Tetrahalocatecholate Rare Earth Complexes: Dinuclear Motifs with Intramolecular RE···XC(Ar) Interactions

Abstract

The reaction of yttrium or cerium nitrate and tetrachloro- or tetrabromocatecholate (X4Cat2– with X = Cl or Br) has afforded the compounds (Et3NH)2[{Y­(Cl4Cat)­(H2O)2}2(μ-Cl4Cat)2]·2MeOH·2H2O (1-Cl), (Et3NH)2[{Y­(Br4Cat)­(H2O)2}2(μ-Br4Cat)2]·1.5MeCN (1-Br), (Et3NH)4[(Cl4Cat)­(H2O)2Y­(μ-Cl4Cat)2Y­(Cl4Cat)2]·2.5MeOH·3.5H2O (2-Cl), (Et3NH)4[{Y­(Cl4Cat)­(Cl4CatH)­(H2O)}2(μ-Cl4Cat)2]·4H2O (3-Cl), (Et3NH)7[{CeIV(Cl4CatH)­(NO3)­(μ2-Cl4Cat)3}2CeIII]­(NO3)2 (4-Cl), and (Et3NH)4[CeIV(X4Cat)4] (5-X with X = Cl, Br). Small variations of the reaction stoichiometry and crystallization methods allow the isolation of dinuclear yttrium complexes with four, five, and six tetrachlorocatecholate ligands in 1-Cl, 2-Cl, and 3-Cl, respectively. Single crystal X-ray diffraction studies of these compounds reveal a conserved tetrachlorocatecholate-bridged dinuclear yttrium core in each case, but with different peripheral ligation. A key feature of the core unit is Y···ClC­(Ar) intramolecular interactions with a catecholate chloro substituent ortho to one of the coordinating oxygen atoms. The tetrabromocatecholate analogue 1-Br has also been obtained. Applying similar methods to redox-active cerium, rather than yttrium, instead affords an unusual mixed-valence trinuclear {CeIIICeIV 2} complex in 4-Cl, as well as two mononuclear cerium­(IV) complexes in 5-Cl and 5-Br. Density functional theory calculations confirm the [CeIV(Cl4Cat)4]4– charge distribution for 5-Cl.

Elucidation of LMCT Excited States for Lanthanoid Complexes: A Theoretical and Solid-State Experimental Framework

“…To date, lanthanoid complexes with redox-active ligands have been primarily investigated from the perspective of catalysis and reaction chemistry . Some of us have been investigating ortho -dioxolene ligands that can exist in three accessible forms: catecholate (Cat), radical semiquinonate (SQ), and quinonate (Q). ,,, While numerous examples of complexes of these ligands with 3d metals are known, including many cobalt species that exhibit valence tautomerism, complexes with f-block metals are rarer. ,,− The reaction of hydrated europium nitrate with 18- crown -6 and deprotonated tetrahalocatechol (X 2 Cat 2– , where X = Cl, Br) affords neutral mononuclear complexes of general formula [Eu­(18- c -6)­(X 4 Cat)­(NO 3 )] in high yield (Scheme S1). While the previously reported lanthanoid analogues were colorless (for X = Cl) or yellow (for X = Br), the trivalent europium compounds are much darker: dark purple for 1-Eu (X = Cl) and dark green for 2-Eu (X = Br) (Figure ).…”

“…37 Some of us have been investigating ortho-dioxolene ligands that can exist in three accessible forms: catecholate (Cat), radical semiquinonate (SQ), and quinonate (Q). 29,30,51,52 While numerous examples of complexes of these ligands with 3d metals are known, including many cobalt species that exhibit valence tautomerism, 53 complexes with f-block metals are rarer. 29,51,54−61 The reaction of hydrated europium nitrate with 18-crown-6 and deprotonated tetrahalocatechol (X 2 Cat 2− , where X = Cl, Br) affords neutral mononuclear complexes of general formula [Eu(18-c-6)(X 4 Cat)(NO 3 )] in high yield (Scheme S1).…”

Magnetic properties and neutron spectroscopy of lanthanoid-{tetrabromocatecholate/18-crown-6} single-molecule magnets

“…[22] Additionally, it can be employed to measure the phonon spectra for a variety of compounds, [23] and has recently been used to observe spin-phonon coupling in a SMM. [24] Our group is interested in the properties of Ln ions with redox-active ligands such as dioxolenes [25] and tetraoxolenes, [26,27] for applications in single-molecule magnetism and other areas. [28] Previously, the magnetic behaviour of the family of compounds [Ln(18-c-6)(NO 3 )(Br 4 Cat)]•CH 3 CN (I-Ln) was reported by some of us, with slow magnetic relaxation observed for Ce, Nd, Tb, and Dy analogues.…”

Modulation of Slow Magnetic Relaxation in Gd(III)‐Tetrahalosemiquinonate Complexes

“…[24,25] In Ln(III) molecular chemistry, tetraoxolene ligands have been used to bridge Ln(III) ions in dinuclear species, with the tetraoxolene in both the diamagnetic and radical forms, [26][27][28] while diamagnetic catecholate ligands have been utilized in both Ln(III) SMM [29][30][31] and other Ln compounds. [32][33][34][35] One group of compounds for which the Ln(III)-dioxolenes are isolable in their semiquinonate redox form are the family of compounds [Ln(Tp) 2 (DBSQ)] (Tp À = hydro-tris(1-pyrazolyl)borate, DBSQ• À = 3,5-di-tertbutyl-1,2-semiquinonate). [36,37] Notably, the Gd(III) analogue has a relatively large antiferromagnetic magnetic exchange coupling of J ex = À 5.7 cm À 1 between the Gd(III) and the DBSQ• À ligand.…”

“…Of the readily available ligands that can be present as a stable radical, dioxolene and tetraoxolene ligands have found widespread use in transition metal molecular magnetism [24,25] . In Ln(III) molecular chemistry, tetraoxolene ligands have been used to bridge Ln(III) ions in dinuclear species, with the tetraoxolene in both the diamagnetic and radical forms, [26–28] while diamagnetic catecholate ligands have been utilized in both Ln(III) SMM [29–31] and other Ln compounds [32–35] . One group of compounds for which the Ln(III)‐dioxolenes are isolable in their semiquinonate redox form are the family of compounds [Ln(Tp) 2 (DBSQ)] (Tp − =hydro‐tris(1‐pyrazolyl)borate, DBSQ⋅ − =3,5‐di‐tertbutyl‐1,2‐semiquinonate) [36,37] .…”