Syntheses,crystal structures,and catalysis by polymeric dioxomolybdenum(VI) complexes with similar (iso)nicotinohydrazones

Polymeric dioxomolybdenum(VI) complexes, [MoO₂L]_n (L?=?L¹?=?N′-(2-hydroxybenzylidene)nicotinohydrazide for 1, L?=?L²?=?N′-(2-hydroxy-5-methoxybenzylidene)isonicotinohydrazide for 2), were prepared and characterized by physico-chemical, spectroscopic methods, and single-crystal X-ray determination. Complex 1 crystallizes in the orthorhombic space group P2₁2₁2₁ with a?=?7.6568(4), b?=?11.6315(7), c?=?15.2211(9)?Å, V?=?1355.59(13)?ų, Z?=?4, R ₁?=?0.0181, wR ₂?=?0.0464, and S?=?1.097. Complex 2 crystallizes in the monoclinic space group P2 ₁ /n with a?=?11.2516(6), b?=?11.8134(7), c?=?12.4371(6)?Å, β?=?116.2210(10)°, V?=?1483.02(14)?ų, Z?=?4, R ₁?=?0.0399, wR ₂?=?0.0874, and S?=?1.096. X-ray analysis indicates that Mo in each complex is octahedral with two oxo groups and N₂O₂ donor set of the nicotinohydrazone or isonicotinohydrazone. The complexes are efficient catalysts for oxidation of olefins.     

Synthesis,structure and methyl methacrylate polymerization of cobalt(II), zinc(II) and cadmium(II) complexes with N,N′,N-bidentate versus N,N′,N-tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines

Mononuclear Co(II), Zn(II) and Cd(II) complexes derived from bidentate or tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines (L_n = L_A, L_B), where L_A is N,N-bis((1H-pyrazol-1-yl)methyl)-3-methoxypropan-1-amine and L_B is 3-methoxy-N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)propan-1-amine, have been synthesized and characterized. The geometry at Co(II) and Cd(II) for [L_ACoCl₂], [L_BCoCl₂] and [L_BCdBr₂] with N,N′,N-tridentate ligands (L_n = L_A, L_B) can be described as a distorted trigonal bipyramid achieved by coordinative interaction of N_pyrazole, two halides and the nitrogen of amine moiety. However, the molecular structure of four-coordinate [L_AZnCl₂] can be best described as tetrahedral, resulting in an eight-membered chelate ring. [L_ACoCl₂] polymerized methyl methacrylate in the presence of modified methylaluminoxane at 60 °C and resulted in poly(methylmethacrylate) (PMMA) with higher molecular weight and narrower polydispersity index compared to the other synthesized complexes. However, all the synthesized complexes yielded syndiospecific PMMA, characterized using ¹H NMR spectroscopy, with ca. 0.70.     

Delayed fluorescence from the lowest 1B+3u state of anthracene,due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

The P-type delayed fluorescence (DF) S_i→S_o of aromatic compounds results from the population of excited singlet states S_i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T₁ : T₁ + T₁

S_i + S_o; S_i may be any excited singlet state whose excitation energy E(S_i ? 2 E(T₁). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T_A¹) < E(T₁^B), hetero-TTA may lead to excited singlet states S_k^A which are not accessible by TTA of 2 T₁^A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S_k^A which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene-h₁₀ or anthracene-d₁₀ or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S_k^A is the lowest ¹B_3U⁺ state (B_b state) of anthracene.