[mu]-Oxo-bis{{2,2'-[2,2-di­methyl­propane-1,3-diyl­bis­(nitrilomethyl­idyne)]­diphenolato}­oxo­rhenium(V)}

The title compound, [Re₂O₃(C₁₉H₂₀N₂O₂)₂], is a hexacoordinate complex containing an [Re₂O₃]⁴⁺ core with a linear O=Re-O-Re=O bridge. The distorted octahedral coordination of the Re^V atom is achieved by an N₂O₂ donor set from the tetradentate imine-phenol ligand. The overall charge of the compound is neutral due to deprotonation of the phenol groups, and the terminating and bridging O atoms. The Re=O and Re-O bond distances of the [Re₂O₃]⁴⁺ core are 1.699 (4) and 1.911 (1) Å, respectively. The Re-O and Re-N bond distances of the equatorial plane are in the ranges 2.024 (4)-2.013 (4) and 2.128 (5)-2.120 (5) Å, respectively.

S1. Comment

Rhenium, being a congener to technetium in Group VIIa, might be expected to form complexes that have structural and biological similarities to the corresponding technetium complexes. With the characters of β emitters, both ¹⁸⁸Re and ¹⁸⁶Re have potential utility in radiotherapy. Recent focus has been on the design and preparation of new rhenium complexes in order to optimize the biodistribution of the potential radiopharmaceuticals. Interest is aroused in exploring the coordination chemistry of the rhenium complexes with tetradentate N₂O₂ ligands (Luo et al., 1995; Tisato et al., 1990; Mazzi et al., 1986). We describe here the synthesis and characterization of the title compound, (I).

The title compound forms a dinuclear complex, the Re atom being hexacoordinated to two imine N, two phenol O and two axial O atoms. The dinuclear structure, with a linear O═Re—O—Re═O bridge, is very similar to those of the µ-oxo-dioxotechnetium(V) or µ-oxo-dioxorhenium(V) complexes reported in the literature (Middleton et al., 1979; Bandoli & Nicolini, 1984; Pietzsch et al., 1995; Pillai et al., 1990, 1994). The compound consists of two independent ReO–dmpn(sal) [dmpn(sal) is N,N'-2,2-dimethylpropane-1,3-diylbis(salicylideneimine) or 2,2'-[2,2-dimethylpropane-1,3-diylbis(nitrilomethylidyne)]diphenolate] units bridged by an O atom and the tetradentate Schiff base occupies the four planar coordination sites of an octahedron. The structure of ReO–dmpn(sal), with an N₂O₂ donor set in the same plane perpendicular to the Re═O bond, is different from the configuration of chloro{1,3-[N,N'-bis(salicylidene)diamino]-2,2-dimethylpropyl}oxorhenium(V) [(II); Herrmann, Rauch & Artus, 1996]. It was reported that substitution reactions on the MO³⁺ (M = Tc, Re) core with N₂O₂ Schiff base ligands might lead to three types of complex, [MOX(N₂O₂)] (X = Cl, Br), {[MO(N₂O₂)]₂O} and [MO(OH₂)(N₂O₂)]⁺ (Herrmann, Rauch & Artus, 1996; Herrmann, Rauch & Roesky, 1996; Bandoli & Nicolini, 1984). The title compound, {[MO(N₂O₂)]₂O}, was facile to form in the solution containing water. The other two types of the compound were presumably formed but the product isolated was the most stable (Bandoli & Nicolini, 1984).

The Re═O bond length [1.699 (4) Å] is similar to the mean value (1.691 Å, σ = 0.025 Å) for a large sample of monooxo Re^V (Mayer, 1988). The Re—N(imine) distance [2.128 (5) Å] observed is similar to that of (II) (Herrmann, Rauch & Artus, 1996). The O2—Re1—N1 and O2—Re1—N2 angles deviate by less than 2.0° from the ideal value of 90°. The trans-O3—Re1—N2 and trans-O4—Re1—N1 angles are 171.5 (2) and 169.7 (2)°, respectively. The compression of both trans-O—Re—N angles from 180° indicates a marked level of tetrahedral distortion from square-planar geometry around the Re^V atom. The least-square-planes data shows that the Re atom is approximately 0.14 Å out of the plane defined by the coordinated atoms of tetradentate ligand toward the terminal O atoms.

S2. Experimental

N,N'-2,2-Dimethylpropane-1,3-diylbis(salicylideneimine) was prepared by condensation of salicylaldehyde (50 mmol) and 1,3-diamino-2,2-dimethylpropane (25 mmol) in absolute ethanol (100 ml). Refluxing was continued for 6 h and the resultant product was placed in a freezer for 24 h. The yellow precipitate which appeared was collected by filtration and washed with cold ethanol (95%). After recrystallization, yellow crystals were harvested and dried in vacuo. Bu₄NReOCl₄ was synthesized following the previous report of Cotton & Lippert (1966). Bu₄NCl (2 M, 20 ml) was added to NH₄ReO₄ (20 mmol) in distilled water. The white precipitate, Bu₄NReO₄, were collected and dried. Bu₄NReO₄ was purged with dry HCl in dry ethanol (100 ml). The brown precipitate were collected and dried. N,N'-2,2-Dimethylpropane-1,3-diylbis(salicylideneimine) (0.84 mmol) was added to solid Bu₄NReOCl₄ (0.42 mmol) in dry ethanol. The reaction mixture was refluxed for 3 h and then stirred for 24 h at room temperature. The green solution was concentrated until dark-green crystals of the Re complex formed. The crystals were then dissolved in 95% ethanol at 348 K and the resulting solution was allowed to stand at room temperature for a few days whereupon crystals suitable for X-ray analysis were formed.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SHELXTL (Sheldrick, 1991); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

µ-oxo-bis-{oxo[N,N'-2,2-dimethylpropane-1,3- diylbis(salicylideneiminato)]rhenium (V)}

Crystal data

[Re2O3(C19H20N2O2)2]	F(000) = 1004
Mr = 1037.14	Dx = 1.929 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.2427 (2) Å	Cell parameters from 6635 reflections
b = 13.3736 (2) Å	θ = 2.5–25°
c = 12.4932 (2) Å	µ = 6.83 mm^−1
β = 108.109 (1)°	T = 293 K
V = 1785.38 (5) Å^3	Tabular, green
Z = 2	0.21 × 0.20 × 0.06 mm

Data collection

CCD area-detector diffractometer	4225 independent reflections
Radiation source: fine-focus sealed tube	3266 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.056
ϕ and ω scans	θmax = 28.8°, θmin = 1.9°
Absorption correction: empirical (using intensity measurements) from equivalent data (sheldrick, 1991) ?	h = −14→14
Tmin = 0.274, Tmax = 0.664	k = −17→17
10934 measured reflections	l = −16→10

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)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.084	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0352P)^2] where P = (Fo^2 + 2Fc^2)/3
4225 reflections	(Δ/σ)max < 0.001
232 parameters	Δρmax = 1.19 e Å^−3
0 restraints	Δρmin = −1.79 e Å^−3

Special details

Experimental. The data collection nominally covered over a hemisphere of reciprocal space by a combination of three sets of exposures; each set had a different ϕ angle for the crystal and each exposure cover 0.3° in ω. The crystal-to-detector distance was 5.89 cm. Converge of the unique set is over 90.8% complete to at least 28.79° in θ. Repeating the initial frames at the end of data collection and analyzing the duplicate reflections monitored, crystal decay was monitored and found to be negligible.

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
Re1	0.048078 (19)	0.134220 (15)	0.546208 (17)	0.03092 (8)
O1	0.0000	0.0000	0.5000	0.0340 (12)
O2	0.1108 (4)	0.2492 (3)	0.5846 (4)	0.0454 (10)
O3	0.0324 (4)	0.1010 (3)	0.6994 (3)	0.0420 (9)
O4	−0.1335 (3)	0.1715 (3)	0.5121 (3)	0.0398 (9)
N1	0.2294 (4)	0.0692 (3)	0.5884 (4)	0.0392 (11)
N2	0.0395 (4)	0.1571 (3)	0.3758 (4)	0.0319 (10)
C1	0.1201 (6)	0.0645 (4)	0.7872 (5)	0.0392 (14)
C2	0.0928 (7)	0.0562 (5)	0.8884 (5)	0.0563 (18)
H2A	0.0147	0.0764	0.8912	0.068*
C3	0.1783 (8)	0.0189 (6)	0.9844 (6)	0.071 (2)
H3A	0.1575	0.0146	1.0507	0.085*
C4	0.2949 (8)	−0.0123 (6)	0.9829 (6)	0.074 (2)
H4A	0.3525	−0.0378	1.0477	0.088*
C5	0.3247 (7)	−0.0053 (5)	0.8853 (6)	0.066 (2)
H5A	0.4034	−0.0266	0.8853	0.079*
C6	0.2409 (6)	0.0332 (4)	0.7839 (5)	0.0454 (15)
C7	0.2841 (5)	0.0344 (4)	0.6881 (5)	0.0432 (15)
H7A	0.3625	0.0063	0.6988	0.052*
C8	0.2910 (5)	0.0462 (4)	0.5034 (5)	0.0438 (14)
H8A	0.2619	−0.0189	0.4715	0.053*
H8B	0.3802	0.0407	0.5413	0.053*
C9	0.2710 (5)	0.1206 (4)	0.4063 (6)	0.0422 (14)
C10	0.1345 (5)	0.1171 (4)	0.3289 (5)	0.0426 (14)
H10A	0.1293	0.1540	0.2607	0.051*
H10B	0.1135	0.0480	0.3074	0.051*
C11	−0.0533 (5)	0.2009 (4)	0.3054 (5)	0.0386 (13)
H11A	−0.0449	0.2139	0.2350	0.046*
C12	−0.1692 (5)	0.2328 (4)	0.3209 (5)	0.0343 (12)
C13	−0.2541 (6)	0.2796 (5)	0.2279 (5)	0.0506 (16)
H13A	−0.2285	0.2957	0.1660	0.061*
C14	−0.3740 (6)	0.3025 (5)	0.2253 (6)	0.0579 (19)
H14A	−0.4288	0.3337	0.1628	0.070*
C15	−0.4115 (6)	0.2786 (5)	0.3164 (6)	0.0509 (17)
H15A	−0.4930	0.2926	0.3148	0.061*
C16	−0.3309 (5)	0.2345 (4)	0.4098 (5)	0.0419 (14)
H16A	−0.3590	0.2184	0.4702	0.050*
C17	−0.2063 (5)	0.2129 (4)	0.4161 (5)	0.0331 (12)
C18	0.3132 (6)	0.2254 (5)	0.4461 (6)	0.0533 (17)
H18A	0.3984	0.2237	0.4942	0.080*
H18B	0.2608	0.2517	0.4872	0.080*
H18C	0.3071	0.2673	0.3823	0.080*
C19	0.3479 (6)	0.0816 (5)	0.3330 (6)	0.0588 (18)
H19A	0.4351	0.0816	0.3759	0.088*
H19B	0.3347	0.1240	0.2683	0.088*
H19C	0.3220	0.0147	0.3088	0.088*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re1	0.03185 (13)	0.03354 (13)	0.02764 (12)	0.00291 (9)	0.00967 (9)	0.00108 (9)
O1	0.033 (3)	0.040 (3)	0.026 (3)	−0.001 (2)	0.006 (2)	−0.002 (2)
O2	0.056 (3)	0.036 (2)	0.042 (2)	−0.0019 (19)	0.012 (2)	−0.0040 (19)
O3	0.046 (2)	0.053 (2)	0.026 (2)	0.003 (2)	0.0090 (19)	0.0048 (18)
O4	0.040 (2)	0.050 (2)	0.033 (2)	0.0133 (18)	0.0176 (19)	0.0078 (18)
N1	0.037 (3)	0.037 (3)	0.043 (3)	0.001 (2)	0.009 (2)	0.001 (2)
N2	0.032 (2)	0.037 (3)	0.030 (2)	0.0008 (19)	0.014 (2)	0.0050 (19)
C1	0.049 (3)	0.038 (3)	0.027 (3)	−0.005 (3)	0.007 (3)	0.004 (2)
C2	0.072 (5)	0.062 (4)	0.033 (3)	−0.012 (4)	0.015 (3)	0.004 (3)
C3	0.100 (6)	0.074 (5)	0.033 (4)	−0.018 (5)	0.012 (4)	0.015 (4)
C4	0.082 (6)	0.081 (6)	0.039 (4)	0.000 (5)	−0.009 (4)	0.021 (4)
C5	0.061 (4)	0.067 (5)	0.054 (4)	0.005 (4)	−0.004 (4)	0.017 (4)
C6	0.047 (4)	0.041 (3)	0.038 (3)	−0.005 (3)	−0.001 (3)	0.004 (3)
C7	0.034 (3)	0.042 (3)	0.048 (4)	0.006 (2)	0.005 (3)	0.001 (3)
C8	0.035 (3)	0.047 (4)	0.051 (4)	0.006 (3)	0.016 (3)	0.005 (3)
C9	0.033 (3)	0.040 (3)	0.058 (4)	0.001 (2)	0.021 (3)	0.003 (3)
C10	0.040 (3)	0.055 (4)	0.041 (3)	0.000 (3)	0.024 (3)	−0.002 (3)
C11	0.040 (3)	0.050 (4)	0.027 (3)	−0.001 (3)	0.013 (3)	0.006 (3)
C12	0.033 (3)	0.040 (3)	0.031 (3)	0.003 (2)	0.011 (2)	0.004 (2)
C13	0.041 (3)	0.072 (4)	0.038 (3)	0.010 (3)	0.010 (3)	0.019 (3)
C14	0.046 (4)	0.070 (5)	0.050 (4)	0.009 (3)	0.003 (3)	0.021 (4)
C15	0.031 (3)	0.056 (4)	0.064 (4)	0.012 (3)	0.012 (3)	0.004 (3)
C16	0.034 (3)	0.051 (4)	0.046 (4)	0.008 (3)	0.019 (3)	0.005 (3)
C17	0.029 (3)	0.031 (3)	0.036 (3)	0.000 (2)	0.007 (2)	−0.004 (2)
C18	0.042 (3)	0.049 (4)	0.074 (5)	−0.001 (3)	0.025 (4)	0.003 (3)
C19	0.048 (4)	0.059 (4)	0.080 (5)	0.008 (3)	0.036 (4)	0.011 (4)

Geometric parameters (Å, º)

Re1—O2	1.697 (4)	C3—C4	1.381 (12)
Re1—O1	1.9114 (2)	C4—C5	1.364 (12)
Re1—O4	2.015 (4)	C5—C6	1.420 (8)
Re1—O3	2.025 (4)	C6—C7	1.425 (9)
Re1—N2	2.123 (5)	C8—C9	1.530 (8)
Re1—N1	2.126 (5)	C9—C18	1.514 (8)
O3—C1	1.320 (6)	C9—C19	1.534 (9)
O4—C17	1.343 (6)	C9—C10	1.540 (8)
N1—C7	1.292 (7)	C11—C12	1.439 (7)
N1—C8	1.470 (8)	C12—C13	1.401 (7)
N2—C11	1.279 (7)	C12—C17	1.404 (8)
N2—C10	1.469 (7)	C13—C14	1.377 (9)
C1—C2	1.395 (9)	C14—C15	1.368 (10)
C1—C6	1.434 (9)	C15—C16	1.369 (8)
C2—C3	1.376 (9)	C16—C17	1.407 (7)
O2—Re1—O1	171.76 (14)	C3—C2—C1	121.8 (7)
O2—Re1—O4	98.06 (18)	C2—C3—C4	120.4 (8)
O1—Re1—O4	89.75 (12)	C5—C4—C3	119.3 (7)
O2—Re1—O3	94.71 (19)	C4—C5—C6	122.9 (7)
O1—Re1—O3	88.86 (12)	C5—C6—C7	116.7 (6)
O4—Re1—O3	82.77 (15)	C5—C6—C1	116.9 (6)
O2—Re1—N2	92.19 (19)	C7—C6—C1	126.4 (5)
O1—Re1—N2	84.94 (12)	N1—C7—C6	129.0 (6)
O4—Re1—N2	91.43 (16)	N1—C8—C9	116.7 (5)
O3—Re1—N2	171.54 (15)	C18—C9—C8	112.9 (6)
O2—Re1—N1	91.05 (18)	C18—C9—C19	109.5 (5)
O1—Re1—N1	81.39 (12)	C8—C9—C19	106.3 (5)
O4—Re1—N1	169.80 (16)	C18—C9—C10	112.6 (5)
O3—Re1—N1	91.95 (18)	C8—C9—C10	110.5 (5)
N2—Re1—N1	92.80 (18)	C19—C9—C10	104.5 (5)
Re1^i—O1—Re1	180.0	N2—C10—C9	116.4 (5)
C1—O3—Re1	127.3 (4)	N2—C11—C12	128.5 (5)
C17—O4—Re1	126.0 (3)	C13—C12—C17	118.8 (5)
C7—N1—C8	115.5 (5)	C13—C12—C11	115.7 (5)
C7—N1—Re1	121.2 (4)	C17—C12—C11	125.3 (5)
C8—N1—Re1	122.5 (4)	C14—C13—C12	122.1 (6)
C11—N2—C10	115.6 (5)	C15—C14—C13	118.8 (6)
C11—N2—Re1	121.9 (4)	C14—C15—C16	121.1 (6)
C10—N2—Re1	122.4 (3)	C15—C16—C17	121.4 (6)
O3—C1—C2	117.7 (6)	O4—C17—C12	125.1 (5)
O3—C1—C6	123.6 (5)	O4—C17—C16	117.0 (5)
C2—C1—C6	118.7 (6)	C12—C17—C16	117.8 (5)

Symmetry code: (i) −x, −y, −z+1.