Crystal structure of bis­(diiso­propyl­ammonium) molybdate

The crystal structure of the title salt, (C₆H₁₆N)₂[MoO₄], results from N—H⋯O hydrogen-bonded rings formed through inter­connections between the (ⁱPr₂NH₂)⁺ cations and [MoO₄]²⁻ anions.

Abstract

The organic–inorganic title salt, (C₆H₁₆N)₂[MoO₄] or (ⁱPr₂NH₂)₂[MoO₄], was obtained by reacting MoO₃ with diiso­propyl­amine in a 1:2 molar ratio in water. The molybdate anion is located on a twofold rotation axis and exhibits a slightly distorted tetra­hedral configuration. In the crystal structure, the diiso­propyl­ammmonium (ⁱPr₂NH₂)⁺ cations and [MoO₄]²⁻ anions are linked to each other through N—H⋯O hydrogen bonds, generating rings with R ₁₂ ¹²(36) motifs that give rise to the formation of a three-dimensional network. The structure was refined taking into account inversion twinning (ratio of ca 4:1 between the two domains).

Chemical context  

As a result of the photochromic properties of alkyl­ammonium molybdates (Arnaud-Neu & Schwing-Weill, 1974 ▸), molybdenum chemistry is an exciting research area. A large variety of oxidoanions based on molybdenum have been synthesized and characterized with numerous counter-cations. Among these, mononuclear and binuclear anions as well as polyoxidomolybdates with a much higher nuclearity are known (Gatehouse & Leverett, 1969 ▸; Matsumoto et al. 1975 ▸; Modec et al., 2004 ▸; Müller & Gouzerh, 2012 ▸; Pouye et al., 2014 ▸; Sarr et al., 2018 ▸). Salts containing the tetra­hedral molybdate anion [MoO₄]^2– combined with cations such as K⁺, Na⁺, (CH₆N₃)⁺, ((C₆H₁₁)₂NH₂)⁺, (NH₃(CH₂)₂NH₃)⁺, (OHRNH₃)⁺ and (CyNH₂)⁺ have been isolated in the past (Gatehouse & Leverett, 1969 ▸; Matsumoto et al., 1975 ▸; Ozeki et al., 1987 ▸; Thiele & Fuchs, 1979 ▸; Bensch et al., 1987 ▸; Sheikhshoaie & Ghazizadeh, 2013 ▸; Pouye et al., 2014 ▸), but never with the diiso­propyl­ammonium cation (ⁱPr₂NH₂)⁺. In a continuation of our work on molybdenum compounds with organic cations, we report here the synthesis and crystal structure of the title compound, (ⁱPr₂NH₂)₂[MoO₄], (I).

Structural commentary  

The asymmetric unit of (I) comprises one (ⁱPr₂NH₂)⁺ cation and an {MoO₂} entity (Fig. 1 ▸). The [MoO₄]^2– molybdate anion is completed by application of twofold rotation symmetry. The two Mo—O distances are 1.732 (2) and 1.7505 (15) Å and the O—Mo—O angles vary in a narrow range between 108.77 (10) and 110.7 (2)° (Table 1 ▸), revealing only slight distortions from ideal values. Similar bond lengths and angles for the molybdate anion were reported in previous studies (Ozeki et al., 1987 ▸; Bensch et al., 1987 ▸; Sheikhshoaie & Ghazizadeh, 2013 ▸; Pouye et al., 2014 ▸) where the Mo—O distances vary between 1.749 (2) and 1.776 (3) Å, and the O—Mo—O angles between 106.85 (4) and 113.2 (1)°.

Figure 1.

Asymmetric unit view of (I) with displacement ellipsoids drawn at the 50% probability level and hydrogen atoms as spheres of arbitrary radius.

Table 1. Selected bond angles (°).

O1i—Mo1—O1	110.33 (12)	O2—Mo1—O1	108.77 (10)
O2—Mo1—O1i	109.13 (11)	O2i—Mo1—O2	110.7 (2)

Symmetry code: (i) .

In the crystal structure of (CyNH₂)₂MoO₄·2H₂O (Cy = cyclo­hexyl; Pouye et al., 2014 ▸) the four Mo—O bond lengths are equal with 1.7613 (12) Å. Although in this structure similar N—H⋯O inter­molecular inter­actions between the (CyNH₂)⁺ cation and the molybdate anion are present in comparison with the (ⁱPr₂NH₂)⁺ cation in the title compound, the small differences in the hydrogen-bonding pattern result in slightly different Mo—O bond lengths between the two structures. On one hand this may be related to the presence of additional water mol­ecules in (CyNH₂)₂MoO₄·2H₂O, on the other hand to steric hindrance between the four diiso­propyl­ammonium cations that surround each molybdate anion in (I). At least the strengths of the N—H⋯O hydrogen bonds do not seem to have a noticeable effect on the different Mo—O distances in (I). Both hydrogen bonds are very similar in terms of N⋯O distances and N—H⋯O angles (Table 2 ▸).

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O2	0.89	1.80	2.684 (3)	170
N1—H1B⋯O1ii	0.89	1.81	2.695 (2)	174

Symmetry code: (ii) .

Supra­molecular features  

In the crystal structure of (I), each [MoO₄]^2– anion is linked to two pairs of symmetry-related diiso­propyl­ammonium cations through N—H⋯O hydrogen bonds (Table 2 ▸). Contrariwise, each (ⁱPr₂NH₂)⁺ cation is linked to two molybdate [MoO₄]²⁻ anions. The inter­action of six molybdate anions with six diiso­propyl­ammonium cations leads to {(ⁱPr₂NH₂)⋯MoO₄}₆ ring systems with an (36) motif (Etter et al., 1990 ▸). Each ring is linked to six adjacent rings giving rise to infinite layers extending parallel to (010) (Fig. 2 ▸). The connection of the rings into a three-dimensional network structure perpendicular to this plane is shown in Fig. 3 ▸.

Figure 2.

The N—H⋯O hydrogen-bonding network in (I) (turquoise dashed lines) in a view approximately along [010].

Figure 3.

The N—H⋯O hydrogen-bonding network in (I) (turquoise dashed lines) in a view approximately along [001].

Database survey  

A search of the Cambridge Structural Database (Version 5.39 plus 1 update, November 2017; Groom et al., 2016 ▸) revealed 226 entries dealing with (ⁱPr₂NH₂)⁺ cations while 32 entries contained the [MoO₄]²⁻ molybdate anion.

Synthesis and crystallization  

Compound (I) was obtained from a mixture of molybdenum trioxide (3.2 g, 22.23 mmol) and diiso­propyl­amine (4 g, 44.46 mmol) in a 1:2 molar ratio in water. A clear, colourless solution was obtained after stirring for approximately one h. After twenty days of evaporation in an oven at 333 K, some colourless single crystals were obtained.

In the IR spectrum of (I) (Fig. 4 ▸ a), the bands at 899 and 786 cm⁻¹ can be attributed to symmetric and asymmetric Mo—O stretching modes, respectively. The diso­propyl­ammonium cation is characterized by a series of vibrational bands in the 3000–2200 cm⁻¹ region, which can be attributed to ν(N—H), ν(C—H) and combination modes. The δ(N—H) bending vibrations probably contribute to the signal observed at 1598 cm⁻¹.

Figure 4.

IR (a) and Raman (b) spectra of (I).

In the Raman spectrum of (I) (Fig. 4 ▸ b), the band at 797 cm⁻¹ is attributed to the anti­symmetric stretching mode of the [MoO₄]²⁻ molybdate anion. The symmetric vibration, ν_s(Mo—O), in the form of a weak shoulder at 839 cm⁻¹ in the infrared spectrum, is very intense in the Raman spectrum at 896 cm⁻¹. In the high wavenumber region of the Raman spectrum, the bands between 3000 and 2800 cm⁻¹ can be assigned to the ν(N—H) and ν(C—H) stretching vibrations of the diiso­propyl­ammonium cation.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. The structure was refined taking into account twinning by inversion (ratio of ca 4:1 between the two domains). H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with N—H distances of 0.89 Å and C—H distances of 0.96 Å for methyl and of 0.98 Å for methyl­ene groups, and with U_iso(H) = 1.2U _eq(C,N) or 1.5U _eq(C_meth­yl).

Table 3. Experimental details.

Crystal data
Chemical formula	(C6H16N)2[MoO4]
M r	364.33
Crystal system, space group	Tetragonal, P43212
Temperature (K)	293
a, c (Å)	9.0166 (1), 23.1158 (3)
V (Å3)	1879.29 (5)
Z	4
Radiation type	Mo Kα
μ (mm−1)	0.71
Crystal size (mm)	0.38 × 0.26 × 0.1
Data collection
Diffractometer	Rigaku Oxford Diffraction SuperNova, Dual, Cu at zero, AtlasS2
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2015 ▸)
T min, T max	0.612, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	111277, 2156, 2109
R int	0.055
(sin θ/λ)max (Å−1)	0.650
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.019, 0.049, 1.12
No. of reflections	2156
No. of parameters	92
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.21, −0.31
Absolute structure	Refined as an inversion twin
Absolute structure parameter	0.19 (7)

Computer programs: CrysAlis PRO (Rigaku OD, 2015 ▸), SHELXS (Sheldrick, 2008 ▸), SHELXL (Sheldrick, 2015 ▸) and OLEX2 (Dolomanov et al., 2009 ▸).

Supplementary Material

CCDC reference: 1874215

Additional supporting information: crystallographic information; 3D view; checkCIF report

supplementary crystallographic information

Crystal data

(C6H16N)2[MoO4]	Dx = 1.288 Mg m−3
Mr = 364.33	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P43212	Cell parameters from 49023 reflections
a = 9.0166 (1) Å	θ = 3.6–27.7°
c = 23.1158 (3) Å	µ = 0.71 mm−1
V = 1879.29 (5) Å3	T = 293 K
Z = 4	Prism, clear light colourless
F(000) = 768	0.38 × 0.26 × 0.1 mm

Data collection

Rigaku Oxford Diffraction SuperNova, Dual, Cu at zero, AtlasS2 diffractometer	2109 reflections with I > 2σ(I)
Detector resolution: 5.3048 pixels mm-1	Rint = 0.055
ω scans	θmax = 27.5°, θmin = 3.5°
Absorption correction: multi-scan (CrysAlis PRO; Rigaku OD, 2015)	h = −11→11
Tmin = 0.612, Tmax = 1.000	k = −11→11
111277 measured reflections	l = −29→30
2156 independent reflections

Refinement

Refinement on F2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F2 > 2σ(F2)] = 0.019	w = 1/[σ2(Fo2) + (0.0245P)2 + 0.4149P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.049	(Δ/σ)max < 0.001
S = 1.12	Δρmax = 0.21 e Å−3
2156 reflections	Δρmin = −0.31 e Å−3
92 parameters	Absolute structure: Refined as an inversion twin
0 restraints	Absolute structure parameter: 0.19 (7)

Special details

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

Refinement. Refined as a 2-component inversion twin.

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

	x	y	z	Uiso*/Ueq
N1	0.6950 (2)	0.2985 (3)	0.57328 (7)	0.0451 (5)
H1A	0.607999	0.280281	0.556562	0.054*
H1B	0.681809	0.289840	0.611289	0.054*
C1	0.8015 (3)	0.1790 (4)	0.55462 (12)	0.0603 (7)
H1	0.897057	0.196363	0.573616	0.072*
C2	0.7411 (5)	0.0325 (4)	0.57499 (18)	0.0827 (10)
H2A	0.725309	0.036136	0.616035	0.124*
H2B	0.810811	−0.044698	0.566106	0.124*
H2C	0.648792	0.012618	0.555832	0.124*
C3	0.8245 (4)	0.1852 (5)	0.48930 (13)	0.0872 (11)
H3A	0.731448	0.169286	0.470093	0.131*
H3B	0.893498	0.109574	0.477926	0.131*
H3C	0.863030	0.280735	0.478768	0.131*
C4	0.7349 (4)	0.4560 (3)	0.56091 (11)	0.0590 (7)
H4	0.745520	0.468318	0.518986	0.071*
C5	0.8813 (4)	0.4960 (4)	0.58963 (15)	0.0750 (10)
H5A	0.876969	0.471035	0.629966	0.112*
H5B	0.899069	0.600390	0.585479	0.112*
H5C	0.960302	0.441624	0.571562	0.112*
C6	0.6069 (4)	0.5518 (4)	0.58154 (14)	0.0735 (10)
H6A	0.518209	0.524379	0.561190	0.110*
H6B	0.628992	0.654184	0.574169	0.110*
H6C	0.592529	0.537236	0.622295	0.110*
Mo1	0.26396 (2)	0.26396 (2)	0.500000	0.03021 (9)
O1	0.2086 (2)	0.1625 (2)	0.43916 (6)	0.0510 (5)
O2	0.4506 (2)	0.2317 (4)	0.51236 (10)	0.0959 (9)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
N1	0.0337 (9)	0.0747 (15)	0.0269 (8)	0.0005 (9)	−0.0009 (7)	−0.0005 (9)
C1	0.0350 (13)	0.095 (2)	0.0510 (15)	0.0047 (13)	0.0011 (11)	−0.0167 (15)
C2	0.069 (2)	0.075 (2)	0.104 (3)	0.006 (2)	0.010 (2)	−0.016 (2)
C3	0.070 (2)	0.138 (3)	0.0536 (17)	0.007 (2)	0.0170 (16)	−0.026 (2)
C4	0.0638 (19)	0.0767 (18)	0.0364 (12)	−0.0047 (17)	−0.0013 (14)	0.0133 (12)
C5	0.064 (2)	0.083 (3)	0.078 (2)	−0.0223 (18)	−0.0017 (18)	0.003 (2)
C6	0.086 (2)	0.071 (2)	0.0631 (18)	0.0121 (18)	−0.0156 (17)	0.0083 (17)
Mo1	0.03380 (10)	0.03380 (10)	0.02304 (12)	−0.00356 (9)	−0.00072 (6)	0.00072 (6)
O1	0.0687 (12)	0.0566 (10)	0.0277 (7)	−0.0072 (9)	−0.0063 (7)	−0.0049 (7)
O2	0.0350 (9)	0.178 (3)	0.0751 (14)	0.0026 (14)	−0.0119 (9)	−0.0308 (18)

Geometric parameters (Å, º)

N1—H1A	0.8900	C4—H4	0.9800
N1—H1B	0.8900	C4—C5	1.521 (5)
N1—C1	1.506 (4)	C4—C6	1.518 (5)
N1—C4	1.493 (4)	C5—H5A	0.9600
C1—H1	0.9800	C5—H5B	0.9600
C1—C2	1.504 (5)	C5—H5C	0.9600
C1—C3	1.525 (4)	C6—H6A	0.9600
C2—H2A	0.9600	C6—H6B	0.9600
C2—H2B	0.9600	C6—H6C	0.9600
C2—H2C	0.9600	Mo1—O1	1.7505 (15)
C3—H3A	0.9600	Mo1—O1i	1.7504 (15)
C3—H3B	0.9600	Mo1—O2	1.732 (2)
C3—H3C	0.9600	Mo1—O2i	1.732 (2)
H1A—N1—H1B	107.1	N1—C4—H4	108.7
C1—N1—H1A	107.8	N1—C4—C5	110.5 (2)
C1—N1—H1B	107.8	N1—C4—C6	107.3 (3)
C4—N1—H1A	107.8	C5—C4—H4	108.7
C4—N1—H1B	107.8	C6—C4—H4	108.7
C4—N1—C1	118.2 (2)	C6—C4—C5	112.9 (3)
N1—C1—H1	108.5	C4—C5—H5A	109.5
N1—C1—C3	110.1 (3)	C4—C5—H5B	109.5
C2—C1—N1	108.0 (3)	C4—C5—H5C	109.5
C2—C1—H1	108.5	H5A—C5—H5B	109.5
C2—C1—C3	113.0 (3)	H5A—C5—H5C	109.5
C3—C1—H1	108.5	H5B—C5—H5C	109.5
C1—C2—H2A	109.5	C4—C6—H6A	109.5
C1—C2—H2B	109.5	C4—C6—H6B	109.5
C1—C2—H2C	109.5	C4—C6—H6C	109.5
H2A—C2—H2B	109.5	H6A—C6—H6B	109.5
H2A—C2—H2C	109.5	H6A—C6—H6C	109.5
H2B—C2—H2C	109.5	H6B—C6—H6C	109.5
C1—C3—H3A	109.5	O1i—Mo1—O1	110.33 (12)
C1—C3—H3B	109.5	O2i—Mo1—O1	109.13 (11)
C1—C3—H3C	109.5	O2—Mo1—O1i	109.13 (11)
H3A—C3—H3B	109.5	O2—Mo1—O1	108.77 (10)
H3A—C3—H3C	109.5	O2i—Mo1—O1i	108.77 (10)
H3B—C3—H3C	109.5	O2i—Mo1—O2	110.7 (2)
C1—N1—C4—C5	−59.1 (3)	C4—N1—C1—C2	176.6 (2)
C1—N1—C4—C6	177.5 (2)	C4—N1—C1—C3	−59.5 (3)

Symmetry code: (i) y, x, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O2	0.89	1.80	2.684 (3)	170
N1—H1B···O1ii	0.89	1.81	2.695 (2)	174

Symmetry code: (ii) y+1/2, −x+1/2, z+1/4.