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Spectral studies help measure the T1 relaxation times of water in the aqueous solutions of the three types of paramagnetic transition metal-substituted heteropoly complexes, alpha-(XW11O39Z(H2O))n-, (X = P or Si and Z = Fe3+ or Mn2+), alpha2-(P2W17O61Z(H2O))m- (Z = Mn2+ or Fe3+) and (GdH2W10O36)7- in a 10.7 MHz magnetic field. The net relaxivity of individual heteropoly complexes vary as a function of the metal type, net complex charge, the size, and the rotational correlation time.

Laser-induced Eu3+ luminescence technique was used to investigate the stability of Eu(HAM)3+ (HAM = hexaazamacrocyclic) complex. Decomposition rate of the complex was not affected by the addition of a chelating agent or competing metal ion but was observed to be dependent on pH and temperature. A similar study with Gd(HAM)3+ showed the effectivity of the compound as relaxation agent for 1H and 89Y NMR analysis.

The dependence of varying hydrogen ion concentration and temperature on the transverse and longitudinal relaxation rates of the solvent water proton in solutions of organochromium(III) complex (H2O)5Cr(CH2CN)2+ are investigated. The transverse relaxation rate increase with increasing temperature and the chemical exchange rate shows dependence on the hydrogen ion concentration. The proton exchange rate and properties of (H2O)5CrCH2CN2+ are similar with other chromium(III) complexes.