Counterion and solvent effects on the primary coordination sphere of copper(II) Bis(3,5-dimethylpyrazol-1-yl)acetic acid coordination compounds

摘要

Four copper(II) coordination compounds with the neutral ligand bis(3,5-dimethylpyrazol-1-yl)acetic acid (Hbdmpza, C_(12)H _(16)N_4O_2) and its anionic form (bdmpza -), namely [Cu(Hbdmpza) _2](HSO_4)_2 (1), [Cu(Hbdmpza) _2]Cl_2 (2), [Cu(bdmpza) _2](CH_3COOH)(H_2O) (3), and [Cu(bdmpza) _2][Cu_2 (O_2CCH_3)_4](4) have been synthesized starting from different metal salts. All the compounds have been fully characterized by physical and analytical methods. In addition, a single-crystal XRD analysis revealed the 3D structure of 1, which exhibits tridentate, vicinal N,N,O-coordination of two symmetry-related Hbdmpza ligands in an elongated octahedral arrangement with four equatorial nitrogen atoms and two axial oxygen atoms. The neutral carboxylic moiety acts as a hydrogen-bond donor to a HSO_4~-counterion. The two hydrogensulfates form a unique hydrogen-bonded pair (HSO_4~-)2 with very short O···O distances (2.59 ?) bridged between adjacent [Cu(HL)_2] ~(2+) coordination units. Also a short O···O contact (2.54 ?) is present between the C-OH and an O of a hydrogensulfate. A characteristic IR C=O vibration is observed at 1700 cm~(-1) for 1 and 2, whereas the ?as(O_2C) vibration is present at 1650 cm~(-1) for 3 and 4. These IR data strongly suggest the presence of Hbdmpza ligands in 1 and 2 and the deprotonated form bdmpza-in 3 and 4. A mononuclear coordination unit [CuL_2], as proven for 1 by X-ray diffraction, is also proposed for the other compounds 2-4.In compound 4, an additional dinuclear [Cu_2 (O_2CCH_3)_4] neutral coordination unit is present, as deduced from the vibration bands ?as(O_2C) at 1600 cm~(-1) and ?_s (O_2C) at 1420 cm~(-1), which are typical of a carboxylate function, and from the two-species analysis of the χMT(T) curve of the magnetic susceptibility data (2J =-322cm~(-1)). Also, the EPR spectra recorded at different temperatures agree with this structure.