Cavitands Incorporating a Lewis Acid Dinickel Chelate Function as Receptors for Halide Anions

The halide binding properties of the cavitand [Ni₂(L^Me2H4)]²⁺ (<b>4</b>) are reported. Cavitand <b>4</b> exhibits a chelating N₃Ni­(μ-S)₂NiN₃ moiety with two square-pyramidal Ni^IIN₃S₂ units situated in an anion binding pocket of ∼4 Å diameter formed by the organic backbone of the (L^Me2H4)^2– macrocycle. The receptor reacts with fluoride, chloride (in MeCN/MeOH), and bromide (in MeCN) ions to afford an isostructural series of halogenido-bridged complexes [Ni₂(L^Me2H4)­(μ-Hal)]⁺ (Hal = F^– (<b>5</b>), Cl^– (<b>6</b>), and Br^– (<b>7</b>)) featuring a N₃Ni­(μ-S)₂(μ-Hal)­NiN₃ core structure. No reaction occurs with iodide or other polyatomic anions (ClO₄^–, NO₃^–, HCO₃^–, H₂PO₄^–, HSO₄^–, SO₄^2–). The binding events are accompanied by discrete UV–vis spectral changes, due to a switch of the coordination geometry from square-pyramidal (N₃S₂ donor set in <b>4</b>) to octahedral in the halogenido-bridged complexes (N₃S₂Hal donor environment in <b>5</b>–<b>7</b>). In MeCN/MeOH (1/1 v/v) the log <i>K</i>₁₁ values for the 1:1 complexes are 7.77(9) (F^–), 4.06(7) (Cl^–), and 2.0(1) (Br^–). X-ray crystallographic analyses for <b>4</b>(ClO₄)₂, <b>4</b>(I)₂, <b>5</b>(F), <b>6</b>(ClO₄), and <b>7</b>(Br) and computational studies reveal a significant increase of the intramolecular distance between two propylene groups at the cavity entrance upon going from F^– to I^– (for the DFT computed structure). In case of the receptor <b>4</b> and fluorido-bridged complex <b>5</b>, the corresponding distances are nearly identical. This indicates a high degree of preorganization of the [Ni₂(L^Me2H4)]²⁺ receptor and a size fit mismatch of the receptor binding cavity for anions larger than F^–

Structure, Magnetic Behavior, and Anisotropy of Homoleptic Trinuclear Lanthanoid 8‑Quinolinolate Complexes

Three complexes of the form [Ln^III₃(OQ)₉] (Ln = Gd, Tb, Dy; OQ = 8-quinolinolate) have been synthesized and their magnetic properties studied. The trinuclear complexes adopt V-shaped geometries with three bridging 8-quinolinolate oxygen atoms between the central and peripheral eight-coordinate metal atoms. The magnetic properties of these three complexes differ greatly. Variable-temperature direct-current (dc) magnetic susceptibility measurements reveal that the gadolinium and terbium complexes display weak antiferromagnetic nearest-neighbor magnetic exchange interactions. This was quantified in the isotropic gadolinium case with an exchangecoupling parameter of <i>J</i> = −0.068(2) cm^–1. The dysprosium compound displays weak ferromagnetic exchange. Variable-frequency and -temperature alternating-current magnetic susceptibility measurements on the anisotropic cases reveal that the dysprosium complex displays single-molecule-magnet behavior, in zero dc field, with two distinct relaxation modes of differing time scales within the same molecule. Analysis of the data revealed anisotropy barriers of <i>U</i>_eff = 92 and 48 K for the two processes. The terbium complex, on the other hand, displays no such behavior in zero dc field, but upon application of a static dc field, slow magnetic relaxation can be observed. Ab initio and electrostatic calculations were used in an attempt to explain the origin of the experimentally observed slow relaxation of the magnetization for the dysprosium complex