Cyanate groups in higher oxidation state metal cluster chemistry: Mixed-valence (II/III) Mn16 and Mn18 clusters

The employment of cyanato (OCN-) group in high oxidation state manganese cluster chemistry, in conjunction with carboxylate ions and the organic chelating/bridging ligand 2-(hydroxymethyl)pyridine (hmpH), is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn16O8(OR)4(OCN)4(O2CMe)12(hmp)6(ROH)2] (R = Me (1), Et (2)) and [Mn18O14(O2CR)18(hmp)4(hmpH)2(H2O)2] (R = Me (3), Et (4)). The 2:1:1:1 reactions of Mn(O2CMe)2·4H2O, hmpH, NaOCN and NEt3 in solvent MeOH or EtOH afford the isostructural complexes [Mn16O8(OR)4(OCN)4(O2CMe)12(hmp)6(ROH)2] (R = Me (1), Et (2)). The [Mn16(μ4-O)4(μ3-O)4(μ-OMe)4(μ3-OR)6(μ-OR)6]10+ core of representative complex 1 comprises a MnII4MnIII4 double-cubane subunit attached on either side to two symmetry-related MnIIMnIII3 defective dicubanes. A similar reaction of Mn(O2CR)2·4H2O, hmpH, NaOCN and NEt3, but in solvent MeCN, led instead to the formation of [Mn18O14(O2CR)18(hmp)4(hmpH)2(H2O)2] (R = Me (3), Et (4)). Compounds 3 and 4 are very similar to each other and can be described as a central [MnIII4(μ-O)6] rodlike subunit attached on either side to two symmetry-related [Mn7O9] subunits. Variable-temperature, solid-state dc and ac magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions in all compounds, and possible S = 2 or 1 (for 1 and 2) and S = 0 (for 3 and 4) ground state spin values. The combined results demonstrate the ability of cyanato groups to facilitate the formation of new polynuclear MnII/III complexes with structures different than these obtained from the use of the related azides

A flow-system array for the discovery and scale up of inorganic clusters

The batch synthesis of inorganic clusters can be both time consuming and limited by a lack of reproducibility. Flow-system approaches, now common in organic synthesis, have not been utilized widely for the synthesis of clusters. Herein we combine an automated flow process with multiple batch crystallizations for the screening and scale up of syntheses of polyoxometalates and manganese-based single-molecule magnets. Scale up of the synthesis of these architectures was achieved by programming a multiple-pump reactor system to vary reaction conditions sequentially, and thus explore a larger parameter space in a shorter time than conventionally possible. Also, the potential for using the array as a discovery tool is demonstrated. Successful conditions for product isolation were identified easily from the array of reactions, and a direct route to `scale up' was then immediately available simply by continuous application of these flow conditions. In all cases, large quantities of phase-pure material were obtained and the time taken for the discovery, repetition and scale up decreased