From Ion Pairs to Ion Triples through a Hydrogen Bonding-Driven Aggregative Process

Complexes [Ru(arene)(κ3-dpk-OR]X (dpk = 2,2‘-dipyridylketone) were synthesized, and their interionic structure was investigated through an integrated approach based on diffusion and NOE NMR experiments and X-ray single-crystal studies. PGSE NMR results indicated that the highest aggregation tendency occurred for complex 2BF4 (arene = p-cymene and R = OH) that showed aggregation numbers consistent with the main presence of 22BF4+ ion triples (N+ = 1.9 and N- = 1.1, in CD2Cl2 at 0.5 mM). X-ray investigations indicated that a [1 × 1] network of HBs is present involving the two OH moieties of the two cationic fragments belonging to the two independent ion pairs of the asymmetric unit. This dication is likely the central moiety of 22BF4+ ion triples. According to 19F,1H-HOESY NMR interionic studies, the counterion was close to two pyridyl rings belonging to two different cations undergoing a π−π-stacking interaction in CD2Cl2 exactly as observed in the solid state. All of the other complexes having an alyphatic OR-tail showed a much smaller aggregation tendency, leading to ion pairs even when OR = OCH2CH2OH. In the latter case, X-ray studies showed that the terminal OH underwent an intracationic HB with the oxygen atom coordinated at the ruthenium.合成了系列配合物[Ru(芳烃(arene))(κ³-dpk)-OR]X，其中dpk为2,2'-联吡啶酮（2,2'-dipyridylketone）；并基于扩散实验与核Overhauser效应核磁共振（NOE NMR）、X射线单晶衍射的整合研究手段，对其离子间结构展开了系统探究。脉冲梯度自旋回波核磁共振（PGSE NMR）结果表明，配合物2BF4（芳烃为对伞花烃(p-cymene)，R为羟基(OH)）呈现出最强的聚集趋势，其聚集数与体系中主要存在的22BF4⁺离子三重体相符（在0.5 mM的氘代二氯甲烷(CD2Cl2)中，N+=1.9，N-=1.1）。X射线衍射研究显示，体系中存在[1×1]型氢键（hydrogen bond, HB）网络，该网络涉及不对称单元内两个独立离子对所包含的两个阳离子片段的羟基基团。该双阳离子大概率为22BF4⁺离子三重体的核心结构单元。基于氟-1/氢-1异核Overhauser增强光谱核磁共振（19F,1H-HOESY NMR）的离子间研究结果证实，在氘代二氯甲烷体系中，抗衡离子靠近两个不同阳离子的吡啶环，二者间存在π-π堆积相互作用，这与固态下的观测结果完全一致。其余所有带有脂肪族OR尾基的配合物均表现出极弱的聚集趋势，即便当OR为羟乙氧基(OCH2CH2OH)时，体系仍主要以离子对形式存在。针对该情况的X射线研究显示，末端羟基与配位在钌中心的氧原子形成了阳离子内部氢键。