CuII-Azide Polynuclear Complexes of Three Different Building Clusters with the Same Schiff-Base Ligand: Synthesis, Structures, Magnetic Behavior, and Density Functional Theory Studies

Three copper-azido complexes [Cu4(N3)8(L1)2­(MeOH)2]n (1), [Cu4(N3)8(L1)2] (2), and [Cu5(N3)10(L1)2]n (3) [L1 is the imine resulting from the condensation of pyridine-2-carboxaldehyde with 2-(2-pyridyl)­ethylamine] have been synthesized using lower molar equivalents of the Schiff base ligand with Cu­(NO3)2·3H2O and an excess of NaN3. Single crystal X-ray structures show that the basic unit of the complexes 1 and 2 contains CuII4 building blocks; however, they have distinct basic and overall structures due to a small change in the bridging mode of the peripheral pair of copper atoms in the linear tetranuclear structures. Interestingly, these changes are the result of changing the solvent system (MeOH/H2O to EtOH/H2O) used for the synthesis, without changing the proportions of the components (metal to ligand ratio 2:1). Using even lower proportions of the ligand, another unique complex was isolated with CuII5 building units, forming a two-dimensional complex (3). Magnetic susceptibility measurements over a wide range of temperature exhibit the presence of both antiferromagnetic (very weak) and ferromagnetic exchanges within the tetranuclear unit structures. Density functional theory calculations (using B3LYP functional, and two different basis sets) have been performed on the complexes 1 and 2 to provide a qualitative theoretical interpretation of their overall magnetic behavior.以较低摩尔比的希夫碱配体（Schiff base ligand）与三水合硝酸铜[Cu(NO₃)₂·3H₂O]及过量叠氮化钠（NaN₃）反应，合成了三种铜叠氮配合物：[Cu₄(N₃)₈(L₁)₂(MeOH)₂]ₙ(1)、[Cu₄(N₃)₈(L₁)₂](2)与[Cu₅(N₃)₁₀(L₁)₂]ₙ(3)。其中L₁为吡啶-2-甲醛与2-(2-吡啶基)乙胺缩合得到的亚胺配体。单晶X射线衍射结构表征显示，配合物1与2的基本结构单元均含有二价铜四核（Cu(II)₄）结构基元；但由于线性四核结构中外围一对铜原子的桥联模式发生细微变化，二者的基本骨架与整体结构存在显著差异。值得注意的是，此类结构差异仅由合成溶剂体系的改变（从甲醇/水（MeOH/H₂O）体系换为乙醇/水（EtOH/H₂O）体系）所致，并未改变反应物的投料比例（金属与配体的摩尔比为2:1）。当进一步降低配体的投料比例时，我们分离得到了另一种独特的配合物3，其结构基元为Cu(II)₅结构单元，整体形成二维配位聚合物。对该系列配合物进行宽温区磁化率测试表明，四核结构单元内部同时存在极弱的反铁磁相互作用与铁磁相互作用。针对配合物1和2，我们采用B3LYP泛函（B3LYP functional）与两种不同基组开展了密度泛函理论（Density Functional Theory, DFT）计算，对其整体磁学行为进行了定性的理论阐释。