Materials and Methods

Compound 1 was synthesized under solvothermal conditions by using our recently reported {Co5} coordination cluster, [CoII3CoIII2(Hbda)2(bda)2(ib)6]. The {Co5} was freshly prepared following the published procedure, followed by drying under reduced pressure.14 All other starting materials were from commercial sources and used as received. Solvents were used without any further purification. The IR spectrum of compound 1 was recorded on a Nicolet Avatar 360 FTIR spectrometer (KBr pellet, ν = 4000–400 cm−1). TG/DT analyses of compound 1 was performed under a flow of dry air and a heating rate of 5 K min−1 in the temperature range 25–700 °C on a Mettler Toledo TGA/SDTA 851e instrument. The ESI-MS spectrum of compound 1 in the positive ion mode was recorded on a 4000 QTRAP mass spectrometer system, using the LC/LC-MS method with direct infusion.
 

Synthesis of [CoII10(OH)2(bda)6(ib)6] (1)

Freshly prepared and vacuum dried {Co5} [CoII3CoIII2(Hbda)2(bda)2(ib)6] (0.030 g; 0.02 mmol) was dissolved in 5 mL of DMSO. The green solution was placed in a sealed autoclaveable glass vial (or a Teflon-lined stainless steel autoclave) and kept in an oven 100 °C for 120 h. The oven was then turned off allowed the vial to cool to room temperature over 4 h. Pink needle-shaped single crystals of 1, suitable for X-Ray analysis, were obtained and washed with cold methanol, yield; 0.020 g (95 %, based on Co). Elemental analysis, calcd. for: Co10C72H146N6O26 (2101.28 g mol–1; no solvent): C, 41.15; H, 7.00 and N, 4.00 %. Found: C, 41.11; H, 6.96 and N 3.98 %. MS (MeCN, ESI +): m/z: 2013.3202 (Co10C68H139N6O24+; 100 %; [CoII10(OH)2(bda)6(ib)5]+ –ib–; theoretical: 2013.3155). IR (KBr pellet), νmax / cm−1: 3441 (s, br), 2960 (s), 2928 (s), 2866 (s), 1556 (s), 1477 (m), 1433 (m), 1375 (w), 1361 (w), 1290 (w), 1167 (w), 1095 (s), 1071 (m), 1043 (w), 928 (vw), 894 (m), 849 (w), 764 (vw), 596 (m), 549 (w).
 
Overall, compound 1 can be synthesized in three steps while only the last step is a solvothermal reaction (scheme 1). A reaction of freshly prepared cobalt(II) isobutyrate (Co(ib)2) and N-butyldiethanolamine (H2bda) in a molar ratio of 5:3 was carried out under similar conditions, however the reaction did not yield the final compound 1. Likewise, a reaction of the {CoII3CoIII2} precursor was carried out in DMSO under non-solvothermal conditions and heated at 100 °C; the recrystallization of the product provided same dark green precursor {Co5}. Thus, use of the precursor complex ({Co5} = {CoII3CoIII2}) along with solvothermal method is necessary for the synthesis of compound 1.