Synthesis, Structures, and Magnetic Behavior of a Series of Copper(II) Azide Polymers of Cu4 Building Clusters and Isolation of a New Hemiaminal Ether as the Metal Complex

Four new neutral copper azido polymers, [Cu4(N3)8(L1)2]n (1), [Cu4(N3)8(L2)2]n (2), [Cu4(N3)8(L3)2]n (3), and [Cu9(N3)18(L4)4]n (4) [L1−4 are formed in situ by reacting pyridine-2-carboxaldehyde with 2-[2-(methylamino)ethyl]pyridine (mapy, L1), N,N-dimethylethylenediamine (N,N-dmen, L2), N,N-diethylethylenediamine (N,N-deen, L3), and N,N,2,2-tetramethylpropanediamine (N,N,2,2-tmpn, L4)], have been synthesized by using 0.5 mol equiv of the chelating tridentate ligands with Cu(NO3)2·3H2O and an excess of NaN3. Single-crystal X-ray structures show that the basic unit of these complexes, especially 1−3, contains very similar CuII4 building blocks. The overall structure of 3 is two-dimensional, while the other three complexes are one-dimensional in nature. Complex 1 represents a unique example containing hemiaminal ether arrested by copper(II). Complexes 1 and 2 have a rare bridging azido pathway: both end-on and end-to-end bridging azides between a pair of CuII centers. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in all four complexes. Density functional theory calculations (B3LYP functional) have been performed on complexes 1−3 to provide a qualitative theoretical interpretation of their overall ferromagnetic behavior.