Exploring the Intricacies of Ancillary Ligand Effects on 4fn5d1 Ln(II) Ions
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Exploring the Intricacies of Ancillary Ligand Effects on 4fn5d1 Ln(II) Ions

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This dissertation explores the effects of ancillary ligands on reductive lanthanide (Ln) chemistry and describes the isolation of Ln(II)-containing complexes with novel structural or magnetic properties. Chapter 1 demonstrates a molecular approach to developing qubits through the synthesis and reduction of the tris(aryloxide) Lu(III) complex, Lu(OAr*)3 (OAr* = 2,6-Ad2-4-tBu-C6H2O−, where Ad is 1-adamantyl). Potassium reduction of Lu(OAr*)3 in the presence of 2.2.2-cryptand (crypt) generated the formally 4f 145d1 Lu(II) complex, [K(crypt)][Lu(OAr*)3]. The OAr* ligand greatly shielded the [Xe]4f 145d1 Lu2+ ion, which increased its thermal stability and enhanced the amount of s mixing into the 5dz² SOMO. The increase in s character led to a large hyperfine clock transition in its EPR spectrum and one of the largest hyperfine interactions ever observed for a molecular system.In contrast to Chapter 1, which described the synthesis of the sterically saturated Lu(II) complex, Chapter 2 explores the limits of steric unsaturation of isolable Ln(II) ions by employing one of the smaller cyclopentadienyl ligands, (C5H4Me)1−. The reduction of CpMe3Ln(THF) (CpMe = C5H4Me; Ln = Nd, Gd) with KC8 in the presence of 18-crown-6 generated the [(18-crown-6)K(μ-(CpMe))K(18-crown-6)][(CpMe)3Ln] complexes, which were isolated and characterized by X-ray crystallography and EPR spectroscopy. The degree of steric saturation was quantified and comparative analysis found that these complexes were the least sterically saturated Ln(II) complexes reported to date. These results corroborated the hypothesis that degree of shielding of the Ln(II) ion by its ancillary ligands has an influence on the thermal stability of the complex. Chapter 3 describes the synthesis of unusual reduced arene complexes of the Ln(II) ions. These bimetallic lanthanide complexes containing reduced bridging ligands may be of value to the field of single-molecule magnet research because these compounds have shown remarkably enhanced magnetic exchange interactions. Previously, the only four crystallographically characterized examples of bimetallic lanthanide (II) complexes containing reduced arene bridging ligands contain cyclopentadienyl ancillary ligands. Reduction of the tris(amide) complexes, Ln(NR2)3 (Ln = La, Ce; R=SiMe3), with potassium in the presence of toluene and crypt allows the isolation of the reduced arene bridged complexes, [K(crypt)]2[{(R2N)2LnII}2(μ-η6:η6-C6H5Me)], with amide ancillary ligands. The crystallographic and spectroscopic data, as well as computational analysis are consistent with the presence of two Ln(II) ions bridged by a toluene diradical dianion. Reduction of [(THF)(R2N)2Tb]2(μ-Cl)2 with KC8 in the presence of toluene and crypt allows the isolation of the first terbium reduced arene bridged complex, [K(crypt)]3[{(R2N)2TbII}2(μ-η6:η6-C6H5Me)][K(NR2)2(THF)2].

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