The literature known high-nuclear planar Co complexes were synthesized under various conditions using different organic ligands and Co sources. The {CoII7} complex of Pattacini et al. [12] was synthesized under inert gas atmosphere with anhydrous CoCl2, pyridine-2-ylmethanol (= HLig1) and NaH in THF at room temperature. [CoII7(Lig1)12]Cl2 was obtained in a yield of 35 % as orange crystals. The complex is dicationic and all oxo-bridges between the Co(II) centers belong to the used ligand. {CoII9CoIII3} was published by Zheng et al. in 2010 [13]. The complex was synthesized at room temperature too, but they used Co(ClO4)2∙6H2O, NaN3, 2-benzimidazolemethanole (= HLig2) and triethanolamine (H3tea) in methanol. [CoII9CoIII3O3(N3)4(Lig2)15](ClO4)2·H3tea·9.5H2O was obtained in yield of 67 % as deep-brown crystals. Although H3tea is not incorporated in the structure, it seems to be necessary for the crystallization as it is co-crystallized, the preparation of the complex under ambient conditions leads to the coordination of three discrete oxygen atoms, which are in the center of the {CoII9CoIII3} complex. [CoII11CoIII2(OH)4(piv)4(acac)6(Lig3)4(H2O)4](piv)2∙H2O (Hpiv = pivalic acid, acac– = acetylacetonate, H3Lig3 = 1,1,1-tris(hydroxymethyl)-propane [2], which was published by Leng and others, was synthesized using Co(acac)2, H3Lig3 and pivalic acid in MeOH. The solution was heated up to 120 °C for 50 h in a Teflon-lined stainless steel autoclave and the {CoII11CoIII2} complex was obtained as red crystals in a yield of 35 %. Here the waiver of the use of inert gas leads to the incorporation of discrete hydroxide groups and water molecules into the complex. In comparison the title compound was synthesized under solvothermal conditions (as {CoII11CoIII2}) without the use of inert gas, as it was done for the homovalent {Co7} complex. In this work the use of a precursor complex ({CoII3CoIII2}) was crucial, instead of using a simple Co(II) salt, to obtain [CoII10(OH)2(bda)6(ib)6] as pink crystals in yield of 95 %, which contains discrete OH–-groups.

IR and Stability (TGA and ESI-MS)

The IR spectrum of compound 1 displays asymmetric (asym.) and symmetric (sym.) stretching vibrational bands of C–H (methyl groups) between 2960 cm–1 to 2866 cm–1. The coordinated carboxylate groups (COO–) cause an asymmetric stretching vibration band at 1556 cm–1 and the corresponding symmetric stretching vibration band at 1433 cm–1. Asymmetric and symmetric deformation vibrational bands of C–H ((methyl groups) are obtained as a strong single band at 1477 cm–1 (asym.), a weak doublet at 1375 cm–1 (sym.) and 1361 cm–1 (sym.). The broad band at 3441 cm–1 is attributed to –OH (hydroxyl), along with some moisture.
The thermogravimetric analysis revealed that the compound 1 is surprisingly thermally stable up to 225 °C (see Fig. S4) when compared with {Co5} precursor (140 °C ). Compound 1 decomposes in two exothermic different sized steps in the temperature range of 225–370 °C with a total weight loss of 61.8 %. The first smaller step (225–268 °C) shows a weight loss of 15.7 %, which could be attributed to the loss of four isobutyrate ligands [D1] [SS2] (∆mcalcd. = 16.6 %) and the second step (268–370 °C) with a weight loss of 46.1 % is in good agreement with the loss of the remaining two isobutyrate ligands, one bda2– ligand, five bda2– ligands without their oxygen atoms and the two hydrogen atoms of the discrete OH groups (∆mcalcd. = 46.2 %). The thermal stability of compound 1 demonstrates that a facile reaction of the recently obtained {CoII3CoIII2} precursor complex, leads to a new coordination complex, where the physical properties are increased and optimized, by a rearrangement and extension of the molecular structure, as well as a reduction of Co(III) to Co(II) oxidation state. In addition, the stability of compound 1 was also evaluated via ESI-MS analysis in acetonitrile. The results showed that an 100% intensity peak is appeared at 2013.3 m/z ratio, which is attributed to Co10C68H139N6O24+ [CoII10(OH)2(bda)6(ib)5]+ theoretical m/z: 2013.3155 (see Fig. S1 and S2). These results further confirms the high stability of [CoII10(OH)2(bda)6(ib)6], in particular in acetonitrile[D3] .
 [D1]Which four?
 [SS2]Not possible to tell, we could assume all four not chelating ib-ligands
 [D3]Please add in the TGA curve and ESI-MS graphs.

Magnetochemical Analysis

The magnetic data of compound 1 are shown in Figure 3 as χmT vs. T plot at 0.1 T and Mm vs. B plot at 2.0 K. The high nuclearity of the complex precludes a detailed analysis of the magnetic data based on a microscopic model Hamiltonian. The value of χmT at 290 K is 29.12 cm3 K mol–1, which is well within the range 23.12 – 33.81 cm3 K mol–1 expected[i] for ten non-interacting high-spin CoII centers. With decreasing temperature, χmT initially slowly increases down to 40 K and then more rapidly increases to reach a maximum value of 41.17 cm3 K mol–1 at 5.0 K, and finally drops off to 37.34 cm3 K mol–1 at 2.0 K. The increasing values as well as the observed maximum reveal dominant ferromagnetic exchange interactions between the ten CoII centers of 1. The decrease of χmT at low temperatures is most likely caused by a minor Zeeman effect due to the applied field in addition to the thermal depopulation of the energy substates rather than antiferromagnetic exchange interactions that can, however, not be excluded. These conclusions are consistent with the observed behavior of the molar magnetization at 2.0 K that increases up to 1 T (xx NA µB) and subsequently increases to 22.1 NμB at 5.0 T without reaching saturation. This is about half the expected saturation value of about 45 NμB derived from the χmT value at 290 K. Considering octahedral coordination geometry of high-spin CoII centers, such a value indicates either no or small exchange interactions.
 
[i] H. Lueken, Magnetochemie, Teubner, Stuttgart, 1999.

Conclusion

In summary, we reported the first planar {CoII10} coordination cluster with a high thermal stability up to 225 °C, which was obtained solvothermally upon reduction of the {CoII3CoIII2} precursor in DMSO. The [CoII10(OH)2(bda)6(ib)6] complex shows predominant ferromagnetic exchange interactions.[JvL1] 
The structural motif of the complex opens perspectives for the development of thin, planar shaped metal-oxo frameworks. [SS2] 
 [JvL1]And what else to conclude?
 [SS2]What do you think?