The first metal chelate of un-substituted 2,6-pyridine-dicarboxamide (pdcam): synthesis, molecular and crystal structure, and properties of [CuII(pdc)(pdcam)] · 2H2O (pdc = 2,6-pyridine-dicarboxylato(2−) ligand)

The compound (2,6-pyridine-dicarboxamide)(2,6-pyridine-dicarboxylato)copper(II) dihydrate ([Cu(pdc)(pdcam)] · 2H2O, compound 1) has been synthesised by reaction of Cu2(CO3)(OH)2, H2pdc acid and pdcam in an aqueous-ethanol medium. The new compound has been characterised by thermal, spectral, magnetic and X-ray diffraction methods. Its crystal consists of a 3D hydrogen bonded network where all N–H(amide) bonds of pdcam act as H-donors for O carboxyl(pdc) or water acceptor atoms. The Cu(II) atom exhibits an elongated octahedral coordination, type 4 + 2. Both pdc and pdcam ligands define a nearly orthogonal dihedral angle (88.4°). The anionic pdc acts as mer-NO2(equatorial) tridentate ligand, supplying three among the four closest to the metal donor atoms (Cu–N 1.913(2), Cu–O 2.022(2) and 2.055(2) Å). The diamide pdcam ligand displays a mer-N(equatorial) + O2(apical) role (Cu–N 2.007(2), Cu–O(amide) 2.295(2) and 2.305(2) Å), thus showing a remarkable conformational flexibility.