[μ-2,3,5,6-Tetra­kis(2-pyrid­yl)pyrazine-κ6 N 6,N 1,N 2:N 3,N 4,N 5]bis­[diaqua(dihydrogen m-phenylene­diphospho­nato-κO)nickel(II)] dihydrate

Paul DeBurgomaster; Jon Zubieta

doi:10.1107/S1600536810041279

. 2010 Oct 23;66(Pt 11):m1424–m1425. doi: 10.1107/S1600536810041279

[μ-2,3,5,6-Tetrakis(2-pyridyl)pyrazine-κ⁶ N ⁶,N ¹,N ²:N ³,N ⁴,N ⁵]bis[diaqua(dihydrogen m-phenylenediphosphonato-κO)nickel(II)] dihydrate

Paul DeBurgomaster ^a, Jon Zubieta ^a,^*

PMCID: PMC3009311 PMID: 21588851

Abstract

The title compound [Ni₂(C₆H₆O₆P₂)₂(C₂₄H₁₆N₆)(H₂O)₄]·2H₂O or [Ni₂(tpyprz)(1,3-HO₃PC₆H₄PO₃H)₂(H₂O)₄]·2H₂O [tpyprz = tetrakis(2-pyridyl)pyrazine, C₂₄H₁₆N₆] is a binuclear complex with a crystallographic inversion center located at the center of the pyrazine ring. The equivalent nickel(II) sites exhibit a distorted {NiO₃N₃} octahedral coordination, with the three nitrogen donors of each terminus of the tpyprz ligand in a meridional orientation. An aqua ligand occupies the position trans to the pyrazine nitrogen donor, while the second aqua ligand is trans to the oxygen donor of the dihydrogen-1,3-phenyldiphosphonate ligand. The Ni—O and Ni—N bond lengths fall in the range 2.011 (3) to 2.089 (3) Å. The protonation sites on the organophosphonate ligand are evident in the significantly longer P—O bonds compared to the unprotonated sites. In the crystal structure, the complex molecules and the solvent water molecules are linked into a three-dimensional hydrogen-bonded framework through O—H⋯O interactions between the aqua ligands, the protonated organophosphonate oxygen atoms and the water molecules of crystallization. Intramolecular π-stacking between the phenyl group of the phosphonate ligand and a pyridyl group of the tpyprz ligand, at a distance of 3.244 (5) Å between ring centroids, is also observed.

Related literature

For general background to metal-organophosphonates, see: Alberti et al. (1978 ▶); Clearfield (1998 ▶); Finn et al. (2003 ▶); Vermeulen (1997 ▶). For nickel–organophosphonates, see: Bauer et al. (2008 ▶). For nickel–tetrakis(2-pyridyl)pyrazine complexes, see: Burkholder et al. (2003 ▶); Burkholder & Zubieta (2004 ▶, 2005 ▶). For the use of tetrakis(2-pyridyl)pyrazine as a component in the construction of metal–organophosphonate materials, see: Armatas et al. (2008 ▶).

Experimental

Crystal data

[Ni₂(C₆H₆O₆P₂)₂(C₂₄H₁₆N₆)(H₂O)₄]·2H₂O
M _r = 1086.04
Triclinic,
a = 7.9702 (6) Å
b = 10.0785 (8) Å
c = 14.0960 (12) Å
α = 85.386 (2)°
β = 81.707 (1)°
γ = 69.364 (1)°
V = 1048.03 (15) Å³
Z = 1
Mo Kα radiation
μ = 1.14 mm⁻¹
T = 298 K
0.20 × 0.14 × 0.11 mm

Data collection

Bruker APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 1998 ▶) T _min = 0.804, T _max = 0.885
10484 measured reflections
5044 independent reflections
4821 reflections with I > 2σ(I)
R _int = 0.023

Refinement

R[F ² > 2σ(F ²)] = 0.066
wR(F ²) = 0.133
S = 1.32
5044 reflections
304 parameters
H-atom parameters constrained
Δρ_max = 0.91 e Å⁻³
Δρ_min = −0.80 e Å⁻³

Data collection: SMART (Bruker, 1998 ▶); cell refinement: SAINT (Bruker, 1998 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg & Putz, 1999 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

Crystal structure: contains datablocks I, New_Global_Publ_Block. DOI: 10.1107/S1600536810041279/pk2273sup1.cif

e-66-m1424-sup1.cif^{(24.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810041279/pk2273Isup2.hkl

e-66-m1424-Isup2.hkl^{(247KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2′⋯O3ⁱ	0.82	1.91	2.536 (4)	132
O5—H5′⋯O6ⁱⁱ	0.82	1.82	2.606 (4)	162
O40—H40A⋯O3ⁱⁱⁱ	0.84	1.95	2.784 (4)	170
O40—H40B⋯O4^iv	0.88	1.83	2.711 (4)	175
O41—H41B⋯O6^iv	0.83	1.82	2.625 (4)	163
O90—H90B⋯O4^v	0.92	1.84	2.747 (4)	166
O41—H41A⋯O90	0.88	1.83	2.643 (4)	151
O90—H90A⋯O1	0.92	1.92	2.780 (4)	154

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) .

Acknowledgments

This work was supported by a grant from the National Science Foundation, CHE-0907787.

supplementary crystallographic information

Comment

The chemistry of metal-organophosphonates has witnessed dramatic growth (Clearfield, 1998; Finn et al., 2003; Vermeulen, 1997) since the first reports in the 1970s of the layered metal-organophosphonates (Alberti et al., 1978). In our investigations of metal oxide materials, we have used organodiphosphonates as tethers between metal or metal oxide nodes (Armatas et al., 2008). Structural expansion and diversity could be accomplished by introducing additional components, most commonly a M(II)-organonitrogen ligand complex. A particularly useful nitrogen donor ligand for structural manipulation is the dipodal tetrakis(2-pyridyl)pyrazine (tpyprz) (Armatas et al., 2008; Bauer et al., 2008). While Cu(II) has generally served as the secondary metal in the M(II)-organonitrogen ligand complex, Ni(II)-containing subunits have also been exploited as subunits (Burkholder et al., 2003; Burkholder and Zubieta, 2004; Burkholder and Zubieta, 2005). While the secondary metal M(II) bonds to the tpyprz ligand and aqua ligands and/or cluster oxide groups in such materials, the title complex was prepared in the absence of metal oxide, affording the binuclear [Ni₂(tpyprz)(1,3-HO₃PC₆H₄PO₃H) (H₂O)₄]dihydrate.

As shown in Fig. 1, the structure of the title compound is binuclear, with a crystallographic inversion center at the mid-point of the pyrazine group. The distorted {NiO₃N₃} octahedral geometry at the Ni(II) site is defined by the nitrogen donors of the tpyprz ligand in a meridional orientation, two aqua ligands and an oxygen donor from the pendant monodentate 1,3-phenyldiphosphonate ligand. One aqua ligand is trans to the pyrazine nitrogen donor of the tpyprz ligand, while the second occupies a position trans to the phosphonate oxygen donor. The shortest Ni—N distance is to the pyrazine nitrogen, Ni—N2 of 2.011 (3) Å, while the Ni-pyridyl bond distances are 2.076 (3) Å and 2.089 (3) Å. The Ni—O(aqua) distances are 2.015 (3) Å and 2.081 (3) Å, while the Ni—O(phosphonate) distance is 2.082 (3) Å.

Charge compensation considerations require that the phenyldiphosphonate ligand be in the doubly deprotonated state [H₂(O₃PC₆H₄PO₃)]^2-. The protonation sites were revealed in the difference Fourier map by peaks adjacent to O2 and O5 at distances consistent with bound hydrogen. The P—O bond lengths support these protonation sites with P—O2 and P—O5 of 1.567 (3) Å and 1.574 (3) Å, respectively, compared to an average P—O distance of 1.515 (4)Å for the remaining P—O distances.

The structure is stabilized by intermolecular hydrogen bonding between the aqua ligands, the P—OH groups and the waters of crystallization. The binuclear complexes and the water of crystallization are linked into a three-dimensional framework through this hydrogen bonding (Fig. 2). There is also intramolecular π-stacking between the phosphonate phenyl ring and a pyridyl group of the tpyprz ligand with a distance of 3.244 (5)Å between centroids. Intermolecular π-stacking between the phosphonate phenyl group and a pyridyl ring of a tpyprz ligand of an adjacent molecule exhibits a distance of 3.584 (5)Å between centroids.

Experimental

A solution of Ni(CH₃CO₂)₂•4H₂O (0.074 g, 0.297 mmol), tpyprz (0.085 g, 0.219 mmol) and 1,3-phenyldiphosphonic acid (0.071 g, 0.301 mmol) in water (10 ml) was placed in a Parr acid digestion bomb and heated to 170°C for 48 h. Yellow blocks of the compound suitable for x-ray diffraction studies were isolated in 65% yield. Anal Calcd. for C₃₆H₄₀N₆Ni₂O₁₈P₄: C, 39.8; H, 3.68; N. 7.73. Found: C, 39.6; H, 3.75; N, 7.65.