That methyl groups attached to carbon atoms are electron donors must not be generally assumed. In boron clusters, Me groups on boron are electron withdrawing. At the B3LYP/6-31G* level of theory, it has been proven that the Mulliken charge on each boron after substitution of -H by -Me increases by +0.18 unit. This leads to a high build-up of positive charge upon permethylation, then hampering it. Experimentally, this is proven by the synthesis of 9-I0.707H0.293-12-Cl0.566H0.434-3,4,5,6,7,8,10,11-Me8-1,2-C2B10H2, in which positions 9 and 12 were first methylated and then attacked by nucleophiles. This is substantiated by the synthesis of 3,6,8,9,10,12-Me6-1,2-C2B10H6 under the same experimental conditions but with time control.

A bridge between classical organic polycyclic aromatic hydrocarbons (PAH) and closo borohydride clusters is established by showing that they share a common origin regulated by the number of valence electrons in an electronic confined space. Application of the proposed electronic confined space analogy (ECSA) method to archetypal PAHs leads to the conclusion that the 4n+2 Wade-Mingos rule for three-dimensional closo boranes is equivalent to the (4n+2)π Hückel rule for two-dimensional PAHs. More importantly, use of ECSA allows design of new interesting fused closo boranes which can be a source of inspiration for synthetic chemists.

o-C2B10H12 isomerizes to m-C2B10H12 upon heating at 400 ºC. Deboronation in o-C2B10H12 is a relatively easy process, whereas it is more difficult in m-C2B10H12. These two experimental facts indicate that m-C2B10H12 is thermodynamically more stable than o-C2B10H12. On the other hand, it is widely accepted that closo boranes and carboranes are aromatic compounds. In this work, we relate difficulty in the deboronation of the carboranes with stability and aromaticity. We do this by combining lab work and by means of DFT calculations. Computationally, our results show that the higher thermodynamic stability of m-C2B10H12 is not related to aromaticity differences but to the location of the C atoms in the carborane structure. It is also demonstrated that the aromaticity observed in closo boranes and carboranes is also present in their nido counterparts and, consequently, we conclude that aromaticity in boron clusters survives radical structural changes. Further, sandwich metallocenes (e.g. ferrocene) and sandwich metallabis(dicarbollides) (e.g.[Co(C2B9H11)2] -) have traditionally been considered similar. Here it is shown that they are not. Metallabis(dicarbollides) display global aromaticity whereas metallocenes present local aromaticity in the ligands. Remarkable and unique is the double probe given by 1 H-and 11 B-NMR tracing the reciprocally antipodal endocyclic open face Hec and B1. These magnetic studies have permitted to correlate both nuclei and relate them to a diatropic current in the plane at the middle of the nido [C2B9H12] -. This observation is the first and unique data that proves experimentally the existence of diatropic currents, thence aromaticity, in clusters and is comparable to the existence of diatropic currents in planar aromatic compounds.Additionally, heteroboranes with two carbon atoms have been compared to heterocycles with two nitrogen or boron atoms, C2B10H12 carboranes against planar N2C4H4 diazines or [B2C4H4] 2diboratabenzenes, proving the higher persistence of the aromaticity of the tri-dimensional compounds in heteroatom substituted species. This research accounts very well for the "Paradigm for the Electron Requirements of Clusters" in which a closo-cluster that is aromatic upon addition of 2ebecomes also an aromatic nido species and explains the nice schemes by R.W. Rudolph and R. E. Williams.

Boranes, heteroboranes and metallacarboranes, all named as boron clusters, offer an alternative to typical organic molecules or organic molecular materials. Carbon and boron share the important property of self-catenation thus these elements can produce individually large and sophisticated molecules. Boron clusters and organic molecules display electronic, physical, chemical and geometrical characteristics manifestly different. These differences highlight the complementarity of organic molecules and boron clusters, and therefore the feasibility or necessity to produce hybrid molecules incorporating both types of fragments. To join these two types of fragments, or alternatively these two types of molecular compounds, tools are needed. In this review the current methods of producing boron clusters with carbon, B-C, nitrogen, B-N, phosphorus, B-P and sulphur bonds, B-S, are indicated. As there are many existing borane clusters of different sizes, heteroboranes and metallacarboranes, the revision of methods to generate the B-C, B-P, B-S, and B-N bonds has been restricted to the most widely used boron clusters; [B12H12](2-), dianionic and an example of a borane, 1,2-C2B10H12, neutral and an example of a heteroborane, and [Co(C2B9H11)2](-), monoanionic and an example of a metallacarborane.

Neutral and especially dianionic 6-and 12-vertex closo ortho-carboranes (o-carboranes) 1,2-R2-1,2-C2BnHn (R ) H, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, as well as e -, CH2 -, NH -, O -, SiH2 -, PH -, and S -) exhibit extremely large variations (over 1 Å!) of the cage CC distances, from 1.626 to 2.638 Å, at the B3LYP/6-31G*//B3LYP/6-31G* DFT level. These CC "bond lengths," among the longest ever reported, generally are greater in the icosahedral than those in the corresponding octahedral systems and depend strongly on the substituents. While 1,2-(NH2)2-1,2-C2B10H10 has the longest Cc‚‚‚Cc separation in neutral species (1.860 Å), Cc‚‚‚Cc distances can be much larger in the corresponding dianions. These range fromRemarkably, there is no abrupt discontinuity over the entire range of CC lengths. Consequently, the relationship between the gradual changes in the distances and the nature of the bonding was analyzed by means of the form of the Kohn-Sham orbitals, the Wiberg Cc‚‚‚Cc bond indices, and Bader AIM method. Cluster carboranes, and possibly other heteroboranes, thus appear to offer unique opportunities for modulating Cc‚‚‚Cc distances.

After uptake by U87 MG and A375 cancer cells, cobaltabisdicarbollide [COSAN] distributes between membrane and nucleus and presents no relevant cytotoxicity against both cell lines even for long incubation times. The cytotoxicity of Na[COSAN] was also tested towards one normal cell line, the V79 fibroblasts, in order to ascertain the noncytotoxic profile of the compound. As the cell's nucleus contains DNA, the interaction between [COSAN] and double-stranded calf thymus DNA (CT-dsDNA) has been investigated. There is a strong interaction between both molecules forming a nanohybrid CT-dsDNA-[COSAN] biomaterial, which was fully characterized. Moreover, Na[COSAN] shows characteristic redox peaks ascribed to the oxidation/reduction of Co at a formal potential of -1.444 V and it can be accumulated at a surface-immobilized DNA layer of glassy carbon electrodes. The equilibrium surface-binding constants (K /K ), which confirm that [COSAN] interacts with DNA by an intercalative or electrostatic mode, depending on the ionic strength of the solution, were estimated. In addition, high binding affinity of Na[COSAN] to proteins was observed by B{ H} NMR and confirmed in vivo. Finally, biodistribution studies of [COSAN] in normal mice were run. After administration, Na[COSAN] was distributed into many organs but mainly accumulated in the reticuloendothelial system (RES), including liver and spleen. After 1 h, the formation of aggregates by plasma protein interaction plays a role in the biodistribution profile; the aggregates accumulate mostly in the lungs. Na[COSAN], which displays low toxicity and high uptake by relevant cancer cells accumulating boron within the nucleus, could act as a suitable compound for further developments as boron neutron capture therapy (BNCT) agents.

Polypyrrole (PPy) is of great potential importance due to its excellent conductive properties; however, a major obstacle to commercialization (like many synthetic metals) is its poor stability, especially to oxidation. Here is reported a new synthesis of PPy in the presence of the cobaltabisdicarbollide anion (see Figure), whose uniform distribution throughout the polymer leads to a dramatic improvement in the overoxidation threshold.

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