The results of the sixth blind test of organic crystal structure prediction methods are presented and discussed, highlighting progress for salts, hydrates and bulky flexible molecules, as well as on-going challenges.

Polymerization of isocyanopeptides results in the formation of high molecular mass polymers that fold in a proteinlike fashion to give helical strands in which the peptide chains are arranged in beta-sheets. The beta-helical polymers retain their structure in water and unfold in a cooperative process at elevated temperatures. The peptide architecture in these polymers is a different form of the beta-helix motif found in proteins. Unlike their natural counterparts, which contain arrays of large beta-sheets stacked in a helical fashion, the isocyanopeptide polymers have a central helical core that acts as a director for the beta-sheet-like arrangement of the peptide side arms. The helical structure of these isocyanopeptide polymers has the potential to be controlled through tailoring of the side branches and the hydrogen-bonding network present in the beta-sheets.

The design of pharmaceutical cocrystals has initiated widespread debate on the classification of cocrystals. Current attempts to classify multicomponent crystals suffer from ambiguity, which has led to inconsistent definitions for cocrystals and for multicomponent crystals in general. Inspired by the work of Aitipamula et al. (Cryst. Growth Des. 2012, 12, 2147–2152), we present a feasible classification system for all multicomponent crystals. The present classification enables us to analyze and classify multicomponent crystal structures present in the Cambridge Structural Database (CSD). This reveals that all seven classes proposed are relevant in terms of frequency of occurrence. Lists of CSD refcodes for all classes are provided. We identified over 5000 cocrystals in the CSD, as well as over 12 000 crystals with more than two components. This illustrates that the possibilities for alternative drug formulations can be increased significantly by considering more than two components in drug design.

SABRE hyperpolarizes substrates by polarization transfer from para-hydrogen in a metal complex. We have measured the signal enhancement of pyridine and its exchange rate in various [Ir(NHC)(Py)3(H)2](+) complexes to gain insight into their dependence on the N-Heterocyclic Carbene (NHC) ligand's steric and electronic properties.

ABSTRACT:A generalized expression is given for the similarity of spectra, based on the normalized integral of a weighted crosscorrelation function. It is shown that various similarity and dissimilarity criteria previously described in literature can be written as special cases of this general expression. A new similarity criterion, based on this generalized expression, is introduced. The benefits of this criterion are that it properly recognizes shifted but otherwise similar details in spectra and that the resulting similarity measure is normalized. Moreover, the criterion can easily be adapted to specific properties of spectra resulting from various analytical methods. The new criterion is applied to the classification of a series of crystal structures of cephalosporin complexes, based on comparison of their calculated powder diffraction patterns. The results are compared with those obtained using previously described criteria.

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One-electron oxidation of [(Me(n)tpa)Ir(I)(ethene)]+ complexes (Me(3)tpa = N,N,N-tri(6-methyl-2-pyridylmethyl)amine; Me(2)tpa = N-(2-pyridylmethyl)-N,N,-di[(6-methyl-2-pyridyl)methyl]-amine) results in relatively stable, five-coordinate Ir(II)-olefin species [(Me(n)tpa)Ir(II)(ethene)](2+) (1(2+): n = 3; 2(2+): n = 2). These contain a "vacant site" at iridium and a "non-innocent" ethene fragment, allowing radical type addition reactions at both the metal and the ethene ligand. The balance between metal- and ligand-centered radical behavior is influenced by the donor capacity of the solvent. In weakly coordinating solvents, 1(2+) and 2(2+) behave as moderately reactive metallo-radicals. Radical coupling of 1(2+) with NO in acetone occurs at the metal, resulting in dissociation of ethene and formation of the stable nitrosyl complex [(Me(3)tpa)Ir(NO)](2+) (6(2+)). In the coordinating solvent MeCN, 1(2+) generates more reactive radicals; [(Me(3)tpa)Ir(MeCN)(ethene)](2+) (9(2+)) by MeCN coordination, and [(Me(3)tpa)Ir(II)(MeCN)](2+) (10(2+)) by substitution of MeCN for ethene. Complex 10(2+) is a metallo-radical, like 1(2+) but more reactive. DFT calculations indicate that 9(2+) is intermediate between the slipped-olefin Ir(II)(CH(2)=CH(2)) and ethyl radical Ir(III)-CH(2)-CH(2). resonance structures, of which the latter prevails. The ethyl radical character of 9(2+) allows radical type addition reactions at the ethene ligand. Complex 2(2+) behaves similarly in MeCN. In the absence of further reagents, 1(2+) and 2(2+) convert to the ethylene bridged species [(Me(n)tpa)(MeCN)Ir(III)(mu(2)-C(2)H(4))Ir(III)(MeCN)(Me(3)tpa)](4+) (n = 3: 3(4+); n = 2: 4(4+)) in MeCN. In the presence of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxo), formation of 3(4+) from 1(2+) in MeCN is completely suppressed and only [(Me(3)tpa)Ir(III)(TEMPO(-))(MeCN)](2+) (7(2+)) is formed. This is thought to proceed via radical coupling of TEMPO at the metal center of 10(2+). In the presence of water, hydrolysis of the coordinated acetonitrile fragment of 7(2+) results in the acetamido complex [(Me(3)tpa)Ir(III)(NHC(O)CH(3)))(TEMPOH)](2+) (8(2+)).

[Structure: see text] A novel P,N-type ligand family (ClickPhine) is disclosed that is easily accessible using the Cu(I)-catalyzed azide-alkyne "click" cycloaddition. A diverse set of ligands was made in just three steps from readily available starting materials to give several homogeneous and a heterogeneous catalyst. Preliminary experiments show the efficacy of these ligands in the Pd-catalyzed allylic alkylation reaction.