One-Dimensional Coordination Polymers of Lanthanide Cations to Cucurbit[7]uril Built Using a Range of Tetrachloride Transition-Metal Dianion Structure Inducers (original) (raw)

A number of linear coordination polymers have been assembled from lanthanide cations (Ln 3+ ) and cucurbit [7]uril (Q[7]) in the presence of [CuCl 4 ] 2− or [CoCl 4 ] 2− anions acting as inorganic structure inducers in HCl solution. X-ray diffraction analysis has revealed that they form three groups of isomorphous structures. Generally, the complexes of Q[7] with light lanthanide cations (those with atomic number below that of neodymium (Nd 3+ )) are in one group. The other two groups, in which the lanthanide cation has atomic number greater than that of europium (Eu 3+ ), seem to follow no obvious rule. For example, the complexes of Q[7] with Eu 3+ and Gd 3+ cations are in the second group in the presence of [CuCl 4 ] 2− anions, while they are in the third group in the presence of [CoCl 4 ] 2− anions. However, whatever group a given complex belongs to, they all show a common honeycomb-patterned supramolecular assembly, in which [CuCl 4 ] 2− or [CoCl 4 ] 2− anions OPEN ACCESS Polymers 2013, 5 419 form a honeycomb structure. The Ln 3+ cations then coordinate to neighboring Q[7] molecules to form 1D coordination polymers that are inserted into the channels of the honeycomb framework, such that each individual coordination polymer is surrounded by [CuCl 4 ] 2− or [CoCl 4 ] 2− anions. Coordination polymers are described as polymers whose repeat units are coordination complexes. Similar supramolecular architectures are also called metal-organic frameworks (MOFs), as well as coordination networks, with some inconsistency in the distinctions between the terms [1-6]. Coordination polymers span scientific fields such as organic and inorganic chemistry, biology, materials science, electrochemistry and pharmacology and have many potential applications [7]. This interdisciplinary nature has led to extensive study over the past few decades [8]. Cucurbit[n]urils(Q[n]s) [9-14] consist of a rigid hydrophobic cavity of low polarity, accessible through two open polar portals rimmed with carbonyl groups, which can interact with various metal ions [15-26], or their complexes [27-40] or clusters [41-50], Consequently, cucurbit[n]uril(Q[n]s)-based coordination chemistry is becoming an important area of study in cucurbit[n]uril chemistry. In particular, Q[n]s interact with metal ions and form various poly-dimensional coordination polymers [51-60]. For example, Kim et al. first demonstrated one-dimensional coordination polymers alternating between alkali-metal ions (K + or Rb + cation) and Q[6] molecules [51,52]. Chen et al. also demonstrated one-dimensional supramolecular chains constructed from the direct coordination of Q[6]s with Na + cations . In recent years, there has been a trend towards introducing an organic or inorganic species into the metal-Q[n] systems as a "structure inducer" or trigger, since the properties, structural novelties, and functionalities of the resulting coordination polymers have often exceeded those observed in the absence of such agents. Following on from Fedin's work , Thuéry focused on the Q[n] complexation of lanthanides and actinides and demonstrated the formation of a series of lanthanide-Q[n] and uranyl-Q[n] supramolecular assemblies in the presence of added organic ligands . Since a novel potassium-Q[5] supramolecular network was first prepared in the presence of p-hydroxybenzoic acid [60], coordination of metal ions to Q[n]s in the presence of various organic molecules has been extensively studied in our laboratory, and a strategy for inorganic or organic molecule-induced coordination polymers of metal ions to Q[n]s has gradually been established. A series of Q[n]-based poly-dimensional polymers have been obtained by using this strategy.