IR analysis of the carboxylate forms in structurally determined [CuII(κ3-L)2] species isolated from different acidic solutions

Abstract

Several copper(II) coordination compounds with the tridentate κ3-N,N,O bisligand (L = bis(3,5-dimethylpyrazol-1-yl)acetate or its molecular acid form HL = Hbdmpza) were synthesized from different starting metal salts in appropriate acidic water solutions as reported. The XRD single crystal structural analysis reveals neutral acidic ligand form in [Cu(HL)2]·2(HSO4) (1) and [Cu(HL)2]·2Cl (2), while ionic in [Cu(L)2]·(CH3COOH)·(H2O) (3), and [Cu(L)2]·2(H2O) (4). The molecular structures of 2 and 3 are first reported herein, thus enabling a clearer insight for the IR - structural analysis. Two carboxylate C-O bond lengths ranges, namely differing 1.29/1.22 Ǻ for 2, and the same 1.24/1.24 Ǻ for 3, respectively, are in agreement with the single(longer)/double(shorter) character of both bonds for the neutral carboxylic HL in 2, and the same character of both bonds for the carboxylate anionic L- in 3, as seen for the related 1 (HL) and 4 (L-). The most distinguished IR spectra difference for the molecular (HL) / ionic (L-) is at the 1700 cm-1 carboxylate band. The C=O free ligand (HL) double bond position at 1740 cm-1 is most similar with 1702 cm-1 in 1, while a split band at 1697, 1665 cm-1 is seen for 2. On the other hand, the anionic asymmetric carboxylate stretching IR band (`nas(COO−)) for 3 (1642 cm-1) and 4 (1635 cm-1) is found at lower energy region. Thus, the additional band within the same region, as seen only for 3 at 1716 cm-1, is assigned to the network neutral acetic acid C=O double bond.

Keywords

• hbdmpza
• copper
• ir
• structure
• carboxylate