Structural diversities and magnetic properties of azide-containing coordination polymers based on flexible tetra-pyridinate ligands

Abstract

By utilizing two similar flexible quadritopic ligands, tetrakis(4-pyridyloxymethyl)methane (4-TPOM) and tetrakis(3-pyridyloxymethyl)methane (3-TPOM), four new azido-containing coordination polymers with formulas [Mn₃(4-TPOM)₃(N₃)₆(H₂O)₆]_n (1), [Ni(4-TPOM)(N₃)₂]_n (2), [Mn(3-TPOM)₂(N₃)₂(H₂O)₃(CH₃OH)₄]_n (3) and [Co(3-TPOM)(N₃)₂]_n (4) have been synthesized and structurally characterized. Compound 1 shows a 1D helical chain composed of six-coordinated Mn^II geometries and two-connected tetra-pyridinate ligands. Compound 2 exhibits a three-dimensional framework based on 1D Ni(II) chains with alternating double end-to-end (EE) and double end-on (EO) azide bridges and tetrapyridyl ligands in a highly distorted conformation. Compound 3 shows a 2D layer composed of six-coordinated Mn^II geometries with mono-dentate azide ions and two types of two-connected tetra-pyridinate ligands. Compound 4 exhibits a three-dimensional framework based on 1D Co(II) chains with double end-to-end (EE) azide bridges and tetrapyridyl ligands in a cross-shaped conformation. Magnetic investigations on complexes 2 and 4 revealed antiferromagnetic interactions through the bridged azide ligands. In addition, the magnetic measurement reveals that 2 exhibits weak antiferromagnets, which might be caused by spin canting.