Thermostructural Behavior in a Series of Lanthanide-Containing Polyoxotungstate Hybrids with Copper(II) Complexes of the Tetraazamacrocycle Cyclam: A Single-Crystal-to-Single-Crystal Transformation Study

• Published in: Inorganic chemistry Vol. 58; no. 7; pp. 4365 - 4375
• Main Authors: Martín-Caballero, Jagoba, Artetxe, Beñat, Reinoso, Santiago, San Felices, Leire, Vitoria, Pablo, Larrañaga, Aitor, Vilas, José Luis, Gutiérrez-Zorrilla, Juan M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.04.2019
• ISSN: 0020-1669; 1520-510X; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b03471

A series of 14 isostructural [Cu­(cyclam)]2[{Cu­(cyclam)}4{(α-GeW11O39)­Ln­(H2O)­(OAc)}2]·18H2O (1-Ln, where Ln = La–Lu; cyclam = 1,4,8,11-tetraazacyclotetradecane) polyoxometalate-based hybrids reported herein represent (i) the first example of a two-dimensional covalent hybrid lattice involving the [{(α-XW11O39)­Ln­(H2O)­(OAc)}2] n− archetype and (ii) the first structural characterization of such a dimeric polyoxotungste for Ln = La and Pr as well as for the combination of X = Ge and Ln = Ce, Nd, Sm, or Lu. Compounds 1-Ln have been characterized by elemental analyses, infrared spectroscopy, and thermogravimetric analysis, and their thermostructural behavior has been monitored by powder and single-crystal X-ray diffraction. The title compounds undergo two single-crystal-to-single-crystal transformations triggered by thermal dehydration leading to the [{Cu­(cyclam)}6{(α-GeW11O39)­Ln­(H2O)­(OAc)}2]·4H2O intermediate (2-Ln, where Ln = Eu or Er) and [Cu­(cyclam)]0.5[{Cu­(cyclam)}5.5{(α-GeW11O39)­Ln­(OAc)}2] (3-Ln, where Ln = Ce or Eu) final anhydrous phases, the latter evidencing a coordinatively unsaturated derivative of the dimeric archetype for the first time. These transitions involve formation and disruption of Cu–OPOM bonds that result in different {Cu­(cyclam)}2+ moieties grafting onto and being released from Keggin surfaces, which reduces the dimensionality of 1-Ln to one-dimensional covalent assemblies for 2-Ln and 3-Ln. While all 3-Ln phases rehydrate fully upon exposure to air for 24 h, the kinetics governing the crystal transitions back toward 1-Ln through 2-Ln depend on the nature of Ln. Under ambient moisture, the anhydrous structures fully revert back to the parent framework for Ln = La–Sm, while the samples containing Eu to Lu afford mixtures of 1-Ln and 2-Ln and require immersion in water for the structural reversion to reach completion. Single-crystal X-ray diffraction analyses of the rehydrated 1R-Ln samples (Ln = Ce, Eu, and Er) support these observations.