Whither Second-Sphere Coordination?

Open AccessCCS ChemistryMINI REVIEW1 Mar 2022Whither Second-Sphere Coordination? Wenqi Liu, Partha J. Das, Howard M. Colquhoun and Fraser Stoddart Liu Department of Chemistry, Northwestern University, Evanston, IL 60208 Google Scholar More articles by this author , Das *Corresponding authors: E-mail Address: [email protected] University Reading, Reading RG6 6DX School New South Wales, Sydney, NSW 2052 Institute Molecular Science, Zhejiang Hangzhou 310027 ZJU-Hangzhou Global Scientific Technological Innovation Center, 311215 https://doi.org/10.31635/ccschem.021.202101286 SectionsAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The properties coordination complexes are dictated both the metals ligands. use molecular receptors as second-sphere ligands enables significant modulation chemical physical complexes. In minireview, we highlight recent advances in functional systems based on ligands, applied recognition, synthesis mechanically interlocked molecules, separation metals, catalysis, biomolecular chemistry. These demonstrate that is an emerging very promising strategy for addressing societal challenges health, energy, environment. Download figure PowerPoint Introduction Coordination chemistry,1 investigation linking directly a central atom—most often metal center—is at heart modern inorganic, organic, materials specific combinations dictate structures resulting complexes, which numerous technologies, including metal–organic frameworks (MOFs),2–16 optical magnetic materials,17,18 catalysis,19,20 biomedical theranostics.21–24 linked center referred (Figure 1) first sphere metal.25–28 Meanwhile, another set can bind first-sphere complex through noncovalent bonding interactions, leading adducts. Thus, centers affords adducts essentially Figure 1 | Structural formulas depicting similarity three-point binding models (a) primary alkyammonium ion [RNH3]+ (b) transition-metal ammine. (c) Graphical representation concept coordination. A transition (M) coordinated with L1, interact L2 interactions. Adapted permission from ref 35. Copyright 1983 Royal Society Chemistry. 1c) was advanced instance Chemistry Nobel Prize Laureate Alfred Werner29,30 1913. He showed could explain number experimental observations not be understood solely basis coordination.29 included (1) formation between amines coordinatively saturated such [M(acac)3]n+, (2) presence solvents crystal many (3) solvent counterion-dependent associated rotations chiral Beginning early 1980s, sought gain insight into nature investigating interactions synthetic receptors.31 Crown ethers well-known form alkylammonium ions, [RNH3]+, hydrogen ion-dipole interactions.32–34 It occurred us geometric electronic (stereoelectronic) features closely resemble (Figures 1a 1b) those ammine complex,35 [MLx(NH3)]n+. recognition led our initial investigations crown ether isolation novel series complexes,36–39 whose superstructures were quickly established X-ray crystallography. 2 presents collage [(a)–(s)] some solid-state reproduced review25 published Angewandte Chemie “Second-Sphere Coordination—A Novel Rôle Receptors” 1986. review one literature copious color: time, it cost equivalent £10,000. One most remarkable examples 2j 2k) 1?1 adduct formed38 dibenzo[30]crown-10 (DB30C10) [Pt(bpy)(NH3)2]2+. fascinating feature superstructure that, addition three pairs [N–H?O] bonds oxygen atoms NH3 there close, complementary [???] stacking (charge transfer) two ?-electron-rich aromatic (catechol) rings receptor molecule ?-electron-poor 2,2?-bipyridine ligand platinum-based substrate. This shown 1H NMR spectroscopy exist stable solution well solid state.38 high stability sustained multiple weak complex. contrast, conventional water or alcohols, only monovalent binding, well-defined observed crystallographically state solution. For example, superstructure38 lanthanum [La(tptz)(NO3)3(H2O)]•2C2H5OH, ethanol molecules H2O molecule. Although well-defined, no suggestion exists receptors, when employed lead stable, robust, predictable contrast formed weakly state. sampling macrocyclic taken 1986 Chemie, where presented space-filling ball-and-stick [{trans-Pt(PMe3)Cl2(NH3)}2•l8C6]; [{cis-Pt(NH3)2Cl2•dma}2•l8C6]; (c d) [Cu(NH3)4(H2O)•18C6]n2n+; (e) [Rh(cod)(NH3)2•DB21C7]+; (f) [Rh(nbd)(NH3)2•DB24C8]+; (g) [diammine-1,1-cyclobutanecarboxylatoplatinum(II)-?-CD]; (h) [Pt(en)2•18C6]n2n+; (i) diamminebis-(1,5-cyclooctadiene)(?-l,4-l0,l3-tetraoxa-7,l6-diazacyclooctadecane-N7,N16)-dirhodium bis(hexafluorophosphate); (j k) [Pt(bpy)(NH3)2•DB30C10]2+; (l) [SnCl4(H2O)2•18C6][H2O]2; (m) [{trans-Ir(CO)(CH3CN)(PPh3)2}2•18C6]2+; (n) [Rh(cod)(NH3)2•?-CD]+; (o) [Mn(H2O)6•18C6]nn+ (ClO4? salt); (p q) [trans-Pt(PMe3)Cl2(NH3)•DB18C6]; (r) [Rh(cod)(NH3)2•DB24C8]+; (s) [Rh(cod)(NH3)2•DB30C10]+. [Pt(bpy)(NH3)2•DB30C10]2+ inside highlighted rectangle will discussed Box 1. 25. John Wiley Sons. may noted bipyridine-based (j) (k) provided (Box inspiration subsequent research dibenzo-crown dicationic bipyridinium herbicides Diquat, derived 2,2?-bipyridine, Paraquat, 4,4?-bipyridine. success latter turn discovery tetracationic cyclophane, cyclobis(paraquat-p-phenylene), known Blue Box, has since proved hugely valuable component developing field (MIMs) eventually artificial machines (AMMs). 40-year trail illustrating how observation 1981 line so on—and dynamic over four decades. Following work using surge study Numerous polycyclic ethers,39–50 cyclodextrins 3a 3b),51–65 calixarenes 3e),66–71 resorcinarenes 3d),72 pillararenes 3f),73 cucurbiturils 3c),74 cyclophanes75–79 all efficient even, examples, acted simultaneously first- 2i).80–83 As result, discovered exploiting whole range bonding, charge transfer, stacking, hydrophobic effects, van der Waals Summaries these chemistry found several reviews,25–28,84–90 other groups. 3 Representative reported researchers. Tubular 2?2?1 ?-cyclodextrin•12-crown-4•K+. 4?5 ?-cyclodextrin•ferrocene. cucurbit[6]uril•[Yb(OH2)8]3+[ReO4]?. (d) resorcinarene•ferrocene. [Cu(NC5H5)2(H2O)4•calix[4]arene sulfonate]. (n-octyl)MgBr(THF)2•pillar[5]arene. Over past decades, been resurgence interest Advances supramolecular, biomolecular, have created91,92 new demands capable wide substrates, constructing MIMs, separating different catalyzing organic reactions. contexts, emerged solving previously intractable problems. minireview highlights Recognition Second-sphere design construction supramolecular incorporating sites followed their metals. participate either indirectly via simultaneous coordination, targeting substrates tailored receptor-substrate metal-ligand Loeb et al.50,80–83,93,94 demonstrated example involves80,94 family thiacyclophane recognize DNA nucleobases. displayed involves types interaction, N atom nucleobase substrate Pd(II) center, NH2 group polyether O spacing units substrates. Single-crystal analyses involving adenine guanine—the BF3 adduct—reveals mentioned above near-ideal interaction parameters 4a 4c). cytosine realized having analysis 4b) reveals direct aided abetted hydrogen-bonding receptor. nucleobases same principles applied81–83 designing barbiturates, amino acids, amines, hydrazinium ions. 4 Stick representations complexed adenine, cytosine, guanine (BF3) combination [?–?] electron-rich electron-poor Huc al.95–98 5a) community capsules metal-coordination-directed folding helical oligomer. key chain segment, pyridazine–pyridine–pyridazine (pyz–pyr–pyz), introduced oligomer.95 segment anti–anti conformation favored repulsion endocyclic atoms, directing oligomer extended instead capsular shape. displays propensity absence ions Cu+, Cu2+, Ag+, alkali Na+ K+, induces shape favoring syn–syn pyz–pyr–pyz segment.96 cases, positioned side cavity wall, leaving its occupied partially available guest. guests enhance affinity helix, while guest inner wall capsule leads size selectivity. Moreover, hydrated Ca2+ Ba2+ occurs entirely second sphere, ion-coordinated oligomeric but still results95 geometry 5 Schematic illustration folding. Stick-and-sphere ?-d-mannopyranose foldamer Cu2+. zoomed-in view hydrogen-bond (dashed lines) hydroxyl groups ?-d-mannopyranose. Cu2+ adopts square pyramidal geometry, coordinating nitrogen molecules. 97. 2018 extension earlier reports, authors carbohydrates97 foldamer-type capsules, taking advantage Depending show affinities diastereoselectivities toward carbohydrates, d/l-threitol, xylitol, d/l-mannopyranose, d/l-glucopyranose, d/l-galactopyranose, d/l-fructopyranose. binds d-threitol 14 times more strongly than K+ counterpart. X-Ray Cu2+-coordinated d/l-mannopyranose 5b 5c) bond hydroxy mannopyranose. d-mannopyranose assumes ?-pyranose configuration predominantly (97%) ?-pyranose CHCl3/Me2SO (4?1, v/v) also single-crystal d/l-threitol smaller analog ion. Here, interacts solvents—a MeOH molecule—that developed strategy98 prepare shells around [2Fe–2S] cluster. shell influences structural spectroscopic cluster, desymmetrization confinement part within cavity. Leigh al.99–102 chloride anions knots. knots synthesized 6a) transmetallation Zn(II) infused pentafoil (51) knot tetrafluoroborate salts Co(II), Cu(II), Ni(II).99 metallated exhibit single anion utilizing [CH?Cl?] electrostatic transmetallated reveal 6b–6d) five 15 bipyridine lined 10 H array located type exhibited molecular-knot geometry. diameter varies depending cation: 3.3 Å Fe(II), Zn(II), Ni(II), 3.5 Co(II). metal-to-metal distance distorted cobalt is, however, case iron, nickel, zinc metal–metal–metal angle higher compared metallic conformational changes knotted distances vary M(II) nearly orders magnitude, Ka = 8 × 104 M?1 (Cu2+ knot) 107 (Fe2+ MeCN. 6 various transmetalation Ni(II). knot, providing Ball-and-stick Co2+, Ni2+, Zn2+. Cl? determined Construction Mechanically Interlocked Molecules MIMs103–108 catenanes,109–122 rotaxanes,123–132 suitanes133–139 become intense activity account potential act machines.140–153 Several effective strategies synthesizing MIMs achieved, template effect.154–156 promote structures.157–168 strategy, advance MIMs. Wisner al.169–173 rotaxanes catenanes. described [2]pseudorotaxanes step employing coordination.169 An isophthalamide-based tetralactam macrocycle, serving ligand, establishes sets trans-palladium dichloride complex, pseudorotaxane. pseudorotaxane diminishes markedly halide increases Cl < Br I. investigation, reported170 [2]rotaxane system. To produce architecture 7a, 4-(3,5-di-tert-butylbenzyloxy)-pyridine terminal sterically demanding function stoppers prevent dethreading macrocycle. rotaxane obtained 89% isolated yield simply mixing trans-bis(benzonitrile)palladium(II) CHCl3 room temperature. soluble remains time under column chromatographic conditions. structure confirmed crystallographic analysis, revealed 7b) amide isophthalamide subunits macrocycle establish palladium(II) driving force formation. investigations, explored172 stabilities pseudorotaxanes varying para-substituted pyridine ligand. They bond-accepting ability tuned electron-donating/-withdrawing coligands. decreases slightly replaced Pt(II). Replacing thiocyanate 7c) (pseudo)rotaxanes (hydrogen bonding) macrocycle.171 directional doubly degenerate ring shuttles back forth 3300 °C. 7 formula tubular constructed shuttle moves along dumb-bell shaped axle CDCl3 170. 2006 al.173 catenanes 8a) acyclic bidentate resembles three-quarter unit designed synthesized. coordinates PdCl2 trans arrangement, product comprises pair catenated macrocycles, each subunit trans-PdCl2L2 scaffold. catenation driven mutual PdCl2L2 orthogonally partner. catenane 87% heating equimolar amount Pd(PhCN)2Cl2 trans-bidentate 8b) effect manifested opposing cavities. Eight [NH?Cl] reversible transformation polarity. Transformation individual macrocycles sample dissolved mixed system (CD3)2SO/CDCl3 result competitive polar NH re-forms redissolved CDCl3. disposed 173. 2007 Metal Separation solubility adducts, utilized We 9c) copper using35 principle 1983. 18C6 9a) polymeric [Cu(NH3)4(H2O)][PF6]2, precipitation aqueous