Orientational disorder and phase transitions in crystals of dioxofluoromolybdate, (NH₄)₂MoO₂F₄

Dioxotetrafluoromolybdate, (NH₄)₂MoO₂F₄, was synthesized in a single-crystal form and its structures [(I) at 297 K and (II) at 223 K] were determined by X-ray diffraction. Two independent states of a cis-MoO₂F₄ octahedron are characteristic of static and dynamic disorder in structure (I). The dynamically disordered Mo atom is displaced from the symmetry axis producing four possible orientations of an anion that allow O and F atoms to be identified in separate orientations owing to the inherent differences between the Mo—O and Mo—F bonding. After the phase transition at lower temperature, (I) transforms into the statically disordered structure (II) with three possible orientations of the cis-MoO₂F₄ octahedron. In this case, it also seemed possible to distinguish between O and F atoms on a local scale. H atoms of two independent NH₄ groups in (II) which form bifurcated N—H...F(O) hydrogen bonds were localized.

Computing details

For both structures, data collection: Bruker Smart v5.054 (Bruker, 1998); cell refinement: Bruker SAINT v6.02a (Bruker, 2000); data reduction: Bruker SAINT v6.02a (Bruker, 2000); program(s) used to solve structure: Bruker SHELXTL v5.1 (Bruker, 1998); program(s) used to refine structure: Bruker SHELXTL v5.1 (Bruker, 1998); molecular graphics: Bruker SHELXTL v5.1 (Bruker, 1998); software used to prepare material for publication: Bruker SHELXTL v5.1 (Bruker, 1998).

ammonium dioxotetrafluoromolybdate (RT)

Crystal data

(F4MoO2)·2(H4N)	F(000) = 464
Mr = 240.02	Dx = 2.595 Mg m^−3
Orthorhombic, Cmcm	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2c 2	Cell parameters from 899 reflections
a = 5.9672 (7) Å	θ = 4.7–43.4°
b = 14.4798 (17) Å	µ = 2.16 mm^−1
c = 7.1105 (9) Å	T = 297 K
V = 614.37 (13) Å^3	Sphere, colorless
Z = 4	0.30 × 0.30 × 0.30 mm

Data collection

Bruker Smart 1000 CCD diffractometer	1276 independent reflections
Radiation source: fine-focus sealed tube	1202 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
Detector resolution: 8.33 pixels mm^-1	θmax = 43.4°, θmin = 4.7°
ω scans	h = −10→11
Absorption correction: multi-scan SADABS v.2.03; Bruker 1999	k = −27→27
Tmin = 0.564, Tmax = 0.564	l = −13→13
8355 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.025	w = 1/[σ^2(Fo^2) + (0.0296P)^2 + 0.3032P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.077	(Δ/σ)max = 0.033
S = 1.30	Δρmax = 0.55 e Å^−3
1278 reflections	Δρmin = −0.64 e Å^−3
41 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.029 (3)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mo1	0.0000	0.10349 (14)	0.2500	0.0240 (10)	0.43 (4)
Mo2	0.0237 (6)	0.1084 (3)	0.2266 (7)	0.0273 (5)	0.141 (10)
N1	0.5000	0.27122 (17)	0.2500	0.0408 (5)
N2	0.0000	0.4382 (2)	0.2500	0.0419 (5)
F1	0.0000	0.24576 (12)	0.2500	0.0605 (7)
O1	0.0000	−0.01262 (13)	0.2500	0.0414 (4)
F2	0.22677 (17)	0.11934 (9)	0.06492 (13)	0.0446 (2)	0.75
O2	0.22677 (17)	0.11934 (9)	0.06492 (13)	0.0446 (2)	0.25

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo1	0.0295 (12)	0.0164 (10)	0.0261 (16)	0.000	0.000	0.000
Mo2	0.0191 (9)	0.0392 (11)	0.0236 (7)	0.0000 (3)	0.0035 (3)	−0.0026 (5)
N1	0.0346 (10)	0.0336 (9)	0.0541 (13)	0.000	0.000	0.000
N2	0.0371 (11)	0.0457 (12)	0.0430 (11)	0.000	0.000	0.000
F1	0.0534 (11)	0.0224 (6)	0.106 (2)	0.000	0.000	0.000
O1	0.0451 (10)	0.0239 (6)	0.0552 (12)	0.000	0.000	0.000
F2	0.0329 (4)	0.0679 (6)	0.0331 (4)	−0.0072 (4)	0.0123 (3)	−0.0052 (4)
O2	0.0329 (4)	0.0679 (6)	0.0331 (4)	−0.0072 (4)	0.0123 (3)	−0.0052 (4)

Geometric parameters (Å, º)

Mo1—Mo2^i	0.229 (6)	N1—F2^viii	3.0589 (17)
Mo1—Mo2^ii	0.229 (6)	N1—O2^ix	3.0589 (17)
Mo1—Mo2^iii	0.229 (6)	N1—O2^x	3.0589 (17)
Mo1—O1	1.681 (3)	N1—O1^xi	3.130 (3)
Mo1—O2^ii	1.9015 (9)	N2—F1	2.787 (3)
Mo1—O2^iii	1.9015 (9)	N2—O2^xii	2.8927 (12)
Mo1—O2^i	1.9015 (9)	N2—F2^viii	2.8927 (12)
Mo1—F2	1.9015 (9)	N2—O2^xiii	2.8927 (12)
Mo1—F1	2.060 (3)	N2—O2^ix	2.8927 (12)
Mo2—Mo2^iii	0.282 (7)	N2—O1^xi	3.0673 (9)
Mo2—Mo2^ii	0.332 (10)	N2—O1^xiv	3.0673 (9)
Mo2—Mo2^i	0.436 (11)	N2—O2^xv	3.356 (3)
Mo2—F2	1.678 (5)	N2—O2^xvi	3.356 (3)
Mo2—O1	1.766 (5)	N2—F2^xvii	3.356 (3)
Mo2—O2^iii	1.892 (3)	N2—F2^xiv	3.356 (3)
Mo2—O2^ii	1.921 (4)	F1—O2^iii	2.6294 (16)
Mo2—F1	2.001 (4)	F1—F2^i	2.6294 (16)
Mo2—O2^i	2.111 (5)	F1—O2^ii	2.6294 (16)
N1—F1	3.0063 (5)	F1—F2	2.6294 (16)
N1—F1^iv	3.0063 (5)	O1—O2^ii	2.6857 (17)
N1—F2	3.037 (2)	O1—F2	2.6857 (17)
N1—O2^ii	3.037 (2)	O1—O2^i	2.6857 (17)
N1—F2^v	3.037 (2)	O1—O2^iii	2.6857 (17)
N1—O2^vi	3.037 (2)	F2—O2^ii	2.6320 (19)
N1—O2^vii	3.0589 (17)	F2—O2^iii	2.706 (2)
O1—Mo1—O2^ii	96.93 (7)	F2—Mo2—O1	102.46 (14)
O1—Mo1—F2^ii	96.93 (7)	F2—Mo2—O2^iii	98.4 (3)
O1—Mo1—O2^iii	96.93 (7)	O1—Mo2—O2^iii	94.42 (18)
O2^ii—Mo1—O2^iii	166.14 (15)	F2—Mo2—F1	90.8 (3)
F2^ii—Mo1—O2^iii	166.14 (15)	O1—Mo2—O2^ii	93.4 (2)
O1—Mo1—F2^iii	96.93 (7)	F2—Mo2—F2^ii	93.76 (18)
O2^ii—Mo1—O2^i	90.74 (7)	O2^iii—Mo2—F2^ii	163.76 (19)
F2^ii—Mo1—O2^i	90.74 (7)	O1—Mo2—F1	166.7 (3)
O2^iii—Mo1—O2^i	87.59 (7)	O2^iii—Mo2—F1	84.93 (16)
F2^iii—Mo1—O2^i	87.59 (7)	O2^ii—Mo2—F1	84.18 (14)
O1—Mo1—F1	180.0	F2—Mo2—O2^i	170.2 (3)
O2^ii—Mo1—F1	83.07 (7)	O1—Mo2—O2^i	87.2 (3)
O2^iii—Mo1—F1	83.07 (7)	O2^iii—Mo2—O2^i	82.03 (15)
O2^i—Mo1—F1	83.07 (7)	O2^ii—Mo2—O2^i	84.2 (2)
F2—Mo1—F1	83.07 (7)	F1—Mo2—O2^i	79.47 (10)

Symmetry codes: (i) −x, y, −z+1/2; (ii) x, y, −z+1/2; (iii) −x, y, z; (iv) x+1, y, z; (v) −x+1, y, −z+1/2; (vi) −x+1, y, z; (vii) x+1/2, −y+1/2, z+1/2; (viii) −x+1/2, −y+1/2, z+1/2; (ix) −x+1/2, −y+1/2, −z; (x) x+1/2, −y+1/2, −z; (xi) x+1/2, y+1/2, z; (xii) x−1/2, −y+1/2, −z; (xiii) x−1/2, −y+1/2, z+1/2; (xiv) x−1/2, y+1/2, z; (xv) −x+1/2, y+1/2, −z+1/2; (xvi) −x+1/2, y+1/2, z; (xvii) x−1/2, y+1/2, −z+1/2.

ammonium dioxotetrafluoromolybdate (LT)

Crystal data

(F4MoO2)·2(H4N)	F(000) = 464
Mr = 240.02	Dx = 2.650 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 969 reflections
a = 7.1452 (4) Å	θ = 2.9–43.4°
b = 5.8979 (3) Å	µ = 2.21 mm^−1
c = 14.2737 (7) Å	T = 223 K
V = 601.52 (5) Å^3	Sphere, colorless
Z = 4	0.30 × 0.30 × 0.30 mm

Data collection

Bruker Smart 1000 CCD diffractometer	2362 independent reflections
Radiation source: fine-focus sealed tube	2237 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
Detector resolution: 8.33 pixels mm^-1	θmax = 43.4°, θmin = 2.9°
ω scans	h = −13→13
Absorption correction: multi-scan SADABS v.2.03; Bruker 1999	k = −11→10
Tmin = 0.558, Tmax = 0.558	l = −26→27
15861 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.023	H-atom parameters not refined
wR(F^2) = 0.063	w = 1/[σ^2(Fo^2) + (0.0239P)^2 + 0.2646P] where P = (Fo^2 + 2Fc^2)/3
S = 1.22	(Δ/σ)max = 0.142
2362 reflections	Δρmax = 0.75 e Å^−3
60 parameters	Δρmin = −1.56 e Å^−3
0 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0150 (15)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mo1	0.30609 (8)	0.2500	0.13002 (5)	0.01391 (9)	0.4104 (14)
Mo2	0.28753 (7)	0.22779 (14)	0.14343 (4)	0.01500 (12)	0.2948 (7)
N1	0.29547 (17)	0.2500	0.47581 (9)	0.02317 (19)
N2	0.27591 (19)	0.7500	0.30300 (9)	0.0247 (2)
O1	0.27924 (16)	0.2500	0.26264 (7)	0.02634 (19)	0.50
F1	0.27924 (16)	0.2500	0.26264 (7)	0.02634 (19)	0.50
O2	0.45390 (11)	0.02252 (14)	0.12209 (6)	0.02736 (14)	0.75
F2	0.45390 (11)	0.02252 (14)	0.12209 (6)	0.02736 (14)	0.25
F3	0.23317 (17)	0.2500	0.00101 (6)	0.02885 (19)
F4	0.08373 (10)	0.01878 (13)	0.13688 (5)	0.02548 (12)
H1	0.3709	0.2500	0.4300	0.065*
H2	0.2260	0.1330	0.4746	0.065*
H3	0.3548	0.2500	0.5260	0.065*
H4	0.3478	0.8696	0.3090	0.065*
H5	0.1863	0.7500	0.3404	0.065*
H6	0.2304	0.7500	0.2453	0.065*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo1	0.01203 (12)	0.01303 (17)	0.01668 (17)	0.000	−0.00041 (10)	0.000
Mo2	0.01531 (12)	0.0136 (3)	0.01606 (13)	0.00071 (9)	−0.00052 (8)	0.00039 (10)
N1	0.0245 (5)	0.0249 (5)	0.0201 (4)	0.000	−0.0001 (3)	0.000
N2	0.0241 (5)	0.0278 (6)	0.0223 (4)	0.000	0.0009 (3)	0.000
O1	0.0318 (5)	0.0309 (5)	0.0164 (3)	0.000	−0.0026 (3)	0.000
F1	0.0318 (5)	0.0309 (5)	0.0164 (3)	0.000	−0.0026 (3)	0.000
O2	0.0212 (3)	0.0212 (3)	0.0397 (4)	0.0075 (2)	−0.0004 (2)	−0.0029 (3)
F2	0.0212 (3)	0.0212 (3)	0.0397 (4)	0.0075 (2)	−0.0004 (2)	−0.0029 (3)
F3	0.0378 (5)	0.0333 (5)	0.0155 (3)	0.000	−0.0010 (3)	0.000
F4	0.0221 (2)	0.0220 (3)	0.0324 (3)	−0.0080 (2)	0.00431 (19)	−0.0041 (2)

Geometric parameters (Å, º)

Mo1—Mo2^i	0.2671 (8)	N1—H2	0.8502
Mo1—O2^i	1.7112 (8)	N1—H3	0.8324
Mo1—O2	1.7112 (8)	N2—F3^vi	2.8270 (16)
Mo1—O1	1.9027 (12)	N2—F4^ix	2.8438 (13)
Mo1—F3	1.9139 (11)	N2—F4^iv	2.8438 (13)
Mo1—F4	2.0961 (8)	N2—F2^viii	3.0034 (14)
Mo1—F4^i	2.0961 (8)	N2—F2^x	3.0034 (14)
Mo2—Mo2^i	0.2619 (16)	N2—O1	3.0048 (3)
Mo2—O1	1.7077 (11)	N2—O1^xi	3.0048 (3)
Mo2—O2	1.7239 (10)	N2—F4^i	3.1655 (14)
Mo2—F4	1.9101 (9)	N2—F4^xi	3.1655 (14)
Mo2—F2^i	1.9169 (10)	N2—F2^i	3.2969 (15)
Mo2—F3	2.0738 (11)	N2—F2^xi	3.2969 (15)
Mo2—F4^i	2.0888 (9)	N2—H4	0.8768
N1—F4^ii	2.9230 (13)	N2—H5	0.8336
N1—F4^iii	2.9230 (13)	N2—H6	0.8855
N1—F4^iv	2.9478 (14)	F1—F4	2.6520 (11)
N1—F4^v	2.9478 (14)	F1—F4^i	2.6520 (11)
N1—F3^vi	2.9778 (3)	F1—O2	2.7171 (12)
N1—F3^iii	2.9778 (3)	F1—O2^i	2.7171 (12)
N1—O1	3.0449 (17)	O2—F3	2.6971 (12)
N1—F2^vii	3.1160 (14)	F3—O2^i	2.6971 (12)
N1—F2^viii	3.1160 (14)	F3—F4^i	2.6002 (11)
N1—F3^v	3.1449 (17)	F3—F4	2.6002 (11)
N1—F2^ii	3.1808 (14)	O2—O2^i	2.6833 (16)
N1—F2^iii	3.1808 (14)	O2—F4	2.6534 (11)
N1—H1	0.8474	F4—F4^i	2.7274 (15)
O2^i—Mo1—F1	97.36 (4)	O1—Mo2—O2	104.71 (5)
O2—Mo1—F1	97.36 (4)	O1—Mo2—F2^i	96.95 (5)
F1—Mo1—F4	82.94 (4)	O1—Mo2—F4^i	88.02 (4)
F1—Mo1—F4^i	82.94 (4)	O1—Mo2—F3	164.90 (6)
O2^i—Mo1—F3	95.99 (4)	F4—Mo2—F3	81.37 (4)
O2—Mo1—F3	95.99 (4)	O2—Mo2—F3	90.01 (4)
F3—Mo1—F4	80.71 (4)	F2^i—Mo2—F3	84.94 (4)
F3—Mo1—F4^i	80.71 (4)	F3—Mo2—F4^i	77.31 (4)
O2—Mo1—F4	87.75 (4)	O2—Mo2—F4^i	167.25 (5)
O2^i—Mo1—F4^i	87.75 (4)	O2—Mo2—F2^i	94.81 (6)
O2^i—Mo1—O2	103.26 (7)	F2^i—Mo2—F4^i	82.85 (5)
F4—Mo1—F4^i	81.17 (5)	F4—Mo2—F4^i	85.88 (5)
F1—Mo1—F3	158.41 (6)	O2—Mo2—F4	93.66 (5)
O2^i—Mo1—F4	168.81 (4)	F4—Mo2—F2^i	163.89 (5)
O1—Mo2—F4	94.12 (4)

Symmetry codes: (i) x, −y+1/2, z; (ii) −x+1/2, y+1/2, z+1/2; (iii) −x+1/2, −y, z+1/2; (iv) x+1/2, −y+1/2, −z+1/2; (v) x+1/2, y, −z+1/2; (vi) −x+1/2, −y+1, z+1/2; (vii) x−1/2, y, −z+1/2; (viii) x−1/2, −y+1/2, −z+1/2; (ix) x+1/2, y+1, −z+1/2; (x) x−1/2, y+1, −z+1/2; (xi) x, y+1, z.