Crystal structure of bromido-fac-tricarbonyl[5-(3,4,5-trimethoxyphenyl)-3-(pyridin-2-yl)-1H-1,2,4-triazole-κ2 N 2,N 3]rhenium(I) methanol monosolvate

The ReI atom in the title methanol solvate is coordinated octahedrally by two N atoms of the chelating organic ligand, one Br atom and three facially configured carbonyl ligands. Hydrogen bonds between the complex and methanol solvent molecules lead to a layered arrangement in the structure.


Chemical context
Rhenium(I) metal complexes have attracted attention because of their chemical characteristics exhibiting increased potentials for biochemical applications (Ferná ndez- Moreira et al., 2010;Lo et al., 2012). Rhenium tricarbonyl complexes with the general formula fac-[Re(CO) 3 (N^N)] (where N^N is an N,N 0chelating ligand) are kinetically stable and have luminescence properties with long life times (Kowalski et al., 2015;Guo et al., 1997), high photostability (Lo, 2015) and large Stokes shifts (Lo, 2015;Stephenson et al., 2004), which makes these compounds ideal candidates for either in vitro or in vivo visualization of biological processes (Shen et al., 2001;Thorp-Greenwood, 2012).

Structural commentary
The three carbonyl ligands bonded to the Re I atom are arranged in a fac configuration. The distances of atoms C1, C2 and C3 to the Re I atom are 1.902 (4), 1.910 (2) and 1.907 (2) Å , respectively, and the Re-N bond lengths involving the chelating organic ligand are 2.151 (2) and 2.205 (2) Å . The two N atoms and two carbonyl C atoms define the equatorial plane, while the octahedral coordination sphere is completed by the third carbonyl C atom and the Br atom

Supramolecular features
In the crystal, the packing of the molecules is influenced by a set of weak interactions, including conventional hydrogen bonding with common NH and OH donor groups and weaker hydrogen bonds formed by CH groups (Table 1). Two pairs of relatively short hydrogen bonds (O7-HÁ Á ÁBr1 and N2-HÁ Á ÁO7), both involving the methanol solvent molecules, assemble the complex molecules into centrosymmetric dimers (Fig. 2). As may be compared with the closely related complex [ReBr(L)(CO) 3 ] [L = 5-phenyl-3-(pyridin-2-yl)-1H-1,2,4-triazole; Piletska et al., 2014], a key prerequisite for the formation of dimers is the presence of acidic NH functions and sterically accessible Br sites. In the latter, they afford two mutual N-HÁ Á ÁBr hydrogen bonds, whereas in the present case, these links appear to be extended by the inclusion of methanol, resulting in an N-HÁ Á ÁO(Me)-HÁ Á ÁBr motif.
Each of the four pyridine CH groups functions as a donor of weak hydrogen bonds (Fig. 2). These groups establish hydrogen bonds to two carbonyl O atoms (C8Á Á ÁO2 iv and C10Á Á ÁO3 ii ), a methoxy O atom (C9Á Á ÁO6 iii ) and a very weak bond with bromine as acceptor (C7Á Á ÁBr v ) (for symmetry codes, see Table 1). These distal yet directional interactions (the hydrogen-bonding angles are in the range 142-165 ; Table 1) unite the above dimers into flat double layers, which extend parallel to the (111) plane. Within a layer, the pyridine and triazole moieties of adjacent molecules are actually parallel, with shortest contacts of C7Á Á ÁN3 v = 3.430 (4) Å [symmetry code: (v) Àx, 1 À y, Àz]. However, this situation is unlikely to be a consequence of slippedinteractions, since the corresponding slippage angle exceeds 56 and the intercentroid distance is as long as Cg(C6-C10/N4)Á Á ÁCg(C4/C5/ N1-N3) v = 4.090 (3) Å [for the lack of an overlap between heteroaromatic planes, see Fig. 2, part (B)]. At the same time, successive double layers are turned towards one another by methyl groups of the trimethoxyphenyl and methanol entities ( Fig. 3). Thus, the interlayer interactions are very weak and the only remarkable contact is found between two inversionrelated carbonyl groups [O1Á Á ÁC1 vi = 3.295 (3) Å and O1Á Á ÁCg(C1 O1) vi = 3.226 (3) Å ; symmetry code (vi) Àx, Ày, Àz]. Although such weak interactions are characteristic of related metal-carbonyl structures (Sparkes et al., 2006), in the present case, their significance is relatively minor.

Figure 3
Packing of successive double layers, which are turned towards one another by the methyl and carbonyl groups (the view is along the direction of the hydrogen-bonded chains indicated with blue and grey bonds). [Symmetry codes:  (Sheldrick, 2008), DIAMOND (Brandenburg, 1999) and WinGX (Farrugia, 2012

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. C-and N-bound H atoms were positioned with idealized geometry and were refined with aryl C-H = 0.94 Å , methyl C-H = 0.97 Å and N-H = 0.87 Å , and with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C,N) otherwise. The O-bound H atom of the methanol solvent molecule was found from a difference map and was refined with O-H = 0.95 Å and U iso (H) = 1.5U eq (O). ; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.77 e Å −3 Δρ min = −0.98 e Å −3 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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq