Structural diversity and magnetic properties in 1D and 2D azido-bridged cobalt(ii) complexes with 1,2-bis(2-pyridyl)ethylene

Abstract

By utilizing a flexible co-ligand 1,2-bis(2-pyridyl)ethylene (2,2′-bpe), two new azido-bridged cobalt(II) complexes with the formulae [Co₃(N₃)₆(OH₂)₂(2,2′-bpe)₂]_n(2,2′-bpe)_n (1) and [Co(N₃)₂(2,2′-bpe)₂]_n (2) have been synthesized and structurally characterized. Compound 1 shows an uncommon 1D chain comprised of double EO azido bridged five- and six-coordinated Co^II geometries in a unique (–5–5–6–)_n sequence of the coordination number. The 2,2′-bpe acts as a terminal co-ligand and an uncoordinated molecule in the crystal lattice. Moreover the adjacent 1D chain is assembled by C–H⋯π interactions and the intermolecular hydrogen bonding between uncoordinated 2,2′-bpe and coordinated water molecules building a 2D layer. Whereas, compound 2 is a 2D coordination network containing the alternating double EO and double EE bridging modes of azides and ditopic 2,2′-bpe bridges. The magnetic investigation of 1 reveals dominant intra-chain ferromagnetic interactions, with the double EO azide-bridge and weak inter-chain antiferromagnetic interactions, with overall metamagnetic behaviour, having magnetic ordering at 6 K. The magnetic behaviour of 2 shows spin-canted antiferromagnetism below a T_N of 12 K.