Palladium(I) and palladium(II) unsaturated carboxylate complexes with small molecules: Synthesis and X-ray structure of Pd4(μ-CO)4(μ-trans-CH3CHCHCO2)4 and Pd4(μ-NO)2(μ-CH2C(CH3)CO2)6

New palladium(I) Pd4(μ-CO)4(μ-RCO2)4 (1) and palladium(II) Pd4(μ-NO)2(μ-RCO2)6 (2) (R = CH2CH, CH2C(Me), trans-MeCHCH, trans-CH3CHC(CH3), trans-PhCHCH) carboxylate complexes were prepared and their structures were set from X-ray diffraction analysis. Earlier for carboxylate complexes with alkyl substitutes it was shown that their properties depends on electronic properties of substitutes and are strongly correlated with the strength of corresponding carboxylic acid. Herein we described the same tendency for carboxylates of α-unsaturated carboxylic acids. The acidity of the used acids RCO2H (pKa = 4.25–4.68) lies between acidity of acetic (R = CH3, pKa = 4.76) and monochloroacetic (R = CH2Cl, pKa = 2.85) acids, so we assumed that properties of corresponding palladium complexes should be close to properties of acetates and monochloroacetates, which are very similar. That is perfectly confirmed by obtained data for two classes of polynuclear palladium carboxylate complexes (1 and 2).