Bis­[benzidinium(1–)] pentamolybdate

The title compound, {(C₁₂H₁₃N₂)₂[Mo₅O₁₆]}_n, was synthesized under hydro­thermal conditions. The structure contains a two-dimensional layer, constructed from [(Mo₄O₁₄)_n]⁴ⁿ⁻ chains linked through MoO₆ octahedra, which lie across twofold axes. The [(Mo₄O₁₄)_n]⁴ⁿ⁻ chain consists of [Mo₄O₁₄]⁴⁻ clusters connected to one another by sharing their MoO₅ square-pyramidal and MoO₆ octahedral vertices in an anti disposition. The layers are linked by the cation, to which they are connected via N—H...O hydrogen bonds.

S1. Comment

From the structural point of view, Mo atoms are easy to condense into clusters, such as {Mo₂O₆} (Quintal, 2001), {Mo₄O₁₃} (Hagrman et al., 1998), {Mo₅O₁₅} (Burkholder et al., 2001; Finn et al., 2001), {Mo₆O₁₉} (Strong et al., 2000; Wang et al., 2003), {Mo₇O₂₂} (Zapf et al., 1997) and {Mo₈O₂₆} (Hagrman et al., 1999), up to giant polyoxomolybdates from the `basket' Mo₁₁₆ anion (Müller et al., 1999a) to the capped cyclic Mo₂₄₈ anion (Müller et al., 1999b). Polymolybdates are thus amongst the most complex compounds containing oxide polyanions; this complexity is a result of the flexible coordination of molybdenum, for example, fourfold (MoO₄, tetrahedron), fivefold (MoO₅, square pyramid) or sixfold (MoO₆, octahedron). Inorganic frameworks constructed from Mo—O polyhedra and exhibiting discrete structures, one-dimensional chains (Xu et al., 2003), two-dimensional layers (Calin et al., 2003) or three-dimensional open structures (Wu et al., 2002) have been reported recently.

However, the structural design of organic–inorganic hybrid materials based on molybdenum oxides remains a challenge in solid-state chemistry. One approach to the design of novel materials is the introduction of organic molecules as structure-directing components to effect (affect?) the inorganic microstructure. As a continuation of our attempts to construct new molybdates by the common Mo—O clusters as fundamental building blocks, we recently demonstrated the strategy in the design of the new compound [(C₁₂H₁₃N₂)₂][Mo₅O₁₆], (I), containing monoprotonated benzidine. Although a large number of organodiamines have been used as structure-directing components in the design of organic–inorganic hybrid materials, to the best of our knowledge, it is the first time that benzidine has been used.

The title compound is composed of [C₁₂H₁₃N₂]⁺ cations and [Mo₅O₁₆]²⁻ anions (Fig. 1). There are three kinds of crystallographically independent molybdenum sites in the Mo₅O₁₆ polyoxomolybdate unit. The Mo1 octahedron is completed by two doubly bridging O atoms, two µ₃-O atoms and two terminal O atoms, with Mo1—O bond distances in the range 1.717 (15)–2.245 (15) Å and O—Mo1—O bond angles in the range 98.6 (6)–147.7 (7)°. The Mo2 square pyramid involves three µ₃-O atoms and two terminal O atoms, with Mo2—O bond distances in the range 1.706 (16)–2.194 (14) Å and O—Mo2—O bond angles in the range 102.9 (8)–157.2 (7)°. The Mo3 octahedron involves two µ₃-O atoms, two terminal O atoms and two doubly bridging O atoms, with Mo3—O bond distances in the range 1.688 (17)–2.480 (16) Å and O—Mo(3)—O bond angles in the range 98.1 (7)–144.1 (6)° (Table 1).

The structure contains a two-dimensional layer, which is constructed from molybdenum oxide chains {Mo₄O₁₄}_n^4n- linked through {MoO₆} octahedra (Fig. 2a). The Mo1 atoms lie on twofold axes, and the {Mo₄O₁₄}_n^4n- chains lie on each sides of the Mo1 octahedron and are connected to it through edge-sharing modes. The {Mo₄O₁₄}_n^4n- chain is composed of {Mo₄O₁₄}⁴⁻ clusters, which may be described in terms of binuclear {Mo₂O₈} subunits of edge-sharing {MoO₅} square pyramids and {MoO₆} octahedra, linked through corner-sharing of oxo groups in an anti disposition (Fig. 2 b).

The benzidine cations participate in a number of N—H···O hydrogen bonds (Table 2), and the cations thereby link adjacent sheets, so forming a pillared-layer framework (Fig. 3).

Additionally, there is a π–π stacking interaction between near-parallel benzidine molecules at (x, y, z) and (−0.5 − x,-0.5 − y, z); the ring separation is ca 3.48 (3) Å, which is close to the sum of the van der Waals radii of two C atoms (Bondi, 1964).

S2. Experimental

Compound (I) was synthesized under hydrothermal conditions. A mixture of (NH₄)₆Mo₇O₂₄·4H₂O (0.309 g, 0.25 mmol), CdCl₂·2.5H₂O (0.144 g, 0.50 mmol), benzidine (0.069 g, 0.375 mmol) and H₂O (10 ml) was stirred mechanically at room temperature in air at pH 5.0. The mixture was then transferred and sealed in to a 37.5 ml Teflon-lined reactor, and heated at 443 K for 3 d. After cooling to room temperature, red prismatic crystals were isolated. The IR spectrum of (I) exhibits characteristic bands at 3368 and 1497 cm⁻¹ for the terminal N—H (NH₃) stretch, and at 3660–3382 cm⁻¹ for the O—H stretch. The powder X-ray diffraction pattern of the bulk product is in a good agreement with the calculated pattern based on the present crystal structure, indicating the phase purity of the sample. Thermogravimetric analysis (TGA) was performed in air from 303 to 1273 K, with a heating rate of 10 K min⁻¹. The TGA of (I) exhibits no weight loss below 623 K; there is only one step (623–773 K) for loss of the organodiamine, where the weight loss is 33.3% (calculated 33.5%).

S3. Refinement

All H atoms were clearly visible in difference maps and their parameters were all refined independently, giving C—H distances of 0.86 (3)–0.95 (3) Å and N—H distances of 0.81 (5)–0.96 (3) Å.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT and XPREP in SHELXTL (Siemens, 1994); program(s) used to solve structure: SHELXTL; program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular components of the title compound, with the atom-numbering scheme. Displacement ellipsoids are shown at the 30% probability level. Symmetry code: (i) −x, y, 0.5 − z. (ii) −x, −y, 1 − z.
	Fig. 2. (a). The structure of the two-dimensional layer, viewed down the b axis. (b). A view of the structure of the {Mo4O14}n^4n- chains.
	Fig. 3. A packing diagram of the title compound, viewed down the b axis, showing N—H···O hydrogen bonds. The broken lines indicate hydrogen-bonding interactions.

Benzidine penta-molybdate, 2[(C₁₂H₁₃N₂)⁺]·(Mo₅O₁₆)²⁻

Crystal data

(C12H13N2)2[Mo5O16]	F(000) = 2144
Mr = 1106.19	Dx = 2.476 Mg m^−3
Monoclinic, C2/C	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 4134 reflections
a = 38.5070 (3) Å	θ = 1.5–28.3°
b = 5.6800 (3) Å	µ = 2.14 mm^−1
c = 14.2961 (8) Å	T = 293 K
β = 108.366 (2)°	Prism, red
V = 2967.6 (2) Å^3	0.25 × 0.15 × 0.10 mm
Z = 4

Data collection

Siemems SMART CCD diffractometer	3681 independent reflections
Radiation source: fine-focus sealed tube	3535 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
ϕ and ω scans	θmax = 28.3°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −48→50
Tmin = 0.687, Tmax = 0.807	k = −7→5
11442 measured reflections	l = −19→19

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)] = 0.019	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.049	All H-atom parameters refined
S = 0.90	w = 1/[σ^2(Fo^2) + (0.0261P)^2 + 12.9482P] where P = (Fo^2 + 2Fc^2)/3
3681 reflections	(Δ/σ)max = 0.001
274 parameters	Δρmax = 0.44 e Å^−3
1 restraint	Δρmin = −0.67 e Å^−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
Mo1	0.0000	0.62822 (4)	0.2500	0.00962 (6)
Mo2	−0.029815 (4)	0.17549 (3)	0.419086 (11)	0.00925 (5)
Mo3	0.053835 (4)	0.27524 (3)	0.416964 (12)	0.01033 (5)
O1	−0.07243 (4)	0.1378 (3)	0.33597 (11)	0.0185 (3)
O2	0.04955 (4)	0.5324 (3)	0.32735 (10)	0.0130 (3)
O3	0.01371 (4)	0.8148 (3)	0.17393 (10)	0.0146 (3)
O4	0.00389 (4)	0.3195 (3)	0.15577 (10)	0.0119 (3)
O5	0.02799 (4)	0.0971 (3)	0.49534 (10)	0.0120 (3)
O6	−0.03610 (4)	0.4022 (3)	0.49033 (11)	0.0173 (3)
O7	0.06553 (5)	0.0513 (3)	0.35531 (11)	0.0205 (3)
O8	0.09381 (4)	0.3308 (3)	0.51012 (12)	0.0210 (3)
C6	−0.15484 (7)	−0.5028 (5)	0.1756 (2)	0.0309 (6)
C9	−0.31204 (7)	−0.1193 (5)	0.1034 (2)	0.0294 (6)
C10	−0.33152 (6)	−0.3072 (4)	0.04937 (18)	0.0233 (5)
C5	−0.19268 (7)	−0.4985 (5)	0.1391 (2)	0.0309 (6)
C11	−0.31156 (7)	−0.4990 (5)	0.0333 (2)	0.0300 (6)
N1	−0.09680 (6)	−0.3214 (4)	0.27505 (18)	0.0248 (4)
C4	−0.21338 (6)	−0.3142 (4)	0.15894 (16)	0.0194 (4)
C2	−0.15581 (7)	−0.1330 (5)	0.2546 (2)	0.0297 (6)
C8	−0.27434 (7)	−0.1221 (5)	0.1377 (2)	0.0277 (5)
C12	−0.27384 (7)	−0.4998 (5)	0.0685 (2)	0.0284 (5)
C7	−0.25380 (6)	−0.3120 (4)	0.12137 (16)	0.0197 (4)
C1	−0.13684 (6)	−0.3187 (4)	0.23297 (17)	0.0204 (4)
C3	−0.19363 (7)	−0.1312 (5)	0.2180 (2)	0.0297 (6)
N2	−0.36922 (7)	−0.3066 (5)	0.0165 (2)	0.0397 (6)
H8	−0.2617 (9)	0.012 (6)	0.172 (2)	0.041 (9)*
H9	−0.3244 (8)	0.000 (6)	0.112 (2)	0.035 (8)*
H12	−0.2619 (9)	−0.626 (7)	0.059 (3)	0.049 (10)*
H11	−0.3229 (10)	−0.633 (7)	0.004 (3)	0.055 (11)*
H2	−0.1434 (9)	−0.016 (6)	0.293 (2)	0.041 (9)*
H2B	−0.3819 (11)	−0.196 (7)	0.029 (3)	0.061 (13)*
H1C	−0.0850 (9)	−0.368 (6)	0.236 (2)	0.036 (9)*
H5	−0.2027 (10)	−0.631 (7)	0.104 (3)	0.060 (12)*
H1A	−0.0869 (8)	−0.165 (6)	0.276 (2)	0.029 (8)*
H3	−0.2060 (10)	−0.013 (7)	0.235 (3)	0.055 (11)*
H2A	−0.3799 (11)	−0.431 (5)	−0.015 (3)	0.076 (14)*
H6	−0.1416 (10)	−0.630 (7)	0.159 (3)	0.048 (10)*
H1B	−0.0891 (12)	−0.389 (9)	0.327 (3)	0.077 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo1	0.01114 (11)	0.00879 (11)	0.00840 (10)	0.000	0.00229 (8)	0.000
Mo2	0.00948 (8)	0.00944 (9)	0.00869 (8)	−0.00002 (6)	0.00265 (6)	0.00212 (6)
Mo3	0.00975 (8)	0.01099 (9)	0.01000 (8)	−0.00009 (6)	0.00277 (6)	0.00238 (6)
O1	0.0129 (7)	0.0228 (8)	0.0172 (7)	−0.0014 (6)	0.0011 (6)	0.0011 (6)
O2	0.0122 (6)	0.0144 (7)	0.0121 (6)	−0.0011 (5)	0.0035 (5)	0.0029 (5)
O3	0.0169 (7)	0.0137 (7)	0.0120 (6)	−0.0012 (6)	0.0030 (5)	0.0013 (5)
O4	0.0140 (7)	0.0120 (7)	0.0094 (6)	0.0006 (5)	0.0034 (5)	−0.0027 (5)
O5	0.0133 (7)	0.0114 (7)	0.0115 (6)	0.0006 (5)	0.0042 (5)	0.0042 (5)
O6	0.0206 (8)	0.0162 (8)	0.0165 (7)	0.0002 (6)	0.0080 (6)	−0.0012 (6)
O7	0.0264 (8)	0.0176 (8)	0.0194 (7)	0.0030 (7)	0.0098 (6)	0.0006 (6)
O8	0.0141 (7)	0.0239 (9)	0.0203 (8)	−0.0022 (6)	−0.0012 (6)	0.0021 (6)
C6	0.0225 (12)	0.0277 (14)	0.0413 (15)	0.0028 (10)	0.0081 (11)	−0.0148 (11)
C9	0.0238 (12)	0.0222 (13)	0.0402 (14)	0.0047 (10)	0.0072 (11)	−0.0064 (11)
C10	0.0184 (11)	0.0239 (12)	0.0274 (12)	−0.0007 (9)	0.0069 (9)	0.0019 (9)
C5	0.0226 (12)	0.0261 (13)	0.0402 (14)	−0.0015 (10)	0.0047 (11)	−0.0166 (11)
C11	0.0247 (12)	0.0240 (13)	0.0392 (14)	−0.0044 (10)	0.0070 (11)	−0.0119 (11)
N1	0.0180 (10)	0.0299 (12)	0.0281 (11)	−0.0002 (8)	0.0095 (8)	−0.0072 (9)
C4	0.0200 (11)	0.0188 (11)	0.0193 (10)	−0.0003 (8)	0.0058 (8)	−0.0007 (8)
C2	0.0198 (11)	0.0249 (13)	0.0436 (15)	−0.0038 (10)	0.0087 (11)	−0.0143 (11)
C8	0.0222 (12)	0.0209 (12)	0.0362 (13)	−0.0017 (9)	0.0038 (10)	−0.0085 (10)
C12	0.0231 (12)	0.0222 (12)	0.0399 (14)	0.0017 (10)	0.0099 (10)	−0.0112 (11)
C7	0.0188 (10)	0.0197 (11)	0.0206 (10)	−0.0012 (8)	0.0064 (8)	−0.0012 (8)
C1	0.0157 (10)	0.0248 (12)	0.0218 (10)	−0.0006 (9)	0.0074 (8)	−0.0026 (9)
C3	0.0208 (12)	0.0238 (13)	0.0444 (15)	−0.0002 (10)	0.0101 (11)	−0.0127 (11)
N2	0.0189 (11)	0.0318 (14)	0.0627 (18)	−0.0010 (10)	0.0047 (11)	−0.0071 (12)

Geometric parameters (Å, º)

Mo1—O3^i	1.7167 (15)	C9—C10	1.390 (4)
Mo1—O3	1.7167 (15)	C9—H9	0.86 (3)
Mo1—O2	1.9572 (14)	C10—N2	1.378 (3)
Mo1—O2^i	1.9572 (14)	C10—C11	1.393 (4)
Mo1—O4	2.2445 (14)	C5—C4	1.398 (3)
Mo1—O4^i	2.2445 (14)	C5—H5	0.92 (4)
Mo2—O6	1.7056 (16)	C11—C12	1.379 (4)
Mo2—O1	1.7094 (15)	C11—H11	0.91 (4)
Mo2—O4^i	1.8669 (14)	N1—C1	1.468 (3)
Mo2—O5^ii	1.9606 (14)	N1—H1C	0.86 (3)
Mo2—O5	2.1936 (14)	N1—H1A	0.96 (3)
Mo3—O7	1.6877 (16)	N1—H1B	0.81 (5)
Mo3—O8	1.7177 (15)	C4—C3	1.403 (3)
Mo3—O2	1.9155 (14)	C4—C7	1.478 (3)
Mo3—O5	1.9933 (14)	C2—C1	1.373 (3)
Mo3—O4^i	2.1514 (14)	C2—C3	1.384 (4)
Mo3—O6^iii	2.4800 (16)	C2—H2	0.90 (3)
O4—Mo2^i	1.8669 (14)	C8—C7	1.400 (3)
O4—Mo3^i	2.1514 (14)	C8—H8	0.95 (3)
O5—Mo2^ii	1.9606 (14)	C12—C7	1.392 (3)
O6—Mo3^iii	2.4800 (16)	C12—H12	0.89 (4)
C6—C1	1.374 (3)	C3—H3	0.90 (4)
C6—C5	1.384 (3)	N2—H2B	0.85 (4)
C6—H6	0.95 (4)	N2—H2A	0.868 (19)
C9—C8	1.378 (3)
O3^i—Mo1—O3	103.74 (10)	Mo2—O6—Mo3^iii	172.59 (9)
O3^i—Mo1—O2	104.69 (6)	C1—C6—C5	119.0 (2)
O3—Mo1—O2	95.16 (6)	C1—C6—H6	121 (2)
O3^i—Mo1—O2^i	95.16 (6)	C5—C6—H6	120 (2)
O3—Mo1—O2^i	104.69 (6)	C8—C9—C10	120.8 (2)
O2—Mo1—O2^i	147.71 (9)	C8—C9—H9	122 (2)
O3^i—Mo1—O4	162.65 (7)	C10—C9—H9	117 (2)
O3—Mo1—O4	90.58 (6)	N2—C10—C9	120.9 (2)
O2—Mo1—O4	83.36 (6)	N2—C10—C11	121.5 (2)
O2^i—Mo1—O4	71.41 (5)	C9—C10—C11	117.6 (2)
O3^i—Mo1—O4^i	90.58 (6)	C6—C5—C4	122.5 (2)
O3—Mo1—O4^i	162.65 (7)	C6—C5—H5	114 (2)
O2—Mo1—O4^i	71.41 (5)	C4—C5—H5	124 (2)
O2^i—Mo1—O4^i	83.36 (6)	C12—C11—C10	121.0 (2)
O4—Mo1—O4^i	77.27 (7)	C12—C11—H11	118 (2)
O6—Mo2—O1	102.93 (8)	C10—C11—H11	121 (2)
O6—Mo2—O4^i	102.34 (7)	C1—N1—H1C	116 (2)
O1—Mo2—O4^i	103.07 (7)	C1—N1—H1A	110.9 (18)
O6—Mo2—O5^ii	101.97 (7)	H1C—N1—H1A	91 (3)
O1—Mo2—O5^ii	99.95 (7)	C1—N1—H1B	115 (3)
O4^i—Mo2—O5^ii	141.56 (6)	H1C—N1—H1B	109 (4)
O6—Mo2—O5	99.74 (7)	H1A—N1—H1B	113 (4)
O1—Mo2—O5	157.16 (7)	C5—C4—C3	116.2 (2)
O4^i—Mo2—O5	74.44 (6)	C5—C4—C7	122.4 (2)
O5^ii—Mo2—O5	72.44 (6)	C3—C4—C7	121.5 (2)
O7—Mo3—O8	102.82 (8)	C1—C2—C3	119.5 (2)
O7—Mo3—O2	101.91 (7)	C1—C2—H2	119 (2)
O8—Mo3—O2	104.23 (7)	C3—C2—H2	121 (2)
O7—Mo3—O5	99.99 (7)	C9—C8—C7	122.5 (2)
O8—Mo3—O5	98.14 (7)	C9—C8—H8	119 (2)
O2—Mo3—O5	144.11 (6)	C7—C8—H8	118 (2)
O7—Mo3—O4^i	103.94 (7)	C11—C12—C7	122.4 (2)
O8—Mo3—O4^i	152.90 (7)	C11—C12—H12	119 (2)
O2—Mo3—O4^i	74.30 (6)	C7—C12—H12	119 (2)
O5—Mo3—O4^i	73.04 (5)	C12—C7—C8	115.8 (2)
O7—Mo3—O6^iii	178.71 (7)	C12—C7—C4	122.1 (2)
O8—Mo3—O6^iii	77.31 (7)	C8—C7—C4	122.1 (2)
O2—Mo3—O6^iii	79.27 (6)	C2—C1—C6	121.0 (2)
O5—Mo3—O6^iii	78.72 (6)	C2—C1—N1	118.7 (2)
O4^i—Mo3—O6^iii	75.84 (5)	C6—C1—N1	120.3 (2)
Mo3—O2—Mo1	116.94 (7)	C2—C3—C4	121.9 (2)
Mo2^i—O4—Mo3^i	109.23 (6)	C2—C3—H3	119 (2)
Mo2^i—O4—Mo1	146.64 (8)	C4—C3—H3	119 (2)
Mo3^i—O4—Mo1	97.32 (6)	C10—N2—H2B	123 (3)
Mo2^ii—O5—Mo3	145.64 (8)	C10—N2—H2A	117 (3)
Mo2^ii—O5—Mo2	107.56 (6)	H2B—N2—H2A	120 (4)
Mo3—O5—Mo2	103.05 (6)

Symmetry codes: (i) −x, y, −z+1/2; (ii) −x, −y, −z+1; (iii) −x, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2B···O8^iv	0.85 (4)	2.26 (4)	3.043 (3)	155 (4)
N1—H1C···O2^v	0.86 (3)	1.95 (3)	2.797 (3)	168 (3)
N1—H1A···O1	0.96 (3)	1.92 (3)	2.816 (3)	153 (3)
N1—H1A···O7^i	0.96 (3)	2.59 (3)	3.289 (3)	130 (2)
N2—H2A···O7^vi	0.87 (2)	2.42 (3)	3.147 (3)	142 (4)
N2—H2A···O8^vi	0.87 (2)	2.56 (3)	3.289 (3)	142 (4)
N1—H1B···O8^ii	0.81 (5)	2.41 (5)	3.037 (3)	135 (4)

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