Self-Assembly and Host-Guest Interactions of Pd3L2 Metallo-cryptophanes with Photoisomerizable Ligands.

New photoswitchable pyridyl-azo-phenyl-decorated tripodal host ligands (Laz) that belong to the cyclotriveratrylene family have been synthesized, and their photoswitching behavior and crystal structures determined. The latter includes a remarkable 7-fold Borromean-weave entanglement of π-π stacked layers. Trigonal bipyramidal {[Pd(en)]3(Laz)2}6+ metallo-cryptophanes (en = ethylenediamine) were formed from these and a previously known pyridyl-azo-phenyl-decorated tripodal host ligand. These coordination cages dissociate at low concentrations and are less robust to photoswitching of the Laz ligands than were previously reported Ir(III)-linked metallo-cryptophanes with similar ligands, reflecting the greater lability of the Pd-N bonds. The {[Pd(en)]3(Laz)2}6+ cages all act as hosts, binding octyl sulfate anions, or N-[2-(dimethylamino)ethyl]-1,8-naphthalimide in a dimethyl sulfoxide solution.

An Area-Specific, International Community-Led Approach to Understanding and Addressing Equality, Diversity, and Inclusion Issues within Supramolecular Chemistry.

Diversity, equality, and inclusion (DEI/EDI) are pressing issues in chemistry and the natural sciences. In this Essay we share how an area-specific approach is "calling in" the community so that it can act to address EDI issues, and support those who are marginalised. Women In Supramolecular Chemistry (WISC) is an international network that aims to support equality, diversity, and inclusion within supramolecular chemistry. WISC has taken a field-specific approach using qualitative research methods with scientists to identify the support that is needed and the problems the supramolecular community needs to address. Herein, we present survey data from the community which highlight the barriers that are faced by those who take career breaks for any reason, a common example is maternity leave, and the importance of mentoring to aid progression post-PhD. In conclusion, we set out an interdisciplinary and creative approach to addressing EDI issues within supramolecular chemistry.

Fully Collapsed Imploded Cryptophanes in Solution and in the Solid State.

Cryptophanes with flexible linkers derived from (±)-tris-(4-formyl-phenyl)-cyclotriguaiacylene with either bisoxydi(ethylamine) or bis(aminopropyl)ether were isolated as single crystals, the crystal structures of which showed the proposed, but previously uncharacterised, out-in conformation, in which both cyclotriguaiacylene fragments adopt a crown conformation with one crown sitting inside the other. The usual cage-like out-out conformation of the cryptophanes was observed when crystals were dissolved upon heating, and the molecules collapsed back to the out-in isomers over time. In contrast, a cryptophane also derived from (±)-tris-(4-formyl-phenyl)-cyclotriguaiacylene but with rigid dibenzalhydrazine linkers was isolated as the more usual out-out isomer.

Complex Phase Behaviour and Structural Transformations of Metal-Organic Frameworks with Mixed Rigid and Flexible Bridging Ligands.

Two new heteroleptic metal-organic framework materials show strong adsorption of H2 and ethanol. [Co2 (L1)(bdc)2 ], where L1=N1 ,N4 -bis(4-pyridinylmethyl)-2,5-dimethylbenzene-1,4-diamine and bdc is benzene-1,4-dicarboxylate, has a twofold interpenetrating pillared layer structure with pcu topology. It has a stepped, hysteretic EtOH adsorption that can be related to complicated phase and structural transformation behaviour that occurs on de-solvation and re-solvation, including major conformational changes to the geometry of the flexible L1 ligand. [Co2 (L1)(bpdc)2 ], where bpdc=biphenyl-4,4'-dicarboxylate, has a unique six-connected self-catenating framework structure. Solvation changes occur without significant structural change and a partially-hydrolysed material binds its own decomposition products as guests.

Multimetallic and Mixed Environment Iridium(III) Complexes: A Modular Approach to Luminescence Tuning Using a Host Platform.

Mononuclear and trinuclear bis-cyclometallated IrIII complexes of the host ligands tris(4-[4'-methyl-2,2'-bipyridyl]methyl)cyclotriguaiacylene (L1) and tris(4-(4'-methyl-2,2'- bipyridyl)carboxy)cyclotriguaiacylene (L2) have been prepared. Complexes [{Ir(ppy)2 }3 (L1)](PF6 )3 (1.1), [{Ir(ppy)2 }(L1)](PF6 )3 (1.2), [{Ir(ppy)2 }3 (L2)](PF6 )3 (2.1) and [{Ir(ppy)2 }(L2)](PF6 )3 (2.2) (where ppy=phenylpyridinato) showed distinct photophysical properties depending on the L ligand. Complexes featuring the L1 ligand were comparatively blue-shifted in solution, with longer lifetimes and higher quantum yields. The mixed bis-cyclometallated IrIII complexes [{Ir(ppy)2 }{Ir(dFppy)2 }2 (L1)](PF6 )3 (1.3), [{Ir(ppy)2 }{Ir(dFppy)2 }2 (L2)](PF6 )3 (2.3), [{Ir(ppy)2 }2 {Ir(dFppy)2 }(L1)](PF6 )3 (1.4) and [{Ir(ppy)2 }2 {Ir(dFppy)2 }(L2)](PF6 )3 (2.4) (where dFppy=2,4-difluorophenylpyrinato) were also synthesised. Steady-state and time-resolved spectroscopy, along with electrochemical investigations, show that the Ir(III) chromophores within these mixed Ir-environment species behave as isolated centres, with no energy transfer or electronic communication between them.

Homochiral Self-Sorted and Emissive IrIII Metallo-Cryptophanes.

The racemic ligands (±)-tris(isonicotinoyl)-cyclotriguaiacylene (L1), or (±)-tris(4-pyridyl-methyl)-cyclotriguaiacylene (L2) assemble with racemic (Λ,Δ)-[Ir(ppy)2 (MeCN)2 ]+ , in which ppy=2-phenylpyridinato, to form [{Ir(ppy)2 }3 (L)2 ]3+ metallo-cryptophane cages. The crystal structure of [{Ir(ppy)2 }3 (L1)2 ]⋅3BF4 has MM-ΛΛΛ and PP-ΔΔΔ isomers, and homochiral self-sorting occurs in solution, a process accelerated by a chiral guest. Self-recognition between L1 and L2 within cages does not occur, and cages show very slow ligand exchange. Both cages are phosphorescent, with [{Ir(ppy)2 }3 (L2)2 ]3+ having enhanced and blue-shifted emission when compared with [{Ir(ppy)2 }3 (L1)2 ]3+ .

Metallo-cryptophanes decorated with bis-N-heterocyclic carbene ligands: self-assembly and guest uptake into a nonporous crystalline lattice.

Pd3L2 metallo-cryptophane cages with cyclotriveratrylene-type L ligands can be stabilized by use of a bis-N-heterocyclic carbene as an auxiliary cis-protecting ligand, while use of more common protecting chelating ligands such as ethylenediamine saw a Pd3L2 to Pd6L8 rearrangement occur in solution. The crystalline Pd3L2 complexes act as sponges, taking up 1,2-dichorobenzene or iodine in a single-crystal-to-single-crystal fashion despite not exhibiting conventional porosity.

Solvent-dependent self-assembly behaviour and speciation control of Pd6L8 metallo-supramolecular cages.

The C3-symmetric chiral propylated host-type ligands (±)-tris(isonicotinoyl)-tris(propyl)-cyclotricatechylene (L1) and (±)-tris(4-pyridyl-4-benzoxy)-tris(propyl)-cyclotricatechylene (L2) self-assemble with Pd(II) into [Pd6L8](12+) metallo-cages that resemble a stella octangula. The self-assembly of the [Pd6(L1)8](12+) cage is solvent-dependent; broad NMR resonances and a disordered crystal structure indicate no chiral self-sorting of the ligand enantiomers in DMSO solution, but sharp NMR resonances occur in MeCN or MeNO2. The [Pd6(L1)8](12+) cage is observed to be less favourable in the presence of additional ligand, than is its counterpart, where L=(±)-tris(isonicotinoyl)cyclotriguaiacylene (L1 a). The stoichiometry of reactant mixtures and chemical triggers can be used to control formation of mixtures of homoleptic or heteroleptic [Pd6L8](12+) metallo-cages where L=L1 and L1 a.

Stable mixed-valent radicals from platinum(II) complexes of a bis(dioxolene) ligand.

Three diplatinum(II) complexes [{PtL}2(µ-thea)] (H4thea = 2,3,6,7-tetrahydroxy-9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene) have been prepared, with diphosphine or bipyridyl "L" co-ligands. One-electron oxidation of these complexes gave radical cations containing a mixed-valent [thea·](3-) ligand with discrete catecholate and semiquinonate centers separated by quaternary methylene spacers. The electronic character of these radicals is near the Robin-Day class II/III border determined by UV/Vis/NIR and EPR spectroscopies. Crystal-structure determinations and a DFT calculation imply that oxidation of the thea(4-) ligand may lead to an increased through-space interaction between the dioxolene π systems.

Solid-phase methodology for synthesis of O-alkylated aromatic oligoamide inhibitors of α-helix-mediated protein-protein interactions.

Rapid access to rigid rods: A method is described for the synthesis of 3-O-alkylated aromatic oligobenzamide foldamers that could be used for assembly of libraries of α-helix mimetic inhibitors of protein-protein interactions (see scheme; Fmoc=9-fluorenylmethoxycarbonyl).

Construction of metal-organic frameworks: versatile behaviour of a ligand containing mono- and bidentate coordination sites.

Five new coordination polymers based on a new 2,2'-bipyridine derived ligand N,N'-bis(pyridin-4-yl)-2,2'-bipyridine-5,5'-dicarboxamide (=L) are reported herein. Isostructural three-dimensional coordination polymers with a rare (4,6)-connected network of {4(4).6(2)}(3){4(6).8(9)}(2) topology were synthesised from Cu(NO(3))(2), Zn(NO(3))(2) or a mixture of Cu(NO(3))(2)/Fe(BF(4))(2) with L in complexes {[Cu(5)L(6)]·(NO(3))(10)·(H(2)O)(18)}(∞) (1), {[Zn(5)L(6)]·(NO(3))(10)·(H(2)O)(18)}(∞) (2) and {[Fe(x)Cu(y)L(6)]·(NO(3))(10)·(H(2)O)(18)}(∞) (3; where x+y=5). Complexes with two-dimensional grid structures resulted from treatment with CoCl(2) or Cd(NO(3))(2) with L in complexes {[CoLCl(2)]·DMF}(∞) (4) and {CdL(NO(3))(2)}(∞) (5).

Coordination polymers utilizing N-oxide functionalized host ligands.

Pyridyl functionalized host molecules are oxidized to their N-oxide analogues and form a series of coordination polymers and discrete complexes with transition metal cations. Complex {[Ag(3)(NMP)(6)(L1)(2)]·3(ClO(4))}(∞) where L1 = tris(isonicotinoyl-N-oxide)cyclotriguaiacylene, NMP = N-methylpyrrolidone, is a three-dimensional (3-D) 3,6-connected coordination polymer of pyrite-like (pyr) topology and features ligand unsupported argentophilic interactions, while two-dimensional (2-D) 3,6-connected coordination polymers with the rarely reported kagome dual (kgd) topology are found for [M(L1)(2)](2+) where M = Zn, Cd, Cu. Ligand L2 = tris(nicotinoyl-N-oxide)cyclotriguaiacylene forms a 2-D coordination polymer with 4(4) (sql) grid topology in complexes {[M(L2)(2)(DMF)(2)]·2ClO(4)·8(DMF)}(∞) M = Cd or Cu, DMF = N,N'-dimethylformamide, and a double-linked chain structure in {[Co(L2)(2)(DMF)(2)]·2NO(3)·4(DMF)·H(2)O}(∞), and both types of structure feature hand-shake self-inclusion motifs either within or between the polymers. 2-D coordination networks with 6(3) (hcb) topologies are found in complexes {[M(L3)(NO(3))(2)]·2(DMF)}(∞) (M = Cd, Zn) and {[Cu(5)(L3)(2)Cl(10)(NMP)(4)]}(∞) where L3 = tris(2-pyridylmethyl)cyclotriguaiacylene, while [Ag(2)(L3)(2)(NMP)(4)]·2(BF(4))·2(NMP) has a discrete dimeric structure which again shows hand-shake host-guest interactions supported by π-π stacking.

2-O-alkylated para-benzamide α-helix mimetics: the role of scaffold curvature.

The design and synthesis of a new 2-O-alklyated benzamide α-helix mimetic is described. Comparison with regioisomeric 3-O-alkylated benzamides permits a preliminary evaluation of the role that mimetic curvature has in determining molecular recognition properties.

Multipurpose made colorimetric materials for amines, pH change and metal ion detection.

Sensors are routinely developed for specific applications, but multipurpose sensors are challenging, due to stability and poor functional design. We report organic materials that operate in solution and gas phase. They show a strong response behaviour to at least three types of environmental changes: pH, amine and metal ion binding/detection. We have confirmed and validated our findings using various analytical and computational methods. We found that the changes in polarity of the solvent and pH not only red shift the tail of the absorption spectra, but also extend the peak optical absorption of these structures by up to 100 nm, with consequential effects on the optical gap and colour changes of the materials. Acid-base response has been studied by spectrophotometric titrations with trifluoroacetic acid (TFA) and triethyl amine (TEA). The experiments show excellent reversibility with greater sensitivity to base than acid for all compounds. Analysis into metal sensing using Zn(ii) and Cu(ii) ions as analytes show that the materials can successfully bind the cations forming stable complexes. Moreover, a strong suppression of signal with copper gives an operative modality to detect the copper ion as low as 2.5 × 10-6 M. The formation of the metal complexes was also confirmed by growing crystals using a slow diffusion method; subsequent single crystal X-ray analysis reveals the ratio of ligand to metal to be 2 to 1. To test sensitivity towards various amine vapours, paper-based sensors have been fabricated. The sensors show a detection capability at 1 ppm of amine concentration. We have employed CIE L*a*b* colour space as the evaluation method, this provides numeric comparison of the samples from different series and allows comparison of small colour differences, which are generally undetectable by the human-eye. It shows that the CIE L*a*b* method can assess both sensitivity to a particular class of analytes and a specificity response to individual amines in this subclass offering an inexpensive and versatile methodology.

Managing research throughout COVID-19: Lived experiences of supramolecular chemists.

The international Women in Supramolecular Chemistry network believes that taking an area-specific approach effectively supports equality, diversity, and inclusion. Science lacks diversity, and this is intersectional. We share effects of coronavirus disease 2019 (COVID-19) by triangulating findings from an online survey, a collaborative autoethnography, and reflective group research meetings. We show how qualitative research with the community offers insights into challenges and supports individuals, and we demonstrate that research leaders have often taken responsibility for their teams' mental health and well-being at the cost of their own.

Recent advances in the chemistry of cyclotriveratrylene.

New chemistry of the cyclic molecular host cyclotriveratrylene (CTV) includes applications such as in sensors and separations; in self-organised materials such as gels, liquid crystals, dendritic systems, and self-assembled monolayers; and in metallo-supramolecular chemistry. This tutorial review covers aspects of CTV chemistry interest to supramolecular, coordination and host-guest chemists as well as those interested in self-organised systems.

Ag(I) organometallic coordination polymers and capsule with tris-allyl cyclotriveratrylene derivatives.

Tris-allyl-cyclotriguaiacylene combines with silver salts to give a range of crystalline network structures and one discrete complex. A number of different coordination modes are found within the complexes including η(2)-allyl, aryl, and OR groups binding to Ag(I). AgSbF(6) gives two types of three-dimensional (3-D) coordination polymer with unusual topologies, along with a discrete Ag(2)L(2) capsule dependent on reaction stoichiometry and reaction conditions. Isostructural coordination chain structures are found with AgBF(4) and AgClO(4), while use of Ag(CF(3)SO(3)) gives two-dimensional (2-D) and 3-D coordination polymers through bridging triflate anions.

Tripodal 4-pyridyl-derived host ligands and their metallo-supramolecular chemistry: stella octangula and bowl-shaped assemblies.

The synthesis of five new cyclotriveratrylene derivatives with 4-pyridyl side arms is reported, along with the crystal structures of three of these. Three ligands with extended 4-pyridylphenyl side arms and a ligand derived from cyclotriphenolene have been shown to form [Pd(6)L(8)](12+) stella octangula assemblies using diffusion-ordered spectroscopy NMR and electrospray MS techniques. This confirms the generality of the stella octagula assembly, providing that the ligand arms show a degree of rigidity. The more flexible ether-linked ligand tris(4-pyridylmethyl)cyclotriguaiacylene forms a smaller [Pd(3)L(4)](6+) bowl-shaped assembly in the solid state and in solution. The previously reported ligand tris(4-pyridylmethylamino)cyclotriguaiacylene forms a similar assembly in solution.

Cyclotriveratrylene-tethered trinuclear palladium(ii)-NHC complexes; reversal of site selectivity in Suzuki-Miyaura reactions.

The trinuclear complexes [{PdI2(pyCl)}3(L1)] C1 and [{PdI2(pyCl)}3(L2)] C2, where pyCl = 3-chloropyridine, L1 = methyl(cyclotriguaiacylenyl)methylbenzimidazol-2-ylidene and L2 = benzyl(cyclotriguaiacylenyl)methylbenzimidazol-2-ylidene, each feature three palladium N-heterocyclic carbene (NHC) centres tethered onto a host-type cyclotriguaiacylene scaffold. Crystal structures of different solvates of complex C1 reveal different host-guest motifs including intra-cavity binding of dioxane guests concomitant with intramolecular halogen bonding interactions of C1. Mononuclear NHC analogues of C1 and C2, namely [PdI2(pyCl)(L3)] C3 and [PdI2(pyCl)(L4)] C4, where L3 = (3-chloropyridyl)-1-(2-methoxyphenyoxy)methyl-3-methylbenzimidazol-2-ylidene and L4 = (3-chloropyridyl)-1-(2-methoxyphenyoxy)methyl-3-benzylbenzimidazol-2-ylidene, were also synthesised and their crystal structures determined. Complexes C1-C4 are competent catalysts for Suzuki Miyaura cross-coupling, and interestingly exhibit a switch in the normal regioselectivity observed for reactions of 2,4-dibromopyridine with aryl boronic acids, usually C2-selective, yielding C4-arylated product preferentially over C2-arylated product.

The dimeric "hand-shake" motif in complexes and metallo-supramolecular assemblies of cyclotriveratrylene-based ligands.

A series of clathrate and metal complexes with cyclotriveratrylene-like molecular host ligands show a similar dimeric homomeric inclusion motif in which a ligand arm of one host is the intra-cavity guest of another and vice versa. This "hand-shake" motif is found in the trinuclear transition metal complex [Cu(3)Cl(6)(1)]CH(3)CN1.5 H(2)O in which 1 is tris(4-[2,2',6',2''-terpyridyl]benzyl)cyclotriguaiacylene; in the self-included M(4)L(4) tetrahedral metallo-supramolecular assembly [Ag(4)(2)(4)] (BF(4))(4) in which 2 is tris-(2-quinolylmethyl)cyclotriguaiacylene; in the 1D coordination chains [Ag(4)]ReO(4) CH(3)CN and [Ag(5)]SbF(6)3 DMFH(2)O in which 4 is tris(1H-imidazol-1-yl)cyclotriguaiacylene and 5 is tris{4-(2-pyridyl)benzyl}cyclotriguaiacylene; and in the acetone clathrate of tris{4-(2-pyridyl)benzyl-amino}cyclotriguaiacylene. Clathrates of ligands 2 and 5 do not show the same dimeric motif, although 2 has an extended homomeric inclusion motif that gives a hexagonal network.