Crystal structure of fac-tricarbonyl(quinoline-2-carboxylato-κ2 N,O)(triphenylarsane-κAs)rhenium(I)

In the title rhenium(I) tricarbonyl complex with triphenylarsane and deprotonated quinaldic acid ligands, the ReI atom is in an octahedral coordination. Weak C—H⋯O interactions lead to a three-dimensional supramolecular architecture.


Chemical context
In recent years, Re and Tc radiopharmaceutical chemistry with the tricarbonyl precursor fac-[M(CO) 3 (H 2 O) 3 ] + (M = 99m Tc, Re) has expanded continuously with the development of suitably derivatized novel ligand systems which efficiently displace the coordinating water molecules to produce complexes with high in vivo stability, favorable pharmacokinetic properties, and target tissue specificity (Mundwiler et al., 2004;Triantis et al., 2013;Jü rgens et al., 2014;Alberto, 2012). In this article, we describe the crystal structure of a '2 + 1' tricarbonyl rhenium(I) complex, fac-[M(CO) 3 (L)(NO-QA)], where L is triphenylarsane and NO-QA deprotonated quinaldic acid. This study is part of our ongoing research in the field of rhenium coordination compounds, particularly complexes bearing the fac-[Re(CO) 3 ] + synthon, to develop new molecular radiopharmaceuticals. Related rhenium(I) tricarbonyl complexes have been reported by Schutte et al. (2011) and Manicum et al. (2015). ISSN 2056-9890

Structural commentary
In the title compound, the Re I cation is in a distorted octahedral environment (Fig. 1). The apical positions of the octahedron are occupied by the monodentate arsane ligand and one of the carbonyl groups (C34 O32). The rhenium atom lies almost on the equatorial plane [displacement = 0.0459 (6) Å ]. The five-membered ring defined by the metal ion and the chelating bidentate NO-QA anion is almost planar [maximum deviation of 0.078 (6) Å for atom N1]. One phenyl ring (C11-C16) of the triphenylarsane ligand exhibits intramolecularinteraction with the NO-QA ligand (Fig. 1), the distance from the centroid of the phenyl ring to the plane of the NO-QA ligand being 3.495 Å and the angle between the planes being 9.1 . In addition, intramolecular hydrogen bonds are established between the phenyl rings of the NO-QA ligand (C9-H9Á Á ÁO31) and between one of the phenyl rings of the triphenylarsane ligand (C24-H24Á Á ÁO1) with one carbonyl oxygen atom and one carboxylate oxygen atom respectively ( Fig.1; Table 1). The Re-C O bond length in the apical position [Re-C34: 1.937 (12) Å ] is longer than those in the equatorial plane [Re-C32 = 1.893 (8) Å and Re-C30 = 1.904 (9) Å ] because of the trans influence of the triphenylarsane ligands, as expected (Coe & Glenwright, 2000;Otto & Johansson, 2002). Taking into account that this is the first structurally characterized Re I triphenylarsane tricarbonyl complex, there are no other Re I compound to compare with, but the measured Re-As distance of 2.5855 (10) Å is close to those given by Commons & Hoskins (1975) of 2.569-2.584 Å where the di(diphenylarsino)methane ligand is coordinating to an Re I ion.

Figure 3
Chains of complexes, formed through C7-H7Á Á ÁO2 hydrogen bonds (dashed orange lines), parallel to the b axis.
actions and build up the three-dimensional set-up of the structure (Fig. 4).

Synthesis and crystallization
To a stirred solution of quinaldic acid (17.3 mg, 0.1 mmol) in 5 ml methanol, a solution of [NEt 4 ] 2 [ReBr 3 (CO) 3 ] (77 mg, 0.1 mmol) in 5 ml methanol was added. The mixture was heated at 323 K and after 30 min a solution of triphenylarsane (0.1 mmol) in 3 ml methanol was added. The mixture was stirred under reflux for 2 h and the reaction progress was monitored by HPLC. The solvent was removed under reduced pressure and the solid residue was recrystallized from a dichloromethane/methanol mixture. The resulting solid was redissolved in a minimum volume of dichloromethane, layered with methanol and left to stand at room temperature. After several days crystals suitable for X-ray analysis were isolated (yield: 46.8 mg, 60%).

Figure 4
The three-dimensional network of neighbouring chains formed through C19-H19Á Á ÁO2 and C21-H21Á Á ÁO2 hydrogen bonds (dashed orange and dashed turquoise lines, respectively) in a view along the b-axis direction.

Crystal data
[Re(C 10 H 6 NO 2 )(C  (7) 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq