Substituent effect of 8-quinolinolato ligands on photo-induced isomerization for linear nitrosylruthenium(II) complexes - Experimental study

cis-1 [RuCl(QN)(QN′)NO] (HQN or HQN′ = 8-quinolinol, 5-chloro-, 5,7-dichloro-, 2-isopropyl-, 2-ethyl-, 2,4-dimethyl- or 2-methyl-8-quinolinol) complexes and the corresponding trans complexes were prepared. The cis-1 to trans and the trans to cis-1 photo-induced isomerizations were carried out to investigate the substituent effect of the 8-quinolinolato ligands on the isomerization and to elucidate the mechanism. The molar ratio of trans to cis-1 isomer for the isomerization was compared among [RuCl(QN)(QN′)NO], [RuCl(QN′)₂NO] and [RuCl(QN)₂NO]. The results clearly indicate that the chloro group and bulkiness of the alkyl group in the 8-quinolinolato ligands influence on the isomerization.     

Dihydroxamic acid complexes of iron (III): ligand pKa and coordinated water hydrolysis constants

A series of dihydroxamic acid ligands of the formula [RN(OH)C(O)]₂(CH₂)_n, (n = 2, 4, 6, 7, 8; R = CH₃, H) has been studied in 2.0 M aqueous sodium perchlorate at 25.0 °C. These ligands may be considered as synthetic analogs to the siderophore rhodotorulic acid. Acid dissociation constants (pK_a) have been determined for the ligands and for N-methylacetohydroxamic acid (NMHA). The pK_a1 and pK_a2 values are: n = 2, R = CH₃ (8.72, 9.37); N = 4, R = CH₃ (8.79, 9.37); N = 6, R = CH₃; N = 7, R = CH₃ (8.95, 9.47); N = 8, R = CH₃ (8.93, 9.45); N = 8, R = H (9.05, 9.58). Equilibrium constants for the hydrolysis of coordinated water (log K) have been estimated for the 1:1 feeric complexes of the ligands n = 2, 4, 8; R = CH₃. The N = 8 ligand forms a monomeric complex with Fe(III) while the n = 2 and 4 ligands form dimeric complexes. For hydrolysis of the n = 8 monomeric complex, log K₁ = −6.36 and log K₂ = −9.84. Analysis of the spectrophotometric data for the dimeric complexes indicates deprotonation of all four coordinated waters. The successive hydrolysis constants, log K_1–4, for the dimeric complexes are as follows: n = 2 (−6.37, −5.77, −10.73, −11.8); n = 4 (−5.54, −5.07, −11.57, −10.17). The log K₂ values for the dimers are unexpectedly high, higher in fact than log K₁, inconsistent with the formation of simple ternary hydroxo complexes. A scheme is proposed for the hydrolysis of the ferric dihydroxamate dimers, which includes the possible formation of μ-hydroxo and μ-oxo bridges.     

The unexpected reactions of [RuCl3(2mqn)NO] (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) and of [RuCl(2cqn)(2mqn)NO] on photoirradiation

The reaction of [RuCl₃(2mqn)NO]⁻ (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) afforded cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 1), cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) (complex 2) and a 1:1 mixture of cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) and cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 3). The reaction was compared with that of [RuCl₃(2mqn)NO]⁻ with 8-quinolinol (Hqn) or 5-chloro-8-quinolinol (H5cqn). Photoirradiation reaction of complex 1 at room temperature in deaerated CH₂Cl₂ in the presence of NO gave trans-[RuCl(2cqn)(2mqn)NO] (the Cl is trans to the NO) and complex 2 with recovery of complex 1. The reaction was contrasted with that of cis-1 [RuCl(qn)(2mqn)NO] or cis-1 [RuCl(5cqn)(2mqn)NO]. The crystal structure of complex 1 was determined by X-ray diffraction. The reactions were examined under consideration of atomic charge of the phenolato oxygen in 8-quinolinol and its derivatives calculated at the restricted Hartree-Fock/6-311G** level.     

Acid-base and metal ion-binding properties of flavin mononucleotide (FMN). Is a ‘dielectric’ effect responsible for the increased complex stability?

Due to contradictions in the literature we have redetermined the acid-base properties of riboflavin (=RiFl; vitamin B₂), i.e. 7,8-dimethyl-10-ribityl-isoalloxazine, and of flavin mononucleotide (FMN²⁻), also known as riboflavin 5′-phosphate, via potentiometric pH titrations (I = 0.1 M, NaNO₃; 25 °C). In contrast to various claims, the isoalloxazine ring cannot be protonated at pH > 1, a result in agreement with an early study (pK_a = −0.2; L. Michaelis, M.P. Schubert and C.V. Smythe, J. Biol. Chem., 116 (1936) 587–607); deprotonation of the ring system occurs in both compounds with pK_a 10. The pK_a value of 0.7 determined for the deprotonation of H₂(FMN) must be attributed to the release of the first proton from the fully protonated phosphate group; its second proton is released with pK_a = 6.18 in agreement with the acidity constants of various other monoprotonated monophosphate esters. The stability constants of the 1:1 complexes formed between Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ or Cd²⁺ (---M²⁺) and FMN²⁻ were determined by potentiometric pH titrations in aqueous solution (I = 0.1 M, NaNO₃; 25 °C). The log stability constants of all these M(FMN) complexes are about 0.2 log units higher than expected from the basicity of the phosphate group. This slight stability increase cannot be attributed to the formation of a seven-membered chelate involving the ribit-hydroxy group at C-4′ as the stability constants for the M²⁺ 1:1 complexes of glycerol 1-phosphate (G1P²⁻) demonstrate: G1P²⁻ contains the same structural unit which would also allow in this case the formation of the mentioned seven-membered chelate; however, the stability of the M(G1P) complexes is solely determined by the basicity of the phosphate group. Hence, in agreement with earlier conclusions (J. Bidwell, J. Thomas and J. Stuehr, J. Am. Chem. Soc., 108 (1986) 820–825) regarding Ni(FMN) one must conclude that the slight stability increase of the M(FMN) complexes has to be attributed to the isoalloxazine ring. The equality of the stability increase of the complexes for all the mentioned ten metal ions precludes its attribution to an interaction with an N site and makes a specific interaction with an O site also somewhat unlikely. In addition, carbonyl oxygens appear as not very favorable for the formation of macrochelates by a further interaction with already phosphate-coordinated metal ions. Therefore, we propose that the slight but significant stability increase originates from M(FMN) species (with a formation degree of about 30%) in which the hydrophobic flavin residue is close to the metal ion, thereby lowering the ‘effective’ dielectric constant in the microenvironment of the metal ion and thus indirectly promoting the −PO₃²⁻/M²⁺ interaction.     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.     

Structural studies on [Mo3S4] and [Mo3S4Cu] complexes with tripodal ligands providing various NxOy (x + Y = 3) donor sets

The interaction of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) and its N-methylated derivative 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci) with the incomplete [Mo₃S₄]⁴⁺ cube and the heterometallic [Mo₃S₄Cu]⁴⁺ cube have been investigated by X-ray analysis. The crystal structures of [Mo₃S₄(taci+ rmC₃H₆O-H₂O)₃-4H]·2OH₂O (1a, rhombohedral, space group R32, A = 15.964(3), C = 40.59(1) Å, Z = 6), [Mo₃S₄(tdci)₃]Br₄·9.5EtOH·5H₂O (2a, triclinic, space group

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and [CuBrMo₃S₄(tdci)₃]Br₃·11 H₂O·EtOH (3a, monoclinic, space group P2,/n, A = 14.887(3), B = 22.570(4), C = 21.974(5) Å, β = 98.54(2)°, Z = 4) revealed andN-N-O and an N-O-O coordination mode for taci and tdci, respectively. In 1a, taci is coordinated as an anion with deprotonated oxygen and nitrogen donors. In addition, the non-coordinating amino group reacted with one equivalent; of acetone, forming a Schiff base condensation product. For 2a, short Mo---O bonds and high pK_a values (compared to the aqua ion [Mo₃S₄(H₂O)₉]⁴⁺) indicate the formation of a zwitterionic form of the tdci ligand with coordinated alkoxo groups and peripheral dimethylammonium groups. No significant differences were found for the structural properties of the Mo-tdci fragment in 2a and 3a. The coordination modes of taci and tdci, as observed in the solid state, are in agreement with the previously reported solution structures, established by NMR spectroscopy. They are attributed to the specific steric requirements of the two ligands and to a pronounced preference of the [Mo₃(μS)₃(μ₃S)]⁴⁺ core to coordinate a nitrogen donor trans to μ₃S.     

Synthesis and biological activity of cis-dichloro mono- and bis(platinum) complexes with N-alkyl-ethylenediamine ligands

Mono- and bis(platinum) complexes containing N-alkyl-ethylenediamine units of the type {cis-PtCl₂[H₂NCH₂CH₂NH(CH₂)_nCH₃]} (n=8, 9, 11, 15) and [{cis-PtCl₂(H₂NCH₂CH₂NH)}₂(CH₂)_n] (n=6, 8, 10, 12) and their corresponding dihydroxo-platinum(IV) complexes were synthesized. The structures of the metal chelates were derived from elemental analyses and their ¹H, ¹³C, IR spectra. The length of the aliphatic chains has been varied systematically, in order to increase the lipophilicity. Enlargement of the linker could also lead to more flexibility of one platinum sphere in reference to the attached DNA species. Using in vitro cytotoxicity tests it is shown that the biological activity of the bis(platinum) complexes increased, up to n=12, with the length of the linker. The longest linker in the ligands resulted in the most effective bis(platinum) complexes against L1210 murine leukemia cells.     

Metal ion-coordinating properties of imidazole and derivatives in aqueous solution: interrelation between complex stability and ligand basicity

The stability constants of the 1:1 complexes formed between Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ or Cd²⁺ (M²⁺) and the simple, sterically unhindered imidazole-type ligands, imidazole, 1-methylimidazole, 5-chloro-1-methylimidazole, N-(2,3,5,6-tetrafluorophenyl)imidazole or 4′-(imidazol-1-yl)acetophenone (L), were determined by potentiometric pH titrations in aqueous solution (25°C; I = 0.5 M, NaNO₃). The construction of log K_ML^M versus pK_HL^H plots results in straight lines; the equations for the least-squares lines are calculated and listed. These data allow calculation of the expected stability constant for a complex of any imidazole-type ligand, provided its pK_HL^H value (in the pK_a range 4–8) is known. For the stabilities of Fe²⁺ complexes with imidazole-type ligands an estimation procedure is provided. It is shown further that the complex formation between 1-methylbenzimidazole (MBI) and Mn²⁺, Ni²⁺, Cu²⁺ or Zn²⁺ is s sterically hindered, i.e. the data points for these M(MBI)²⁺ complexes do not fall on the straight lines defined by the imidazole-type ligands.     

Intermolecular Re---H·H---X hydrogen bonding (X = N, C) involving ReH5(PPh3)3

Ab initio (B3LYP) calculations show that PD·H---ReH₄(PH₃)₃ (PD = Proton donor) interactions follow the order PD = pyrrole > NH₃ > HCCH > C₂H₄ > CH₃---H 0 and decrease with the pK_a of the PD. For equivalent pK_a's, NH interacts more strongly than CH. However, intermolecular hydrogen-bonding of the M---H·H---C type is too weak to be detected experimentally in FTIR or UV-vis studies between ReH₅(PPh₃)₃ and PhCCH, C₆F₅H or PhCHCl₂.     

Synergistic Mixtures of Fungitoxic Monochloro and Dichloro-8-Quinolinols against Five Fungi

Fourteen mono- and dichloro-8-quinolinols were tested against five fungi (Aspergillus niger, A. oryzae, Myrothecium verrucaria, Trichoderma viride, and Mucor circinelloides) and compared with the fungitoxicity of 8-quinolinol in Yeast Nitrogen Base containing 1% D-glucose and 0.088% L-asparagine. All of the compounds were more fungitoxic than 8-quinolinol except for the surprising activity of 8-quinolinol against A. oryzae. Mixtures of the MICs of monochloro- and dichloro-8-quinolinols in which the halogens were in different positions of the quinoline ring showed synergism. Comparable mixtures in which one position of each compound was occupied by the same halogen showed additive activity. In a different study we showed that 3,5,6-, 3,5,7-, 4,5,7-, and 5,6,7-trichloro-8-quinolinols were not toxic to M. circinelloides, whereas the combinations of the correspondingly substituted mono- and dichloro-8-quinolinols as well as 3,6-dichloro- and 5,7-dichloro-8-quinolinols were inhibitory. This indicated that a steric factor can be involved in affecting fungitoxicity.     

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO or NCS, and reaction of isocyanato complexes under acidic conditions

Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)₂]ⁿ⁺ (bpy=2,2′-bipyridine, PY=pyridine; X=O, Y=NO₂ for n=0, and Y=py for n=1; X=S, Y=NO₂ for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO₂)(bpy)(py)₂] and [Ru(NCO)(bpy)(py)₃]⁺, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH₃)(bpy)(py)₂]³⁺. The molecular structures of [Ru(NCO)(bpy)(py)₃]ClO₄, [Ru(NCS)(NO)(bpy)(py)₂](PF₆)₂ and [Ru(NO)(NH₃)(bpy)(py)₂](PF₆)₃ were determined by X-ray crystallography.     

Study of the swelling dynamics with overshooting effect of hydrogels based on sodium alginate-g-acrylic acid

A series of hydrogels were synthesized by graft cross-link copolymerization of sodium alginate (SA) and acrylic acid (AA) using N, N-methylene-bis-(acrylamide) as a cross-linker. By study of the swelling kinetics of the hydrogels in different buffer solutions, the overshooting effect was observed in acidic medium, namely the gels firstly swelled to a maximum value following by a gradual deswelling until the equilibrium. The phenomenon is interpreted as a cooperative physical cross-linking caused by the hydrogen bond formation between the carboxyl groups of the hydrogels in a hydrophobic environment. The hydrogen bond formation was further confirmed by FT-IR spectra. The dependence of overshooting effect on the pH of buffer solution was more noticeable in comparison with the composition of hydrogels, demonstrating that the cooperative physical cross-linking caused by the hydrogen bond formation is dominant. Whether or not the overshooting effect appears is not only relative to the pH of buffer solution, but also depends on the pK_a of carboxyl groups on the network. The overshoot processes of the hydrogels under acidic medium at pH below the pK_a follow a quantitative model proposed by Díez-Peńa et al., and the theoretical curves are in very good agreement with the experimental data. While in pH > pK_a buffer solutions, the overshoot phenomenon does not appear arising from the repulsive interaction between the ionized carboxyl groups, the swelling processes follow Schott second-order rate equation.     

Multinucleating ligands from multiple palladium(0)-catalysed cross-coupling reactions — synthesis and characterisation of a trinuclear cyclometallated ruthenium(II) complex and a hexanuclear EPR-active molybdenum complex

Two multinucleating ligands have been prepared from 1,3,5-tris(3,5-dibromophenyl)benzene by multiple Pd(0)-catalysed cross-coupling reactions. 1,3,5-Tris[3,5-bis(4-pyridylethenyl)phenyl]benzene (L¹) has six remote pyridyl moieties, each of which can coordinate a 17 valence-electron Mo(tp^*)(NO)Cl fragment (tp^* = hydrotris(3,5-dimethylpyrazolyl)borate), affording the hexanuclear complex [Cl(NO)(tp^*)Mo₆(L¹) (1). 1,3,5-Tris[3,5-bis(2-pyridyl)phenyl]benzene (L²) incorporates three potentially terdentate, cyclometallating N,C,N-donor sets, and can coordinate three Ru(tpy)²⁺ fragments (tpy = 2,2′:6′,2″-terpyridine) giving the trinuclear complex [(tpy)Ru₃(L²)][PF₆]₃ (2). Complex 1 is EPR active, with nearest-neighbour pairs of molybdenum centres displaying magnetic exchange interactions. Electrochemical studies of the two complexes suggest that there is little ground-state interaction between the metal centres in either case.     

Electrospray mass spectrometry of trans-[Ru(NO)Cl(dpaH)2] (dpaH=2,2′-dipyridylamine) and ‘caged NO’, [RuCl3(NO)(H2O)2]: loss of HCl and NO from positive ions versus NO and Cl from negative ions

The positive ion electrospray mass spectrometry (ESI-MS) of trans-[Ru(NO)Cl)(dpaH)₂]Cl₂ (dpaH=2,2′-dipyridylamine), obtained from the carrier solvent of H₂O–CH₃OH (50:50), revealed 1+ ions of the formulas [Ru^II(NO⁺)Cl(dpaH)(dpa)]⁺ (m/z=508), [Ru^IIICl(dpaH)(dpa⁻)]⁺ (m/z=478), [Ru^II(NO⁺)(dpa)₂]⁺ (m/z=472), [Ru^III(dpa)₂]⁺ (m/z=442), originating from proton dissociation from the parent [Ru^II(NO⁺)Cl(dpaH)₂]²⁺ ion with subsequent loss of NO (17.4% of dissociative events) or loss of HCl (82.6% of dissociative events). Further loss of NO from the m/z=472 fragment yields the m/z=442 fragment. Thus, ionization of the NH moiety of dpaH is a significant factor in controlling the net ionic charge in the gas phase, and allowing preferential dissociation of HCl in the fragmentation processes. With NaCl added, an ion pair, {Na[Ru^II(NO)Cl(dpa)₂]}⁺ (m/z=530; 532), is detectable. All these positive mass peaks that contain Ru carry a signature ‘handprint’ of adjacent m/z peaks due to the isotopic distribution of ¹⁰⁴Ru, ¹⁰²Ru, ¹⁰¹Ru, ⁹⁹Ru, ⁹⁸Ru and ⁹⁶Ru mass centered around ¹⁰¹Ru for each fragment, and have been matched to the theoretical isotopic distribution for each set of peaks centered on the main isotope peak. When the starting complex is allowed to undergo aquation for two weeks in H₂O, loss of the axial Cl⁻ is shown by the approximately 77% attenuation of the [Ru^II(NO⁺)Cl(dpaH)(dpa)]⁺ ion, being replaced by the [Ru^II(NO⁺)(H₂O)(dpa)₂]⁺ (m/z=490) as the most abundant high-mass species. Loss of H₂O is observed to form [Ru^II(NO⁺)(dpa)₂]⁺ (m/z=472). No positive ion mass spectral peaks were observed for RuCl₃(NO)(H₂O)₂, ‘caged NO’. Negative ions were observed by proton dissociation forming [Ru^II(NO)Cl₃(H₂O)(OH)]⁻ in the ionization chamber, detecting the parent 1− ion at m/z=274, followed by the loss of NO as the main dissociative pathway that produces [Ru^IIICl₃(H₂O)(OH)]⁻ (m/z=244). This species undergoes reductive elimination of a chlorine atom, forming [Ru^IICl₂(H₂O)(OH)]⁻ (m/z=208). The ease of the NO dissociation is increased for the negative ions, which should be more able to stabilize a Ru^III product upon NO loss.     

Dinuclear sulfide–thiolate complexes [Pt2(μ-S)(μ-SR)(PPh3)4] as cationic metalloligands

The cationic monoalkylated derivatives of the well-known metalloligand [Pt₂(μ-S)₂(PPh₃)₄], viz. [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (R = n-Bu, CH₂Ph) are themselves able to act as metalloligands towards the Ph₃PAu⁺ and R′Hg⁺ (R′ = Ph or ferrocenyl) fragments, by reaction with Ph₃PAuCl or R′HgCl, respectively. The resulting dicationic products [Pt₂(μ-SR)(μ-SAuPPh₃)(PPh₃)₄]²⁺ and [Pt₂(μ-SR)(μ-SHgR′)(PPh₃)₄]²⁺ are readily isolated as their hexafluorophosphate salts, and have been fully characterised by spectroscopic techniques and an X-ray structure determination on [Pt₂(μ-SR)(μ-SHgFc)(PPh₃)₄](PF₆)₂.     

The use of the borocaptate anion as a ligand. Synthesis and X-ray crystal structure of pentaammine (1-thiolato-closo-undecahydrododecaborane)ruthenium(III) dihydrate

The complex [Ru(SB₁₂H₁₁)(NH₃)₅]·2H₂O has been prepared by the reaction of Cs₂B₁₂H₁₁SH with [RuCl(NH₃)₅]Cl₂ in aqueous solution. The complex represents the first reported example of the borocaptate anion acting as a ligand. The structure of the complex has been determined by single crystal X-ray diffraction analysis. The crystal parameters are monoclinic, space group P2₁/c, A = 8.056(1), B = 14.240(2), C = 15.172(2) Å, β=98.48° and Z = 4. The ruthenium atom has a distorted octahedral coordination. The distortion is probably due to the high (3⁻) charge and the large bulk of the borocaptate ligand. These features can also be observed in the spectroscopic properties of the complex.     

Acid dissociation constants of diphytanylglycerolphosphorylglycerol-methylphosphate, and diphytanylglycerolphosphorylglycerophosphate and its deoxy analog

Acid dissociation constants of 2,3-diphytanyl-sn-glycero-1-phosphoryl-sn-3′-glycero-1′-methylphosphate (PGP-Me), the major phospholipid in extreme halophiles (Halobacteriaceae), and of the demethylated 2,3-diphytanyl-sn-glycero-1-phosphoryl-sn-3′-glycero-1′-phosphate (PGP) and its deoxy analog 2,3-diphytanyl-sn-glycero-1-phosphoryl-1′-(1′,3′-propanediol-3′-phosphate) (dPGP), were calculated by an original mathematical procedure from potentiometric titration data in methanol/water (1:1, v/v) and found to be as follows: for PGP-Me (and presumably PGP), pK₁=3.00 and pK₂=3.61; for PGP, pK₃=11.12; and for dPGP, pK₁=2.72, pK₂=4.09, and pK₃=8.43. High-resolution ³¹P NMR spectra of intact PGP-Me in benzene/methanol or in aqueous dispersion showed two resonances corresponding to the two P-OH groups, each of which exhibited a chemical shift change in the pH range 2.0–4.5, corresponding to acid dissociation constants pK₁=pK₂=3.2; no further ionization (pK₃) was detected at higher pH values in the range 5–12. The present results show that PGP-Me titrates as a dibasic acid in the pH range 2–8, but above pH 8, it titrates as a tribasic acid, presumably PGP, formed by hydrolysis of the methyl group during the titration with KOH. Calculation of the concentrations of the ionic molecular species of PGP-Me, PGP and dPGP as a function of pH showed that the dianionic species predominate in the pH range 5–9, covering the optimal pH for growth of Halobacteriaceae. The results are consistent with the concept that the hydroxyl group of the central glycerol moiety in PGP-Me and PGP is involved in the formation of an intramolecular hydrogen-bonded cyclic structure of the polar headgroup, which imparts greater stability to the dianionic form of PGP-Me and PGP in the pH range 5–9 and facilitates lateral proton conduction by a process of diffusion along the membrane surface of halobacterial cells.     

One-dimensional polymeric chlorocadmate(II) systems of N-methylpiperazinium and N,N′-dimethylpiperazinium compounds: synthesis, structural and thermal properties

The chlorocadmate(II) systems of (H₂me₂pipz)[Cd₂Cl₆(H₂O)₂] (1) and (H₂mepipz)₂[Cd₃Cl₁₀(H₂O)] (2) (L = me₂pipz = N,N′-dimethylpiperazine; L′ = mepipz = N-methylpiperazine) were prepared and their structural and thermal properties investigated. Compound 1 is monoclinic, space group P2₁/c, A = 7.664(1), B = 7.472(4), C = 15.347(1) Å, β = 99.468(7)°, Z = 2, R = 0.024. The crystal structure consists of organic cations and infinite one-dimensional chains of [CdCl₃(H₂O)]_n³⁻ anions. Each Cd atom is octahedrally surrounded by bridged and terminal chlorine atoms and by a water molecule, which is in trans position with respect to the terminal chlorine atom. Inter- and intrachain hydrogen bond interactions between the terminal chlorine atoms and the water molecules contribute to the crystal packing. Compound 2 is orthorhombic, space group Cmc2₁, A = 15.286(3), B = 13.354(3), C = 13.154(3) Å, R = 0.023. The crystal structure consists of organic dications and infinite chains of [Cd₂Cl₆(CdCl₄H₂O]_n⁴⁻ units running along the [001] axis. Each unit is formed of regularly alternate six-coordinated Cd atoms, one of them linking one pentacoordinated Cd atom which completes its coordination througha water molecule. A strong hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential hydrogen bond interaction involving the organic dication and the inorganic chain contributes to the crystal packing. Differential scanning calorimetry measurements did not show the presence of any structural phase transitions. The structures are compared with those of (H₂pipz)[Cd₂Cl₆(H₂O)₂] (3), (H₂mepipz)[Cd₂Cl₆(H₂O)₂]·H₂O (4) and (H₂mepipz)[Cd₂Cl₆] (5) (L = pipz = piperazine, L′ = mepipz = N-ethylpiperazine).     

Photochemical reactions of transition metal organyl complexes with olefins Part 10. Light-induced formal [5+2] cycloadditions at manganese

Tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-manganese (1) forms upon UV irradiation in THF at 208 K solvent stabilized dicarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese (2). With butynedioic acid dimethyl ester (3) and diphenylacetylene (5) complex 2 yields tricarbonyl-η⁵-1,2-dimethoxycarbonyl-4,6-dimethyl- cyclohepta-2,4-dien-1-yl-manganese (4) and tricarbonyl-η-4,6-dimethyl-1,2-diphenyl-cyclohepta-2,4-dien-1-yl- manganese (6) in a formal [5+2] cycloaddition. Addition of carbon monoxide and a 1,4-H shift completes the reaction. Propynoic acid methyl ester (7) forms the 2:1 adduct dicarbonyl-η^5:2-1,3-dimethyl-6-methoxycarbonyl-6- (E-2′-methoxycarbonylvinyl)-cyclohepta-2,4-dien-1-yl-manganese (8). The crystal and molecular structure of 8 was determined by X-ray structure analysis. The molecular structures of the complexes 4 and 6 were established by IR and NMR spectroscopy. Formation mechanisms of 4, 6 and 8 are discussed. Crystal data for 8: monoclinic space group P2₁/c, a=802.6(3), b=1136.6(1), c=8872.3(3) pm, β=93.14(2)°, V=1.705 nm³, Z=4.     

Studies of the cation complexing ability of crowns Part I. Synthesis, characterization and crystal structure of diazacrowns and their barium complexes

A number of N,N′-bis(4-substituted phenyl)-1,7-diaza-12-crown-4 and N,N′-bis(4-substituted phenyl)-1, 10-diaza-18-crown-6 (where the substituents are OCH₃, CH₃, H, Cl, respectively) have been prepared by cyclization reaction of a ditosylate with the appropriately substituted diol. These new macrocyclic ligands have been characterized by means of elemental analysis, IR, ¹H NMR and MS spectra. The crystal structures of N,N′-bis(4-chlorophenyl)-1,10-diaza-18-crown-6 (21) and its complex with barium thiocyanate Ba(SCN)₂ (22) have been determined by single crystal X-ray diffraction. The crystallographic data are as follows: 21: C₂₄H₃₂Cl₂N₂O₄, orthorhombic, P2₁2₁2₁, A=4.852(1), B=11.989(2), C=41.231(8) Å, V=2398.7(8) ų, Z=4; 22: C₂₆H₃₂Cl₂N₄O₄S₂Ba, monoclinic, P2₁/c, A=8.801(2), B=11.653(9), C=15.756(6) Å, ß=105.96(3)°, V=1553.7(14) ų, Z=2. In the complex, the Ba atom is eight-coordinate (O(1), O(2), O(1)′, O(2)′, N(1), N(1)′, N(21), N(21)′) to form a distorted D_6h geometry with the Ba atom at the center of crystallographic symmetry.