The crystal and molecular structure of bis(L-methioninato)copper(II), Cu(L-Met)/sub 2/, Cu(C/sub 5/H/sub 10/NO/sub 2/S)/sub 2/, has been determined from single-crystal three-dimensional x-ray data collected by counter methods. The compound crystallizes as elongated blue six-sided plates in the space group P2/sub 1/(C/sub 2//sup 2/, No. 4) with Z = 2, a = 9.487 (5) A, b = 5.061 (3) A, c = 15.563 (8) A, ..beta.. = 92.46 (3)/sup 0/, d/sub calcd/ = 1.601 g/cm/sup 3/, and d/sub obsd/ = 1.60(1)g/cm/sup 3/. Least-squares refinement of 1191 reflections having F/sup 2/ greater than or equal to 3sigma(F/sup 2/) gave a conventional R factor of 0.046. There are no discrete molecules in the crystal; it consists of isolated sheets of Cu(II) ions with tetragonal N/sub 2/O/sub 4/ ligand sets formed by trans coordination of two L-methionine molecules. Additional interactions with carboxylate ions from neighboring methionine molecules lead to two apical Cu--O bonds and link the Cu(II) ions to form a carboxylate-bridged sheet structure. The structure of Cu(L-Met)/sub 2/ is compared with that reported by others for racemic Cu(D,L-Met)/sub 2/. Infrared spectra and magnetic properties of both complexes are presented and discussed. Effective magnetic moments of the racemic complex fell in the range 1.85 tomore » 1.90 ..mu../sub B/ at temperatures between 270 and 6.2/sup 0/K and followed Curie law behavior. Similarly, effective magnetic moments of Cu(L-Met)/sub 2/ fell in the range 1.76 to 1.87 ..mu../sub B/ at temperatures between 270 and approx. 13.5 K; below 13.5 K, the magnetic moment steadily decreased to 1.65 ..mu../sub B/ at 4.2/sup 0/K. ESR spectra of both polycrystalline complexes were measured at Q- and X-band frequencies over wide temperature ranges. Crystallographic similarities between the free methionine ligands and their complexes with Cu(II), Zn(II), and Cd(II) are presented and discussed.« less