Synthesis, characterization and solid state structures of thiosemicarbazone palladacycles: Influence of hydrogen bonding in the molecular arrangement

Treatment of the thiosemicarbazones 4-FC₆H₄C(Me)NN(H)C(S)NHR, (R = Me, a; Ph, b) and 2-ClC₆H₄C(Me)NN(H)C(S)NHR (R = Ph, c) with lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complex [Pd{4-FC₆H₃C(Me)NNC(S)NHR}]₄ (1a, 1b) and [Pd{2-ClC₆H₃C(Me)NNC(S)NHPh}]₄ (1c). Reaction of these tetramers with the diphosphines dppe, t-dppe, dppp or dppb in a 1:2 molar ratio gave the dinuclear cyclometallated complexes [(Pd{4-FC₆H₃C(Me)NNC(S)NHR})₂(μ-Ph₂P(CH₂)_nPPh₂)], (n = 2, 2a, 2b; 3, 4a, 4b; 4, 5a, 5b), [(Pd{4-FC₆H₃C(Me)NNC(S)NHPh})₂(μ-Ph₂PCHCHPPh₂)], (3a, 3b) and [(Pd{2-ClC₆H₃C(Me)NNC(S)NHR})₂(μ-Ph₂P(CH₂)_nPPh₂)], (n = 2, 2c, 2d; 3, 4c, 4d; 4, 5c, 5d), [(Pd{2-ClC₆H₃C(Me)NNC(S)NHPh})₂(μ-PPh₂CHCHPPh₂)], (3c, 3d). The X-ray crystal structure of the ligand b and the complexes 3c, 4a and 4d were determined. The structures of complexes 4a and 4d show that the different disposition of the chain cyclometallated of the thiosemicarbazones (in the same orientation or in the opposite one) is due to the different H bonds produced.     

Syntheses, structural and spectroscopic characterization of novel zinc(II)-bis(trithiocarbimato) complexes and bis(N-methylsulfonyldithiocarbimate)-sulfide

Four zinc(II)-bis(trithiocarbimato) complexes with the general formula A₂[Zn(RSO₂NCS₃)₂] [A = Ph₄P⁺: R = CH₃ (1), 4-CH₃C₆H₄ (2); A = Bu₄N⁺: R = CH₃ (3), 4-CH₃C₆H₄ (4)] were obtained by the reaction of sulfur with the correspondent zinc(II)-bis(dithiocarbimato) complexes. Additionally, the compound (Ph₄P)₂[(CH₃SO₂NCS₂)₂S)] (5) was prepared from the potassium methylsulfonildithiocarbimate by oxidation with iodine. The compounds were characterized by elemental analyses and IR, ¹H NMR and ¹³C NMR spectroscopies. The compounds 4 and 5 were also characterized by X-ray diffraction techniques. The compound 4 crystallizes in the centrosymmetric space group C2/c of the monoclinic system. The Zn(II) is in a distorted tetrahedral environment (ZnS₄) in compound 4, and differ from the coordination mode observed in compound 1, which involves one sulfur and one nitrogen atom of each trithiocarbimate ligand. Compound 5 is the first example of a compound containing a bis(N-alkylsulfonyldithiocarbimate)-sulfide dianion and crystallises in the non-centrosymmetric space group P4₁2₁2 of the tetragonal system.     

Linear homobimetallic palladium complexes with end-capped SC(O)Me units

Rigid-rod structured homobimetallic palladium complexes of type [{trans-(Me(O)CS-4-C₆H₄-C₆H₄)(Ph₃P)₂Pd}₂(μ-N^∩N)](OTf)₂ (8a, μ-N^∩N = 4,4′-bipyridine, bpy; 8b, μ-N^∩N = C₅H₄N-CHN-NCH-C₅H₄N; 8c, μ-N^∩N = C₅H₄N-CHCH-C₆H₄-CHCH-C₅H₄N; 8d, μ-N^∩N = C₅H₄N-CHN-C₆H₄-NCH-C₅H₄N) were synthesized by the reaction of trans-[(Me(O)CS-4-C₆H₄-C₆H₄)(Ph₃P)₂Pd](OTf) (6) with 0.5 equivalents of N^∩N (7a, N^∩N = bpy; 7b, N^∩N = C₅H₄N-CHN-NCH-C₅H₄N; 7c, N^∩N = C₅H₄N-CHCH-C₆H₄-CHCH-C₅H₄N; 7d, N^∩N = C₅H₄N-CHN-C₆H₄-NCH-C₅H₄N) in high yield. Complex 6 was accessible by the subsequent reaction of I-4-C₆H₄-C₆H₄-4′-SC(O)Me (2) with [(PPh₃)₄Pd] (3) to produce trans-[(I)(Me(O)CS-4-C₆H₄-C₆H₄)(Ph₃P)₂Pd] (4) which further reacted with AgOTf (5) to give 6.The structures of 4 and 8c in the solid state are reported. Most characteristic for these systems is the square-planer coordination geometry of palladium with trans-positioned PPh₃ groups. This automatically positions the iodo ligand and the Me(O)CS-4-C₆H₄-C₆H₄ unit (complex 4) or the nitrogen donor atoms of the C₅H₄N-CHCH-C₆H₄-CHCH-C₅H₄N connectivity and the thio-acetyl group Me(O)CS-C₆H₄-C₆H₄ (complex 8c) trans to each other. In 8c a Pd-Pd separation of 20.156 Å is typical.The electrochemical redox behavior of 2, 4 and 8 is discussed.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of tungsten (R′O)2(ArN)WCH-SiR2-CHW(NAr)(OR′)2 (R = Me, Ph) and (R′O)2(ArN)WCH-SiMe2SiMe2-CHW(NAr)(OR′)2

Bimetallic alkylidene complexes of tungsten (R′O)₂(ArN)WCH-SiR₂-CHW(NAr)(OR′)₂ (R = Me (1), Ph (2)) and (R′O)₂(ArN)WCH-SiMe₂SiMe₂-CHW(NAr)(OR′)₂ (3) (Ar = ; R′ = CMe₂CF₃) have been prepared by the reactions of divinyl silicon reagents R₂Si(CHCH₂)₂ with known alkylidene compounds R′′-CHMo(NAr)(OR′)₂. (R′′ = Bu^t, PhMe₂C) Complexes 1-3 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1-3 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and 3 and predominant cis-units content in the case of 2.     

Cyclometallated thiosemicarbazone palladium(II) compounds: The first crystal and molecular structures of mononuclear complexes with a η-diphosphine ligand

Treatment of the thiosemicarbazones 2-XC₆H₄C(Me)NN(H)C(S)NHR (R = Me, X = F, a; R = Et, X = F, b; R = Me, X = Cl, c; R = Et, X = Br, d) with potassium tetrachloropalladate(II) in ethanol, lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid, as appropriate, gave the tetranuclear cyclometallated complexes [Pd{2-XC₆H₃C(Me)NNC(S)NHR}]₄ (1a-1d). Reaction of 1a-1d with the diphosphines Ph₂PCH₂PPh₂ (dppm), Ph₂P(CH₂)₂PPh₂ (dppe), Ph₂P(CH₂)₃PPh₂ (dppp) or trans-Ph₂PCHCHPPh₂ (trans-dpe) in 1:2 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-XC₆H₃C(Me)NNC(S)-NHR]}₂(μ-diphosphine-P,P)] (2a-5a, 3b, 3d, 4c, 5c). Reaction of 1a, 1b with the short-bite or long-bite diphosphines, dppm or cis-dpe, in a 1:4 molar ratio gave the mononuclear cyclometallated complexes [Pd{2-XC₆H₃C(Me)NNC(S)NHR}(diphosphine-P)] (6a, 6b, 7a). The molecular structure of ligand a and of complexes 1a, 3d, 5a, 5c, 6a, 6b and 7a have been determined by X-ray diffraction analysis. The structure of complex 7a shows that the long-bite cis-bis(diphenylphosphino)ethene phosphine appears as monodentate with an uncoordinated phosphorus donor atom.     

Synthesis, structures and some reactions of Ru(CCCCFc)(PP)Cp (PP = dppm, dppe) and related compounds

The compounds Ru(CCCCFc)(PP)Cp [PP = dppe (1), dppm (2)], have been obtained from reactions between RuCl(PP)Cp and FcCCCCSiMe₃ in the presence of KF (1) or HCCCCFc and K[PF₆] (2), both with added dbu. The dppe complex reacts with Co₂(CO)₆(L₂) [L₂ = (CO)₂, dppm] to give 3, 4 in which the Co₂(CO)₄(L₂) group is attached to the outer CC triple bond. The PPh₃ analogue of 3 (5) has also been characterised. In contrast, tetracyanoethene reacts to give two isomeric complexes 6 and 7, in which the cyano-olefin has added to either CC triple bond. The reaction of RuCl(dppe)Cp with HCCCCFc, carried out in a thf/NEt₃ mixture in the presence of Na[BPh₄], gave [Ru{CCC(NEt₃)CHFc}(dppe)Cp]BPh₄ (8), probably formed by addition of the amine to an (unobserved) intermediate butatrienylidene [Ru(CCCCHFc)(dppe)Cp]⁺. The reaction of I₂ with 8 proceeds via an unusual migration of the alkynyl group to the Cp ring to give [RuI(dppe){η-C₅H₄CCC(NEt₃)CHFc}]I₃ (9). Single-crystal X-ray structural determinations of 1, 2 and 4-9 are reported.     

Cyclometallated platinum(II) compounds with imine ligands derived from amino acids: Synthesis and oxidative addition reactions

The reactions of [PtMe₂(μ-SMe₂)]₂ with imines 4-ClC₆H₄CHNCHRCO₂Me (R = H (1a), Me (1b), ⁱPr (1c), CH₂C₆H₄(4’-OH) (1d), C₆H₅ (1e), CH₂C₆H₅(1f)) derived from natural amino acids produced under mild conditions cyclometallated platinum(II) compounds [PtMe{κ²-(C,N)-4-ClC₆H₃CHNCHRCO₂Me}(SMe₂)] (2a-2f). These compounds gave the corresponding phosphine derivatives [PtMe{κ²-(C,N)-4-ClC₆H₃CHNCHRCO₂Me}(PPh₃)] (3a-3f). The corresponding cyclometallated platinum(IV) compounds [PtMe₂I{κ²-(C,N)-4-ClC₆H₃CHNCHRCO₂Me}(PPh₃)] (4) arising from intermolecular oxidative addition of methyl iodide were obtained with a high degree of stereo selectivity. Analogous results were obtained for imine 2,6-Cl₂C₆H₃CHNCH(CH₂C₆H₅)CO₂Me (1g) in a process involving intramolecular oxidative addition of a C-Cl bond. The obtained compounds were fully characterized including structure determinations for compounds 3f, 4d and 4f.     

Further reactions of some bis(vinylidene)diruthenium complexes

Whereas {Ru(dppm)Cp*}₂(μ-CCCC) (2) is the only product formed by deprotonation of [{Ru(dppm)Cp*}₂{μ(CCHCHC)}]⁺ with dbu, a mixture of 2 with Ru{CCCHCH(PPh₂)₂[RuCp*]}(dppm)Cp* (3) and {Cp*Ru(PPh₂CHCCH-)}₂ (4) is obtained with KOBu^t. A similar reaction with [{Ru(dppm)Cp*}₂{μ(CCMeCMeC)}]⁺ (5) gave Ru{CCCMeCH(PPh₂)₂[RuCp*]}(dppm)Cp* (6). X-ray structures of 4, 5 and 6 confirm the presence of the 1-ruthena-2,4-diphosphabicyclo[1.1.1]pentane moiety, which is likely formed by an intramolecular attack of the deprotonated dppm ligand on C(1) of the vinylidene ligand. Protonation of {Ru(dppe)Cp*}₂(μ-CCCC) (8-Ru) regenerates its precursor [{Ru(dppe)Cp*}₂{μ(CCHCHC)}]²⁺ (7-Ru). Ready oxidation of the bis(vinylidene) complex affords the cationic carbonyl [Ru(CO)(dppe)Cp*]PF₆ (9) (X-ray structure).     

Synthesis of ruthenium phenylindenylidene, carbyne, allenylidene and vinylmethylidene complexes from (PPh3)3−4RuCl2: A mechanistic and structural investigation

The reaction of (Ph₃P)₃RuCl₂ with 1,1-diphenyl-2-propyn-1-ol was investigated in various solvents. The reaction in thf under reflux is reported to produce the (PPh₃)₂Cl₂Ru(3-phenylindenylidene) complex (3) which has undergone rearrangement of the allenylidene C₃-spine. We have improved the reliability of the reported synthesis by adding acetyl chloride which converts the formed water of the reaction and thus increases the acidity of the reaction solution. Without the additive, we observed the exclusive formation of an intermediate of the transformation and identified it as dinuclear (PPh₃)₂ClRu(μ-Cl)₃(PPh₃)₂RuCCCPh₂ complex (5). The reaction of (Ph₃P)₃₋₄RuCl₂ with 1,1-diphenyl-2-propyn-1-ol in CH₂Cl₂ or C₂H₄Cl₂ under reflux in the presence of excess conc. aqueous HCl afforded the new, neutral (PPh₃)₂Cl₃RuC-CHCPh₂ carbyne complex (7), an HCl adduct of previously elusive (PPh₃)₂Cl₂RuCCCPh₂ complex 6 in high yields. In contrast to the formation of complex 3, the reaction in a non-coordinating solvent did not afford the rearrangement of the allenylidene C₃-spine. Complex 7 was converted into complex 3 in thf under reflux under loss of a molecule HCl. Complex 7 was converted with triethylamine under loss of HCl to complex 6. Pentacoordinate complex 6 was crystallized in the presence of O-donor ligands (EtOH, MeOH and H₂O) to give hexacoordinate (PPh₃)₂Cl₂(ROH)RuCCCPh₂ (R = H, CH₃, C₂H₅) complexes (9)-(11) with the O-donor coordinating in trans-position to the allenylidene moiety. The reaction of complex 7 with 2 equiv. of 4-(N,N-dimethylamino)pyridine (DMAP) gave hexacoordinate (PPh₃)₂Cl₂(DMAP)RuCCCPh₂complex (12) with one molecule DMAP also coordinating in trans-position to the allenylidene group. Methanol and acetic acid in the absence of strong bases afforded the Fischer-carbene complexes (PPh₃)₂Cl₂RuC(OCH₃)-CHCPh₂ (14) and (PPh₃)₂Cl₂RuC(OAc)-CHCPh₂ (15) where the nucleophile added to the α-carbon atom. The structures of complexes 5, 7, 9-11, 14, and 15 were solved via X-ray crystallography.     

Cyclometallation of phenylhydrazones: Synthesis, reactivity, crystal structure analysis and novel trinuclear palladium(II) cyclometallated compounds with [C, N, N′] terdentate ligands

Reaction of the ligand C₆H₅N(H)NCMe(C₅H₄N) (a) with palladium(II) acetate in toluene gave the mononuclear cyclometallated complex [Pd{C₆H₄N(H)NCMe(C₅H₄N)}(AcO)] (1a). Reaction of 1a with sodium chloride gave the analogous chlorine compound [Pd{C₆H₄N(H)NCMe(C₅H₄N)}(Cl)] (3a) which could also be prepared by reaction of a with lithium tetrachloropalladate and sodium acetate in methanol for 48 h; whereas shorter reaction times afforded the non-cyclometallated complex [Pd{C₆H₅N(H)NCMe(C₅H₄N)}(Cl)₂] (2a). Reaction of the ligand 2-ClC₆H₄N(H)NCMe(C₅H₄N) · HCl (b), with palladium(II) acetate, or with lithium tetrachloropalladate and sodium acetate, yielded the cyclometallated complex [Pd2-ClC₆H₃N(H)NCMe(C₅H₄N)(Cl)] (1b). Treatment of 3a and 1b with silver trifluoromethanesulphonate (triflate) and triphenylphosphine in acetone gave the mononuclear complexes [Pd{2-RC₆H_nN(H)NCMe(C₅H₄N)}(PPh₃)][CF₃SO₃], (R = H, n = 4, 4a; R = Cl, n = 3, 2b) with the ligand as C,N,N′ terdentate and substitution of chlorine by triphenylphosphine. Reaction of 3a and 1b with silver triflate and the tertiary diphosphine Ph₂P(CH₂)₄PPh₂ (dppb) in a 2:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-RC₆H₃N(H)NCMe(C₅H₄N)]}₂(μ-Ph₂P(CH₂)₄PPh₂)][CF₃SO₃]₂ (R = H, 5a; R = Cl, 3b) with a μ₂-diphosphine bridging ligand. Similarly, treatment of 3a and 1b with silver triflate and the tertiary triphosphines MeC(CH₂PPh₂)₃ (tripod) and (Ph₂PCH₂CH₂)₂PPh (triphos), in 3:1 molar ratio, gave the novel trinuclear complexes [{Pd[C₆H₄N(H)NCMe(C₅H₄N)]}₃{μ₃-MeC(CH₂Ph₂)₃}][CF₃SO₃]₃ (6a) and [{Pd[2-ClC₆H₃N(H)NCMe(C₅H₄N)]}₃{μ₃-(PPh₂CH₂CH₂)₂PPh}][CF₃SO₃] ₃ (4b) regioselectively, with the phosphine as a μ₃-bridging ligand. When the reaction between 3a and triphos was carried out in 1:1 molar ratio the mononuclear complex [Pd{C₆H₄N(H)NCMe(C₅H₄N)}{(PPh₂CH₂CH₂)₂PPh-P,P,P}][ClO₄] (7a) was obtained. The crystal structures of 2b, 3a and 4a have been determined by X-ray crystallography.     

A ruthenium(II) allenylidene complex with a 4,5-diazafluorene functional group: A new building-block for organometallic molecular assemblies

The synthesis of the new ruthenium(II) allenylidene complex [ClRu(dppe)₂CCC₁₁H₆N₂][OTf] (4) (dppe = 1,2-bis(diphenylphosphino)ethane) terminated with a 4,5-diazafluorene ligand is reported. Further coordination of that metal allenylidene to ruthenium and rhenium moieties leads to the bimetallic adducts [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(bpy)₂}][B(C₆F₅)₄]₃ (5a), [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(^tBu-bpy)₂}][PF₆]₃ (5b) and [ClRu(dppe)₂CCC₁₁H₆N₂{Re(CO)₃Cl}][OTf] (6). Their optical and electrochemical properties show that the allenylidene moiety is an attractive molecular clip for the access to larger original redox-active homo/heteronuclear multi-component supramolecular assemblies. The X-ray crystal structure of the allenylidene metal building block is also described.     

Study of the reactivity of palladacycles containing [C(sp, ferrocene),N,S] or [C(sp),N,S] terdentate ligands with symmetric alkynes

The study of the reactivity of the cyclopalladated complex [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (1c) with the alkynes R¹-CC-R¹ (with R¹ = CO₂Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO₂C-CC-CO₂Me in refluxing CH₂Cl₂ to give [Pd{[(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (2c), which arises from the monoinsertion of the alkyne into the σ[Pd-C(sp², ferrocene)] bond.However, when the reaction was performed using Ph-CC-Ph or Et-CC-Et no evidence of the insertion of these alkynes into the σ[Pd-C(sp², ferrocene)] bond was detected.In contrast with these results, when 1c was treated with the Tl[BF₄] followed by the removal of the TlCl formed and the subsequent addition of MeO₂C-CC-CO₂Me the reaction gave 2c and [Pd{[(MeO₂C-CC-CO₂Me)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}][BF₄] (3c); but when the alkyne was R¹-CC-R¹ (with R¹ = Ph or Et), the ionic palladacycles [Pd{[(R¹-CC-R¹)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}][BF₄] · CH₂Cl₂ [with R¹ = Ph (5c) or Et (6c)] were isolated. In compounds 3c, 5c and 6c, the mode of binding of the butadienyl unit is η³. The reactions of 2c, 3c, 5c and 6c with PPh₃ are also reported. The results obtained from these studies reveal that the σ(Pd-S) bond in 2c is more prone to cleave than in 4c-6c. X-ray crystal structures of 2c, 5c and [Pd{[(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (7c), are also described. Compound 7c arises from 2c by cleavage of the Pd-S bond and the incorporation of a PPh₃ in the coordination sphere of the palladium. A parallel study focused on the reactions of [Pd{[2-CH₂-4,6-Me₂-C₆H₂]-CHN-(C₆H₄-2-SMe)}Cl] (1d) (with a [Csp³,N,S]⁻ terdentate group) with the three alkynes reveals that the σPd-C(sp², ferrocene)] bond of 1c is more reactive than the σ[Pd-C(sp³)] bond of 1d.     

Synthesis and characterization of (CHCH)n-bridged (n = 1, 2, 3) heterobimetallic and trimetallic ferrocene-ruthenium complexes

A series of heterobinuclear ferrocene-ruthenium complexes Fc(CHCH)_nRuCl(CO)(PMe₃)₃ (n = 1, 3; n = 2, 12), Fc(CHCH)RuCl(CO)(Py)(PPh₃)₂ (4), and trimetallic Fc(CHCH)RuCl(CO)(PPh₃)₂(Py-E-(CHCH)Fc) (6) have been prepared. The length of the molecular rods is extended by successive insertion of CHCH spacers in the bridging ligands or the ancillary ligands. The respective products have been fully characterized and the structures of 3 and 12 have been established by X-ray crystallography. Electrochemical studies have revealed that ethenyl heterobimetallic complexes display two successive one-electron processes, and that intermetallic electronic communication between the two endgroups is attenuated with the increase of the length of the conjugated bridge. The electrochemical behavior of the trimetallic complex reveals strong electronic communication between ruthenium and ferrocene transmitted through the ethenyl bridge, however, it also reveals a very weak interaction between ruthenium and ferrocene transmitted through the (E)-CHCH-Py bridge.     

The synthesis and single-crystal X-ray structures of palladium(II) and platinum(II) complexes of the difluorovinyl and 1-chloro-2-fluorovinyl-substituted phosphines, PPh2(Z-CFCFH) and PPh2(E-CClCFH)

The coordination chemistry of the fluorovinyl substituted phosphines PPh₂(Z-CFCFH) and PPh₂(E-CClCFH) with K₂MX₄ (M = Pd, Pt; X = Cl, Br, and I) salts has been investigated resulting in the first reported palladium(II) and platinum(II) complexes of phosphines containing partially fluorinated vinyl groups. The complexes have been characterised by a combination of multinuclear [¹H, ¹³C{¹H}, ¹⁹F, ³¹P{¹H}] NMR spectroscopy, and IR/Raman spectroscopy. The single-crystal X-ray structures of trans-[PdX₂{PPh₂(CFCFH)}₂], X = Cl (1), Br (2), I (3), trans-[PdCl₂{PPh₂(CClCFH)}₂] (4), cis-[PtX₂{PPh₂(CFCFH)}₂], X = Cl (5), Br (6), trans-[PtI₂{PPh₂(CFCFH)}₂] (7), and both cis- and trans-[PtCl₂{PPh₂(CClCFH)}₂] (8), have been determined. Results obtained from spectroscopic and crystallographic data suggest that replacement of a β-fluorine by hydrogen, whilst reducing the steric demand of the ligand, has little effect on the electronic character of the ligand. The presence of a proton in the vinyl group results in short proton-halide secondary interactions in the solid state (d(H?X) = 2.72(3) for 1, and 2.92(5) Å for 2) forming an infinite chain ribbon motif.