Could someone please give me some hints or direct me to some literature that explains how it is that the carbons in carborane can have six bonds? All throughout organic chemistry they kept emphasizing how carbon can never have more than four covalent bonds, but here in carborane the carbons have six bonds. My only hypothesis is that the bonds are not entirely covalent. When I asked my polymer chemistry professor he said that thinking about carborane gave him a headache and he advised me to try to figure it out on my own. Thanks!