Exploring the Coordination Chemistry of 3,3′-Di(picolinamoyl)-2,2′-bipyridine: One Ligand, Multiple Nuclearities

The syntheses, structures, and magnetic properties of three new coordination complexes, tetranuclear [Zn2L3(OAc)­(OMe)]2·3MeOH·H2O (3), trinuclear [Ni3(L3)3]·6H2O (4), and a 1-D chain {[Cu2L3(OAc)2]2·H2O}n (6), of a polydentate, doubly deprotonated, 3,3′-disubstituted bipyridine ligand [L3]2‑ are reported. The X-ray crystal structures demonstrate that the ditopic ligand provides a flexible N3 donor set for transition metal ions where each binding pocket shifts from fac to intermediate fac/mer to the mer isomer affording a Ni3 triangle, a Zn4 tetramer, and a 1-D Cu­(II) polymer, respectively. This variation in coordination preference is rationalized with the aim of designing future ligands with controlled coordination modes. Magnetic susceptibility studies on 4 reveal it belongs to the rare family of ferromagnetically coupled [Ni3] clusters. In contrast, magnetic studies of the 1-D chain 6 reveal weak antiferromagnetic interactions due to the poor orbital overlap of the singly occupied Cu­(II) dx2–y2 orbitals with the one-atom bridge that connects them along the Jahn–Teller distortion axis.本文报道了一种双去质子化多齿3,3′-二取代联吡啶配体[L3]²⁻所形成的三种新型配位配合物的合成、结构与磁性质，分别为四核配合物[Zn₂L₃(OAc)(OMe)]₂·3MeOH·H₂O (3)、三核配合物[Ni₃(L₃)₃]·6H₂O (4)以及一维链状配合物{[Cu₂L₃(OAc)₂]₂·H₂O}ₙ (6)。 X射线晶体结构(X-ray crystal structure)分析表明，该双位点配体可为过渡金属离子提供灵活的N₃供体配位环境，各结合位点分别从面式(fac)异构体、面式/经式(intermediate fac/mer)中间态转变为经式(mer)异构体，据此分别构筑得到三核镍三角形簇、四核锌聚集体与一维铜(II)聚合物。 针对配位偏好的这种变化，本文开展了合理化分析，以期为设计具备可控配位模式的未来配体提供指导思路。 对配合物4的磁化率(magnetic susceptibility)研究显示，其隶属于一类罕见的铁磁耦合(ferromagnetically coupled)三核镍簇家族。 与之形成鲜明对比的是，对一维链状配合物6的磁学研究表明，由于单电子占据的Cu(II) d_{x²-y²}轨道与沿姜-泰勒(Jahn-Teller)畸变轴连接的单原子桥之间的轨道重叠程度极低，该体系表现出弱反铁磁相互作用(antiferromagnetic interactions)。