Hexanuclear Molecular Precursors as Tools to Design Luminescent Coordination Polymers with Lanthanide Segregation

Abstract

Solvothermal reactions between hexanuclear complexes with the general chemical formula [Ln 6 (μ 6 -O)(μ 3 -OH) 8 (NO 3 ) 6 (H 2 O) 12 ]•2NO 3 •2H 2 O and 2-bromobenzoic acid (2-bbH) lead to a series of isostructural one-dimensional coordination polymers with the general chemical formula [Ln 2 (2-bb) 6 ] ∞ with Ln = Sm, Eu, Tb, Dy, and Y. These coordination polymers crystallize in the orthorhombic space group Fdd2 (No. 43) with the following cell parameters: a = 29.810(3) Å, b = 51.185(6) Å, c = 11.7913( 14) Å, V = 17992(4) Å 3 , and Z = 16. The europium-and terbium-based derivatives show sizable luminescence intensities under UV excitation. Isostructural heterolanthanide coordination polymers have also been prepared. Their luminescent properties suggest that during the synthetic process the starting hexanuclear complexes are destroyed but strongly influence the distribution of the different lanthanide ions over the metallic sites of the crystal structure. Indeed, it is possible to prepare heterolanthanide coordination polymers in which lanthanide-ion segregation is controlled.

Synthesis, Crystal Structure, and Luminescence Properties of the Iso-Reticular Series of Lanthanide Coordination Polymers Synthesized from Hexa-Lanthanide Molecular Precursors

“…This structural feature supports again the hexa-nuclear complex structuring effect. Indeed, similar straight chain-like molecular motifs have already been observed previously for coordination polymers prepared from hexa-nuclear reactants . The Tb 3+ ion is eight coordinated by eight oxygen atoms that form a slightly distorted triangular dodecahedron (Continuous Shape Measurements (CShM) agreement factor is 0.938) (Table S5).…”

“…Therefore, we have prepared a series of coordination polymers with general chemical formulas [Y x Tb 1– x (4-fb)] ∞ , [Y x Tb 1– x (4-cb)] ∞ , [Y x Tb 1– x (4-bb)] ∞ , [Y x Tb 1– x (3-fb)] ∞ , and [Y x Tb 1– x (3-cb)] ∞ with 0 < x < 1 (Tables S1 and S3) in which the optically nonactive Y 3+ ions act as spacers. These compounds have been prepared from the corresponding hetero-hexa-nuclear complexes [Y 6 x Tb 6–6 x ] with 0 < x < 1 to avoid segregation of the two lanthanide ions . Their overall quantum yields and luminescent lifetimes have been measured (Table ).…”

“…Indeed, similar straight chain-like molecular motifs have already been observed previously for coordination polymers prepared from hexa-nuclear reactants. 61 The Tb 3+ ion is eight coordinated by eight oxygen atoms that form a slightly distorted triangular dodecahedron (Continuous Shape Measurements (CShM) 74 agreement factor is 0.938) (Table S5). Two oxygen atoms are from two coordination water molecules, one from one DMSO coordination molecule and five from five different 4-fb − ligands (Figure 2).…”

“…These compounds have been prepared from the corresponding hetero-hexa-nuclear complexes [Y 6x Tb 6−6x ] with 0 < x < 1 to avoid segregation of the two lanthanide ions. 61 Their overall quantum yields and luminescent lifetimes have been measured (Table 4).…”

“…More recently, it has been shown that the microwave-assisted reaction in acetonitrile, between the same hexa-lanthanide molecular precursor and 2-bromobenzoic acid as ligands, followed by a maturation period in a closed vessel leads to straight molecular chains (Scheme 2). 61 It was assumed that during the maturation the hydrolysis goes on and provokes the opening out of the hexagons. Luminescence evidence supports this assumption, but the driving force (halogen bonds, hydrolysis, carboxylate clip...) of these structural transformations is still unclear.…”