Abstract: ¹H NMR spectra of single optal of potassium pentaborate tetrahydrate(KB₅) have ben obtained at RT with different orientations with respect to the external magnetic field.It was found that there were at most 6 peaks in a ¹H NMR spectrum when the external magnetic field was in its be plane, and 5 peaks in ah and ac planes. Combined with the computer calculations of NMR spectrum, the results indicate that the hydrogen atoms in KB₅ are in the form of hydroxyl and water groups. The O-H distances in the hydroxyl groups are 0.1005±0.001 nm and 0.1054±0.001 nm. The O-H distances in the water groups are 0.0983±0.001nm and 0.0968±0.0001nm with H-O-H angle of 108±1°.These show that the proton position data obtained by X-ray diffraction are far from our values,and the data by neutron diffraction are more close to our values.

Key words: Potassium pentaborate tetrahydrate, NMR, Secular determinant