Nickel(II) xanthates with nitrogen heterocycles as bridging ligands

Abstract

New homopolynuclear nickel(II) xanthate complexes with nitrogen donor heterocycles as bridging ligands have been prepared, namely [Ni(Rxa)2(μ-L)]n and [Ni2(Rxa)4(μ-L1)], where R=i-Pr,i-Am; xa=OCS2− L=1,2-bis(4- pyridyl)ethane (bpe), 4,4′-dithiodipyridyl (dtp), 1,2-bis(4- pyridyl)ethylene (dpe), 4,4′-trimethylene-dipyridine (tmd); L1=2,3-bis(2-pyridyl)pyrazine (bpp), 2,4-bis(5,6- diphenyl-1,2,4-triazine-3-yl)pyridine (bdt), or 2,4,6-tris(2- pyridyl)-1,3,5-triazine (tpt). The compounds have been characterized by elemental analyses, i.r. and electronic spectroscopies, magnetochemical and conductivity measurements. The results show that the [Ni(Rxa)2(μ-L)]n complexes are linear polymers in which the nitrogen heterocycles bridge between the nickel(II) ions, which are coordinated by four sulfur and two nitrogen atoms and have trans-octahedral geometry. The nearly constant values of the effective magnetic moment (3.36–3.34 μeff/μB) over the 77–295 K temperature range indicate that exchange interactions are lacking among the paramagnetic centres in the linear structure, [Ni(i-Amxa)2(dpe)]n. The variable- temperature magnetic susceptibilities of the [Ni2(i-Prxa)4(bpp)] (3.00–2.95μeff/μB per Ni atom), [Ni2(i-Prxa)4(bdt)] (2.72–2.63 μeff/μB per Ni atom), and [Ni2(i-Amxa)4(tpt)] (2.76–1.87 μeff/μB per Ni atom) were measured down to liquid nitrogen temperature. In the case of binuclear nickel(II) complexes with bdt or tpt, antiferromagnetic coupling between the nickel(II) ions was detected, giving the exchange integral J=−4.0cm−1 and −29.6cm−1, respectively.