Position of substituent dependent dimensionality in Ln–Cu heterometallic coordination polymers

The reaction of two derivatives of iminodiacetic acid, including H2ANMA (H2ANMA = L-alanine-N-monoacetic acid) and H2MIDA (H2MIDA = N-methyl-iminodiacetic acid), with Ln(NO3)3 (Ln = La, Pr, Nd) and Cu(NO3)2 generates two types of Ln–Cu coordination polymers of different dimensionality, {[Ln2Cu3(ANMA)6](H2O)3} and {[Ln2Cu(MIDA)4(H2O)6](H2O)4} (Ln = La, Pr, Nd). Crystal structure analysis reveals that the position of the methyl group in the two ligands plays an important role, which can be described as follows: (1) adjusting the coordination direction of ligand via the steric hindrance; (2) serving as an electron donating group to enhance the coordination ability of the amino group, where the H2MIDA ligand displays a new coordination mode. It is found that the position of the methyl groups in the two ligands plays a critical role in their structural differences.