Bispidine Based Hg(II) 1D Coordination Polymers of Helical Topology: Stability, Selective Adsorption and 1D to 2D Dimensionality Change Via SC-to-SC Transformation.

Bispidine based Hg(II) coordination polymers of helical topology CP-MeOH and CP-EtOH are almost isostructural (they mainly differ for the solvent included in their lattice and by a small % in unit cell parameters) but they differ for everything else: i) their intrinsic stability, ii) their ability to adsorb solvents upon prior evacuation, iii) their accessible structural transformations. In particular, one of the two starting materials, once evacuated, is capable to adsorb methanol from atmospheres containing binary and ternary mixtures of volatile organic compounds (MeOH, CHCl3 and EtOH) under ambient conditions (25 °C, 1 atm) and with a marked selectivity. The other one is not, but undergoes a 1D to 2D dimensionality change which can be monitored in situ by SC-XRD through a SC-to-SC process.

Aryl Boronic Acids in Columnar Stacked Co-crystalline Materials: Key-Factors Governing the Assembly with Quinones.

The assembly of aryl boronic acids B with quinones Q into columnar mixed stacked materials, as previously observed in the solid-state, has been here subjected to a detailed theoretical analysis focusing on the properties of the isolated synthons (HOMO-LUMO energies, electron affinity, ionization potential, reorganization hole/electron energies, partial Hirshfeld atomic charges and conformation stabilities) as well as those of the 1 : 1 adducts (Hirshfeld analysis, IRI surfaces, Hirshfeld atomic charges, hydrogen bond and slipped stacked π-π contributions). The overall picture obtained throught this study shows an intricate pattern of interconnected factors contributing to the formation and stability of the Bx Qy adducts, and it unveils the importance of parameters such as HOMO-LUMO gap, polarization and charge transfer, in addition to the more evident hydrogen bond and slipped-stacked π-π interactions in the formation of 1 : 1 adducts. An explanation has been also given for the presence in some Bx Qy adducts of the rare anti-anti conformation for the BO-H group with respect to the most studied and common anti-syn conformation.

Systematic Study of Podand Molecules for Synergistic Halogen and Hydrogen Bond-Driven Anion Recognition in the Solid State.

The increasing demand of species for the efficient capture and sensing of anions benefits from a systematic study of anion binding capabilities in the solid state. This work reports a detailed crystallographic study of ten structurally related podands and shows that these charged receptors bind anions with a combination of charge-assisted halogen and hydrogen bonds. Computational tools helped in highlighting the role of the different involved interaction and afforded possible design principles for the design of improved podands.

Different Topologies of Hg(II)-Bispidine 1D Coordination Polymers: Dynamic Behavior in Solvent Adsorption and Exchange Processes.

One-dimensional (1D) coordination polymers (CPs) featuring three different topologies, comprising zig-zag, ribbon-like and poly-[n]-catenane structures, were obtained by reaction of Hg(II) ions with a novel bispidine ligand L3, and structurally characterized by SC- and P-XRD methods. The CPs obtained in the form of microcrystalline powders were tested for their ability to undergo solvent adsorption and exchange by P-XRD and 1 H NMR spectroscopy. The extent of their dynamic behavior was then correlated to their structural features, highlighting the role of interchain interactions established among their constituting linear arrays. Zig-zag CPs proved to be resilient to external chemical stimuli, while they differently respond to thermal treatments, depending on the solvent originally included within the CP. In the case of polycatenated structures, we observed transformations where the original topology was maintained upon guest exchange, but also cases where it changed to zig-zag, even under solid/vapor conditions (i. e., no complete dissolution of the CP). Given the presence of linear interconnected 1D channels, 3 ⋅ ClBz-polycatenanePwd is also able to trap volatile guests such as n-hexane when exposed to its vapors.

Tuneable solvent adsorption and exchange by 1D bispidine-based Mn(II) coordination polymers via ligand design.

Here we report novel bispidine-based coordination polymers (CPs) 2·TCM, 3·TCM, 3·NB, 5·TCM and 5·TCM·NB, of compostition [Mn(Cl)2(L2)2·(TCM)2], [Mn(Cl)2(L3)2·(TCM)5], [Mn(Cl)2(L3)2·(NB)8], [Mn(Cl)2(L5)2·(TCM)4], [Mn(Cl)2(L5)2·(TCM)2·(NB)2], respectively (NB = nitrobenzene; TCM = chloroform). They were obtained starting from novel bispidine ligands L2 (dimethyl 7-isopropyl-3-methyl-9-oxo-2,4-di(pyridin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate), L3 (dimethyl 7-(cyclohexylmethyl)-3-methyl-9-oxo-2,4-di(pyridin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate) and L5 (dimethyl 7-(4-(dimethylamino)benzyl)-3-methyl-9-oxo-2,4-di(pyridin-4-yl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylate), The novel CPs were characterized by single crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD) and thermal analyses (TGA). We describe their structural and dynamic properties in terms of solvent exchange and adsorption processes, and we outline the general trends observed on the basis of a total of 16 X-ray structures (4 new) and 21 microcrystalline powder phases (10 new), which have been obtained so far for CPs by coordination of ligands L1-L5, having different substitution at the N7 position. This large set of CPs comprises monosolvated, bisolvated and desolvated species, and it shows a good demonstration of how small differences in the functionalization of the organic ligand can have a strong impact on the resulting structural and dynamic properties of this class of 1D CPs.

Combined structural and theoretical investigation on differently substituted bispidine ligands: predicting the properties of their corresponding coordination polymers.

Pyridine-based bispidine ligands L1-L7, which differ in the substituent at the N7 position of the bispidine scaffold, have been studied by single crystal X-ray diffraction and density functional theory (DFT) calculations, also including solid-state algorithms. Qualitative description of the packing interactions and quantitative data on the stability of each ligand in the solid-state have been employed to draw reasonable predictions on the ligand potential for the formation of linear 1D coordination polymers (CPs) with Mn(ii)Cl2 and on their resulting dynamic properties, in terms of adsorption and solvent exchange capabilities. The basic assumption lies in the fact that volume and polarizability of the ligands would similarly affect packing energies in both molecular solids and CP materials. The results here obtained confirm the data previously reported on CPs (those made from L4 are less dynamic than the ones with L1), but they also allow the prediction that CPs made with L2 and L5 should be more dynamic than expected, while CPs with L6 and L7 should not form altogether. This latter prediction was derived from the analysis of the steric and electronic factors of the ligand substituents on the N7 position and it is further substantiated by the obtainment of a 2 : 1 molecular complex, and not a CP, by crystallization of L6 with MnCl2.

Ab initio powder X-ray diffraction structural analysis of bispidine based 1D coordination polymers: insights into their guest responsive behaviour.

The first ab initio synchrotron powder X-ray diffraction (XRD) data structure solution, employing real-space global optimization strategies followed by Rietveld refinement, was obtained for a bispidine based one-dimensional ribbon-like coordination polymer (CP) 1. The structure solution of 1, a non-dynamic phase containing no solvent molecules, is crucial to obtain a more comprehensive view of the dynamic behaviour of a new family of 1D CPs, in terms of solvent adsorption and exchange processes by direct comparison among the structures, solvent-ribbon and inter-ribbon interactions of the CP materials. This work also reports novel bisolvated phases, 1·TCM·oNT, 1·TCM·pCT and 1·TCM·NB, in the form of single crystals and microcrystalline powders and shows that 1 can be thermally activated to regain dynamic selective adsorption features.

ON/OFF Control of the Flipping Motion of Diuranyl Bis(Salophen) Macrocycle by Extremely Strong Binding with Fluoride Ion.

Diuranyl bis(salophen) complex 1 features a relatively slow conformational motion, induced by an intramolecular O═U═O···UO2 binding motif, which interconverts the two nonsymmetric halves of the ligand. This flipping motion, which constitutes one of the fundamental molecular motions, can be completely halted by addition of fluoride anion, which is bound to 1, reaching one of the highest affinities reported to date. This system represents a model to study flipping dynamics in light of the possibility of developing novel types of molecular machines based on it.

Selective Cu(ii) sensing by a versatile AIE cyanostilbene-based gel system.

Cyanostilbene-based derivatives 1-3 were designed, synthesized and fully characterized. By screening their gelating abilities, we observed that the subtle difference in the position of the pyridine nitrogen greatly affected the resulting fluorescence and gelation properties. Notably, 1 was found to be a versatile ambidextrous gelator capable of forming organo-, hydro-, and Cu(ii) specific metallogels. Furthermore, a rare organogel-to-metallogel transformation at room temperature was also observed upon exposure of the 1-DMSO/H2O gel to aqueous Cu(ii). This process, accompanied by colour and fluorescence changes, provides an effective strategy for the preparation of novel sensing soft materials.

Naked-Eye Heterogeneous Sensing of Fluoride Ions by Co-Polymeric Nanosponge Systems Comprising Aromatic-Imide-Functionalized Nanocellulose and Branched Polyethyleneimine.

Heterogeneous colorimetric sensors for fluoride ions were obtained by cross-linking TEMPO-oxidized cellulose nanofibers (TOCNF) with chemically modified branched polyethyleneimine 25 kDa (bPEI). Functionalization of bPEI primary amino groups with aromatic anhydrides led to the formation of the corresponding mono- and bis-imides on the grafted polymers (f-bPEI). A microwave-assisted procedure allowed the optimization of the synthetic protocol by reducing reaction time from 17 h to 30 minutes. Hydrogels obtained by mixing different ratios of TOCNF, bPEI and f-bPEI were lyophilized and thermally treated at about 100 °C to promote the formation of amide bonds between the amino groups of poly-cationic polymers and the carboxylic groups of cellulose nanofibers. This approach generated a series of cellulose nanosponges S1-S3 which were characterized by FT-IR and by solid state 13 C CPMAS NMR. These sponge materials can act as colorimetric sensors for the selective naked-eye recognition of fluoride ions over chloride, phosphate and acetate ions at concentrations of up to 0.05 M in DMSO. Moreover, when the sponges were functionalized with perylene tetracarboxylic diimide, successful naked-eye detection was achieved with only 0.02 % w/w of chromophore units per gram of material.

Highly Dynamic and Tunable Behavior of 1D Coordination Polymers Based on the Bispidine Ligand.

Ligands L1 and L2 have been designed, synthesized, and used to build for the first time bispidine-based coordination polymers (CPs) in combination with MnII . The novel CPs have been structurally characterized by single-crystal (SC) and powder X-ray diffraction (P-XRD) techniques, showing that they are composed of 1D ribbon-like chains that adopt various arrangements depending on the trapped solvent species. These materials show highly dynamic behavior as they undergo heterogeneous solid/liquid and solid/vapor multiple solvent exchange processes, comprising crystalline-amorphous-crystalline, selective adsorption and SC-to-SC transformations, where major structural reorganization of the 1D ribbons are observed. By tuning inter-ribbon interactions through expansion of the ligand's accessible surface, the dynamic behavior can be effectively modulated.

Lipophilic N-Hydroxyphthalimide Catalysts for the Aerobic Oxidation of Cumene: Towards Solvent-Free Conditions and Back.

A new class of lipophilic N-hydroxyphthalimide (NHPI) catalysts designed for the aerobic oxidation of cumene in solvent-free conditions was synthesized and tested. The specific strategy proposed for the introduction of lipophilic tails on the NHPI moiety leads to lipophilic catalysts that-while completely preserving the activity of the precursor-allow the catalytic oxidation to be conducted in neat cumene, for the first time. The corresponding cumyl hydroperoxide is obtained in good yields (28-52 %) and with high selectivity (95-97 %), under mild conditions. Importantly, the presence of a polar solvent is no longer required to guarantee complete solubilization of the catalyst. On the other hand, the oxidation conducted in neat cumene reveals the unexpected necessity of using small amounts of acetonitrile to fully promote the hydrogen atom transfer process and prevent the catalyst from detrimental hydrogen-bond (HB) driven aggregation.

X-Ray crystallographic and computational study on uranyl-salophen complexes bearing nitro groups.

In the solid state, salophen-UO2 complexes bearing one, two, or three NO2 groups lack the pronounced ligand curvature that represents a structural hallmark for this class of compounds. A detailed structural study based on single-crystal X-ray crystallography and computational methods, comprising molecular dynamics, gas-phase Hartree Fock, and DFT calculations, was carried out to investigate the coordination properties of the uranyl cation.

Crystal Engineering of a Two-Dimensional Lead-Free Perovskite with Functional Organic Cations by Second-Sphere Coordination.

Hybrid lead halide perovskite semiconductors are attracting increasing attention for applications in optoelectronics. However, the high lead content calls for the development of greener and smarter alternatives through crystal engineering. This is extremely challenging since the use of functional cations often results in the disruption of the metal halide framework. Here we show the rational design of a new lead-free, copper-based hybrid perovskite following a second-sphere coordination approach. Our synthetic strategy allows the incorporation of an organic cationic fluorophore within the two-dimensional Cu-Cl framework of a layered copper perovskite. The functionalization results in a moisture-stable and near-UV/blue-emitting copper perovskite. Along with the possibility of extending the emission in the visible range by further synthetic design, our approach paves the way for the development of a new class of Pb-free perovskites with potential applications in solid-state lighting.

Crystal Engineering of a Two-Dimensional Lead-Free Perovskite with Functional Organic Cations by Second-Sphere Coordination.

Invited for this month's cover are collaborators from the Istituto Italiano di Tecnologia, Nanyang Technological University, and Politecnico di Milano. The cover picture shows the 2 D layered nature of lead-free perovskite having a functional organic cation. Read the full text of the article at 10.1002/cplu.201600477.

Mechanical and Drug Release Properties of Sponges from Cross-linked Cellulose Nanofibers.

All-organic porous sponges were obtained throughout the direct and solvent-free (oven 105 °C, time>6 h) crosslinking of TEMPO-oxidized cellulose nanofibers (TOCNF) with 25 kDa branched polyethyleneimine (bPEI) in the presence of different amounts of citric acid (CA) as co-crosslinker. The chemical and mechanical stability of these materials was provided by the formation of amide bonds between the carboxylic moieties of TOCNF and CA with the primary amines of bPEI. The mechanical properties were investigated under static and dynamic loads with both dry and wet samples. The materials had the interesting capability to recover their shape with reduced losses in mechanical resistance, while their Young's modulus progressively increased with the content of CA. In work toward developing possible applications of bPEI-TOCNF sponges in drug delivery, amoxicillin (AM) and ibuprofen (IB) were considered as model drugs. All materials showed very good performance in adsorbing both AM and IB (ca. 200 mg g-1 ) from methanol solution. In particular, an increased adsorption of IB was observed in parallel to the increase of citrate moieties in the samples. Moreover, samples crosslinked in presence of CA showed slower kinetic release in aqueous environments than materials obtained without CA.

Selective adsorption of chlorinated volatile organic compound vapours by microcrystalline 1D coordination polymers.

Microcrystalline 1D coordination polymers 1-3Pwd are able to adsorb vapours of chlorinated volatile organic compounds (Cl-VOCs), displaying interesting selectivity patterns, as demonstrated by 1H-NMR and X-ray diffraction analyses. Due to their dynamic breathing-like behavior, chemical and thermal stabilities and adsorption selectivity, these isostructural coordination polymers are promising to be used as filters for toxic Cl-VOCs.

Metallogel formation in aqueous DMSO by perfluoroalkyl decorated terpyridine ligands.

Terpyridine based ligands 1 and 2, decorated with a C8F17 perfluorinated tag, are able to form stable thermoreversible gels in the presence of several d-block metal chloride salts. The gel systems obtained have been characterized by NMR, X-ray diffraction, electron microscopies and Tgel experiments in order to gain insights into the observed different behaviour of the two similar ligands, also in terms of the effect of additional common anionic species.

Dynamic single crystal to polycrystal transformation of a 1D-coordination polymer and its second harmonic generation.

Upon guest CHCl3 release, the one-dimensional (1D) coordination polymer ·CHCl3 gives rise to a non-porous structure, , following a unit cell volume reduction of ca. 22%. Due to the considerable structural transformation, the single crystal does not maintain its integrity, and therefore the structure determination has been carried out by combining single crystal X-ray diffraction and ab initio X-ray powder diffraction analyses. The result shows a symmetry breaking transformation leading to an acentric crystalline material (), which shows nonlinear optical properties such as second harmonic generation.

Insights into the formation of chiral second sphere coordination complexes with aromatic tris amines: combined single crystal X-ray crystallography and molecular modeling analyses.

A family of isostructural, chiral supramolecular networks have been obtained in the solid state by exploiting second sphere coordination interactions in the self-assembly of achiral tris amines and with tetrahalometallate and halide ions. Quantum-Mechanical (QM) calculations specific for solid phases provided additional insights into the intramolecular and packing interactions which determine chirality, pointing to a direct effect of the methyl groups of the central benzene ring.