Thermal Expansion Behavior of M^I[AuX₂(CN)₂]‑Based Coordination Polymers (M = Ag, Cu; X = CN, Cl, Br)

Two sets of <i>trans-</i>[AuX₂(CN)₂]⁻-based coordination polymer materialsM­[AuX₂(CN)₂] (M = Ag; X = Cl, Br or M = Cu; X = Br) and M­[Au­(CN)₄] (M = Ag, Cu)were synthesized and structurally characterized and their dielectric constants and thermal expansion behavior explored. The M­[AuX₂(CN)₂] series crystallized in a tightly packed, mineral-like structure featuring 1-D <i>trans-</i>[AuX₂(CN)₂]⁻-bridged chains interconnected via a series of intermolecular Au···X and M···X (M = Ag, Cu) interactions. The M­[Au­(CN)₄] series adopted a 2-fold interpenetrated 3-D cyano-bound framework lacking any weak intermolecular interactions. Despite the tight packing and the presence of intermolecular interactions, these materials exhibited decreased thermal stability over unbound <i>trans-</i>[AuX₂(CN)₂]⁻ in [^<i>n</i>Bu₄N]­[AuX₂(CN)₂]. A significant dielectric constant of up to ε_r = 36 for Ag­[AuCl₂(CN)₂] (1 kHz) and a lower ε_r = 9.6 (1 kHz) for Ag­[Au­(CN)₄] were measured and interpreted in terms of their structures and composition. A systematic analysis of the thermal expansion properties of the M­[AuX₂(CN)₂] series revealed a negative thermal expansion (NTE) component along the cyano-bridged chains with a thermal expansion coefficient (α_CN) of −13.7(11), −14.3(5), and −11.36(18) ppm·K^–1 for Ag­[AuCl₂(CN)₂], Ag­[AuBr₂(CN)₂], and Cu­[AuBr₂(CN)₂], respectively. The Au···X and Ag···X interactions affect the thermal expansion similarly to metallophilic Au···Au interactions in M­[Au­(CN)₂] and AuCN; replacing X = Cl with the larger Br atoms has a less significant effect. A similar analysis for the M­[Au­(CN)₄] series (where the volume thermal expansion coefficient, α_V, is 41(3) and 68.7(19) ppm·K^–1 for M = Ag, Cu, respectively) underscored the significance of the effect of the atomic radius on the flexibility of the framework and, thus, the thermal expansion properties

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

Two vapochromic coordination polymers Cu­[AuX₂(CN)₂]₂ (X = Cl, <b>1</b>; X = Br, <b>2</b>) 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 analysis. Single-crystal structures of Cu­(analyte)₄[AuX₂(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 O-bound to the Cu­(II) centers while axially bound [AuX₂(CN)₂]⁻ units bridged these Cu­(II) centers, while Cu­(glycol)₄[AuBr₂(CN)₂]₂ is molecular, with monodentate glycol units. The structure of Cu₂(OH₂)₄[AuCl₂(CN)₂]₄·4dioxane is a 2-D coordination polymer network with H₂O-bridged Cu­(II) centers and dioxane units hydrogen bonded between the 2-D sheets. The intense Raman <i>v</i>_CN stretches for <b>1</b>, <b>2</b>, and their adducts form distinct, signature patterns. These “antenna” Raman <i>v</i>_CN stretches are an effective means for sensing VOCs, and their characteristic patterns can be used to identify the VOC being detected

Thermal Expansion Behavior of M^I[AuX₂(CN)₂]‑Based Coordination Polymers (M = Ag, Cu; X = CN, Cl, Br)

Two sets of <i>trans-</i>[AuX₂(CN)₂]⁻-based coordination polymer materialsM­[AuX₂(CN)₂] (M = Ag; X = Cl, Br or M = Cu; X = Br) and M­[Au­(CN)₄] (M = Ag, Cu)were synthesized and structurally characterized and their dielectric constants and thermal expansion behavior explored. The M­[AuX₂(CN)₂] series crystallized in a tightly packed, mineral-like structure featuring 1-D <i>trans-</i>[AuX₂(CN)₂]⁻-bridged chains interconnected via a series of intermolecular Au···X and M···X (M = Ag, Cu) interactions. The M­[Au­(CN)₄] series adopted a 2-fold interpenetrated 3-D cyano-bound framework lacking any weak intermolecular interactions. Despite the tight packing and the presence of intermolecular interactions, these materials exhibited decreased thermal stability over unbound <i>trans-</i>[AuX₂(CN)₂]⁻ in [^<i>n</i>Bu₄N]­[AuX₂(CN)₂]. A significant dielectric constant of up to ε_r = 36 for Ag­[AuCl₂(CN)₂] (1 kHz) and a lower ε_r = 9.6 (1 kHz) for Ag­[Au­(CN)₄] were measured and interpreted in terms of their structures and composition. A systematic analysis of the thermal expansion properties of the M­[AuX₂(CN)₂] series revealed a negative thermal expansion (NTE) component along the cyano-bridged chains with a thermal expansion coefficient (α_CN) of −13.7(11), −14.3(5), and −11.36(18) ppm·K^–1 for Ag­[AuCl₂(CN)₂], Ag­[AuBr₂(CN)₂], and Cu­[AuBr₂(CN)₂], respectively. The Au···X and Ag···X interactions affect the thermal expansion similarly to metallophilic Au···Au interactions in M­[Au­(CN)₂] and AuCN; replacing X = Cl with the larger Br atoms has a less significant effect. A similar analysis for the M­[Au­(CN)₄] series (where the volume thermal expansion coefficient, α_V, is 41(3) and 68.7(19) ppm·K^–1 for M = Ag, Cu, respectively) underscored the significance of the effect of the atomic radius on the flexibility of the framework and, thus, the thermal expansion properties

Color-Tunable and White-Light Luminescence in Lanthanide–Dicyanoaurate Coordination Polymers

The new lanthanide–dicyanoaurate coordination polymers [^<i>n</i>Bu₄N]₂­[Ln­(NO₃)₄­Au­(CN)₂] (Ln = Sm, Dy) and Sm­[Au­(CN)₂]₃·3H₂O were prepared and structurally characterized and their luminescence spectra described. The emissions of solid-solutions of [^<i>n</i>Bu₄N]₂­[Ln­(NO₃)₄­Au­(CN)₂] (Ln = Ce, Sm, Eu, Tb, and Dy) were explored with an emphasis on their capacity for luminescent color tuning and white-light emission via the selection of composition, excitation wavelength, and temperature. Specifically, the binary solid-solutions [^<i>n</i>Bu₄N]₂­[Ce_0.4Dy_0.6(NO₃)₄­Au­(CN)₂] and [^<i>n</i>Bu₄N]₂­[Sm_0.75Tb_0.25(NO₃)₄­Au­(CN)₂], and the ternary solid-solutions [^<i>n</i>Bu₄N]₂­[Ce_0.2Sm_0.6­Tb_0.2(NO₃)₄­Au­(CN)₂] and [^<i>n</i>Bu₄N]₂­[Ce_0.33Eu_0.17­Tb_0.5(NO₃)₄­Au­(CN)₂], were prepared and examined in terms of suitability for color-tuning capacity. These results showcase that the emission from the [^<i>n</i>Bu₄N]₂­[Ln­(NO₃)₄­Au­(CN)₂] framework has the capacity to be tuned to extremes corresponding to deep reds (CIE coordinates 0.65, 0.35), greens (0.28, 0.63), and deep blue/violet (0.16, 0.06) as well as white (0.31, 0.33). Conversely, the emission of the Sm­[Au­(CN)₂]₃·3H₂O framework, when doped with the green phosphor Tb­(III), changes only slightly because of the predominantly Au­(I)-based emission and Sm­(III) → Au­(I) energy transfer

Copper(II) Dihalotetracyanoplatinate(IV) Coordination Polymers and Their Vapochromic Behavior

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, <i>N,N</i>-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

Structural Design Parameters for Highly Birefringent Coordination Polymers

A series of coordination polymer materials incorporating the highly anisotropic 2-(2-pyridyl)-1,10-phenanthroline (phenpy) building block have been synthesized and structurally characterized. M­(phenpy)­[Au­(CN)₂]₂ (M = Cd, Mn) are isostructural and form a 1-D chain through bridging [Au­(CN)₂]⁻ units and extend into a 2-D sheet through aurophilic interactions. M­(phenpy)­(H₂O)­[Au­(CN)₂]₂·2H₂O (M = Cd, Mn, and Zn) are also isostructural but differ from the first set via the inclusion of a water molecule into the coordination sphere, resulting in a 1-D topology through aurophilic interactions. In­(phenpy)­(Cl)₂[Au­(CN)₂]·0.5H₂O forms a dimer through bridging chlorides and contains a free [Au­(CN)₂]⁻ unit. In the plane of the primary crystal growth direction, the birefringence values (Δ<i>n</i>) of 0.37(2) (Cd­(phenpy)­[Au­(CN)₂]₂), 0.50(3) (In­(phenpy)­(Cl)₂[Au­(CN)₂]·0.5H₂O), 0.56(3) and 0.59(6) (M­(phenpy)­(H₂O)­[Au­(CN)₂]₂·2H₂O M = Cd and Zn, respectively) were determined. β, a structural parameter defined by phenpy units rotated in the <i>A</i>–<i>C</i> plane relative to the light propagation (<i>C</i>) direction, was found to correlate to Δ<i>n</i> magnitudes. The addition of a carbon–carbon double bond to terpy has increased the molecular polarizability anisotropy of the building block, and all structures have reduced deviation from planarity in comparison to terpy and terpy derivative structures, leading to these higher Δ<i>n</i> values, which are among the highest reported for crystalline solids

An Extremely Air-Stable 19π Porphyrinoid

A one-electron reduced species of a cationic phosphorus­(V) tetraazaporphyrin complex has been isolated as an air-stable solid. Cyclic voltammetry and magnetic measurements showed the species to be a neutral π radical, and the solid state structure was elucidated by single crystal X-ray diffraction analysis. Magnetic circular dichroism spectroscopy and theoretical calculations also support a 19π electron conjugated electronic circuit

Heterobimetallic Coordination Polymers Based on the [Pt(SCN)₄]^2– and [Pt(SeCN)₄]^2– Building Blocks

New complexes and the first coordination polymers containing [Pt­(SCN)₄]^2– of the type [M­(L)_<i>x</i>]­[Pt­(SCN)₄] (where L = 2,2′-bipyridine (bipy), <i>x</i> = 2, M = Co­(II), Ni­(II), Cu­(II); L = ethylenediamine (en), <i>x</i> = 2, M = Ni­(II), Cu­(II); L = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine (tmeda), <i>x</i> = 1, M = Cu­(II); L = 2,2′;6′,2″-terpyridine (terpy), <i>x</i> = 1, M = Mn­(II), Co­(II); L = 1,10-phenanthroline (phen), <i>x</i> = 2, M = Pb­(II)) were prepared by reacting the appropriate metal–ligand cations with K₂[Pt­(SCN)₄] and structurally characterized. [M­(bipy)₂Pt­(SCN)₄]₂·2MeOH (M = Co (<b>1</b>), Cu (<b>4</b>)) consist of supramolecular tetranuclear distorted squares containing two [M­(bipy)₂]²⁺ and two [Pt­(SCN)₄]²⁺ units. [Cu­(bipy)₂(NCS)]₂[Pt­(SCN)₄] (<b>6</b>) is a double salt of the [Pt­(SCN)₄]^2– anion and two [Cu­(bipy)­(NCS)]⁺ cations. [Cu­(en)₂Pt­(SCN)₄] (<b>7</b>, <b>8</b>) are 1-D coordination polymers that are coordinated in either cis or trans fashion at the [Pt­(SCN)₄]^2– unit, for <b>7</b> and <b>8</b>, respectively. Complexes [Cu­(en)₂Pt­(SeCN)₄] (<b>9</b>) and [Ni­(en)₂Pt­(SCN)₄] (<b>10</b>) are similar to <b>8</b> and <b>7</b>, respectively, but complex <b>9</b> (prepared using (ⁿBu₄N)₂[Pt­(SeCN)₄]) also presents intermolecular Se–Se interactions which resulted in an increased dimensionality. Compounds [M­(terpy)­Pt­(SCN)₄] (M = Mn (<b>11</b>), Co (<b>13</b>)) involve 2-D sheets of [M­(terpy)]²⁺ and [Pt­(SCN)₄]^2– units, whereas [Mn­(terpy)₂]­[Pt­(SCN)₄] (<b>12</b>) is a double salt of one [Mn­(terpy)₂]²⁺ unit and one [Pt­(SCN)₄]^2–. [Cu­(tmeda)­Pt­(SCN)₄] (<b>14</b>) contains a five-coordinate Cu²⁺ metal center coordinated to one tmeda ligand and three different [Pt­(SCN)₄]^2– units, resulting in 2-D sheets. [Pb­(phen)₂Pt­(SCN)₄] (<b>15</b>) contains an 8-coordinate Pb²⁺ metal center coordinated to two phen ligands and four [Pt­(SCN)₄]^2–, generating a 3-D network in the solid state. Structural correlations were established between the ancillary ligand, the choice of metal, the structure of the [Pt­(SCN)₄]^2– building block, and the resulting dimensionality of the coordination polymers

Interpreting Effects of Structure Variations Induced by Temperature and Pressure on Luminescence Spectra of Platinum(II) Bis(dithiocarbamate) Compounds

Luminescence spectra of two square-planar dithiocarbamate complexes of platinum­(II) with different steric bulk, platinum­(II) bis­(dimethyldithiocarbamate) (Pt­(MeDTC)₂) and platinum­(II) bis­(di­(<i>o</i>-pyridyl)­dithiocarbamate) (Pt­(dopDTC)₂), are presented at variable temperature and pressure. The spectra show broad d–d luminescence transitions with maxima at approximately 13500 cm^–1 (740 nm). Variations of the solid-state spectra with temperature and pressure reveal intrinsic differences due to subtle variations of molecular and crystal structures, reported at 100 and 296 K for Pt­(dopDTC)₂. Luminescence maxima of Pt­(MeDTC)₂ shift to higher energy as temperature increases by +320 cm^–1 for an increase by 200 K, mainly caused by a bandwidth increase from 3065 to 4000 cm^–1 on the high-energy side of the band over the same temperature range. Luminescence maxima of Pt­(dopDTC)₂ shift in the opposite direction by −460 cm^–1 for a temperature increase by 200 K. The bandwidth of approximately 2900 cm^–1 does not vary with temperature. Both ground and emitting-state properties and subtle structural differences between the two compounds lead to this different behavior. Luminescence maxima measured at variable pressure show shifts to higher energy by +47 ± 3 and +11 ± 1 cm^–1/kbar, for Pt­(MeDTC)₂ and Pt­(dopDTC)₂, respectively, a surprising difference by a factor of 4. The crystal structures indicate that decreasing intermolecular interactions with increasing pressure are likely to contribute to the exceptionally high shift for Pt­(MeDTC)₂

Interpreting Effects of Structure Variations Induced by Temperature and Pressure on Luminescence Spectra of Platinum(II) Bis(dithiocarbamate) Compounds

Luminescence spectra of two square-planar dithiocarbamate complexes of platinum­(II) with different steric bulk, platinum­(II) bis­(dimethyldithiocarbamate) (Pt­(MeDTC)₂) and platinum­(II) bis­(di­(<i>o</i>-pyridyl)­dithiocarbamate) (Pt­(dopDTC)₂), are presented at variable temperature and pressure. The spectra show broad d–d luminescence transitions with maxima at approximately 13500 cm^–1 (740 nm). Variations of the solid-state spectra with temperature and pressure reveal intrinsic differences due to subtle variations of molecular and crystal structures, reported at 100 and 296 K for Pt­(dopDTC)₂. Luminescence maxima of Pt­(MeDTC)₂ shift to higher energy as temperature increases by +320 cm^–1 for an increase by 200 K, mainly caused by a bandwidth increase from 3065 to 4000 cm^–1 on the high-energy side of the band over the same temperature range. Luminescence maxima of Pt­(dopDTC)₂ shift in the opposite direction by −460 cm^–1 for a temperature increase by 200 K. The bandwidth of approximately 2900 cm^–1 does not vary with temperature. Both ground and emitting-state properties and subtle structural differences between the two compounds lead to this different behavior. Luminescence maxima measured at variable pressure show shifts to higher energy by +47 ± 3 and +11 ± 1 cm^–1/kbar, for Pt­(MeDTC)₂ and Pt­(dopDTC)₂, respectively, a surprising difference by a factor of 4. The crystal structures indicate that decreasing intermolecular interactions with increasing pressure are likely to contribute to the exceptionally high shift for Pt­(MeDTC)₂