catena-Poly[[diaquabis{μ2-3,5-bis[(pyridin-4-yl)methylamino]benzoato}nickel] monohydrate]

In the title coordination polymer, {[Ni(C19H17N4O2)2(H2O)2]·H2O}n, the Ni2+ cation is located on an inversion center and coordinated by two carboxylate O atoms from two different 3,5-bis(pyridin-4-ylmethylamino)benzoate anions, two O atoms from two coordinated water molecules and two N atoms from two different 3,5-bis(pyridin-4-ylmethylamino)benzoate anions, displaying a slightly distorted NiN2O4 octahedral geometry. Each 3,5-bis(pyridin-4-ylmethylamino)benzoate anion acts as a μ2-bridge, linking different nickel ions into a chain along [010]. In the crystal, adjacent chains are further linked through N—H⋯O, O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds into a three-dimensional network. The coordinated water molecules and a disordered water molecule of hydration with 0.50 site occupancy play an important role in the formation of these hydrogen-bonding interactions.

In the title coordination polymer, {[Ni(C 19 H 17 N 4 O 2 ) 2 (H 2 O) 2 ]Á-H 2 O} n , the Ni 2+ cation is located on an inversion center and coordinated by two carboxylate O atoms from two different 3,5-bis(pyridin-4-ylmethylamino)benzoate anions, two O atoms from two coordinated water molecules and two N atoms from two different 3,5-bis(pyridin-4-ylmethylamino)benzoate anions, displaying a slightly distorted NiN 2 O 4 octahedral geometry. Each 3,5-bis(pyridin-4-ylmethylamino)benzoate anion acts as a 2 -bridge, linking different nickel ions into a chain along [010]. In the crystal, adjacent chains are further linked through N-HÁ Á ÁO, O-HÁ Á ÁO, O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds into a three-dimensional network. The coordinated water molecules and a disordered water molecule of hydration with 0.50 site occupancy play an important role in the formation of these hydrogen-bonding interactions.

Comment
During the past few decades, growing interests have been focused on the rapidly expanding field of crystal engineering of metal-organic frameworks (MOFs) due to their intriguing architectures as well as their tremendous potential applications in heterogeneous catalysis, ion-recognition, nonlinear optics and molecular adsorption (Bradshaw et al., 2005;Das & Bharadwaj, 2009;Hua et al., 2010). One of the effective strategies for construction of such polymers is to select suitable multidentate organic ligands as building blocks to link metal centers into infinite framework. Among popularly employed organic ligands, N-, or O-multidentate donor ligands are regarded as excellent candidates for building the blocks of desirable frameworks (Peng et al., 2010). Herein, we report the crystal structure of the title coordination polymer.
The asymmetric unit of the title complex consists of half of a nickel ion, a 3,5-bis(pyridin-4-ylmethylamino)benzoate anion, a coordinated water molecule, and one half water molecule of crystallization. The Ni ion is located on an inversion center and coordinated by two carboxylate O atoms from two different 3,5-bis(pyridin-4-ylmethylamino)benzoate anions, two O atoms from two coordinated water molecules, and two N atoms from two different 3,5-bis(pyridin-4ylmethylamino)benzoate anions, displaying a slightly distorted NiN 2 O 4 octahedral geometry. (Fig. 1). Each 3,5-bis(pyridin-4-ylmethylamino)benzoate anion acts as a µ 2 -bridge, linking different nickel ions to form a one-dimensional chain (Fig. 2).
In the crystal structure, adjacent chains are further linked through N-H···O, O-H···O, O-H···N and C-H···O hydrogen bonds into a three-dimensional network ( Fig. 3 and Table 1). Water molecules as donor or acceptor, including coordinated water molecules and lattice water molecule, play very important roles in the formation of these hydrogen bonding interactions.

Experimental
A mixture of nickel nitrate hexahydrate (29.1 mg, 0.1 mmol), 3,5-bis(pyridin-4-ylmethylamino)benzoic acid (33.4 mg, 0.1 mmol), and potassium hydroxide (5.61 mg, 0.1 mmol) in 8 ml H 2 O was sealed in a 16 ml Teflon-lined stainless steel container and heated to 373 K for 3 days. After cooling to the room temperature, green block crystals of the title complex were obtained.

Refinement
The hydrogen atoms bonded to C atoms were included in geometrically idealized positions and constrained to ride on their parent atoms, with C-H = 0.93-0.97 Å and U iso (H) = 1.2U eq (C). The hydrogen atoms bonded to N and O atoms were located from the difference Fourier maps and fixed at those positions with U iso (H) = 1.2U eq (N or O)].
supplementary materials sup-2 Figures Fig. 1. The coordination environment of nickel ion in the title complex with the ellipsoids drawn at the 30% probability level; hydrogen atoms have been omitted for clarity. Symmetry codes: