Mary Jane Heeg

The crystal structure of dimethylphenyltin(IV) acetate

Dimethylphenyltin(IV) acetate, (CH3)2(C6H5)SnOC(O)CH3, crystallizes in the orthorhombic space group Pbca with a 10.068(3), b 15.065(7), c 14.976(5) A; Z = 8; V 2271(2) A3. The structure was determined from 1793 observed out of 2348 unique reflections and refined on an R factor of 0.034. The geometry at tin is trigonal bipyramidal, with the oxygen atom of the acetate and the carbonyl oxygen of the adjacent symmetry-related (12 + x, 12 − y, 1 − z) acetate occupying the axial positions of the trans-C3SnO2 polyhedron to result in a polymer whose backbone, formed by the repetition of Snue5f8Oue5f8C(O) fragment, adopts a conformation that is closer to the zig-zag configuration of trimethyltin acetate than to the helical form of triphenyltin acetate.

Effects of Excited State-Excited State Configurational Mixing on Emission Bandshape Variations in Ruthenium-Bipyridine Complexes

The 77 K emission spectra of 21 [Ru(L) 4bpy] ( m+ ) complexes for which the Ru/bpy metal-to-ligand-charge-transfer ( (3)MLCT) excited-state energies vary from 12 500 to 18 500 cm (-1) have vibronic contributions to their bandshapes that implicate excited-state distortions in low frequency ( lf; hnu lf < 1000 cm (-1)), largely metal-ligand vibrational modes which most likely result from configurational mixing between the (3)MLCT and a higher energy metal centered ( (3)LF) excited state. The amplitudes of the lf vibronic contributions are often comparable to, or sometimes greater than those of medium frequency ( mf; hnu mf > 1000 cm (-1)), largely bipyridine (bpy) vibrational modes, and for the [Ru(bpy) 3] (2+) and [Ru(NH 3) 4bpy] (2+) complexes they are consistent with previously reported resonance-Raman (rR) parameters. However, far smaller lf vibronic amplitudes in the rR parameters have been reported for [Os(bpy) 3 ] (2+), and this leads to a group frequency approach for interpreting the 77 K emission bandshapes of [Ru(L) 4bpy] ( m+ ) complexes with the vibronic contributions from mf vibrational modes referenced to the [Os(bpy) 3] (2+) rR parameters (OB3 model) and the envelope of lf vibronic components represented by a progression in an equivalent single vibrational mode ( lf1 model). The lf1 model is referenced to rR parameters reported for [Ru(NH 3) 4bpy] (2+). The observation of lf vibronic components indicates that the MLCT excited-state potential energy surfaces of Ru-bpy complexes are distorted by LF/MLCT excited-state/excited-state configurational mixing, but the emission spectra only probe the region near the (3)MLCT potential energy minimum, and the mixing can lead to larger distortions elsewhere with potential photochemical implications: (a) such distortions may labilize the (3)MLCT excited state; and (b) the lf vibrational modes may contribute to a temperature dependent pathway for nonradiative relaxation.

Low-temperature structural determination of anhydrous Li2SeO4

Anhydrous Li2SeO4 crystallizes in the trigonal space group R3 with a = 13.931(2), c = 9.304(3) A, V = 1563.7 A3, Z = 18, Dc = 2.988 g cm−3. The unit cell transforms to the rhombohedral coordinate system as a = 8.620 A, α = 107.81(2)°, V = 521.2 A3, Z = 6. The structure contains selenate anions bridged by Li in the phenacite structural type. Data collection was performed at low temperature for precise placement of the Li cations which are tetrahedrally surrounded by oxygen atoms. Some problems with secondary extinction were apparent and a correction was made. The structure refined to an R value of 0.034.