Unusual lanthanoid contraction in crystal structures of 1,10-phenanthroline-2,9-diamides complexes with lanthanoid and yttrium trinitrates and the effect of chlorine substituents

Abstract

Two series of crystal structures of 1:1 complexes of lanthanoid (excluding Pm) and yttrium trinitrates with N,N,N',N'-tetrabutylamide of 1,10-phenanthroline-2,9-dicarboxylic acid (L1) and N,N,N',N'-tetrabutylamide of 4,7-dichloro-1,10-phenanthroline-2,9-dicarboxylic acid (L2) that we started to study in previous works, have been completed. In all complexes, the ligands L1 and L2 coordinate central ions via two phenanthroline nitrogen atoms and two amide oxygen atoms. In complexes formed by early and middle lanthanoids, all three nitrate ions are bidentate, which gives a total coordination number equal to 10. In heavy lanthanoids complexes, starting from Ho for L1 and Yb for L2, coordination number was reduced to 9 because one nitrate turns to a monodentate coordination mode or is replaced by a water molecule. The Ln-N bonds in complexes with L2 are by 0.02–0.06 Å longer that those in L1 complexes throughout the whole lanthanoid row. With a decrease in the radius of the central ion, all coordination bonds become shorter, but their shortening occurs unevenly. In complexes with L1, between Dy and Ho, along with the reduction of the coordination number, the Ln(Y)–N bond lengths decrease abruptly, whereas the bonds Ln(Y)–O(NO3) shorten to a much lesser extent, and the Ln(Y)–O(amide) distances change almost continuously. In complexes with L2, a similar sharp shortening of Ln(Y)–N bonds takes place before the coordination number decreases to 9. The observed structural changes agree with the results of DFT calculations.