Counterion and Solvent Effects on the Primary Coordination Sphere of Copper(II) Bis(3,5‐dimethylpyrazol‐1‐yl)acetic Acid Coordination Compounds

Abstract

AbstractFour copper(II) coordination compounds with the neutral ligand bis(3,5‐dimethylpyrazol‐1‐yl)acetic acid (Hbdmpza, C12H16N4O2) and its anionic form (bdmpza–), namely [Cu(Hbdmpza)2](HSO4)2 (1), [Cu(Hbdmpza)2]Cl2 (2), [Cu(bdmpza)2](CH3COOH)(H2O) (3), and [Cu(bdmpza)2][Cu2(O2CCH3)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 HSO4– counterion. The two hydrogensulfates form a unique hydrogen‐bonded pair (HSO4–)2 with very short O···O distances (2.59 Å) bridged between adjacent [Cu(HL)2]2+ coordination units. Also a short O···O contact (2.54 Å) 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 νas(O2C) 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 [CuL2], as proven for 1 by X‐ray diffraction, is also proposed for the other compounds 2–4. In compound 4, an additional dinuclear [Cu2(O2CCH3)4] neutral coordination unit is present, as deduced from the vibration bands νas(O2C) at 1600 cm–1 and νs(O2C) 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 = –322 cm–1). Also, the EPR spectra recorded at different temperatures agree with this structure.