catena-Poly[[μ2-aqua-diaquabis(μ4-pyridazine-3,6-dicarboxylato)tetralithium] monohydrate]

In the polymeric structure of the title compound {[Li2(C6H2N2O4)2Li(H2O)2Li(H2O)]·H2O}n, the coordination of two independent LiI ions is distorted trigonal–bipyramidal and that of the other two independent LiI ions is distorted tetrahedral. The former two LiI ions are bridged by hetero-ring N atoms of two independent pyridazine-3,6-dicarboxylate ligands, making a dimeric moiety. The carboxylato-O atoms of both bidentate ligands bridge the dimers to adjacent independent aqua-coordinated LiI ions, forming molecular ribbons. The latter are bridged by ligand carboxylato and aqua O atoms, forming molecular layers parallel to (100) which are held together by an extended system of O—H⋯O hydrogen bonds.

In the polymeric structure of the title compound {[Li 2 (C 6 H 2 -N 2 O 4 ) 2 Li(H 2 O) 2 Li(H 2 O)]ÁH 2 O} n , the coordination of two independent Li I ions is distorted trigonal-bipyramidal and that of the other two independent Li I ions is distorted tetrahedral. The former two Li I ions are bridged by heteroring N atoms of two independent pyridazine-3,6-dicarboxylate ligands, making a dimeric moiety. The carboxylato-O atoms of both bidentate ligands bridge the dimers to adjacent independent aqua-coordinated Li I ions, forming molecular ribbons. The latter are bridged by ligand carboxylato and aqua O atoms, forming molecular layers parallel to (100) which are held together by an extended system of O-HÁ Á ÁO hydrogen bonds.

Related literature
For the crystal structure of a Li I complex with water and pyridazine-3,6-dicarboxylate ligands, see: Starosta & Leciejewicz (2010).

Experimental
Crystal data [Li 4 (C 6  H atoms treated by a mixture of independent and constrained refinement Á max = 0.52 e Å À3 Á min = À0.40 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).  (Starosta & Leciejewicz, 2010). It has been of interest to study structural changes brought about by removal of the bridging protons. Hydrazine has been selected as the deprotonating agent. The structure of a complex obtained when the amount of added hydrazine was very small is described in this report.
The title compound is a polymeric complex with four symmetry independent Li ions in the asymmetric unit. Two of them show distorted trigonal bipyramidal geometry, the other two exhibit distorted tetrahedral coordination environment.
The asymmetric unit contains also two pyridazine-3,6-dicarboxylate ligand molecules (PY1 with atoms labels starting with 1 and PY2 with atoms labels starting with 2), three coordinated water molecules and a solvation water molecule (Fig.1).
The Li-O and Li-N bond distances are close to those observed in the other Li complex with the title ligand (Starosta & Leciejewicz, 2010). Both pyridazine rings are planar with r.m.s. deviation of 0.0154 (2)Å and 0.0123 (2)Å for the ring PY1 and PY2, respectively. Carboxylate groups C17/O11/O12 and C18/O13/O14 make with the hetero-ring PY1 dihedral angles of 14.3 (1)° and 22.2 (2)°, respectively. Dihedral angles formed with the hetero-ring PY2 by carboxylate groups C27/O21/O22 and C28/O23/O24 amount to 3.8 (1)° and 17.2 (2)°, respectively. The Li1 and Li2 ions bridged by hetero-ring N atoms donated by both ligands along the Li1-N11-N12-Li2-N22-N21-Li1 pathway form a dimeric moiety. The C27/O21/O22 and C27 iii /O21 iii /O22 iii groups act as bidentate bridge between the Li3 and Li3 iii ions to form a loop which joins two dimers via O21 and O21 iii atoms since the latter are also bonded to the Li1 and Li1 iii ions, respectively. A similar loop bridges the dimers from the other side as the bidentate O13 atom links the Li2 and Li4 iv ions. A molecular ribbon propagating along the c direction can be visualized (Fig. 2). The ribbons bridged by carboxylate and coordinated water O atoms form molecular layers which are parallel to the bc plane and stacked along the a axis direction. The bridging of ribbons proceeds via carboxylato O12 and O24 atoms: atom O12 is coordinated to the Li2 ii atom in an adjacent ribbon, while the Li2 ion by the O12 ii atom from the same adjacent ribbon. The O24 atom is chelated to the Li1 i ion in the other adjacent ribbon, while the O24 i atom is coordinated to the Li1 ion. In addition, pairs of ribbons are bridged by coordinated aqua O42 atoms via Li4-O42-Li3 ii and Li3-O42 ii -Li4 ii links. An extended system of hydrogen bonds in which coordinated water supplementary materials sup-2 molecules are donors and carboxylato O atoms in adjacent layers act as acceptors, maintains the stability of the structure (Table 1). Two intra-molecular hydrogen bonds are also observed.

Experimental
The title complex was obtained by adding three drops of hydrazine to the aqueous solution containing ca 1 mmol of the complex previously synthetized (Starosta & Leciejewicz, 2010). The solution was kept at 320 K with constant stirring for 6 h, then left to evaporate at room temperature. Colorless single-crystal columns were washed with cold ethanol and dried in the air.