Analogies between Vanadoborates and Planar Aromatic Hydrocarbons: A High-Spin Analogue of Aromaticity

The vanadium-vanadium interactions in the polygonal aggregates of d(1) vanadium(IV) atoms, with a total of 4k + 2 vanadium electrons (k an integer) imbedded in an electronically inactive borate matrix in certain vanadoborate structures are analogous to the ring carbon-carbon interactions in diamagnetic planar cyclic hydrocarbons. They thus represent a high-spin analogue of aromaticity. Thus, the vanadoborate anion [V(6)B(20)O(50)H(8)](8−) with six V(IV) electrons (i.e., 4k + 2 for k = 1) contains a macrohexagon of d(1) V(IV) atoms with four unpaired electrons. This high-spin system is related to the low-spin aromaticity in the diamagnetic benzene having six π electrons. Similarly, the vanadoborate anion [V(10)B(28)O(74)H(8)](16−) with ten V(IV) electrons (i.e., 4k + 2 for k = 2) contains a macrodecagon of d(1) V(IV) atoms with eight unpaired electrons. Again, this high-spin system is related to the aromaticity in the diamagnetic 1,6-methanol[10]annulene, having ten π electrons.