The effective Bohr magneton number mu(eff) of Cu(II) adsorbed at the boehmite/water interface is 14% to 21% less than anticipated for a uniform dispersal of Cu(II) ions throughout the interface, Insufficient evidence for exchange coupling indicates the lost electron paramagnetic resonance signal intensity must largely result from spin-spin relaxation. Polynuclear Cu(II) clusters at the silica/water interface are superparamagnetic with a blocking temperature between 5 K and 7 K, Superparamagnetic Cu(II) clusters at the silica/water interface do not saturate at magnetic fields as high as 10,000 G.