Crystallographic studies and physicochemical properties of π-electron systems. 21. Structure of N,N'-bis(p-chlorophenyl)formamidine

Anulewicz, R.; Krygowski, Tadeusz M.; Pniewska, B.

doi:10.1107/s0108270190000907

Cited by 6 publications

(5 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Comparing these histograms, we see that the upper peak close to log( G / G 0 ) = −4 can be assigned to compound 1b . On the other hand, the lower peak at log( G / G 0 ) = −4.8 agrees with the low-conductance peak described above for compound 2 (see Figure S6) and may originate from the formation of 2·2 dimers. − Figures S12 and S13 show a closer comparison of the histograms for 1b·2 with those of 1b and 2 , separately.…”

Section: Resultssupporting

confidence: 84%

Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

et al. 2019

View full text Add to dashboard Cite

The effect of the in-backbone presence of charge-assisted hydrogen bonds (CAHBs) in the conductance of single-molecule junctions has been studied by the scanning tunneling microscope break junction technique. In particular, two amidinium−carboxylate supramolecular complexes of different lengths have been tested. We observed that the ionic character that gives extra stability to the CAHB is a hindrance toward the electron transport through the complexes. Theoretical calculations using the DFT + Σ method indicate that both the highest occupied molecular orbital and lowest unoccupied molecular orbital of the complexes are fully localized in only one of the moieties of the complex explaining the low singlemolecular conductance of the compounds.

show abstract

Section: Resultssupporting

confidence: 84%

Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

et al. 2019

View full text Add to dashboard Cite

show abstract

“…The symmetry of II and III automatically resulted from the previous assumption of a C 2/ c space group. , However, we note that the XRD symmetries at room temperature are not perfect, and it is conceivable that XRD measurements at cryogenic temperatures may reveal a lower symmetry, i.e., space group Cc , corresponding to type A dimers. In order to determine whether the symmetry of Figure a is intrinsic or only realized within the margin of the experimental error, a Hamilton test 28 was performed on the XRD data, but it was not possible to differentiate between these two cases since the number of reflexes was not sufficient.…”

Section: Resultsmentioning

confidence: 74%

“…Evidence was obtained that only the s-trans conformers are able to form cyclic hydrogen-bonded dimers (Figure b) in which fast double proton transfers can take place, in analogy to carboxylic acid dimers. On the other hand, X-ray diffraction techniques (XRD) showed that neither substituted acetamidines nor benzamidines form cyclic dimers in the solid state. , These species have, however, finally been observed in recent years in the case of some N , N -bisarylformamidines with the aryl substituents phenyl ( I ), p -bromophenyl ( II ), and p -chlorophenyl ( III ) . In these compounds the amidine planes are generally not planar; in addition, − the aryl rings are considerably twisted out from the amidine planes.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, X-ray diffraction techniques (XRD) showed that neither substituted acetamidines nor benzamidines form cyclic dimers in the solid state. , These species have, however, finally been observed in recent years in the case of some N , N -bisarylformamidines with the aryl substituents phenyl ( I ), p -bromophenyl ( II ), and p -chlorophenyl ( III ) . In these compounds the amidine planes are generally not planar; in addition, − the aryl rings are considerably twisted out from the amidine planes. The observed twist angles result from the balance between the potential coupling of these two π-electron systems and the steric and other components of the crystal packing forces.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

et al. 1997

View full text Add to dashboard Cite

Crystal structures of a series of five symmetrically substituted N,N-bisarylformamidines ArNHsCHdNAr with Ar ) X-C 6 H 4 , X ) p-OCH 3 (IV), p-CH 3 (V), p-F (VI), p-NO 2 (VII), and m-Br (VIII) have been determined by single-crystal X-ray diffraction (XRD) and complete the series studied previously where X ) H (I), p-Br (II), and p-Cl (III). In addition, the results of variable-temperature 15 N CPMAS NMR experiments performed on 15 Nlabeled I, II, and IV are reported. All compounds form cyclic dimers linked by two NsH‚‚‚N hydrogen bonds which can form two different tautomers, a and b, interconverting by fast double proton transfers. The NMR experiments indicate three types of amidines characterized by different magnitudes of the equilibrium constants K ab of the tautomerism. In dimers of type such as V-VIII, we find K ab , 1 (i.e., only a single tautomer in the temperature range between 100 and 300 K). In this case, the hydrogen-bonded protons are ordered and can be localized by XRD. Furthermore, the C‚‚‚N bond lengths and torsional and valence angles involving the two aryl groups of an amidine unit are different. For dimers such as II and III, characteristic temperature dependent 15 N CPMAS NMR line shape changes are observed indicating that K ab ) 1 within the margin of error. Rate constants of the tautomerism can in this case be obtained by line shape analysis. For this degeneracy to occur, the aryl group conformations at both amidine nitrogen atoms must be similar. XRD then observes disordered hydrogen-bond protons and, in principle, also disordered nitrogen atoms. However, in practice, the disorder of the latter is not resolved leading to the observation of equalized C‚‚‚N bond lengths. Finally, dimers (I, IV) represent an intermediate case with K ab < 1, which could be labeled as "dynamic partial order". The implications of the molecular structure and the hydrogen bond and proton transfer characteristics are discussed.

show abstract

“…3). The acetamidine (R = Me) crystallized as the hydrogen-bonded dimer (11), typical of N,N -diarylformamidines (R = H), 19 with the substituents in an E anti arrangement. In contrast, the derivative containing a p-tolyl carbon substituent (12) formed an intimate mixture of the Z anti and E syn tautomers in the solid state (differing only in the position of the double bond and the hydrogen atom) whereas the corresponding p-methoxyphenyland trifluoromethyl compounds (13 and 14) were shown to be pure Z anti .…”

Section: Isomers and Tautomersmentioning

confidence: 99%

Application of neutral amidines and guanidines in coordination chemistry

2006

View full text Add to dashboard Cite

The aim of this perspective is to highlight the continued development and application of amidines and guanidines as neutral, N-based donor ligands in coordination chemistry. From a sporadic interest dating back to the 1980s, work on these two closely related classes of compounds has steadily grown, with examples of evermore sophisticated substitution about the common ligand framework being developed to address specific problems in a number of fields of chemistry. These compounds have shown varied coordination modes at metals from across the periodic table, and examples of their application in a number of catalytic processes are emerging as the field matures.

show abstract

Crystallographic studies and physicochemical properties of π-electron systems. 21. Structure of N,N'-bis(p-chlorophenyl)formamidine

Cited by 6 publications

References 7 publications

Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Application of neutral amidines and guanidines in coordination chemistry

Contact Info

Product

Resources

About

Crystallographic studies and physicochemical properties of π-electron systems. 21. Structure of N,N'-bis(p-chlorophenyl)formamidine

Cited by 6 publications

References 7 publications

Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

Combined X-ray Diffraction and 15N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers

Application of neutral amidines and guanidines in coordination chemistry

Contact Info

Product

Resources

About

Combined X-ray Diffraction and ¹⁵N CPMAS NMR Study of Molecular Structure and Proton Order/Disorder Phenomena in Cyclic N,N‘-Bisarylformamidine Dimers