Copper(II) Dihalotetracyanoplatinate(IV) Coordination Polymers and

Jun 27, 2017 - All single-crystal diffraction data were processed and initial solutions found with the Bruker ApexII software suite. Subsequent refine...
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Copper(II) Dihalotetracyanoplatinate(IV) Coordination Polymers and Their Vapochromic Behavior Ania S. Sergeenko, Jeffrey S. Ovens, and Daniel B. Leznoff* Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada S Supporting Information *

ABSTRACT: The coordination polymers [Cu(H2O)2(μ2-NC)4PtX2] (X = Cl, Br) form networks of square grid sheets that align in a staggered manner with one another via weak X···X interactions. Upon stepwise dehydration, the layers fuse, forming a 3-D network of distorted cubes. The materials were tested for visible vapochromic, Raman, and IR response to dimethyl sulfoxide, N,N-dimethylformamide, and pyridine. Analyte-bound coordination polymers of the form Cu(analyte)2[PtX2(CN)4] were structurally characterized by PXRD and found to form layers of square grids that align through X···X interactions. The reaction of [Cu(H2O)2(μ2-NC)4PtX2] with concentrated aqueous NH3 generated [PtBr(CN)4(NH3)]− and [PtCl(CN)4(OH)]2− anions that were incorporated into 1-D chain structures. UV−visible reflectance data show that a combination of shifting d−d transitions and the visible Br−Pt LMCT absorption band in [Cu(H2O)2(μ2-NC)4PtBr2] results in a greater vapochromic effect in comparison to that in chlorine-containing analogues.

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Oxidation of the linear Au(I) center in [Au(CN)2]− with halogens yields [AuX2(CN)2]− (X = Cl, Br, I), which aggregate using X···X interactions19−23 rather than aurophilic bonding. In an effort to determine the role of X···X interactions in the structures and vapochromism, we recently reported the structures and response to analyte exposure of the two vapochromic coordination polymers Cu[AuX2(CN)2]2, where X = Cl, Br. Similarly, oxidation of [Pt(CN)4]2− with halogens results in the formation of [PtIVX2(CN)4]2−,24−29 which no longer show any platinophilic interactions and instead potentially can utilize X···X interactions to aggregate. A few coordination polymers containing [PtX2(CN)4]2− units have been previously synthesized and their infrared spectra reported, but no structural data have been described, although the crystal structures of some simple alkali and alkaline-earth salts of [PtIVX2(CN)4]2− have been reported.30−36 Herein we report the crystal structures of [Cu(H2O)2(μ2-NC)4PtX2] (X = Br, Cl), a spectroscopic analysis on the effect of hydration on their structure, and their vapochromic properties with select donor-atom-contain-

INTRODUCTION

Coordination polymers are a class of materials that, through their modular nature, can be designed to possess properties such as porosity, fluorescence, and magnetism and have the potential to be used in a variety of applications, including chemical sensing.1−4 Cyanometallate-based coordination networks, exemplified by cubic Prussian Blue analogues5,6 and 2-D Hoffman clathrates,7 can act as chemical sensors due to their characteristic cyanide absorptions, which can be monitored via Raman and infrared spectroscopy,8 as well as by exhibiting either a vapochromic9 or vapoluminescent10 response to the exposure of gases and volatile compounds. In particular, squareplanar [PtII(CN)4]-containing materials can not only form 2-D sheets but also often incorporate additional metallophilic platinum−platinum interactions;11−15 these are often emissive, and as a result tetracyanoplatinate-containing materials such as [Pt(aryl isocyanide)4][Pt(CN)4], [PtL2(CN)2] (L = αdiimine), and related derivatives have been extensively studied for their vapochromic and vapoluminescent qualities.4,16,17 Similarly, emissive [Au(CN)2]-based materials, which often contain aurophilic interactions, have been harnessed for their vapochromic9 and vapoluminescent10 properties as well.18 © 2017 American Chemical Society

Received: March 9, 2017 Published: June 27, 2017 7870

DOI: 10.1021/acs.inorgchem.7b00596 Inorg. Chem. 2017, 56, 7870−7881

Article

Inorganic Chemistry

(w; νOH), 3517 (w; νOH), 2237 (vs; νCN), 2194 (w), 1599 (m). Raman (cm−1): 2255 (s, νCN), 2240 (m, νCN), 327 (vs; νPtCl), 276 (w), 170 (br, w), 105 (w). Anal. Calcd for C4H4N4Cl2CuO2Pt: C, 10.23; H, 0.86; N, 11.93. Found: C, 10.27; H, 0.88; N, 11.57. Precipitation can be slowed by performing the reaction in a 15/1 H2O/ethylene glycol solution, resulting in the isolation of turquoise crystals of 2. Aqua(μ-bromo)tetrakis(μ-cyano)copper(II) Bromoplatinate(IV) Hydrate, [Cu(H2O)(μ2-Br)(μ2-NC)4PtBr]·H2O (3). Upon gentle heating or placement under a nitrogen atmosphere (see below), 1 undergoes a single-crystal to single-crystal rearrangement to form [Cu(H2O)(μ2Br)(μ2-NC)4PtBr]·H2O (3), which has only been isolated in situ while mounted under a nitrogen stream in the X-ray diffractometer enclosure. Bis(μ-bromo)tetrakis(μ-cyano)copper(II) Platinate(IV), [Cu(μ2NC)4PtBr2] (4). Heating 1 to 330 K resulted in dehydration within a few minutes, generating the anhydrous material [Cu(μ2-NC)4PtBr2] (4) as a green powder. Placing 1 under nitrogen can also result in transformation to 4 within 30 min. In both cases the product can be rehydrated to 1 by re-exposure to air and cooling to room temperature. Raman (cm−1): 2250 (s; νCN), 2236 (m; νCN), 282 (w; δMCN), 203 (vs; νPtBr), 148 (m; δCMC). Anal. Calcd for C4N4Br2CuPt: C, 9.20; H, 0.00; N, 10.72. Found: C, 9.04; H, 0.00; N, 10.68. Bis(μ-chloro)tetrakis(μ-cyano)copper(II) Platinate(IV), [Cu(μ2NC)4PtCl2] (5). Heating 2 to 400 K for 10 min or placing it under a nitrogen stream for 30 min generated the anhydrous material [Cu(μ2NC)4PtCl2] (5) as a blue powder. The product can be rehydrated to 2 by re-exposure to air and cooling to room temperature. Raman (cm−1): 2252 (m), 2237 (m), 577 (vw), 333 (s; νPtCl), 280 (w), 164 (m), 106 (w). Anal. Calcd for C4N4CuCl2Pt: C, 11.08; H, 0.00; N, 12.92. Found: C, 11.25; H, 0.00; N, 12.79. Hexakis(dimethyl sulfoxide)copper(II) Dibromotetracyanoplatinate(IV), Cu(DMSO)6[PtBr2(CN)4] (6). An 89 mg portion (0.096 mmol) of [nBu4N]2[PtBr2(CN)4] and 50 mg (0.135 mmol) of Cu(ClO4)2·6H2O were dissolved separately in a minimum amount of DMSO. The Cu(II) solution was added to the platinum-containing solution, and overnight large kite-shaped lime green crystals of Cu(DMSO)6[PtBr2(CN)4] (6) formed. No yield for 6 could be determined, as the material rapidly desolvated to 7 upon removal from the solvent. IR (cm−1): 3451 (vs), 3011 (m; νCH), 2913 (w; νCH), 2163 (m; νCN), 1666 (w), 1439 (m), 1409 (m), 1318 (m), 1025 (vs), 1019 (vs), 990 (vs), 954 (vs), 941 (s; νSO), 712 (m; νSC). Raman (cm−1): 201 (s; νPtBr). Anal. Calcd for C16H36N4Br2CuO6PtS6: C, 19.38; H, 3.66; N, 5.65. Found: C, 20.20; H, 3.67; N, 5.88. The elevated % C is consistent with a small amount of excess DMSO coating the crystals from the mother liquor (to prevent desolvation during analysis). Bis(dimethyl sulfoxide)tetrakis(μ-cyano)copper(II) Dibromoplatinate(IV) Dihydrate, [Cu(DMSO)2(μ2-NC)4PtBr2]·2H2O (7). Upon vacuum filtration, crystals of 6 quickly desolvated and became an orange powder of [Cu(DMSO)2(μ2-NC)4PtBr2]·2H2O (7). Yield: 43 mg (63%). Rinsing crystals of 6 with methanol or deionized water also caused the immediate transformation of 6 into 7. IR (cm−1): 3274 (br; νOH), 3007 (w; νCH), 2923 (w; νCH), 2223 (vs; νCN), 2181 (w; νCN), 1666 (w), 1434 (m; δCH), 1402 (m), 1026 (m), 989 (vs), 924 (vs). Raman (cm−1): 3001 (w; νCH), 2915 (m; νCH), 2248 (w; νCN), 2227 (m; νCN), 2194 (w; νCN), 503 (vs), 500 (sh), 496 (s), 407 (w), 202 (vs; νPtBr). Anal. Calcd for C8H16N4Br2CuO4PtS2: C, 13.44; H, 2.26; N, 7.84. Found: C, 13.52; H, 2.29; N, 7.74. The same product can also be obtained by vapor absorption of DMSO by 1. Bis(dimethyl sulfoxide)tetrakis(μ-cyano)copper(II) Dichloroplatinate(IV) Dihydrate, [Cu(DMSO)2(μ2-NC)4PtCl2]·2H2O (8). A 44 mg portion (0.098 mmol) of K2[PtCl2(CN)4] and 58 mg (0.157 mmol) of Cu(ClO4)2·6H2O were dissolved separately in a minimum amount of DMSO. The Cu(II) solution was added to the platinum-containing solution, resulting in an instant light blue precipitate of [Cu(DMSO)2(μ2-NC)4PtCl2]·2H2O (8). Yield: 57 mg (93%). IR (cm−1): 3179 (br; νOH), 2924 (w; νCH), 2227 (s; νCN), 2185 (m; νCN), 1673 (w), 1437 (w), 1416 (m), 1402 (m), 1317 (w), 1030 (w), 989 (vs), 943 (vs), 906 (m). Raman (cm−1): 2198 (νCN), 2225 (sh; νCN), 2239 (νCN), 717 (νSC), 680 (w), 335 (νPtCl), 199 (br), 146 (w), Anal. Calcd for C8H16N4Cl2CuO4PtS2: C, 15.35; H, 2.58; N, 8.95.

ing analytes, including dimethyl sulfoxide (DMSO), N,Ndimethylformamide (DMF), pyridine, and ammonia. The series of materials herein represents the first structurally characterized coordination polymers for this cyanometallate building block.

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EXPERIMENTAL SECTION

Caution! Although we have experienced no difficulties, perchlorate salts are potentially explosive and should be used in small quantities and handled with care. Chlorine, bromine, and ammonia should only be handled in a well-ventilated fume hood. General Procedures and Physical Measurements. All reactions were performed in air at room temperature. K2[PtBr2(CN)4] and K2[PtCl2(CN)4] were synthesized using literature procedures;34 all other reagents were purchased from commercial sources and used as received. Infrared spectra were measured on a Thermo Nicolet Nexus 670 FT-IR spectrometer equipped with a Pike MIRacle attenuated total reflection (ATR) sampling accessory. Raman spectra were measured using a Renishaw inVia Raman microscope with a 514 nm laser at 1−10% intensity for 10−40 s. A Linkam THMS600 temperature-controlled stage was added for the collection of Raman spectra for the anhydrous materials 4 (110 °C) and 5 (120 °C). Solidstate UV−visible reflectance spectra were measured using an Ocean Optics FLAME-S-XR1-ES spectrometer with a deuterium halogen lamp and referenced to magnesium oxide. Microanalyses (% C, H, N) were performed by Paul Mulyk on a Carlo Erba EA 1110 CHN elemental analyzer. Thermogravimetric analyses were performed by Dr. Rajendra Sharma using a Shimadzu TGA-50 instrument in air at a rate of 2 °C/min. Synthetic Procedures. Tetrabutylammonium Dibromotetracyanoplatinate(IV), [nBu4N]2[PtBr2(CN)4]. A 1000 mg portion (2.65 mmol) of K2[Pt(CN)4] was dissolved in 30 mL of a 1/2 H2O/CH3OH mixture. To this solution was added 4 mL of liquid Br2. The dark red solution was stirred for 3 h, and then nitrogen was bubbled through it until the color lightened to yellow. An excess of [nBu4N]Br (1995 mg, 6.18 mmol) in 20 mL of CH3OH was then added to the stirred solution. The solvent was removed by rotary evaporation, leaving yellow crystals of [nBu4N]2[PtBr2(CN)4], which were rinsed with deionized water, filtered, and dried in air overnight. Yield: 2141 mg (87%). IR (cm−1): 2961 (vs; νCH), 2961 (s; νCH), 2875 (s; νCH), 2160 (m; νCN), 1483 (s), 1381 (m), 1153 (w), 1032 (w), 880 (m), 751 (w). Raman (cm−1): 2188 (sh, νCN), 2180 (s; νCN), 2169 (s; νCN), 2154 (sh, νCN), 1447 (m), 1320 (w), 199 (s), 109 (m). Anal. Calcd for C36H72N6Br2Pt: C, 45.81; H, 7.69; N, 8.90. Found: C, 46.11; H, 7.40; N, 9.03. Bis(aqua)tetrakis(μ2-cyano)copper(II) Dibromoplatinate(IV), [Cu(H2O)2(μ2-NC)4PtBr2] (1). A light blue 10 mL aqueous solution of 81 mg (0.219 mmol) of Cu(ClO4)2·6H2O was added to a pale yellow 10 mL aqueous solution of 109 mg (0.210 mmol) of K2[PtBr2(CN)4], resulting in the formation of an orange-yellow precipitate that was filtered, and the residual solution was left to evaporate. Orange block crystals of [Cu(H2O)2(μ2-NC)4PtBr2] (1) formed overnight and were isolated by filtration and dried. Yield: 48 mg (41%). Alternatively, 94 mg (0.10 mmol) of [nBu4N]2[PtBr2(CN)4] was dissolved in 3 mL of methanol, resulting in a bright yellow solution. To this solution was added a blue 2 mL methanol solution of 40 mg (0.11 mmol) of Cu(ClO4)2·6H2O, resulting in an instant green precipitate (see compound 4). The precipitate was rinsed with water and centrifuged three times and air-dried. Yield: 45 mg (79%) of a yellow powder of 1 was isolated. IR (cm−1): 3586 (m; νOH), 3526 (m; νOH), 2231 (vs; νCN), 2191(w; νCN), 1559 (w). Raman (cm−1): 2247 (m; νCN), 2232 (m; νCN), 199 (vs; νPtBr), 162 (w). Anal. Calcd for C4H4N4Br2CuO2Pt: C, 8.60; H, 0.72; N, 10.03. Found: C, 8.69; H, 0.79; N, 10.04%. Bis(aqua)tetrakis(μ2-cyano)copper(II) Dichloroplatinate(IV), [Cu(H2O)2(μ2-NC)4PtCl2] (2). A 15 mL aqueous solution of 88 mg (0.238 mmol) of Cu(ClO4)2·6H2O was added to a 40 mL aqueous solution of 65 mg (0.145 mmol) of K2[PtCl2(CN)4], resulting in the formation of a light blue precipitate of [Cu(H2O)2(μ2-NC)4PtCl2] (2). The precipitate was rinsed with water followed by centrifugation three times to remove unwanted salts. Yield: 31 mg (46%). IR (cm−1): 3640 7871

DOI: 10.1021/acs.inorgchem.7b00596 Inorg. Chem. 2017, 56, 7870−7881

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Inorganic Chemistry

NC)PtCl(CN)2] (14) were obtained from dissolution and subsequent evaporation of 2 in a few drops of concentrated aqueous NH3. IR (cm−1): 3734 (w; νOH), 3721 (m; νOH), 3357 (s; νNH), 3277 (m; νNH), 2172 (m; νCN), 1611 (m), 1251(m), 1221 (s), 1147 (w), 1138 (w), 708 (s). Raman: 2199 (s; νCN), 2192 (m; νCN), 2155 (w; νCN), 2135 (w; νCN), 548 (m), 459 (m), 185 (m), 115 (m). X-ray Crystallographic Analysis. Samples were mounted on MiTeGen sample holders using Paratone oil. All crystallographic data were collected on a Bruker SMART ApexII Duo CCD diffractometer with TRIUMPH graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation for single-crystal data collection and a Cu Kα (λ = 1.54184 Å) Incoatec microsource using ω and ϕ scans for powder data collection. Data for 3 were collected at 320 K, those for 4 and 5 were collected at 330 K, and those for 6 were collected at 150 K; data for all others were collected at room temperature. Additional crystallographic information can be found in Tables S1−S5 in the Supporting Information and in cif format at CCDC deposition nos. 1554361− 1554366. All single-crystal diffraction data were processed and initial solutions found with the Bruker ApexII software suite. Subsequent refinements were performed in SHELXle.37 All hydrogen atoms were added geometrically and refined using a riding model, except in 13, where they were found and placed using the difference map and refined without constraint, and except for the hydrogen atoms on OH in 14 and H2O in 1−3, which were omitted due to unstable refinements or poor data quality. Compound 2 crystallized as a pseudomerohedral twin. Analysis of twinning was performed using Rotax.38 Figures were made using ORTEP-3, POV-Ray, and SigmaPlot.39−41 Compound 14, which generated a lower-quality data set, crystallized in the chiral orthorhombic space group P212121, and structure determination was complicated by twinning and possibly cocrystallization of the two enantiomers, as reflected in the ambiguous Flack parameter of 0.3. All powder X-ray diffraction data were processed using the Bruker ApexII software suite and analyzed using Topas Academic software.42 Peak fitting, indexing, and Pawley refinement were used to determine the unit cell for each compound. Initial structure solutions were determined using Monte Carlo methods, and subsequent Rietveld refinements were performed using Topas Academic, where unit cell parameters and the rotation of the rigid bodies about the a, b, and c axes were allowed to refine. Solutions of 7−10 initially had N−Cu−O angles refining to extremely small angles (∼45°) which were not physically possible; therefore, they were restrained to 90° and allowed to refine a few degrees. Due to the nature of the powder X-ray solution, distances and angles between light atoms such as carbon, nitrogen, and hydrogen cannot be reported with a high degree of certainty. Collected, calculated, and residual data for the powder pattern solutions can be found in Figures S1−S8 in the Supporting Information; the raw data in the form of xy files and cif files have also been included.

Found: C, 15.44; H, 2.58; N, 8.53. The same product can also be obtained by vapor absorption of DMSO by 2. Bis(dimethylformamide)tetrakis(μ-cyano)copper(II) Dibromoplatinate(IV), [Cu(DMF)2(μ2-NC)4PtBr2] (9). An 84 mg portion (0.091 mmol) of [nBu4N]2[PtBr2(CN)4] and 51 mg (0.138 mmol) of Cu(ClO4)2·6H2O were dissolved separately in a minimum amount of DMF. The copper(II) solution was added to the platinumcontaining solution, resulting in an instant lime green precipitate of [Cu(DMF)2(μ2-NC)4PtBr2] (9). Yield: 48 mg (79%). IR (cm−1): 2952 (vw; νCH), 2222 (m; νCN), 2202 (w; νCN), 2185 (w; νCN), 1650 (vs; νCO), 1644 (vs; νCO), 1373 (s; νCN amide), 1121 (m), 844 (w). Raman (cm−1): 2221 (vs; νCN), 2195 (vs, νCN), 1434 (w), 1408 (w), 402 (w), 340 (w), 200 (vs; ν P t B r ). Anal. Calcd for C10H14N6Br2CuO2Pt: C, 17.96; H, 2.11; N, 12.57. Found: C, 18.08; H, 2.28; N, 12.30. The same product can also be obtained by vapor absorption of DMF by 1. Bis(dimethylformamide)tetrakis(μ-cyano)copper(II) Dichloroplatinate(IV), [Cu(DMF)2(μ2-NC)4PtCl2] (10). A 42 mg portion (0.094 mol) of K2[PtCl2(CN)4] and 58 mg (0.157 mol) of Cu(ClO4)2·6H2O were dissolved separately in DMF. The Cu(II) solution was added to the platinum-containing solution, resulting in an instant light blue-green precipitate of [Cu(DMF)2(μ2-NC)4PtCl2] (10). Yield: 30 mg (56%). IR (cm−1): 2960 (w; νCH), 2227 (m; νCN), 2186 (w; νCN), 1658 (vs; νCO), 1650 (vs; νCO), 1377 (vs; νCN amide), 1122 (s). Raman (cm−1): 2237 (s; νCN), 2196 (s; νCN), 1438 (w), 1421 (w), 328 (vs; νPtCl), 189 (w), 118 (w). Anal. Calcd for C10H14N6Br2CuO2Pt: C, 20.72; H, 2.43; N, 14.50. Found: C, 20.71; H, 2.47; N, 14.33. The same product can also be obtained by vapor absorption of DMF by 2. Bis(pyridine)tetrakis(μ-cyano)copper(II) Dibromoplatinate(IV), [Cu(Py)2(μ2-NC)4PtBr2] (11). A 93 mg portion (0.10 mmol) of n [ Bu4N]2[PtBr2(CN)4] was dissolved in 15 mL of methanol, to which 1 mL (0.978 g/mL, 12.4 mmol) of pyridine was added. A solution of 51 mg (0.138 mmol) of Cu(ClO4)2·6H2O in 5 mL of methanol was then added, resulting in an instant green precipitate. The precipitate was purified by washing and centrifuging twice with methanol and once with deionized water to give [Cu(Py)2(μ2-NC)4PtBr2] (11). Yield: 47 mg (69%). IR (cm−1): 2222 (m; νCN), 2181 (m; νCN), 1612 (s), 1450 (s), 1222 (m), 1157 (w), 1073 (m), 1047 (m), 758 (s), Raman (cm−1): 2232 (m; νCN), 2193 (m; νCN), 1042 (w), 1016 (m), 396 (vw), 230 (w), 199 (s; νPtBr), 162 (w). Anal. Calcd for C14H10N6Br2CuPt: C, 24.70; H, 1.48; N, 12.35. Found: C, 24.63; H, 1.41; N, 12.04. Bis(pyridine)tetrakis(μ-cyano)copper(II) Dichloroplatinate(IV), [Cu(Py)2(μ2-NC)4PtCl2] (12). A 44 mg portion (0.098 mmol) of K2[PtCl2(CN)4] was dissolved in 25 mL of water. A 2 mL portion (0.978 g/mL, 24.7 mmol) of pyridine was added. A solution of 45 mg (0.121 mmol) of Cu(ClO4)2·6H2O in 4 mL of deionized water was added, resulting in an instant blue precipitate. The precipitate was purified by washing three times with water to give [Cu(Py)2(μ2NC)4PtCl2] (12). Yield: 39 mg (67%). IR (cm−1): 2223 (m; νCN), 2186 (m; νCN), 1612 (m), 1492 (w), 1451 (vs), 1223 (m), 1158 (m), 1075 (s), 1048 (m), 758 (s). Raman (cm−1): 2233 (m; νCN), 2197 (m; νCN), 1608 (w), 1571 (w), 1222 (w), 1154 (w), 1043 (m), 1018 (m), 644 (w), 530 (w), 466 (w), 327 (vs; νPtCl), 238 (w), 163 (m), 125 (w), 103 (m). Anal. Calcd for C14H10N6Cl2CuPt: C, 28.41; H, 1.70; N, 14.20. Found: C, 28.23; H, 1.58; N, 13.85. The same product can also be obtained by vapor absorption of pyridine by 2. Bis(ammine)copper(II) Bis((ammine)bromobis(μ-cyano)dicyanoplatinate(IV)) Dihydrate, [Cu(NH 3 )2 {(μ 2-NC)2 PtBr(NH3 ) (CN)2}2]·2H2O (13). A few blue crystals of [Cu(NH3)2{(μ2-NC)2PtBr(NH3) (CN)2}2]·2H2O (13) were obtained from dissolution and subsequent evaporation of 1 in a few drops of concentrated aqueous NH3. IR (cm−1): 3362 (vs; νOH), 3214 (br, vs; νNH), 2184 (w), 2180 (w; νCN), 2173 (m; νCN), 2167 (m; νCN), 2126 (m; νCN), 1614 (m), 1431 (m), 1249 (m), 780 (w). Raman: 2117 (m; νCN), 2199 (s; νCN), 2189 (sh; νCN) 2182 (s; νCN), 2157 (m; νCN), 2151 (m; νCN), 522 (w), 231 (s) 105 (vs). Tris(ammine)(η 2 -cyano)(μ-cyano)(μ-hydroxo)copper(II) Chlorodicyanoplatinate(IV), [Cu(NH3)3(μ-OH)(η2-CN)(μ2-NC)PtCl(CN)2] (14). A few blue crystals of [Cu(NH3)3(μ-OH)(η2-CN)(μ2-

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RESULTS AND DISCUSSION Reaction of K2[PtX2(CN)4] (X = Cl, Br) with Cu(II) salts in water resulted in formation of the coordination polymers [Cu(H2O)2(μ2-NC)4PtBr2] (1) by slow evaporation and [Cu(H2O)2(μ2-NC)4PtCl2] (2) by instant precipitation. Both products are insoluble in typical solvents, including water, dichloromethane, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile, and ethylene glycol. Performing the synthesis in DMSO or DMF did not prevent precipitate formation. However, crystals of 2 could be obtained by adding a small amount of ethylene glycol to the aqueous reaction at the outset, which did retard the precipitation rate. Compounds 1 and 2 are isostructural. Both the Pt(IV) and Cu(II) metal centers are in an octahedral environmentthe platinum(IV) has equatorial carbon-bound cyanide and axial halide ligands, while the Cu(II) center has four N-bound equatorial cyanide and two axially bound aqua ligands. The 7872

DOI: 10.1021/acs.inorgchem.7b00596 Inorg. Chem. 2017, 56, 7870−7881

Article

Inorganic Chemistry

Figure 1. (a) Two-dimensional square-grid structure of 1. (b) Additional dimensionality resulting from X···X interactions between sheets. Color scheme: platinum, gray; bromine, violet; carbon, black; nitrogen, blue; copper, bronze; oxygen, red.

Since the supramolecular structures of both 1 and 2 are of the same nature, even though the strength of the halogen− halogen interactions are greater in 1 than 2, it is likely that the presence of halogen−halogen interactions does not direct coordination polymer formation; rather, the network formed by the bridging cyanides results in the formation of sheets, which preferentially orient such that the weak interactions hold the sheets together. Varying Levels of Hydration. Thermogravimetric analyses of 1 and 2 are shown in Figure 2. Both compounds lose water

network propagates in two dimensions via Pt−CN−Cu linkages in square-planar nets (Figure 1a). Selected bond lengths for 1 and 2 are shown in Table 1. The Pt−Br bond length in 1 is 2.4742(6) Å, and the Pt−Cl bond Table 1. Selected Interatomic Distances (Å) in 1−3 Pt(1)−C(1) Pt(1)−C(2) Pt(1)−X(1) Pt(1)−X(2) Cu(1)−O(1) Cu(1)−X(1) Cu(1)−N(1) Cu(1)−N(2) C(1)−N(1) C(2)−N(2) X(1)−X(1) X(2)−X(2) O(1)−O(1)

1 (X = Br)

2 (X = Cl)

3 (X = Br)

2.000(3)

2.015(8)

2.4742(6)

2.328(4)

2.404(6)

2.386(15)

1.979(2)

1.987(7)

1.145(4)

1.127(11)

3.67993(12)

3.6529(9)

3.6958(16)

3.642(3)

1.98(3) 2.02(3) 2.476(6) 2.478(5) 2.28(3) 3.265(8) 1.92(3) 1.97(2) 1.21(4) 1.12(3) 4.282(7) 3.712(3) 3.712(14)

length in 2 is 2.328(4) Å. Both compounds have Pt−X distances comparable to those of the related alkaline-earth compounds: e.g., Pt−Br = 2.482 Å and Pt−Cl = 2.330 Å in Ba[PtX2(CN)4]·4.5H2O.36,43 The νCN stretches for 2 (2237, 2239, and 2255 cm−1) appear at energies higher than those of 1 (2231, 2232, and 2247 cm−1); N-cyano binding generally results in a higher energy cyanide stretch in comparison to unbound salts (e.g. 2164 cm−1 for (nBu4N)2[PtBr2(CN)4]).44 The distance between bromine atoms (3.680 Å) in 1 is slightly less than the sum of van der Waals radii (3.7 Å),45,46 suggesting the presence of Br···Br interactions, whereas the distance between chlorine atoms (3.653 Å) in 2 is outside the sum of van der Waals radii (3.5 Å).45−47 The weak interactions (X···X) link the 2-D sheets in the third dimension; the halide units form sheets of distorted hexagons parallel to and offset from the Pt−CN−Cu nets, as shown in Figure 1b. Along the ab plane, sheets of halogens are connected through weak interactions and run parallel to one another in an alternating fashion. Distances between the halogen and metal-bound aqua units in the alternating sheets are 3.602 and 3.642 Å when X = Br, Cl, respectively, and could indicate the presence of weak H···X interactions. The distance between oxygen atoms in these sheets (both 1 and 2) is greater than 3.6 Å, suggesting that they are too far to be connected by hydrogen bonding.

Figure 2. Thermogravimetric analysis of [Cu(H2O)2(μ2-NC)4PtBr2] (1) and [Cu(H2O)2(μ2-NC)4PtCl2] (2) showing the successive losses of water, halogens, and cyanides.

easily and reversibly. Dehydration begins at room temperature and ends just after 80 °C for 1, whereas in 2 water loss begins slightly higher, above 30 °C, and ends at 105 °C. Bromine− bromine interactions in 1 appear to affect the temperature for halogen loss, which commences at 180 °C, almost 100 °C lower than the 270 °C required for removal of the chlorides (as Cl2(g)) in 2. The loss of the cyanides in the form of cyanogen (C2N2(g)) requires elevated temperatures of above 400 °C.48 Collection of single-crystal and powder X-ray diffraction data of 1 and 2 showed that, under a stream of nitrogen gas at room temperature, water was lost, such that the materials became completely anhydrous after a few hours. In 1 this change was slow enough that the transition of Cu(H2O)n[PtBr2(CN)4] from n = 2 to n = 0 could be monitored via a single-crystal to single-crystal transformation to [Cu(H 2 O)(μ 2 -Br)(μ 2 7873

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Cu−Br have been reported to be between 3.25 and 3.85 Å.49 The remaining bound aqua ligand becomes more tightly bound to the Cu(II) center (Cu−O 2.28(3) Å in 3 in comparison to 2.404(6) Å in 1). The highlighted portion of the box in Figure 3 provides a side-on view of the effect of the reorganization on the bromine−bromine interactions. While the Br(2)−Br(2) distance lengthens slightly (3.712 Å vs 3.67993 Å in 1), the Br(1)−Br(1) distance (4.282 Å) lengthens significantly, beyond the van der Waals sum. Thus, the previously planar sheet containing bromine−bromine interactions in [Cu(H2O)2(μ2-NC)4PtBr2] becomes extremely distorted. While the analogous chlorine-containing compound [Cu(H2O)(μ2-Cl)(μ2-NC)4PtCl]·H2O was not isolated, both [Cu(H 2 O) 2 (μ 2 -NC) 4 PtBr 2 ] (1) and [Cu(H 2 O) 2 (μ 2 NC)4PtCl2] (2) dehydrate to the isostructural compounds [Cu(μ2-NC)4PtBr2] (4) and [Cu(μ2-NC)4PtCl2] (5) (powder X-ray data are given in Table S2 in the Supporting Information). The resulting structures (Figure 4, right) are three-dimensional networks of sheets fused into distorted cubes with bent bridging cyanides as well as halides coordinating to the copper in place of aqua ligands; there are two unique halogens with X(1)−X(1) and X(2)−X(2) distances of 4.1 Å and X(1)−X(2) distances of 6.4 Å in both 4 and 5. In 4, the Cu−Br distance is 3.076(3) Å, shorter than the weak Cu−Br interaction in 3 (3.265 Å); the Cu−Cl distance in 5 of 2.90(6) Å is reasonable for a single bond in comparison to 2.716 Å in Rb2CuCl4 and 2.934 Å in CuCl2.50,51 Thus, overall, upon dehydration from 1 to 3, stacked 2-D sheets with weak X···X interactions cross-link via stepwise axial Cu−X bond formation to eventually generate a 3-D array. In order to measure the change in Raman spectra due to water loss, crystals of [Cu(H2O)2(μ2-NC)4PtBr2] were placed on a temperature-controlled stage and the Raman spectra were taken at room temperature: first after heating to 110 °C and once more upon cooling to room temperature. Upon heating, the initially orange crystals lose both equivalents of water, becoming green [Cu(μ2-NC)4PtBr2] (4) (Figure 5). Dehydration results in a small increase in the energy of the νCN peaks from 2232/2247 cm−1 to 2236/2250 cm−1.

NC)4PtBr]·H2O (3). The structure of 3 (Figure 3, bottom; bond lengths are given in Table 1) illustrates that, prior to

Figure 3. View down the c axis on one net of 3 (top). Layers of nets of 3 looking down the b axis, where the effect of the structural distortion on the X···X interactions is highlighted in the box (bottom). Color scheme: platinum, gray; bromine, violet; carbon, black; nitrogen, blue; copper, bronze; oxygen, red.

water loss, one copper-bound water becomes free and is replaced by a bromide such that the sheets effectively “slip”. The disordered, unbound water molecule sits within alternating squares in the net. The new interaction between Cu1 and Br1 results in the formation of a ribbonlike bilayer (Figure 3b). The Cu−Br distance is long (3.265(8) Å) in comparison to a singlebond length of 2.9 Å. The sum of the van der Waals radii for

Figure 5. Reversible dehydration of crystals of 1 (left) into 4 (right) at 50× magnification.

Figure 4. Structural changes upon stepwise dehydration of 1 to 4 via intermediate 3. Color scheme: platinum, gray; bromine, violet; CN, black; copper, bronze; oxygen, red. 7874

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Figure 6. Vapochromic response of solid 1 and 2 to vapors of DMSO, DMF, pyridine, and ammonia.

Upon dehydration, 2 turns from pale turquoise at room temperature to the dark blue [Cu(μ2-NC)4PtCl2] (5) at 120 °C. Dehydration has the opposite effect on the cyanide absorption in comparison to 1, causing the stretches to shift from 2240/2255 cm−1 to 2237/2252 cm−1. Cooling to room temperature in ambient air results in the full rehydration of both materials. Vapochromism. The observation of color changes as a result of dehydration and rehydration suggested that 1 and 2 could have noteworthy vapochromic properties. Strips of filter paper dipped in DMSO, DMF, pyridine, and ammonia were placed in vials containing samples of 1 and 2 that were then capped. The resulting vapors were sensed by 1 and 2, resulting in color changes that are similar to the vapochromism of the related Cu[AuX2(CN)4]; in both cases, the color changes are attributed to the result of a modification in the Cu(II) coordination environment as the analytes replace copper-bound aqua ligands (Figure 6).52 The colorations of 1 and 2 are due to a combination of the X−Pt LMCT and d−d transitions in Cu(II). A greater change in color (and reflectance spectra) due to analyte binding can be seen in the bromine-containing compounds, which have a Br−Pt LMCT band with λmax 347 nm that tails into the visible region; the Cl−Pt LMCT band in 2 is completely in the UV region with λmax 288 nm (Figure S9 in the Supporting Information) and thus does not contribute to any visible color.53 These vapochromic responses were investigated by infrared, Raman, and reflectance spectroscopy (reflectance spectra for analyte-adduct compounds are shown in Figures S10 and S11 in the Supporting Information). Reactions were also carried out in analyte-containing solutions, which resulted in the formation of compounds identical with those from vapor exposure, except in the case of 1 with pyridine. Structural solutions of analyte-bound compounds were achieved through the use of Rietveld refinements of PXRD data and are described below. D M S O . T h e a d d i t i o n o f C u ( C l O 4 ) 2 · 6H 2 O t o [nBu4N]2[PtBr2(CN)4] in DMSO yielded crystals of an ionic material with a DMSO-saturated Cu(II) center, [Cu(DMSO)6][PtBr2(CN)4] (6), consisting of isolated [Cu(DMSO)6]2+ complex cations and [PtBr2(CN)4]2− anions (Figure 7). Salts of [Cu(DMSO)6]2+ have been reported with counterions such as ClO4−, OTf−, and HSO4−.54−56 The related salt Cu(DMSO)6[B2(CN)6] has unbound cyanides and Cu−O distances of 2.387 Å (axial) and 1.996 and 1.982 Å (equatorial) and can be described as a tetragonally elongated octahedron.57,58 In 6 the Cu−O distances are similar, at 2.405 Å (axial) and 1.985 and 1.987 Å (equatorial). Desolvation of 6 occurs easily, either by filtration under reduced pressure or by rinsing with methanol or water, resulting in the formation of an orange powder, [Cu(DMSO)2(μ2-NC)4PtBr2]·2H2O (7). In comparison, addition of the Cu(II) salt to K2[PtCl2(CN)4] in DMSO does not form

Figure 7. Crystal structure of 6. Color scheme: platinum, gray; bromine, violet; carbon, black; nitrogen, blue; copper, bronze; oxygen, red; sulfur, yellow. Hydrogens are omitted for clarity.

the analogous ionic material Cu(DMSO)6[PtCl2(CN)4] but yields [Cu(DMSO)2(μ2-NC)4PtCl2]·2H2O (8) directly. Exposure of solid 1 and 2 to DMSO vapor also resulted in the formation of 7 and 8, respectively. Compound 8 is isostructural with 7 (see fit and simulated PXRD in Figures S3 and S4 and Table S4 in the Supporting Information). Both 7 and 8 are twodimensional square nets that propagate through Pt−CN−Cu bridges (Figure 8). Similar to the structures of 1 and 2, in place of H2O Cu(II) has four equatorial N-cyano groups and two axial oxygen-bound DMSO molecules. In both 7 and 8, the halogens are oriented parallel to the DMSO molecules, and halogen−halogen interactions hold the sheets together in a layerlike fashion. In [Cu(DMSO)2(μ2-NC)4PtCl2]·2H2O very short Cl−Cl distances of 3.0251(18) Å are observed, whereas in [Cu(DMSO) 2 (μ2 -NC) 4PtBr 2]·2H 2 O Br−Br distances of 3.4251(5) Å are present. While the exact positions of the unbound water molecules could not be determined with certainty, they most likely reside in the void space between two sheets in the center of a square. DMF. The reaction of Cu(II) salts and [PtX2(CN)4]2− (X = Cl, Br) in DMF results in the formation of instant precipitates of [Cu(DMF)2(μ2-NC)4PtBr2] (9) and [Cu(DMF)2(μ2NC)4PtCl2] (10). Exposure of solid 1 and 2 to DMF vapor also results in the formation of 9 and 10 (Figures S5 and S6 and Table S5 in the Supporting Information). The DMF adducts are isostructural coordination polymers that propagate in 2-D nets, with DMF and halogens in the Cu(II) and Pt(IV) axial positions, respectively (Figure 9), similar to the structure of the DMSO adducts. Bromine−bromine interactions of 3.325(8) Å and chlorine−chlorine interactions of 3.437(6) Å are present in 9 and 10, respectively. Pyridine. The reaction of [PtX2(CN)4]2− (X = Br, Cl) building blocks with Cu(II) salts in water with excess pyridine results in the formation of a green precipitate, [Cu(Py)2(μ27875

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Figure 8. (a) View down the c axis onto one net of 7. (b) View down the b axis at two sheets of 7 aligning through X···X interactions. Color scheme: platinum, gray; bromine, violet; carbon, black; nitrogen, blue; copper, bronze; oxygen, red; sulfur, yellow. Hydrogens are omitted for clarity.

in 12) and the hydrogen−halogen (d(CH−Cl) = 3.609 Å) interaction prevent the same degree of formation of intersheet X···X interactions. Pyridine rings with π−π interactions have been shown to orient in a variety of ways, with distances of 3.6 Å or less between either the centers of the rings or from the nitrogen of one ring to the center of another ring.59 Thus, overall the analyte-adduct compounds 7−12 result in 2-D sheets of coordination polymer networks that form layers with X···X and H···X interactions (Table 2 and Figure 11). The flexibility of coordination polymer networks allowing for structural rearrangement in response to analyte exposure in the solid state has been well-documented.60 The νCN peaks in the infrared and Raman spectra and the wavelength of maximum reflectance for selected compounds are shown in Table 3. There is no measurable change in the M−X stretch for either 1 or 2 upon analyte binding. While there is a measurable shift in the cyanide stretches in both the infrared and Raman spectra upon exposure of 1 and 2 to analytes (∼10 cm−1, Table 3), there is little to no difference between the signals for different analyte-bound materials such that it is difficult to use the cyanide stretch alone to measure which analyte has bound (e.g., νCN 2227 cm−1 for [Cu(DMSO)2(μ2-NC)4PtCl2]·2H2O and 2227 cm−1 for [Cu(DMF)2(μ2-NC)4PtCl2]; vibrational spectra collected for 11 and 12 show the characteristic C−H and aromatic C−C and C−N stretches attributable to the analyte ligand). The vibrational spectra of 6 are quite simple in that the only signals are due to νPtBr at 201 cm−1 (Raman) and νCN at 2164 cm−1 (IR). The bromine-containing analyte−adducts show a broader range in the wavelengths of maximum reflectance in comparison to the chlorine analogues (530−621 nm vs 483− 527 nm, Table 3). Thermal Stability and Reversibility. In general, all of the chlorine-containing materials herein required elevated temperatures to remove both analytes and halogens, in comparison to the bromine-containing materials. Most compounds showed simultaneous loss of analyte and halogen (except for the aqua complexes 1 and 2 and the DMF adduct, 10), preventing them from being used as thermally resetting chemical sensors. For example, in 7, both equivalents of water are lost between 48 and 86 °C, the DMSO and bromine are lost concurrently between 110 and 170 °C, and cyanogen is sharply lost at 430 °C. Other analyte-containing compounds follow a similar

Figure 9. Side view of layers of 10. Color scheme: platinum, gray; chlorine, lime green; carbon, black; nitrogen, blue; copper, bronze; oxygen, red; sulfur, yellow. Hydrogens are omitted for clarity.

NC)4PtBr2] (11), and a blue precipitate, [Cu(Py)2(μ2NC)4PtCl2] (12), respectively. Exposure of solid 1 to pyridine vapor results in the formation of mixed, multiple products. Due to the ease of dehydration of 1 to the partially hydrated 3 and anhydrous 4, it is possible that some of 3 and 4 can bind pyridine, resulting in other products beyond that of 1 with pyridine; these were not identified. On the other hand, exposure of solid 2 to pyridine vapor results in the clean formation of 12. Compounds 11 and 12 follow the same motif as previously shown for the DMSO and DMF adducts, where the coordination polymer propagates via 2-D nets with cyanide bridges between Cu(II) and Pt(IV) centers in the plane, axial halogens on the Pt(IV) center, and axial analyte ligands coordinated to Cu(II) (Figure 10). The distances between intersheet halogens are substantially longer, 3.60310(12) Å (X = Br) and 3.5123(4) Å (X = Cl), indicating that the π−π interactions between the pyridines (3.566 Å in 11 and 3.622 Å 7876

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Figure 10. (left) Alignment of one sheet of 12 viewed down the a axis. (right) Side view of the interaction between two layers. Color scheme: platinum, gray; chlorine, lime green; carbon, black; nitrogen, blue; copper, bronze.

vapor exposure of [Cu(H2O)2(μ2-NC)4PtBr2] (1) to the headspace of concentrated aqueous NH3 in a sealed vial resulted in the condensation of the analyte, dissolution of 1, and isolation of a few blue plate crystals of [Cu(NH3)2{(μ2NC)2PtBr(NH3) (CN)2}2]·2H2O (13) after evaporation. Attempts at synthesis of 13 by dissolution of 1 in 5% aqueous ammonia and crystallization by volume resulted in a mixture of products, including crystals that quickly desolvated. In the structure of 13, both Cu(II) and Pt(IV) centers remain in octahedral environments, each with four equatorial cyanide ligands. The axial aqua ligands on Cu(II) in 1 were replaced by ammine units, and one of the Br− ligands coordinated to the Pt(IV) center was substituted by ammonia as well, to give a [PtBr(NH3)(CN)4]− unit, which has not been previously reported to our knowledge. The coordination polymer forms a ladderlike chain which is propagated through a central Cu(II) center connected to four [PtBr(NH3)(CN)4]− units through N-cyano bridging (Figure 12a; selected bond lengths are given in Table 4). Only two cyanide units from each Pt(IV) center contribute to propagation of the coordination polymer; the other two participate in hydrogen-bonding interactions with the free water molecules (Table S7 in the Supporting Information). This hydrogen bonding connects the

Table 2. Halogen−Halogen Distances (Å) in CuL2[PtX2(CN)4] for 1, 2, and 7−12 d(X−X)

L, X (compound no.) H2O, Br (1) H2O, Cl (2) DMSO, Br (7) DMSO, Cl (8) DMF, Br (9) DMF, Cl (10) pyridine, Br (11) pyridine, Cl (12) X = Br X = Cl

3.67993(12) 3.6530(9) 3.4251(5) 3.0251(18) 3.325(8) 3.437(6) 3.60310(12) 3.5123(4) X···X sum of van der Waals (Å) 3.7 3.5

pattern (see Figure S12a−h and Table S6 in the Supporting Information for detailed mass losses vs temperature for 1, 2, and 7−12). Ammonia. Unlike the three prior analytes that add to the Cu(II) site and induce a solid-state structural change in the 2-D network, reaction with ammonia is more drastic and irreversible, affecting both Cu(II) and Pt(IV) sites. Thus,

Figure 11. Summary of structural motifs for CuL2[PtX2(CN)4]. Color scheme: platinum, gray; halogen, violet; CN, black; copper, bronze; ligand on copper, red. 7877

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Inorganic Chemistry Table 3. Selected Infrared/Raman Absorptions and Maximum Visible Reflectance Data νCN absorption (cm−1) compound

IR

K2[PtBr2(CN)4]34 K2[PtCl2(CN)4]34 [nBu4N]2[PtBr2(CN)4]

2171 2176 2161

[Cu(H2O)2(μ2-NC)4PtBr2] (1) [Cu(H2O)2(μ2-NC)4PtCl2] (2) Cu(DMSO)6[PtBr2(CN)4](6) [Cu(DMSO)2(μ2-NC)4PtBr2]·2H2O (7) [Cu(DMSO)2(μ2-NC)4PtCl2]·2H2O (8) [Cu(DMF)2(μ2-NC)4PtBr2] (9) [Cu(DMF)2(μ2-NC)4PtCl2] (10) [Cu(Py)2(μ2-NC)4PtBr2] (11) [Cu(Py)2(μ2-NC)4PtCl2] (12) [Cu(NH3)2{(μ2-NC)2PtBr(NH3) (CN)2}2]·2H2O (13) [Cu(NH3)3(μ-OH)(η2-CN)(μ2-NC) PtCl(CN)2] (14) [Cu(NH3)]2[Pt(CN)6]61

2231 2237 2163 2223

Raman

max visible reflectance (nm)

201 328 199 (vs)

Figure S9 Figure S9

601 ± 5 510 ± 4

2248 (sh), 2227 (m), 2194 (w)

199 327 201 202

2227

2198 (m), 2239 (s)

335

527 ± 10

2222 2227 2222 2223 2223 (w), 2184 (w), 2173 (w), 2169 (m), 2126 (m) 2172 (m)

2221 (vs), 2195 (vs) 2237 (vs), 2196 (vs) 2232, 2193 2235, 2198 2218 (m), 2198 (m), 2182 (m), 2153 (br, m) 2199 (s), 2192 (m), 2155 (w), 2135 (w) 2223, 2210

200 328 199 328 231 (m)

590 512 530 483

(vs), 2191 (w) (vs), 2194 (w) (m) (vs), 2180 (w)

2195

2195, 2182 2199, 2187 2188 (sh), 2180 (s), 2169 (s), 2154 (sh) 2247 (m), 2232 (m) 2255, 2239

M−X absorption (cm−1) Raman

(vs) (vs) (vs) (vs)

621 ± 3

± ± ± ±

6 (br) 10 (br) 3 5

327 (w)

Figure 12. (a) Ladder structure of 13. (b) Hydrogen-bonding interactions, with a view of two layers, half of a ladder in each case. Color scheme: platinum, gray; bromine, violet; carbon, black; nitrogen, blue; copper, bronze; oxygen, red; hydrogen, white.

ladders into 2-D sheets, with ladders linked via the interstitial H2O units. The Pt−Br bonds all face “down” on one side of the ladder and face “up” on the other side (Figure 12b). Exposure of [Cu(H2O)2(μ2-NC)4PtCl2] (2) to concentrated aqueous NH3 in a sealed vial resulted in the condensation of NH3, dissolution of 2, and the formation of blue plate crystals of [Cu(NH3)3(μ-OH)(η2-CN)(μ2-NC)PtCl(CN)2] (14) upon evaporation (selected bond lengths are given in Table 5). The octahedral Pt(IV) center has trans Cl− and OH− ligands in the axial positions; the [PtCl(μ−OH) (CN)4]2− complex anion has been previously reported, where addition of aqueous NH3 to a solution of [Pt(CN)4]2− and perchloric acid in water resulted in the formation of [nBu4N]2[PtCl(OH)(CN)4].62 Substitution of only one halogen occurred in the formation of 14, as it did in the formation of 13, which is likely due to bromide and chloride being strongly trans directing.

Table 4. Selected Bond Distances (Å) in [Cu(NH3)2{(μ2NC)2PtBr(NH3)(CN)2}2]·2H2O (13) bond

distance

Pt(1)−C(1) Pt(1)−C(2) Pt(1)−C(3) Pt(1)−C(4) C(1)−N(1) C(2)−N(2) C(3)−N(3) C(4)−N(4) Pt(1)−Br(1) Pt(1)−N(5) Cu(1)−N(1) Cu(1)−N(2) Cu(1)−N(6)

2.023(4) 2.019(4) 2.012(4) 2.014(4) 1.130(5) 1.130(6) 1.146(6) 1.131(6) 2.4646(5) 2.074(4) 2.073(4) 2.383(4) 1.980(5) 7878

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ing interactions can be seen between dangling cyanides and ammines. The distance between Cl(1) and N(6) (3.316 Å) is also consistent with the metal-bound chloride acting as a hydrogen bond acceptor.67 There are no chlorine−chlorine interactions (Cl−Cl = 3.894 Å), likely due to the multitude of hydrogen-bonding interactions involving the ammine ligands on the copper.

Table 5. Selected Bond Distances (Å) in [Cu(NH3)3(μOH)(η2-CN)(μ2-NC)PtCl(CN)2] (14) bond

distance

Pt(1)−C(1) Pt(1)−C(2) Pt(1)−C(3) Pt(1)−C(4) Pt(1)−Cl(1) Pt(1)−O(1) Cu(1)−O(1) Cu(1)−N(1) Cu(1)−N(5) Cu(1)−N(6) Cu(1)−N(7)

2.00(2) 2.04(2) 2.03(2) 2.01(2) 2.359(5) 2.09(2) 2.00(2) 2.34(2) 2.01(2) 2.04(2) 2.05(2)

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CONCLUSION In this study, the structures of the coordination polymers [Cu(H2O)2(μ2-NC)4PtX2], where X = Br (1), Cl (2), have been determined, their structural changes upon dehydration elucidated, and their reaction with selected N- and O-donor analytes examined for their ability to act as vapochromic sensors. These [PtX2(CN)4]2−-based materials arrange preferentially in two-dimensional nets through Pt−CN−Cu bridging cyanide linkages, and the sheets further align via axial halogen interactions. While evidence of X···X interactions was observed in the parent materials 1 and 2, the formation of X···X interactions was much more prevalent in most analyte adducts. The identity of the halogen had no significant effect on the overall structures of the materials, except in the case of the ammonia adducts. Exposure of both 1 and 2 to ammonium hydroxide resulted in the replacement of one halogen; in the case of 1, ammonia added in a trans fashion to the bromide, whereas in 2 the trans hydroxide was favored. Overall, the presence of a Pt-based absorption band in the visible region of [Cu(H2O)2(μ2-NC)4PtBr2] resulted in greater color changes in comparison to those for the chlorine-containing coordination polymers. On the basis of this assessment, the materials could be further investigated as chemical dosimeters for a range of Oand N-donor analytes.

The Cu(II) center in 14 is a five-coordinate square-based pyramid with one bridging cyanide in the axial position. In the related Cu(NH3)4[Pt(CN)4] compound, the Cu(II) center is also in a square-pyramidal geometry, with the four ammonia ligands in the base and an apical bent cyanide bridge from the [Pt(CN)4]2− anion.63 A long interaction between Cu(II) and the π bond of a CN(2) (d(Cu−C) = 2.934 Å and d(Cu−N) = 3.249 Å; therefore, d(Cu−CN) = 3.04 Å) in 14 could be considered as a weak η2-coordinated cyanide, which has been previously documented, although with much shorter distances (d(Cu−C) = 2.252 Å and d(Cu−N) = 2.465 Å).64,65 The coordination polymer 14 propagates in a zigzag fashion along the b axis through alternating cyanide and hydroxide bridges between the Pt(IV) and Cu(II) centers (Figure 13).

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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.7b00596. Crystallographic data, powder X-ray diffractograms of 4, 5, and 7−12, and thermogravimetric analyses of 1, 2, and 7−12 (PDF) Raw xy data (ZIP) Accession Codes

CCDC 1554361−1554366 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

Figure 13. Zigzag chain of 14 with weak interactions shown as dashed lines. Color scheme: platinum, gray; chlorine, lime green; carbon, black; nitrogen, blue; copper, bronze; oxygen, red; hydrogen, white.

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There are short contacts between the unbound cyanides with the Cu−OH and Cu−NH3 ligands, which result in a complex 3-D network. A short distance between a nonbridging Pt−CN unit and the bridging hydroxide, N(3)−O(1) = 3.094 Å, suggests a hydrogen-bonding interaction similar to that between the previously reported nonbridging thiocyanate and a bridging hydroxide (N−O = 3.015 Å) in [Cu 2 (μOH)2(tmeda)2Pt(SCN)4].66 Additional weak hydrogen-bond-

AUTHOR INFORMATION

Corresponding Author

*E-mail for D.B.L.: dleznoff@sfu.ca. ORCID

Daniel B. Leznoff: 0000-0002-3426-2848 Notes

The authors declare no competing financial interest. 7879

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ACKNOWLEDGMENTS The authors thank the Natural Sciences and Engineering Research Council (NSERC) of Canada for financial support via Discovery and Strategic grants (D.B.L.).

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