Raman Detected Sensing of Volatile Organic Compounds by Vapochromic Cu[AuX₂(CN)₂]₂ (X = Cl, Br) Coordination Polymer Materials

Abstract

Two vapochromic coordination polymers Cu-[AuX 2 (CN) 2 ] 2 (X = Cl, 1; X = Br, 2) were prepared and spectroscopically characterized. Exposure of these solid materials to the volatile organic compounds dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, 1,4-dioxane, and ethylene glycol (glycol) resulted in distinct color, and IR and Raman changes. The thermal stability of the analyte-bound materials was assessed by thermogravimetric a n a l y s i s . S i n g l e -c r y s t a l s t r u c t u r e s o f C u -(analyte) 4 [AuX 2 (CN) 2 ] 2 (analyte = DMF, DMSO; X = Cl, Br) revealed an isostructural set of 1-D coordination polymer chains, where the analyte molecules were equatorially Obound to the Cu(II) centers while axially bound [AuX 2 (CN) 2 ] − units bridged these Cu(II) centers, while Cu(glycol) 4 [AuBr 2 (CN) 2 ] 2 is molecular, with monodentate glycol units. The structure of Cu 2 (OH 2 ) 4 [AuCl 2 (CN) 2 ] 4 ·4dioxane is a 2-D coordination polymer network with H 2 O-bridged Cu(II) centers and dioxane units hydrogen bonded between the 2-D sheets. The intense Raman v CN stretches for 1, 2, and their adducts form distinct, signature patterns. These "antenna" Raman v CN stretches are an effective means for sensing VOCs, and their characteristic patterns can be used to identify the VOC being detected. ■ INTRODUCTIONOver the past decade, coordination polymers have been receiving increased attention due to the ability to tailor them toward various properties such as magnetism, 1−6 porosity, 7−12 luminescence, 13−18 and vapochromism 19−25 through the strategic choice of metal centers and bridging and ancillary ligands. 26−31 More recently, coordination polymers have been explored as solid-state sensors for the detection of explosive materials 32−34 and volatile organic compounds (VOCs) in industrial settings. 16,24,25,35 Such devices have important applications in defense, industry, and safety and security. 36,37 Coordination polymers such as the Co 2+ /[Re 6 Q 8 (CN) 6 ] 4− -based (Q = S, Se) Prussian Blue analogues 19 can act as vapochromic sensors due to their highly visible color change upon exposure to certain VOCs. The porous metal−organic framework [(WS 4 Cu 4 )I 2 (dptz) 3 ]·3DMF (dptz = 3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine; DMF = dimethylformamide) exhibits solvatochromism when immersed in solvents such as MeCN and CHCl 3 , lending it the potential to sense the presence of these small molecules in solution. 38 In another example, cyanoaurate-based coordination polymers have demonstrated high potential as VOC sensors. For example, the M[Au(CN) 2 ] 2 (M = Co, Cu) series exhibits stark color changes when exposed to a range of VOCs, 24,25 whereas the four polymorphs of Zn[Au(CN) 2 ] 2 display a significant change in luminescence in the presence of ammonia vapor. 16 Although not substantially porous, these materials bind and detect certain vapor-phase molecules due to the flexible nature of their coordination polymer frameworks. 39 Gold-containing materials in general have also been extensively employe...

Zinc Tetracyanoplatinate: A Reversible Luminescence‐Based Ammonia Sensor

“…Taking the Raman and emission data together, there are four distinct species observed in the degassing of an ammonia‐saturated sample of ZnPt(CN) 4 (Scheme ): a saturated species termed Zn(NH 3 ) 2.5+ y Pt(CN) 4 , the blue‐emitting Zn(NH 3 ) 2.5 Pt(CN) 4 , the cyan‐emitting Zn(NH 3 ) x Pt(CN) 4 (that is not observable by Raman), and ammonia‐free ZnPt(CN) 4 . It is worth noting that this illustrates the utility of the ν CN bands in cyanometallate‐based coordination polymers to monitor the coordination of ligands …”

“…Cyanometallate‐containing coordination polymers make excellent candidates for chemical vapor sensors, since they are robust and there are many examples of vapochromic and vapoluminescent species . Many of these utilize cyanometallates with close d 10 –d 10 or d 8 –d 8 metal distances (especially between Au I or Pt II centers)—referred to as being metallophilic—since such materials often display emissive behavior .…”

Synthesis and Structure of (4Fluorobenzyl)triphenylphosphonium Dicyanodihaloaurates [Ph3PCH2C6H4F-4][Au(CN)2Hlg2]

“…Complexes of metal dicyanides can be used in the preparation of semiconductor, optically and magnetically active materials [1][2][3][4][5][6][7], drugs-metabolites based on Au(I) [8], and luminescent substances [4,[9][10][11][12]. Complexes of dicyanodihalogenoaurates with various cations, which also exhibit similar properties [13][14][15], are less studied. Several Au(I) cyanide complexes [16,17] and Au(III) cyanodihalide complexes with ammonium cations [18][19][20][21] are known; information on [Cat] + [Au(CN) 2 Hlg 2 ]complexes with organoelement cations is present only in two papers [22,23].…”

Reversible Vapochromic Luminescence Accompanied by Planar Half‐Chair Conformational Change of a Propeller‐Shaped Boron β‐Diketiminate Complex

“…PMs which exhibit luminescent chromism in response to exposure to vapors of volatile organic compounds (VOCs), especially, are attractive materials for detecting a small amount of leakage of toxic or explosive gases and for security ink. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] However, these compounds possess potential instability toward the air, moisture, and/or other harsh chemical conditions, and therefore a growing number of studies have recently reported chemically and physically stable PMs. [32,33] Nonporous molecular crystals (NMCs), on the other hand, have no such functional voids in their packing patterns because of the absence of the polymeric or supramolecular structures derived from continuous valence, coordination, or hydrogen bonds.…”

“…The physical properties of PMs depend drastically on the existence and absence, size, and electronic nature of guests. PMs which exhibit luminescent chromism in response to exposure to vapors of volatile organic compounds (VOCs), especially, are attractive materials for detecting a small amount of leakage of toxic or explosive gases and for security ink [17–31] . However, these compounds possess potential instability toward the air, moisture, and/or other harsh chemical conditions, and therefore a growing number of studies have recently reported chemically and physically stable PMs [32,33] …”