112764-09-7Relevant academic research and scientific papers
First X-ray crystal structures of nickel(II)-oxocyclam complexes. Effects of the deprotonated amide and of an intramolecular pendant pyridine on the cyclam ligand field
Kimura, Eiichi,Koike, Tohru,Nada, Hiroko,Iitaka, Yoichi
, p. 1036 - 1040 (2008/10/08)
The nickel(II) complex NiIIH-1L (3b) of a 14-membered macrocyclic tetraamine containing a deprotonated amide (oxocyclam) and bearing a phenyl pendant (1b) remains low spin in both the solid state and aqueous solution. On the other hand, the nickel(II) complex NiIIH-1L (5) of oxocyclam with a pyridyl pendant (1c) is always high spin. The X-ray crystal structures of 3b and 5 have been determined to find the effects of the deprotonated amide and of the pendant pyridine on the cyclam ligand field. The crystals of 3b (as the perchlorate salt), C16H25N4ONiClO4·H 2O, are monoclinic, space group P21, with two molecules in the unit cell of dimensions a = 12.019 (5) A?, b = 8.915 (4) A?, c = 10.209 (5) A?, and β = 110.95 (5)°. Crystals of 5 (as the perchlorate salt), C15H24N5ONiClO4·2H 2O, are triclinic, space group P1, with two molecules in the unit cell of dimensions a = 11.669 (6) A?, b = 11.388 (6) A?, c = 8.535 (5) A?, a = 110.51 (6)°, β = 90.44 (5)°, and γ = 96.37 (6)°. These structures were solved by the heavy-atom method and refined by block-diagonal least-squares calculations: for 3b, R = 0.044 for 2005 independent reflections, and for 5, R = 0.060 for 4014 independent reflections. The effects of amide incorporation in place of the NH of cyclam is well demonstrated by comparison with cyclam congeners. The deprotonated oxocyclam can stretch its ring size distinctively with the axial pendant donor. The pH-metric titrations of 3b and 5 have determined complexation constants (log ([NiIIH-1L]aH+/[NiII][L]) at 35°C, I = 0.1 (NaClO4)) of 6.3 ± 0.3 and 8.2 ± 0.3, respectively.
