The second crystal structure of boryllithium 2 with two coordinating THF solvent molecules was obtained. The B-11 NMR chemical shift of a THF solution, made by dissolving single crystals of 2 center dot(THF)(2) in THF-d(8), significantly and reversibly changed depending on temperature (from 20 to -100 degrees C). The calculated B-11 chemical shift by GIAO method was close to two experimental values. The character of the sp(2) lone pair on the boron center in opt-2 center dot(THF)2 was shown to be similar to those in the calculated free phenyl anion and boryl anion. AIM analyses for opt-2 center dot(THF)2 suggested that the B-Li bond of boryllithium is polarized, similar to the C-Li bond of alkyllithium.