Syntheses and Crystal Structures of Tetrakis(arylamidine)nickel(II) Chloride and Bis[2,4-dipyridyl-1,3,5-triazapentadienato]nickel(II)

The reaction of LiN(SiMe₃)₂ with arylnitrile, followed by the addition of anhydrous NiCl₂ gives ionic complexes of the general formula [Ni{H₂NC(Ar)=NH}₄]Cl₂ (Ar = Ph 1, p-tolyl 2). When the above reaction is carried out with cyanopyridine instead of arylnitrile under the same reaction conditions, neutral complexes of the general formula [{HN=C(Py)N= C(Py)NH}₂Ni] (Py = 4-pyridyl, 3; 3-pyridyl, 4] are obtained. Compound 1 undergoes a metathesis reaction with sodium benzoate to give the neutral complex [(PhCO₂)₂Ni {H₂NC(Ph)=NH}₄] (5). Magnetic susceptibility measurements show that 1-4 are diamagnetic and that 5 is paramagnetic with two unpaired electrons. These results suggest that 1-4 are d⁸ square-planar complexes and 5 is an octahedral complex. The solid state structures of compounds 1-5 were determined by X-ray crystallography. Structural analyses reveal that 1 and 2 form a one-dimensional network through charge-assisted hydrogen bonds; whereas 5 forms a one-dimensional network through hydrogen bonds only. In complexes 3 and 4, the 2,4-dipyridyl-1,3,5-triazapentadienyl ligand behaves as a bidentate ligand forming a six-membered ring with the metal ion.