Sensitization of Lanthanoid Luminescence by Organic and Inorganic Ligands in Lanthanoid-Organic-Polyoxometalates

Abstract

The reaction of terbium and europium salts with the lacunary polyxometalate (POM) [As(2)W(19)O(67)(H(2)O)](14-) and 2-picolinic acid (picH) affords the ternary lanthanoid-organic-polyoxometalate (Ln-org-POM) complexes [Tb(2)(pic)(H(2)O)(2)(B-β-AsW(8)O(30))(2)(WO(2)(pic))(3)](10-) (1), [Tb(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (2), and [Eu(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (3). A detailed synthetic investigation has established the conditions required to isolate pure bulk samples of the three complexes as the mixed salts H(0.5)K(8.5)Na[1]·30H(2)O, K(4)Li(4)H(4)[2]·58H(2)O, and Eu(1.66)K(7)[3]·54H(2)O, each of which has been characterized by single crystal X-ray diffraction. Complexes 2 and 3 are isostructural and can be considered to be composed of two molecules of 1 linked through an inversion center with four additional picolinate-chelated lanthanoid centers. When irradiated with a laboratory UV lamp at room temperature, compounds K(4)Li(4)H(4)[2]·58H(2)O and Eu(1.66)K(7)[3]·54H(2)O visibly luminesce green and red, respectively, while compound H(0.5)K(8.5)Na[1]·30H(2)O is not luminescent. A variable temperature photophysical investigation of the three compounds has revealed that both the organic picolinate ligands and the inorganic POM ligands sensitize the lanthanoid(III) luminescence, following excitation with UV light. However, considerably different temperature dependencies are observed for Tb(III) versus Eu(III) through the two distinct sensitization pathways.

A new organic-inorganic hybrid tetrameric polyoxometalate assembled by monovacant Dawson [α2-P2W17O61]10− and trivalent cerium cations

“…Organic functionalized LSLPs have stimulated much recent interest as the organic components were introduced in LSLPs system to prepare hybrid POMs materials with multifunctionality [17]. In recent years, organic-inorganic hybrid LSLPs were constantly reported [18][19][20][21]. Since 2009, we began to concentrate on this branch and targeting the combination of organic carboxylic acids as auxiliary ligands to access the LSLPs.…”

Polyoxometalate-Supported Lanthanoid Single-Molecule Magnets

“…This includes numerous lanthanoid complexes with POM ligands (Ln-POMs), which are of interest for their magnetic, luminescent, catalytic, and electronic properties. [29][30][31][32][33] Ln-POM Single-Molecule Magnets Inorganic POMs offer several advantages over organic species as supporting ligands for Ln-SMMs. Due to the steric bulk and intrinsic diamagnetism of the oxidised forms, they can ensure good magnetic insulation of the lanthanoid ions in neighbouring B molecules, minimising intermolecular interactions that can give rise to unwanted quantum tunnelling and loss of magnetisation.…”

Synthesis and Characterization of 8-Yttrium(III)-Containing 81-Tungsto-8-Arsenate(III), [Y8(CH3COO)(H2O)18(As2W19O68)4(W2O6)2(WO4)]43−

“…Most of the OPEN ACCESS work in this area has been focused on 3d transition metal-containing derivatives [11][12][13][14][15][16][17]. However, also the area of rare earths-containing POMs has undergone a significant expansion in recent years [18][19][20][21][22][23]. Lanthanide ions usually have larger coordination numbers (8,9 or more) than d-block metal ions, and exhibit various coordination geometries [24].…”

“…In addition, the larger size of these lanthanide ions usually restricts their full incorporation into the lacunary POM sites. Such coordination behavior renders lanthanide ions frequently as linkers of two or more lacunary POM units, forming large structures [18][19][20][21][22][23][25][26][27]. Yttrium is formally not a lanthanide, but can be considered as a pseudolanthanide, due to its comparable size and coordination number.…”