The solid-state properties of a series of fused-ring oligothiophenes were studied by UV−visible absorption spectroscopy and single crystal X-ray diffraction. Although the degree of ring fusion has little effect on the solution absorption spectra, the solid-state spectra are dramatically different. Three thieno[3,2-b]thiophene-containing oligomers display spectral blue shifts when comparing the solid state to solution because they adopt a herringbone packing motif that leads to H aggregation. The solid-state structure of a dithieno[3,2-b:2‘,3‘-d]thiophene-based oligomer contains both herringbone and slipped π−π interactions, and the overlap of transitions from these different interaction modes results in a broad absorption spectrum in the solid state. The fully fused pentathienoacene adopts a π-stacked packing motif and displays a small blue shift in the solid-state spectrum compared to solution. Time-dependent density functional theory calculations of the electronic transitions of isolated molecules and interacting dimers provide support that the different behavior in the solid-state spectra is due to the unique intermolecular interactions arising in each packing motif.

The synthesis and characterization of 4,4′-dinonyl-2,2′-bisoxazole (NBO) and its oligomers are described. The optical, electronic, and structural properties of these oligomers, NBO, NBO 2 , and NBO 3 , are compared to their sulfur analogues (NBT, NBT 2 , and NBT 3 ). In the series (NBO) n and (NBT) n , there is a red shift in the λ max as "n" increases. This effect is observed in both the solid and solution states. The bithiazole oligomers have longer wavelength absorbances than those of the bisoxazole oligomers; however, the observed red shift is greater as "n" increases for the bisoxazole oligomers leading to a merging of the absorption maxima between the two systems. The larger red shift for the bisoxazole series is explained by the larger atomic orbital coefficients at the coupling sites of the bisoxazole oligomers versus those of the bithiazole derivatives. Both systems exhibit thermochromic behavior corresponding to a transition from an ordered to disordered state. Upon heating, the bisoxazole system shows a gradual conformational change indicated by continual blue shifts of the absorption maximum. Conversely, the less rigid bithiazole system exhibits an immediate order-disorder transition upon heating evidenced by the appearance of an isosbestic point in the absorption spectrum. The solid-state packing of the n ) 2 and 3 oligomers is very similar; however, the solid-state structures of NBO and NBT are different as determined by single-crystal X-ray diffraction. NBO packs in a two-layered "ribbonlike" structure, whereas NBT forms molecular stacks. The reduction potentials of (NBO) n increase (become more positive) from -2.97 to -2.60 to -2.46 V for n ) 1, 2, and 3, respectively, and the number of reductions observed corresponds to the number of NBO units.

Two general polymorphs of Ln III (NO 3 ) 3-x (OH) x [15-MC Cu II (N)S-pheHA -5] (where

The reaction of 1-chloro-1-boracyclohexa-2,5-diene with (3-(dimethylamino)propyl)magnesium chloride followed by reaction with tert-butyllithium in ether affords lithium 1-(3-(dimethylamino)propyl)boratabenzene (8). The reaction of 8 with Mn(CO)3(CH3CN)3PF6 affords tricarbonyl[1-(3-(dimethylamino)propyl)boratabenzene]manganese(I) (15B). The crystal structure of 15B shows that it exists in the intramolecularly B−N-coordinated form with a B−N bond distance of 1.716(5) Å. However in toluene-d 8 solution 15B is in mobile equilibrium with its ring-opened isomer 15A. Using 11B NMR spectroscopy the equilibrium constants for 15B → 15A have been measured over the temperature range −35 to 48 °C, allowing evaluation of ΔH° (6.0 kcal/mol) and ΔS° (23 cal/mol K).