Five Co(ii) coordination polymers with different counter anions based on [3,5-di(4H-1,2,4-triazol-4-yl)benzoato]− ligand: directed synthesis, structures and magnetic properties

Abstract

As a continuing challenge to obtain the desired coordination polymers in the synthesis stage, the counter ions, the metal–ligand ratio and the involvement of template have great impact on their structure construction and crystal growth. In this paper, three different crystals of coordination polymers 1–3 {{[CoL(μ₂-OH)]}_n (1), {[CoL₂(H₂O)]·H₂O}_n (2), {[Co₃L₃(H₂O)]·3NO₃·4H₂O}_n (3)} {L = [3,5-di(4H-1,2,4-triazol-4-yl)benzoate]⁻} were obtained in one pot with HL and Co(NO₃)₂. By tuning the reactants ratio and employing different templates, each complex could also be synthesized separately. Single-crystal X-ray analyses show that complex 1 exhibited a two-dimensional (2D) layered gek2 net structure. Complex 2 with deprotonated [L]⁻ has two dimensional (2D) nets structure with 3,5L66 topology. Complex 3 displays a new 5,5,6,6-connected three-dimensional (3D) topological network with a point symbol of (4¹⁰·6⁵)(4⁵·6⁵)₂(4⁷·6³)₂(4⁸·6⁷). When the reactant Co(NO₃)₂ was changed to CoCl₂ or CoSO₄, 4 and 5 {{[CoL(Cl)]·H₂O}_n (4) and {[Co₂L₂(SO₄)(H₂O)]·2H₂O}_n (5)} was formed with a similar structure to that of 1. Complexes 4 and 5 are two-dimensional (2D) frameworks with 4,6L26 topology. Five complexes have been characterized by elemental analysis, infrared spectroscopy, powder X-ray diffraction and thermogravimetry measurements. The magnetic properties of 1–5 are also investigated. The magnetic property investigation reveals that complex 1 exhibits frequency-dependent behavior.