Synthetic, Spectroscopic and X-Ray Crystallographic Studies of Bivalent Metal Complexes with Amino Acids Having a Thiazolidine Ring. III. The Properties of Bivalent Metal Complexes with Racemic 2-Thiazolidinecarboxylic Acid and the Structure oftrans-Diaquabis(2-thiazolidinecarboxylato)zinc(II)