Pure monoclinic MgBO2(OH) nanowhiskers were synthesized by room temperature co-precipitation followed by hydrothermal treatment at 220—240℃ for 6.0—30.0 h

using MgCl2·6H2O

H3BO3

and NaOH as raw materials with molar ratio of Mg:B:Na=2:3:4.Enlightened by mechanical mixture model and group contribution method

a novel subunit contribution model for the assessment of thermodynamic properties such as ΔfHm and ΔfGm of borates was developed

by introducing correction factor k and reasonably decomposing the complex double salt metal borates into constitutional subunits according to mass conservation.The as-developed model was utilized to assess ΔfHm and ΔfGm at various temperatures for precipitate Mg7B4O13·7H2O and hydrothermal product MgBO2(OH)

based on which the values of ΔrHm and ΔrGm of the co-precipitation of Mg7B4O13·7H2O and hydrothermal conversion to MgBO2(OH) were obtained.The results show that

the room temperature co-precipitation can occur spontaneously whereas the hydrothermal conversion can only be performed spontaneously at high temperature. The feasibility for the co-precipitation as well as the hydrothermal conversion turns to be higher with the increase in the temperature and time.The subunit contribution model is beneficial for the analysis and prediction of controllable synthesis of other complex double salt nanostructures via the soft-chemistry based method.