A metal ion nanocluster having a formula of X(OH)a Y b Z c M d(H2O)e. X, Y, Z,M,a, b, c, d, and e are defined herein. The nanocluster has a particle size of 2to 500 nm anda molecular weight of 3500 to 1000000 Dalton. Also disclosed are a compositioncontaining the nanocluster and a method of preparing the nanocluster.