Tetrakis­[μ-N,N′-bis(4-bromo­phenyl)­formamidinato-N:N′]­dimolybdenum(II)

The title compound, [Mo₂(C₁₃H₉Br₂N₂)₄], is a tetra-chelate `paddle wheel' complex of quadruply bonded dimolybdenum(II). The centroid of the Mo—Mo bond is located on an inversion center and the bond length is 2.0869 (19) Å.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.016 Å
• Disorder in main residue
• R factor = 0.064
• wR factor = 0.110
• Data-to-parameter ratio = 14.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.601     0.825
          Tmin and Tmax expected:      0.404     0.823
          RR =      1.484
          Please check that your absorption correction is appropriate.

PLAT_301  Alert C Main residue disorder ........................       3.00 Perc.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 2 Alert Level C = Please check

---

S1. Comment

The present structural report is the complement of the accompanying communication of tetrakis[µ-N,N'-bis(4-chlorophenyl)formamidinato-N:N']dimolybdenum(II) (Lynn et al., 2001). Both reports describe the structural determination of Mo—Mo bound compounds studied by Lichtenberger and colleagues via gas-phase photoelectron spectroscopy (Lichtenberger et al., 1999, 2000). Compounds of the general form Mo₂(form)₄ [form = N,N'-bis(4-X-phenyl)formamidinate] feature a quadruple metal–metal bond with unique electronic characteristics. Thorough investigation of such systems will elucidate some of the subtle nature of metal–metal interactions, which are of fundamental interest to a wide range of research efforts (Lin et al., 1995, 1996).

S2. Experimental

The substituted formamidines and the Mo₂(form)₄ systems were prepared according to published syntheses (Cotton et al., 1989). Crystals were grown by the diffusion of hexanes into a dichloromethane solution.

S3. Refinement

One of the bromine substituents (Br1) of a formamidinate ligand was found to be disordered. This disorder was likely due to librational motion of the entire PhBr group perpendicular to the PhBr plane. To address the disorder, Br1 was split into two sites (Br1 and Br1'), which were forced to have identical displacement parameters. Subsequent refinement of the bromine site-occupancy factors resulted in occupancies of 0.828 and 0.172 (4) for Br1 and Br1', respectively. The least occupied site (Br1') is out of the PhBr plane, while the Br1 site is in the plane. The sites of the phenyl ring C atoms were not split as an approximation. H atoms were added at idealized positions, constrained to ride on the atom to which they are bonded and given displacement parameters equal to 1.2 or 1.5 times U_iso of that bonded atom.

Computing details

Data collection: CAD-4 Operations Manual (Enraf-Nonius, 1977); cell refinement: CAD-4 Operations Manual; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXTL.

Tetrakis[µ-N,N'-bis(4-bromophenyl)formamidinato-N:N']dimolybdenum(II)

Crystal data

[Mo2(C13H9Br2N2)4]	Z = 1
Mr = 1604.05	F(000) = 768
Triclinic, P1	Dx = 1.989 Mg m^−3
a = 10.437 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 11.610 (2) Å	Cell parameters from 25 reflections
c = 12.801 (3) Å	θ = 10–15°
α = 107.00 (3)°	µ = 6.48 mm^−1
β = 92.56 (3)°	T = 296 K
γ = 113.31 (3)°	Plate, yellow
V = 1339.4 (5) Å^3	0.18 × 0.12 × 0.03 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	2283 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 25.0°, θmin = 1.7°
ω–2θ scans	h = 0→12
Absorption correction: ψ scan (North et al., 1968)	k = −13→12
Tmin = 0.601, Tmax = 0.825	l = −15→15
4717 measured reflections	3 standard reflections every 60 min
4717 independent reflections	intensity decay: 1.2%

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)] = 0.064	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.110	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0265P)^2] where P = (Fo^2 + 2Fc^2)/3
4717 reflections	(Δ/σ)max = 0.003
320 parameters	Δρmax = 0.58 e Å^−3
0 restraints	Δρmin = −0.75 e Å^−3
0 constraints

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	0.41030 (8)	0.44048 (8)	0.43772 (7)	0.0328 (2)
N1	0.5175 (7)	0.4954 (7)	0.3112 (6)	0.038 (2)
N3	0.7173 (7)	0.6314 (7)	0.4452 (6)	0.037 (2)
N4	0.3508 (7)	0.6044 (7)	0.4617 (6)	0.042 (2)
Br3	1.34044 (11)	1.02096 (11)	0.55244 (11)	0.0712 (4)
Br4	−0.06996 (12)	0.60134 (13)	0.11544 (10)	0.0733 (4)
Br1'	0.3185 (15)	0.1719 (17)	−0.1768 (13)	0.1051 (10)	0.172 (4)
Br1	0.2441 (3)	0.1352 (3)	−0.1660 (2)	0.1051 (10)	0.828
C1	0.6517 (10)	0.5802 (9)	0.3412 (8)	0.045 (3)
H1	0.7020	0.6049	0.2872	0.054*
C2	0.4298 (10)	0.7176 (9)	0.5429 (7)	0.037 (2)
H2	0.4074	0.7899	0.5557	0.045*
C31	0.8595 (9)	0.7300 (9)	0.4735 (8)	0.036 (2)
C32	0.9203 (9)	0.8018 (8)	0.4052 (7)	0.040 (2)
H32A	0.8638	0.7913	0.3418	0.048*
C34	1.1451 (10)	0.9051 (8)	0.5216 (9)	0.045 (3)
C35	1.0869 (9)	0.8388 (8)	0.5930 (8)	0.045 (3)
H35A	1.1428	0.8529	0.6582	0.054*
C36	0.9449 (9)	0.7511 (9)	0.5673 (8)	0.041 (3)
H36A	0.9065	0.7054	0.6154	0.050*
C33	1.0615 (11)	0.8878 (9)	0.4283 (9)	0.055 (3)
H33A	1.0999	0.9340	0.3806	0.067*
C12	0.5428 (11)	0.3898 (10)	0.1210 (8)	0.065 (3)
H12A	0.6399	0.4205	0.1434	0.078*
C11	0.4633 (11)	0.4226 (9)	0.1962 (8)	0.044 (3)
C15	0.2569 (12)	0.2912 (11)	0.0518 (10)	0.068 (3)
H15A	0.1593	0.2570	0.0295	0.082*
C16	0.3198 (11)	0.3738 (10)	0.1598 (8)	0.056 (3)
H16A	0.2639	0.3969	0.2090	0.067*
C13	0.4795 (13)	0.3107 (11)	0.0108 (10)	0.080 (4)
H13A	0.5347	0.2923	−0.0410	0.096*
C14	0.3357 (14)	0.2606 (11)	−0.0203 (9)	0.070 (4)
C42	0.1081 (10)	0.5406 (9)	0.3775 (8)	0.047 (3)
H42A	0.0748	0.4998	0.4295	0.056*
C41	0.2520 (9)	0.6057 (8)	0.3811 (7)	0.035 (2)
C43	0.0137 (11)	0.5367 (10)	0.2955 (9)	0.052 (3)
H43A	−0.0832	0.4881	0.2898	0.063*
C44	0.0605 (10)	0.6024 (9)	0.2239 (8)	0.040 (2)
C46	0.2967 (10)	0.6713 (9)	0.3078 (9)	0.053 (3)
H46A	0.3935	0.7184	0.3115	0.063*
C45	0.2025 (11)	0.6696 (10)	0.2287 (9)	0.060 (3)
H45A	0.2352	0.7140	0.1787	0.072*
N2	0.5395 (8)	0.7277 (7)	0.6051 (6)	0.040 (2)
Br2	0.80372 (15)	1.18852 (13)	1.04535 (11)	0.0919 (5)
C21	0.5989 (10)	0.8394 (9)	0.7057 (7)	0.036 (2)
C22	0.5170 (11)	0.8916 (9)	0.7671 (8)	0.054 (3)
H22A	0.4201	0.8568	0.7411	0.064*
C23	0.5791 (12)	0.9969 (10)	0.8689 (9)	0.068 (3)
H23A	0.5229	1.0297	0.9110	0.081*
C24	0.7213 (12)	1.0507 (9)	0.9056 (8)	0.052 (3)
C25	0.8037 (11)	1.0022 (9)	0.8471 (9)	0.060 (3)
H25A	0.9005	1.0389	0.8744	0.072*
C26	0.7450 (10)	0.8964 (9)	0.7447 (9)	0.056 (3)
H26A	0.8029	0.8649	0.7038	0.067*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo1	0.0301 (5)	0.0341 (5)	0.0285 (5)	0.0107 (4)	0.0027 (4)	0.0073 (4)
N1	0.031 (4)	0.036 (4)	0.028 (5)	−0.002 (4)	−0.004 (4)	0.006 (4)
N3	0.023 (4)	0.041 (5)	0.036 (5)	0.010 (4)	0.004 (4)	0.005 (4)
N4	0.033 (4)	0.043 (5)	0.048 (5)	0.019 (4)	0.006 (4)	0.011 (4)
Br3	0.0394 (7)	0.0550 (8)	0.0990 (11)	0.0049 (6)	0.0163 (7)	0.0191 (7)
Br4	0.0646 (8)	0.1045 (10)	0.0660 (9)	0.0469 (8)	0.0070 (7)	0.0357 (8)
Br1'	0.146 (2)	0.109 (2)	0.0444 (11)	0.073 (2)	−0.0297 (17)	−0.0161 (11)
Br1	0.146 (2)	0.109 (2)	0.0444 (11)	0.073 (2)	−0.0297 (17)	−0.0161 (11)
C1	0.045 (6)	0.039 (6)	0.052 (7)	0.013 (5)	0.015 (5)	0.021 (5)
C2	0.049 (6)	0.031 (6)	0.037 (6)	0.021 (5)	0.014 (5)	0.011 (5)
C31	0.038 (6)	0.046 (6)	0.041 (7)	0.028 (5)	0.021 (5)	0.022 (5)
C32	0.044 (6)	0.038 (6)	0.030 (6)	0.015 (5)	0.009 (5)	0.003 (5)
C34	0.033 (6)	0.026 (6)	0.061 (7)	0.000 (4)	0.020 (5)	0.008 (5)
C35	0.033 (6)	0.031 (6)	0.055 (7)	0.007 (5)	−0.007 (5)	0.003 (5)
C36	0.032 (6)	0.044 (6)	0.044 (7)	0.012 (5)	0.006 (5)	0.016 (5)
C33	0.052 (7)	0.040 (6)	0.065 (8)	0.007 (5)	0.015 (6)	0.023 (6)
C12	0.046 (7)	0.078 (8)	0.034 (7)	0.006 (6)	0.000 (6)	−0.001 (6)
C11	0.051 (7)	0.050 (7)	0.034 (6)	0.020 (6)	0.012 (5)	0.020 (5)
C15	0.059 (8)	0.073 (8)	0.054 (8)	0.028 (7)	−0.008 (7)	0.000 (7)
C16	0.065 (8)	0.071 (8)	0.033 (6)	0.038 (6)	0.005 (6)	0.006 (6)
C13	0.083 (10)	0.094 (10)	0.054 (9)	0.044 (8)	0.027 (8)	0.000 (7)
C14	0.084 (10)	0.075 (9)	0.037 (7)	0.039 (8)	−0.018 (7)	−0.002 (6)
C42	0.054 (7)	0.062 (7)	0.044 (7)	0.033 (6)	0.020 (5)	0.032 (6)
C41	0.030 (5)	0.034 (6)	0.036 (6)	0.011 (4)	−0.007 (5)	0.008 (5)
C43	0.054 (7)	0.057 (7)	0.069 (8)	0.037 (6)	0.021 (6)	0.033 (6)
C44	0.046 (6)	0.037 (6)	0.046 (7)	0.027 (5)	0.003 (5)	0.013 (5)
C46	0.037 (6)	0.053 (7)	0.076 (8)	0.016 (5)	0.014 (6)	0.036 (6)
C45	0.061 (8)	0.076 (8)	0.053 (8)	0.024 (7)	0.018 (6)	0.041 (6)
N2	0.040 (5)	0.032 (5)	0.033 (5)	0.007 (4)	−0.006 (4)	0.002 (4)
Br2	0.1013 (11)	0.0716 (9)	0.0542 (9)	0.0133 (8)	0.0076 (8)	−0.0118 (7)
C21	0.049 (6)	0.034 (6)	0.023 (5)	0.022 (5)	0.001 (5)	0.001 (4)
C22	0.059 (7)	0.045 (6)	0.041 (7)	0.017 (5)	0.006 (6)	0.000 (5)
C23	0.065 (8)	0.068 (8)	0.058 (8)	0.034 (7)	0.016 (7)	−0.004 (6)
C24	0.059 (7)	0.034 (6)	0.044 (7)	0.011 (6)	0.002 (6)	−0.001 (5)
C25	0.050 (7)	0.040 (7)	0.064 (8)	0.006 (5)	−0.005 (6)	0.001 (6)
C26	0.046 (7)	0.046 (7)	0.062 (8)	0.019 (6)	−0.003 (6)	0.002 (6)

Geometric parameters (Å, º)

Mo1—Mo1^i	2.0869 (19)	C12—H12A	0.9300
Mo1—N1	2.117 (7)	C11—C16	1.376 (12)
Mo1—N2^i	2.144 (7)	C15—C14	1.327 (14)
Mo1—N4	2.171 (7)	C15—C16	1.381 (13)
Mo1—N3^i	2.178 (7)	C15—H15A	0.9300
N1—C1	1.310 (10)	C16—H16A	0.9300
N1—C11	1.421 (10)	C13—C14	1.367 (14)
N3—C1	1.315 (11)	C13—H13A	0.9300
N3—C31	1.418 (10)	C42—C41	1.379 (11)
N3—Mo1^i	2.178 (7)	C42—C43	1.385 (12)
N4—C2	1.324 (10)	C42—H42A	0.9300
N4—C41	1.434 (10)	C41—C46	1.362 (12)
Br3—C34	1.890 (9)	C43—C44	1.347 (12)
Br4—C44	1.894 (9)	C43—H43A	0.9300
Br1'—Br1	0.765 (15)	C44—C45	1.363 (12)
Br1'—C14	1.929 (19)	C46—C45	1.369 (13)
Br1—C14	1.914 (10)	C46—H46A	0.9300
C1—H1	0.9300	C45—H45A	0.9300
C2—N2	1.310 (10)	N2—C21	1.428 (10)
C2—H2	0.9300	N2—Mo1^i	2.144 (7)
C31—C36	1.362 (12)	Br2—C24	1.897 (10)
C31—C32	1.386 (11)	C21—C22	1.381 (12)
C32—C33	1.370 (11)	C21—C26	1.398 (11)
C32—H32A	0.9300	C22—C23	1.406 (13)
C34—C33	1.362 (13)	C22—H22A	0.9300
C34—C35	1.374 (12)	C23—C24	1.359 (13)
C35—C36	1.382 (11)	C23—H23A	0.9300
C35—H35A	0.9300	C24—C25	1.346 (13)
C36—H36A	0.9300	C25—C26	1.412 (12)
C33—H33A	0.9300	C25—H25A	0.9300
C12—C11	1.367 (13)	C26—H26A	0.9300
C12—C13	1.395 (13)
Mo1^i—Mo1—N1	93.60 (19)	C16—C15—H15A	120.0
Mo1^i—Mo1—N2^i	93.7 (2)	C11—C16—C15	121.4 (10)
N1—Mo1—N2^i	87.4 (3)	C11—C16—H16A	119.3
Mo1^i—Mo1—N4	91.3 (2)	C15—C16—H16A	119.3
N1—Mo1—N4	88.5 (3)	C14—C13—C12	119.4 (11)
N2^i—Mo1—N4	173.7 (3)	C14—C13—H13A	120.3
Mo1^i—Mo1—N3^i	91.98 (19)	C12—C13—H13A	120.3
N1—Mo1—N3^i	174.3 (3)	C15—C14—C13	120.8 (11)
N2^i—Mo1—N3^i	91.1 (3)	C15—C14—Br1	119.0 (10)
N4—Mo1—N3^i	92.5 (3)	C13—C14—Br1	120.1 (10)
C1—N1—C11	118.2 (8)	C15—C14—Br1'	139.8 (11)
C1—N1—Mo1	117.0 (6)	C13—C14—Br1'	99.1 (11)
C11—N1—Mo1	122.9 (6)	Br1—C14—Br1'	23.0 (5)
C1—N3—C31	119.3 (8)	C41—C42—C43	119.4 (9)
C1—N3—Mo1^i	115.3 (6)	C41—C42—H42A	120.3
C31—N3—Mo1^i	125.3 (6)	C43—C42—H42A	120.3
C2—N4—C41	118.1 (8)	C46—C41—C42	118.6 (9)
C2—N4—Mo1	117.6 (6)	C46—C41—N4	121.5 (8)
C41—N4—Mo1	122.9 (6)	C42—C41—N4	120.0 (9)
Br1—Br1'—C14	77.4 (14)	C44—C43—C42	120.9 (10)
Br1'—Br1—C14	79.6 (13)	C44—C43—H43A	119.6
N1—C1—N3	122.0 (9)	C42—C43—H43A	119.6
N1—C1—H1	119.0	C43—C44—C45	120.0 (9)
N3—C1—H1	119.0	C43—C44—Br4	120.4 (8)
N2—C2—N4	120.0 (8)	C45—C44—Br4	119.5 (8)
N2—C2—H2	120.0	C41—C46—C45	121.6 (9)
N4—C2—H2	120.0	C41—C46—H46A	119.2
C36—C31—C32	117.3 (9)	C45—C46—H46A	119.2
C36—C31—N3	120.1 (8)	C44—C45—C46	119.5 (10)
C32—C31—N3	122.4 (9)	C44—C45—H45A	120.3
C33—C32—C31	121.9 (10)	C46—C45—H45A	120.3
C33—C32—H32A	119.0	C2—N2—C21	116.6 (8)
C31—C32—H32A	119.0	C2—N2—Mo1^i	117.0 (6)
C33—C34—C35	119.9 (9)	C21—N2—Mo1^i	125.5 (6)
C33—C34—Br3	119.8 (8)	C22—C21—C26	118.7 (9)
C35—C34—Br3	120.3 (8)	C22—C21—N2	122.5 (9)
C34—C35—C36	119.5 (9)	C26—C21—N2	118.8 (9)
C34—C35—H35A	120.2	C21—C22—C23	120.5 (10)
C36—C35—H35A	120.2	C21—C22—H22A	119.8
C31—C36—C35	121.7 (9)	C23—C22—H22A	119.8
C31—C36—H36A	119.1	C24—C23—C22	120.0 (10)
C35—C36—H36A	119.1	C24—C23—H23A	120.0
C34—C33—C32	119.6 (10)	C22—C23—H23A	120.0
C34—C33—H33A	120.2	C25—C24—C23	120.8 (10)
C32—C33—H33A	120.2	C25—C24—Br2	119.3 (8)
C11—C12—C13	120.6 (10)	C23—C24—Br2	119.8 (9)
C11—C12—H12A	119.7	C24—C25—C26	120.8 (10)
C13—C12—H12A	119.7	C24—C25—H25A	119.6
C12—C11—C16	117.8 (10)	C26—C25—H25A	119.6
C12—C11—N1	124.1 (9)	C21—C26—C25	119.3 (10)
C16—C11—N1	117.9 (9)	C21—C26—H26A	120.4
C14—C15—C16	120.1 (11)	C25—C26—H26A	120.4
C14—C15—H15A	120.0

Symmetry code: (i) −x+1, −y+1, −z+1.