Poly[[{μ3-2-[4-(2-hy­droxy­eth­yl)piperazin-1-yl]ethane­sulfonato}­silver(I)] trihydrate]

Stephanie M Bilinovich; Matthew J Panzner; Wiley J Youngs; Thomas C Leeper

doi:10.1107/S160053681103008X

. 2011 Aug 2;67(Pt 9):m1178–m1179. doi: 10.1107/S160053681103008X

Poly[[{μ₃-2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonato}silver(I)] trihydrate]

Stephanie M Bilinovich ^a, Matthew J Panzner ^a, Wiley J Youngs ^a, Thomas C Leeper ^a,^*

PMCID: PMC3200587 PMID: 22058835

Abstract

Ethanesulfonic acid-based buffers like 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid (HEPES) are commonly used in biological experiments because of their ability to act as non-coordinating ligands towards metal ions. However, recent work has shown that some of these buffers may in fact coordinate metal ions. The title complex, {[Ag(C₈H₁₇N₂O₄S)]·3H₂O}_n, is a metal–organic framework formed from HEPES and a silver(I) ion. In this polymeric complex, each Ag atom is primarily coordinated by two N atoms in a distorted linear geometry. Weaker secondary bonding interactions from the hydroxy and sulfate O atoms of HEPES complete a distorted seesaw geometry. The crystal structure is stabilized by O—H⋯O hydrogen-bonding interactions.

Related literature

For other compounds with silver bound to ethanesulfonic acid derivatives that are used as buffers, see: Jiang, Liu et al. (2008 ▶), where HEPES is used, and Jiang, Ma et al. (2008 ▶), where MES is used. For background on metal coordination to buffer compounds like HEPES, see: Soares & Conde (2000 ▶); Sokolowska & Bal (2005 ▶). For copper complexes of HEPES interfering with protein assays, see: Gregory & Sajdera (1970 ▶); Lleu & Rebel (1991 ▶); Kaushal & Barnes (1986 ▶). For general information on HEPES and related buffers, see: Good et al. (1966 ▶).

Experimental

Crystal data

[Ag(C₈H₁₇N₂O₄S)]·3H₂O
M _r = 399.21
Monoclinic,
a = 11.2811 (19) Å
b = 10.0973 (17) Å
c = 12.875 (2) Å
β = 90.910 (3)°
V = 1466.4 (4) Å³
Z = 4
Mo Kα radiation
μ = 1.55 mm⁻¹
T = 100 K
0.25 × 0.10 × 0.07 mm

Data collection

Bruker APEXI CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2001 ▶) T _min = 0.699, T _max = 0.900
11308 measured reflections
2946 independent reflections
2446 reflections with I > 2σ(I)
R _int = 0.050

Refinement

R[F ² > 2σ(F ²)] = 0.036
wR(F ²) = 0.090
S = 1.09
2946 reflections
190 parameters
9 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 1.58 e Å⁻³
Δρ_min = −0.73 e Å⁻³

Data collection: SMART (Bruker, 2007 ▶); cell refinement: SAINT (Bruker, 2007 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S160053681103008X/mw2014sup1.cif

e-67-m1178-sup1.cif^{(19.2KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S160053681103008X/mw2014Isup2.hkl

e-67-m1178-Isup2.hkl^{(144.6KB, hkl)}

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

Table 1. Selected geometric parameters (Å, °).

Ag1—N1	2.266 (3)
Ag1—N2	2.280 (3)
Ag1—O2ⁱ	2.666 (2)
Ag1—O4	2.581 (2)

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N1—Ag1—N2	167.73 (11)
N1—Ag1—O2ⁱ	92.58 (8)
N1—Ag1—O4	115.41 (8)
N2ⁱⁱ—Ag1—O2ⁱ	94.22 (9)
N2—Ag1—O4	75.16 (9)
O2ⁱ—Ag1—O4ⁱⁱ	87.18 (7)

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Symmetry codes: (i) Inline graphic ; (ii) .

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O7—H7C⋯O5ⁱⁱⁱ	0.85 (2)	1.96 (2)	2.777 (4)	161 (4)
O6—H6A⋯O3^iv	0.84 (2)	1.88 (2)	2.706 (4)	166 (4)
O6—H6C⋯O1^v	0.86 (2)	2.02 (2)	2.868 (4)	169 (4)
O5—H5C⋯O7^vi	0.85 (2)	2.01 (2)	2.834 (4)	163 (5)
O5—H5D⋯O6^vii	0.86 (2)	2.02 (2)	2.864 (4)	171 (4)
O4—H4⋯O6^vii	0.84	1.89	2.726 (4)	178

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Symmetry codes: (iii) Inline graphic ; (iv) ; (v) ; (vi) ; (vii) .

Acknowledgments

We thank the National Science Foundation (USA) for support for the X-ray facilities at The Univeristy of Akron under the grant CHE-0116041.

supplementary crystallographic information

Comment

HEPES is one of twelve buffers introduced by Good and coworkers as ideal for biological studies based on their physiologically relevant buffering capacities. It was also initially stated that HEPES would not form complexes with metals (Good et al. 1966). However, several studies show that HEPES can form complexes with copper that account for interferences in protein quantification assays like Lowry and BCA (Gregory & Sajdera, 1970; Lleu & Rebel, 1991; Kaushal & Barnes, 1986). In addition, recent electrochemical and spectroscopic studies have shown that HEPES can act as a weak chelator with lead(II) and copper(II) (Soares & Conde, 2000; Sokolowska & Bal, 2005). Due to the recent interest in studying the role that silver(I)-containing compounds play as medicinal agents, the identification of buffers that prevent precipitation or complex formation with silver(I) ion are needed. Based on their established properties it was surmised that one of Good's non-coordinating buffers would be ideal for such investigations. However, as is evident from the title compound, HEPES does in fact form a stable complex with silver(I) ion making it a poor choice for use with systems containing silver ions. In the title compound, the Ag(I) ion is coordinated by one nitrogen atom and one hydroxyl oxygen atom of a HEPES molecule, one nitrogen atom of a second HEPES molecule, and one sulfate oxygen atom from a third HEPES molecule affording a distorted see-saw geometry about the metal center. Precedence for similar weak Ag···O interactions as well as the distorted see-saw geometry can be found in the literature and by a search of the Cambridge Crystallographic Database (Jiang, Liu et al. 2008). As is indicated by the bond distances, the nitrogen atoms form covalent bonds with the Ag(I) atom (2.266 (3) and 2.280 (3) Å) in a near linear fashion (N—Ag—N = 167.73 (11)°). The interactions of the hydroxyl and sulfate oxygen atoms with the Ag(I) ion are weaker (HO···Ag = 2.581 (2) and O₂SO···Ag = 2.666 (2) Å) but well within the sum of the Van der Waals radii for silver and oxygen (3.24 Å). The interaction of HEPES with Ag(I) affords a layered two-dimensional network perpendicular to the c axis, and these layers are further associated into a three-dimensional network through hydrogen bonding with the water molecules, directly via water O6, of the structure (Figure 2).

Experimental

A 250 ml 1 M stock solution of HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) buffer was prepared by dissolving 59.57 grams of HEPES in 200 ml of water and adjusting the pH to 7 with 5M NaOH before adjusting the volume to 250 ml. A 250 ml stock solution of 1M silver nitrate was prepared by dissolving 41.96 grams in 250 ml of water. To form the compound, 90 ml of the 1M silver nitrate stock solution was added to 10 ml of the 1M HEPES buffer stock solution to yield final concentrations of 0.9M silver nitrate and 0.1M HEPES in the solution. After one hour the experiment had gone to completion and long gray needle-like crystals were observed.