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Chemical composition is leading among the numerous factors that determine the spin transition properties of coordination compounds. Classic dicyanometallic bridges {M(CN)2}− are commonly used to build Hofmann-like spin-crossover frameworks, but some extended bridges are also synthetically available. In this paper, we describe a successful synthesis of two very similar spin-crossover frameworks that differ in the cyanometallic bridges involved, namely [Fe(etpz)2{Ag(CN)2}2] (1) and {Fe(etpz)2[Ag2(CN)3][Ag(CN)2]} (2) (where etpz = 2-ethylpyrazine). Magnetic and Mössbauer studies demonstrated the occurrence of abrupt one-step high-spin (HS) ↔ low-spin (LS) transitions for both complexes. The spin transition temperatures are T1/2 ↓ = 233 K and T1/2 ↑ = 243 K for 1 and T1/2 ↓ = 188 K and T1/2 ↑ = 191 K for 2 with thermal hysteresis loops of 10 K for 1 and 3 K for 2. The bridging mononuclear [Ag(CN)2]− units and FeII cations assemble to form infinite 2D layers in the structure of 1. Interestingly, compound 2 forms 2D layers of FeII cations bridged by both binuclear [Ag2(CN)3]− and mononuclear [Ag(CN)2]− units. The structures of 1 and 2 comprise different types of intermolecular interactions including Ag⋯Ag and Ag⋯Netpz, which induce the creation of supramolecular 3D frameworks. The synergy between metallophilic interactions and the spin transition is also confirmed by the variation of Ag⋯Ag distances during spin crossover. The characterization of such analogues allowed us to analyze in detail the effect of the cyanometallic bridge on the structure of new frameworks and on the bistability in Hofmann-like complexes. [ABSTRACT FROM AUTHOR]

In the crystal structure of the title compound, [Cu(NO3)2(C3H5N3)4], the CuII atom is situated on an inversion center (Wyckoff position 2c of space group P21/n) and shows an octahedral [N4O2] coordination environment. The axial positions are occupied by O atoms of nitrate anions, while the equatorial positions are taken up by the N atoms of four 3-aminopyrazole ligands. As a result of the tautomerism of the latter, two coordinate with the N¹-atom of 3-aminopyrazole while the other two with the N²-atom. The presence of pyrrole-like N--H groups and amine substituents as donor groups leads to numerous intra- and intermolecular hydrogen-bonding interactions, which were quantified by Hirshfeld surface analysis. [ABSTRACT FROM AUTHOR]

Lead halide hybrid perovskites incorporating chiral organic cations attract considerable attention due to their promising application in multifarious optoelectronic devices. However, the examples of chiral hybrid perovskites are still limited, which greatly impedes their further studies in various optoelectronic fields. Herein, we report on new low-dimensional lead-halide hybrid perovskites incorporating the enantiopure chiral α-amino acid L -proline. Two hybrid perovskites (L -proH)PbBr3·H2O (Pro-PbBr3) and (L -proH)4Pb3Br10·4H2O (Pro-Pb3Br10) have been synthesized by employing different ratios of organic and inorganic precursors. According to structural analysis, the inorganic sublattice of compound Pro-PbBr3 is built of one-dimensional (1D) [PbX3]∞n− lead halide chains, whereas the inorganic sublattice of compound Pro-Pb3Br10 is built upon a rare two-dimensional (2D) [Pb3Br10]∞4n− honeycomb-type inorganic framework. Hirshfeld surface analysis revealed an important role of various hydrogen bonding interactions in providing the binding between organic and inorganic parts of these hybrid perovskites. The optical band gap values of new hybrid perovskites as estimated using the Tauc plot approach are 4.19 eV (Pro-PbBr3) and 4.13 eV (Pro-Pb3Br10). Also, new compounds display low-temperature broadband photoluminescence which can be attributed to the self-trapped excitons. These results show the potential of α-proline for constructing novel and highly demanded chiral hybrid perovskites, which will hold great promise for further optoelectronic applications. [ABSTRACT FROM AUTHOR]

3D hybrid perovskites based upon small organic cations gave start to a new intensively growing class of semiconducting materials. Here we report on the elaboration of quantum dots of a recently emerged new perovskite (AzrH)PbBr3 (AzrH = aziridinium cation). By employing the antisolvent precipitation technique and stabilization with a cationic surfactant we succeeded in obtaining quantum dots that display tunable luminescence. This piece of work shows the perspective of aziridinium-based materials for the elaboration of advanced photonic nanostructures. [ABSTRACT FROM AUTHOR]

Novel chiral hybrid perovskites are highly demanded for various advanced applications such as spintronics, optoelectronics, photovoltaics etc. However, the scope of these new materials is still limited. Herein, we present new 2D hybrid perovskites based upon chiral α-amino acid L -histidine. The generalized formula of these new compounds can be denoted as (L -HisH)2PbBrxI4−x (where L -His = L -histidine; x = 4, 3, 2, 1, 0.4 and 0). All perovskites are characterized by a very similar structural motif that consists of corner-sharing lead halide octahedra arranged in one-layer thin inorganic slabs interleaved by organic layers established by L -histidinium(1+) cations. L -Histidine provides a breaking of spatial parity of these perovskites that results in their non-centrosymmetric crystal structures. These compounds show a multiband absorption up to 590 nm for iodide perovskite. In addition, new compounds display pronounced single-peak photoluminescence, which finely blue shifts upon the gradual substitution of iodine by bromine. New perovskites exhibit excellent thermal stability up to 490 K and 445 K for bromide and iodide compounds, respectively. These results show the ability of L -histidine to produce novel and highly demanded chiral hybrid perovskites. [ABSTRACT FROM AUTHOR]

Spin‐crossover complexes with multistep transitions attract much attention due to their potential applications as multi‐switches and for data storage. A four‐step spin crossover is observed in the new iron(II)‐based cyanometallic guest‐free framework compound Fe(2‐ethoxypyrazine)2{Ag(CN)2}2 during the transition from the low‐spin to the high‐spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct FeII sites which exist due to the packing of the ligand with a bulky substituent. [ABSTRACT FROM AUTHOR]

Reconfigurable radio‐frequency components are in high demand for modern communication systems as they can be involved in multiband and multistandard electronic devices. The key part of such components is an active switching element. This work offers a way to obtain an efficient microwave switch using vanadium dioxide‐poly (methyl methacrylate) composite. Differential scanning calorimetry, SQUID magnetometery, and impedance spectroscopy measurements were used to characterize the phase transition in the proposed composite. Temperature induced metal‐insulator transition occurs at technologically attractive 341 K. The transition leads to a change of microwave transmission trough VO2‐PMMA composite from −4.9 dB for low‐temperature monoclinic form to −5.8 dB for high‐temperature rutile form. This provides an ability to tune the material's transparency in the microwave range, while the shaping polymer matrix provides the proper mechanical processability of the switching element. [ABSTRACT FROM AUTHOR]

This study describes the synthesis of the first aziridinium-based compounds, namely hybrid perovskites (AzrH)PbHal3 (where AzrH = aziridinium, Hal = Cl, Br or I). This highly reactive species was stabilized in 3D lead halide frameworks and was found to be a small enough organic cation to promote the formation of semiconducting organo-inorganic materials. [ABSTRACT FROM AUTHOR]

9-Amino­acridinium chloride N,N-di­methyl­formamide monosolvate, C13H11N2+Cl−·C3H7NO, crystallizes in the monoclinic space group P21/c. The salt was crystallized from N,N-di­methyl­formamide. The asymmetric unit consists of two C13H11N2+Cl− formula units. The 9-amino­acridinium (9-AA) mol­ecules are protonated with the proton on the N atom of the central ring. This N atom is connected to an N,N-di­methyl­formamide mol­ecule by a hydrogen bond. The H atoms of the amino groups create short contacts with two chloride ions. The 9-AA cations in adjacent layers are oriented in an anti­parallel manner. The mol­ecules are linked via a network of multidirectional π–π inter­actions between the 9-AA rings, and the whole lattice is additionally stabilized by electrostatic inter­actions between ions. [ABSTRACT FROM AUTHOR]

Chiral hybrid organic–inorganic perovskites (HOIPs) attract attention due to their potential for application in optoelectronic, spintronic and photovoltaic devices. However, to this day the range of available chiral HOIPs is still scarce. In this context, we synthesized and thoroughly characterized two pairs of enantiomeric HOIPs incorporating enantiopure α-alanine, the simplest chiral amino acid: (AlaH)PbX3 (Ala = R-alanine or S-alanine, X = Br or I). Single-crystal XRD measurements revealed an unusual 2D anionic motif, which consists of haloplumbate octahedra bonded together in an edge-sharing manner along the c axis and in a corner-sharing manner along the b axis. Four compounds undergo melting/crystallization at unusually low temperatures. New compounds also display photoluminescence in the visible range: 380–640 nm (X = Br) and 480–640 nm (X = I). Electronic spectroscopy reveals an optical response typical for semiconductive materials with optical band gaps of 3.12 eV (X = Br) and 2.48 eV (X = I). These results show that the incorporation of simple and easily accessible α-alanine (and other chiral amino acids) as a cationic part is an efficient way for obtaining highly demanding chiral HOIPs. [ABSTRACT FROM AUTHOR]

Hofmann-like cyanometallic complexes represent one of the biggest and well-known classes of FeII spin-crossover compounds. In this paper, we report on the first FeII Hofmann clathrate analogues with unsubstituted 1,2,3-triazole, which exhibit temperature induced spin transition. Two new coordination polymers with the general formula [FeII(1,2,3-triazole)2MII(CN)4] (M = Pt, Pd) undergo abrupt hysteretic spin crossover in the range of 190–225 K as revealed by magnetic susceptibility measurements. Two compounds are isostructural and are built of infinite cyanometallic layers which are supported by 1,2,3-triazole ligands. The thermal hysteresis loop is very stable at different scan rates from 0.5 to 10 K min−1. The compounds display strong thermochromic effect, changing their colour from pink in the low-spin state to white in the high-spin state. Our findings show that 1,2,3-triazole is suitable for elaboration of spin-crossover Hofmann clathrate analogues, and its use instead of more classical azines can advantageously expand this family of complexes. [ABSTRACT FROM AUTHOR]

Spin‐crossover complexes form one of the biggest families of switchable compounds. Here we show a new way to obtain spin‐crossover materials by direct synthesis from metallic iron. Four complexes of FeII with 4‐R‐1,2,4‐triazoles have been synthesized by a direct metal oxidation: [Fe(NH2trz)3]SO4, [Fe(NH2trz)3](BF4)2 and two polymorphs of [Fe(Htrz)2(trz)]BF4. Surprisingly high quality of PXRD pattern of [Fe(NH2trz)3]SO4 allowed to perform Rietveld refinement and obtain reliable crystal structure of the latter. All compounds have been studied by magnetic susceptibility measurements, optical reflectivity, differential scanning calorimetry and Raman spectroscopy. Importantly, spin‐crossover characteristics of the complexes obtained by this unusual method are preserved, thus revealing a new effective approach of "direct synthesis" towards switchable coordination compounds. [ABSTRACT FROM AUTHOR]

We studied the spin-state dependence of the electrical conductivity of two nanocrystalline powder samples of the spin crossover complex [Fe(pyrazine){Au(CN)2}2]. By applying an external pressure (up to 3 kbar), we were able to tune the charge transport properties of the material from a more conductive low spin state to a crossover point toward a more conductive high spin state. We rationalize these results by taking into account the spin-state dependence of the activation parameters of the conductivity. [ABSTRACT FROM AUTHOR]

In the title polymeric complex, {[Fe(CN)2(C10H8N2)2(H2O)2][Au(CN)2]}n, the FeII ion, which is located on a twofold rotation axis, has a slightly distorted FeN4O2 octahedral geometry. It is coordinated by two phenylpyrazine molecules, two water molecules and two dicyanoaurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated dicyanoaurate anions bridge the FeII ions to form polymeric chains propagating along the b-axis direction. In the crystal, the chains are linked by Owater--H···Ndicyanoaurate anions hydrogen bonds and aurophillic interactions [Au···Au = 3.5661 (3) Å], forming layers parallel to the bc plane. The layers are linked by offset π-π stacking interactions [intercentroid distance = 3.643 (3) Å], forming a supramolecular metal-organic framework. [ABSTRACT FROM AUTHOR]

In the title metal-organic framework, [Fe(C6H8N2)2{Cu(CN)2}2]n, the low-spin FeII ion lies at an inversion centre and displays an elongated octahedral [FeN6] coordination environment. The axial positions are occupied by two symmetryrelated bridging 2-ethylpyrazine ligands, while the equatorial positions are occupied by four N atoms of two pairs of symmetry-related cyanide groups. The CuI centre is coordinated by three cyanide carbon atoms and one N atom of a bridging 2-ethylpyrazine molecule, which form a tetrahedral coordination environment. Two neighbouring Cu atoms have a short Cu···Cu contact [2.4662 (7) Å] and their coordination tetrahedra are connected through a common edge between two C atoms of cyanide groups. Each Cu2(CN)2 unit, formed by two neighbouring Cu atoms bridged by two carbons from a pair of μ-CN groups, is connected to six FeII centres via two bridging 2-ethylpyrazine molecules and four cyanide groups, resulting in the formation of a polymeric three-dimensional metal-organic coordination framework. [ABSTRACT FROM AUTHOR]

In the title metal-organic framework, [Fe(C4H3BrN2)2{Cu(CN)2}2]n, the FeII cation is located on an inversion center and has a slightly elongated octa­hedral coordination environment [FeN6], ligated by two pyrazine N atoms of symmetry-related bridging 2-bromo­pyrazine mol­ecules in the axial positions and by four N atoms of pairs of symmetry-related cyanido groups in the equatorial positions. The CuI center has a fourfold coordination environment [CuC3N], with an almost perfect trigonal–pyramidal geometry, formed by three cyanido C atoms and an N atom of a bridging 2-bromo­pyrazine mol­ecule. Copper(I) centers related by a twofold rotation axis are bridged by two carbon atoms from a pair of μ-CN groups, resulting in Cu2(CN)2 units. Each Cu2(CN)2 unit is linked to six FeII cations via a pair of linear CN units, the pair of μ-CN groups and two bridging 2-bromo­pyrazine ligands, resulting in the formation of a metal–organic framework, which is additionally stabilized by the short CuCu contacts of 2.4450 (7) Å. [ABSTRACT FROM AUTHOR]

In the title polymeric complex, [Au2Fe(CN)4(C4H3IN2)2(C2H6O)]n, the FeII cation is coordinated by two iodo­pyrazine mol­ecules, one ethanol mol­ecule and three di­cyano­aurate anions in a distorted N5O octa­hedral geometry. In the crystal, the di­cyano­aurate anions bridge the FeII cations to form polymeric chains propagating along the b-axis direction. Stabilization of the crystal structure is provided by O—H···N hydrogen bonds and π–π stacking between parallel iodo­pyrazine rings of neighbouring chains, the centroid–centroid distances being 3.654 (10) and 3.658 (9) Å. [ABSTRACT FROM AUTHOR]

In the title polymeric complex, [Fe{OS(CH3)2}2{Ag(CN)2}2], the FeII cation is located at an inversion centre and is coordinated by four cyanide (CN-) anions and two dimethyl sulfoxide molecules in a slightly compressed N4O2 octahedral geometry, the AgI cation is C-coordinated by two CN- anions in a nearly linear geometry. The CN- anions bridge the FeII and AgI cations to form a twodimensional polymeric structure extending parallel to (102). In the crystal, the NEAREST Ag...Ag distance between polymeric sheets is 3.8122 (12) Å. The crystal studied was a twin with a contribution of 0.2108 (12) for the minor component. [ABSTRACT FROM AUTHOR]

Discovery of spin-crossover (SCO) behavior in the family of FeII-based Hofmann clathrates has led to a "new rush" in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe2+, square planar tetracyanometalates MII(CN)42- (MII = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes FeII ion has a pseudo-octahedral coordination environment supported by four µ4-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and MII = Ni (1), Pd (2), Pt (3); X = Me and MII = Ni (4), Pd (5)) or one 2X-pyrazine and one water molecule (X = I and MII = Ni (7), Pd (8), Pt (9)), or, alternatively, two distinct FeII positions with either two pyrazines or two water molecules (X = Me and MII = Pt (6)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN6 units (1-6) display cooperative spin transition, while FeII ions in N5O or N4O2 surrounding are high spin (HS). Structural changes in the nearest FeII environment upon low-spin (LS) to HS transition, which include ca. 10% Fe-N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of1-9 (see abstract figure). Effects of a pyrazine substituent and MII nature on the hyperfine parameters in both spin states are established. [ABSTRACT FROM AUTHOR]

The diversity of spin crossover (SCO) complexes that, on the one hand, display variable temperature, abruptness and hysteresis of the spin transition, and on the other hand, are spin-sensitive to the various guest molecules, makes these materials unique for the detection of different organic and inorganic compounds. We have developed a homochiral SCO coordination polymer with a spin transition sensitive to the inclusion of the guest 2-butanol, and these solvates with ( R)- and ( S)-alcohols demonstrate different SCO behaviours depending on the chirality of the organic analyte. A stereoselective response to the guest inclusion is detected as a shift in the temperature of the transition both from dia- to para- and from para- to diamagnetic states in heating and cooling modes respectively. Furthermore, the Mössbauer spectroscopy directly visualizes how the metallic centres in a chiral coordination framework differently sense the interaction with guests of different chiralities. [ABSTRACT FROM AUTHOR]

Microwave electromagnetic radiation that ranges from one meter to one millimetre wavelengths is finding numerous applications for wireless communication, navigation and detection, which makes materials able to tune microwave radiation getting widespread interest. Here we offer a new way to tune GHz frequency radiation by using spin-crossover complexes that are known to change their various physical properties under the influence of diverse external stimuli. As a result of electronic re-configuration process, microwave absorption properties differ for high spin and low spin forms of the complex. The evolution of a microwave absorption spectrum for the switchable compound within the region of thermal transition indicates that the high-spin and the low-spin forms are characterized by a different attenuation of electromagnetic waves. Absorption and reflection coefficients were found to be higher in the high-spin state comparing to the low-spin state. These results reveal a considerable potential for the implementation of spin-crossover materials into different elements of microwave signal switching and wireless communication. [ABSTRACT FROM AUTHOR]