The possible stereochemical conformations of the isolated ethylenediammonium dication were discussed, along with an assessment of their relative stabilities. Crystals of ethylenediammonium tetrafluoroborate-fluoride and tetrafluoroborate salts were prepared and structurally characterised. The crystal packing and hydrogen bonding interactions involving the ethylenediammonium dication were also described and analysed. In the structure of [enH2](BF4)F, the ethylenediammonium dication adopts a superposition of left-handed and right-handed C2-symmetrical gauche (synclinal) conformations, with an NCCN torsion angle of ± 75.49(10)°. These conformers form a cyclic <InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\text{R}}_{2}^{1}(7)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mtext>R</mtext> <mrow> <mn>2</mn> </mrow> <mn>1</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mn>7</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> [enH2]F+ fragment through hydrogen bonding with the fluoride anion. Three such <InlineEquation ID="IEq2"> <EquationSource Format="TEX">${\text{R}}_{2}^{1}(7)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mtext>R</mtext> <mrow> <mn>2</mn> </mrow> <mn>1</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mn>7</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> [enH2]F+ fragments, along with a fluoride anion from a fourth [enH2]F+ unit, associate into a more complex <InlineEquation ID="IEq3"> <EquationSource Format="TEX">${\text{R}}_{8}^{4}(16)$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mtext>R</mtext> <mrow> <mn>8</mn> </mrow> <mn>4</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mn>16</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> ring motif within the hydrogen-bonded network of [enH2](BF4)F. In the [enH2](BF4)2 salt, the ethylenediammonium dications adopt a trans configuration, corresponding to C2h point group symmetry. Raman and IR spectra were recorded and tentatively interpreted. A clear spectroscopic distinction between the trans and gauche conformations of the <InlineEquation ID="IEq4"> <EquationSource Format="TEX">${\mathbf{e}\mathbf{n}\text{H}}_{2}^{2+}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mrow> <mi mathvariant="bold">e</mi> <mi mathvariant="bold">n</mi> <mtext>H</mtext> </mrow> <mrow> <mn>2</mn> </mrow> <mrow> <mn>2</mn> <mo>+</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation> dication was observed and discussed.

Gauche and trans ethylenediammonium in the structures of ethylenediammonium tetrafluoroborate and tetrafluoroborate-fluoride crystals

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2025年8月12日

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Andrii Vakulka,
Evgeny Goreshnik

摘要

The possible stereochemical conformations of the isolated ethylenediammonium dication were discussed, along with an assessment of their relative stabilities. Crystals of ethylenediammonium tetrafluoroborate-fluoride and tetrafluoroborate salts were prepared and structurally characterised. The crystal packing and hydrogen bonding interactions involving the ethylenediammonium dication were also described and analysed. In the structure of [enH₂](BF₄)F, the ethylenediammonium dication adopts a superposition of left-handed and right-handed C₂-symmetrical gauche (synclinal) conformations, with an NCCN torsion angle of ± 75.49(10)°. These conformers form a cyclic ${\text{R}}_{2}^{1}(7)$ $R_{2}^{1} (7)$ [enH₂]F⁺ fragment through hydrogen bonding with the fluoride anion. Three such ${\text{R}}_{2}^{1}(7)$ $R_{2}^{1} (7)$ [enH₂]F⁺ fragments, along with a fluoride anion from a fourth [enH₂]F⁺ unit, associate into a more complex ${\text{R}}_{8}^{4}(16)$ $R_{8}^{4} (16)$ ring motif within the hydrogen-bonded network of [enH₂](BF₄)F. In the [enH₂](BF₄)₂ salt, the ethylenediammonium dications adopt a trans configuration, corresponding to C_2h point group symmetry. Raman and IR spectra were recorded and tentatively interpreted. A clear spectroscopic distinction between the trans and gauche conformations of the ${\mathbf{e}\mathbf{n}\text{H}}_{2}^{2+}$ ${e n H}_{2}^{2 +}$ dication was observed and discussed.