*2.1. Characterization*

### 2.1.1. Structural Description

Crystal structures were obtained as described in [43,44], and will be briefly described in order to understand the catalytic results. X-ray structural analyses of LaCuODA (**1**) and LaCoODA (**2**) reveal that both belong to the hexagonal crystal system, with space group *P*-62c for **1** and *P*6/mcc for **2**. The skeleton of the structures is similar in both porous MOFs. The LaIII is coordinated by three tridentate ODA ligands, thus nine oxygen atoms define the coordination sphere of this metal centre. Each [La(ODA)3] 3− unit is connected to six MII (M = CuII, CoII) ions via single *syn-anti* μ-carboxylato-O-O' bridges. The MII ions are surrounded by four oxygen atoms from [La(ODA)3] 3− units in (**1**) and (**2**). The di fference in the coordination pattern of (**1**) and (**2**) is that CoII ion in (**2**) is bound to two water molecules in the axial positions, forming a slightly distorted octahedron. On the other hand, CuII in (**1**) is bound to just one molecule of water, being penta-coordinated. In spite of this di fference, the main structural feature of these MOFs is the formation of hexagonal channels along the crystallographic *c* axis (Figure 1). The maximum size of the channel can be estimated in 11.39 Å for (**1**) and 11.09 Å for (**2**). Crystallization water molecules are hosted in the channels. In the special case of (**1**), one of the crystallization water molecules per unit formula is in a fixed position forming a μ2-H2O bridge between LaIII ions.

**Figure 1. Left**: partial view of complex (**2**) along the crystallographic *c* axis, showing the generated hexagonal channels. H atoms and crystallization water molecules are omitted for clarity. **Right**: cross-section of the channel showing the inner exposed surface. Color code: La, orange; Co, pink; O, red; C, light grey.

The determination of the acid strength for LaCoODA showed an initial potential of 24.5 mV after 4 h of stabilization with the first addition of N-butylamine, while LaCuODA presented a higher value of 93.7 mV. The ranges of initial potential defined for the strength of acid sites are as follows: potential > 100 mV, very strong acid site; 100 mV > potential > 0 mV, strong acid site; 0 mV > potential > −100 mV weak acid site; −100 mV > potential, very weak acid site. Thus, LaCuODA presents acid sites that can be defined as nearly strong, while LaCoODA presents weak acid sites. As for the number of acid sites, LaCoODA has 0.295 miliequivalent of acid sites per gram and LaCuODA has 0.783 miliequivalent of acid sites per gram (Table 1).


**Table 1.** Determination of acid strength and number of acid sites for LaM(ODA).

The Thermogravimetric (TGA) profile of both complexes was reported and analyzed previously [43,44]. Compound (**1**) presents two mass losses. The first one between 56 and 94 ◦C corresponds to all water molecules per formula unit. The second one appears around 240 ◦C and can be associated with the beginning of the decomposition of the structure. Thermal analyses of (**2**) show that the loss of water involved a well-defined two-step process. The first step corresponds to twelve molecules of crystallization water (below 50 ◦C). The second step (between 110 and 135 ◦C) includes the six water molecules coordinated to CoII. The decomposition of the structure is evident above 260 ◦C.

Table 2 shows the pore diameter and estimated surface area of the catalysts obtained by the BET and Langmuir models from the CO2 adsorption isotherm at 273 K. The LaCoODA has a BET surface area of 762 m<sup>2</sup>/g, which is greater than that of LaCuODA (514 m<sup>2</sup>/g); a similar trend was obtained from the Langmuir area values. On the other hand, the pore size is the same for both catalysts, and it is consistent with the pore size described by the crystallographic data (11.39 (**1**) and 11.09 (**2**) Å). These results permit to classify the catalysts in the range of microporous materials.

**Table 2.** Textural properties from CO2 adsorption measures.


### 2.1.2. Catalytic Results

LaCuODA and LaCoODA were used as catalysts for the aerobic oxidation of cyclohexene, in the absence of additional organic solvent or co-oxidant. The obtained results are summarized in Table 3, while the obtained products are shown in Scheme 1.

**Table 3.** Catalytic results after 24 h of the aerobic oxidation of cyclohexene at 75 ◦C using LaMODA (M=CoII, CuII).


*Reactions conditions*: cyclohexene (50 mmol) and (0.01 mmol) of LaM(ODA) (M = CoII, CuII), 1 bar of continuous oxygen flow. The mixture is stirred (960 rpm) at 75 ◦C for 24 h.

**Scheme 1.** Products derived from the catalytic oxidation of cyclohexene (**a**). Cyclohexene oxide (**b**); 2-cyclohexen-1-ol (**c**); 2-cyclohexen-1-one (**d**).

The conversion after 24 h of reaction shows that the MOF based on cobalt (II) has a better catalytic performance than that of the catalyst based on copper (II) (Table 2). The main product for both catalysts was 2-cyclohexen-1-one, with the selectivity for this product being 75% for LaCoODA and 55% for LaCuODA. Thus, the influence on both the conversion and selectivity of the reaction of the nature of the *3d* transition metal ion becomes evident.
