fastgugl.blogg.se

The two crystallographically independent mol­ecules of the nitro-substituted compound have dihedral angles of 0.18 (3) and 1.07 (2)°, while this angle is 4.93 (2)° for the dimeric complex. The five 2,3-di­methyl­quinoxaline structures have a range of the dihedral angle between a best-fit plane through the six-membered carbon ring and a best-fit plane through the six-membered nitro­gen heterocycle of 0.02 (5)–1.59 (7)°. The dimeric version has also been characterized crystallographically, 2,2′,3,3′-tetra­methyl-6,6′-biquinoxaline, in which a single bond between the two six-membered carbon rings links a pair of 2,3-di­methyl­quinoxaline mol­ecules (Salvatore et al., 2006 ▸). A related compound, 2,3-dimethyl-6-nitro­quinoxaline, has been reported (Ghalib et al., 2010 ▸) in which there is a nitro group bonded to the six-membered carbon ring of the quinoxaline. There are five reported crystal structures of 2,3-di­methyl­quinoxaline the unsolvated species (Wozniak et al., 1993 ▸), the di­methyl­glyoxime co-crystal (Hökelek et al., 2001 ▸ Radhakrishnan et al., 2007 ▸), the 2,6-di­hydroxy­toluene co-crystal, and the 2,6-di­hydroxy­toluene/4-di­methyl­amino­pyridine co-crystal (Mir et al., 2015 ▸). It appears the methyl groups on the quinoxaline prevent the layers from coming closer together.Ī search of the Cambridge Crystal Database (Groom & Allen, 2014 ▸) returns zero results for 2,3-di­methyl­quinoxalin-6-yl groups attached to a phenyl ring. The centroid(C7–N1–C8–C9–N2–C10)⋯centroid(C7–N1–C8–C9–N2–C10) distance between the layers of 4.721 (3)Å is too long to be considered another π–π inter­action.

The distance between the centroid of C7 ii–N1 ii–C8 ii–C9 ii–N2 ii–C10 ii ring and C3 is 3.311 (3)Å.

The dihedral angle between a best fit plane through the C1–C2–C3–C4–C3 i–C2 i ring and a best-fit plane through the C7 ii–N1 ii–C8 ii–C9 ii–N2 ii–C10 ii ring is 41.70 (11)°. The orientation of these inter­acting groups is between ‘parallel offset’ and ‘perpendicular t-shaped’ as the C3-H3 A bond points towards the C7 ii–N1 ii–C8 ii–C9 ii–N2 ii–C10 ii ring centroid. The inter­actions occur between the central benzene ring and one of the heterocycles on a neighboring mol­ecule. The two-dimensional layers lie parallel to the ab-plane and stack along the c axis, Fig. 2 ▸ c. The mol­ecules of (I) form extended layers via inter­molecular π–π inter­actions linking each mol­ecule to its four nearest neighbors, Fig. 2 ▸ a, b. Similarly, the two methyl groups are not quite coplanar with a C13-C8-C9-C14 torsion angle of 3.5 (2)°. The methyl groups also lie slightly out of the plane of the C7–N1–C8–C9–N2–C10 ring. The two six-membered rings of the 2,3-di­methyl­quinoxalin-6-yl group deviate from planarity as well the dihedral angle between a best fit plane through the C5–C6–C7–C10–C11–C12 ring and a best fit plane through the C7–N1–C8–C9–N2–C10 ring is 3.8 (15)°. The 2,3-di­methyl­quinoxalin-6-yl group is twisted significantly out of the plane of the central phenyl ring as evidenced by the C1-C2-C5-C6 torsion angle of −39.8 (2)°. The C1 and C4 carbon atoms of the central phenyl ring each occupy special positions (, y, ) and thus one-half of the mol­ecule is generated by the symmetry operation (− x + 1, y, − z + ). These results confirmed our hypothesis on the crystal face dependence of stability as a photocathode.The mol­ecular structure of (I) (Fig. 1 ▸) consists of a central phenyl ring with 2,3-di­methyl­quinoxalin-6-yl groups at the 1 and 3 positions. Also, when oxygen was removed from the aqueous solution, the predominantly -terminated films generated photocurrents one order of magnitude smaller compared to the predominantly -terminated films, indicating the stability of the -terminated surface against photodecomposition into Cu. When used as photocathodes, the predominantly -terminated films did not deteriorate as readily as the predominantly -terminated films did. To examine our hypothesis, the stability and photochemical behavior were compared between electrodeposited films with predominantly -terminated surfaces and ones with predominantly -terminated surfaces. The well-known instability of single-crystal is attributed to predominant (211) and (311) surfaces, where the photodecomposition into Cu is inevitable at the exposed sites. Previously we hypothesized that the reported stability of electrodeposited films is attributed to the predominant -terminated (111) surface, where the -supported reduction occurs and the -assisted reduction, which is the decomposition of, does not happen.