Polymer Axis Research Articles

Efficient Synthesis of Metastable Cyclodextrin-Based Polyrotaxanes with Tunable Threading Ratios.

Cyclodextrin-based polyrotaxanes (CD-PRs) are gaining attention for their dynamic sliding rings along the polymer axis, enabling various applications in molecular shuttles, drug delivery, and durable polymers with slidable cross-links. However, the conventional synthesis of CD-PRs with tunable threading ratios is typically laborious, time-consuming, and complicated, which limits their scalability and cost-effectiveness. Herein, we highlight the great potential of planetary centrifugal mixing, a process that significantly accelerates and simplifies the initial synthesis of polypseudorotaxanes (PPRs), followed by a thiol-ene click reaction as an efficient end-capping reaction for the synthesis of PRs. Notably, PRs synthesized with glutathione (GSH) as the end-capping reagent are in a metastable state, where GSH act as a molecular bumper that significantly prevent de-threading of α-CD rings at room temperature. Moreover, the rate of ring de-threading can be precisely controlled by heating, enabling the preparation of metastable PRs with tunable threading ratios over a wide range. The developed strategy is of great significance to the efficient synthesis of CD-PRs, thus marking a significant step towards their practical application in advanced functional materials and devices.

Efficient Synthesis of Metastable Cyclodextrin‐Based Polyrotaxanes with Tunable Threading Ratios

AbstractCyclodextrin‐based polyrotaxanes (CD‐PRs) are gaining attention for their dynamic sliding rings along the polymer axis, enabling various applications in molecular shuttles, drug delivery, and durable polymers with slidable cross‐links. However, the conventional synthesis of CD‐PRs with tunable threading ratios is typically laborious, time‐consuming, and complicated, which limits their scalability and cost‐effectiveness. Herein, we highlight the great potential of planetary centrifugal mixing, a process that significantly accelerates and simplifies the initial synthesis of polypseudorotaxanes (PPRs), followed by a thiol‐ene click reaction as an efficient end‐capping reaction for the synthesis of PRs. Notably, PRs synthesized with glutathione (GSH) as the end‐capping reagent are in a metastable state, where GSH act as a molecular bumper that significantly prevent de‐threading of α‐CD rings at room temperature. Moreover, the rate of ring de‐threading can be precisely controlled by heating, enabling the preparation of metastable PRs with tunable threading ratios over a wide range. The developed strategy is of great significance to the efficient synthesis of CD‐PRs, thus marking a significant step towards their practical application in advanced functional materials and devices.

Supermolecule-Drug Conjugates Based on Acid-Degradable Polyrotaxanes for pH-Dependent Intracellular Release of Doxorubicin.

Doxorubicin (DOX)-conjugated acid-degradable polyrotaxanes (PRXs) were designed as supramolecular drug carriers capable of releasing drugs in acidic cellular environments. Acid-degradable PRXs composed of α-cyclodextrin (α-CD) as a cyclic molecule, poly(ethylene glycol) (PEG) as a polymer axis, and N-triphenylmethyl (N-Trt) groups as an acid-labile stopper molecules were synthesized and DOX was conjugated with the threaded α-CDs in the PRXs. Because the acid-induced cleavage of N-Trt groups in PRXs leads to PRX dissociation, the DOX-modified α-CDs were released under acidic conditions (pH 5.0). The cytotoxicity of DOX-conjugated PRXs in colon-26 cells revealed significant cell death for DOX-conjugated PRXs after 48 h of treatment. Confocal laser scanning microscopy (CLSM) analysis revealed that the fluorescence signals derived from DOX-conjugated PRXs were observed in cellular nuclei after 48 h, suggesting that the DOX-modified α-CDs were released and accumulated in cellular nuclei. These results confirmed that acid-degradable PRXs can be utilized as drug carriers capable of releasing drug-modified α-CDs in acidic lysosomes and eliciting cytotoxicity. Overall, acid-degradable PRXs represent a promising supramolecular framework for the delivery and intracellular release of drug-modified α-CDs, and PRX-drug conjugates are expected to contribute to the development of pH-responsive drug carriers for cancer therapy.

Satellite ligand effects on magnetic exchange in dimers. A structural, magnetic and theoretical investigation of Cu2L2X4 (L = methylisothiazolinone and X = Cl-, Br-).

Halide-bridged polymers have gained significant interest due to their diverse properties and potential applications. Stacked Cu2L2X4 dimers, where L is an organic ligand and X can be Cl- or Br-, are of interest because a chloride analogue where L = 2-pyridone, had previously been reported to exhibit bulk ferromagnetism, which augured great potentiality for this class of compounds. The synthesis, structural characterization, magnetic susceptibility measurements, and computational studies of two isostructural CuClMI (MI = methylisothiazolinone) and CuBrMI polymers of Cu(II), along with a related CuClPYR (PYR = 2-pyridone) is reported. CuClMI and CuBrMI were found to exhibit AFM bulk properties, due to FM/AFM alternating chains along the halide-bridged polymer axis, while FM bulk properties were confirmed for CuClPYR exhibiting a FM spin ladder. In combination with a benzamide analogue, CuClBA, three O-donor amides, CuClMI, CuClBA and CuClPYR were analyzed and revealed that the kinetic exchange is affected by the identity, but more importantly, the orientation of the satellite ligands. The torsional angle of the ligand with the dimer plane is shown to significantly affect the magnetic exchange in the dimer, and between dimers, explaining the reported FM bulk properties of CuClPYR. This finding is exceedingly important, as it suggests that a spin device can be constructed to flip between singlet/triplet states by manipulating the orientation of the satellite/terminal ligand.

Cothreading of Unmodified and Monoazidated β-Cyclodextrins in Polyrotaxanes for Orthogonal Modification of Cell-Penetrating Peptides via Click Chemistry

To establish a method for the orthogonal chemical functionalization of β-cyclodextrin (β-CD)-based polyrotaxane (PRX), unmodified and monoazidated β-CDs (N3-β-CDs) were utilized as cyclic host molecules for synthesizing PRXs. PRXs were successfully synthesized by using N3-β-CD, and the molar ratio of unmodified β-CD and N3-β-CD in the resulting PRXs could be regulated by the feed ratio of unmodified β-CD and N3-β-CD. It was revealed that all PRX molecules contained N3-β-CD, indicating that unmodified and monoazidated β-CDs were cothreaded onto a single polymer axis. Physicochemical characterization of β-CD/N3-β-CD cothreaded PRXs suggested that their crystalline structures were unaffected by the molar ratio of N3-β-CD, whereas their thermal stability was slightly improved with increasing molar ratio of N3-β-CD. To facilitate cellular internalization of PRXs, threaded N3-β-CD in PRXs was modified with cell-penetrating octaarginine (R8) peptides via a copper(I)-catalyzed azide–alkyne click reaction. The cellular internalization efficiency of the R8-modified PRXs increased with the number of R8 peptides modified on PRXs. However, PRXs modified with a large number of R8 peptides precipitated in serum solutions and exhibited high cytotoxicity. PRXs modified with the optimal number of R8 peptides did not exhibit precipitation and showed high cellular uptake compared to unmodified PRXs without cytotoxicity. Consequently, PRXs modified with the optimal number of R8 peptides showed superior cholesterol-reducing effects in fibroblasts derived from patients with Niemann–Pick type C disease. As demonstrated here, the number of modified functional molecules plays a crucial role in the treatment effects of PRXs, and β-CD/N3-β-CD cothreaded PRXs can offer potential for orthogonal postmodification. Thus, β-CD/N3-β-CD cothreaded PRXs could introduce benefits that enable the material applications of PRXs.

Quasiparticles and Band Structures in Organized Nanostructures of Donor–Acceptor Copolymers

The performance of organic semiconductor devices is linked to highly ordered nanostructures of self-assembled molecules and polymers. Many-body perturbation theory is employed to study the excited states in bulk copolymers. The results show that acceptors in the polymer scaffold introduce a, hitherto unrecognized, conduction impurity band that leads to electron localization. The donor states are responsible for the formation of conjugated bands, which are only mildly perturbed by the presence of the acceptors. Along the polymer axis, the nonlocal electronic correlations among copolymer strands hinder efficient band transport, which is, however, strongly enhanced across individual chains. Holes are most effectively transported along the π-π stacking, while electrons in the impurity band follow the edge-to-edge directions. The copolymers exhibit regions with inverted transport polarity, in which electrons and holes are efficiently transported in mutually orthogonal directions.

The MUC5B mucin polymer is dominated by repeating structural motifs and its topology is regulated by calcium and pH

The polymeric mucin MUC5B provides the structural and functional framework of respiratory mucus, conferring both viscoelastic and antimicrobial properties onto this vital protective barrier. Whilst it is established that MUC5B forms disulfide-linked linear polymers, how this relates to their packaging in secretory granules, and their molecular form in mucus remain to be fully elucidated. Moreover, the role of the central heavily O-glycosylated mucin domains in MUC5B conformation is incompletely described. Here we have completed a detailed structural analysis on native MUC5B polymers purified from saliva and subsequently investigated how MUC5B conformation is affected by changes in calcium concentration and pH, factors important for mucin intragranular packaging and post-secretory expansion. The results identify that MUC5B has a beaded structure repeating along the polymer axis and suggest that these repeating motifs arise from distinct glycosylation patterns. Moreover, we demonstrate that the conformation of these highly entangled linear polymers is sensitive to calcium concentration and changes in pH. In the presence of calcium (Ca2+, 10 mM) at pH 5.0, MUC5B adopted a compact conformation which was lost either upon removal of calcium with EGTA, or by increasing the pH to 7.4. These results suggest a pathway of mucin collapse to enable intracellular packaging and mechanisms driving mucin expansion following secretion. They also point to the importance of the tight control of calcium and pH during different stages of mucin biosynthesis and secretion, and in the generation of correct mucus barrier properties.

Polaron Delocalization in Conjugated Polymer Films

A theory describing the spatial coherence length of polarons in disordered conjugated polymer films is presented, revealing a simple relationship between oscillator strength of the mid-IR absorption band and the polaron coherence function. Applications are made to positively charged polarons or holes in poly(3-hexylthiophene) π-stacks where polaron delocalization occurs in essentially two dimensions: along the polymer axis (x-axis) and along the interchain stacking axis (y-axis). Based on a lattice model consisting of a 2D array of thiophene units linked electronically along the polymer axis (tintra) and between adjacent chains (tinter), a disordered 2D Holstein-style Hamiltonian is developed. The Hamiltonian includes vibronic coupling involving the polaron-forming vibrational mode responsible for aromatic/quinoidal oscillations. The hole absorption spectrum for light polarized along each axis is calculated along with the corresponding hole coherence function, CP(r). For diagonal disorder arising from a random distribution of hole site energies, the band oscillator strength for light polarized along x (y) scales directly as the product of tintra (tinter) and the coherence function, CP(r), for a separation r equal to one unit along x (one unit along y). For off-diagonal disorder arising from a distribution of electronic couplings, the relationship becomes approximate with tintra (tinter) replaced by its mean value. Calculated spectral line shapes are in good agreement with previously published experimental charge-modulated spectra. Further investigation reveals that the polaron is delocalized isotropically over about six thiophene units in each direction for high molecular weight (MW) films (270 kDa), In the low MW films (15 kDa), the coherence length becomes anisotropic, with delocalization numbers of only three along the polymer axis and two along the interchain axis. The drop in coherence lengths tracks a similar drop in the calculated band oscillator strengths, consistent with experimental observations.

Effect of electric field on the infrared spectrum of a ferroelectric poly(vinylidene fluoride-co-hexafluoropropylene) film

We have used infrared spectroscopy to study electric-field induced motions of polymer chains in a ferroelectric uniaxially drawn film of poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] (molar ratio, 1:0.18) consisting mainly of the polar crystalline β phase. We analyzed the observed spectra under the C2v symmetry of an infinite poly(vinylidene fluoride) (PVDF) chain. The changes in intensity of the a1 bands (2979, 1432, 1280, and 842cm−1), b1 bands (1073cm−1), and b2 bands (3017, 1168, and 880cm−1) showed butterfly-shaped hysteresis loops characteristic of ferroelectricity when the electric field was varied from 1.4 to −1.4MV/cm. The changes in intensity of the a1 and b2 bands with transition dipole moments perpendicular to the polymer chain were large, whereas those of the b1 bands with transition dipole moments parallel to the polymer chain were small. The changes in intensity of the a1 and b2 bands were mainly attributed to the inversion of the polymer chain around the polymer axis. On the other hand, the changes in intensity of the b1 band were attributed to the motion of a polar crystallite.

New insights on the nature of two-dimensional polarons in semiconducting polymers: infrared absorption in poly(3-hexylthiophene).

Infrared absorption of positively charged polarons in conjugated polymer chains and π-stacked aggregates is investigated theoretically, employing a Holstein-based Hamiltonian which treats electronic coupling, electron-vibrational coupling, and disorder on equal footing. The spectra evaluated from the Hamiltonian expressed in a one- and two-particle basis set are essentially exact, insofar as the main, aromatic-quinoidal vibrational mode is treated fully nonadiabatically. Diagonal and off-diagonal ("paracrystalline") disorder are resolved along the polymer axis (x) and the aggregate stacking axis (y). Disorder along the polymer axis selectively attenuates the x-polarized spectrum, which is dominated by the polaron peak P1. Disorder along the stacking axis selectively attenuates the y-polarized spectrum, which is dominated by the lower-energy charge-transfer peak, DP1. Calculated spectra are in excellent agreement with the measured induced-absorption and charge-modulation spectra, reproducing the peak positions and relative peak intensities within a line shape rich in vibronic structure. Our nonadiabatic approach predicts the existence of a weak, x-polarized peak P0, slightly blueshifted from DP1. The peak is intrinsic to single polymer chains and appears in a region of the spectrum where narrow infrared active vibrational modes have been observed in nonaggregated conjugated polymers. The polaron responsible for P0 is composed mainly of two-particle wave functions and cannot be accounted for in the more conventional adiabatic treatments.

Dissecting the Energies that Stabilize Sickle Hemoglobin Polymers

Sickle hemoglobin forms long, multistranded polymers that account for the pathophysiology of the disease. The molecules in these polymers make significant contacts along the polymer axis (i.e., axial contacts) as well as making diagonally directed contacts (i.e., lateral contacts). The axial contacts do not engage the mutant β6 Val and its nonmutant receptor region on an adjacent molecule, in contrast to the lateral contacts which do involve the mutation site. We have studied the association process by elastic light scattering measurements as a function of temperature, concentration, and primary and quaternary structure, employing an instrument of our own construction. Even well below the solubility for polymer formation, we find a difference between the association behavior of deoxy sickle hemoglobin molecules (HbS), which can polymerize at higher concentration, in comparison to COHbS, COHbA, or deoxygenated Hemoglobin A (HbA), none of which have the capacity to form polymers. The nonpolymerizable species are all quite similar to one another, and show much less association than deoxy HbS. We conclude that axial contacts are significantly weaker than the lateral ones. All the associations are entropically favored, and enthalpically disfavored, typical of hydrophobic interactions. For nonpolymerizable Hemoglobin, ΔHo was 35 ± 4 kcal/mol, and ΔS was 102.7 ± 0.5 cal/(mol−K). For deoxyHbS, ΔHo was 19 ± 2 kcal/mol, and ΔS was 56.9 ± 0.5 cal/(mol−K). The results are quantitatively consistent with the thermodynamics of polymer assembly, suggesting that the dimer contacts and polymer contacts are very similar, and they explain a previously documented significant anisotropy between bending and torsional moduli. Unexpectedly, the results also imply that a substantial fraction of the hemoglobin has associated into dimeric species at physiological conditions.

Empirical potential structure refinement of semi-crystalline polymer systems: polytetrafluoroethylene and polychlorotrifluoroethylene

Empirical potential structure refinement (EPSR) simulations are performed on total neutron scattering data from powder samples of polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), both at 300 K. Starting from single strands of polymer consisting of between 30 and 60 monomers of tetrafluoroethylene and chlorotrifluoroethylene in each case, hexagonal simulation cells are constructed consisting of an array 25 (5×5) such strands placed on a hexagonal lattice. Allowed simulation moves are polymer translation moves along all three Cartesian axes, whole polymer rotations about the polymer axis, and individual atom moves within each polymer. For PTFE a number of Bragg peaks are visible in the scattering data and these are found to be consistent with a lattice spacing a(=b) = 5.69(1) Å with a dihedral angle along the (helical) chain of 166° which gives a repeat distance along the chain (c-axis) of ∼19.6 Å. The positions of the Bragg peaks are well reproduced by this model, although there is a mismatch in the amplitudes of some of the higher order reflections between simulation and data. For PCTFE there is only one visible Bragg peak (100) which is well reproduced by a hexagonal lattice of atactic parallel polymers with a spacing of a(=b) = 6.37(1) Å. In this case the absence of distinct reflections along the polymer c-axis makes characterization of the internal dihedral angle difficult, but a model with a dihedral angle of 166° was less successful at fitting the diffuse scattering than a model where this angle was set to 180°, giving a nearly straight trans (zig-zag) structure. For PCTFE little change in structure could be discerned when the material was heated to 550 K, apart from a slight increase in lattice spacing. In both cases there is substantial diffuse scattering between the Bragg peaks, and this is correctly replicated by the EPSR simulations.

Brownian dynamics simulations of charge mobility on conjugated polymers in solution

A model is developed for the mobility of a charge carrier along a conjugated polymer dissolved in solution, as measured by time-resolved microwave conductivity. Each unit cell of the polymer is assigned a torsional degree of freedom, with Brownian dynamics used to include the effects of solvent on the torsions. The barrier to torsional motion is substantially enhanced in the vicinity of the charge, leading to self-trapping of the charge onto a planarized region of the polymer chain. Within the adiabatic approximation used here, motion arises when regions of the polymer on either side of the charge fluctuate into planarity and the wavefunction spreads in the corresponding direction. Well-converged estimates for the mobility are obtained for model parameters where the adiabatic approximation holds. For the parameters expected for conjugated polymers, where crossing between electronic surfaces may lead to breakdown in the adiabatic approximation, estimates for the mobility are obtained via extrapolation. Nonadiabatic contributions from hopping between electronic surfaces are therefore ignored. The resulting mobility is inversely proportional to the rotational diffusion time, trot, of a single unit cell about the polymer axis in the absence of intramolecular forces. For trot of 75 ps, the long-chain mobility of poly(para-phenylene vinylene) is estimated to be between 0.09 and 0.4 cm(2)∕Vs. This is in reasonable agreement with experimental values for the polymer, however, the nonadiabatic contribution to the mobility is not considered, nor are effects arising from stretching degrees of freedom or breaks in conjugation.

Polymer networks characterized by slidable crosslinks and the asynchronous dynamics of interlocked components

In mechanically interlocked molecules like rotaxanes and catenanes, each component has asynchronous microscopic motion within the topological restrictions. The motions can be expressed macroscopically by incorporating the mechanically interlocked molecules in polymers and their networks. Rotaxane develops into polyrotaxane having a polymer axis, and then polyrotaxane forms a polymer network so-called slide-ring material. Because the polymer chains in the material are topologically connected to each other via a figure-eight crosslink, the chains can slide through the crosslink. This microscopic slidability at the crosslink drastically affects the mechanical properties. This article first presents an overview of significant studies on slide-ring materials in the first decade that deal with single species material consisting of polyethylene glycol and α-cyclodextrin. These studies have revealed abnormal statics and network structures, most of which can be interpreted in terms of slidability. Next, we describe our recent designs of materials and findings in mechanical properties attributed to the slidable crosslinks that are built on a synthetic breakthrough that yields a new series of slide-ring materials composed of various backbone polymers. The finding of a sliding transition reveals the dynamics of sliding, the significance of the entropy of uncrosslinked cyclic compounds, and helps in determining the mechanical properties of slide-ring materials.

Effects of several inter-molecular interactions on the inclusion between methyl substituted β-cyclodextrin and some linear macromolecule in supercritical carbon dioxide medium

In this work, the inclusion between methyl substitute β-cyclodextrin and some linear macromolecule in supercritical carbon dioxide medium was investigated. The contributions from several factors were studied; such as the hydrogen bonding interaction between the host and guest, the hydrogen bonding interaction between the neighborhood cyclodextrin rims threaded on the polymer chain, and the matching between the host cavity and the size of the polymer axis.

Crystal Engineering: Synthesis and Structural Analysis of Coordination Polymers with Wavelike Properties

Supramolecular coordination polymers with wavelike structures have been synthesized by self-assembly and their structures analyzed using the sine trigonometric function. Slow evaporation of a methylene chloride-methanol solution of a 1:1 molar mixture of [M(tmhd)2], where M = Co or Ni, and quinoxaline; a 1:2:1 molar mixture of [M(acac)2], where M = Co or Ni, 2,2,6,6-tetramethyl-3,5-heptadione and quinoxaline; or a 1:2:1 molar mixture of [Co(acac)2], dibenzoylmethane, and quinoxaline, yielded the crystalline coordination polymers. In the presence of the nitrogenous base, ligand scrambling occurs yielding the most insoluble product. The synthesis and structures of the following wavelike polymers are reported: trans-[Co(DBM)2(qox)]n·nH2O (2), trans-[Co(tmhd)2(qox)]n (3), trans-[Ni(tmhd)2(qox)]n (4), where DBM− = dibenzoylmethanate, tmhd− = 2,2,6,6-tetramethyl-3,5-heptadionate, and qox = quinoxaline. The wavelike structures are generated by intramolecular steric interactions and crystal packing forces between the chains. Some of the tert-butyl groups show a two-fold disorder. The sine function, φ = A sin 2πx/λ, where φ = distance (Ǻ) along the polymer backbone, λ = wavelength (Ǻ), A = amplitude (Ǻ), x = distance (Ǻ) along the polymer axis, provides a method to approximate and visualize the polymer structures.

High Yield Synthesis of Polyrotaxane Constructed from Pillar[5]arene and Viologen Polymer and Stabilization of Its Radical Cation

New polyrotaxane composed of pillar[5]arene and viologen polymer was successfully prepared with extremely high yield by capping the chain ends with adamantyl moieties. Pillar[5]arene and viologen polymer are soluble in various solvents such as acetone, acetonitrile, methanol, DMF, and DMSO, while the polyrotaxane was soluble in DMF and DMSO and insoluble in the other organic solvents. Formation of inter-molecular hydrogen bonds between the OH moieties of pillar[5]arenes stabilized the structure and reduced the solubility. The polyrotaxane exhibited a thermally induced color change from yellow to violet. On heating, the inter-molecular hydrogen bond became weakened, and the shuttling motion of pillar[5]arenes on the polymer axis was fast. Thus, efficient electron transfer from the electron donors of pillar[5]arenes to the electron acceptor of viologen polymer occurred in the whole polymer chain and the radical cation species were stabilized.

Cysteine‐Containing Polyisocyanides as Versatile Nanoplatforms for Chromophoric and Bioscaffolding

The straightforward syntheses of polyisocyanides containing the alanine-cysteine motif in their side chains have been achieved. Detailed characterization of the polymers revealed a well-defined and highly stable helical conformation of the polyimine backbone responsible for the formation of rodlike structures of over one hundred nanometers. The 4(1) helix is further stabilized by beta-sheet-like interactions between the peptide arms. As a result, the cysteine sulfur atoms are regularly aligned along the polymer axis, which provides a unique platform for the scaffolding of various entities by using versatile click-chemistry postmodification approaches. For instance, pyrene derivatives were introduced through thio-specific reactions involving either maleimide, iodoacetamide, or thioester groups, leading to arrays of stacked chromophores with excimer-like emission. A water-soluble cysteine-rich polyisocyanide was successfully biotinylated and coupled to streptavidin.

Stationary Electric Birefringence of Flexible Polyelectrolyte Solutions: Experimental Evidence of Different Counterion Polarization Mechanisms

Transient electric birefringence (TEB) measurements on aqueous solutions of flexible polyelectrolytes (in pure water, with added salt and with oppositely charged surfactants) are presented. The results evidence the different polarization mechanism of free and condensed counterions. Free counterions polarize perpendicular to the main polymer axis and give a negative contribution to the birefringence; condensed counterions polarize parallel to the main polymer axis and give a positive contribution. We present a simple model that allows to explain the change in sign of the birefringence when polymer, salt and surfactant concentrations are varied, according to which polarization mechanism prevails. From the model we can estimate the fraction of free counterions obtaining values which are close to the values calculated with Manning theory. We demonstrate the interest of TEB technique in the study of polyelectrolyte/surfactant systems.

1 : 1 complexes of silver(i) thiocyanate with (substituted) thiourea ligands

Syntheses and single crystal X-ray structural characterizations, together with infrared spectroscopic studies, are recorded for 1 : 1 adducts of silver(I) thiocyanate with thiourea ('tu') and N,N'-diethylthiourea ('detu' identical with (EtNH)(2)CS). The two complexes display novel and different polymeric forms. That formed with tu is a double-stranded form, comprising a pair of Ag(mu-S-tu)Ag(mu-... strands linked by pairs of mu-SCN anions, the whole array having quasi-2 symmetry about the polymer axis. The detu adduct takes the ionic form [Ag(detu)2](infinity|infinity)[Ag(SCN)2](infinity|infinity), both cation and anion being one-dimensional polymers lying in parallel, and both of the form ...Ag(mu-S-L)2Ag(mu-... (L = SCN or detu), disposed about crystallographic 4 axes. Redeterminations of the structures of AgSCN : tu, etu (1 : 2) ('etu' = ethylenethiourea, (CH2NH)2CS)) with quasi-trigonal silver atom environments (the etu adduct the more closely so), are also recorded as a basis for an IR spectroscopic characterization of the [(NCS)Ag(S-xtu)2] array. A mechanochemical/infrared study of the AgSCN:etu (1 : 1) system showed that no 1 : 1 complex exists in this case, the product being a mixture of the 1 : 2 complex and a novel 1 : 0.5 complex. The latter complex was prepared both mechanochemically and from solution, and characterized by infrared spectroscopy. Diagnostic ligand and metal-ligand bands in the IR and far-IR spectra are assigned for all of the complexes studied and for AgSCN and are discussed in relation to the structures of the complexes. The double degeneracy of the delta(SCN) mode of the coordinated thiocyanate is lifted and the first overtone of this band at gains intensity in the IR in the 1 : 1 complexes, behaviour that is not observed for the terminal bonding mode that is present in the 1 : 2 complexes.