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1. Geometric isomers of dichloridoiron(III) complexes of CTMC (5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradecane)

   https://doi.org/10.1107/S205322962200849X  

   DeLancey, Stephanie S.; Clendening, Reese A.; Zeller, Matthias; Ren, Tong (September 2022, Acta Crystallographica Section C Structural Chemistry)

   Both trans and cis iron–CTMC complexes, namely, trans -dichlorido[(5 SR ,7 RS ,12 RS ,14 SR )-5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradecane]iron(III) tetrachloridoferrate, [Fe(C 14 H 32 N 4 )Cl 2 ][FeCl 4 ] ( 1a ), the analogous chloride methanol monosolvate, [Fe(C 14 H 32 N 4 )Cl 2 ]Cl·CH 3 OH ( 1b ), and cis -dichlorido[(5 SR ,7 RS ,12 SR ,14 RS )-5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradecane]iron(III) chloride, [Fe(C 14 H 32 N 4 )Cl 2 ]Cl ( 2 ), were successfully synthesized and structurally characterized using X-ray diffraction. The coordination geometry of the macrocycle is dependent on the stereoisomerism of CTMC. The packing of these complexes appears to be strongly influenced by extensive hydrogen-bonding interactions, which are in turn determined by the nature of the counter-anions ( 1a versus 1b ) and/or the coordination geometry of the macrocycle ( 1a/1b versus 2 ). These observations are extended to related ferric cis - and trans- dichloro macrocyclic complexes. 

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2. A unique series of chromium( iii ) mono-alkynyl complexes supported by tetraazamacrocycles

   https://doi.org/10.1039/d1dt00707f  

   Schuman, Ashley J.; Robey, Sarah F.; Judkins, Eileen C.; Zeller, Matthias; Ren, Tong (April 2021, Dalton Transactions)

   null (Ed.)

   Described herein is the synthesis and characterization of macrocyclic Cr III mono-alkynyl complexes. By using the meso -form of the tetraazamacrocycle HMC (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), trans -[Cr(HMC)(C 2 Ph)Cl]OTf ( 1a ), trans -[Cr(HMC)(C 2 Np)Cl]OTf ( 2a ), trans -[Cr(HMC)(C 2 C 6 H 4 t Bu)Cl]OTf ( 3a ), and trans -[Cr(HMC)(C 2 (3,5-Cl 2 C 6 H 3 ))Cl]OTf ( 4a ) complexes have been realized. These complexes were synthesized in high yield through the reaction of trans -[Cr( meso -HMC)(C 2 Ar) 2 ]OTf ( 1b–4b ) with stoichiometric amounts of methanolic HCl. Single crystal X-ray diffraction showed that the trans -stereochemistry and pseudo-octahedral geometry is retained in the desired mono-alkynyl complexes. The absorption spectra of complexes 1a–4a display d–d bands with distinct vibronic progressions that are slightly red shifted from trans -[Cr(HMC)(C 2 Ar) 2 ] + with approximately halved molar extinction coefficients. Time-delayed measurements of the emission spectra for complexes 1a–4a at 77 K revealed phosphorescence with lifetimes ranging between 343 μs ( 4a ) and 397 μs ( 1a ). The phosphorescence spectra of 1a–4a also exhibit more structuring than the bis-alkynyl complexes due to a strengthened vibronic coupling between the Cr III metal center and alkynyl ligands. 

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3. Crystal structures of two new six-coordinate iron(III) complexes with 1,2-bis(diphenylphosphane) ligands

   https://doi.org/10.1107/S2056989018006898  

   McNeil, Derek L.; Beckford, Daihlia J.; Kneebone, Jared L.; Carpenter, Stephanie H.; Brennessel, William W.; Neidig, Michael L. (June 2018, Acta Crystallographica Section E Crystallographic Communications)

   Structural characterization of the ionic complexes [FeCl 2 (C 26 H 22 P 2 ) 2 ][FeCl 4 ]·0.59CH 2 Cl 2 or [(dppen) 2 FeCl 2 ][FeCl 4 ]·0.59CH 2 Cl 2 (dppen = cis -1,2-bis(diphenylphosphane)ethylene, P 2 C 26 H 22 ) and [FeCl 2 (C 30 H 24 P 2 ) 2 ][FeCl 4 ]·CH 2 Cl 2 or [(dpbz) 2 FeCl 2 ][FeCl 4 ]·CH 2 Cl 2 (dpbz = 1,2-bis(diphenylphosphane)benzene, P 2 C 30 H 24 ) demonstrates trans coordination of two bidentate phosphane ligands (bisphosphanes) to a single iron(III) center, resulting in six-coordinate cationic complexes that are balanced in charge by tetrachloridoferrate(III) monoanions. The trans bisphosphane coordination is consistent will all previously reported molecular structures of six coordinate iron(III) complex cations with a (PP) 2 X 2 ( X = halido) donor set. The complex with dppen crystallizes in the centrosymmetric space group C 2/ c as a partial-occupancy [0.592 (4)] dichloromethane solvate, while the dpbz-ligated complex crystallizes in the triclinic space group P 1 as a full dichloromethane monosolvate. Furthermore, the crystal studied of [(dpbz) 2 FeCl 2 ][FeCl 4 ]·CH 2 Cl 2 was an inversion twin, whose component mass ratio refined to 0.76 (3):0.24 (3). Beyond a few very weak C—H...Cl and C—H...π interactions, there are no significant supramolecular features in either structure. 

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4. D -Mannosamine hydrochloride (2-amino-2-deoxy- D -mannose hydrochloride): ionic hydrogen bonding in saccharides involving chloride and aminium ions

   https://doi.org/10.1107/S2053229622002121  

   Lin, Jieye; Oliver, Allen G.; Serianni, Anthony S. (April 2022, Acta Crystallographica Section C Structural Chemistry)

   D-Mannosamine hydrochloride (2-amino-2-deoxy-D-mannose hydrochloride), C 6 H 14 NO 5 + ·Cl − , (I), crystallized from a methanol/ethyl acetate/ n -hexane solvent mixture at room temperature in a 4 C 1 chair conformation that is slightly distorted towards the C3,O5 B form. A comparison of the structural parameters of (I) with the corresponding parameters in α-D-glucosamine hydrochloride, (II), and β-D-galactosamine hydrochloride, (III)/(III′), was undertaken to evaluate the effects of ionic hydrogen bonding on structural properties. Three types of ionic hydrogen bonds are present in the crystals of (I)–(III)/(III′), i.e. N + —H...O, N + —H...Cl − , and O—H...Cl − . The exocyclic structural parameters in (I), (II), and (III)/(III′) appear to be most influenced by this bonding, especially the exocyclic hydroxy groups, which adopt eclipsed conformations enabled by ionic hydrogen bonding to the chloride anion. Anomeric disorder was observed in crystals of (I), with an α:β ratio of 37:63. However, anomeric configuration appears to exert minimal structural effects; that is, bond lengths, bond angles, and torsion angles are essentially identical in both anomers. The observed disorder at the anomeric C atom of (I) appears to be caused by the presence of the chloride anion and atom O3 or O4 in proximal voids, which provide opportunities for hydrogen bonding to atom O1 in both axial and equatorial orientations. 

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5. Synthesis, reactivity, structures, and dynamic properties of gyroscope like iron complexes with dibridgehead diphosphine cages: pre- vs. post-metathesis substitutions as routes to adducts with neutral dipolar Fe(CO)(NO)(X) rotors

   https://doi.org/10.1039/c6dt03258c  

   Lang, Georgette M.; Skaper, Dirk; Hampel, Frank; Gladysz, John A. (January 2016, Dalton Transactions)

   Three routes are explored to the title halide/cyanide complexes trans -Fe(CO)(NO)(X)(P((CH 2 ) 14 ) 3 P) ( 9c-X ; X = Cl/Br/I/CN), the Fe(CO)(NO)(X) moieties of which can rotate within the diphosphine cages (Δ H ‡ /Δ S ‡ (kcal mol −1 /eu −1 ) 5.9/−20.4 and 7.4/−23.9 for 9c-Cl and 9c-I from variable temperature 13 C NMR spectra). First, reactions of the known cationic complex trans -[Fe(CO) 2 (NO)(P((CH 2 ) 14 ) 3 P)] + BF 4 − and Bu 4 N + X − give 9c-Cl /- Br /- I /- CN (75–83%). Second, reactions of the acyclic complexes trans -Fe(CO)(NO)(X)(P((CH 2 ) m CHCH 2 ) 3 ) 2 and Grubbs’ catalyst afford the tris(cycloalkenes) trans -Fe(CO)(NO)(X)(P((CH 2 ) m CHCH(CH 2 ) m ) 3 P) ( m /X = 6/Cl,Br,I,CN, 7/Cl,Br, 8/Cl,Br) as mixtures of Z / E isomers (24–41%). Third, similar reactions of trans -[Fe(CO) 2 (NO)(P((CH 2 ) m CHCH 2 ) 3 ) 2 ] + BF 4 − and Grubbs’ catalyst afford crude trans -[Fe(CO) 2 (NO)P((CH 2 ) m CHCH(CH 2 ) m ) 3 P)] + BF 4 − ( m = 6, 8). However, the CC hydrogenations required to consummate routes 2 and 3 are problematic. Crystal structures of 9c-Cl /- Br /- CN are determined. Although the CO/NO/X ligands are disordered, the void space within the diphosphine cages is analyzed in terms of horizontal and vertical constraints upon Fe(CO)(NO)(X) rotation and the NMR data. The molecules pack in identical motifs with parallel P–Fe–P axes, and without intermolecular impediments to rotation in the solid state. 

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