catena-Poly[[[tetrakis(4-methylpyridine-κN)copper(II)]-μ-sulfato-κ2 O:O′] 4.393-hydrate]

The structure of the title compound, {[Cu(SO4)(C6H7N)4]·4.393H2O}n, consists of Cu2+ ions surrounded in a square-planar fashion by 4-methylpyridine ligands, forming two crystallographically independent Cu{H3C(C5H4N)}4 units that are both located on crystallographic inversion centers. The Cu(4-methylpyridine)4 units are, in turn, connected with each other via bridging sulfate anions, leading to the formation of infinite [Cu{H3C(C5H4N)}4SO4]n zigzag chains along [001]. The completed coordination spheres of the Cu2+ ions are slightly distorted octahedral. The axial Cu—O bonds are elongated [average length = 2.42 (4) Å] compared to the equatorial Cu—N bonds [average length = 2.043 (2) Å]. The interstitial space between the chains is filled with uncoordinated water molecules that consolidate the structure through O—H⋯O hydrogen bonding. One of the five crystallographically independent solvent water molecules is partially occupied with an occupancy factor of 0.396 (4). Due to hydrogen bonding between symmetry-equivalent water molecules across inversion centers, several of the water H atoms are disordered in 1:1 ratios over mutually exclusive positions. The crystal under investigation was found to be non-merohedrally twinned in a 0.789 (1):0.211 (1) ratio by a 180° rotation around the reciprocal b axis.

The structure of the title compound, {[Cu(SO 4 )(C 6 H 7 N) 4 ]Á-4.393H 2 O} n , consists of Cu 2+ ions surrounded in a squareplanar fashion by 4-methylpyridine ligands, forming two crystallographically independent Cu{H 3 C(C 5 H 4 N)} 4 units that are both located on crystallographic inversion centers. The Cu(4-methylpyridine) 4 units are, in turn, connected with each other via bridging sulfate anions, leading to the formation of infinite [Cu{H 3 C(C 5 H 4 N)} 4 SO 4 ] n zigzag chains along [001]. The completed coordination spheres of the Cu 2+ ions are slightly distorted octahedral. The axial Cu-O bonds are elongated [average length = 2.42 (4) Å ] compared to the equatorial Cu-N bonds [average length = 2.043 (2) Å ]. The interstitial space between the chains is filled with uncoordinated water molecules that consolidate the structure through O-HÁ Á ÁO hydrogen bonding. One of the five crystallographically independent solvent water molecules is partially occupied with an occupancy factor of 0.396 (4). Due to hydrogen bonding between symmetry-equivalent water molecules across inversion centers, several of the water H atoms are disordered in 1:1 ratios over mutually exclusive positions. The crystal under investigation was found to be nonmerohedrally twinned in a 0.789 (1):0.211 (1) ratio by a 180 rotation around the reciprocal b axis.

Comment
In relation to our previous work on the structural chemistry of copper complexes (Shahid et al., 2008;2009) the title compound was prepared as the unintended product of the reaction of CuSO 4 . 5H 2 O with pyrolidine in acetone and 4-methylpyridine.
In the title structure ( Fig. 1), two crystallographically independent Cu 2+ ions are each located on an inversion center.  Parallel zigzag chains interdigitate as shown in Fig. 3 5H 2 O (0.30 g, 1.21 mmol) was added directly to a stirred solution of pyrolidine (0.5 g, 2.43 mmole) in 20 ml acetone.
The contents were stirred until complete dissolution of the salt to which about 30 ml of 4-methylpyridine was added and stirring was continued for another hour. Insoluble matter was removed by filtration and slow evaporation of the reaction mixture at room temperature gave the title compound as blue crystals after three weeks. Yield 60% (0.44 g), m.p. 373 K.

Refinement
The crystal under investigation was found to be non-merohedrally twinned by a 180° rotation around the reciprocal b-axis.
The orientation matrices for the two components were identified using the program CELL NOW ( Hydrogen atoms of the water molecules are partially disordered over mutually exclusive positions due to hydrogen bonding between symmetry equivalent water molecules across inversion centers. The H atoms in question are H6A and H8C, which are each located close to a crystallographic inversion center between pairs of symmetry equivalent atoms of O6 and O8. Both H atoms were thus refined as 50% occupied. For both water molecules O6 and O8 a second half occupied hydrogen atom is located in a position in which it hydrogen-bonds with the a neighboring water molecule of O8 and O6, respectively, thus again creating a pair of close by half occupied H atoms (H6C and H8B) in mutually exclusive positions.
The water solvate molecule of O9 is only partially occupied with a refined occupancy factor of 0.396 (4). Water hydrogen atoms were located in difference density Fourier maps, assigned occupancies as described above and their positions were refined with an O-H distance of 0.84 (1) Å and H···H distances of 1.30 (1) Å. In the final refinement cycles the water H atoms were set to ride on their carrying oxygen atoms. All other hydrogen atoms were immediately placed in calculated positions and all H atoms were refined with an isotropic displacement parameter U iso of 1.5 (methyl, hydroxyl) or 1.2 times (aromatic) that of U eq of the adjacent carbon or oxygen atom. Fig. 1. View of the molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level with atom labeling. Symmetry transformations used to generate equivalent atoms: (i) -x + 1,-y + 2,-z + 1; (ii) -x + 1,-y + 2,-z. For the water molecules all disordered H atoms are shown.