Synthesis and Characterization of Axially Linked Heteroleptic Polymeric and Monomeric Lewis Base Adducts of bis-(2-mercaptobenzothiazolato) Nickel(II) and Its Extraordinary Thermal Decomposition
作者:M.S. Suresh、M. Padmanabhan
DOI:10.14233/ajchem.2013.14564
日期:——
Six coordinated axially bridged heteroleptic polymeric and monomeric Lewis base adducts from coordinatively unsaturated bis-(2-mercaptobenzothiazolato) nickel(II) Ni(mbt)2, [NiC14H8N2S4]} have been synthesized and charecterized by elemental analysis, spectral techniques, magnetic susceptibility measurements and thermal analysis using coordination sphere expansion method. These adducts have general molecular formula [Ni(mbt)2L]n for polymeric adducts and [Ni(mbt)2L*2] for monomeric adducts, where L = pyrazine, 4,4-bipyridine and 4,4-azopyridine, L* = pyridine and 4-amino pyridine. The infrared spectral studies suggested that 2-mercaptobenzothiazole is bidentate coordinating through its nitrogen and sulphur atoms. The bidentate Lewis bases used were capable to act as bridging ligand coordinated to two metal atoms which resulted into octahedral species with MN4S2 chromophore but 4-aminopyridine is coordinating through its pyridyl nitrogen eventhough it was bidentate. The perceptible changes in the spectroscopic parameters like Dq, Nephelauxetic parameter (b) and Racah parameter (B) of all adducts were evaluated and explained. The variation of magnetic behaviour on adduct formation was also studied. Ni(mbt)2 decomposes to yield NiS, a stable residue with Ni(SCN)2 as one of the major intermediate but the adducts show an additional step due to the loss of Lewis bases leaving back the parent compound. The kinetic and thermodynamic parameters were also evaluated using Coats-Redfern equation. In most of the cases, it follows random nucleation, one nucleus on each particle obeying Mampel equation.
利用配位球膨胀法,通过元素分析、光谱技术、磁感应强度测量和热分析,合成了六种由配位不饱和的双-(2-巯基苯并噻唑)镍(II)Ni(mbt)2, [NiC14H8N2S4]} 合成的配位轴桥异极性聚合物和单体路易斯碱加合物。这些加合物的分子通式为:聚合加合物为[Ni(mbt)2L]n,单体加合物为[Ni(mbt)2L*2],其中 L = 吡嗪、4,4-联吡啶和 4,4-氮杂吡啶,L* = 吡啶和 4-氨基吡啶。红外光谱研究表明,2-巯基苯并噻唑是通过其氮原子和硫原子进行双齿配位的。所使用的双齿路易斯碱能够作为桥式配体与两个金属原子配位,从而形成具有 MN4S2 发色团的八面体物种,但 4-氨基吡啶尽管是双齿的,却通过其吡啶基氮配位。对所有加合物的 Dq、Nephelauxetic 参数 (b) 和 Racah 参数 (B) 等光谱参数的明显变化进行了评估和解释。此外,还研究了磁性在加合物形成过程中的变化。Ni(mbt)2分解生成NiS,这是一种稳定的残留物,Ni(SCN)2是主要的中间体之一,但加合物由于路易斯碱的损失而显示出一个额外的步骤,母体化合物又重新返回。我们还使用 Coats-Redfern 方程评估了动力学和热力学参数。在大多数情况下,都是随机成核,每个粒子上都有一个核,符合 Mampel 方程。