# Steric, Activation Method and Solvent Effects on the Structure of Paddlewheel Diruthenium Complexes
## 3 Results and Discussion
### Crystal Structures  
The crystal structures of complexes **1b** and **1c** have been solved by single crystal X-ray methods. Both compounds adopt a paddlewheel arrangement with the two ruthenium atoms connected by four bridging carboxylate ligands. Thus, each Ru atom shows a distorted octahedral environment having a RuO4 (carboxylates) environment in the equatorial positions and the axial sites occupied by one chloride ligand or solvent molecule and by the other Ru atom of the bimetallic unit (Figures 1 and 2).  
Compound **1b** is formed by single bimetallic molecules that have two different axial ligands: chloride and ethanol (Figure 1 Left). This structure displays a degree of disorder concerning the positions of the carbon atoms in the rings C2-C7 and C18-C23.  
This compound shows a 1D supramolecular ordering. Chains are formed along the _a_-axis through hydrogen bonds between the chloride axial ligand of a bimetallic unit and the ethanol axial ligand of the adjacent unit (Figure 1 Right).  
Complex **1c** is a salt with anionic and cationic diruthenium units. The cationic complex has methanol molecules at the axial positions, whereas in the anionic complex these positions are occupied by chloride ligands (Figure 2).  
In complex **1c**, both bimetallic units are bridged by solvent molecules through hydrogen bonds, giving rise to chains (Figure 3) in a similar way to the supramolecular packing observed in compound **1b**.  
Figure 1: (**Left**) Dimetallic unit of complex **1b**. Ellipsoids are drawn at 50% probability level. (**Right**) Packing of compound **1b** viewed along crystallography b axis. Hydrogen atoms and atoms involved in disorder are omitted for clarity.  
Figure 2: Bimetallic complexes of compound **1c**. Ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity.  
In **1c**, the Ru-Ru distance in the anionic unit is longer than in the cationic unit [2.2950(5) and 2.2667(5) A, respectively] due to the different donor character of the axial ligands (Table 2). These distances are very similar to those found in the complexes [Ru\({}_{2}\)Cl(\(\mu\)-O\({}_{2}\)CCH\({}_{2}\)OEt)\({}_{4}\)\({}_{4}\)\(\cdot\)H\({}_{2}\)O] [2.294(2) and 2.261(1) A] [31], and [Ru\({}_{2}\)I(\(\mu\)-O\({}_{2}\)CCH\({}_{2}\)CH\({}_{2}\)OPh)\({}_{4}\)(H\({}_{2}\)O)] 0.5H\({}_{2}\)O [2.310(2) and 2.265(2) A] [32], which form analogous anionic and cationic diruthenium complexes, in addition to zig-zag chains in the case of the former. Chloride ligands are better donors than methanol ligands and, therefore, the diruthenium atoms are richer in electronic density. Consequently, \(\pi^{\bullet}\)and \(\delta^{\bullet}\) orbitals are more populated, giving a larger Ru-Ru distance. The Ru-Cl and Ru-O\({}_{\rm axial}\) bond distances have the usual values in diruthenium complexes [1; 2; 4; 33].  
The Ru-Ru distance [2.2827(6)] in **1b** is in the range of the values found in compound **1c** [2.2950(5) and 2.26267(5)], which seems reasonable, taking into account the presence of chloride and ethanol axial ligands in this complex (Table 2).  
In order to determine the influence of the positions of the aromatic ring in the packing of these complexes, the dihedral angle \(\theta\) has been examined. This can be defined as the angle formed by the plane of the phenyl ring and the plane occupied by COO group and the ruthenium atoms. These angles vary from 15.51\({}^{\circ}\) to 80.66\({}^{\circ}\) for compound **1c** and from 12.73\({}^{\circ}\) to 71.73\({}^{\circ}\) for **1b** (Table S1 and Figure S1, Supplementary Materials). The deviation of the methoxy group of the aromatic ring planes vary from 3.59\({}^{\circ}\) to 10.59\({}^{\circ}\) (**1c**) and 1.80\({}^{\circ}\) to 12.03\({}^{\circ}\) (**1b**) (Table S2, Supplementary Materials). These values are in a broad range and are similar in both compounds. Thus, these angles do not seem to have any significant influence on the arrangement of these complexes in the solid state.