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1. Crystal structures of trans -acetyldicarbonyl(η ⁵ -cyclopentadienyl)(1,3,5-triaza-7-phosphaadamantane)molybdenum(II) and trans -acetyldicarbonyl(η ⁵ -cyclopentadienyl)(3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane)molybdenum(II)

   https://doi.org/10.1107/S2056989020003679  

   Anstey, Mitchell R.; Bost, John L.; Grumman, Anna S.; Kennedy, Nicholas D.; Whited, Matthew T. (April 2020, Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   The title compounds, [Mo(C 5 H 5 )(COCH 3 )(C 6 H 12 N 3 P)(CO) 2 ], (1), and [Mo(C 5 H 5 )(COCH 3 )(C 9 H 16 N 3 O 2 P)(C 6 H 5 ) 2 ))(CO) 2 ], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C 5 H 5 )(CO) 3 (CH 3 )]. The molecular structures of these complexes are quite similar, exhibiting a four-legged piano-stool geometry with trans -disposed carbonyl ligands. The extended structures of complexes (1) and (2) differ substantially. For complex (1), the molybdenum acetyl unit plays a dominant role in the organization of the extended structure, joining the molecules into centrosymmetrical dimers through C—H...O interactions with a cyclopentadienyl ligand of a neighboring molecule, and these dimers are linked into layers parallel to (100) by C—H...O interactions between the molybdenum acetyl and the cyclopentadienyl ligand of another neighbor. The extended structure of (2) is dominated by C—H...O interactions involving the carbonyl groups of the acetamide groups of the DAPTA ligand, which join the molecules into centrosymmetrical dimers and link them into chains along [010]. Additional C—H...O interactions between the molybdenum acetyl oxygen atom and an acetamide methyl group join the chains into layers parallel to (101). 

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2. trans -Acetyldicarbonyl(η ⁵ -cyclopentadienyl)[tris(3,5-dimethylphenyl)phosphane-κ P ]molybdenum(II)

   https://doi.org/10.1107/S2414314617000426  

   Whited, Matthew T.; Ruffer, Eli J.; Zhang, Jia; Rabaey, Dominique J.; Janzen, Daron E. (January 2017, IUCrData)

   The title compound, [Mo(C 5 H 5 )(C 2 H 3 O)(C 24 H 27 P)(CO) 2 ], was prepared by reaction of [Mo(C 5 H 5 )(CO) 3 (CH 3 )] with tris(3,5-dimethylphenyl)phosphane. The complex exhibits a four-legged piano-stool geometry with trans -disposed acetyl and phosphane ligands. The molecular geometry is nearly identical to that of the triphenylphosphane derivative, but introduction of methyl groups on the aromatic phosphane substituents significantly impacts supramolecular organization. In the crystal, non-classical C—H...O interactions involving the acetyl carbonyl group lead to a chain motif along [010], and another set of C—H...O close contacts join inversion-related molecules. 

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3. Clarifying the structures of imidines: using crystallographic characterization to identify tautomers and localized systems of π-bonding

   https://doi.org/10.1107/S2053229623002036  

   Aristov, Michael M.; Geng, Han; Harris, James W.; Berry, John F. (April 2023, Acta Crystallographica Section C Structural Chemistry)

   Nitrogen heterocycles are a class of organic compounds with extremely versatile functionality. Imidines, HN[C(NH) R ] 2 , are a rare class of heterocycles related to imides, HN[C(O) R ] 2 , in which the O atoms of the carbonyl groups are replaced by N—H groups. The useful synthesis of the imidine compounds succinimidine and glutarimidine, as well as their partially hydrolyzed imino–imide congeners, was first described in the mid-1950s, though structural characterization is presented for the first time in this article. In the solid state, these structures are different from the proposed imidine form: succinimidine crystallizes as an imino–amine, 2-imino-3,4-dihydro-2 H -pyrrol-5-amine, C 4 H 7 N 2 ( 1 ), glutarimidine as 6-imino-3,4,5,6-tetrahydropyridin-2-amine methanol monosolvate, C 5 H 9 N 3 ·CH 3 OH ( 2 ), and the corresponding hydrolyzed imino–imide compounds as amino–amides 5-amino-3,4-dihydro-2 H -pyrrol-2-one, C 4 H 6 N 2 O ( 3 ), and 6-amino-4,5-dihydropyridin-2(3 H )-one, C 5 H 8 N 2 O ( 4 ). Imidine 1 was also determined as the hydrochloride salt solvate 5-amino-3,4-dihydro-2 H -pyrrol-2-iminium chloride–2-imino-3,4-dihydro-2 H -pyrrol-5-amine–water (1/1/1), C 4 H 8 N 3 + ·Cl − ·C 4 H 7 N 3 ·H 2 O ( 1 ·HCl). As such, 1 and 2 show alternating short and long C—N bonds across the molecule, revealing distinct imino (C=NH) and amine (C—NH 2 ) groups throughout the C—N backbone. These structures provide definitive evidence for the predominant imino–amine tautomer in the solid state, which serves to enrich the previously proposed imidine-focused structures that have appeared in organic chemistry textbooks since the discovery of this class of compounds in 1883. 

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4. 5-([( Z )-Methoxyimino]{2-[(2-methylphenoxy)methyl]phenyl}methyl)-1,3,4-oxadiazole-2(3 H )-thione dimethyl sulfoxide monosolvate

   https://doi.org/10.1107/S2414314623002377  

   Shripanavar, Chetan Shrimandhar; Balerao, Rishik; Butcher, Ray J. (March 2023, IUCrData)

   The title compound, C 18 H 17 N 3 O 3 S·C 2 H 6 OS, crystallizes in the monoclinic space group P 2 1 /c . In the crystal, C 1 1 (9) chains of C—H...O interactions are formed, propogating in the c -axis direction. The N—H hydrogen atom forms a strong hydrogen bond with the oxygen atom of a DMSO solvate molecule. 

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5. A structural and computational comparison of close contacts and related intermolecular energies of interaction in the structures of 1,3-diiodo-5-nitrobenzene, 1,3-dibromo-5-nitrobenzene, and 1,3-dichloro-5-nitrobenzene

   https://doi.org/10.1107/S2053229622009275  

   Bosch, Eric; Bowling, Nathan P.; Speetzen, Erin D. (October 2022, Acta Crystallographica Section C Structural Chemistry)

   1,3-Diiodo-5-nitrobenzene, C₆H₃I₂NO₂, and 1,3-dibromo-5-nitrobenzene, C₆H₃Br₂NO₂, crystallize in the centrosymmetric space groupP2₁/m, and are isostructural with 1,3-dichloro-5-nitrobenzene, C₆H₃Cl₂NO₂, that has been redetermined at 100 K for consistency. While the three-dimensional packing in all three structures is similar, the size of the halogen atom affects the nonbonded close contacts observed between molecules. Thus, the structure of 1,3-diiodo-5-nitrobenzene features a close Type 1 I...I contact, the structure of 1,3-dibromo-5-nitrobenzene features a self-complementary nitro-O...Br close contact, while the structure of 1,3-dichloro-5-nitrobenzene also has a self-complementary nitro-O...Cl interaction, as well as a bifurcated C—H...O(nitro) close contact. Notably, the major energetically attractive intermolecular interaction between adjacent molecules in each of the three structures corresponds to a π-stacked interaction. The self-complementary halogen...O(nitro) and C—H...O(nitro) interactions correspond to significant cohesive attraction between molecules in each structure, while the Type 1 halogen–halogen contact is weakly cohesive. 

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