# Steric, Activation Method and Solvent Effects on the Structure of Paddlewheel Diruthenium Complexes
## 3 Results and Discussion  
### Synthesis  
Three synthetic methods have been used to obtain compounds [Ru2 Cl(u-O2 CC6H4-R)4], with R = _o_-OMe (**1a**, **1b**, **1c**), _m_-OMe (**2**) and _p_-OMe (**3**): (a) microwave assisted solvothermal synthesis, (b) conventional synthesis and (c) solvothermal synthesis. These methods make possible the complete replacement of the four acetate groups in the starting compound [Ru2 Cl(u-O2 CC6H3)4]n by the corresponding methoxybenzoate group. In all cases, a 50% excess of the methoxybenzoic ligand was used to favor the reaction. The preparation of compounds **1a**, **1b** and **1c** depends on the synthetic method or the experimental conditions, such as the solvent or the cooling time, whereas compounds **2** and **3** have been obtained by the three methods. The microwave assisted solvothermal method allowed the synthesis of compounds **1a**, **2** and **3** with yields of 76, 77 and 48%, respectively. Conventional metathesis reactions in MeOH/H2O (1:1) under reflux conditions also yielded compounds **1a**, **2** and **3** (yields = 53, 76 and 61%, respectively). In the three cases, due to the insolubility of the product, only one metathesis cycle was enough to get a pure phase of the compound. Solvothermal synthesis was valid to obtain compounds **2** and **3**. Although the solvothermal synthesis is a very useful method to obtain single crystals, it very often leads to a mixture of complexes. In this work, the elemental analyses of complexes **2** and **3** obtained by this method could indicate that these compounds are not very pure. For this reason, the best characterization data of **2** and **3** have been obtained with the samples prepared by conventional heating. On the other hand, using solvothermal activation with the _o_-methoxybenzoate ligand did not make possible obtaining compound **1a**; compounds **1b** and **1c** were obtained instead. In this method, slight differences in the reaction conditions have been used to obtain each compound with the best yield. In this way, compound **2** was obtained in methanol applying an isotherm of 100 \({}^{\circ}\)C and 16 h of cooling ramp (yield = 76%). In the synthesis of compound **3**, 90 \({}^{\circ}\)C, ethanol and a cooling ramp of 24 h (yield = 61%) have been used. Compound **1b** was synthesized with a good yield (71%) at 100 \({}^{\circ}\)C in ethanol and a cooling ramp of 40 h. However, only a few crystals of compound **1c** were obtained in a similar reaction in methanol at 100 \({}^{\circ}\)C and 16 h of cooling. Scheme 1 summarizes the synthetic methods used to obtain compounds **1a**, **1b**, **1c**, **2** and **3**. Moderate or high yields were obtained except for compound **1c**, and there are no appreciable differences between the synthetic methods. This seems to indicate that microwave activation does not improve the yield in relation to conventional methods, as it has been previously observed for the synthesis of other diruthenium(II,III) complexes [20,21,23,24,25,26]. Nevertheless, the microwave method allows the use of ethanol as solvent, which is less toxic and contaminant than the methanol required in the conventional synthesis. Long-time controlled cooling ramps up to room temperature of the solvothermal syntheses have allowed the formation of single crystals of compounds **1b** and **1c**. The use of the solvothermal synthesis to get single crystals of insoluble products is well known and it has been previously described for diruthenium derivatives [23,24,25,26]. The rest of products (**1a**, **2** and **3**) have been obtained as microcrystalline solids. However, single crystals of compound **3** were obtained previously from the reaction mixture by diffusion of methanolic solutions of _p_-methoxybenzoic acid and [Ru\({}_{2}\)Cl(\(\mu\)-O\({}_{2}\)CMe)\({}_{4}\)]\({}_{\rm In}\)[28]. The insolubility of compounds **1a**, **2** and **3** in the most usual solvents, indicates a polymeric nature as it is usual in the major part of the tetracarboxylatochloriodidoriuthenium(II,III) compounds [1,2,4].