Crystal structure and magnetic study of the complex salt [RuCp(PTA)2–μ-CN-1κC:2κN–RuCp(PTA)2][Re(NO)Br4(EtOH)0.5(MeOH)0.5]

In this work, we present the complex salt [RuCp(PTA)2–μ-CN–1κC:2κ2 N-RuCp(PTA)2][Re(NO)Br4(EtOH)0.5(MeOH)0.5]. The synthesis, single-crystal X-ray crystal structure, and magnetic properties are discussed.

The complex anion is constituted by an Re II atom and displays a distorted octahedral geometry formed by four bromide ions in the equatorial plane, one nitrogen atom from the nitrosyl ligand, and one oxygen atom from an -OH group in apical positions. The -OH group comes from a methanol or an ethanol molecule, both with an s.o.f. of 0.5. The O1M and C1E atomic positions are the same for both the MeOH and the EtOH ligand. The Re1-O1m-C1e angle is 128.3 (6) . The NO group is practically linear with an O101-N101-Re1 angle of 178.6 (10) . The three atoms are also aligned with the O1M atom of the alcohol ligand, exhibiting a N101-Re1-O1M angle of 178.9 (3) . The rhenium atom is shifted from the main plane of Br ligands towards the apical NO group by 0.157 Å . The asymmetric unit of the title compound, including atom labelling. Displacement ellipsoids are drawn at the 50% probability level. For clarity, H atoms have been omitted. Table 1 Hydrogen-bond geometry (Å , ).

Supramolecular features
The complex crystallizes in the monoclinic P2 1 /c space group. The cations interconnect adjacent anions via O-HÁ Á ÁN hydrogen bonds and C-HÁ Á ÁBr interactions, forming an infinite three-dimensional framework ( Table 1). The O-HÁ Á ÁN interactions are given along the bc plane and are defined by O1m as the donor atom from the MeOH/EtOH ligand and N8 i atom from a PTA ligand at (x À 1, y, z) (Fig. 2). The H1MÁ Á ÁN8 i and O1MÁ Á ÁN8 i distances are 1.88 and 2.709 (9) Å , respectively. The angle defined by O1M-H1MÁ Á ÁN8 i is 165.5 . The remaining hydrogen bonds are found between the PTA ligands from one cationic unit [RuCp(PTA) 2 --CN-1C:2 2 N-RuCp(PTA) 2 ] + and bromides from [Re(NO)Br 4 -(EtOH) 0.5 (MeOH) 0.5 ] À units. The multiplicity and lack of defined directionality in the hydrogen-bond network are related to the fact that the major forces that stabilize the crystal are of electrostatic origin. The C-HÁ Á ÁBr and the CÁ Á ÁBr distances range from 2.53-3.12 Å and 3.208 (11)-3.944 (12) Å , respectively. The hydrogen-bond angle involving the C-HÁ Á ÁBr atoms vary between 127 and 169 . These geometrical values are in concordance with weak hydrogenbonding interactions (Desiraju, 1995;Metrangolo et al., 2006;Steed & Atwood, 2009). The effect of the combined weak C-HÁ Á ÁBr bonds and their effect on the crystal assembly can be as significant as that of the strong interactions (Desiraju & Steiner, 2001). The C2E-HÁ Á ÁN6 bond is probably negligible because of the low energy expected for all C-H bonds (Steed & Atwood, 2009) and particularly considering the C2E 50% atomic site occupation.

Hirshfeld analysis
To further understand the intermolecular interactions between the ionic complexes within the crystal structure, a Hirshfeld surface (Spackman & Jayatilaka, 2009) was constructed around each ion. In addition, a 2D fingerprint plot analysis (Spackman & McKinnon, 2002) was performed for each case. Crystal Explorer17 (Turner et al., 2017) was used to determine the surface and construct the plots. The Hirshfeld surfaces of both the anion and cation are illustrated in Fig. 3 (left) and 3 (right), respectively, showing surfaces that have been mapped over a d norm range of À0.6854 to 1.6426 a.u. (McKinnon et al., 2007). The color code employed for d norm is red for the shortest d norm and blue for the longest d norm . Red spots in the surface correspond to the shortest contacts within the surface, indicating the formation of intermolecular bonds as those detailed in the previous section (supramolecular features).
The anion Hirshfeld surface shows how the most significant interaction is due to the O1m-HÁ Á ÁN8 bond, which is illustrated by bright-red spots in Fig. 3 (left), while the weaker spot corresponds to the C2E-HÁ Á ÁN6 bond. What is more, the other minor red spots can be identified as BrÁ Á ÁH interactions. These red spots (and thus the interionic interactions) can be correlated with the spikes observed in the twodimensional fingerprint plots. In fact, the anion fingerprint for all interactions exhibits characteristic spikes in the region 1.8 Å < d i + d e < 2.8 Å resulting from HÁ Á ÁN and BrÁ Á ÁH interactions. There is a high-density area close to the BrÁ Á ÁH spike, indicating a significant number of BrÁ Á ÁH contacts in the crystal structure. In addition, the broad central spike extending up to the (d i ,d e ) region of (0.65 Å , 0.78 Å ) reflects the significant amount of HÁ Á ÁH contacts in the structure. Nevertheless, it is important to point out that the HÁ Á ÁH contacts are usually difficult to localize in the Hirshfeld surface as they are spread all over the crystal packing. The Hirshfeld surface analysis for the cationic unit and its fingerprint also shows how HÁ Á ÁN, NÁ Á ÁH, HÁ Á ÁBr, and HÁ Á ÁH contacts surround the [RuCp(PTA) 2 --CN-1C:2 2 N-RuCp(PTA) 2 ] unit. The relative contributions of the different intermolecular contacts to the Hirshfeld area for both ions are shown in Fig. 4. In the anion, the major contributors ($93%) research communications   View along the a axis of the title compound, with the O1M-HÁ Á ÁN8 contacts (see Table 1 for details) represented by blue dashed lines. For clarity, H atoms have been omitted.
Given that C-HÁ Á ÁBr bonds account for a significant fraction of intermolecular contacts, as seen in section 4, a search was conducted involving this bonding scheme to check if the values presented in this article are within the bin frequently encountered in transition-metal compounds. The search restrained metal-BrÁ Á ÁH distances to be lower than the sum of the vdW radius ($3.5 Å ). Compounds containing a C-BrÁ Á ÁH angle of less than 90 were discarded, as the hydrogen atom in the hydrogen bond must not point away from the acceptor atom (Aakerö y et al., 1999). The search resulted in 36099 hits from 12143 structures. The histograms of CÁ Á ÁBr distances and C-HÁ Á ÁBr angles (Figs. 4 and 5 in the supporting information) confirm that these HÁ Á ÁBr contacts, considering the distance/angle criteria, can be identified as hydrogen bonds (Aakerö y et al., 1999;Metrangolo et al., 2006;Shimpi et al., 2007;Zhang et al., 2008).

Magnetic measurements
Magnetic susceptibility measurements on polycrystalline samples were carried out with a Superconducting Quantum Interference Design (SQUID) magnetometer in the temperature range 2.0-300 K. In order to avoid saturation phenomena, we used external dc magnetic fields of 500 G Relative contributions to Hirshfeld surface area for the close molecular contacts. (T < 20 K) and 5000 G (T ! 50 K). Experimental susceptibilities were carefully corrected for the diamagnetism of the holder (gelatine capsule) and constituent atoms by applying Pascal's constants.
The magnetic behaviour of [RuCp(PTA) 2 --CN-1C:2 2 N-RuCp(PTA) 2 ][Re(NO)Br 4 (EtOH) 0.5 (MeOH) 0.5 ] is shown in Fig. 5 in the form of a M T versus T plot where M is the molar magnetic susceptibility per one Re II ion and T the absolute temperature. As expected, a straight line is observed for this compound (Pacheco et al., 2013). The thermal dependence of M T is in line with one unpaired electron (S = 1 2 ) and a temperature independent paramagnetic contribution (TIP). The M T value at room temperature is higher than that expected for an S = 1 2 with g = 2.0 (0.375 cm 3 K mol À1 ) due to the temperature-independent paramagnetism (TIP). The slight decrease below 10 K must be attributed to very weak intermolecular antiferromagnetic (AF) interactions between the [Re(NO)Br 4 (EtOH) 0.5 (MeOH) 0.5 ] À anions.
In this sense, we use equation (1), with S = 1 2 , to fit the experimental data.

Synthesis
A solution of (NBu 4 )[Re(NO)Br 4 (EtOH)] (0.012 mmol, 10 mg) dissolved in 5 mL of a methanol-DMSO (400:1, v/v) mixture was layered in an test tube with a solution of [RuCp(PTA) 2 --CN-1C:2 2 N-RuCp(PTA) 2 ](CF 3 SO 3 ) (0.012 mmol, 13 mg) in 5 mL of the same methanol-DMSO mixture; ca 5 mL of the solvent mixture should be added between the two reactant layers to decrease diffusion time. Deep reddish-brown plate-like crystals, suitable for single crystal X-ray diffraction were obtained after one week. The product was filtered and washed by decantation with methanol. Yield: 24%. Analysis calculated for Ru 2 C 36.5 N 14-

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were included in calculated positions and treated as riding: C-H distance between 0.94 and 0.98 Å with U iso (H) = 1.2U eq (C). Methanol/ethanol coordinating molecules were treated as positionally disordered utilizing the PART instruction with occupancy fixed to 0.5 applied to C1E, C1M, and C2E. C1M and C1E were constrained to occupy equivalent positions. Meanwhile, C2E was located in the Fourier difference map and refined freely.  Data collection: APEX2 (Bruker, 2007); cell refinement: APEX2 (Bruker, 2007); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXT2014/4 (Sheldrick, 2015a); program(s) used to refine structure: