Structure−Spectroscopy Correlation in Distorted Five-Coordinate Cu(II) Complexes: A Case Study with a Set of Closely Related Copper Complexes of Pyridine-2,6-dicarboxamide Ligands

Eight Cu(II) complexes with the [Cu(dmppy)] moiety (dmppyH2 = tridentate ligand N,N‘-dimethylpyridine-2,6-dicarboxamide; H's are dissociable amide protons) and ligands like pyridine, water, N-methylimidazole, substituted
and unsubstituted o-phenanthroline, and bipyridine have been isolated and structurally characterized. The basal
angles of these structurally related five-coordinate Cu(II) complexes (and two previously reported ones) correlate
well with the EPR hyperfine splitting parameter A∥. However, the values of the parameter τ which provides a
measure of the degree of square pyramid versus trigonal bipyramid geometry adopted by these complexes do not
correlate linearly with the A∥ values. It is evident that out-of-plane distortions and ligand strain make calculation
of τ inconsistent in certain sets of five-coordinate Cu(II) complexes. Structure−spectroscopy correlation involving
τ is not feasible in such cases.

已成功分离并结构表征了八个含有[Cu(dmppy)]片段（dmppyH2 = 三齿配体 N,N'-二甲基吡啶-2,6-二羧酰胺；氢原子为可解离的酰胺质子）的Cu(II)配合物，以及诸如吡啶、水、N-甲基咪唑、取代及未取代的邻菲罗啉和双吡啶等配体。这些结构相关的五配位Cu(II)配合物的基面角（包括先前报道的两个）与EPR超精细分裂参数A∥具有良好的相关性。然而，表征这些配合物采用的四面体与三角双锥几何构型程度的参数τ的数值并未与A∥值呈线性相关。显然，平面外畸变和配体张力使得在某些五配位Cu(II)配合物系列中τ的计算存在不一致性。在这些情况下，涉及τ的结构-光谱相关性研究是不可行的。