Long-range superexchanged magnetic interaction observed in heterometallic complex: {[Fe(Tpms)(CN)3][Mn(H2O)2(DMF)2]} · DMF

A new tri-cyanometalate building block for heterometallic complexes, [PPh₄]₂[Fe^II(Tpms)(CN)₃] (2) (PPh₄ = tetraphenylphosphonium; Tpms = tris(pyrazolyl) methanesulfonate), has been prepared. Using it as a building block, a one-dimensional chain compound, {[Fe^II(Tpms)(CN)₃][Mn^II(H₂O)₂( DMF)₂]} · DMF (3), has been synthesized and structurally characterized. The magnetic properties of 3 correspond to a ferromagnetic chain with weak long-range superexchanged magnetic interaction between the high-spin manganese(II) ions.     

Substitution reactions of tetrahydrofuran in [Cr(thf)3Cl3] with mono and bidentate N-donor ligands: X-ray crystal structures of [Cr(bipy)(OH2)Cl3] and [HpyNH2][Cr(bipy)Cl4]

Substitution of thf ligands in [Cr(thf)₃Cl₃] and [Cr(thf)₂(OH₂)Cl₃] was investigated. 2,2′-Bipyridine (bipy) was reacted with [Cr(thf)₃Cl₃] to form [Cr(bipy)(thf)Cl₃] (1), which was subsequently reacted with water to give [Cr(bipy)(OH₂)Cl₃] (2). Reaction of 1 with acetonitrile (CH₃CN), pyridine (py) and pyridine derivatives to form [Cr(bipy)(L)Cl₃] (L = CH₃CN 3, py 4 and 4-pyR with R = NH₂5, Bu^t6 and Ph 7). In addition, the substitution of bipy in [Cr(thf)₃Cl₃] was followed by ¹H NMR spectroscopy at room temperature, which showed completion of the reaction in ca. 100 min. Complex 2 was characterised by single crystal X-ray diffraction. The theoretical powder diffraction pattern of 2 was compared to the experimentally obtained powder X-ray diffraction pattern, and shows excellent agreement. The dimer [Cr₂(bipy)₂Cl₄(μ-Cl)₂] was cleaved asymmetrically to give the anionic complex [Cr(bipy)Cl₄]⁻ (8) and [Cr(bipy)₂Cl₂]⁺ (9). Complexes 8 and 9 were characterised by single crystal X-ray diffraction.     

Cyano-bridged cluster-metal coordination compound: synthesis and crystal structure of [Cu(NH3)3][Cu(NH3)4][Cu(NH3)5][W4Te4(CN)12]·5H2O

Dark-brown single crystals of the title compound 1 were obtained in high yield by layering a CuCl₂ solution in 25% aqueous ammonia on a glycerol solution of K₆[W₄Te₄(CN)₁₂]·5H₂O. The complex 1 was characterized by single crystal X-ray diffraction analysis and IR spectroscopy. The X-ray structure of 1 reveals a polymeric chain cyano-bridged cluster-metal coordination compound. The [W₄Te₄(CN)₁₂]⁶⁻ cluster anions are linked one to another by Cu²⁺ cations through coordination by nitrogen atoms of the CN groups.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Sn-S and Ru-Ru bonds cleavage reactions between [Ph3SnS(CH2)3SSnPh3] and Ru3(CO)12: X-ray crystal structures of [Ph3SnS(CH2)3SSnPh3] and trans-[Ru(CO)4(SnPh3)2]

The organotin complex [Ph₃SnS(CH₂)₃SSnPh₃] (1) was synthesized by PdCl₂ catalyzed reaction between Ph₃SnCl and disodium-1,3-propanedithiolate which in turn was prepared from 1,2-propanedithiol and sodium in refluxing THF. Reaction of 1 with Ru₃(CO)₁₂ in refluxing THF affords the mononuclear complex trans-[Ru(CO)₄(SnPh₃)₂] (2) and the dinuclear complex [Ru₂(CO)₆(μ-κ²-SCH₂CH₂CH₂S)] (3) in 20 and 11% yields, respectively, formed by cleavage of Sn-S bond of the ligand and Ru-Ru bonds of the cluster. Treatment of pymSSnPPh₃ (pymS = pyrimidine-2-thiolate) with Ru₃(CO)₁₂ at 55-60 °C also gives 2 in 38% yield. Both 1 and 2 have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction analysis.     

A trinuclear copper(II) complex with 2,5-pyridine-dicarboxylato bridges - [Cu3(2,5-pydc)2(Me5dien)2(H2O)2(BF4)2] · H2O: Synthesis, crystal structure and magnetic properties

A trinuclear copper(II) complex, [Cu₃(2,5-pydc)₂(Me₅dien)₂(BF₄)₂(H₂O)₂] · H₂O 1, has been constructed from 2,5-pyridine-dicarboxylato bridges (2,5-pydc²⁻) and N,N,N′,N″,N″-pentamethyl-diethylenetriamine (Me₅dien) acting as a blocking ligand. The copper ions, within the centrosymmetric trinuclear cations, are connected by two 2,5-pydc²⁻ bridges, with an intramolecular Cu···Cu separation of 8.432 Å. The central copper ion exhibits an elongated octahedral geometry, with semicoordinated ions, while the terminal ones are pentacoordinated (distorted square-pyramidal geometry). The cryomagnetic investigation of 1 reveals an antiferromagnetic coupling of the copper(II) ions (J = −5.9 cm⁻¹, H = −JS_Cu1S_Cu2 − JS_Cu2S_Cu1a).     

Dioxouranium complexes as ligand. Synthesis and characterization of sandwich-type polyoxometalates [X2W18(UO2)2{(H2O)3M}2O68] (X = As and P) (M = Co, Cu, Mn, Ni and Zn)

The title complexes are synthesized by the reaction of an unusual ligand of [K₂P₂W₁₈(UO₂)₂O₆₈]¹²⁻ (1) and [KAs₂W₁₈(UO₂)₂O₆₈]¹³⁻ (2) with divalent metal ions of Co^II, Cu^II, Mn^II, Ni^II and Zn^II in 1:2 mole ratio and are characterized by elemental analysis, IR, ³¹P NMR, UV-Vis spectroscopy, TGA, and single crystal structure analysis. Crystals of [P₂W₁₈(UO₂)₂{(H₂O)₃Co}₂O₆₈]¹⁰⁻ (1a) and [As₂W₁₈(UO₂)₂{(H₂O)₃Cu}₂O₆₈]¹⁰⁻ (2b) are orthorhombic space group Cmca. Both 1a and 2b have structures in which two [M(H₂O)₃] (M = Co^II, Cu^II) and two UO₂ groups are sandwiched between two symmetry equivalent (XW₉) (X = P, As) units in a virtual C_i symmetry. In solution, 1a and [P₂W₁₈(UO₂)₂{(H₂O)₃Zn}₂O₆₈]¹⁰⁻ (1d) give two-line P NMR spectra that are consistent with a C_s symmetry structures so, are not consistent with the solid-state structures. The sodium salts of them give one-line P NMR spectra and are consistent with the C_i symmetry of solid-state structures. The uranium atoms have pentagonal-bipyramidal coordination, achieved by three equatorial bonds to the one XW₉ and two bonds to the other. The M atoms have octahedral or square pyramidal coordination, but only one bond to the one XW₉ and one bond to the other.     

A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine-phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1-4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)₂I₂(P∩S)] (1a) {P∩S = η²-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)₂I₂(P∼S)] (1b-d) {P∼S = η¹-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)₂I₂]_n with equimolar quantity of the ligands Ph₂P(CH₂)_nP(S)Ph₂ {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)₂I₂(P∼S)₂] (2a-d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028-2103 cm⁻¹. The ν(PS) band of complex 1a occurs 23 cm⁻¹ lower region compared to the corresponding free ligand suggesting chelation via metal-sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopy.     

Synthesis, structure and reactivity of complexes containing [M(S2)2] fragments (M=Ru, Os; (S2)=1,2-benzenedithiolate (2−))

Subsequent addition of 1,2-benzenedithiol (S₂-H₂) and nBuLi to a solution of [Ru(NO)Cl₃ · xMeOH] in THF afforded exclusively the monomeric species NBu₄[Ru^II(NO)(S₂)₂] (1). Formation of dimeric (NBu₄)₂[Ru^II(NO)(S₂)₂]₂ (2) has been confirmed when the deprotonated ligand S₂-Li₂ was added to [Ru(NO)Cl₃ · xMeOH] and allowed to stir for 30 h. The monomer 1 undergoes aerial oxidation to give (NBu₄)₂[Ru^IV(S₂)₃] (3). The reaction between RuCl₃ · xH₂O and S₂-H₂ in the presence of NaOMe, afforded the dinulear Ru^III species (NMe₄)₂[Ru^III(S₂)₂]₂ (4). A modified method for the preparation of 1 is being employed to synthesize the osmium analogue NBu₄[Os(NO)(S₂)₂] (5) effectively. The solid state structures of 1, 2 and 3 were determined by X-ray crystal structure analysis. A comparison of relevant bond distance data suggests that 1,2-benzenedithiolate acts as an “innocent” ligand.     

New ruthenium complexes from Ru3(CO)12 and 6-Alkyl- or 6-Phenyl-2-hydroxypyridines

Trirutheniumdodecacarbonyl (Ru₃(CO)₁₂) reacts with 2-hydroxy-6-methylpyridine and with 2-hydroxy-5,6,7,8-tetrahydroquinoline in toluene to form centrosymmetric tetranuclear complexes of the type [Ru(η², μ-L)(CO)₂(μ₃-L)Ru(CO)₂]₂, where L is the respective (N,O)-pyridonate ligand (2 and 3). The structures of these complexes, which are almost insoluble in all common solvents, could be determined by single-crystal X-ray diffraction. Reaction of Ru₃(CO)₁₂ with 2-hydroxy-4,6-diphenylpyridine in methanol includes ortho-metallation at the phenyl ring, furnishing the dinuclear complex [Ru(κ²N,C-L)(CO)₂(μ-OCH₃)₂Ru(CO)₂ (κ²N,C-L)] (4), where L = (2-(6-hydroxy-4-phenylpyridin-2-yl)phenyl), according to an X-ray crystal structure determination.     

Synthesis of [SnPh2(SR)2] SR = SC6F4-4-H, SC6F5: Reactivity towards group 10 transition metal complexes

The organometallic tin(IV) complexes [SnPh₂(SR^F)₂] SR^F = ⁻SC₆F₄-4-H (1), ⁻SC₆F₅ (2), were synthesized and their reactivity with [MCl₂(PPh₃)₂] M = Ni, Pd and Pt explored. Thus, transmetallation products were obtained affording polymeric [Ni(SR^F)(μ-SR^F)]_n, monomeric cis-[Pt(PPh₃)₂(SC₆F₄-4-H)₂] (3) and cis-[Pt(PPh₃)₂(SC₆F₅)₂] (4) and dimeric species [Pd(PPh₃)(SC₆F₄-4-H)(μ-SC₆F₄-4-H)]₂ (5) and [Pd(PPh₃)(SC₆F₅)(μ-SC₆F₅)]₂ (6) for Ni, Pt and Pd, respectively. The crystal structures of complexes 1, 2, 3, 4 and 6 were determined.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Bis(acetylacetonato)ruthenium(II) complexes containing bulky tertiary phosphines. Formation and redox behaviour of Ru(acac)2 (PR3) (R = Pr, Cy) complexes with ethene, carbon monoxide, and bridging dinitrogen

Reaction of cis-[Ru(acac)₂(η²-C₈H₁₄)₂] (1) (acac = acetylacetonato) with two equivalents of PⁱPr₃ in THF at −25 °C gives trans-[Ru(acac)₂(PⁱPr₃)₂], trans-3, which rapidly isomerizes to cis-3 at room temperature. The poorly soluble complex [Ru(acac)₂(PCy₃)₂] (4), which is isolated similarly from cis-[Ru(acac)₂(η²-C₂H₄)₂] (2) and PCy₃, appears to exist in the cis-configuration in solution according to NMR data, although an X-ray diffraction study of a single crystal shows the presence of trans-4. In benzene or toluene 2 reacts with PⁱPr₃ or PCy₃ to give exclusively cis-[Ru(acac)₂(η²-C₂H₄)(L)] [L = PⁱPr₃ (5), PCy₃ (6)], whereas in THF species believed to be either square pyramidal [Ru(acac)₂L], with apical L, or the corresponding THF adducts, can be detected by ³¹P NMR spectroscopy. Complexes 3-6 react with CO (1 bar) giving trans-[Ru(acac)₂(CO)(L)] [L = PⁱPr₃ (trans-8), PCy₃ (trans-9)], which are converted irreversibly into the cis-isomers in refluxing benzene. Complex 5 scavenges traces of dinitrogen from industrial grade dihydrogen giving a bridging dinitrogen complex, cis-[{Ru(acac)₂(PⁱPr₃)} ₂(μ-N₂)] (10). The structures of cis-3, trans-4, 5, 6 and 10 · C₆H₁₄ have been determined by single-crystal X-ray diffraction. Complexes trans- and cis-3, 5, 6, cis-8, and trans- and cis-9 each show fully reversible one-electron oxidation by cyclic voltammetry in CH₂Cl₂ at −50 °C with E_1/2(Ru^3+/2+) values spanning −0.14 to +0.92 V (versus Ag/AgCl), whereas for the vinylidene complexes [Ru(acac)₂ (CCHR)(PⁱPr₃)] [R = SiMe₃ (11), Ph (12)] the process is irreversible at potentials of +0.75 and +0.62 V, respectively. The trend in potentials reflects the order of expected π-acceptor ability of the ligands: PⁱPr₃, PCy₃ <C ₂H₄ < CCHR < CO. The UV-Vis spectrum of the thermally unstable, electrogenerated Ru^III-ethene cation 6⁺ has been observed at −50 °C. Cyclic voltammetry of the μ-dinitrogen complex 10 shows two, fully reversible processes in CH₂Cl₂ at −50 °C at +0.30 and +0.90 V (versus Ag/AgCl) corresponding to the formation of 10⁺ (Ru^II,III) and 10²⁺ (Ru^III,III). The former, generated electrochemically at −50 °C, shows a band in the near IR at ca. 8900 cm⁻¹ (w_1/2 ca. 3700 cm⁻¹) consistent with the presence of a valence delocalized system. The comproportionation constant for the equilibrium 10 + 10²⁺ ? 2 10⁺ at 223 K is estimated as 10^13.6.     

Coordinative versatility of 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (L) to different metal ions: syntheses, crystal structures and properties of [Cu(I)L]2 and [ML] (M=Cu(II), Ni(II), Zn(II) and Co(II))

The complexes of Cu(I), Cu(II), Ni(II), Zn(II) and Co(II) with a new polypyridyl ligand, 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline (L), have been synthesized and characterized. The crystal structures of these complexes have been elucidated by X-ray diffraction analyses and three types of coordination modes for L were found to exist in them. In the dinuclear complex [Cu(I)L(CH₃CN)]₂·(ClO₄)₂ (1), L acts as a tridentate ligand with two Cu(I) centers bridged by two L ligands to form a box-like dimeric structure, in which each Cu(I) ion is penta-coordinated with three nitrogen atoms and a methoxyl oxygen atom of two L ligands, and an acetonitrile. In [Cu(II)L(NO₃)₂]·CH₃CN 2, the Cu(II) center is coordinated to the two nitrogen atoms of the two pyridine rings of L which acts as a bidentate ligand. The structures of [Ni(II)L(NO₃)(H₂O)₂]·2CH₃CN·NO₃ (3), [Zn(II)L(NO₃)₂ (H₂O)]·2CH₃CN (4) and [Co(II)LCl₂(H₂O)] (5) are similar to each other in which L acts as a tridentate ligand by using its half side, and the metal centers are coordinated to a methoxyl oxygen atom and two bipyridine nitrogen atoms of L in the same side. The formation of infinite quasi-one-dimensional chains (1, 4 and 5) or a quasi-two-dimensional sheet (2) assisted by the intra- or intermolecular face-to-face aryl stacking interactions and hydrogen bonds may have stabilized the crystals of these complexes. Luminescence studies showed that 1 exhibits broad, structureless emissions at 420 nm in the solid state and at 450 nm in frozen alcohol frozen glasses at 77 K. Cyclic voltammetric studies of 1 show the presence of an irreversible metal-centered reduction wave at approximately −0.973 V versus Fc^+/0 and a quasi-reversible ligand-centered reduction couple at approximately −1.996 V versus Fc^+/0. The solution behaviors of these complexes have been further studied by UV-Vis and ESR techniques.     

Two cyano-bridged heterotrinuclear complexes built from [(Tp)Fe(CN)3] (Tp = hydrotris(pyrazolyl)borate): synthesis, crystal structures and magnetic properties

Using an anionic precursor [(Tp)Fe^III(CN)₃]⁻ (1) as a building block, two cyano-bridged centrosymmetric heterotrinuclear complexes, (2) and (3) (en = ethylenediamine), have been synthesized and structurally characterized. In each complex, [TpFe(CN)₃]⁻ acts as a monodentate ligand toward a central [Mn(C₂H₅OH)₄]²⁺ or [Ni(en)₂]²⁺ core through one of its three cyanide groups, the other two cyanides remaining terminal. The intramolecular Fe-Mn and Fe-Ni distances are 5.2354(4) and 5.0669(11) Å, respectively. The magnetic properties of complexes 2 and 3 have been investigated in the temperature range of 2.0-300 K. A weak antiferromagnetic interaction between the Mn(II) and Fe(III) ions has been found in complex 2. The magnetic data of 2 can be fitted with the isotropic Hamiltonian: where J and J′ are the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively. This leads to values of J = −1.37 cm⁻¹ and g = 2.05. The same fitting method is applied to complex 3 to give values of J = 1.2 cm⁻¹ and g = 2.25, showing that there is a ferromagnetic interaction between the Fe(III) and Ni(II) ions.     

Synthesis, structure and properties of TTF-carboxylate bridged paddlewheel dirhodium complexes, Rh2(BuCO2)3(TTFCO2) and Rh2(BuCO2)2(TTFCO2)2

Reaction of tetrathiafulvalene carboxylic acid (TTFCO₂H) with paddlewheel dirhodium complex Rh₂(Bu^tCO₂)₄ yielded TTFCO₂-bridged complexes Rh₂(Bu^tCO₂)₃(TTFCO₂) (1) and cis- and trans-Rh₂(Bu^tCO₂)₂(TTFCO₂)₂ (cis- and trans-2). Their triethylamine adducts [1(NEt₃)₂] and cis-[2(NEt₃)₂] were purified and isolated with chromatographic separation, and characterized with single crystal X-ray analysis. Trans-[2(NEt₃)₂] is not completely separated from a mixture of cis- and trans-[2(NEt₃)₂], but its single crystals were obtained from a solution of the mixture. A three-step quasi-reversible oxidation process was observed for 1 in MeCN. The first two steps correspond to the oxidation of the TTFCO₂ moiety and the last one is the oxidation of the Rh₂ core. The oxidation of cis-2 is observed as a two-step process with very similar E_1/2 values to those of the first two processes for 1. Both 1⁺ and cis-2²⁺ in MeCN at room temperature show isotropic ESR spectra with a g value of 2.008 and a_H = 0.135 mT for two equivalent H atoms and a_H = 0.068 mT for one H atom. The redox and ESR data of cis-2 suggest that the intramolecular interaction between the TTF moieties is very small.     

Mixed-valency with cyanides as terminal ligands: Diruthenium(III,II) complexes with the 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine bridge and variable co-ligands (CN vs. bpy or NH3)

New diruthenium complexes (PPN)₄[(NC)₄Ru(μ-bptz)Ru(CN)₄], (PPN)₄1, and [(bpy)₂Ru(μ-bptz)Ru(CN)₄], 2, (PPN⁺ = bis(triphenylphospine)iminium; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; bpy = 2,2′-bipyridine), were synthesised and characterised by spectroscopic and electrochemical techniques. The comproportionation constant K_c = 10^7.0 of the mixed-valent species [(NC)₄Ru(μ-bptz)Ru(CN)₄]³⁻ as obtained by oxidation of 1⁴⁻ in CH₃CN is much lower than the K_c = 10^15.0 previously detected for [(H₃N)₄Ru(bptz)Ru(NH₃)₄]⁵⁺, reflecting the competition between CN⁻ and bptz for the π-electron density of the metals. Comparison with several other bptz-bridged diruthenium(II,III) complexes reveals an approximate correlation between K_c and the diminishing effective π acceptor capacity of the ancillary terminal ligands. In addition to the intense MLCT absorption at λ_max = 624 nm, the main IVCT (intervalence charge transfer) band of 1³⁻ was detected by spectroelectrochemistry at λ_max = 1695 nm (in CH₃CN; ε = 3200 M⁻¹ cm⁻¹). The experimental band width at half-height, Δν_1/2 = 2700 cm⁻¹, is slightly smaller than the theoretical value Δν_1/2 = 3660 cm⁻¹, calculated from the Hush approximation for Class II mixed-valent species. In agreement with comparatively moderate metal-metal coupling, the mixed-valent intermediate 1³⁻ was found to be EPR silent even at 4 K. The unsymmetrical mixed-valent complex [(bpy)₂Ru^II(μ-bptz)Ru^III(CN)₄]⁺, obtained in situ by bromine oxidation of 2 in CH₃CN/H₂O, displays a broad NIR absorption originating from an IVCT transition at λ_max = 1075 nm (ε ≈ 1000 M⁻¹ cm⁻¹, Δν_1/2 ≈ 4000 cm⁻¹). In addition, the lifetime of the excited-state of the mononuclear precursor complex [Ru(bptz)(CN)₄]²⁻ was measured in H₂O by laser flash photolysis; the obtained value of τ = 19.6 ns reveals that bptz induces a metal-to-ligand electronic delocalisation effect intermediate between that induced by bpy and bpz (bpz = 2,2′-bipyrazine) in analogous tetracyanoruthenium complexes.     

TTF charge transfer salts containing cyanometallate anions [M(phen)(CN)4] (M = Cr or Fe; phen = 1,10-phenanthroline)

Two new charge transfer salts of TTF with the counter anions [M(phen)(CN)₄]⁻ (phen = 1,10-phenanthroline, M = Cr (I) and Fe (II)) are described. The structures consist of alternating stacks of dimerised TTF⁺ cations and [M(phen)(CN)₄]⁻ anions and they are linked together by many short S?S contacts and hydrogen bonds. Within the organic stack, two dimerised TTF⁺ cations are arranged in a slipped face-to-face mode with short intra-dimer and long inter-dimer S?S distances. Strong antiferromagnetic exchange was found in the TTF⁺ dimers. Conductivity measurements show that compound I is a semiconductor.     

A new example of a tetranuclear iron(III) cluster containing the [Fe4O2] core: preparation, X-ray crystal structure, magnetochemistry and Mössbauer study of [Fe4O2(O2CMe)6(N3)2(phen)2]

Two synthetic procedures have been employed that allow access to the new tetranuclear cluster [Fe₄O₂(O₂CMe)₆(N₃)₂(phen)₂] (1), where phen is 1,10-phenanthroline. Complex 1 · 3MeCN displays an unusual structural asymmetry (observed for the second time) in its [Fe₄O₂]⁸⁺ core that can be considered as a hybrid of the bent (butterfly) and planar dispositions of four metal ions seen previously in such compounds with transition metals. Complex 1 has been characterized by variable-temperature magnetic susceptibility studies, and by IR and variable-temperature ⁵⁷Fe Mössbauer spectroscopies. Magnetochemical data reveal a diamagnetic ground state (S=0) with antiferromagnetic body-body and body-wingtip interactions between the iron(III) ions of the butterfly core (J_bb=−11 cm⁻¹, J_wb=−70 cm⁻¹). Magnetochemical and Mössbauer studies on 1 show that its structural asymmetry has practically no influence on these properties compared with the more symmetric types.     

Stereosensitive formation and interconversion of sulfur-bridged cobalt(III)-mercury(II) polynuclear complexes with d- and/or l-penicillaminates

The reaction of trans(N)-[Co(d-pen)₂]⁻ (pen = penicillaminate) with HgCl₂ or HgBr₂ in the molar ratios of 1:1 gave the sulfur-bridged heterodinuclear complex, [HgX(OH₂){Co(d-pen)₂}] (X = Cl (1a) or Br (1b)). A similar reaction in the ratio of 2:1 produced the trinuclear complex, [Hg{Co(d-pen)₂}₂] (1c). The enantiomers of 1a and 1c, [HgCl(OH₂){Co(l-pen)₂}] (1a′) and [Hg{Co(l-pen)₂}₂] (1c′), were also obtained by using trans(N)-[Co(l-pen)₂]⁻ instead of trans(N)-[Co(d-pen)₂]⁻. Further, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]⁻ with HgCl₂ in the molar ratio of 1:1 resulted in the formation of [HgCl(OH₂){Co(d-pen)(l-pen)}] (2a). During the formations of the above six complexes, 1a, 1b, 1c, 1a′, 1c′, and 2a, the octahedral Co(III) units retain their configurations. On the other hand, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]⁻ with HgCl₂ in the molar ratio of 2:1 gave not [Hg{Co(d-pen)(l-pen}₂] but [Hg{Co(d-pen)₂}{Co(l-pen)₂}] (2c), accompanied by the ligand-exchange on the terminal Co(III) units. The X-ray crystal structural analyses show that the central Hg(II) atom in 1c takes a considerably distorted tetrahedral geometry, whereas that in 2c is of an ideal tetrahedron. The interconversion between the complexes is also examined. The electronic absorption, CD, and NMR spectral behavior of the complexes is discussed in relation to the crystal structures of 1c and 2c.