Ligand Effects on the Structures of Extended Networks of Dicyanamide-Containing Transition-Metal Ions

The structural characterization of a series of complexes of formula [M(dca)2L]n, where dca = dicyanamide, L =
1,10-phenanthroline (phen) [1−4] and 2,9-dimethylphenanthroline (2,9-dmphen) [9−12], and M = Mn (1 and 9), Fe
(2 and 10), Co (3 and 11), and Ni (4 and 12), has revealed the effect of the presence of the methyl substituents
of L on the resulting network. The structure of [Mn(dca)2(phen)]n (1), which is identical to those of 2−4, together
with the investigation of its magnetic properties in the temperature range of 77−300 K were reported elsewhere.
The use of the 4,7-dimethylphenanthroline (4,7-dmphen) as the co-ligand yielded a series of compounds of formula
[M(dca)2(4,7-dmphen)]n [M = Mn (5), Fe (6), Co (7), and Ni (8)], which are isostructural with 1−4. Compounds
containing phen (1−4) and 4,7-dmphen (5−8) are made of two-dimensional grids of metal atoms, each metal atom
being linked to three other metal centers through single (three metal atoms involved) and double (two metal atoms
involved) dca bridges exhibiting the μ-1,5 coordination mode. The isostructural complexes [M(dca)2(2,9-dmphen)]n
(9−12) also have a sheetlike structure, the metal atoms in each layer being linked by two single and one double
μ-1,5-dca units, as in 1−8. However, the topology of the network in 9−12 is different from that in 1−8 because of
the different arrangement of the two single μ-1,5 dca bridges:  cis in 1−8 versus trans in 9−12. The magnetic study
of compounds 1−12 in the temperature range of 1.9−290 K has revealed the occurrence of weak ferromagnetic
(M = Ni) and antiferromagnetic interactions (M = Mn, Fe, and Co). The different magnetic behavior in 1−12 was
analyzed in the light of their structures, and the values of the magnetic interactions were compared to those of
related systems.

一系列通式为[M(dca)₂L]ₙ的配合物的结构表征结果显示，配体L上的甲基取代基会对最终形成的网络结构产生影响。该系列配合物中，dca为二氰酰胺（dicyanamide），L可选1,10-邻菲啰啉（1,10-phenanthroline，phen）[1−4]与2,9-二甲基邻菲啰啉（2,9-dimethylphenanthroline，2,9-dmphen）[9−12]，金属中心M可选锰（Mn，对应化合物1和9）、铁（Fe，对应2和10）、钴（Co，对应3和11）与镍（Ni，对应4和12）。[Mn(dca)₂(phen)]ₙ（化合物1）的结构与2−4完全一致，其在77−300 K温度区间内的磁性质研究已在其他文献中报道。以4,7-二甲基邻菲啰啉（4,7-dimethylphenanthroline，4,7-dmphen）作为辅助配体，可得到通式为[M(dca)₂(4,7-dmphen)]ₙ的一系列化合物（M分别为Mn（5）、Fe（6）、Co（7）与Ni（8）），该系列化合物与1−4为同构体。包含phen的1−4与包含4,7-dmphen的5−8均由金属原子构成的二维网格结构组成，每个金属原子通过单桥（涉及3个金属原子）与双桥（涉及2个金属原子）的二氰酰胺桥连配体连接至另外3个金属中心，此类桥连配体均采取μ-1,5配位模式。同构配合物[M(dca)₂(2,9-dmphen)]ₙ（9−12）同样具有片状层状结构，每层内的金属原子通过2个单μ-1,5-二氰酰胺桥与1个双μ-1,5-二氰酰胺桥相连，与1−8的结构特征一致。但由于两条单μ-1,5-二氰酰胺桥的空间排布方式存在差异，9−12的网络拓扑结构与1−8有所不同：1−8中为顺式排布，而9−12中为反式排布。对1−12在1.9−290 K温度区间内开展的磁学研究表明，体系中存在弱铁磁相互作用（M=Ni）与反铁磁相互作用（M=Mn、Fe、Co）。研究人员结合配合物的结构特征分析了1−12之间各异的磁学行为，并将各体系的磁相互作用数值与相关同类体系进行了对比。