Copper(I) cyanide exposed to various liquid or vapor-phase amines (L) at ambient temperature produces a variety of visible photoluminescence colors via reversible formation of amine adducts. The adducts show phase matches to authentic (CuCN)Ln, n = 0.75–2.0, produced by heating CuCN with liquid amine

al., et

Brewster, Timothy P.

Dembo, Matthew D.

Dunaway, Lars E.

Ley, Amanda N.

Pike, Robert D.

English

College of William & Mary: W&M Publish

W&M ScholarWorks Arts & Sciences Articles Arts and Sciences 7-2010 Reversible Luminescent Reaction of Amines with Copper(i) Cyanide Amanda N. Ley Lars E. Dunaway Timothy P. Brewster Matthew D. Dembo et al. See next page for additional authors Follow this and additional works at: https://scholarworks.wm.edu/aspubs  Part of the Chemistry Commons Authors Amanda N. Ley, Lars E. Dunaway, Timothy P. Brewster, Matthew D. Dembo, et al., and Robert D. Pike CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 3.1) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS ARTICLE TYPE www.rsc.org/xxxxxx  |  XXXXXXXX This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00  |  1 Reversible Luminescent Reaction of Amines with Copper(I) Cyanide Amanda N. Ley,a Lars E. Dunaway,a Timothy P. Brewster,a Matthew D. Dembo,a T. David Harris,b François Baril-Robert,c Xiaobo Li,c Howard H. Pattersonc and Robert D. Pike*a Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X First published on the web Xth XXXXXXXXX 200X 5 DOI: 10.1039/b000000x Copper(I) cyanide exposed to various liquid or vapor-phase amines (L) at ambient temperature produces a variety of visible photoluminescence colors via reversible formation of amine adducts. The adducts show phase matches to authentic 10 (CuCN)Ln, n = 0.75–2.0, produced by heating CuCN with liquid amine. One of the significant on-going challenges in chemistry is the specific and convenient detection of compounds of interest in the environment.1 Detection of volatile organic compounds 15 (VOCs) via chemical “sniffing” requires an interaction between the VOC and a detector substrate, resulting in a measureable change. Crystal inclusion of VOCs into various d8 and d10 metal complexes has been found to affect intermetallic or other weak interactions, yielding visible color 20 changes.2 In contrast, direct and reversible VOC-metal bonding is very unusual.3 Bonding of various nucleophiles to metal centers can serve to modulate substrate photophysics, leading to a wider variety of responses. Herein we report that reversible surface bonding of amines to CuCN gives rise to a 25 remarkable range of visible photoluminescent responses.  We have recently reported the structures and luminescence behavior of copper(I) cyanide networks with bridging diamine ligands.4 Luminescence emission of CuCN-amine adducts occurs in the visible region, representing a bathochromic shift 30 from the 392 nm emission of CuCN. A DFT examination of [Cun(CN)n+1]– polymeric chains (as models for the infinite chains found in CuCN) showed that the favored excitations are of -symmetry, corresponding roughly to dCu/CN → pCu/*CN.5 Evidence was found for a low-energy triplet 35 excited state with bent geometry at copper. Since bending at copper is an outcome of ligand coordination, this finding is consistent with the lower energy emission associated with CuCN-amine complexes compared to that of CuCN itself.4a    The observation that CuCN luminescence wavelength is 40 modulated by various incoming ligands suggests that this system might provide the foundation for an amine vapor-sensing device.1 We have now found that direct addition of amine (L) liquid or diffusion of amine vapor to solid CuCN at room temperature produces a variety of visible colored 45 luminescence responses (see Fig. 1, Pipd = piperidine, Cy = cyclohexyl, Morph = morpholine, Pipz = piperazine, Py = pyridine). While CuCN produces barely visible luminescence emission centered at 392 nm,4a CuCN samples exposed to many liquid or vapor amines luminesce at wavelengths shifted 50 well into the visible region.  To probe the nature of the interaction between CuCN and     55      60     Fig 1. Luminescence of CuCN + liquid L under 254 nm light 65 at room temperature. A: Pipd B: N-MePipd, C: N-Et-Pipd, D: N-MePyrrolidine, E: Me2NCy, F: NEt3, G: N-MeMorph, H: N-MePipz, I: N,N'-Me2Pipz, J: Py, K: 2-MePy, L: 3-MePy, M: 4-MePy, N: 2-EtPy, O: 3-EtPy, P: 4-EtPy, Q: 4-tBuPy.  70 the amines, CuCN suspensions in various neat amines were heated at 70 oC.‡ In most cases the CuCN did not dissolve in the amine, transforming directly to the solid (CuCN)Ln complex. Thermogravimetry (TGA) of the (CuCN)Ln products revealed clean, quantitative loss of amine between 25 and 250 75 oC, depending on amine volatility. The following complexes were prepared: L = Py (n = 2, 1a; 0.8, 1b), 2-MePy (n = 1.5, 2a; 1, 2b), 3-MePy (n = 1.5, 3a; 1, 3b), 4-MePy (n = 1.5, 4), 2-EtPy (n = 1, 5), 3-EtPy (n = 1.5, 6a; 1, 6b), 4-EtPy (n = 1, 7), 4-tBuPy (n = 1.5, 8), Pipd (n = 1.25, 9), N-MePipd (n = 1, 80 10), N-EtPipd (n = 0.75, 11), MeMorph (n = 1, 12), and Me2NCy (n = 1, 13). For those amines that yielded more than one product (1a/b, 2a/b, 3a/b, 6a/b) the more amine-rich species was produced directly, and overnight vacuum treatment converted it cleanly to the less amine-rich species. 85 These conversions are also evident in the TGA traces (see ESI†). Thus in Fig. 2, trace A (2a), reflects the conversion:     90      95     Fig 2. TGA traces, A: 2a, B: 2b, C: CuCN + 2-MePy vapor. 100  2  |  Journal Name, [year], [vol], 00–00 This journal is © The Royal Society of Chemistry [year] 2a → 2b → (CuCN)2(2-MePy) → CuCN. Trace B (2b) shows reactions identical to steps 2 and 3 of trace A.  In several cases, X-ray structure determinations were carried out on crystals formed during the neat reactions. All of the new CuCN-amine X-ray structures (2b, 6a, 8, 9, 12, and 5 13, see Fig. 3), as well as those already known (1a, 2a, 4, and  (CuCN)L, L = NHEt2, NEt3, quinoline, 3- and 4-acetylPy, and 2,4,6-collidene),6 reveal CuCN chains decorated with 1–2 amine ligands per Cu site. In N-MeMorph complex 12, additional long Cu…O (2.537(3) Å) interactions were found, 10 linking the chains into sheets. In the CuCN chains cyano C/N atom positions are disordered in most cases. The cyano–Cu–cyano angles and Cu–amine bond lengths are relatively large (128.6–154.2o, 2.04–2.25 Å for 3-coordinate Cu and 120.7–139.5o, 2.09–2.26 Å for 4-coordinate Cu). The latter 15 observations are suggestive of relatively weak Cu–amine bonding. In each (CuCN)Ln structure, all amine molecules are bonded to copper, with one exception. Complex 8 proved to be (CuCN)(4-tBuPy)•1/2(4-tBuPy), having a half molecule of free 4-tBuPy in the asymmetric unit. Powder diffraction 20 patterns for neat-reaction bulk products 1a, 2a, 4, 8, 9, 12, and 13 showed good agreement to those calculated from the corresponding X-ray structures (see ESI†), while those of 2b and 6a did not, possibly reflecting polymorphism.  25      30      35      40      45 Fig 3. X-ray structures of 2b, 6a, 8, 9, 12, and 13. Copper and cyano atoms shown as spheres. Amine ligands shown as wireframe. Orange = Cu, grey = C, blue = N, red = O. Hydrogen atoms omitted.  50  Importantly, the luminescence behavior of these authentic (CuCN)Ln samples was found to be analogous in color to that observed in amine-exposed CuCN (see Fig. 1 above and S1, ESI†). X-ray powder patterns were collected for samples of CuCN that were exposed to amine vapor or liquid at ambient 55 temperature. Fig. 4 shows the resulting patterns for CuCN exposed to Py vapor (A), CuCN (B), and (CuCN)5Py4 (1b, C). It can readily be seen that CuCN exposed to Py shows traces    60      65      70 Fig 4. X-ray powder traces, A: CuCN + Py vapor, B: CuCN, C: 1b.  of the 1b phase, while remaining mostly CuCN. Under these mild conditions, it seems reasonable to infer that 1b is formed 75 through partial surface reaction of amine with the CuCN particles whose bulk remains unaffected. TGA further reveals that the amine-exposed CuCN samples indeed lose amine at the same temperature as do the authentic (CuCN)Ln compounds. Thus, as illustrated in Fig. 2 above, while 80 (CuCN)Ln samples show volatilization of 40–60% of their mass (A and B), the amine-exposed samples lose less than 3% (C). Finally, it is noteworthy that the liquid- or vapor-exposed samples quickly lose their visible luminescence when placed under vacuum, in stark contrast to the authentic (CuCN)Ln 85 compounds which only partially lose amine over a period of weeks under vacuum (although 1a, 2a, 3a and 6a transform over a few hours to 1b, 2b, 3b and 6b, see above). The overall behavior of the CuCN-amine system is summarized in Scheme 1. The top pathway describes the essentially irreversible 90 formation of authentic (CuCN)Ln via the reaction of CuCN in neat heated amine. The bottom pathway traces the reversible surface formation of CuCN-amine adducts through ambient temperature exposure of CuCN to amine liquid or vapor.    95      100      105    The aromatic amine complexes of CuCN luminesce upon either long (365 nm) or short (254 nm) wavelength excitation, while the aliphatic amine adducts luminesce only upon short 110 wavelength excitation. Initial studies of (CuCN)Ln photophysics reveal high energy (HE) blue emission, often accompanied by a less intense low energy (LE) band. For example, two CuCN complexes have been found with 2-MePy: yellow-emitting 2a and blue-emitting 2b (Note that 115 evidence of both the yellow and blue emission is evident in  This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00  |  3 Fig. 1K.) In Fig. 5 the 77 K emission spectra of 2a show both HE and LE bands, but 2b exhibits only a HE band. Preliminary studies show emission lifetimes in the microsecond range and quantum yields in the range of 0.5. Importantly, with regard to the luminescence sensor potential 5 of CuCN for amines, we note the diverse emission colors for the CuCN-adducts of chemically similar amines: compare e.g. Pipd (Fig. 1A, blue-green), N-MePipd (Fig. 1B, yellow), and N-EtPipd (Fig. 1C, pink) or Py (Fig. 1J, dark), 2-MePy (Fig. 1K, blue/yellow), 3-MePy (Fig. 1L, green), 4-MePy (Fig. 1M, 10 dark), 2-EtPy (Fig. 1N, blue), 3-EtPy (Fig. 1O, yellow), 4-EtPy (Fig. 1P, dark), and 4-tBuPy (Fig. 1Q, orange).      15      20    Fig 5. Luminescence spectra (77 K) of 2a, A–B: excitation (emission  = 458, 561 nm, respectively), C–F: emission 25 (excitation  = 315, 340, 365, 420 nm, respectively) and 2b, G: excitation (emission  = 452 nm), H–I: emission (excitation  = 329, 356 nm, respectively).   In conclusion, we report unique and remarkable ligand-30 dependent luminescence behavior upon the fully-reversible reaction of a number of amines with CuCN. The ligand-induced CuCN emission shift from the UV into the visible region offers the potential for a sniffing detection system for amines or other nucleophilic VOCs. Emission color 35 differences resulting from very similar amines are noted in some cases, offering the potential for independent monitoring of multiple chemically related analytes.   We gratefully acknowledge the National Science Foundation (CHE-0848109, RDP), (CHE-0351877, HHP), 40 (CHE-0443345, X-ray equipment), the Petroleum Research Fund (RDP, 44891-B3), the Howard Hughes Medical Institute. We thank Prof. Jeffrey R. Long (Univ. Calif. Berkeley) for generously allowing use of facilities. Notes and references 45 a Department of Chemistry, College of William and Mary, Williamsburg, VA 23187-8795. Fax: (757)221-2715; Tel: (757)221-2555; E-mail: rdpike@wm.edu b Department of Chemistry, University of California, Berkeley, CA 94720-1460 50 c Department of Chemistry, University of Maine, Orono, ME 04469-5706 † Electronic Supplementary Information (ESI) available: [(1) synthetic details, yields, and analyses (2) crystal structure determination tables. (3) TGA traces for all (CuCN)Ln compounds, (4) experimental and calculated X-ray powder patterns for all (CuCN)Ln. (5) X-ray Powder Patterns for 55 CuCN + L experiments. (6) luminescence photograph and spectra for authentic (CuCN)Ln.]. See DOI: XX.XXXX/XXXXXXX ‡ Representative Synthesis: 1a. Copper(I) cyanide (0.150 g, 1.67 mmol) was suspended in about 5 mL Py in a sealed tube under Ar. The mixture was heated to 70 oC in an oil bath overnight without stirring. After 60 cooling, the suspended solid was collected by means of filtration, washed with diethyl ether, and then air dried for 15 min. A yellow powder was isolated (0.393 g, 1.59 mmol, 94.7%). See ESI for additional synthesis and analytical data. General Method for Vapor Diffusion Reactions. 80 mg CuCN powder or pressed pellet (prepared using an IR press) in a 10 65 mL beaker was placed in a small jar containing about 1-2 mL of liquid amine. After a few min. the CuCN luminescence reflected formation of the surface CuCN-amine phase. § Crystal Data: All crystals from neat reactions, data collection: T = 100(2) K (except 8),  = 1.54178 Å. 2b: C7H7CuN2, M 182.69, 70 monoclinic, P21/c, a 10.0593(2), b 8.7276(1), c 8.9901(2) Å,  108.709(1)o, V 747.57(2) Å3, Z 4, 7274 refl., 1273 independ., Rint = 0.0362, R1 = 0.0276 (I > 2(I)), wR2 = 0.0791 (all data), CCDC 743728. 6a: C23H27Cu2N5, M 500.58, orthorhombic, P212121, a 8.6557(2), b 16.5520(4), c 17.2948(4) Å, V 2477.8(1) Å3, Z 4, 26626 refl., 4362 75 independ., Rint = 0.0362, R1 = 0.0217 (I > 2(I)), wR2 = 0.0574 (all data), Flack = 0.00(2), CCDC 743729. 8: C29H39Cu2N5, M 584.73, orthorhombic, Fdd2, a 14.9500(2), b 35.3082(4), c 11.6471(1) Å, V 6148.0(1) Å3, Z 8, T = 296(2) K, 16270 refl., 2594 independ., Rint = 0.0307, R1 = 0.0311 (I > 2(I)), wR2 = 0.0934 (all data), Flack = 0.02(5), 80 CCDC 743727. 9: C23H44Cu3N7, M 609.27, monoclinic, C2/c, a 26.3331(2), b 5.2292(1), c 23.7064(2) Å,  122.6785(3)o, V 2747.68(6) Å3, Z 4, 14544 refl., 2413 independ., Rint = 0.0294, R1 = 0.0212 (I > 2(I)), wR2 = 0.0594 (all data), CCDC 743724. 12: C6H11CuN2O, M 190.71, orthorhombic, Ama2, a 9.7119(2), b 12.2714(3), c 6.2836(2) Å, V 85 748.87(3) Å3, Z 4, 3902 refl., 661 independ., Rint = 0.0379, R1 = 0.0175 (I > 2(I)), wR2 = 0.0406 (all data), Flack = 0.03(4), CCDC 743726. 13: C9H17CuN2, M 216.79, orthorhombic, P212121, a 6.3145(1), b 9.3450(1), c 17.4458(3) Å, V 1029.46(3) Å3, Z 4, 10747 refl., 1814 independ., Rint = 0.0285, R1 = 0.0164 (I > 2(I)), wR2 = 0.0440 (all data), Flack = 0.53(2), 90 CCDC 743725. 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Reversible Luminescent Reaction of Amines with Copper(i) Cyanide

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Reversible Luminescent Reaction of Amines with Copper(i) Cyanide

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