High Nuclearity Assemblies and One-Dimensional (1D) Coordination Polymers Based on Lanthanide–Copper 15-Metallacrown-5 Complexes (Ln^III = Pr, Nd, Sm, Eu)

Abstract

Complexes {[LnCu(GlyHA)(m-bdc)(HO)][LnCu(GlyHA)(SO)(m-bdc)(HO)]}·(30 + 2x)HO (where GlyHA = glycinehydroxamate, m-bdc = m-phthalate; Ln = Pr and x = 0.21 for compound 1, or Ln = Sm and x = 0.24 for 3) and one-dimensional (1D) coordination polymers {[NdCu(GlyHA)(HO)(m-bdc)]n[NdCu(GlyHA)(HO)(μ-CO)(m-bdc)]}·13nHO (2) and {[EuCu(GlyHA)(HO)](m-bdc)[EuCu(GlyHA)(m-bdc)(HO)]}·17nHO (4) were obtained starting from the 15-metallacrown-5 complexes {[LnCu(GlyHA)(SO)(HO)]}(SO)·6HO (Ln = Pr, Nd, Sm, Eu) by the partial or complete metathesis of sulfate anions with m-phthalate. Compounds 1 and 3 contain unprecedented quadruple-decker neutral metallacrown assemblies, where the [LnCu(GlyHA)] cations are linked by m-phthalate dianions. In contrast, in complexes 2 and 4, these components assemble into 1D chains of coordination polymers, the adjacent {[NdCu(GlyHA)(HO)(m-bdc)]} 1D chains in 2 being separated by discrete [NdCu(GlyHA)(HO)(μ-CO)(m-bdc)]} complex anions. The crystal lattices of 2 and 4 contain voids filled by solvent molecules. Desolvated 4 is able to absorb up to 0.12 cm/g of methanol vapor or 0.04 cm/g of ethanol at 293 K. The isotherm for methanol absorption by compound 4 is consistent with a possible "gate opening" mechanism upon interaction with this substrate. The χT vs T data for complexes 1-4 and their simpler starting materials {[LnCu(GlyHA)(SO)(HO)]}(SO)·6HO (Ln(III) = Pr, Nd, Sm, Eu) were fitted using an additive model, which takes into account exchange interactions between lanthanide(III) and copper(II) ions in the metallamacrocycles via a molecular field model. The exchange interactions between adjacent Cu(II) ions in metallacrown fragments were found to fall in the range of -47 < J < -63 cm. These complexes are the first examples of a Ln(III)-Cu(II) 15-metallacrowns-5 (Ln(III) = Pr, Nd, Sm, Eu), for which values of exchange parameters have now been reported.

Magnetic Properties of LnIII–CuII 15‐Metallacrown‐5 Dimers with Terephthalate (LnIII = Pr, Nd, Sm, Eu)

“…Reactions of terephthalate with initial metallacrown blocks {PrCu 5 } 3+ and {NdCu 5 } 3+ resulted in formation of two isostructural discrete complexes {[LnCu 5 (GlyHA) 5 (CO 3 )(H 2 O) 4 ] 2 ( p ‐bdc)} · 15H 2 O (Ln = Pr ( 1 ) and Nd ( 2 )) with carbonate anions coordinated to the Ln III ions in the 15‐metallacrown‐5 units. The presence of carbonate anions is attributed to carbon dioxide uptake from the air, which is quite typical both for 3d and 4f complexes, and was recently reported for some Ln III –Cu II 15‐metallacrown‐5 complexes …”

“…Formation of discrete dimers {LnCu 5 } 2 with dicarboxylates is quite typical for 15‐metallacrowns‐5 and has been confirmed both in the solid state and in solution for aromatic (terephthalate, dithiophenedicarboxylate, naphthalenedicarboxylate), and aliphatic (adipate, pimelate, muconate, fumarate), dicarboxylates. However, interactions of 15‐metallacrowns‐5 with the same polycarboxylate linkers under quite similar reaction conditions also led to the formation of 1D‐, , [29b], [30a], or 2D‐polymers, tetramers and discrete complexes, where the metallacrowns are non‐oligomerised. [29b] The diversity of oligomerisation levels which were found for 15‐metallacrown‐5 units can presumably result from several factors, such as: i ) the ionic radii and preferred coordination number of the lanthanide ion in the center of the 15‐metallacrown‐5 fragment; ii ) the size and nature of peripheral substituents in the hydroxamate ligand; iii ) the solvent system used for crystallisation, etc .…”

“…It was previously reported that reactions between different 15‐metallacrown‐5 complexes with terephthalate led to the formation of discrete non‐oligomerised and dimerised complexes, 1D‐ or 2D‐polymers depending on the peripheral substituent on the hydroxamic acid and on the central lanthanide(III) ion in the 15‐metallacrown‐5 unit , ,. [28a], , [30a]…”

“…Though 15‐metallacrown‐5 complexes have been known for about 20 years, the magnetic properties of these metallamacrocycles are still not completely understood when compared to other metallacrown structural types, and their investigation continues . Beyond several reports devoted to the qualitative magnetic properties of Ln III ‐containing 15‐metallacrowns‐5 published so far only two reports have demonstrated successful quantitative analysis of experimentally observed χ M T vs. T data , …”

“…The aims of this investigation were: i ) to see which products are obtained from the reactions between {[LnCu 5 (GlyHA) 5 (SO 4 )(H 2 O) 6.5 ]} 2 (SO 4 ) · 6H 2 O (Ln III = Pr III , Nd III , Sm III and Eu III ) and terephthalate; ii ) to examine the magnetic properties of the complexes obtained and test the applicability of the previously proposed additive model, which assumes that exchange interactions between adjacent Cu II ions in {LnCu 5 } 3+ units are dominant; iii ) to obtain values for the parameters which describe magnetic properties of these assemblies with {LnCu 5 } 3+ units (Ln III = Pr III , Nd III , Sm III and Eu III ) and clarify their typical ranges of values.…”