The synthesis and crystal structure of [NiL(NCS)₂] (L = 3-hydroxyethyl-1,3,5,8,12-pentaazacyclotetradecane)

The reaction of H₂CO and H₂NCH₂CH₂OH with the nickel(II) complex of 1,9-diamino-3,7-diazanonane (2,3,2-tet) in the presence of Et₃N gives the nickel(II) complex of the macrocycle 3-hydroxyethyl-1,3,5,8,12-pentaazacyclotetradecane (L), which can be readily isolated as the perchlorate salt. The reaction of KCNS with the perchlorate salt in aqueous solution gives [NiL(NCS)₂] and the crystal structure of this complex has been determined. The complex is octahedral and trans with the two N-bonded thiocyanates in the axial sites with Ni - NCS bond lengths of 2.106 and 2.145 Å. The equatorial sites are occupied by N₂, N₅, N₈ and N₁₂ with Ni - N bond distances of 2.053 to 2.076 Å, which are typical for octahedral nickel(II) complexes. The ligand has a trans III configuration of the sec-NH centres, leading to chair six-membered rings and gauche five-membered rings. The hydroxyethyl group on N₃ is axial. There is no evidence for hydrogen-bonding interactions involving the hydroxyethyl group in the crystal lattice.