Poly[(μ₃-N-acetyl-L-histidinato-κ⁴N,O:O:O′)silver(I)]

The 1:2 molar ratio reaction of Ag₂O with N-acetyl-L-histidine (H₂achis) possessing the partial structure O=C—N—C—COOH, as well as imidazole units, afforded the light-stable and water-insoluble silver(I) title complex, [Ag(C₈H₁₀N₃O₃)]_n. This complex showed modest anti­microbial activity against selected bacteria and yeasts in a water-suspension system. X-ray crystallography revealed that the complex in the solid state forms a helical polymeric structure with an AgNO₃ core based on chelating Hachis⁻ (one carboxyl­ate O atom and one imidazole N atom) and two O atoms of the other two Hachis⁻ ligands that can be described as ∞{[Ag(Hachis)]}; this differs from the structure of the related silver(I) complex ∞{[Ag(Hhis)]} (L-histidine = H₂his) based on an AgN₂ core. Polymer chains of the title complex form three-dimensional inter­molecular hydrogen-bonding networks in the crystal structure.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.028
• wR factor = 0.064
• Data-to-parameter ratio = 12.8

checkCIF/PLATON results

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Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           25.35
           From the CIF: _reflns_number_total               1765
           Count of symmetry unique reflns         1063
           Completeness (_total/calc)            166.04%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured       702
           Fraction of Friedel pairs measured     0.660
           Are heavy atom types Z>Si present        yes
PLAT791_ALERT_1_G Confirm the Absolute Configuration of C6     = .          S

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   0 ALERT level C = Check and explain
   2 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Although Ag—N and Ag—O bonding complexes are potential bioinorganic materials such as antimicrobial activities (Gimeno et al., 2004.), light-sensitivity and poor solubility made them harder to be handled. Their crystallization was not easy. Silver imidazolate ∞{[Ag(im)]} (Him=imidazole), which showed strongly effective and a wide spectrum of antimicrobial activities but insoluble in most solvents (Nomiya et al., 1997.), was structurally characterized by powder X-ray diffraction (Masciocchi et al., 1995.) and its single crystals were prepared by hydrothermal method only in 2006 (Huang et al., 2006.). Recently, we noticed that reactions of Ag₂O with ligands having an OOC-C—X (X=N or O)—C=O moiety (such as 2-pyrrolidone-5-carboxylic acid, 5-oxo-2-tetrahydrofurancarboxylic acid, camphanic acid, and N-acetylglycine) afforded water-soluble and relatively light-stable (i.e. stable for a few hours to days at ambient temperature) Ag—O bonding complexes (Kasuga et al., 2006, and references therein). Herein, we report crystal structure of the (N-acetyl-L-histidinato)silver(I) (complex 1), whose ligand containing both the OOC-C—N—C=O moiety and imidazole ring (Fig. 1).

Reaction of N-acetyl-L-histidine (H₂achis) and Ag₂O at ambient temperature in water followed by the vapor-diffusion crystallization gave water-insoluble complex 1, which showed modest antimicrobial activities against E. coli, B. subtilis, P. aeruginosa, C. albicans and S. cerevisiae in water-suspension system.

The closely related complex, water-insoluble ∞{[Ag(Hhis)]} (H₂his=L-histidine), was a helical polymer consisting of a bent 2-coordinate silver(I) atom linking with the N_amino atom in one Hhis^- ligand and the Nπ atom of imidazole in a different Hhis^- ligand (Nomiya et al., 2000). In complex 1, Nπ atom also coordinated to Ag1, but N_amido atom did not. Instead, an oxygen atom (O2) of the carboxylate group and two oxygen atoms (O1ⁱ and O2ⁱⁱ) in different Hachis^- ligands coordinated to Ag1 (symmetry codes: (i) x + 1/2, -y + 1/2, -z + 2; (ii) x - 1/2, -y + 1/2, -z + 2). Therefore, the geometry around Ag1 was disordered 4-coordinate with AgN₁O₃ core (Fig. 2). The O2 in complex 1 was bridged by two silver(I) atoms (Ag1 and Ag1ⁱ). The six-membered ring formed by Ag1, O2ⁱⁱ, Ag1ⁱⁱ, O1, C1 and O2 was connected through silver(I) and O2 atoms to form ladder polymer chain of ∞{[Ag(Hachis)]} across the a axis. The distance and angle of N2—H2N···O1ⁱⁱⁱ indicated that hydrogen bond was formed between carboxylate and imidazole ring (symmetry code: (iii) -x + 1/2, -y, z - 1/2). For one pitch of the chain, four hydrogen bonds were observed as shown in dashed lines in Fig. 3.

In summary, ∞{[Ag(Hachis)]} is a ladder polymer, which forms three-dimensional network of hydrogen bonds between the ladders chains.

Related literature

For related literature, see: Gimeno & Laguna (2004); Huang et al. (2006); Kasuga et al. (2006); Masciocchi et al. (1995); Nomiya et al. (1997, 2000).

S2. Experimental

To a suspension of 116 mg (0.5 mmol) of Ag₂O in 20 ml of water was added 198 mg of H₂achis (0.5 mmol), followed by stirring for 1 h at room temperature. The black suspension changed to a clear, colorless solution and the solution was filtered through a folded filter paper (Whatman #5). Vapor diffusion was performed at room temperature by using the colorless filtrate as the inner solution and acetone as the external solvent. The colorless platelet crystals that were formed were collected on a membrane filter (JG 0.2 mm) and they were washed with acetone and ether (50 ml each) (0.1375 g of ∞{[Ag(Hachis)]} (complex 1), 90.4% yield).

Complex 1 is insoluble in H₂O and other organic solvents (MeOH, DMSO, acetone, EtOH, CH₃CN, CH₂Cl₂, CHCl₃, ether, and EtOAc). The color of the crystals did not change for at least two weeks. Complex 1 was characterized by EA, IR, and TG/DTA.

Prominent IR bands at 1800–400 cm^-1 (KBr) 1629vs, 1590vs, 1438w, 1399m, 1297w, 1105w, 1087w, 939w, 692 s, 663 s, 622 s, 552 s. No weight loss before decomposition (ca 226 °C). Anal. Calcd. for C₈H₁₀N₃O₃Ag. C 31.60, H 3.32, N 13.82. Found (Perkin Elmer PE2400 series II CHNS/O Analyzer) C 31.59, H 2.79, N 13.77.

Complex 1 showed modest activity against Gram-negative bacteria (minimum inhibitory concentration (=MIC) for E. coli and P. aeruginosa was both 250 µ g mL^-1), Gram-positive bacterium (MIC for B. subtilis was 500 µ g mL^-1) and yeasts (MIC for C. albicans and S. cerevisiae was both 125 µ g mL^-1).

S3. Refinement

The H atoms were placed at geometrically calculated positions and refined using riding and rotating models.

Computing details

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. Chemical structures of H2achis and the related ligands.
	Fig. 2. ORTEP-3 drawing (Farrugia, 1997) of complex 1 with 50% probability thermal ellipsoids.
	Fig. 3. Hydrogen bonding network of complex 1 viewed along the a axis. Symmetry codes: (i) x + 1/2, -y + 1/2, -z + 2, (ii) x - 1/2, -y + 1/2, -z + 2 and (iii) -x + 1/2, -y, z - 1/2.

Poly[(µ₃-N-acetyl-L-histidinato-κ⁴N,O:O:O')silver(I)]

Crystal data

[Ag(C8H10N3O3)]	F(000) = 600
Mr = 304.06	Dx = 2.090 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 86 reflections
a = 5.039 (3) Å	θ = 3.3–25.4°
b = 13.656 (8) Å	µ = 2.08 mm^−1
c = 14.043 (9) Å	T = 173 K
V = 966.4 (10) Å^3	Prism, colorless
Z = 4	0.32 × 0.29 × 0.01 mm

Data collection

Rigaku Mercury diffractometer	1765 independent reflections
Radiation source: fine-focus sealed tube	1715 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
Detector resolution: 14.892 pixels mm^-1	θmax = 25.4°, θmin = 3.3°
dtcell.ref scans	h = −6→6
Absorption correction: numerical (ABSCOR; Higashi, 1999)	k = −16→15
Tmin = 0.556, Tmax = 0.980	l = −16→15
9224 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.028	H-atom parameters not refined
wR(F^2) = 0.064	w = 1/[σ^2(Fo^2) + (0.0275P)^2 + 0.9828P] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max = 0.001
1765 reflections	Δρmax = 0.80 e Å^−3
138 parameters	Δρmin = −0.65 e Å^−3
0 restraints	Absolute structure: Flack (1983), with 0000 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.03 (5)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
C1	0.5974 (8)	0.1081 (3)	1.0856 (3)	0.0156 (9)
C2	0.3599 (10)	0.0856 (3)	0.7963 (3)	0.0246 (10)
H2	0.2450	0.1308	0.7656	0.030*
C3	0.6681 (9)	0.0232 (3)	0.8858 (3)	0.0186 (8)
C4	0.5516 (9)	−0.0520 (3)	0.8383 (3)	0.0230 (10)
H4	0.5955	−0.1194	0.8433	0.028*
C5	0.8765 (8)	0.0227 (3)	0.9608 (3)	0.0194 (9)
H5A	0.9866	0.0823	0.9538	0.023*
H5B	0.9933	−0.0347	0.9506	0.023*
C6	0.7665 (8)	0.0188 (3)	1.0637 (3)	0.0171 (9)
H6	0.9228	0.0211	1.1076	0.021*
C7	0.7649 (8)	−0.1554 (3)	1.1000 (3)	0.0237 (9)
C8	0.6020 (9)	−0.2448 (3)	1.1236 (3)	0.0294 (10)
H8A	0.4149	−0.2318	1.1094	0.044*
H8B	0.6215	−0.2603	1.1914	0.044*
H8C	0.6638	−0.3003	1.0853	0.044*
Ag1	0.66858 (6)	0.25670 (2)	0.89688 (2)	0.02431 (11)
N1	0.6274 (7)	−0.0723 (2)	1.0830 (2)	0.0186 (7)
H1N	0.4528	−0.0734	1.0835	0.022*
N2	0.3583 (8)	−0.0117 (3)	0.7818 (3)	0.0264 (8)
H2N	0.2522	−0.0438	0.7430	0.032*
N3	0.5423 (8)	0.1095 (3)	0.8590 (3)	0.0217 (8)
O1	0.3590 (6)	0.09409 (18)	1.1138 (2)	0.0205 (6)
O2	0.6944 (6)	0.1908 (2)	1.0741 (2)	0.0239 (7)
O3	1.0065 (6)	−0.1576 (2)	1.0979 (2)	0.0282 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.018 (2)	0.0183 (19)	0.011 (2)	0.0011 (16)	−0.0047 (16)	0.0001 (15)
C2	0.026 (2)	0.027 (2)	0.021 (2)	−0.006 (2)	−0.006 (2)	0.0099 (18)
C3	0.021 (2)	0.0176 (18)	0.017 (2)	0.0004 (17)	0.001 (2)	−0.0021 (16)
C4	0.027 (3)	0.020 (2)	0.022 (2)	−0.0045 (19)	0.0021 (18)	−0.0050 (17)
C5	0.015 (2)	0.019 (2)	0.024 (2)	0.0019 (17)	0.0018 (18)	−0.0012 (17)
C6	0.019 (2)	0.016 (2)	0.017 (2)	0.0004 (16)	0.0004 (16)	0.0004 (16)
C7	0.026 (2)	0.020 (2)	0.025 (2)	0.0069 (16)	−0.001 (2)	−0.002 (2)
C8	0.031 (2)	0.016 (2)	0.041 (3)	0.0042 (19)	−0.0045 (18)	0.002 (2)
Ag1	0.02532 (17)	0.01610 (16)	0.03151 (18)	−0.00361 (14)	−0.00139 (14)	0.00172 (14)
N1	0.0122 (17)	0.0166 (16)	0.027 (2)	0.0041 (14)	−0.0002 (15)	0.0010 (14)
N2	0.026 (2)	0.0271 (19)	0.026 (2)	−0.0082 (19)	−0.0051 (18)	−0.0035 (15)
N3	0.024 (2)	0.0180 (18)	0.0229 (18)	−0.0042 (16)	−0.0052 (16)	0.0009 (15)
O1	0.0163 (15)	0.0152 (13)	0.0301 (17)	0.0006 (11)	0.0041 (15)	0.0047 (12)
O2	0.0212 (15)	0.0167 (14)	0.0337 (17)	−0.0049 (13)	0.0023 (14)	0.0009 (12)
O3	0.0208 (16)	0.0263 (16)	0.0376 (18)	0.0061 (13)	−0.0010 (17)	−0.0043 (16)

Geometric parameters (Å, º)

C1—O2	1.241 (5)	C6—N1	1.454 (5)
C1—O1	1.279 (5)	C6—H6	1.0000
C1—C6	1.519 (6)	C7—O3	1.218 (5)
C2—N3	1.313 (6)	C7—N1	1.350 (5)
C2—N2	1.345 (5)	C7—C8	1.508 (6)
C2—H2	0.9500	C8—H8A	0.9800
C3—C4	1.358 (6)	C8—H8B	0.9800
C3—N3	1.390 (5)	C8—H8C	0.9800
C3—C5	1.488 (6)	Ag1—N3	2.174 (4)
C4—N2	1.371 (6)	Ag1—O1^i	2.257 (3)
C4—H4	0.9500	Ag1—O2^ii	2.528 (3)
C5—C6	1.548 (6)	Ag1—O2	2.649 (3)
C5—H5A	0.9900	N1—H1N	0.8800
C5—H5B	0.9900	N2—H2N	0.8800
O2—C1—O1	123.1 (4)	N1—C7—C8	116.1 (4)
O2—C1—C6	118.9 (4)	C7—C8—H8A	109.5
O1—C1—C6	118.0 (3)	C7—C8—H8B	109.5
N3—C2—N2	110.6 (4)	H8A—C8—H8B	109.5
N3—C2—H2	124.7	C7—C8—H8C	109.5
N2—C2—H2	124.7	H8A—C8—H8C	109.5
C4—C3—N3	108.1 (4)	H8B—C8—H8C	109.5
C4—C3—C5	130.5 (4)	N3—Ag1—O1^i	160.48 (13)
N3—C3—C5	121.2 (3)	N3—Ag1—O2^ii	91.43 (13)
C3—C4—N2	106.8 (4)	O1^i—Ag1—O2^ii	99.02 (10)
C3—C4—H4	126.6	N3—Ag1—O2	86.01 (12)
N2—C4—H4	126.6	O1^i—Ag1—O2	110.37 (10)
C3—C5—C6	114.1 (3)	O2^ii—Ag1—O2	89.49 (9)
C3—C5—H5A	108.7	C7—N1—C6	120.3 (4)
C6—C5—H5A	108.7	C7—N1—H1N	119.9
C3—C5—H5B	108.7	C6—N1—H1N	119.9
C6—C5—H5B	108.7	C2—N2—C4	107.7 (4)
H5A—C5—H5B	107.6	C2—N2—H2N	126.2
N1—C6—C1	112.3 (3)	C4—N2—H2N	126.2
N1—C6—C5	112.0 (3)	C2—N3—C3	106.8 (3)
C1—C6—C5	111.2 (3)	C2—N3—Ag1	126.8 (3)
N1—C6—H6	107.0	C3—N3—Ag1	125.7 (3)
C1—C6—H6	107.0	C1—O1—Ag1^ii	104.1 (2)
C5—C6—H6	107.0	C1—O2—Ag1^i	127.5 (3)
O3—C7—N1	122.0 (4)	C1—O2—Ag1	114.4 (2)
O3—C7—C8	121.9 (4)	Ag1^i—O2—Ag1	95.84 (10)

Symmetry codes: (i) x+1/2, −y+1/2, −z+2; (ii) x−1/2, −y+1/2, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2N···O1^iii	0.88	2.02	2.834 (5)	153

Symmetry code: (iii) −x+1/2, −y, z−1/2.