is found to bridge in both μ-1,2- and μ-1,3-coordination modes. These are the first examples of squarato Pd(II) complexes characterized structurally up to now.