一维[Pd(mnt)2]-自旋体系磁交换作用的密度泛函理论(DFT)分析

4个一维磁链化合物[R-BzPy][Pd(mnt)2](R-BzPy+=对位取代苄基吡啶阳离子;R=Cl(化合物1),Br(化合物2),I(化合物3)和NO2(化合物4))具有相似的晶体堆积结构,即,[Pd(mnt)2]-和R-BzPy+分别形成完全分列的柱状堆积。这一结构特征与其类似化合物[R-BzPy][Ni(mnt)2]相似。但是,[Pd(mnt)2]-和[Ni(mnt)2]-2个系列化合物结构之间存在明显差异:(1)室温下,[R-BzPy][Ni(mnt)2]晶体中[Ni(mnt)2]-和R-BzPy+堆积柱是均匀的;而[R-BzPy][Pd(mnt)2]晶体中[Pd(mnt)2]-和R-BzPy+堆积柱是不均匀的。(2)在两个系列化合物阴离子堆积柱内,相邻[Pd(mnt)2]-分子平面之间距离比相邻[Ni(mnt)2]-分子平面之间距离短。在[Pd(mnt)2]-堆积柱内,[Pd(mnt)2]-离子之间反铁磁交换作用非常强,导致了化合物几乎呈抗磁性。在密度泛函理论框架下,利用对称性破损方法,我们计算了[Pd(mnt)2]-离子之间磁交换常数。在svwn/lanl2dz和bpw91/lanl2dz水平上的计算结果与磁化率拟合结果一致。理论分析揭示,在[Pd(mnt)2]-堆积柱内,[Pd(mnt)2]-离子之间强反铁磁交换与其π-型前线轨道有效重叠密切相关。

Observation of Strongly Antiferromagnetic Exchange Interactions in Four Quasi-One-Dimensional Bis(maleonitriledithiolato) Palladate Monoanion Spin Systems: an Insight from DFT Calculation

Four quasi-one-dimensional (quasi-1D) compounds consist of bis (maleonitriledithiolato)palladate monoanions ([Pd(mnt)2]-) with benzylpyridinium derivatives (R-BzPy+,where R represents the substituent in the para-site of the phenyl ring; R=Cl,Br,I and NO2 for 1 ～4,respectively),which show similar stacking structures to the [Ni(mnt)2]- analogues.The [Pd(mnt)2]- and R-BzPy+ ions form the segregated stacks,each stack is surrounded by four counterion stacks.In comparison of [Pd(mnt)2]- with [Ni(mnt)2]- analogues,the structural distinctions involving both anion and cation stacks are regular for [Ni(mnt)2]- series; while irregular for [Pd(mnt)2]- analogues at room temperature.The inter-plane distances are shorter in [Pd(mnt)2]- than those in [Ni(mnt)2]- stack.There exist strongly antiferromagnetic (AFM) interactions in [Pd(mnt)2]- stack,which magnetic exchange constants are evaluated via broken-symmetry approach in DFT framework,and the calculated results at svwn/lanl2dz and bpw9l/lanl2dz levels are parallel to the experimental results,disclosing that the strongly AFM interactions is due to larger overlap of π-type frontier molecular orbitals.