The effect of the surface charge of nucleation agents on the crystallization behavior of poly(vinylidene fluoride) (PVDF) has been investigated. Ion-dipole interaction between the positive surface of nucleation agents and the partially negative CF(2) dipoles of PVDF is established as a main factor for further lowering the free energy barrier for nucleation, and thus increasing significantly the crystallization kinetics. This is in contrast to the behavior observed for nucleation agents possessing either negative surface or neutral charges. Positive nucleation agents led to a remarkable increase in the crystallization temperature of PVDF (lower supercooling) as compared with that of neat PVDF. The dispersion of each type of nucleation agent is also important. The melting temperatures of nucleation agents need to be higher than the melting temperature of PVDF. The melting point and degree of crystallinity of PVDF can also be raised by using specific nucleation agents. The detailed crystallization kinetics and conformational changes of the PVDF chain have been investigated. With the addition of positive nucleation agents, the γ and β chain conformations, instead of the α phase, dominate.

Reaction of TaCl 5 with 2 equiv of an amine in the presence of sodium silicate and pyridine affords Ta(NR)Cl 3 (py) 2 in good yield. Reaction of NbCl 5 with ZnCl 2 followed by addition of an amine RNH 2 and pyridine affords M(NR)Cl 3 (dme) (dme is 1,2-dimethoxyethane). For niobium this reaction proceeds smoothly regardless of the amine but is ineffective with tantalum and alkyl amines. An alternative route involves reaction of TaCl 5 with 3 equiv of RNH 2 to form [RNH 3 ] 2 [Ta(NR)Cl 5 ], followed by reaction of this salt with ZnCl 2 in the presence of dme. The molecular structure of Nb(N t Bu)Cl 3 (dme) (formula C 8 H 19 Cl 3 NNbO 2 ) was determined by X-ray crystallography (monoclinic space group Cc with a ) 30.565(4) Å, b ) 7.2406(13) Å, c ) 13.915(2) Å, β ) 90.626(7)°, V ) 3079.4(8) Å 3 , Z ) 8). The Nb-N bond length is 1.72 Å with a Nb-N-C bond angle of 177°in a distorted octahedral structure. In order to characterize the M-N stretching frequencies in these compounds, IR data for each compound are compared with calculated stretching frequencies using the commercially available Spartan calculation package. These experiments reveal that there is no real M-N stretching frequency in these imidos. Rather, the M-N modes are strongly coupled to N-C and C-H or C-C modes in these imidos. IR active modes are observed at ∼1260 cm -1 for tantalum alkyl imidos and ∼1350 cm -1 for tantalum aryl imidos. These correspond to a Ta-(N-C) stretch coupled to the CR 3 umbrella deformation.

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One of the most dramatic examples of multielectron chemistry is the reversible interconversion of nitrosyl and ammine in polypyridyl complexes of ruthenium and osmium, eq l,2-9 where bpy is 2,2'-bipyridine and tpy is 2,2':6',2"-terpyridine.[M(bpy)2(py)(NO)]3+ .fe,_5H++H2Q-[M(bpy)2(py)(NH3)]2+ (1) In this overall 6-electron change there is evidence for a series of one-electron intermediates beginning with [Mn(bpy)2(py)-(NO°)]2+ on reduction and [Mra(bpy)2(py)(NH3)]3+ on oxidation.

The photophysical properties of the chromophore−quencher complexes, fac-[(4,4‘-R2bpy)ReI(CO)3(LA)] n + (4,4‘-R2bpy = 4,4‘-R2-2,2‘-bipyridine, R = Me or t Bu, and LA = the quinone acceptor ligands, benz[g]isoquinoline-5,10-dione (BIQD), 2-oxy-1,4-naphthoquinone anion (ONQ-), 1/2 2,6-dihydroxyanthraquinone dianion (AFA2-), or the pyridinium acceptor, 1-methyl-6-oxyquinoline (OQD)) in 1,2-dichloroethane are described. Following ReI → 4,4‘-R2bpy metal-to-ligand charge transfer (MLCT) excitation, intramolecular electron transfer leads to the transients, fac-[(4,4‘-R2bpy)ReII(CO)3(LA•-)] n+. They have been characterized by emission spectral fitting and transient absorption measurements and, for LA = OQD, by transient infrared measurements. As shown by analysis of excited-state emission, there is weak-to-moderate electronic coupling between the electron donor and acceptor sites in the transients with H DA varying from 153 cm-1 for the BIQD complex to 3.9 cm-1 for the OQD complex. The transients are redox-separated (RS) states with the electronic configurations dπ5πLA* for BIQD or σ(Re−O)1πLA*1 for ONQ-, AFA -, and OQD. They are weak emitters and return to the ground state largely by nonradiative decay which occurs by back electron transfer (k ET). Reasonable agreement has been reached between k ET and values calculated from kinetic parameters derived by emission spectral fitting and excited-state decay. The RS states for the AFA2- and OQD complexes are remarkably long-lived (τ = 4 μs for LA = AFA2- in DCE at 296 K and 16 μs for LA = OQD in DCE at 296 K) due to orbital and spin restrictions on back electron transfer.

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