The low-temperature phase of morpholinium tetra­fluoro­borate

Magdalena Owczarek; Przemyslaw Szklarz; Ryszard Jakubas; Tadeusz Lis

doi:10.1107/S1600536808004339

. 2008 Mar 5;64(Pt 4):o667. doi: 10.1107/S1600536808004339

The low-temperature phase of morpholinium tetrafluoroborate

Magdalena Owczarek ^a, Przemyslaw Szklarz ^a,^*, Ryszard Jakubas ^a, Tadeusz Lis ^a

PMCID: PMC2961037 PMID: 21202061

Abstract

The crystal structure of the low-temperature form of the title compound, C₄H₁₀NO⁺·BF₄ ⁻, was determined at 80 K. Two reversible phase transitions, at 158/158 and 124/126 K (heating/cooling), were detected by differential scanning calorimetry for this compound, and the sequence of phase transitions was subsequently confirmed by single-crystal X-ray diffraction experiments. The asymmetric unit at 80 K consists of three BF₄ ⁻ tetrahedral anions and three morpholinium cations (Z′ = 3). Hydrogen-bonded morpholinium cations form chains along the [100] direction. The BF₄ ⁻ anions are connected to these chains by N—H⋯F hydrogen bonds. In the crystal structure, two different layers perpendicular to the [001] direction can be distinguished, which differ in the geometry of the hydrogen bonds between cationic and anionic species.

Related literature

For the crystal structures of morpholinium chlorate(VII) (isostructural with the title compound) and morpholinium hydrogensulfate, see: Grigoriev et al. (2008 ▶); Yin et al. (2006 ▶).

Experimental

Crystal data

C₄H₁₀NO⁺·BF₄ ⁻
M _r = 174.94
Orthorhombic,
a = 8.106 (4) Å
b = 9.417 (4) Å
c = 28.572 (11) Å
V = 2181.0 (16) Å³
Z = 12
Mo Kα radiation
μ = 0.17 mm⁻¹
T = 80 (2) K
0.5 × 0.5 × 0.4 mm

Data collection

Kuma KM-4 CCD κ-geometry diffractometer
Absorption correction: none
20616 measured reflections
4642 independent reflections
3913 reflections with I > 2σ(I)
R _int = 0.033

Refinement

R[F ² > 2σ(F ²)] = 0.037
wR(F ²) = 0.092
S = 1.13
4642 reflections
298 parameters
H-atom parameters constrained
Δρ_max = 0.46 e Å⁻³
Δρ_min = −0.31 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2006 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 1998 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808004339/gk2132sup1.cif

e-64-0o667-sup1.cif^{(22.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808004339/gk2132Isup2.hkl

e-64-0o667-Isup2.hkl^{(227.4KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1C⋯F2	0.92	1.96	2.742 (2)	142
N1—H1D⋯O3ⁱ	0.92	1.96	2.857 (2)	164
N2—H2C⋯F8	0.92	1.96	2.799 (2)	151
N2—H2D⋯O2ⁱⁱ	0.92	1.95	2.842 (2)	164
N3—H3C⋯F9	0.92	1.96	2.742 (2)	141
N3—H3D⋯O1ⁱ	0.92	1.96	2.856 (2)	164

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Symmetry codes: (i) Inline graphic ; (ii) .

supplementary crystallographic information

Comment

The morpholinium tetrafluoroborate (I) undergoes two reversible phase transitions at 158/158 K and 124/126 K (heating/cooling). At the room temperature it crystallizes in the orthorhombic space group Pnma with Z'=1. The intermediate phase appeared to be incommensurately modulated. The structure of (I) in the low-temperature phase contains ordered BF₄^- tetrahedral units and morpholinium cations in the chair conformation. The bond distances and angles in the BF₄^- anions and morpholinium cations are in agreement with the expected values. The N–H morpholinium protons are involved in the hydrogen bonds N–H···O (morpholine-morpholine zigzag chains) and N—H···F with BF₄^- anions. The tetrahedral BF₄^- anions occupy voids between morpholinium chains.

The title compound I appeared to be isostructural with morpholinium chlorate(VII) at 100 K (Grigoriev et al., 2008). Both structures are characterized by two independent hydrogen bonded layers and only slight differences in geometry of hydrogen bonds between morpholinium and anionic species are observed.

The room-temperature phase of I is isostructural with the morpholinium hydrogensulfate (Yin et al., 2006). The tetrafluoroborate anions appear to be dynamically disordered in this phase. During the phase transition from modulated to the low temperature phase at 124 K threefold increase of the lattice parameter b is observed.

Experimental

The title compound was prepared by reaction of stoichiometric amounts of morpholine and concentrated tetrafluoroboric acid in water. The resulting solid was recrystallized from methanol at room temperature. The crystal for X-ray measurements was slowly cooled from room temperature to 80 K. During cooling, the crystal undergoes phase transition from centrosymmetric (Pnma), through modulated phase, to the non-centrosymmetric P2₁2₁2₁ space group.