Synchrotron X-ray analysis of the electron density in CoF₂ and ZnF₂

Accurate structure factors for small crystals of the rutile-type structures CoF₂, cobalt difluoride, and ZnF₂, zinc difluoride, have been measured with focused λ = 0.8400 (2) Å synchrotron X-radiation at room temperature. Phenomenological structural trends across the full series of rutile-type transition metal difluorides are analysed, showing the importance of the metal atom in the degree of distortion of the metal–F₆ octahedra in these structures. Multipole models reveal strong asphericities in the electron density surrounding the transition metals, which are consistent with expectations from crystal field theory and the structural trends in these compounds. Transition metal 3d-orbital populations were computed from the multipole refinement parameters, showing significant repopulation of orbitals compared with the free atom, particularly for CoF₂.

Computing details

For both compounds, data reduction: Xtal DIFDAT ADDREF SORTRF ABSORB; program(s) used to solve structure: Xtal; program(s) used to refine structure: Xtal CRYLSQ; molecular graphics: Xtal; software used to prepare material for publication: Xtal CIFIO.

Figures

(cof2)

Crystal data

CoF2	Dx = 4.592 Mg m^−3
Mr = 12.12	Synchrotron radiation, λ = 0.84 Å
Tetragonal, P42/mnm	Cell parameters from 6 reflections
Hall symbol: -P 4n 2n	θ = 45.7–52.4°
a = 4.6956 (5) Å	µ = 18.22 mm^−1
c = 3.1793 (3) Å	T = 293 K
V = 70.10 (2) Å^3	Rectangular, pink
Z = 16	× × mm
F(000) = 90

Data collection

BL14A Four circle diffractometer	2502 reflections with I > 2σ(I)
Radiation source: Photon Factory BL14A	Rint = 0.039
Si(111) monochromator	θmax = 67.4°, θmin = 7.3°
ω–2θ scans	h = −10→10
Absorption correction: analytical ?	k = −10→10
Tmin = 0.801, Tmax = 0.864	l = −6→6
2883 measured reflections	6 standard reflections every 94 reflections
2883 independent reflections	intensity decay: 3%

Refinement

Refinement on F	0 constraints
Least-squares matrix: full	w = 1/σ^2(F)
R[F^2 > 2σ(F^2)] = 0.019	(Δ/σ)max = 0.00005
wR(F^2) = 0.015	Δρmax = 1.17 e Å^−3
S = 2.42	Δρmin = −1.07 e Å^−3
235 reflections	Extinction correction: Zachariasen, Eq22 p292 "Cryst. Comp." Munksgaard 1970
9 parameters	Extinction coefficient: 9132 (847)
0 restraints

Special details

Refinement. Sfls F σ weight full matrix

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Co	0.00000	0.00000	0.00000	0.00634 (4)
F	0.30341 (11)	0.30341 (11)	0.00000	0.01063 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co	0.00685 (3)	0.00685 (3)	0.00533 (5)	−0.00073 (5)	0.00000	0.00000
F	0.01194 (15)	0.01194 (15)	0.0080 (2)	−0.0053 (2)	0.00000	0.00000

(znf2)

Crystal data

ZnF2	Dx = 4.952 Mg m^−3
Mr = 12.92	Synchrotron radiation, λ = 0.84 Å
Tetragonal, P42/mnm	Cell parameters from 6 reflections
Hall symbol: -P 4n 2n	θ = 45.6–53.5°
a = 4.7038 (15) Å	µ = 26.55 mm^−1
c = 3.1336 (7) Å	T = 293 K
V = 69.33 (5) Å^3	Rectangular, clear
Z = 16	× × mm
F(000) = 96

Data collection

BL14A Four circle diffractometer	2460 reflections with I > 2σ(I)
Radiation source: Photon Factory BL14A	Rint = 0.04
Si(111) monochromator	θmax = 67.5°, θmin = 7.3°
ω–2θ scans	h = −10→10
Absorption correction: analytical ?	k = −10→10
Tmin = 0.527, Tmax = 0.754	l = −6→6
2727 measured reflections	6 standard reflections every 94 reflections
2727 independent reflections	intensity decay: 3%

Refinement

Refinement on F	0 constraints
Least-squares matrix: full	w = 1/σ^2(F)
R[F^2 > 2σ(F^2)] = 0.014	(Δ/σ)max = 0.00013
wR(F^2) = 0.016	Δρmax = 0.72 e Å^−3
S = 2.39	Δρmin = −0.68 e Å^−3
237 reflections	Extinction correction: Zachariasen, Eq22 p292 "Cryst. Comp." Munksgaard 1970
9 parameters	Extinction coefficient: 3273 (120)
0 restraints

Special details

Refinement. Sfls F σ weight full matrix

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Zn	0.00000	0.00000	0.00000	0.00876 (5)
F	0.30350 (9)	0.30350 (9)	0.00000	0.01231 (12)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn	0.00917 (4)	0.00917 (4)	0.00793 (7)	−0.00111 (3)	0.00000	0.00000
F	0.01307 (10)	0.01307 (10)	0.01080 (17)	−0.00515 (17)	0.00000	0.00000