Copper(II) acetate mediated coupling reactions between 2,6-bis(azidomethyl)pyridine or 2-picolylazide and two terminal alkynes afford 1,2,3-triazolyl-containing ligands L(1)-L(6). These ligands contain various nitrogen-based Lewis basic sites including two different pyridyls, two nitrogen atoms on a 1,2,3-triazolyl ring, and the azido group. A rich structural diversity, which includes mononuclear and dinuclear complexes as well as one-dimensional polymers, was observed in the copper(II) complexes of L(1)-L(6). The preference of copper(II) to two common bidentate 1,2,3-triazolyl-containing coordination sites was investigated using isothermal titration calorimetry and, using zinc(II) as a surrogate, in (1)H NMR titration experiments. The magnetic interactions between the copper(II) centers in three dinuclear complexes were analyzed via temperature-dependent magnetic susceptibility measurements and high-frequency electron paramagnetic resonance spectroscopy. The observed magnetic superexchange is strongly dependent on the orientation of magnetic orbitals of the copper(II) ions and can be completely turned off if these orbitals are arranged orthogonal to each other. This work demonstrates the versatility of 1,2,3-triazolyl-containing polyaza ligands in forming metal coordination complexes of a rich structural diversity and interesting magnetic properties.

Oxime-based tridentate Schiff base ligands 3-[2-(diethylamino)ethylimino]butan-2-one oxime (HL(1)) and 3-[3-(dimethylamino)propylimino]butan-2-one oxime (HL(2)) produced the dinuclear complex [Ni2L(1)2](ClO4)2 (1) and trinuclear complex [Ni3(HL(2))3(μ3-O)](ClO4)4·CH3CN (2), respectively, upon reaction with Ni(ClO4)2·6H2O. However, in a slightly alkaline medium, both of the ligands underwent hydrolysis and resulted in tetranuclear complexes [{Ni(deen)(H2O)}2(μ3-OH)2{Ni2(moda)4}](ClO4)2·2CH3CN (3) and [{Ni(dmpn)(CH3CN)2}2(μ3-OH)2{Ni2(moda)4}](ClO4)2·CH3CN (4), where deen = 2-(diethylamino)ethylamine, dmpn = 3-(dimethylamino)-1-propylamine, and modaH = diacetyl monoxime. All four complexes have been structurally characterized. Complex 1 is a centrosymmetric dimer where the square planar nickel(II) atoms are joined solely by the oximato bridges. In complex 2, three square planar nickel atoms form a triangular core through a central oxido (μ3-O) and peripheral oximato bridges. Tetranuclear complexes 3 and 4 consist of four distorted octahedral nickel(II) ions held together in a rhombic chair arrangement by two central μ3-OH and four peripheral oximato bridges. Magnetic susceptibility measurements indicated that dinuclear 1 and trinuclear 2 exhibited diamagnetic behavior, while tetranuclear complexes 3 and 4 were found to have dominant antiferromagnetic intramolecular coupling with concomitant ferromagnetic interactions. Despite its singlet ground state, both 3 and 4 serve as useful examples of Kahn's model for competing spin interactions. High-frequency EPR studies were also attempted, but no signal was detected, likely due to the large energy gap between the ground and first excited state. Complexes 3 and 4 exhibited excellent catecholase-like activity in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone, whereas 1 and 2 did not show such catalytic activity. Kinetic data analyses of this oxidation reaction in acetonitrile revealed that the catalytic activity of 3 (kcat = 278.4 h(-1)) was slightly lower than that of 4 (kcat = 300.0 h(-1)). X-band EPR spectroscopy indicated that the reaction proceeded through the formation of iminoxyl-type radicals.

Magnetic properties of the series of three linear, trimetallic chain compounds Cr2Cr(dpa)4Cl2, 1, Mo2Cr(dpa)4Cl2, 2, and W2Cr(dpa)4Cl2, 3 (dpa = 2,2'-dipyridylamido), have been studied using variable-temperature dc and ac magnetometry and high-frequency EPR spectroscopy. All three compounds possess an S = 2 electronic ground state arising from the terminal Cr(2+) ion, which exhibits slow magnetic relaxation under an applied magnetic field, as evidenced by ac magnetic susceptibility and magnetization measurements. The slow relaxation stems from the existence of an easy-axis magnetic anisotropy, which is bolstered by the axial symmetry of the compounds and has been quantified through rigorous high-frequency EPR measurements. The magnitude of D in these compounds increases when heavier ions are substituted into the trimetallic chain; thus D = -1.640, -2.187, and -3.617 cm(-1) for Cr2Cr(dpa)4Cl2, Mo2Cr(dpa)4Cl2, and W2Cr(dpa)4Cl2, respectively. Additionally, the D value measured for W2Cr(dpa)4Cl2 is the largest yet reported for a high-spin Cr(2+) system. While earlier studies have demonstrated that ligands containing heavy atoms can enhance magnetic anisotropy, this is the first report of this phenomenon using heavy metal atoms as "ligands".

A family of five host–guest assemblies comprising different metal ions inside a cuboid 12-palladium-oxo cage, [MO8Pd12L8] n− (MPd 12 L 8 , M = ScIII, CoII, CuII, L = AsO4 3–; M = CdII, HgII, L = PhAsO3 2–), was synthesized and structurally characterized in the solid state by single-crystal X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis, and their solution and gas-phase stability were validated by multinuclear NMR spectroscopy and electrospray-ionization mass spectrometry (ESI-MS). The polyoxopalladates (POPs) ScPd 12 As 8 , CoPd 12 As 8 , and CuPd 12 As 8 represent the first three examples of the MPd12As8 archetype. The unique cubic ligand field of {MO8} allows for collecting the speciation profiles of the POPs in solution using 45Sc and 113Cd NMR techniques. Detailed magnetic and electron paramagnetic resonance (EPR) studies were performed on CuPd 12 As 8 . Catalytic studies on MPd12As8 (M = CuII and CoII) supported on SBA-15 unveiled a guest metal-dependent structure–function relationship, with CuPd 12 As 8 being the more efficient precatalyst for the hydroconversion of o-xylene in a fixed-bed reactor.

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW9O34]10- with cobalt(II), nickel(II) and zinc(II) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M4-containing heteropolytungstates [M4(OH)3(H2O)2(α-SiW10O36.5)2]13-...