MONOMERIC MOLECULES IN THE ISOSTRUCTURAL CALCIUM(II) AND STRONTIUM(II) COMPLEXES WITH PYRAZINE-2-CARBOXYLIC ACID

The crystals of tetraquobis(pyrazine-2-carboxylato-O,N)calcium(II) con tain monomeric molecules, in which the calcium ion has a distorted dod ecahedral coordination, formed by four water molecules (mean Ca-O = 2. 441 Angstrom), two oxygen atoms from monodentate carboxylic groups of two pyrazinic acid molecules (mean Ca-O = 2.458 Angstrom) and two nitr ogen atoms located next to the above carboxylic groups (mean Ca-N = 2. 619 Angstrom). In the crystals of traquobis(pyrazine-2-carboxylato-O,N )strontium(II) the coordination of the Sr2+ ion is identical with that of the calcium complex, the corresponding mean distances being Sr-O(w ater) 2.572 Angstrom, Sr-O 2.588 Angstrom, Sr-N 2.751 Angstrom. The mo nomeric molecules of both compounds are linked via a network of hydrog en bonds.