Bis(hydrazin-1-ium) bis(μ2-pyridazine-3,6-dicarboxylato)bis(aqualithiate) octaaquabis(μ3-pyridazine-3,6-dicarboxylato)tetralithium

The unit cell of the title compound, (N2H5)2[Li2(C6H2N2O4)2(H2O)2]·[Li4(C6H2N2O4)2(H2O)8], comprises two centrosymmetric complexes, one double negatively charged and one neutral, and two mono-protonated hydrazine cations. The anionic complex molecule is a dimer, built of a pair of symmetry-related pyridazine-3,6-dicarboxylate ligands and a pair of LiI ions, each coordinated by two N,O-chelating sites donated by a ligand molecule and an aqua O atom at the apical position. The pentacoordination around the LiI ions is partway between a trigonal–bipyramidal and a square-pyramidal arrangement. The two carboxylic acid groups of the ligand are deprotonated and one carboxylate O atom of each group is not involved in the coordination, and this applies to both the anionic and the neutral complex. The neutral complex molecule is also composed of a pair of LiI ions and a pair of ligand molecules related by a centre of symmetry. They form a dimeric core in which the pentacoordination of the LiI ions includes two N,O-bonding groups donated by two ligands and an aqua O atom. The pentacoordination is described as partway between a trigonal–bipyramidal and a square-pyramidal arrangement. The coordinated carboxylate group is bidentate–bridging, forming with an Li(H2O)3 unit a neutral tetrameric molecule. The coordination of the tetracoordinated LiI ion shows a slightly distorted tetrahedral geometry. An extended system of O—H⋯O and N—H⋯O hydrogen bonds contributes to the stability of the crystal structure.


Wojciech Starosta and Janusz Leciejewicz Comment
The structure of the original Li I complex with pyridazine-3,6-dicarboxylate and water ligands was reported to consist of molecular ribbons in which Li I ions are octahedrally coordinated by two fully deprotonated ligand molecules and two aqua O atoms are bridged by protons located in a centre of symmetry (Starosta & Leciejewicz, 2010). Removal of these protons by adding a few drops of hydrazine resulted in a two-dimensional catenated polymeric structure (Starosta & Leciejewicz, 2011). When few more drops of hydrazine were added to the aqueous solution of the original complex, crystals of a new compound with a triclinic centrosymmetric structure were identified. This structure is built of two mono protonated hydrazine cations, a centrosymmetric dimeric anion and a neutral centrosymmetric tetrameric molecule. The dimeric anion consists of pairs of symmetry related: Li I ions, fully deprotonated ligand molecules and water O15 atom ( Fig. 1). The Li1 ion, coordinated by two N,O bonding groups donated by two ligands and the aqua O15 atom shows transition from a distorted trigonal-bipyramidal geometry [with an equatorial plane composed of O13, N11 ii and O15 atoms with r.m.s. of 0.0059 (1) Å, the Li1 ion is 0.0119 (1) Å out of this plane, N12 and O11 ii atoms are at axial positions; symmetry code: i -x, -y + 1, -z; ii -x, -y + 2, -z + 1] to a square-pyramidal geometry [where the aqua O15 is at the apical position]. The pyridazine ring is planar (r.m.s. of 0.0017 (1) Å); carboxylate groups C17/O11/O12 and C18/O13/O14 make with it dihedral angles of 1.4 (1)° and 1.7 (1)°, respectively. An anionic dimer constitutes the core of the other complex molecule. The coordination of the Li2 ion can be described by transition from trigonal-bipyramidal arrrangement [N22, O24 i and O25 atoms form the equatorial plane, r.m.s. 0.0044 (1) Å, the Li2 ion is 0.0088 (1) Å out of the equatorial plane; O21 and N21 i are at the apices] to the square-pyramdidal one [with the water O25 at the apical position]. The pyridazine ring is planar [r.m.s. 0.0009 (1) Å]; the carboxylate C27/O21/O22 and C28/O23/O24 groups make with it dihedral angles of 5.9 (1)° and 0.7 (1)°, respectively. In contrast to the anion complex, the carboxylato O21 atom in the neutral complex molecule acts as bidentate bridging to a Li(H 2 O) 3 group completing a tetranuclear molecule.
The coordination environment of the Li3 ion formed by the O1, O2, O3 and O21 atoms is distorted tetrahedral.
Pyridazine ring planes of the anion and the tetrameric molecule are inclined by an angle of 65.7 (1)° each to the other (Fig. 2). The observed Li-O and Li-N bond distances (Table 1) are close to those reported in two other Li I complexes with the title ligand (Starosta & Leciejewicz, 2010, 2011. Bond distances in the protonated hydrazine cations are almost the same as those reported in the structure of an hydrazine adduct of the pyridazine-3,6-dicarboxylate acid (Starosta & Leciejewicz, 2008). An extended hydrogen bond system in which coordinated water molecules act as donors, carboxylate O atoms are as acceptors contributes to the stability of the structure (

Experimental
Single crystals of the compound obtained earlier (Starosta & Leciejewicz, 2010) were dissolved in warm water. Few drops of hydrazine were then added and the solution was stirred for 3 h without heating. Left to crystallize at room temperature, single-crystal blocks of the title compound were found after three days. They were washed with cold ethanol and dried in air.

Refinement
Water and hydrazine H atoms were located in a difference map and refined isotropically, while H atoms attached to pyridazine-ring C atoms were located at calculated positions and treated as riding on the parent atoms with C-H = 0.93 Å and U iso (H) = 1.2U eq (C).

Figure 1
Structural units of the title compound with atom labelling scheme and 50% probability displacement ellipsoids.

Figure 2
Crystal packing of the title compound. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.