Bioactive SilverâOrganic Networks Assembled from 1,3,5-Triaza-7

Article pubs.acs.org/IC

Bioactive Silver−Organic Networks Assembled from 1,3,5-Triaza-7phosphaadamantane and Flexible Cyclohexanecarboxylate Blocks Sabina W. Jaros,† M. Fátima C. Guedes da Silva,*,† Jarosław Król,‡ M. Conceiçaõ Oliveira,† Piotr Smoleński,*,§ Armando J. L. Pombeiro,† and Alexander M. Kirillov*,† †

Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049−001 Lisbon, Portugal ‡ Department of Pathology, Wrocław University of Environmental and Life Sciences, ul. Norwida 31, 50-375 Wrocław, Poland § Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland S Supporting Information *

ABSTRACT: Three novel bioactive silver−organic networks, namely, the 2D polymer [Ag(μ3-PTA)(chc)]n·n(Hchc)·2nH2O (1), the 3D bioMOF [Ag2(μ3-PTA)2(μ2-chdc)]n·5nH2O (2), and the 2D polymer [Ag2(μ2-PTA)2(μ4-H2chtc)]n·6nH2O (3), were constructed from 1,3,5-triaza-7-phosphaadamantane (PTA) and various flexible cyclohexanecarboxylic acids as building blocks {cyclohexanecarboxylic (Hchc), 1,4-cyclohexanedicarboxylic (H2chdc), and 1,2,4,5-cyclohexanetetracarboxylic (H4chtc) acid, respectively}. The obtained products 1−3 were fully characterized by IR and NMR spectroscopy, ESI-MS(±) spectrometry, elemental and thermogravimetric (TGA) analyses, and single-crystal and powder X-ray diffraction. Their structural diversity originates from distinct coordination modes of cyclohexanecarboxylate moieties as well as from the presence of unconventional N,N,P-tridentate or N,P-bidentate PTA spacers. Topological classification of underlying metal−organic networks was performed, disclosing the hcb, 4,4L28, and a rare fsc-3,4-Pbcn-3 topology in 1, 2, and 3, respectively. Moreover, combination of aqueous solubility (S25°C ≈ 4− 6 mg mL−1), air stability, and appropriate coordination environments around silver centers favors a release of bioactive Ag+ ions by 1−3, which thus act as potent antibacterial and antifungal agents against Gram-positive (S. aureus) and Gram-negative (E. coli and P. aeruginosa) bacteria as well as a yeast (C. albicans). The best normalized minimum inhibitory concentrations (normalized MIC) of 10−18 (for bacterial strains) or 57 nmol mL−1 (for a yeast strain) were achieved. Detailed ESI-MS studies were performed, confirming the relative stability of 1−3 in solution and giving additional insight on the self-assembly formation of polycarboxylate Ag−PTA derivatives and their crystal growth process.

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networks.14−20,30−32 However, despite a high efficiency and a wide spectrum of potential antimicrobial applications, a number of bioactive silver(I) MOFs or CPs that meet the demand for water solubility and light stability is still very limited.30−33 Moreover, finding and developing a synthetic strategy for the generation of active silver-based antimicrobial materials in a controlled and regular way is a challenging task, which also requires comprehensive synthetic and structural studies. In this regard, the generation of new coordination networks by applying a water-soluble cage-like aminophosphine 1,3,5triaza-7-phospaadamantane (PTA) is a promising research direction that still remains little explored.34−40 The presence of four potential donor atoms (one P and three N) within the adamantane cage provides a good platform for creating various coordination environments around metal centers.34−47 Recent

INTRODUCTION

In recent years, considerable attention has been devoted to the design of new bioactive metal−organic frameworks (bioMOFs) or coordination polymers (CPs)1−8 due to a worldwide movement toward the development of new efficient antimicrobial, disinfecting, and sanitizing agents. A key advantage that makes this type of materials to be attractive biocidal agents lies in their molecular architectures and capability to slowly release metal ions, ligands, or guest molecules with a recognized antimicrobial potential.1−20 In particular, different silver(I) compounds constitute a family of potent antimicrobial ion-releasing materials.1−3,21−25 The soft character of silver21 not only provides a flexible coordination sphere but also favors slow release of Ag+ ions via coordination with the ligand through soft P- and N-donor or hard O-donor atoms.21−29 Thus, judicious selection of bioorganic components makes a mixed-ligand strategy a perfect tool for assembly of desired antimicrobial silver−organic © XXXX American Chemical Society

Received: September 29, 2015

A

DOI: 10.1021/acs.inorgchem.5b02235 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

combined with a carboxylic acid [cyclohexanecarboxylic (Hchc, 0.25 mmol, 32.0 mg) for 1, 1,4-cyclohexanedicarboxylic (H2chdc, 0.25 mmol, 43.1 mg) for 2, and 1,2,4,5-cyclohexanetetracarboxylic (H4chtc, 0.25 mmol, 65.1 mg) acid for 3] and PTA (0.2 mmol, 31.4 mg). The obtained pink mixture was stirred for 30 min in air at room temperature, resulting in the formation of a white precipitate. This was dissolved by dropwise addition of aqueous 1 M NH4OH solution (until pH = 8−9; ∼0.5 mL). The obtained cloudy solution was filtered off, and a pink-colored filtrate was left for crystallization. Colorless or light pink crystals of 1−3 (including those suitable for single-crystal Xray diffraction) were obtained by a slow evaporation method in air at room temperature in ∼50% yield (based on Ag2O). [Ag(μ3-PTA)(chc)]n·n(Hchc)·2nH2O (1). Compound 1 is soluble in H2O (S25°C ≈ 6 mg mL−1) and slightly soluble in MeOH. Anal. Calcd for C20H35AgN3O4P (1-2H2O, MW 520.4): C, 46.16; N, 8.07; H, 6.78. Found: C, 45.81; N, 7.51; H, 6.60. IR (KBr, cm−1): 3436 (s, br) ν(H2O), 2930 (vs) νas(CH), 2854 (s) νs(CH) + νas(COOH), 1707 (s), 1550 (vs) νas(COO), 1450 (m) and 1410 (s) νs(COO), 1294 (m), 1242 (m), 1204 (w), 1137 (w), 1099 (w), 1015 (s), 974 (s), 962 (m), 897 (m), 792 (m), 750 (m), 615 (m), 512 (w), 547 (w). TGA (1, N2, 10 °C/min): 135−200 °C (−2H2O, −Hchc; Δm 28.2% exptl, 29.3% calcd), >200 °C (decomp). 1H NMR (300 MHz, D2O): δ 4.61 and 4.50 (2d, 6H, JAB = 13.0 Hz, NCHAHBN, PTA), 4.24 (d, 6H, JPH = 1.86 Hz, PCH2N, PTA), 2.08−1.11 (m, 22H, chc and Hchc). 31P{1H} NMR (202.5 MHz, D2O): δ −78.2 (s, PTA). ESI-MS(±) (H2O/ MeOH), MS(+) m/z: 422.1 (100%) [Ag(PTA)2]+, 438.1 (7%) [Ag(PTA)(PTA-H)OH]+, 657.2 (40%) [Ag2(PTA)2(chc)]+, 892.2 (5%) [Ag3(PTA)2(chc)2]+, 1049.3 (10%) [Ag3(PTA)3(chc)2]+. MS(−) m/z: 127.1 (100%) [chc]−, 362.1 (10%) [Ag(chc)2]−, 597.2 (40%) [Ag2(chc)3]−, 832.3 (20%) [Ag3(chc)4], 1067.2 (15%) [Ag4(chc)5]−, 1302.2 (10%) [Ag5(chc)6]−. [Ag2(μ3-PTA)2(μ2-chdc)]n·5nH2O (2). Compound 2 is soluble in H2O (S25°C ≈ 5.5 mg mL−1). Anal. Calcd for C20H48Ag2N6O11P2 (2 + 2H2O, MW 826.3): C, 29.07; N, 10.17; H, 5.86. Found: C, 28.95; N, 9.98; H, 5.87. IR (KBr, cm−1): 3375 (vs, br) ν(H2O), 2930 (w) νas(CH), 2858 (w) νs(CH), 1641 (s, br) νas(COO), 1545 (vs) and 1400 (vs) νs(COO), 1293 (s), 1245 (s), 1109 (m), 1015 (vs), 975 (vs), 961(s), 898 (m), 791 (m), 750 (m), 720 (w), 675 (w), 457(w). TGA (2 + 2H2O, N2, 10 °C/min): 50−135 °C (−7H2O; Δm 15.3% exptl, 15.5% calcd), >190 °C (decomp). 1H NMR (300 MHz, D2O): δ 4.49 and 4.31 (2d, 12H, JAB = 13,0 Hz, NCHAHBN, PTA), 4.24 (d, 12H, JPH = 2.27 Hz, PCH2N, PTA), 2.07 (m, 2H, H1,4 chdc), 1.92− 1.24 (2m, 8H, H2,3,5,6 chdc). 31P{1H} NMR (202.5 MHz, D2O): δ −78.3 (s, PTA). ESI-MS(±) (H2O/MeOH), MS(+) m/z: 422.1 (100%) [Ag(PTA)2]+, 438.1 (8%) [Ag(PTA)(PTA-H)OH]+, 701.2 (30%) [Ag2(PTA)2(Hchdc)]+, 965.2 (10%) [Ag3(PTA)3(chdc)]+. MS(−) m/z: 171.1 (100%) [Hchdc]−, 278.1 (10%) [Ag(chdc)]−, 435.1 (7%) [Ag(chdc)(PTA)]−, 450.2 (15%) [Ag(Hchdc)2]−, 557.1 (20%) [Ag2(Hchdc)(chdc)]−, 664.1 (50%) [Ag3(chdc)2]−, 942.9 (40%) [Ag4(Hchdc)(chdc)2]−, 1049.9 (30%) [Ag5(chdc)3]−. [Ag2(μ2-PTA)2(μ4-H2chtc)]n·6nH2O (3). Compound 3 is soluble in H2O (S25°C ≈ 4 mg mL−1). Anal. Calcd for C22H46Ag2N6O14P2 (MW 896.3): C, 29.48; N, 9.37; H, 5.17. Found: C, 29.55; N, 9.34; H, 4.42. (KBr, cm−1): 3459 (s, br), 2942 (w), 2895 (w), 1715 (vs) and 1643(s) νas(COO), 1572 (s) and 1451 (s) νs(COO), 1401 (m), 1293 (m), 1238 (s), 1162 (w), 1107(w), 1037 (m), 1015 (m), 975 (m), 898 (w), 808 (w), 753 (w), 652 (w), 598 (w), 456 (w). TGA (3, N2, 10 °C/ min): 50−220 °C (−6H2O; Δm 11.6% exptl, 12.1% calcd), >230 °C (decomp). 1H NMR (300 MHz, D2O): δ 4.58 and 4.46 (2d, 12H, JAB = 13.8 Hz, NCHAHBN, PTA), 4.20 (s, 12H, PCH2N, PTA), 2.75 (m, 4H, H1,2,4,5 chtc), 2.36−2.03 (2m, 4H, H3,6 chtc). 31P{1H} NMR (202.5 MHz, D2O): δ −77.9 (s, PTA). ESI-MS(±) (H2O/MeOH), MS(+) m/z: 422.1 (100%) [Ag(PTA)2]+, 438.1 (5%) [Ag(PTA)(PTA-H)OH]+, 789.2 (20%) [Ag2(PTA)2(H3chtc)]+. MS(−) m/z: 259.1 (100%) [H3chtc]−, 366.1 (15%) [Ag(H2chtc)]−, 523.1 (5%) [Ag(H2chtc)(PTA)]−, 626.2 (30%) [Ag(H3chtc)2]−, 733.1 (20%) [Ag2(H3chtc)(H2chtc)]−, 839.9 (15%) [Ag3(H2chtc)2]−. X-ray Crystallography. The X-ray diffraction data of 1−3 were collected using a Bruker AXS-KAPPA APEX II diffractometer with graphite-monochromated Mo Kα radiation. Data were collected using

and limited examples of water-soluble silver−PTA derivatives demonstrate that PTA can be applied as a convenient N,Pbuilding block in the construction of bioMOFs or CPs.35−44 Moreover, identification of [Ag(PTA)2]+ ion as a key secondary building block in these compounds has already provided some predictability, thus allowing us to propose a template for the controlled and facile synthesis of silver−PTA networks by straightforward modulation of the ancillary ligand.35 Therefore, the coordination architectures of such compounds can be directly influenced by various polycarboxylate building blocks.35−40 Thus, the main objective of the present work was to extend our synthetic methodology35 and investigate the influence of various cyclohexanecarboxylate building blocks on the formation, structural features, and antimicrobial efficiency of mixed-ligand Ag−PTA−cyclohexanecarboxylate coordination networks. For this purpose, as ancillary ligands we selected three cyclohexanecarboxylic acids with one, two, or four COOH groups, namely, cyclohexanecarboxylic (Hchc), 1,4cyclohexanedicarboxylic (H2chdc), and 1,2,4,5-cyclohexanetetracarboxylic (H4chtc) acid. Their adjustable skeletons and various conformation conversions may induce the structural modulation and give rise to novel metal−organic networks, varying in dimensionality, topology, coordination environments, and biological properties.48−55 Hence, we report herein the synthesis, full characterization, ESI-MS(±) study, structural and topological features, as well as antimicrobial activity of a new series of water-soluble silver−organic networks, [Ag(μ3PTA)(chc)]n·n(Hchc)·2nH2O (1), [Ag2(μ3-PTA)2(μ2-chdc)]n· 5nH2O (2), and [Ag2(μ2-PTA)2(μ4-H2chtc)]n·6nH2O (3).

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EXPERIMENTAL SECTION

Materials and Methods. All synthetic work was performed in air. 1,3,5-Triaza-7-phosphaadamantane (PTA) was prepared by a published method developed by Daigle and co-workers.56,57 All other reagents were purchased from commercial sources and used without further purification. The Microanalytical Service of the Instituto Superior Técnico carried out C, N, and H elemental analyses. Infrared (IR) spectra were measured in the 4000−400 cm−1 range on BIORAD FTS 3000MX or Bruker IFS 1113v instruments using KBr disks (abbreviations: vs, very strong; s, strong; m, medium; w, weak; br, broad; sh, shoulder). 1H and 31P{1H} NMR spectra were recorded on a Bruker 300 AMX spectrometer at ambient temperature. The 31P chemical shifts are relative to an external 85% H3PO4 aqueous solution. No good-quality 13C NMR spectra could be obtained due to modest solubility of compounds in D2O. Mass spectra were recorded on a LCQ Fleet ion trap mass spectrometer equipped with an ESI ion source (Thermo Scientific). The mass spectrometer was operated in the ESI positive/negative-ion modes, with the following optimized parameters: ion spray voltage, ±4.5 kV; capillary voltage, 16/−18 V; tube lens offset, −63/58 V; sheath gas (N2), 80 arbitrary units; auxiliary gas (N2), 5 arbitrary units; capillary temperature, 300 °C. Spectra typically correspond to the average of 20−35 scans and were recorded in the range between 100 and 1500 Da. Tandem mass spectra (collision-induced dissociation experiments) were obtained with an isolation window of 4−9 Da, a 20−30% relative collision energy, and an activation energy of 30 ms. Data acquisition and processing were performed using the Xcalibur software. The powder X-ray diffraction (PXRD) patterns were recorded with a Bruker D8 ADVANCE diffractometer (Bragg−Brentano geometry, Cu radiation). Thermal analyses were measured with a PerkinElmer STA 6000 instrument. The microcrystalline samples of 1−3 were heated at a rate of 10 °C min−1 in the temperature range of 30−650 °C under N2 atmosphere. General Synthetic Procedure for 1−3. A suspension of silver(I) oxide (0.1 mmol, 23 mg) in 7 mL of MeOH and 3 mL of H2O was B


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Inorganic Chemistry Table 1. Structure Refinement and Crystal Data for Compounds 1−3 compound empirical formula fw T (K) λ (Å) cryst system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρcalcd (g/cm3) α(Mo Kα) (mm−1) no. of collected reflns no. of independent reflns Rint final R1,a wR2b (I ≥ 2σ) GOF on F2 a

1 C20H39AgN3O6P 556.38 150(2) 0.71073 orthorhombic Pbca 11.2060(5) 11.6166(5) 37.2209(9) 90 90 90 4845.3(3) 8 1.525 0.938 25 421 4393 0.0741 0.0912, 0.1801 1.195

2 C10H17AgN3O2P 350.11 150(2) 0.71073 orthorhombic Pbcn 20.9473(8) 13.3532(4) 11.1554(4) 90 90 90 3120.32(19) 8 1.491 1.389 22 722 2853 0.0400 0.0520, 0.1241 1.195

3 C11H17AgN3O4P 394.12 150(2) 0.71069 monoclinic P121/m1 6.9853(9) 20.315(3) 13.5218(19) 90 96.782 90 1905.4(5) 4 1.374 1.154 31 705 3598 0.0356 0.0617, 0.1379 1.290

R1 = Σ||F0| − |Fc||/Σ|F0|. bwR2 = [Σ[w(F02 − Fc2)2]/Σ[w(F02)2]]1/2.

Scheme 1. Simplified Synthetic Procedure and Structural Formula for Compounds 1−3

omega scans of 0.5° per frame, and a full sphere of data was obtained. Cell parameters were retrieved using Bruker SMART software and refined using Bruker SAINT on all observed reflections. Absorption corrections were applied using SADABS.58 Structures were solved by direct methods using the SHELXS 97 program and refined with SHELXL 97.59 Calculations were performed with the WinGX System, Version 1.80.03.59 The hydrogen atoms were inserted at geometrically calculated positions and included in the refinement using the ridingmodel approximation; Uiso(H) were defined as 1.2Ueq of the parent carbon atoms for methylene residues. Crystal data for compounds 1−3 are summarized in Table 1. Antibacterial and Antifungal Activity Tests. The antimicrobial activity of 1−3 and AgNO3 and Ag(CH3COO) as references was evaluated by the method of serial dilutions using Antibiotic Broth ([g L−1 (H2O)]: dextrose 1.0; K2HPO4 3.68; beef extract 1.5; peptone 5.0;

KH2PO4 1.32; NaCl 3.5; yeast extract 1.5), according to Grove and Randall.61,62 The Staphylococcus aureus PCM 2054 (=ATCC 25923) and Escherichia coli PCM 2057 (=ATCC 25922) strains were obtained from the Polish Collection of Microorganisms of the Institute of Immunology and Experimental Therapy in Wroclaw, whereas Pseudomonas aeruginosa and Candida albicans were isolated from clinical samples in the Department of Veterinary Microbiology, University of Environmental and Life Sciences, Wrocław (Poland). The two latter strains were identified using conventional methods and the miniaturized identification systems API 20 NE and ID 32 C (bioMérieux), respectively, as well as by conventional methods. An overnight culture of each strain was diluted 1:1000 in Antibiotic Broth (AB). To a series of tubes containing appropriate amounts of AB, aqueous solutions of 1, 2, and 3 were added to obtain 0.9 mL. To each well, 0.1 mL of the microbial suspension was pipetted. The following C


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Inorganic Chemistry concentrations of tested compounds were obtained [μg mL−1]: 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, and 1. In addition, the antimicrobial activity of the “free” PTA was examined using the same method, showing that it is inactive at the maximum concentration. Broth sterility control and (for each strain) growth controls were included. The tubes were incubated at 37 °C for 24 h. The minimum inhibitory concentration (MIC, μg mL −1 ) was defined as the lowest concentration of the compound that fully inhibited the growth of bacteria or fungi. For the sake of comparison, the MIC values were normalized for the molar content of silver in 1−3 and are also given in a nmol mL−1 scale.

silver in solution. The 31P{1H} NMR spectra exhibit a broad singlet at δ −78.2 (1), −78.3 (2), and −77.9 (3), being consistent with the presence of silver−PTA motifs in solution. Nevertheless, partial dissociation of polymeric structures of 1− 3 with generation of mono- and oligomeric complex fragments upon dissociation in D2O cannot be excluded. ESI-MS(+) Studies. To obtain additional information about the crystallization process and speciation in solution, the ESIMS technique was employed to investigate the solution composition of compounds 1−3 directly from a postreaction mixture during the process of crystal growth and after the dissolution of the final microcrystalline products (for additional data and discussion, see Supporting Information). Several intermediate species that are formed in the course of the crystallization and dissolution processes have been trapped, characterized, and identified by the CID-MS (collision-inducted dissociation) method. The monitoring of these particular steps not only makes possible identification of the most common species in solution but also provides new insights and evidence for a proposed mechanism of the self-assembly of Ag(I)−PTA coordination networks. Moreover, the collective results of various ESI-MS experiments demonstrate that compounds 1−3 exist in solution only as aqua-soluble Ag−PTA-based monomers and oligomers of different chain size, thereby indicating that the polymeric form is maintained only in the solid form. Initial measurements involved the evaluation of samples prepared upon dissolution of microcrystalline compounds 1−3. The obtained ESI-MS data are in agreement with those previously identified for other silver−PTA derivatives.35 In all these cases, the [Ag(PTA)2]+ (m/z 421) and [Ag 2 (PTA) 2 (carboxylate)] + cationic products, namely, [Ag2(PTA)2(chc)]+ (m/z 657) for 1, [Ag2(PTA)2(Hchdc)]+ (m/z 701) for 2, and [Ag2(PTA)2(H3chtc)]+ (m/z 789) for 3, are the dominating species in the ESI-MS(+) spectra. Further ESI tandem mass spectrometric experiments of the group of peaks centered at m/z 657 (1), 701 (2), and 787 (3) indicate a similar fragmentation pathway with the formation of characteristic fragment ions. The loss of one PTA moiety (−157 Da) leads to [Ag2(PTA)(chc)]+ (m/z 500; for 1), [Ag2(PTA)(Hchdc)]+ (m/z 544; for 2), and [Ag2(PTA)(H3chtc)]+ (m/z 632; for 3) species. The elimination of the [Ag(Hacid)] moiety results in the most stable [Ag(PTA)2]+ species at m/z 421, whereas the conjugated loss of PTA plus [Ag(Hacid)] gives rise to the [Ag(PTA)]+ species in all samples of 1−3. The MS3 spectrum of [Ag(PTA)]+ displays fragment ions at m/z 235, 221, 194, and 177 due to successive cleavage of adamantane cage, as previously reported.35 The MS3 spectrum of [Ag(PTA)2]+ gives only a signal at m/z 264 assigned to [Ag(PTA)]+, which in its MS4 spectrum yields the characteristic fragmentation of adamantane cage. This provides information about the structure and stability of the most relevant species in solution, which are probably responsible for the self-assembly and high antimicrobial action of compounds 1−3. All experimental isotopic distributions of the suggested silver-containing species matched the theoretical isotopic patterns, which were simulated by ChemCal software.66 Therefore, the next step involved the analysis of postreaction mixtures of 1−3 by measuring the variation of solution composition with time required for the crystallization process (from 1 week to 1 month). The postreaction mixtures of 1−3 were prepared according to the synthetic approach presented in Scheme 1 and then subjected to ESI-MS analysis at 24 h

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RESULTS AND DISCUSSION Synthesis and Spectroscopic Characterization of 1−3. The nature of flexible dicarboxylate ligands is an important factor in the Ag−PTA system35 that affects the resulting structure and its dimensionality and topological features. Thus, we tested herein the influence of different cyclohexanecarboxylic acids on the generation of PTA-driven silver−organic networks. A stepwise synthetic procedure has been employed; it consists in the treatment of Ag2O with PTA as the main ligand and a carboxylic acid as the ancillary building block in a mixed-solvent system (MeOH/H2O), followed by further alkalization of the obtained mixture by an aqueous NH3 solution until pH = 8−9. Hence, the use of cyclohexanecarboxylic (Hchc), 1,4-cyclohexanedicarboxylic (H2chdc), or 1,2,4,5cyclohexanetetracarboxylic (H4chtc) acid has resulted in three new structurally distinct silver−PTA derivatives (Scheme 1), namely, 2D [Ag(μ3-PTA)(chc)]n·n(Hchc)·2nH2O (1), 3D [Ag2(μ3-PTA)2(μ2-chdc)]n·5nH2O (2), and 2D [Ag2(μ2PTA)2(μ4-H2chtc)]n·6nH2O (3) coordination polymers, respectively. All products have been isolated in good yields as airstable and water-soluble microcrystalline solids and characterized by IR and NMR spectroscopy, ESI-MS(±) spectrometry, elemental analysis, and single-crystal X-ray diffraction. The IR spectra of 1−3 show a set of characteristic asymmetric and symmetric CO stretching vibrations with the major bands at 1550 and 1410 cm−1 for 1, 1641 and 1400 cm−1 for 2, and 1572 and 1451 cm−1 for 3.63,64 A rather lowfrequency difference (Δν = 140 cm−1) calculated for 1 suggests a bidentate η1:η1 mode of the carboxylate group in the chc moiety.63 In 2, an estimated Δν value is above 200 cm−1, indicating a bis(monodentate) coordination mode of μ2-chdc ligand.62 In 3, a Δν parameter of 121 cm−1 can evidence a μ2η2:η0 monatomic bridging fashion of the μ4-H2chtc moiety. Strong carboxyl bands also occur at 1707 and 1717 cm−1, which can be attributed to uncoordinated COOH groups in 1 and 3, respectively. In addition, the presence of PTA blocks is supported by typical vibrations in the 1430−550 cm−1 region. The 1H NMR data of compounds 1−3 show characteristic features that confirm the presence of silver(I) coordination compounds in solution. The methylene protons of carboxylate ligands are observed in the δ 2.30−1.20 range and appear as separate doublets or multiplets. A slight shift of all signals suggests the coordination of chc, chdc, and H2chtc anions to the metal center. The presence of an inclusion Hchc molecule in 1 is evidenced by the appearance of additional signals in the δ 2.21−1.11 region. However, identification of Hchc/chc moieties is hampered by their overlapping signals. Other characteristic resonances are observed in the δ 4.61−4.24 region and correspond to the NCH2N and PCH2N methylene protons of PTA.65 Moreover, a downfield shift of these signals with respect to free PTA (δ 4.46−3.94) supports the binding of N,P-atoms and preservation of the coordination environment of D


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Inorganic Chemistry

Figure 1. ESI-MS(+) spectrum of a postreaction mixture of 2 (after 1 day) prepared according to the synthetic approach presented in Scheme 1.

Figure 2. Structural fragments of 1 demonstrating the (a) coordination environment of the Ag center (50% probability ellipsoids), (b) 2D Ag−PTA layer composed of repeating trinuclear [Ag3(PTA)3]3+ motifs, (c) side view of the 2D metal−organic layer (view along the a axis), and (d) topological representation of an underlying uninodal 3-connected 2D net with the hcb topology. Further details: (a−c) H atoms and (b, c) Hcdc moieties are omitted for clarity; view along the c (b, d) or a (c) axis; color scheme (a−c) Ag (magenta), N (blue), O (red), P (orange), and C (cyan); (d) centroids of 3-connected μ3-PTA nodes (blue), centroids of 1-connected cdc ligands (cyan), 3-connected Ag nodes (magenta). Selected distances (Angstroms) and angles (degrees): Ag1−O1 2.563(7), Ag1−O2 2.613(8), Ag1−N12 2.416(6), Ag1−N13 2.392(6); P1−Ag1−N13 113.95(15), P1−Ag1−N12 122.35(15), N13−Ag1−N12 105.3(2), P1−Ag1−O1 106.37(18), N13−Ag1−O1 89.4(2), N12−Ag1−O1 114.7(2), P1−Ag1−O2 90.2(2), O2−Ag1−N12 87.3(2), O2−Ag1−N13 137.9(2). Symmetry codes: (i) 0.5 + x, y, 0.5 − z; (ii) 1 − x, y, −z + 0.5.

intervals. In all cases, the obtained spectra were similar to those of parent samples 1−3. As a representative example, a brief discussion of the ESI-MS(+) results of 2 is presented herein. A more detailed analysis is given in the Supporting Information. ESI-MS monitoring of the initial step of the crystallization

process of 2 discloses several sets of isotopic clusters, displaying a characteristic distribution of silver-containing species corresponding to complex fragments expected in solution, as shown in Figure 1. Reported m/z ratios are those of the most abundant isotopologue ions. The most abundant species in all E


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Inorganic Chemistry

Figure 3. Structural fragments of 2 demonstrating the (a) coordination environment of the Ag center (50% probability ellipsoids), (b) 3D metal− organic freamwork, and (c) topological representation of an underlying binodal 3,4-connected 3D net with the fsc-3,4-Pbcn-3 topology (view along the c axis). Further details: (a, b) H atoms are omitted for clarity; color scheme (a,b) Ag (magenta), N (blue), O (red), P (orange), and C (cyan), (c) 4-connected Ag nodes (magenta), centroids of 3-connected μ3-PTA nodes (blue), centroids of 2-connected μ2-chdc linkers (cyan). Selected distances (Angstroms) and angles (degrees): Ag−P1 2.380(1), Ag1−N12 2.467(5), Ag1−N11 2.502(5), Ag1−O1 2.333(5); P1−Ag1−O1 124.31(13), O1−Ag1−N12 94.03(18), P1−Ag1−N12 120.07(12), O1−Ag1−N11 90.28(17), P1−Ag1−N11 119.58(13), N12−Ag1−N11 101.99(17). Symmetry codes: (i) 1.5 − x, 0.5 − y, 0.5 +z; (ii) x, −y, 0.5 + z; (iii) 1 − x, −y, 1 − z; (iv) 1 − x, y, 0.5 − z; (v) −0.5 + x, −0.5 + y, 0.5 − z.

measurements belong to [Ag(PTA)2]+ ions, the ESI-MS2 spectrum of which in a positive mode yields the characteristic fragmentation of adamantane cage.35 In order to fully characterize the complex ions identified in the solution of 2, all isotopic clusters were isolated for CID experiments. The MS2 fragmentation of precursor ions at m/z 701, 965, and 1087 occurs mainly by loss of a PTA molecule, leading to fragments at m/z 544, 808, and 930, respectively. It is surprising that further dissociation of peaks at m/z 808 and 930 proceeds only via a consecutive elimination of a PTA molecule, which indicates a lower stability of species with higher molecular mass and suggests the N-coordination of this aminophosphine ligand (see Figures S1a and S1b, Supporting Information). A direct monitoring of crystal growth during 1 week revealed the presence of all of the above-described species having a variable intensity (Figure S2, Supporting Information).

However, monitoring of postreaction mixtures does not allow one to detect the direct formation of the more abundant [Ag(PTA)2]+, [Ag2(PTA)2(Hchc)]+ (1), [Ag2(PTA)2(Hchdc)]+ (2), and [Ag2(PTA)2(H3chtc)]+ (3) species. Since the presence of this type of ion was always observed at the initial state of crystal growth without any significant relationship to other species in solution, we suppose that these ions are mostly involved in the initiation and termination of crystal growth and crystallization processes. Taking into consideration all of the obtained results from ESI-MS and CID experiments on 1−3 and previously investigated compounds,35,39 the following mechanism of crystal growth of silver−PTA-based coordination polymers can be proposed. In all cases, analysis of solution composition in the starting environment shows a shift of the solution equilibrium toward the formation of [Ag(PTA)2]+ ion. Thus, the first step involves most likely the formation of [Ag(PTA)2]+ F


Article

Inorganic Chemistry

Figure 4. Structural fragments of 3 demonstrating the (a) coordination environment of the Ag center (50% probability ellipsoids), front (b) and side (c) views of the 2D metal−organic layer composed of 1D Ag−PTA zigzag motifs, (d) topological representation of an underlying binodal 4,4connected 2D net with the 4,4L28 topology. Further details: (a−c) H atoms are omitted for clarity; view along the c (b, d) or b (c) axis; color scheme (a−c) Ag (magenta), N (blue), O (red), P (orange), and C (cyan); (d) centroids of 4-connected μ4-H2chtc nodes (cyan), centroids of 2connected μ2-PTA linkers (blue), 4-connected Ag nodes (magenta). Selected distances (Angstroms) and angles (degrees): Ag1−P1 2.344(5), Ag− N12 2.391(5), Ag1−O1 2.363(4), Ag1−O1 2.363(4); P1−Ag1−O1 132.3(1), O1−Ag1−N12 85.6(2), O1−Ag1−O1 78.2(1), P1−Ag1−N12 125.3(1), P1−Ag1−O1 129.0(1), N12−Ag1−O1 90.6(2). Symmetry codes: (i) −1 + x, y, z; (ii) −1 − x, −y, 2 − z; (iii) 1 + x, y, z; (iv) −x, −y, 2 − z; (v) 1 − x, −y, 2 − z; (vi) x, 0.5 − y, z; (vii) −x, 0.5 + y, 2 − z.

platform for the replacement of PTA and cyclohexanecarboxylate blocks by bioligands and easy penetration of active Ag+ ions into the microbial cells. This assumption is supported by the identification of a product ion at m/z 323 assigned to [Ag3]+ resulting from the consecutive fragmentation of complexes species with higher masses (e.g., MS4 spectrum of [Ag3(PTA)3(chdc)]+ at m/z 964, Supporting Information, Figure S1b). Structural and Topological Description. [Ag(μ3-PTA)(chc)]n·n(Hchc)·2nH2O (1). The crystal structure of 1 reveals a 2D metal−organic network (Figure 2) composed of Ag1 center, μ3-PTA block, chc(1−) terminal ligand, as well as one uncoordinated Hchc moiety and two crystallization water molecules per asymmetric unit. As shown in Figure 2a, each Ag1 center is five coordinated by two chc oxygen atoms [Ag1− O1 2.563(7) Å, Ag1−O2 2.613(8) Å], two nitrogens [Ag1− N12 2.416(6) Å, Ag1−N13 2.392(6) Å], and one phosphor atom [Ag1−P1 2.391(3) Å] from three individual μ3-PTA spacers. The coordination environment around the Ag1 atom manifests a {AgN2O2P} square pyramidal geometry; its distortion is evidenced by the value of Addison parameter τ5 = 0.26 (τ5 = 0 for an ideal square pyramid).67 The carboxylate

ion (Scheme S1, Supporting Information), which is considered as the most stable species in solution in which PTA adopts alternating N,P-coordination. The next step is most probably characterized by the formation of the [Ag2(PTA)2(chc)]+ (1), [Ag2(PTA)2(Hchdc)]+ (2), and [Ag2(PTA)2(H3chtc)]+ (3) species. The slow evaporation process shifts the solution equilibrium toward formation of the above fragments, favoring polymeric chain growth and activating preferential crystallization of a solid form of 1, 2, and 3. In summary, the present ESI-MS studies gave new insights about the self-assembly of silver−PTA coordination polymers and linked the solution speciation to their solid-state chemistry. Moreover, we believe that the same fragmentation pathway of cationic [Ag2(PTA)2(carboxylate)]+ species plays a crucial role in the antimicrobial efficiency of complexes 1−3. As presented above, their dissociation proceeds mainly by elimination of [Ag(chc)] (1), [Ag(chdc)] (2), and [Ag(chtc)] (3) to form [Ag(PTA)2]+ or loss of PTA to give [Ag2(PTA)(carboxylate)]+. The collective effect of different Ag−N, Ag−O, and Ag−P bonding [Ag(chtc)], [Ag2(PTA)(chc)]+ (1), [Ag2(PTA)(Hchdc)]+ (2), and [Ag2(PTA)(H3chtc)]+ (3) gives a moderate stability of cationic species, thus providing a good G


Article

Inorganic Chemistry Scheme 2. Coordination Modes of the chc, μ2-chdc, and μ4-H2chtc Blocks in 1−3

group of chc(1−) acts in a η1:η1 fashion and adopts a chair conformation. The μ3-PTA blocks behave as the 3-connecting spacers and display alternating N,N,P-coordination, thus bridging three Ag1 atoms into trinuclear [Ag3(PTA)3]3+ blocks with an Ag···Ag separation of 6.891 Å. These blocks are arranged into a honeycomb-like 2D layer (Figure 2b and 2c). For the sake of topological classification, we performed the analysis of this 2D metal−organic network in 1 by following the concept of the simplified underlying net.67−71 Such a net has been generated by reducing all ligands to their centroids, thus giving rise to a uninodal 3-connected 2D layer driven by topologically equivalent Ag and μ3-PTA nodes (Figure 2d). Its analysis68,69 reveals the hcb [Shubnikov hexagonal plane net/ (6,3)] topology and the point symbol of (63). [Ag2(μ3-PTA)2(μ2-chdc)]n·5nH2O (2). Compound 2 represents a 3D metal−organic framework structure (Figure 3). An asymmetric unit bears one Ag1 atom, one μ3-PTA block, onehalf a μ2-chdc(2−) moiety, and five crystallization water molecules (Figure 3a). Each four-coordinate Ag1 atom exhibits a geometry intermediate between a trigonal pyramid and a seesaw (τ4 = 0.82) involving a {AgN2OP} donor atom set. Three distinct μ3-PTA ligands provide two N and one P atoms [Ag−P1 2.380(1) Å, Ag1−N12 2.467(5) Å, Ag1−N11 2.502(5) Å], while the μ2-chdc linker brings the O atom [Ag1−O1 2.333 Å] to the coordination sphere of Ag1. As in compound 1, the μ3-PTA spacer in 2 adopts a N2P coordination, giving rise to [Ag3(PTA)3]3+ units that are also arranged into infinite 2D Ag−PTA layer motifs. However, in spite of the presence of similar Ag−PTA motifs in 1 and 2, introduction of a flexible dicarboxylate μ2-chdc linker results in the generation of a 3D layer-pillared framework in 2 (Figure 3b). Both carboxylate groups of μ2-chdc moieties act in a η1:η0 coordination mode, which influences spontaneous transformation of conformation to a more thermodynamically stable 1,4-trans-e,e form.49 To better understand the structure of this 3D MOF we performed its simplification68−71 and topological analysis. Thus, the obtained underlying net is assembled from the 4-connected Ag1 nodes, 3-connected μ3-PTA nodes, and 2connected μ2-chdc linkers (Figure 3c). From the topological viewpoint, this net can be considered as a binodal 3,4connected framework with the fsc-3,4-Pbcn-3 topology. It is described by the point symbol of (63)(65.8), wherein the (63) and (65.8) indices correspond to the μ3-PTA and Ag1 nodes, respectively. To our knowledge, the present topological type is very rare and has only been observed in one compound.71,72 [Ag2(μ2-PTA)2(μ4-H2chtc)]n·6nH2O (3). Compound 3 is a 2D coordination polymer (Figure 4) assembled from one Ag1 atom, one μ2-PTA block, and one-half a μ4-H2chtc(2−) moiety per asymmetric unit. As shown in Figure 4a, the fourcoordinate Ag1 atoms bind μ2-PTA and μ4-H2chtc ligands, providing the alternately coordinated phosphor [Ag1−P1 2.344(5) Å], nitrogen [Ag−N12 2.391(5) Å], and two oxygen [Ag1−O1 2.363(4) Å] atoms. The Ag1 center reveals a distorted {AgNO2P} seesaw geometry with the τ4 parameter of

0.70. In contrast to 1 and 2, PTA ligands in 3 exhibit a bidentate N,P-coordination mode and act only as μ2-linkers, giving rise to simple 1D Ag−PTA chain motifs with the Ag···Ag distance of 6.967 Å. Two of the four carboxylic groups of the μ4-H2chtc moiety link two neighboring Ag1 atoms and adopt a μ2-η2:η0 coordination fashion that forces spontaneous transformation of a chair conformation to an a,e,e,a form.50 This leads to infinite 1D [Ag2(μ4-H2chtc)2]n chain motifs with Ag··· Ag separations of 9.7101(15) and 10.7589(28) Å (Figure 4b). These motifs are further interlinked by the μ2-PTA moieties, generating a 2D double-layer network (Figure 4b and 4c). From the topological perspective, an underlying layer of 3 (Figure 4d) can be considered as a binodal 4,4-connected 2D net constructed from the 4-connected Ag1 and μ4-H2chtc nodes as well as the 2-connected μ2-PTA linkers. This net features the 4,4L28 topology68,69 described by the point symbol of (4.64.8)2(42.64), wherein the (4.64.8) and (42.64) notations are those of the Ag1 and μ4-H2chtc nodes, respectively. Influence of Cyclohexanecarboxylate Ligands on Structural Versatility. Minor changes in the organic ligand such as size, length, bulkiness, and flexibility can strongly influence the self-assembly process of a resulting product and lead to the alteration of its structural and topological characteristics as well as functional properties. As demonstrated in Scheme 1, the reaction of silver(I) oxide, PTA, and different cyclohexanecarboxylic acids yielded three distinct 2D or 3D metal−organic networks. Their structural and spectroscopic data demonstrate that cyclohexanecarboxylate ligands act as terminal (in 1) or μ2 (in 2) and μ4 (in 3) bridging ligands, with the carboxylate groups adopting η2:η0, η1:η0 and μ2-η2:η0 modes, respectively (Scheme 2). Thus, the combination of PTA with Hcdc, H2chdc, or H4chtc most likely forces their conformation transformation to give more thermodynamically stable forms. This changes the symmetry of cyclohexanecarboxylates and, as a consequence, generates various orientations of neighboring building units, thus leading to structural and topological differences in 1−3. In fact, the 2D network in 1 with the hcb topology is driven by the Ag and μ3-PTA nodes, whereas the cyclohexanecarboxylate moieties adopt a chair conformation. In 2, the 1,4-trans-e,e form of flexible μ2-chdc pillar favors formation of the 3D MOF with a very rare fsc-3,4Pbcn-3 topology, which is constructed from the 4-connected Ag and 3-connected μ3-PTA nodes and μ2-chdc linkers. In 3, the number and arrangement of COO/COOH groups of a,e,e,a-cyclohexane-1,2,4,5-tetracarboxylate have an influence on the formation of polymeric motifs. Since only two of four carboxylate groups are coordinated to silver centers, their steric arrangement may prevent further linkage to Ag centers and facilitate a bidentate N,P-coordination of μ2-PTA moieties, thus resulting in the 2D double layer with the 4,4L28 topology. Antibacterial and Antifungal Activity of 1−3. Although a variety of bioactive silver(I)-based compounds has been reported,1−20 Ag bioMOFs or CPs with recognized antimicroH


Article

Inorganic Chemistry

Table 2. Antimicrobial Activity of Compounds 1−3 Expressed in Minimal Inhibitory Concentration (MIC) and Its Normalized Values MIC [μg mL−1]

normalized MIC [nmol mL−1]a

entry

strains

1

2

3

AgNO3

Ag(CH3COO)b

1

2

3

AgNO3

Ag(CH3COO)b

1 2 3 4

S. aureus E. coli P. aeruginosa C. albicans

10 7 5 30

10 7 6 >50

7 8 20 40

9 9 20 40

9 4 4 90

19 14 10 57

24 16 15 >121

18 20 51 102

53 53 118 236

54 24 24 539

a

These values were normalized for the molar content of silver in each compound. bThese data could have been affected by a light-induced degradation of silver acetate that was observed during antimicrobial activity tests.

bial activity are still rather scant.1,6 Such compounds can be considered as an excellent reservoir of bioactive Ag+ ions, thus leading to promising antibacterial and antifungal action that relies upon progressive release of Ag+ ions into the biological fluids. In this regard, a certain level of solubility of silver(I) materials plays a crucial role in the antimicrobial activity. However, in many cases the complete insolubility of some MOFs or coordination polymers in aqueous medium significantly limits their potential use as antimicrobial agents. Thus, the combination of solubility in water, light stability, and high biological activity in Ag−PTA metal−organic networks makes them rather promising candidates for antimicrobial applications. As a continuation of our efforts35 on extending a number of water-soluble and bioactive silver derivatives of 1,3,5-triaza-7phosphaadamantane, we evaluated the antimicrobial activity of compounds 1−3 against standard strains of Gram-positive (Staphylococcus auereus) and Gram-negative (Escherchia coli, Pseudomonas aeruginosa) bacteria and a yeast (Candida albicans). The results of in vitro bioassays of 1−3 are summarized in Table 2 as the minimal inhibitory concentrations (MIC; μg mL−1) and their normalized values (MIC normalized for molar content of silver in each compound; nmol mL−1). Hence, compounds 1−3 are active against the tested bacteria and yeast, representing the best MIC values (μg mL−1) in the range of 7−10 (for S. aureus), 7−8 (for E. coli), 5−6 (for P. aeruginosa), and 30−40 (for C. albicans). Although these MIC values expressed in μg mL−1 scale (Table 2) are somewhat comparable to those of AgNO3 (standard topical antimicrobial agent) and Ag(CH3COO),73 the MIC parameters normalized for the molar content of silver and expressed in nmol mL−1 scale are lower for 1−3, thus allowing their efficient antimicrobial administration in substantially inferior concentrations. In fact, the best normalized MIC values obtained for the antimicrobial performance of 1−3 are ∼2−12 times inferior than those achieved when using AgNO3 (i.e., 18 vs 53 nmol mL−1 for S. aureus, 14 vs 53 nmol mL−1 for E. coli, 10 vs 118 nmol mL−1 for P. aeruginosa, and 57 vs 236 nmol mL−1 for C. albicans) or Ag(CH3COO) (i.e., 18 vs 54 nmol mL−1 for S. aureus, 14 vs 24 nmol mL−1 for E. coli, 10 vs 24 nmol mL−1 for P. aeruginosa, and 57 vs 539 nmol mL−1 for C. albicans). Interestingly, a considerable difference in antibacterial behavior of 1−3 was noticed against the P. aeruginosa strain. In this case, the normalized MIC for 3 (51 nmol mL−1) is significantly higher than the values (10−15 nmol mL−1) observed for 1 and 2. Taking into account the speciation of compounds in solution, this difference in antimicrobial efficiency and selectivity is probably due to the inferior solubility of 3 and structural differences. Despite the fact that the [Ag(PTA)2]+ ion was found to be the most abundant and stable species in solution, it cannot be considered as the most

active species due to a noticeable divergence in MIC values between 1−3 and previously tested compounds.35 We believe that cationic products, namely, [Ag2(PTA)2(chc)]+ (1), [Ag2(PTA)2(Hchdc)]+ (2), and [Ag2(PTA)2(H3chtc)]+ (3), are essentially responsible for the antimicrobial efficiency of compounds 1−3. In fact, the {AgN2O2P}, {AgN2OP}, and {AgNO2P} coordination environments in 1, 2, and 3, respectively, contain the same set of O-, N-, and P-donor atoms but different quantities of N- and O-donors. PTA and cyclohexanecarboxylate ligands not only occupy Ag(I) coordination spheres in different manners and participate in stabilization of silver atoms but may also play a role of effective carriers of bioactive Ag+ ions.35 Thus, the antimicrobial activity of 1−3 is a consequence of different metal−ligand bonding affinities (Ag−O, Ag−N, Ag−P) that enable easy ligand replacement by S-, N-, or O-donor biological moieties. Moreover, the position of the carboxylic group of many clinically used antibiotics can be essential for their bioactivity.74 We suspect that the different molecular structures of Hchc, H2chdc, and H4chtc ligands with the electron-withdrawing COOH substituents at the cyclohexane ring in different positions can change the bioavailability of [Ag2(PTA)2(chc)]+ (1), [Ag2(PTA)2(Hchdc)]+ (2), and [Ag2(PTA)2(H3chtc)]+ (3) moieties, thereby significantly affecting their antimicrobial behavior of 1−3 and selectivity against specific pathogens. However, this effect should be further investigated and compared with other carboxylate ligands in order to establish some structure−activity relationships.

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CONCLUSIONS In this study we synthesized three novel structurally distinct and bioacitive Ag−PTA 2D or 3D coordination networks derived from various cyclohexanecarboxylic acids bearing one (Hchc), two (H2chdc), or four (H4chtc) COOH groups. The analysis of 1−3 along with previously reported silver−PTA derivatives35,37 shows that their structural architectures are mostly directed by flexibility and conformation of ancillary carboxylate ligands as well as the relative position of COOH groups. This has resulted in an interesting structural and topological diversity of 1−3, which feature either 2D underlying layers with the hcb (in 1) and 4,4L28 (in 3) topology or a 3D metal−organic framework with the rare fsc3,4-Pbcn-3 topology (in 2). Apart from notable architectural diversity, compounds 1−3 also reveal significant structuredependent antimicrobial properties against common Grampositive and Gram-negative bacteria and a yeast, with the normalized minimum inhibitory concentration values being ∼3−12 times inferior than those of a standard antimicrobial agent AgNO3. Moreover, the ESI-MS study of solution behavior not only proved the stability of compounds 1−3 after dissolution but also allowed us to identify many I


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Inorganic Chemistry

(9) Huang, C.; Ji, F.; Liu, L.; Li, N.; Li, H.; Wu, J.; Hou, H.; Fan, Y. CrystEngComm 2014, 16, 2615−2625. (10) Singh, N.; Anantharaman, G. CrystEngComm 2014, 16, 7914− 7925. (11) Furukawa, S.; Reboul, J.; Diring, S.; Sumida, K.; Kitagawa, S. Chem. Soc. Rev. 2014, 43, 5700−5734. (12) Sun, D.; Xu, M.-Z.; Liu, S.-S.; Yuan, S.; Lu, H.-F.; Feng, S.-Y.; Sun, D.-F. Dalton Trans. 2013, 42, 12324−12333. (13) Stock, N.; Biswas, S. Chem. Rev. 2012, 112, 933−969. (14) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334−2375. (15) Batten, S. R.; Turner, D. R.; Neville, S. M. Coordination Polymers: Design, Analysis and Application; RSC: London, 2009. (16) Czaja, A.; Leung, E.; Trukhan, N.; Muller, U. In Metal−Organic Framework Application from Catalysis to Gas Storage; Farrusseng, D., Ed.; Wiley-VCH: Singapore, 2011. (17) Holman, R. T.; Pivovar, A. M.; Swift, J. A.; Ward, M. D. Acc. Chem. Res. 2001, 34, 107−118. (18) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127−1129. (19) Eddaoudi, E.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469−472. (20) Horcajada, P.; Gref, R.; Baati, T.; Allan, P. K.; Maurin, G.; Couvreur, P.; Férey, G.; Morris, R. E.; Serre, C. Chem. Rev. 2012, 112, 1232−1268. (21) Berchel, M.; Le Gall, T.; Denis, C.; Le Hir, S.; Quentel, F.; Elléouet, C.; Montier, T.; Reuff, J.-M.; Salaün, J.-Y.; Haelters, J.-P.; Hix, G. B.; Lehn, P.; Jaffrés, P.-A. New J. Chem. 2011, 35, 1000−1003. (22) Altaf, M.; Stoeckli-Evans, H.; Cuin, A.; Sato, D. N.; Pavan, F. R.; Leite, C. Q. F.; Ahmad, S.; Bouekka, M.; Mimouni, M.; Khardli, F. Z.; Hadda, T. B. Polyhedron 2013, 62, 138−147. (23) Ansari, M. A.; Khan, H. M.; Khan, A. A.; Malik, A.; Sultan, A.; Shahis, M.; Shujatullah, F.; Azan, A. Biol. Med. 2011, 3, 141−146. (24) Fong, J.; Wood, F. Int. J. Nanomedicine 2006, 1, 441−449. (25) Lansdown, A. B. G. Silver in Healthcare: Its Antimicrobial Efficacy and Safety in Use; Royal Society of Chemistry: London, 2010. (26) Takayama, A.; Yoshikawa, R.; Iyoku, S.; Kasuga, N. C.; Nomiya, K. Polyhedron 2013, 52, 844−847. (27) Kasuga, N. C.; Yoshikawa, R.; Sakai, Y.; Nomiya, K. Inorg. Chem. 2012, 51, 1640−1647. (28) Nomiya, K.; Yoshizawa, A.; Tsukagoshi, K.; Kasuga, N. C.; Hirakawa, S.; Watanabe, J. J. Inorg. Biochem. 2004, 98, 46−60. (29) Kasuga, N. C.; Yamamoto, R.; Hara, A.; Amano, A.; Nomiya, K. Inorg. Chim. Acta 2006, 359, 4412−4416. (30) Wang, X.; Luan, J.; Lin, H.; Lu, Q.; Xu, C.; Liu, G. Dalton Trans. 2013, 42, 8375−8386. (31) Wen, G.-F.; Wang, Y.-Y.; Zhang, W.-H.; Ren, C.; Liu, R.-T.; Shi, Q.-Z. CrystEngComm 2010, 12, 1238−1251. (32) Yang, E.-C.; Zhao, H.-K.; Ding, B.; Wang, X.-Y.; Zhao, X.-J. Cryst. Growth Des. 2007, 7, 2009−2015. (33) See the Cambridge Structural Database (CSD, version 5.36, 2015): Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, 58, 380− 388. (34) (a) Smoleński, P.; Pettinari, C.; Marchetti, F.; Guedes da Silva, M. F. C.; Lupidi, G.; Patzmay, G. V. B.; Petrelli, D.; Vitali, L. A.; Pombeiro, A. J. L. Inorg. Chem. 2015, 54, 434−440. (b) Jaremko, L.; Kirillov, A. M.; Smoleński, P.; Lis, T.; Pombeiro, A. J. L. Inorg. Chem. 2008, 47, 2922−2924. (c) Kirillov, A. M.; Smolenski, P.; Haukka, M.; Guedes da Silva, M. F. C.; Pombeiro, A. J. L. Organometallics 2009, 28, 1683−1687. (d) Jaremko, L.; Kirillov, A. M.; Smolenski, P.; Pombeiro, A. J. L. Cryst. Growth Des. 2009, 9, 3006−3010. (35) Jaros, S. W.; Guedes da Silva, M. F. C.; Florek, M.; Conceiçaõ Oliveira, M.; Smoleński, P.; Pombeiro, A. J. L.; Kirillov, A. M. Cryst. Growth Des. 2014, 14, 5408−5417. (36) Smoleński, P.; Jaros, S. W.; Pettinari, C.; Lupidi, G.; Quassinti, L.; Bramucci, M.; Vitali, L. A.; Petrelli, D.; Kochel, A.; Kirillov, A. M. Dalton. Trans. 2013, 42, 6572−6581.

intermediate species that play an important role in the crystal growth process. This investigation links the solution speciation to solid-state chemistry and provides new insights about the crystallization process of Ag−PTA-based compounds. Hence, the present work not only widens the number of antimicrobial silver coordination networks but also discloses a promising preparation route for the controlled assembling of such materials. Since an understanding of the solution behavior is crucial for the design of target coordination networks, we are currently attempting to employ this synthetic approach as well as ESI-MS studies for another series of polycarboxylic ancillary ligands in order to generalize a proposed crystal growth mechanism of Ag−PTA derivatives and to find their structure− antimicrobial activity relationship.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02235. Additional ESI-MS data and discussion, crystal growth mechanism, PXRD patterns, TGA curves (PDF) Crystallographic files for 1−3 (CIF) Crystallographic files for 1−3 (CIF) Crystallographic files for 1−3 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Foundation for Science and Technology (FCT) (projects PTDC/QUI-QUI/121526/2010, UID/QUI/00100/2013, REM2013, and PhD grant SFRH/ BD/77024/2011), Portugal, as well as by the NCN program (Grant No. 2012/07/B/ST5/00885), Poland. We also thank Dr. M. Florek for assistance with antimicrobial tests and Ms. Ana Dias for assistance with ESI-MS measurements.

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REFERENCES

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