RESUMEN

Seven new inorganic-organic coordination polymer compounds have been synthesized and their structures are determined by single-crystal structure determination. The compounds were prepared by the sequential assembly of a [Cu6(mna)6]6- moiety in the presence of a Mn salt and a secondary amine ligand. Of the seven compounds, [{Cu6(mna)6}Mn3(H2O)(H2O)1.5]·5.5H2O (I), [{Cu6(mna)6}Mn3(H2O)(Im)1.5]·3.5H2O (Ia), [{Cu6(mna)6}{Mn(BPY)(H2O)}2{Mn(H2O)4}]·2H2O (III), and [{Cu6(mna)6}{Mn(BPE)0.5(H2O)2}2{Mn(BPE)(H2O)2}] (IV) have a three-dimensional structure, whereas [{Cu6(mna)4.5(Hmna)1.5}{Mn(BPA)(H2O)2}{Mn(H2O)}]{Mn0.25(H2O)3}·7H2O (II), [{Cu6(mna)6}{Mn(4-BPDB)0.5H2O}{Mn(H2O)2}].{Mn(H2O)6}·6H2O (V), and [{Cu6(mna)4(Hmna)2}·{Mn(H2O)3}2]·(4-APY)2·6H2O (VI) have a two-dimensional structure. Some of the prepared compounds exhibit structures that closely resemble the classical inorganic structures, such as NaCl (Ia, III), NiAs (I), and CdI2 (IV and VI). The stabilization of such simple structures from the assembly of octahedral Cu6S6 clusters and different Mn species and aromatic nitrogen-containing ligands suggests the subtle interplay between the constituent reactants. The compounds were examined for the multicomponent Hantzsch reaction, which gave the product in good yields. The compounds, II and VI, on heating to 70 °C change color reversibly from pale yellow to deep red, which suggests the possible use of these compounds as thermochromic materials. The present study suggests that the Cu6S6 octahedral clusters can be assembled into structures that resemble classical inorganic structures.

RESUMEN

The article deals with the newly designed mononuclear and asymmetric dinuclear osmium(ii) complexes Os(II)(bpy)2(HL(2-)) (1) and [(bpy)2Os(II)(µ-HL(2-))Os(II)(bpy)2](Cl)2 ([2](Cl)2)/[(bpy)2Os(II)(µ-HL(2-))Os(II)(bpy)2](ClO4)2 ([2](ClO4)2), respectively, (H3L = 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid and bpy = 2,2'-bipyridine). The identity of 1 has been established by its single crystal X-ray structure. The ligand (HL(2-))-based primary oxidation process (E, 0.23 V versus SCE) along with the partial metal contribution (∼20%) in 1 has been revealed by the ligand-dominated HOMO of 1 (HL(2-): 88%, Os: 8%), as well as by the Mulliken spin density distribution of 1(+) (HL(2-): 0.878, Os: 0.220). Accordingly, 1(+) exhibits a free radical type EPR at 77 K with a partial metal-based anisotropic feature (g1 = 2.127, g2 = 2.096, g3 = 2.046; = 2.089; Δg = 0.08). (1)H-NMR of the dinuclear 2(2+) in CDCl3 suggests an intimate mixture of two diastereomeric forms in a 1 : 1 ratio. The DFT-supported predominantly Os(ii)/Os(iii)-based couples of asymmetric 2(2+) at 0.24 V and 0.50 V versus SCE result in a comproportionation constant (Kc) value of 8.2 × 10(4). The class I mixed valent state of 2(3+) (S = 1/2) has, however, been corroborated by the Mulliken spin density distribution of Os1: 0.887, Os2: 0.005, HL(2-): 0.117, as well as by the absence of a low-energy IVCT (intervalence charge transfer) band in the near-IR region (up to 2000 nm). The appreciable spin accumulation on the bridge in 2(3+) or 2(4+) (S = 1, Os1: 0.915, Os2: 0.811 and HL(2-): 0.275) implies a mixed electronic structural form of [(bpy)2Os(III)(µ-HL(2-))Os(II)(bpy)2](3+)(major)/[(bpy)2Os(II)(µ-HL˙(-))Os(II)(bpy)2](3+)(minor) or [(bpy)2Os(III)(µ-HL(2-))Os(III)(bpy)2](4+)(major)/[(bpy)2Os(III)(µ-HL˙(-))Os(II)(bpy)2](4+) (minor), respectively. The mixed valent {Os(III)(µ-HL(2-))Os(II)} state in 2(3+), however, fails to show EPR at 77 K due to the rapid spin relaxation process. The DFT-supported bpy-based two reductions for both 1(+) and 2(2+) appear in the potential range of -1.5 V to -1.8 V versus SCE. The electronic transitions in 1(n) and 2(n) are assigned by the TD-DFT calculations. Furthermore, the potential anion sensing features of 1 and 2(2+)via the involvement of the available N-H proton in the framework of coordinated HL(2-) have been evaluated by different experimental investigations, in conjunction with the DFT calculations, using a wide variety of anions such as F(-), Cl(-), Br(-), I(-), OAc(-), SCN(-), HSO4(-) and H2PO4(-). This, however, establishes that both 1 and 2(2+) are equally efficient in recognising the F(-) ion selectively, with log K values of 6.83 and 5.89, respectively.

RESUMEN

Bis(acetylacetonato)ruthenium complexes [Ru(acac)2(Q1-3)], 1-3, incorporating redox non-innocent 9,10-phenanthrenequinonoid ligands (Q1 = 9,10-phenanthrenequinone, 1; Q2 = 9,10-phenanthrenequinonediimine, 2; Q3 = 9,10-phenanthrenequinonemonoimine, 3) have been characterised electrochemically, spectroscopically and structurally. The four independent molecules in the unit cell of 2 are involved in intermolecular hydrogen bonding and π-π interactions, leading to a 2D network. The oxidation state-sensitive bond distances of the coordinated ligands Q(n) at 1.296(5)/1.289(5) Å (C-O), 1.315(3)/1.322(4) Å (C-N), and 1.285(3)/1.328(3) Å (C-O/C-N) in 1, 2 and 3, respectively, and the well resolved (1)H NMR resonances within the standard chemical shift range suggest DFT supported variable contributions from valence formulations [Ru(III)(acac)2(Q˙(-))] (spin-coupled) and [Ru(II)(acac)2(Q(0))], respectively. Complexes 1-3 exhibit one oxidation and two reduction steps with comproportionation constants Kc∼ 10(7)-10(22) for the intermediates. The electrochemically generated persistent redox states 1(n) (n = 0, 1-, 2-) and 2(n)/3(n) (n = 1+, 0, 1-, 2-) have been analysed by UV-vis-NIR spectroelectrochemistry and by EPR for the paramagnetic intermediates in combination with DFT and TD-DFT calculations, revealing significant differences in the oxidation state distribution at the {Ru-Q} interface for 1(n)-3(n). In particular, the diminished propensity of the NH-containing systems for reduction results in the preference for Ru(II)(Q(0)) relative to Ru(III)(Q˙(-)) (neutral compounds) and for Ru(II)(Q˙(-)) over the Ru(III)(Q(2-)) alternative in the case of the monoanionic complexes.

Asunto(s)

Electrones , Compuestos Organometálicos/química , Fenantrenos/química , Rutenio/química , Absorción , Electroquímica , Ligandos , Modelos Moleculares , Conformación Molecular

RESUMEN

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.

Asunto(s)

Compuestos Organometálicos/química , Rutenio/química , Aniones/química , Electrones , Ligandos , Modelos Moleculares , Estructura Molecular , Compuestos Organometálicos/síntesis química

RESUMEN

Five diruthenium(II) complexes [Cl(L)Ru(µ-tppz)Ru(L)Cl] (1-5) containing differently substituted ß-diketonato derivatives (1: L = 2,4-pentanedionato; 2: L = 3,5-heptanedionato; 3: L = 2,2,6,6-tetramethyl-3,5-heptanedionato; 4: L = 3-methyl-2,4-pentanedionato; 5: L = 3-ethyl-2,4-pentanedionato) as ancillary ligands (L) were synthesized and studied by spectroelectrochemistry (UV-Vis-NIR, electron paramagnetic resonance (EPR)). X-ray structural characterisation revealed anti (1, 2, 5) or syn (3) configuration as well as non-planarity of the bis-tridentate tppz bridge and strong dπ(Ru(II)) → π*(pyrazine, tppz) back-bonding. The widely separated one-electron oxidation steps, Ru(II)Ru(II)/Ru(II)Ru(III) and Ru(II)Ru(III)/Ru(III)Ru(III), result in large comproportionation constants (K(c)) of ≥10(10) for the mixed-valent intermediates. The syn-configurated (n) exhibits a particularly high K(c) of 10(12) for n = 1+, accompanied by density functional theory (DFT)-calculated minimum Ru-N bond lengths for this Ru(II)Ru(III) intermediate. The electrogenerated mixed-valent states 1(+)-5(+) exhibit anisotropic EPR spectra at 110 K with average values of 2.304-2.234 and g anisotropies Δg = g(1)-g(3) of 0.82-0.99. Metal-to-metal charge transfer (MMCT) absorptions occur for 1(+)-5(+) in the NIR region at 1660 nm-1750 nm (ε ≈ 2700 dm(3) mol(-1) cm(-1), Δν(1/2) ≈ 1800 cm(-1)). DFT calculations of 1(+) and 3(+) yield comparable Mulliken spin densities of about 0.60 for the metal ions, corresponding to valence-delocalised situations (Ru(2.5))(2). Rather large spin densities of about -0.4 were calculated for the tppz bridges in 1(+) and 3(+). The calculated electronic interaction values (V(AB)) for 1(+)-5(+) are about 3000 cm(-1), comparable to that for the Creutz-Taube ion at 3185 cm(-1). The DFT calculations predict that the Ru(III)Ru(III) forms in 1(2+)-5(2+) prefer a triplet (S = 1) ground state with ΔE (S = 0 - S = 1) ∼5000 cm(-1). One-electron reduction takes place at the tppz bridge which results in species [Cl(L)Ru(II)(µ-tppz˙(-))Ru(II)(L)Cl](-) (1˙(-)-3˙(-), 5˙(-)) which exhibit free radical-type EPR signals and NIR transitions typical of the tppz radical anion. The system 4(n) is distinguished by lability of the Ru-Cl bonds.

RESUMEN

An effective anion sensor, [Ru(II)(bpy)(2)(H(2)L(-))](+) (1(+)), based on a redox and photoactive {Ru(II)(bpy)(2)} moiety and a new ligand (H(3)L = 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid), has been developed for selective recognition of fluoride (F(-)) and acetate (OAc(-)) ions. Crystal structures of the free ligand, H(3)L and [1](ClO(4)) reveal the existence of strong intramolecular and intermolecular hydrogen bonding interactions. The structure of [1](ClO(4)) shows that the benzimidazole N-H of H(2)L(-) is hydrogen bonded with the pendant carboxylate oxygen while the imidazole N-H remains free for possible hydrogen bonding interaction with the anions. The potential anion sensing features of 1(+) have been studied by different experimental and theoretical (DFT) investigations using a wide variety of anions, such as F(-), Cl(-), Br(-), I(-), HSO(4)(-), H(2)PO(4)(-), OAc(-) and SCN(-). Cyclic voltammetry and differential pulse voltammetry established that 1(+) is an excellent electrochemical sensor for the selective recognition of F(-) and OAc(-) anions. 1(+) is also found to be a selective colorimetric sensor for F(-) or OAc(-) anions where the MLCT band of the receptor at 498 nm is red shifted to 538 nm in the presence of one equivalent of F(-) or OAc(-) with a distinct change in colour from reddish-orange to pink. The binding constant between 1(+) and F(-) or OAc(-) has been determined to be logK = 7.61 or 7.88, respectively, based on spectrophotometric titration in CH(3)CN. The quenching of the emission band of 1(+) at 716 nm (λ(ex) = 440 nm, Φ = 0.01 at 298 K in CH(3)CN) in the presence of one equivalent of F(-) or OAc(-), as well as two distinct lifetimes of the quenched and unquenched forms of the receptor 1(+), makes it also a suitable fluorescence-based sensor. All the above experiments, in combination with (1)H NMR, suggest the formation of a 1:1 adduct between the receptor (1(+)) and the anion (F(-) or OAc(-)). The formation of 1:1 adduct {[1(+)·F(-)] or [1(+)·OAc(-)]} has been further evidenced by in situ ESI-MS(+) in CH(3)CN. Though the receptor, 1(+), is comprised of two N-H protons associated with the coordinated H(2)L(-) ligand, only the free imidazole N-H proton participates in the hydrogen bonding interactions with the incoming anions, while the intramolecularly hydrogen bonded benzimidazole N-H proton remains intact as evidenced by the crystal structure of the final product (1). The hydrogen bond mediated anion sensing mechanism, over the direct deprotonation pathway, in 1(+) has been further justified by a DFT study and subsequent NBO analysis.

RESUMEN

Using the [RuCl(µ-tppz)ClRu](2+) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] platform for bridging two o-quinone/catecholate two-step redox systems (unsubstituted, Q(n), or 3,5- di-tert-butyl-substituted, DTBQ(n)), we have obtained the stable complexes [(Q(•-))Ru(II)Cl(µ-tppz)ClRu(II)(Q(•-))] (1) and the structurally characterized [(DTBQ(•-))Ru(II)Cl(µ-tppz)ClRu(II)(DTBQ(•-))] (2). The compounds exhibit mostly quinone-ligand-based redox activity within a narrow potential range, high-intensity near-IR absorptions (λ(max) ≈ 920 nm; ε > 50,000 M(-1) cm(-1)), and variable intra- and intermolecular spin-spin interactions. Density functional theory calculations, electron paramagnetic resonance (EPR), and spectroelectrochemical results (UV-vis-near-IR region) for three one-electron-reduction and two one-electron-oxidation processes were used to probe the electronic structures of the systems in the various accessible valence states. EPR spectroscopy of the singly charged doublet species showed semiquinone-type response for 1(+), 2(+), and 2(-), while 1 exhibits more metal based spin, a consequence of the easier reduction of Q as compared to DTBQ. Comparison with the analogous redox series involving a more basic N-phenyliminoquinone ligand reveals significant differences related to the shifted redox potentials, different space requirements, and different interactions between the metals and the quinone-type ligands. As a result, the tppz bridge is reduced here only after full reduction of the terminal quinone ligands to their catecholate states.

Asunto(s)

Benzoquinonas/química , Compuestos Organometálicos/química , Rutenio/química , Cristalografía por Rayos X , Dimerización , Espectroscopía de Resonancia por Spin del Electrón , Modelos Moleculares , Estructura Molecular , Compuestos Organometálicos/síntesis química , Oxidación-Reducción , Teoría Cuántica , Espectrofotometría Ultravioleta , Espectroscopía Infrarroja Corta , Estereoisomerismo

RESUMEN

The neutral title complexes [(L(1-3))ClRu(II)(mu-tppz)Ru(II)Cl(L(1-3))] [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine with L(1) = 2-picolinate, L(2) = 2-quinolinecarboxylate (quinaldate) and with the hitherto little used L(3) = 8-quinolinecarboxylate] have been structurally characterized as approximately anti- (1 and 3) and syn-configured isomers (2) with L ligand N (1 and 3) or O atoms (2) trans to the pyrazine N atoms of tppz. In contrast to 1 and 2 with five-membered chelate rings, complex 3 (which is isomeric with 2) contains six-membered chelate rings. Each system 1-3 thus features a significantly different coordination situation, and all complexes exhibit a considerably distorted tppz bridge, including a twisted central pyrazine ring. In spite of this, double one-electron reduction of the bridge is always possible, as is evident from electron paramagnetic resonance (EPR) and UV/vis spectroelectrochemistry. Two separate (DeltaE approximately 0.4 V and K(c) approximately 10(7)) one-electron oxidations occur on the metals, producing invariably EPR-silent (4 K) Ru(III)Ru(II) intermediates with moderately intense near-IR absorptions, ranging from 1500 to 1900 nm. IR spectroelectrochemistry of the carboxylato carbonyl stretching bands did not result in any noticeable shift, in contrast to what was observed with dipyridyl ketones and related coligands. Density functional theory (DFT)/time-dependent DFT calculations confirm the experimental structures and explain the noted spectroscopic trends: destabilized and closer-spaced frontier orbitals for 3 over 2, with the comparison to 1 suggesting that the configuration is a major factor. Nevertheless, the rather unperturbed electronic structure of the [Ru(mu-tppz)Ru](n) entity, despite different coordination situations at the metal sites, is remarkable and suggests further use of this entity as a robust, carboxylate-tolerant redox-active platform in extended frameworks.

RESUMEN

The paramagnetic ruthenium-biimidazole complexes [(acac)(2)Ru(III)(LH(-))] (1 = red-brown), [(acac)(2)Ru(III)(LH(2))](ClO(4)) (2 = pink) and Bu(4)N[(acac)(2)Ru(III)(L(2-))] (3 = greenish yellow) comprising of monodeprotonated, neutral and bideprotonated states of the coordinated biimidazole ligand (LH(n), n = 1, 2, 0), respectively, have been isolated (acac(-) = acetylacetonate). Single-crystal X-ray diffraction of 1 reveals that the asymmetric unit consists of three independent molecules: A-C, where molecule A corresponds to complex 1 and the other two molecules B and C co-exist as a hydrogen bonded dimeric unit perhaps between the cationic 2(+) and anionic 3(-). The packing diagram further reveals that the molecule A in the crystal of 1 also forms a hydrogen bonded dimer with the neighbouring another unit of molecule A. The formation of [(acac)(2)Ru(III)(LH(2))](ClO(4)) (2) has also been authenticated independently by its single-crystal X-ray structure. The packing diagram of 2 shows multiple hydrogen bonds between the N-H protons of coordinated LH(2) and the counter ClO(4)(-). Paramagnetic complexes show (1)H NMR spectra over a wide range of chemical shift, delta (ppm), +10 to -35 in CDCl(3). One-electron paramagnetic 1-3 (mu/B.M. approximately 1.9) exhibit distinct rhombic-EPR spectra with relatively large g anisotropic factors: 2.136-2.156 and Deltag 0.65-0.77, typical for distorted octahedral ruthenium(III) complexes. The complexes 1-3 are inter-convertible as a function of pH. The pK(a1) and pK(a2) of 6.8 and 11, respectively, for 2 are estimated by monitoring the pH dependent spectral changes. The Ru(III)-Ru(IV) couple near 1.25 V vs. SCE remains almost invariant in 1-3 whereas the corresponding Ru(III)-Ru(II) couple varies appreciably in the range of -0.52 to -0.85 V vs. SCE based on the protonated-deprotonated states of the coordinated biimidazole ligand. Compounds 1-3 exhibit one weak ligand to metal charge transfer (LMCT) transition near 500 nm and intense intraligand transitions in the higher energy UV region. The spectrophotometric titrations of 2 with the TBA (TBA = tetrabutylammonium) salts of a wide variety of anions, F(-), Cl(-), Br(-), I(-), HSO(4)(-), OAc(-), H(2)PO(4)(-) in CH(3)CN reveal that the possible hydrogen bonds between the N-H protons of LH(2) in 2 and Cl(-) or Br(-) or I(-) or HSO(4)(-) or H(2)PO(4)(-) anion are rather weak or negligible. However, in presence of excess H(2)PO(4)(-) anion, the molar ratio of 2 to H(2)PO(4)(-) being 1 : 4, simple liberation of one N-H proton of the coordinated LH(2) in 2 has been taken place which in effect yields 1 and H(3)PO(4). On the contrary, the spectrophotometric titrations of 1 : 1 molar solution of 2 and OAc(-) or F(-) anion suggest the initial formation of hydrogen bonds between the N-H protons of LH(2) in 2 and the anion with the calculated log K value of 5.92 or 4.7, respectively, which eventually leads to the transfer of one of the N-H protons of LH(2) in 2 to the anion, resulting in 1 and HOAc or HF. On addition of excess OAc(-) to the above solution of 1 (molar ratio of OAc(-) to 1, 4 : 1), further hydrogen bonding between the N-H proton of LH(-) in 1 and OAc(-) occurs but without the abstraction of the N-H proton of LH(-). However, excess F(-) anion concentration (molar ratio of anion to 1, 5 : 1) facilitates the removal of the remaining N-H proton of LH(-) in 1 which in turn yields 3 incorporating the bideprotonated form L(2-).