Design of a flexible ligand for the construction of a one-dimensional metal-organic coordination polymer

A new ligand LH (where LH = N-(picolinoyl)-biurate) has been prepared and characterized. The presence of three amide linkages make this ligand sufficiently flexible to act as N,N,O donor tridentate blocking ligand in the formation of a one dimensional metal-ligand layer like structure. Reaction of LH and dicyanamide (dca) with Co(NO3)2 · 6H2O gives [CoL(dca)]n (1). In this compound picolinamide modulated ligand L coordinated the central Co(II) ion in a meridonal-fashion. The single crystal X-ray crystallography revealed that in 1, dca acts as μ1,5− singly bridging ligand whereas μ1,5− doubly bridging is the more common type. This gives rise to the 1D undulated waves like structure. The Co(II) centre is surrounded in a distorted square pyramidal coordination geometry. The variable temperature magnetic (VTM) susceptibility measurements show that the global feature of the χMT versus T curve for 1 is characteristic of very weak antiferromagnetic interactions through the dicyanamide ligand and between 300 and 5 K the best fit parameter was determined as J = −3.52 cm−1. The X-ray structure, VTM study and UV–Vis spectrum of the compound show that 1 is a low-spin square-pyramidal compound whereas high-spin compounds are more common for the five coordinated cobalt (II) compounds. The X-band EPR spectrum of 1 at room temperature shows only one isotropic band centred at g = 2.08.

A new picolinamide modulated N,N,O donor ligand has been synthesised and characterized. It was used as blocking ligand association with the unusual single bridging μ1,5− dca coligand for the synthesis of a low-spin five coordinated 1D cobalt(II) compound whereas generally high-spin compound is more commonly found. The VTM study was performed and found antiferromagnetic interaction propagated through the dca bridges beween the cobalt(II) centres and the best fit parameter between 300 and 5 K was determined as J = −3.52 cm−1. The X-band EPR spectrum of the compound at room temperature shows only one isotropic band centred at g = 2.08.Figure optionsDownload as PowerPoint slide