Ni(2,2':6',2''-terpyridine)2: a high-spin octahedral formal Ni(0) complex.

We have synthesised and characterised the complex Ni(tpy)2 (tpy = 2,2':6',2''-terpyridine). This formally Ni(0) complex is paramagnetic both in the solid state and in solution (S = 2). The crystal structure shows an octahedral geometry, with molecules arranged in independent dimers involving π-stacking between pairs of complexes. Magnetic measurementes and DFT calculations suggest the existence of temperature-dependent intermolecular antiferromagnetic coupling in the solid state.

Bidirectional noninnocence of hinge-like deprotonated bis-lawsone on selective ruthenium platform: a function of varying ancillary ligands.

The present work aimed to obtain discrete heavier metal complexes of unperturbed deprotonated bis-lawsone (hinge-like H2L = 2,2'-bis(3-hydroxy-1,4-napthoquinone). This is primarily due to its limited examples with lighter metal ions (Co, Zn, and Ga) and the fact that our earlier approach with the osmium ion facilitated its functionalisation. Herein, we demonstrated the successful synthesis and structural characterisation of L2--derived diruthenium [(bpy)2RuII(µ-L2-)RuII(bpy)2](ClO4)2 [1](ClO4)2 (S = 0), (acac)2RuIII(µ-L2-)RuIII(acac)22 (S = 1) and monoruthenium (pap)2Ru(L2-) 3 (S = 0) derivatives (bpy = 2,2'-bipyridine, acac = acetylacetonate, and pap = 2-phenylazopyridine). The crystal structures established that (i) O,O-/O,O- donating five-membered bis-bidentate and O-,O- donating seven-membered bidentate chelating modes of deprotonated L2- in rac (ΔΔ/ΛΛ) diastereomeric [1](ClO4)2, 2 and 3, respectively. (ii) The L2- bridging unit in [1](ClO4)2, 2 and 3 underwent twisting its two naphthoquinone rings with respect to the ring connecting C-C bond by 73.01°, 62.15° and 59.12°, respectively. (iii) Intermolecular π-π interactions (∼3.5 Å) between the neighbouring molecules. The paramagnetic complex 2 (S = 1) with two non-interacting Ru(III) (S = 1/2) ions exhibited weak antiferromagnetic coupling only at very low temperatures. In agreement with the magnetic results, 2 displayed typical RuIII-based anisotropic EPR in CH3CN (/Δg: 2.314/0.564) but without any forbidden g1/2 signal at 120 K. The complexes exhibited multiple redox processes in CH3CN in the experimental potential window of ± 2.0 V versus SCE. The analysis of the redox steps via a combined experimental and theoretical (DFT/TD-DFT) approach revealed the involvement of L2- to varying extents in both the oxidative and reductive processes as a consequence of its bidirectional redox non-innocent feature. The mixing of the frontier orbitals of the metal ion and L2- due to their closeness in energy indeed led to the resonating electronic form in certain redox states instead of any precise electronic structural state.

Three Bis-BODIPY Analogous Diruthenium Redox Series: Characterization and Electronic Structure Analysis.

The dianion derived from (2Z,6Z)-3,7-diphenyl-N2,N6-di(pyridin-2-yl)pyrrolo[2,3-f]indole-2,6(1H,5H)-diimine (H2 BL), a modified BODIPY ligand precursor, is shown to be capable of bridging two metal complex fragments RuL2 , L=2,4-pentanedionato (acac- ), 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap) in [Ru(acac)2 Ru(µ-BL)Ru(acac)2 ] (1/2), [Ru(bpy)2 Ru(µ-BL)Ru(bpy)2 ](ClO4 )2 ([3](ClO4 )2 ) and [Ru(pap)2 Ru(µ-BL)Ru(pap)2 ](ClO4 )2 ([4](ClO4 )2 ). The compounds, including a diastereoisomeric pair 1 (meso) and 2 (rac) were spectroscopically and structurally characterized. Reversible electron transfers as revealed by cyclic and differential pulse voltammetry allowed for an EPR and UV-vis-NIR spectroelectrochemical investigation of several neighboring charge states. Together with susceptibility measurements and TD-DFT calculations the assignment of oxidation states reveals that 1, 2 are diruthenium(III) species which can be oxidized or reduced by one electron whereas 32+ and 42+ contain ruthenium(II) and get reduced or oxidized mainly at the dianionic bridge (32+ ) or are reduced at the ancillary ligands pap (42+ ).

Preparation of Dimeric Monopentamethylcyclopentadienyltitanium(III) Dihalides and Related Derivatives.

The synthesis, crystal structure, and reactivity of a series of half-sandwich titanium(III) dihalide complexes [Ti(η5-C5Me5)X2] (X = Cl, Br, I) and several of its Lewis base derivatives were investigated. The reaction of the trihalides [Ti(η5-C5Me5)X3] (X = Cl (1), Br (2), I (3)) with LiAlH4 (≥1 equiv) in toluene at room temperature results in the formation of the halide-bridged dimers [{Ti(η5-C5Me5)X(µ-X)}2] (X = Cl (4), Br (5), I (6)). The treatment of 4 with [Li{N(SiMe3)2}] (≥2 equiv) at room temperature affords the precipitation of the amido titanium(III) complex [{Ti(η5-C5Me5)(µ-Cl){N(SiMe3)2}}2] (7), but analogous reactions of 4 with other lithium reagents [LiR] (R = Me, CH2SiMe3, NMe2) lead to disproportionation into titanium(IV) [Ti(η5-C5Me5)R3] and presumably titanium(II) derivatives. Similarly, complex 4 in solution at temperatures higher than 100 °C undergoes disproportionation as demonstrated by its reactions with cobaltocene and N-(4-methylbenzylidene)aniline yielding the ionic paramagnetic compound [Co(η5-C5H5)2][Ti(η5-C5Me5)Cl3] (8) and the diamagnetic diazatitanacyclopentane [Ti(η5-C5Me5)Cl{N(Ph)CH(p-tolyl)}2], respectively. Treatment of complex 4 with 2 equiv of 2,6-dimethylphenylisocyanide or tert-butylisocyanide in toluene at room temperature affords the paramagnetic titanium(III) dinuclear adducts [{Ti(η5-C5Me5)Cl(µ-Cl)(CNR)}2] (R = 2,6-Me2C6H3 (9), tBu (10)). Magnetic studies for polycrystalline 9 show that it displays a weak intramolecular antiferromagnetic coupling between the Ti ions, which is consistent with the long Ti-Ti distance of 3.857(1) Å determined by X-ray diffraction. The isocyanide ligands in complex 10 undergo a reductive coupling reaction in toluene to give the titanium(IV) iminoacyl derivative [{Ti(η5-C5Me5)Cl2}2(µ-η2:η2-tBuN═C-C═NtBu)] (11). Whereas an analogous dinuclear structure was found in the aqua titanium(III) complex [{Ti(η5-C5Me5)Cl(µ-Cl)(OH2)}2] (12), resulting from the reaction of 4 with adventitious amounts of water, compound 4 reacts with excess ammonia to give a mononuclear adduct [Ti(η5-C5Me5)Cl2(NH3)2] (13) with a robust layered pattern in the solid state.

Questions of Noninnocence and Ease of Azo Reduction in Diruthenium Frameworks with a 1,8-Bis(( E)-phenyldiazenyl)naphthalene-2,7-dioxido Bridge.

Ligands containing the azo group are often used in various metal complexes owing to their facile one-electron reduction, which in effect extends the means of degrading environmentally harmful azo dyes. In order to probe the idea of the generally accepted ease of reduction of azo-containing compounds, we present here three different diruthenium complexes [(acac)2RuIII(µ-L2-)RuIII(acac)2] (diastereomeric 1/2), [(bpy)2RuII(µ-L2-)RuII(bpy)2](ClO4)2 ([3](ClO4)2), and [(pap)2RuII(µ-L2-)RuII(pap)2](ClO4)2 ([4](ClO4)2 ) with a bridging ligand (L2- = 1,8-bis(( E)-phenyldiazenyl)naphthalene-2,7-dioxido) that contains azo groups in addition to phenoxide-type donors. The RuIII-RuIII complexes (1/2) display interesting one-dimensional-chain effects, as revealed by temperature-dependent magnetic studies. The stability of the RuIII oxidation state in 1/2 under ambient conditions correlates well with the σ-donating acetylacetonato (acac) coligands. However, with π-accepting 2,2/-bipyridine (bpy) or phenylazopyridine (pap) the RuII state is preferably stabilized in 32+ or 42+, respectively, but there are interesting differences in their oxidative chemistry. The moderately π accepting bpy allows for the RuII to RuIII oxidation at reasonably low anodic potentials. However, for the strongly π accepting pap, no RuII to RuIII oxidation is observed within the solvent window. Instead, a phenoxide to phenoxyl radical type of oxidation based on the bridging ligand is observed. Surprisingly, the reductive chemistry of all three complexes is dominated by either the ruthenium centers or the coligands (bpy or pap), with no reductions observed on the azo function associated with the central bridging ligand (L2-). All of the above conclusions were drawn from combined structural, electrochemical, magnetic, spectroelectrochemical, and DFT investigations. Our results thus conclusively establish that the ease of reduction of an azo group in a particular compound is critically dependent on its substituents and that the noninnocence of the bridging ligands (L2-) in the dinuclear complexes can be decisively tuned by the appropriate choice of ancillary ligands.

Unsymmetric (µ-oxido)/(µ-pyrazolato) and Symmetric (µ-pyrazolato)2 Bridged Diosmium Frameworks: Electronic Structure and Magnetic Properties.

The present article deals with the structurally characterized unsymmetric oxido/pyrazolato-bridged [(bpy)2Os(III)(µ-oxido)(µ-pz)Os(III)(bpy)2](ClO4)3 ([1](ClO4)3) and symmetric dipyrazolato-bridged [(bpy)2Os(II)(µ-pz)2Os(II)(bpy)2](ClO4)2 ([2](ClO4)2) (pz = pyrazolato, bpy = 2,2'-bipyridine) complexes with the Os···Os separations of 3.484 and 4.172 Å, respectively. The anti-ferromagnetically coupled Os(III) centers [E(S = 1)-E(BS(1,1) S = 0) = 322.504 cm(-1)] in 1(3+) and diamagnetic (S = 0) 2(2+) exhibit well-resolved (1)H NMR resonances. [1](ClO4)3 shows temperature- and magnetic field-dependent paramagnetism at low magnetic field and diamagnetism at high magnetic field. 1(3+) and 2(2+) display successive metal-based oxidation processes involving the intermediate mixed-valent states and isovalent congeners: Os(IV)Os(IV) (1(5+))→Os(III)Os(IV) (1(4+))⇌Os(III)Os(III) (1(3+))⇌Os(III)Os(II) (1(2+)) and Os(III)Os(III) (2(4+))→Os(II)Os(III) (2(3+))⇌Os(II)Os(II) (2(2+)) as well as bpy-centered reductions. The effect of π donor O(2-) and σ/π-donating pz(-) in 1(3+) and 2(2+), respectively, leads to varying oxidation state of the metal ions in the isolated complexes: Os(III)Os(III) versus Os(II)Os(II). UV-visible-near-IR-electron paramagnetic resonance spectro-electrochemistry and density functional theory (DFT)/time-dependent DFT calculations collectively reveal overlapping of the metal- and ligand (pz, O, bpy)-based frontier orbitals in the delocalized mixed-valent states in 1(4+) and 1(2+) with comproportionation constant (Kc) value > 1 × 10(14) as well as in isovalent 1(3+), resulting in mixed metal/ligand to metal/ligand near-IR transitions in all the three states. The mixed-valent Os(II)Os(III) state in 2(3+) exhibits high Kc value of 1 × 10(22) corresponding to a strong electrochemical coupling situation. However, closeness of the bandwidth (Δν1/2, 4861 cm(-1)) of broad and weak intervalence charge transfer transition of 2(3+) at 1360 nm (ε/M(-1) cm(-1): 490) with the calculated Δν1/2 of 4121 cm(-1) based on the Hush formula as well as spin-density distributions of Os1: 0.811/0.799, Os2: 0.045/0042, and pz: 0.162/0.173 in meso and rac diastereomeric forms, respectively, attribute its localized class II state.

Metal-Induced Thiophene Ring Opening and C-C Bond Formation To Produce Unique Hexa-1,3,5-trienediyl-Coupled Non-Innocent Ligand Chelates.

Ring opening of thiophenes containing an azo function in 2-position and subsequent dimerization through C-C coupling were observed on reaction with [Ru(acac)2 (CH3 CN)2 ] (acac=acetylacetonate) to produce two 1,3,5-hexatriene-linked redox-active azothiocarbonyl chelate systems. Interaction of the non-innocent chelate ligands and of the metals at a nanoscale distance of 1.45 nm via the conjugated hexatriene bridge was studied by magnetic and electron spectroscopic measurements in conjunction with DFT calculations, revealing four-center magnetic interactions of this unique setting and weak intervalence coupling after reduction.

Sensitivity of the valence structure in diruthenium complexes as a function of terminal and bridging ligands.

The compounds [(acac)2Ru(III)(µ-H2L(2-))Ru(III)(acac)2] (rac, 1, and meso, 1') and [(bpy)2Ru(II)(µ-H2L(•-))Ru(II)(bpy)2](ClO4)3 (meso, [2](ClO4)3) have been structurally, magnetically, spectroelectrochemically, and computationally characterized (acac(-) = acetylacetonate, bpy = 2,2'-bipyridine, and H4L = 1,4-diamino-9,10-anthraquinone). The N,O;N',O'-coordinated µ-H2L(n-) forms two ß-ketiminato-type chelate rings, and 1 or 1' are connected via NH···O hydrogen bridges in the crystals. 1 exhibits a complex magnetic behavior, while [2](ClO4)3 is a radical species with mixed ligand/metal-based spin. The combination of redox noninnocent bridge (H2L(0) → → → →H2L(4-)) and {(acac)2Ru(II)} → →{(acac)2Ru(IV)} or {(bpy)2Ru(II)} → {(bpy)2Ru(III)} in 1/1' or 2 generates alternatives regarding the oxidation state formulations for the accessible redox states (1(n) and 2(n)), which have been assessed by UV-vis-NIR, EPR, and DFT/TD-DFT calculations. The experimental and theoretical studies suggest variable mixing of the frontier orbitals of the metals and the bridge, leading to the following most appropriate oxidation state combinations: [(acac)2Ru(III)(µ-H2L(•-))Ru(III)(acac)2](+) (1(+)) → [(acac)2Ru(III)(µ-H2L(2-))Ru(III)(acac)2] (1) → [(acac)2Ru(III)(µ-H2L(•3-))Ru(III)(acac)2](-)/[(acac)2Ru(III)(µ-H2L(2-))Ru(II)(acac)2](-) (1(-)) → [(acac)2Ru(III)(µ-H2L(4-))Ru(III)(acac)2](2-)/[(acac)2Ru(II)(µ-H2L(2-))Ru(II)(acac)2](2-) (1(2-)) and [(bpy)2Ru(III)(µ-H2L(•-))Ru(II)(bpy)2](4+) (2(4+)) → [(bpy)2Ru(II)(µ-H2L(•-))Ru(II)(bpy)2](3+)/[(bpy)2Ru(II)(µ-H2L(2-))Ru(III)(bpy)2](3+) (2(3+)) → [(bpy)2Ru(II)(µ-H2L(2-))Ru(II)(bpy)2](2+) (2(2+)). The favoring of Ru(III) by σ-donating acac(-) and of Ru(II) by the π-accepting bpy coligands shifts the conceivable valence alternatives accordingly. Similarly, the introduction of the NH donor function in H2L(n) as compared to O causes a cathodic shift of redox potentials with corresponding consequences for the valence structure.

Influence of ancillary ligands on the electronic structure and anion sensing features of ligand bridged diruthenium complexes.

The present article deals with a newer class of ligand bridged asymmetric complexes incorporating ancillary ligands (AL) with varying electronic characteristics: [(bpy)2Ru(II)(µ-HL(2-)) Ru(II)(bpy)2](ClO4)2·([1](ClO4)2); [(pap)2Ru(II)(µ-HL(2-))Ru(II)(pap)2](ClO4)2 ([2](ClO4)2); [(bpy)2Ru(II)(µ-HL(2-))Ru(II)(pap)2](ClO4)2 ([3](ClO4)2); [(acac)2Ru(III)(µ-HL(2-))Ru(III)(acac)2] (4) and [(bpy)2Ru(II)(µ-HL(2-))Ru(III)(acac)2]ClO4 ([5]ClO4) (H3L: 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid, bpy = moderately π-accepting 2,2'-bipyridine, pap = strongly π-accepting 2-phenylazopyridine, acac(-) = σ-donating acetylacetonate). The molecular identity of [1](ClO4)2 was established by its single crystal X-ray structure. A large shift in Ru(II)/Ru(III) potential of 0.7-2.0 V took place on switching the ancillary ligands from AL = bpy to pap to acac(-), leading to the stabilisation of ruthenium(II) and ruthenium(III) states in 1(2+), 2(2+), 3(2+), 4 and 5(+), respectively. The detailed magnetic studies revealed that the paramagnetic Ru(III)Ru(III) state in 4 essentially behaves as a system with two independent S = 1/2 spins and it exhibits an anisotropic EPR at 77 K ( = 2.192, Δg = g1-g3 = 0.70) but without any half-field signal near g∼ 4. The isolated mixed valent Ru(II)Ru(III) state in 5(+) exhibits weak antiferromagnetic coupling of -0.25 cm(-1) and anisotropic EPR with = 2.155, Δg = 0.704 but fails to show a Ru(II)→ Ru(III) IVCT (intervalence charge transfer) transition in the near-IR region up to 2000 nm. The complexes 1(2+), 2(2+) and 4 encompassing identical metal fragments, exhibited weak to moderate electrochemical coupling at the intermediate mixed valent states with Kc values of 10(2)-10(5). The coulometrically generated mixed valent Ru(II)Ru(III) state in 1(3+) or 4(-) also failed to display any prominent absorption in the near-IR region, but exhibited Ru(III) based rhombic EPR, implying valence localised situation with negligible intermetallic electronic coupling. The complexes 2(2+), 3(2+), 4 and 5(+) having one NH proton associated with the bridging ligand HL(2-) do not show any interaction with the anions F(-), Cl(-), Br(-), I(-), HSO4(-), H2PO4(-), OAc(-) and SCN(-) in CH3CN, though 1(2+) selectively recognises the fluoride ion.

The intricate paramagnetic state of [Os(Q)2(bpy)]+, Q = 4,6-di-tert-butyl-o-iminobenzoquinone.

The combination of two highly non-innocent ligands with a third-row transition metal produces the title complex ion which was crystallised as [Os(Q)(2)(bpy)](ClO(4))·C(6)H(6) (Q = 4,6-di-tert-butyl-o-iminobenzoquinones, bpy = 2,2'-bipyridine) and could be structurally characterised to exhibit a tris-chelate situation at the metal with trans-positioned N and cis-positioned O donor atoms. The metrical ligand parameters are in agreement with two partially reduced ligands. A 3-spin interaction (Q˙(-))Os(III)(Q˙(-)) can rationalise the observed S = 1/2 situation with ligand-centred resulting spin. Ligand-based spin is confirmed by DFT (calculated spin populations Q: 1.113; Os: -0.113; bpy: 0.001) and is also apparent from the EPR signal (g(1) 1.981, g(2) 1.955, g(3) 1.803, Δg 0.178, 1.915) which is influenced by the high spin-orbit coupling constant of the osmium centre. The susceptibility measurements reveal antiferromagnetic behaviour. A one-electron oxidation and two one-electron reductions could be monitored spectroelectrochemically (UV-VIS-NIR) and analysed by TD-DFT, in comparison with the results from the ruthenium analogue. The analysis reflects the strong orbital mixing between the metal and the two Q-ligand MOs.