2-DIMENSIONAL MOLECULAR LAYERS IN THE CRYSTALS OF CALCIUM COMPLEX WITH PYRAZINE-2,3-DICARBOXYLIC ACID

The crystals of diaquo(mu-pyrazine-2,3-dicarboxylato)calcium(II) dihyd rate are monoclinic, space group P2(1), a = 6.832(1) Angstrom, b = 16. 765(3) Angstrom, c = 8.410(2) Angstrom, beta = 106.53(3) deg. It conta ins two symmetrically independent Ca ions, each coordinated by one nit rogen and seven oxygen atoms. Calcium ions are bridged in the directio n of the a axis by oxygen atoms belonging to a bidentate carboxylic gr oup of the acid molecule. The bridging in the direction of the b axis is accomplished by the same carboxylic group and by the second, monode ntate carboxylic group as well as by the nearest to it nitrogen atom o f the pyrazine ring (N,O-bonding moiety). In addition, each calcium io n is coordinated by two water molecules. The mean Ca-O and Ca-N bond d istances are 2.441 Angstrom and 2.645 Angstrom respectively. Molecular sheets parallel to the (001) plane can be visualized. They are held t ogether by strong hydrogen bonds operating via two solvation water mol ecules located in the space between the sheets.