Ab initio calculations for the [Y(H2O)(4)(BH4)(2)](+) complex, a model of [Y(THF)(4)(BH4)(2)](+), have been carried out to study the metal-BH4- ligand interactions. Our calculations for various isomers with different BH4- coordination modes allow us to explore the electronic and electrostatic interactions in details. It is found that both electronic and electrostatic effects are of almost equal importance.