Aggregation effects in visible-light flavin photocatalysts: synthesis, structure, and catalytic activity of 10-arylflavins.

A series of 10-arylflavins (10-phenyl-, 10-(2',6'-dimethylphenyl)-, 10-(2',6'-diethylphenyl)-, 10-(2',6'-diisopropylphenyl)-, 10-(2'-tert-butylphenyl)-, and 10-(2',6'-dimethylphenyl)-3-methylisoalloxazine (2 a-f)) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with (1)H-DOSY NMR spectroscopic experiments in CD(3)CN, CD(3)CN/D(2)O (1:1), and D(2)O confirm the decreased ability of 10-arylflavins 2 to form aggregates relative to tetra-O-acetyl riboflavin (1). 10-Arylflavins 2 a-d do not interact by π-π interactions, which are restricted by the 10-phenyl ring oriented perpendicularly to the isoalloxazine skeleton. On the other hand, N3-H⋅⋅⋅O hydrogen bonds were detected in their crystal structures. In the structure of 10-aryl-3-methylflavin (2 f) with a substituted N3 position, weak C-H⋅⋅⋅O bonds and weak π-π interactions were found. 10-Arylflavins 2 were tested as photoredox catalysts for the aerial oxidation of 4-methoxybenzyl alcohol to the corresponding aldehyde (model reaction), thus showing higher efficiency relative to 1. The quantum yields of 4-methoxybenzyl alcohol oxidation reactions mediated by arylflavins 2 were higher by almost one order of magnitude relative to values in the presence of 1.

A new [(1R,2R)-1,2-diaminocyclohexane]platinum(II) complex: formation by nitrate-acetonitrile ligand exchange.

The title compound, cis-diacetonitrile[(1R,2R)-1,2-diaminocyclohexane-κ(2)N,N']platinum(II) dinitrate monohydrate, [Pt(C(2)H(3)N)(2)(C(6)H(14)N(2))](NO(3))(2)·H(2)O, is a molecular salt of the diaminocyclohexane-Pt complex cation. There are two formula units in the asymmetric unit. Apart from the two charge-balancing nitrate anions, one neutral molecule of water is present. The components interact via N-H...O and O-H...O hydrogen bonds, resulting in supramolecular chains. The title compound crystallizes only from acetonitrile with residual water, with the acetonitrile coordinating to the molecule of cis-[Pt(NO(3))(2)(DACH)] (DACH is 1,2-diaminocyclohexane) and the water forming a monohydrate.

Alaptide from synchrotron powder diffraction data.

THE TITLE COMPOUND [SYSTEMATIC NAME: (8S)-8-methyl-6,9-diaza-spiro-[4.5]decane-7,10-dione], C(9)H(14)N(2)O(2), consists of two connected rings, viz. a piperazine-2,5-dione (DKP) ring and a five-membered ring. The DKP ring adopts a slight boat conformation and the bonded methyl group is in an equatorial position. The five-membered ring is in an envelope conformation. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds link mol-ecules into chains running parallel to the c axis.

10-Methyl-isoalloxazine 5-oxide from synchrotron powder diffraction data.

THE TITLE COMPOUND [SYSTEMATIC NAME: 10-methyl-benzo[g]pteridine-2,4(3H,10H)-dione 5-oxide], C(11)H(8)N(4)O(3), consists of a large rigid isoalloxazine group which is approximately planar (r.m.s. deviation = 0.037 Å). In the crystal, inter-molecular N-H⋯O hydrogen bonds link the mol-ecules into centrosymmetric dimers. Dimers related by translation along the c axis form stacks through π-π inter-actions [centroid-centroid distances = 3.560 (5) and 3.542 (5) Å]. Weak inter-molecular C-H⋯O inter-actions further consolidate the crystal packing.