Homoleptic Rare Earth Dipyridylamides [Ln₂(N(NC₅H₄)₂)₆], Ln = Ce, Nd, Sm, Ho, Er, Tm, Yb, and Sc:  Metal Oxidation by the Amine Melt and in 1,2,3,4-Tetrahydroquinoline with the Focus of Different Metal Activation by Amalgams, Liquid Ammonia, and Microwaves

Abstract

Homoleptic dimeric dipyridylamide complexes of the rare earth elements are obtained by solvent-free oxidation reactions of the metals with melts of 2,2'-dipyridylamine. As the thermal stabilities of the ligand as well as the amide complexes are limiting factors in these high-temperature syntheses, several different metal activation procedures have been investigated: the formation of Ln amalgams and dissolution of the metals in liquid ammonia as well as coupling to microwaves. For comparison with a solvent that shows low solubility of the metals and products, reactions in 1,2,3,4-tetrahydroquinoline were also carried out. For all lanthanides and group 3 metals used homoleptic dimers of the formula [Ln(2)(Dpa)(6)], Ln = Ce (1), Nd (2), Sm (3), Ho (4), Er (5), Tm (6), Yb (7), and Sc (8) and Dpa- = (C5H4N)2N-, were obtained, all containing trivalent rare earth ions with a distorted square antiprismatic nitrogen coordination. Due to the large differences in the ionic radii of the metal ions, two different structure types are found that crystallize in the space groups P2(1)/c and P2(1)/n with the border of the two types being between Tm and Yb. The orientations of two 1,3/1,3-double chelating and linking dipyridylamide ligands (Dpa(-) = (C(5)H(4)N)(2)N(-)) result in different overall orientations of the dimers and thus two structure types. All compounds were identified by single-crystal X-ray analysis. Mid-IR, far IR, and Raman spectroscopy, microanalyses, and simultaneous DTA/TG as well as mass spectrometry regarding their thermal behavior were also carried out to characterize the products. Crystal data for the two types follow. Ce (1): P2(1)/n; T = 170(2) K; a = 1063.0(1), b = 1536.0(1), c = 1652.0(2) pm; beta = 101.60(1) degrees ; V = 2642.2(3) x 10(6) pm(3); R(1) for F(o) > 4sigma(F(o)) = 0.046, wR(2) = 0.120. Sc (8): P2(1)/c; T = 170(2) K; a = 1073.0(1), b = 1506.2(2), c = 1619.8(2) pm; beta = 103.16(9) degrees ; V = 2548.9(5) x 10(6) pm(3); R(1) for F(o) > 4sigma(F(o)) = 0.038, wR(2) = 0.091.

Preparation, characterization and properties of four new trivalent lanthanide complexes constructed using 2-bromine-5-methoxybenzoic acid and 1,10-phenanthroline

“…[1][2][3][4] Lanthanide ions have unique optical, electrical, and magnetic properties due to their special electronic structure. [1][2][3][4] Lanthanide ions have unique optical, electrical, and magnetic properties due to their special electronic structure.…”

Coordination Chemistry of 2,2’-Dipyridylamine: The Gift That Keeps on Giving

“…In this structure there are four dpa ligands that adopt coordination mode VI and only two dpa ligands in the ciscis conformation chelated through mode III. [32,34] Leary et al were able to synthesize and isolate the eight coordinate La isomer that falls in line with the other type II and type III structures; therefore, completing the series of eight coordinate lanthanide complexes from La to Yb. [35] Their synthetic route to the eight coordinate La 2 (dpa) 6 compound was different than that established by Mϋller-Buschbaum and Quitmann.…”

“…[32][33][34][35] Mϋller-Buschbaum and Quitmann have synthesized a series of Ln 2 (dpa) 6 (Ln = La, Ce, Nd, Sm, Gd, Ho, Er, Tm, Yb, and Sc) compounds by stoichiometric redox melt reactions between the lanthanide metal (activated by a mercury amalgam) and dpaH, equation 3. [32,34] The rare earth ions are trivalent in these structures and adopt a distorted square antiprismatic configuration. The homoleptic Ln 2 (dpa) 6 compounds crystallize in three distinct classes based on their relative size: type I) lanthanum (C c ) , type II) cerium to thulium (P2 1 /n), and type III) ytterbium, lutetium, and scandium (P2 1 /c).…”

“…Molecular structure of type II and type III Ln 2 (dpa) 6 complexes. [34] Downloaded by [Monash University Library] at 08:49 10 October 2015 Figure 12. Molecular structure of [Yb 3 N(dpa) 6 ].…”

Frameworks by Solvent‐Free Synthesis of Rare Earth Chlorides with Molten 1,3‐Benzodinitrile and Tailoring of the Particle Size: ∞3[LnCl3{1,3‐C6H4(CN)2}], Ln = Y, Dy, Ho, Er, Yb

“…Thus, it is interesting to investigate the possibility to tailor the properties of coordination polymers and frameworks by a rational synthesis of different particle sizes down to the nanoscale by the use of different reaction conditions and treatments. [12][13][14][15][16][17] For solvent-tions both as chemical scissors and replaces chloride linkages by degrading the rare earth chloride structures, and subsequently forms new 3D-framework structures. [3][4][5][6][7][8] This chemistry therefore strongly depends on the solvents used.…”