Crystal structures of bis[2-(pyridin-2-yl)phenyl-κ2 N,C 1]rhodium(III) complexes containing an acetonitrile or monodentate thyminate(1−) ligand

Bis[2-(pyridin-2-yl)phenyl]rhodium(III) complexes bearing acetonitrile or monodeprotonated thyminate (Hthym−) were characterized by X-ray analysis, and in the latter complexes it was revealed that Hthym− coordinated to an RhIII centre through the N1 atom together with a hydrogen-bonded methanol or ethanol co-ligand in the cis position.


Chemical context
Thymine (= H 2 thym) is one of the nucleobases, which are biologically important and fundamental organic molecules, and can release one or two protons, giving a thyminate(1À) (= Hthym À ) or thyminate(2À) (= thym 2-) anion. These anions can act as suitable bridging ligands for the construction of functional polymetallic coordination compounds because they provide multiple donor atoms to metal atoms in a configurationally fixed fashion. For example, some tetra-and pentanuclear Pt II complexes bridged by thym 2have been described (Khutia et al., 2011;Rauterkus & Krebs, 2004). We have also reported some cyclic tetranuclear Cp*Rh III (Cp* = pentamethylcyclopentadienyl) complexes bridged by thym 2and incorporating an another metal cation in the central hydrophilic cavity of their metallacalix[4]arene motifs (Kashima et al., 2015;Sakate et al., 2016). In contrast, monoanionic thyminate (Hthym À ) often acts as an N 1 -coordinating monodentate ligand, for example, in  Cross et al., 1995]. These examples also indicate the strong trans influence of the phenyl-C donor in the trans position.
In both 2 and 3, there is an intramolecular hydrogen bond between atom O2 of the Hthym À and O51-H1 of MeOH or EtOH in the mutually cis-position (Tables 2 and 3). These hydrogen bonds may stabilize the coordination of solvent MeOH and EtOH molecules in 2 and 3, even though the Rh-O bonds for these ligands are relatively long. In fact, a reaction of complex 2 or 3 with an equivalent amount of PPh 3 , P(OMe) 3 , imidazole or a mixture of adenine and triethylamine (L) gave a complicated mixture of products, from which no desirable ligand-substituted complexes of the formula, [Rh(ppy) 2 (Hthym)(L)] could be isolated.
In each crystal of the thyminato(1À) complexes of 2 and 3, together with an intramolecular hydrogen bond mentioned above, there is a pair of intermolecular N-HÁ Á ÁO hydrogen bonds (Tables 2 and 3) with an R 2 2 (8) ring motif between the neighboring Hthym À ligands, forming an inversion dimer (Figs. 4 and 5). The methanol and ethanol molecules of crys-tallization in 2 and 3 are each linked to the Hthym À ligand via an intermolecular O-HÁ Á ÁO hydrogen bond.

Figure 5
A perspective view of 3, showing the intra-and intermolecular O-HÁ Á ÁO hydrogen-bonds (dotted lines) between the Hthym À and EtOH ligands. To a methanol suspension (10 mL) of [Rh(ppy) 2 Cl] 2 (0.090 g, 0.10 mmol) was added Ag(CF 3 SO 3 ) (0.051 g, 0.20 mmol). The mixture was stirred at room temperature in the dark overnight, and the resulting white precipitate of AgCl was filtered off. A methanol solution (10 mL) containing thymine (0.025 g, 0.20 mmol) and triethylamine (28 mL, 0.20 mmol) was carefully layered on the filtrate, and the mixture was allowed to stand overnight to give yellow crystals of 2. Yield: 0.082 g (68%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms bonded to C and N atoms in 1-3 were refined using a riding model, with C-H = 0.95 or 0.98 Å and N-H = 0.88 Å , and with U iso (H) = 1.2U eq (C, N). The positions of the O-bound H atoms of the coordinating methanol molecule in 2 and the coordinating and solvated ethanol molecules in 3 were refined with the restraints O-H = 0.84 (1) Å , and with U iso (H) = 1.2U eq (O), while the H atom of the solvated methanol in 2 was refined using a riding model with O-H = 0.84 Å and U iso (H) = 1.2U eq (O). In the crystal of 2, other than the complex and methanol molecules, there is a small electron density remaining in the void, and this was assumed to be a water molecule of crystallization. The H atoms of this water mol-ecule were not introduced in the calculation because of the highly disordered state of the water molecule, which resulted in large thermal displacement parameters for the O atom. SHELXS2013 (Sheldrick, 2008) for (2), (3). Program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015) for (1), (3); SHELXL2013 (Sheldrick, 2008) for (2). For all compounds, molecular graphics: ORTEP-3 for Windows (Farrugia, 2012). Software used to prepare material for publication: SHELXL2013 (Sheldrick, 2015) for (1), (3); SHELXS2013 (Sheldrick, 2008) for (2).