J. August Ridenour

RE-p-halobenzoic acid–terpyridine complexes, Part II: structural diversity, supramolecular assembly, and luminescence properties in a series of p-bromobenzoic acid rare-earth hybrid materials

Twenty-four new rare-earth p-bromobenzoic acid complexes, [RE(L1)3(L2)(H2O)]2 (RE = La3+ (1), Ce3+ (2), Pr3+ (3), Nd3+ (4)), [RE(L1)3(L2)(H2O)]2 (RE = La3+ (1′), Ce3+ (2′), Pr3+ (3′), Nd3+ (4′)), [RE(L1)3(L2)]2·H2O (RE = Sm3+ (5), Eu3+ (6), Gd3+ (7), Tb3+ (8)), RE(L1)3(L2)(H2O) (RE = Gd3+ (7′), Tb3+ (8′), Dy3+ (9), Ho3+ (10), Er3+ (11), Tm3+ (12), Yb3+ (13), Lu3+ (14), Y3+ (15)), and RE2(L1)4(L2)2(Ox) (RE = Tm3+ (12′), Yb3+ (13′) Lu3+ (14′)); L1: p-bromobenzoic acid; L2: 2,2′:6′,2′′-terpyridine; Ox: oxalic acid, have been hydrothermally synthesized and structurally characterized by single crystal and powder X-ray diffraction. The series includes binuclear molecular complexes [(La3+–Nd3+), (La′3+–Nd′3+), (Sm3+–Tb3+)], which transition to pseudo-dimeric units (Gd3+–Y3+) as a result of the lanthanide contraction. The range of structures is completed by distinct oxalate-bridged binuclear complexes (Tm3+–Lu3+), formed via in situ synthesis, that appear only with the smallest lanthanides and only from higher temperature syntheses. There are subtle differences in coordination environments between the five structure types as a result of the lanthanide contraction, despite all complexes in this study containing binuclear units. All twenty-four complexes feature halogen- and π-based supramolecular interactions which assemble the molecular complexes into one, two, and three dimensions. Visible and near-IR solid state luminescence spectra were collected on complexes 3, 4, 5, 6, 8, 8′, 9, 12, and 13 and characteristic terpyridine sensitized luminescence was observed.

RE-p-halobenzoic acid–terpyridine complexes, part III: structural and supramolecular trends in a series of p-iodobenzoic acid rare-earth hybrid materials

A series of twenty-one new rare-earth p-iodobenzoic acid complexes, [RE(L1)3(L2)(H2O)]2 (RE = La3+ (1) Ce3+ (2)), [RE(L1)3(L2)]2·H2O (RE = Ce3+ (2′), Pr3+ (3), Nd3+ (4), Sm3+ (5)), Eu3+ (6), Gd3+ (7), Tb3+ (8), Dy3+ (9), Ho3+ (10), Er3+ (11), Tm3+ (12), Yb3+ (13), Lu3+ (14), Y3+ (15)), [RE(L1)3(L2)(H2O)]2 (RE = Yb3+ (13′), Lu3+ (14′), Y3+ (15′)), and RE2(L1)4(L2)2(Ox) (RE = Er3+ (11′), Tm3+ (12′)); L1: p-iodobenzoic acid; L2: 2,2′:6′,2′′-terpyridine; Ox: oxalic acid, have been hydrothermally synthesized and structurally characterized by single crystal and powder X-ray diffraction. The series includes binuclear complexes [(La3+–Ce3+), (Ce3+–Y3+)], mononuclear complexes (Yb3+–Y3+), and oxalate-bridged binuclear complexes (Er3+–Tm3+), formed as a result of in situ ligand synthesis. All twenty-one complexes feature halogen- and π-based supramolecular interactions which assemble the molecular complexes into one, two, and three dimensions. Solid-state visible and near-IR luminescence spectra were collected on complexes 5, 6, 8, 9, 12, and 13 and characteristic emission was observed. The local coordination geometry over the p-iodobenzoic acid series were analyzed and then compared to the previously described and characterized RE-p-chlorobenzoic acid and RE-p-bromobenzoic acid analogues. Additionally, structural trends and supramolecular motifs were extracted from this series of materials and compared with the previously reported p-chloro- and p-bromo materials.

Synthesis, structure, and photoluminescent behaviour of molecular lanthanide–2-thiophenecarboxylate–2,2′:6′,2′′-terpyridine materials

The preparation of a lanthanide series, with the exception of promethium, incorporating 2,2′:6′,2′′-terpyridine (terpy) and 2-thiophenecarboxylate (TC) functionality has been achieved via hydrothermal reaction conditions. The structures of the crystalline products were determined using single crystal X-ray diffraction and bulk purity was confirmed via powder X-ray diffraction and elemental analysis. The series is comprised of four structure types wherein the effects of the lanthanide contraction are manifested in changes in the coordination number and nuclearity of the complexes. From lanthanum through holmium an isomorphous series of symmetric dimers of the general formula [Ln2(terpy)2(TC)4(μ-TC)2(H2O)2]·nH2O (Ln-1, Ln = La–Ho, excluding Pm) was isolated. Using holmium oxide resulted in the formation of Ho-1 whereas use of the holmium chloride precursor resulted in the formation of [Ho2(terpy)2(TC)3(μ-TC)2(H2O)2]TC (Ho-2), that consists of an asymmetric dimer. Beyond Ho, Er–Lu were found to form compounds of the general formula [Ln(terpy)(TC)3(H2O)], the structures of which consist of monomeric units. While Er adopts Er-3, Tm–Lu adopt another structure type (Ln-4, where Ln = Tm, Yb, and Lu), the latter arising from differences in intramolecular hydrogen bonding interactions as well as π–π stacking interactions. The luminescent behaviour of the solid samples was examined and showed ligand-sensitized metal-based visible (Sm, Eu Tb, Dy) and NIR (Nd, Sm, and Yb) emission, with lifetimes up to hundreds of microseconds for select samples. Quantum yields of the visible light emitters have been measured and are additionally presented.

Synthesis, structural analysis, and supramolecular assembly of a series of in situ generated uranyl–peroxide complexes with functionalized 2,2′-bipyridine and varied carboxylic acid ligands

The crystal structures of eight new binuclear peroxo-bridged uranyl (UO22+) complexes containing chelating N-donating ligands (2,2′-bipyridine [BPY] and 4,4′-dibromo-2,2′-bipyridine [BrBPY]) and various O-donating ligands (m-halobenzoic acid (where halo = fluoro, chloro, or iodo), p-toluic acid, 2-thiophenecarboxylic acid, acetic acid, benzoic acid, and p-(bromomethyl)-benzoic acid [BrMeBA]) are reported. Single crystal and powder X-ray diffraction analyses have been used to characterize these materials and provide insight into local coordination environments and supramolecular assembly, including π-stacking and halogen-based interactions. The bridging-peroxide ligands were generated in situ via photoexcitation of the uranyl cation induced by incident sunlight. Notably, five of the eight complexes presented have linear U–O2–U dihedral angles and the non-covalent interactions (NCIs) observed in all complexes suggest a direct influence on this structural feature.

Nine isomorphous lanthanide–uranyl f–f bimetallic materials with 2-thiophenecarboxylic acid and terpyridine: structure and concomitant luminescent properties

A series of nine new 4f–5f lanthanide–uranyl complexes, [(UO2)2(O)(L1)(L2)2]2[UO2(L1)3]2[Ln2(L1)6(L2)2]·2H2O, (where L1 and L2 are 2-thiophenecarboxylic acid (C5H3SO2) and 2,2′:6′2′′-terpyridine (C15H11N3), respectively, and Ln = Pr3+ (1), Nd3+ (2), Sm3+ (3), Eu3+ (4), Gd3+ (5), Tb3+ (6), Dy3+ (7), Ho3+ (8), Er3+ (9)), and a uranyl only complex (10), [(UO2)2(O)(L1)(L2)2]2[UO2(L1)3](NO3)·(H2O)3, have been hydrothermally synthesized and characterized with single crystal and powder X-ray diffraction. The nine bimetallic complexes are isomorphous, where only the identity of the lanthanide metal center changes, and contain two distinct uranyl units: a monomer with a formal negative charge and a dimer with a formal positive charge, as well as a single neutral dimeric lanthanide unit. The uranyl only phase (10) contains two unique dimers and a monomer, both similar to the units observed in the heterometallic series. Comparative analyses of speciation and the first coordination spheres between of title complexes and building units in the literature reveal common motifs and a possible structural influence of uranyl units. Further, the units in all complexes are held together primarily through weak hydrogen and offset π-stacking interactions. Raman and visible luminescent spectroscopic techniques found concurrent and selective emission from the uranyl and lanthanide metal centers in certain compounds.