ABSTRACT
A family of heterometallic rings [Me4N]2[CrIII6MII2F8(O2CtBu)16] is reported using tetramethylammonium hydroxide pentahydrate as the source of a template, where M = Zn, Mn, Ni, and Co. The metal cores are octagons with metal-metal edges bridged by one fluoride and two carboxylate ligands. The divalent metal ions are found ordered at positions 1 and 5 in the octagon. The tetramethylammonium cations are above and below the metal plane of the ring in the crystal structure. Magnetic studies show antiferromagnetic coupling between the paramagnetic metal ions present, leading to paramagnetic ground states in each case. 1H NMR spectroscopy confirms that the structure of the {CrIII6CoII2} ring exists in solution, and electron paramagnetic resonance spectroscopy confirms the magnetic structure of the other three rings.
ABSTRACT
A finite chain of thirty-one paramagnetic centers is reported, synthesized by reaction of hydrated chromium fluoride, copper carbonate and pivalic acid in the presence of 1,4,7,10-tetrazacyclododecane (cyclen). Magnetic studies show predominantly anti-ferromagnetic exchange leading to a high density of low-lying spin states and large saturation field.
ABSTRACT
A series of lanthanide complexes bearing organic radical ligands, [Ln(CpR)2(bipy·-)] [Ln = La, CpR = Cptt (1); Ln = Ce, CpR = Cptt (2); Ln = Ce, CpR = Cpâ³ (3); Ln = Ce, CpR = Cpâ´ (4)] [Cptt = {C5H3tBu2-1,3}-; Cpâ³ = {C5H3(SiMe3)2-1,3}-; Cpâ´ = {C5H2(SiMe3)3-1,2,4}-; bipy = 2,2'-bipyridyl], were prepared by reduction of [Ln(CpR)2(µ-I)]2 or [Ce(Cpâ´)2(I) (THF)] with KC8 in the presence of bipy (THF = tetrahydrofuran). Complexes 1-4 were thoroughly characterized by structural, spectroscopic, and computational methods, together with magnetism and cyclic voltammetry, to define an unambiguous Ln(III)/bipy·- radical formulation. These complexes can act as selective reducing agents; for example, the reaction of 3 with benzophenone gives [{Ce(Cp")2(bipy)}2{κ2-O,O'-OPhC(C6H5)CPh2O}] (7), a rare example of a "head-to-tail" coupling product. We estimate the intramolecular exchange coupling for 2-4 using multiconfigurational and spin Hamiltonian methods and find that the commonly used Lines-type isotropic exchange is not appropriate, even for single 4f e-/organic radical pairs.
ABSTRACT
Addition of 1,4,8,11-tetrazacyclotetradecane (cyclam) to a reaction that produces octametallic rings when simpler amines are used, produces {Cr11M2} "pretzels" (M = ZnII or CuII) where the cyclam coordinates to the MII ion which then sits at the centre of a twelve-metal macrocycle. Magnetic studies were fitted using the finite-temperature Lanczos method (FTLM), and the results demonstrate that exchange interactions are transferable from previous exchange-coupled CrIII rings.
ABSTRACT
The trinuclear complexes [{PdI2(pyCl)}3(L1)] C1 and [{PdI2(pyCl)}3(L2)] C2, where pyCl = 3-chloropyridine, L1 = methyl(cyclotriguaiacylenyl)methylbenzimidazol-2-ylidene and L2 = benzyl(cyclotriguaiacylenyl)methylbenzimidazol-2-ylidene, each feature three palladium N-heterocyclic carbene (NHC) centres tethered onto a host-type cyclotriguaiacylene scaffold. Crystal structures of different solvates of complex C1 reveal different host-guest motifs including intra-cavity binding of dioxane guests concomitant with intramolecular halogen bonding interactions of C1. Mononuclear NHC analogues of C1 and C2, namely [PdI2(pyCl)(L3)] C3 and [PdI2(pyCl)(L4)] C4, where L3 = (3-chloropyridyl)-1-(2-methoxyphenyoxy)methyl-3-methylbenzimidazol-2-ylidene and L4 = (3-chloropyridyl)-1-(2-methoxyphenyoxy)methyl-3-benzylbenzimidazol-2-ylidene, were also synthesised and their crystal structures determined. Complexes C1-C4 are competent catalysts for Suzuki Miyaura cross-coupling, and interestingly exhibit a switch in the normal regioselectivity observed for reactions of 2,4-dibromopyridine with aryl boronic acids, usually C2-selective, yielding C4-arylated product preferentially over C2-arylated product.
ABSTRACT
The racemic ligand (±)-tris-(4-methylthiazolyl)cyclotriguaiacylene forms a homochiral crystalline Ag12L8 cube with spontaneous resolution. The ligand itself likewise crystallises in a chirally pure fashion in two clathrate complexes. Ag12L8 is the first example of a cyclotriguaiacylene-type coordination cube and a rare example of a M12L8-type metallo-cube.