Crystal structures and Hirshfeld surface analysis of [κ2-P,N-{(C6H5)2(C5H5N)P}Re(CO)3Br]·2CHCl3 and the product of its reaction with piperidine, [P-{(C6H5)2(C5H5N)P}(C5H11N)Re(CO)3Br]

The reaction of the ligand dipyridylphosphine with (Re(CO)3(OC4H8)Br)2 followed by crystallization in chloroform leads to [κ2-P,N-{(C6H5)2(C5H5N)P}Re(CO)3Br]·2CHCl3. Reaction of this complex with piperidine leads to partial decoordination of the 2-pyridylphosphine in the product, [P-{(C6H5)2(C5H5N)P}(C5H11N)Re(CO)3Br], which displays an intramolecular hydrogen bond between the piperidine aminic hydrogen atom and the uncoordinated pyridyl group, with D⋯A = 2.992 (9) Å.

The coordination of the ligands with respect to the central atom in the complex bromidotricarbonyl[diphenyl(pyridin-2-yl)phosphane-2 N,P]rhenium(I) chloroform disolvate, [ReBr(C 17 H 14 NP)(CO) 3 ]Á2CHCl 3 or [ 2 -P,N-{(C 6 H 5 ) 2 (C 5 H 5 N)P}Re(CO) 3 Br]Á2CHCl 3 , (IÁ2CHCl 3 ), is best described as a distorted octahedron with three carbonyls in a facial conformation, a bromide atom, and a biting P,N-diphenylpyridylphosphine ligand. Hirshfeld surface analysis shows that C-ClÁ Á ÁH interactions contribute 26%, the distance of these interactions are between 2.895 and 3.213 Å . The reaction between I and piperidine (C 5 H 11 N) at 313 K in dichloromethane leads to the partial decoordination of the pyridylphosphine ligand, whose pyridyl group is replaced by a piperidine molecule, and the complex bromidotricarbonyl[diphenyl-(pyridin-2-yl)phosphane-P](piperidine-N)rhenium(I), [ReBr(C 5 H 11 N)-(C 17 H 14 NP)(CO) 3 ] or [P-{(C 6 H 5 ) 2 (C 5 H 5 N)P}(C 5 H 11 N)Re(CO) 3 Br] (II). The molecule has an intramolecular N-HÁ Á ÁN hydrogen bond between the noncoordinated pyridyl nitrogen atom and the amine hydrogen atom from piperidine with DÁ Á ÁA = 2.992 (9) Å . Thermogravimetry shows that IÁ2CHCl 3 losses 28% of its mass in a narrow range between 318 and 333 K, which is completely consistent with two solvating chloroform molecules very weakly bonded to I. The remaining I is stable at least to 573 K. In contrast, II seems to lose solvent and piperidine (12% of mass) between 427 and 463 K, while the additional 33% loss from this last temperature to 573 K corresponds to the release of 2-pyridylphosphine. The contribution to the scattering from highly disordered solvent molecules in II was removed with the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18] in PLATON. The stated crystal data for M r , etc. do not take this solvent into account.

Chemical context
Phosphine-type ligands having a second type of atom or coordinating function have been of great interest in many areas of chemistry. The existence of a second coordination atom with different properties, coordination capability or trans effect adds possibilities during a catalytic cycle (Guiry & Saunders, 2004). In particular, much attention has been paid to one of the simplest molecules of this kind, diphenylpyridylphosphine P(C 6 H 5 ) 2 (C 5 H 5 N) (PPh 2 Py). The molecule is a rigid bidentate ligand (Abram et al., 1999;Knebel & Angelici, 1973). The reaction of the diphenylpyridylphosphine ligand with the rhenium dimer (Re(CO) 3 (OC 4 H 8 )Br) 2 in chloroform as solvent leads to the complex P,N-{(C 6 H 5 ) 2 (C 5 H 5 N)P}Re-(CO) 3 Br]Á2CHCl 3 (IÁ2CHCl 3 ). It presents a similar structure to the widely studied [(N,N)Re(CO) 3 (L)] complexes, which have interesting photophysical and photochemical properties (Cannizzo et al., 2008). Complex I has been shown to be a dual emitter (Pizarro et al., 2015). It is also interesting to note that the PPh 2 Py ligand can be partially decoordinated by reaction of the complex with a monodentate ligand, like piperidine (C 5 H 11 N), leading to the complex [P-{(C 6 H 5 ) 2 (C 5 H 5 N)P}-(C 5 H 11 N)Re(CO) 3 Br] (II).

Structural commentary
The mononuclear Re I complex I with a bidentate P,N (chelating) ligand crystallized from a chloroform solution in the monoclinic space P2 1 /c. Selected geometrical data are summarized in Table 1, and the molecular structure of complex IÁ2CHCl 3 is given in Fig. 1. The coordination environment of the central rhenium atom is defined for phosphorus and nitrogen atoms from PPh 2 Py, a bromide atom in an apical position and three carbonyl carbon atoms in a fac correlation, generating a distorted octahedral environment. Additionally, two chloroform molecules crystallize together with the complex molecule.
The mononuclear Re I complex II, crystallized from a CH 2 Cl 2 /CH 3 CN (2:1) solution in the triclinic space group P1. Selected geometrical data are given in Table 2, and the molecular structure of the complex is illustrated in Fig. 2. The Table 1 Selected geometric parameters (Å , ) for IÁ2CHCl 3 .

Figure 2
Molecular view of complex II showing the numbering scheme. Displacement ellipsoids are shown at the 33% probability level. For clarity, the C-bound H atoms have been omitted.

Figure 1
Molecular view of complex IÁ2CHCl 3 , showing the numbering scheme. Displacement ellipsoids are shown at the 33% probability level. For clarity, the C-bound H atoms of I have been omitted.
central rhenium atom displays a non-regular octahedral coordination geometry, with three facial carbonyl groups, a monodentate PPh 2 Py ligand, a piperidine C 5 H 11 N molecule and a bromide anion. The piperidine ring displays a chair-like conformation. An intramolecular hydrogen bond is defined between the non-coordinated pyridyl nitrogen atom and the amine hydrogen atom from piperidine, N2-H2NÁ Á ÁN1, with DÁ Á ÁA = 2.992 (9) Å (Table 4). There are also two C-HÁ Á ÁBr intramolecular contacts present involving atom Br1 and a phenyl H atom (H14) and a methylene H atom (H22B) of the pypridine ring (Table 4).

Supramolecular features
In the crystal of IÁ2CHCl 3 , the lattice has two solvating molecules of chloroform per complex molecule. The cell has a larger volume than for the unsolvated one [2836.7 (15) vs 2119.2 (3) Å 3 (Venegas et al., 2011)] whose geometrical parameters are very similar to those of complex I. In the crystal, the chloroform solvent molecules are involved in weak C-HÁ Á ÁBr hydrogen bonds and they link the complex molecules to form layers lying parallel to the bc plane ( Fig. 3 and Table 3).
In the crystal of II, a region of highly disordered electron density was equated to the present of a disordered acetonitrile molecule. The contribution to the scattering was removed with the SQUEEZE routine in PLATON (Spek, 2015). A view of the crystal packing, showing the regions, or voids, occupied by this disordered solvent in given in Fig. 4.

Hirshfeld surface analysis of complex IÁ2CHCl 3
In order to visualize and quantify the intermolecular interactions in the crystal packing of complex IÁ2CHCl 3 , in particular those involving the chloroform solvent molecules, an Hirshfeld surface analysis was performed and two-dimensional fingerprint plots generated. The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots (McKinnon et al., 2007) were performed with CrystalExplorer17 (Turner et al., 2017). The Hirshfeld surface mapped over d norm = d e + d i , is given in Fig. 5a (d e represents the distance from the surface to the nearest nucleus external to the surface, and d i is the distance from the surface to the nearest nucleus internal to the surface). In this d norm view (Fig. 5a), blue represents the longest distances while the shortest distances are depicted as red spots (Dalal et al., 2015).
The two-dimensional fingerprint plot for the whole complex is given in Fig. 5b Table 4 Hydrogen-bond geometry (Å , ) for II.

Figure 4
A view along the b axis of the crystal packing of complex II. The voids occupied by the disordered solvent molecules are shown in yellow-brown (calculated using Mercury; Macrae et al., 2008).  contacts that contribute ca 15% the other most relevant intermolecular interactions, as determined from the Hirshfeld surface analysis of complex IÁ2CHCl 3 , are shown in Fig. 6

Thermogravimetric analysis
Thermogravimetric analyses from 25 to 300 C were performed for both compounds under an N 2 flux at a heating rate of 1 C min À1 (see Fig. 7). Thermogravimetric analysis for compound IÁ2CHCl 3 (Fig. 7, red line), shows that it loses 28% of its mass in a narrow range, between 45 and 60 C. This mass loss is completely consistent with the two solvating chloroform molecules detected by the crystal structure analysis. The boiling point of chloroform, 61 C, is almost identical to the temperature where the mass loss stops, suggesting that the chloroform molecules are weakly bonded to the rhenium ones in the solid. From 60 to 300 C the remaining matrix is completely stable.
Compound II loses 12% of its initial mass between 154 and 190 C (Fig. 7, blue line). This loss of mass can be associated with the release of the acetonitrile and piperidine molecules (14.7%). The relatively high temperature at which decomposition begins compared to the piperidine boiling point, 105 C, suggest that it is strongly bonded to II. From 190 to 300 C, another 33% of mass loss is registered, which can be associated with the release of the PPh 2 Py (36.6%, b.p.163 C).

Database survey
The diphenylpyridylphosphine ligand has been extensively studied and used as a monodentate and bidentate ligand with different metals, including Ru II (Ooyama & Sato, 2004) where the CO 2 -reducing properties of the complex were studied. Another Ru II complex with PPh 2 Py (Kumar et al., 2011) has been studied as an inhibitor of DNA-topoisomerases of the filarial parasite S. cervi. Re I -nitrosil complexes with PPh 2 Py have been studied structurally and photophysically (Machura & Kruszynski, 2006).
Piperidine is a ligand that has been widely used with various transition metals. It has been used as a ligand with tungsten and molybdenum to study the cis-trans effect by using larger ligands and increasing the steric hindrance (Darensbourg et al., 2007).

Figure 7
Weight loss for IÁ2CHCl 3 (red line) and II (blue line) between room temperature and 300 C. any further purification. Standard Schlenck techniques under argon atmosphere were used for all manipulations.
Synthesis of I. 500 mg of (Re(CO) 3 (OC 4 H 8 )Br) 2 (0.590 mmol) were dissolved in 5 ml of chloroform. 312 mg of diphenyl-2-pyridylphosphine (1.18 mmol) was dissolved in 10 ml of chloroform. The two solutions were mixed, changing from colourless to a translucent yellow after 10 minutes of reaction. The reaction was left to continue for a further 2 h. Addition of 2 ml of pentane to the mixture and standing by one day lead to yellow diffraction-quality crystals of IÁ2CHCl 3 (601 mg, 82.8% yield).
Synthesis of II. The compound was prepared by direct reaction between I and an excess of piperidine (C 5 H 11 N) at 313 K in CH 2 Cl 2 . 50.0 mg of [P,N-{(C 6 H 5 ) 2 (C 5 H 5 N)P}Re-(CO) 3 Br] (0.082 mmol) were dissolved in 10 ml of CH 2 Cl 2 giving rise to a yellow solution. Then, 40 mL of piperidine (0.51 mmol) was slowly added. The reaction was allowed to continue for six days with constant agitation at 313 K. After cooling, the reaction mixture was layered with acetonitrile.
Small orange-yellow diffraction-quality crystals were obtained after one week.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. For both compounds, the hydrogen atoms were positioned geometrically and refined using a riding model: C-H = 0.93-0.97 Å with U iso (H) = 1.2U eq (C). For II, the amine hydrogen atom of the piperidine ring was located in a Fourier-difference map and then subsequently refined with a distant constraint of 0.82 Å . During the last stages of the refinement of II, a region of highly disordered electron density was detected within the crystal structure. As no meaningful model could be achieved, SQUEEZE (Spek, 2015) was used to model the unresolved electron density resulting from the disordered solvent. 25 electrons per cell suggest, in addition to thermogravimetry, a half acetonitrile   For both structures, data collection: SMART (Bruker, 2012); cell refinement: SMART (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2014 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )