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The two commercially available zirconium complexes tetrakis(dimethylamido)zirconium, Zr(NMe2)4, and tetrabenzylzirconium, ZrBn4, were investigated for their utility as starting materials in the synthesis of bis(pyridine dipyrrolide)zirconium photosensitizers, Zr(PDP)2. Reaction with one equivalent of the ligand precursor 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine, H2MePDPPh, resulted in the isolation and structural characterization of the complexes (MePDPPh)Zr(NMe2)2thf and (MePDPPh)ZrBn2, which could be converted to the desired photosensitizer Zr(MePDPPh)2upon addition of a second equivalent of H2MePDPPh. Using the more sterically encumbered ligand precursor 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine, H2MesPDPPh, only ZrBn4yielded the desired bis-ligand complex Zr(MesPDPPh)2. Careful monitoring of the reaction at different temperatures revealed the importance of the organometallic intermediate (cyclo-MesPDPPh)ZrBn, which was characterized by X-ray diffraction analysis and 1H NMR spectroscopy and shown to contain a cyclometalated MesPDPPhunit. Taking inspiration from the results for zirconium, syntheses for two hafnium photosensitizers, Hf(MePDPPh)2and Hf(MesPDPPh)2, were established and shown to proceed through similar intermediates starting from tetrabenzylhafnium, HfBn4. Initial studies of the photophysical properties of the photoluminescent hafnium complexes indicate similar optical properties compared to their zirconium analogues.

The synthesis of two new radical-bridged compounds [Co3(bptz)3(dbm)3]·2toluene (1) and [Co4(bptz)4(dbm)4]·4MeCN (2) (bptz = 3,6-bis(pyridyl)-1,2,4,5-tetrazine; dbm = 1,3-diphenyl-1,3-propanedionate) is reported. The presence of the ligand-centered radical has been confirmed by X-ray crystallography and SQUID magnetometry. These complexes are the first metallacycles bearing nitrogen heterocyclic radicals as bridges. Magnetic studies reveal strong antiferromagnetic metal···radical coupling with coupling constants of J= −67.5 and −66.8 cm–1for 1and 2, respectively. DFT calculations further support the strong antiferromagnetic coupling between CoIIions and bptz radicals and confirm S= 3 and S= 4 spin ground states for 1and 2, respectively.

The radical bridged compound [(Ni(TPMA))2-μ-bmtz•–](BF4)3·3CH3CN (bmtz = 3,6-bis(2′-pyrimidyl)-1,2,4,5-tetrazine, TPMA = tris(2-pyridylmethyl)amine) exhibits strong ferromagnetic exchange between the S= 1 NiIIcenters and the bridging S= 1/2 bmtz radical with J= 96 ± 5 cm–1(−2JNi-radSNiSrad). DFT calculations support the existence of strong ferromagnetic exchange.

Single-molecule magnets (SMMs), are regarded as excellent nanomaterials for high-density information storage and quantum computing. The local symmetry of the crystal field for the metal ion plays an important role in pursuing a high-performance SMM. Herein, two highly stable distorted hexagonal bipyramidal (quasi-D6h) Dy complexes exhibiting slow relaxation of the magnetization are reported. A hexagonal bipyramidal Dy model complex with 18-crown-6 was also designed to study the relationship between magnetic anisotropy and symmetry. The combined experimental and theoretical results indicate that quantum tunneling is highly dependent on the local symmetries of the crystal field. The magnetic anisotropy becomes much stronger when the symmetry is closer to a standard D6hgeometry. These results support the conclusion that the hexagonal bipyramidal geometry is a viable one for the design of new classes of SMMs.

This paper describes the synthesis and reactivity studies of three cobalt complexes bearing aminophenol-derived ligands without nitrogen substitution: CoII(tBu2APH)2(tBu2AP)2(1), CoIII2(tBu2APH)2(tBu2AP)2(μ-tBu2BAP)2(2), and CoIII(tBu2AP)3(3), where tBu2APH = 2-amino-4,6-di-tert-butylphenol, tBu2AP = 2-amino-4,6-di-tert-butylphenolate, and μ-tBu2BAP = bridging 2-amido-4,6-di-tert-butylphenolate. Stoichiometric reactivity studies of these well-defined complexes demonstrate the catalytic competency of both cobalt(II) and cobalt(III) complexes in the aerobic oxidative cyclization of tBu2APH with tert-butylisonitrile. Reactions with O2reveal the aerobic oxidation of the cobalt(II) complex 1to generate the cobalt(III) species 2and 3. UV–visible time-course studies and electron paramagnetic resonance spectroscopy indicate that this oxidation proceeds through a ligand-based radical intermediate. These studies represent the first example of well-defined cobalt aminophenol complexes that participate in catalytic aerobic oxidation reactions and highlight a key role for a ligand radical in the oxidation sequence.