A method for magnetic resonance imaging of a human or animal body includes providing a spin crossover complex having the general formula [Mx+(Ly)Hw]AN)z wherein, MX+ is a positively charged metal ion, Ly is a heteroaromatic ligand containing at least one nitrogen atom in its ring system, AN is a negatively charged inorganic anion, w is 0, 1 or 2, x is 2 or 3, y is 2 or 3, and z is 2, 3 or 4. The spin crossover complex is applied as a contrast agent in a magnetic resonance imaging of the human or animal body.