Mononuclear [NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- (L = thiolate, selenolate, PPh3, and Cl) complexes with intramolecular [Ni...S...H...S]/[Ni...H...S] interactions modulated by the coordinated ligand L: relevance to the [NiFe] hydrogenases

The shift of the IR nu(S)(-)(H) frequency to lower wavenumbers for the series of complexes [Ni(II)(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- (L = PPh3 (1), Cl (6), Se-p-C6H4-Cl (5), S-C4H3S (7), SePh (4)) indicates that a trend of increasing electronic donation of the L ligands coordinated to the Ni(II) center promotes intramolecular [Ni-S...H-S] interactions. Compared to the Ni...S(H) distance, in the range of 3.609-3.802 A in complexes 1 and 4-7, the Ni...S(CH3) distances of 2.540 and 2.914 A observed in the [Ni(II)(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] complexes (8a and 8b, two conformational isomers with the chemical shift of the thioether methyl group at delta 1.820 (-60 degrees C) and 2.109 ppm (60 degrees C) (C4D8O)) and the Ni...S(CH3) distances of 3.258 and 3.229 A found in the [Ni(II)(L)(P(o-C6H4S)2(o-C6H4-SCH3))]1- complexes (L = SPh (9), SePh (10)) also support the idea that the pendant thiol protons of the Ni(II)-thiol complexes 1/4-7 were attracted by both the sulfur of thiolate and the nickel. The increased basicity (electronic density) of the nickel center regulated by the monodentate ligand attracted the proton of the pendant thiol effectively and caused the weaker S...H bond. In addition, the pendant thiol interaction modes in the solid state (complexes 1a and 1b, Scheme 1) may be controlled by the solvent of crystallization. Compared to complex 1a, the stronger intramolecular [Ni-S...H-S] interaction (or a combination of [Ni-S...H-S]/[Ni...H-S] interactions) found in complexes 4-7 led to the weaker S-H bond strength and accelerated the oxidation (by O2) of complexes 4-7 to produce the [Ni(Y)(L)(P(o-C6H4S)3)]1- (L = Se-p-C6H4-Cl (11), SePh (12), S-C4H3S (13)) complexes.     

Ruthenium complexes with chiral tetradentate imino-sulfoxide ligands

Treatment of 2-(methylsulfinyl)benzaldehyde (1) with ethylenediamine or (1R,2R)-(-)-1,2-diaminocyclohexane afforded N,N'-bis[2-(methylsulfinyl)benzylidene]ethylenediamine (L(1)) or (1R,2R)-N,N'-bis[2-(methylsulfinyl)benzylidene]-1,2-cyclohexanedia mine (L(2)), respectively. Lithiation of 2-bromobenzaldehyde diethylacetal with n-BuLi/TMEDA followed by reaction with (1R,2S,5R)-(-)-menthyl-(S)-p-toluenesulfinate afforded 2-(S)-(p-tolylsulfinyl)benzaldehyde diethyl acetal (2). Deprotection of 2 with pyridinium tosylate followed by condensation with ethylenediamine, (1R,2R)-(-)-diaminocyclohexane, or (S,S)-(+)-diaminocyclohexane afforded N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]ethylenediamine (L(3)), (1R,2R)-N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]-1,2-cyclohexanediamine ((R,R)-L(4)), or (S,S)-N,N'-bis[2-(S)-(p-tolylsulfinyl)benzylidene]-1,2-cyclohexanediamine ((S,S)-L(4)), respectively. Treatment of [Ru(PPh(3))(3)Cl(2)] with L afforded trans-[Ru(L)Cl(2)] [L = L(1) (3), L(2) (4), L(3) (5), (R,R)-L(4) ((R,R)-6), (S,S)-L(4) ((S,S)-6)]. The X-ray structures of (S(S),R(S))-4, (R,R)-6, and (S,S)-6 have been determined. The average Ru-N, Ru-S, and Ru-Cl distances in (S(S),R(S))-4 are 2.063, 2.2301, and 2.4039 A, respectively. The corresponding distances in (R,R)-6 are 2.071, 2.256, and 2.411 A, and those in (S,S)-6, 2.058, 2.2275, and 2.3831 A. Compound 3 exhibited a reversible Ru(III/II) couple at 0.56 V vs Cp(2)Fe(+/0) in CH(2)Cl(2). Treatment of 3 with AgNO(3) in water afforded the aqua compound trans-[Ru(L(1))Cl(H(2)O)][PF(6)] (7), which has been characterized by X-ray crystallography. The Ru-Cl, Ru-O, average Ru-N, and average Ru-S distances in 7 are 2.3733(6), 2.1469(16), 2.071, and 2.2442 A, respectively. Treatment of 3 with AgNO(3) followed by reaction with PPh(3) afforded [Ru(L(1))(PPh(3))(2)][PF(6)](2) (8). Treatment of [Os(PPh(3))(3)Cl(2)] with L(1) resulted in deoxygenation of one sulfoxide group of L(1) and formation of [Os(L(5))Cl(2)(PPh(3))] (9) (L(5) = N-[2-(methylsulfinyl)benzylidene]-N'-[2-(methylthio)benzylididene]ethylenediamine), which has been characterized by X-ray crystallography. The average Os-S(O), Os-N(trans to P), Os-N(trans to S), Os-P, and Os-Cl distances are 2.1931, 2.085, 2.175, 2.3641, and 2.4266 A, respectively.     

Ruthenium(II) ammine and hydrazine complexes with [N(Ph2PQ)2]- (Q = S, Se) ligands

Reactions of coordinatively unsaturated Ru[N(Ph2PQ)2]2(PPh3) (Q = S (1), Se (2)) with pyridine (py), SO2, and NH3 afford the corresponding 18e adducts Ru[N(Ph2PQ)2]2(PPh3)(L) (Q = S, L = NH3 (5); Q = Se, L = py (3), SO2 (4), NH3 (6)). The molecular structures of complexes 2 and 6 are determined. The geometry around Ru in 2 is pseudo square pyramidal with PPh3 occupying the apical position, while that in 6 is pseudooctahedral with PPh3 and NH3 mutually cis. The Ru-P distances in 2 and 6 are 2.2025(11) and 2.2778(11) A, respectively. The Ru-N bond length in 6 is 2.185(3) A. Treatment of 1 or 2 with substituted hydrazines L or NH2OH yields the respective adducts Ru[N(Ph2PQ)2]2(PPh3)(L) (Q = S, L = NH2NH2 (12), t-BuNHNH2 (14), l-aminopiperidine (C5H10NNH2) (15); Q = Se, L = PhCONHNH2 (7), PhNHNH2 (8), NH2OH (9), t-BuNHNH2 (10), C5H10NNH2 (11), NH2NH2 (13)), which are isolated as mixtures of their trans and cis isomers. The structures of cis-14 and cis-15 are characterized by X-ray crystallography. In both molecular structures, the ruthenium adopts a pseudooctahedral arrangement with PPh3 and hydrazine mutually cis. The Ru-N bond lengths in cis-14.CH2Cl2 and cis-15 are 2.152(3) and 2.101(3) A, respectively. The Ru-N-N bond angles in cis-14.CH2Cl2 and cis-15 are 120.5(4) and 129.0(2) degrees, respectively. Treatment of 1 with hydrazine monohydrate leads to the isolation of yellow 5 and red trans-Ru[N(Ph2PS)2]2(NH3)(H2O) (16), which are characterized by mass spectrometry, 1H NMR spectroscopy, and elemental analyses. The geometry around ruthenium in 16 is pseudooctahedral with the NH3 and H2O ligands mutually trans. The Ru-O and Ru-N bond distances are 2.118(4) and 2.142(6) A, respectively. Oxidation reactions of the above ruthenium hydrazine complexes are also studied.     

Structural diversity within analogous compounds: syntheses and studies of M(SCH2CH2NH2)Cl (M = Zn, Cd, Hg)

The novel complexes [Zn(L)Cl] (1), [Cd(L)Cl] (2), [Hg(L)Cl] (3), {[Hg(L)Cl].NaOH.2H2O} (3.NaOH.2H2O), and {[Hg3(HL)2Cl6].2H2O} (4) (L = -SCH2CH2NH2) were prepared and investigated by means of IR spectroscopy and single-crystal X-ray diffraction. The crystal structures of 1, 2, and 3.NaOH.2H2O show chelating N,S-coordination of the cysteaminate ligand, bridging S, and terminally coordinating Cl. Apart from these common features, the coordination geometries and modes of intermolecular association are different. 1 forms a cyclic tetramer with a Zn4S4 ring, and 3.NaOH.2H2O contains one-dimensional [Hg(L)Cl]n chains with S-bridged Hg atoms. Zn and Hg atoms in 1 and 3.NaOH.2H2O are tetracoordinate with a distorted tetrahedral M(ClNS2) geometry (M = Zn, Hg). Each Cd atom of 2 binds to three S atoms and vice versa, such that layers of distorted Cd3S3 hexagons are formed. 2 is the first example for a compound exhibiting a group 12-group 16 layer structure, which can be described as an analogue of a graphite layer. Additionally, each Cd atom binds to a chlorine atom and a nitrogen atom from a cysteaminate ligand resulting in pentacoordination with a distorted trigonal bipyramidal Cd(ClNS3) geometry. 4 contains two differently coordinate Hg atoms. One displays a distorted trans-octahedral Hg(Cl4S2) geometry, while the other is coordinated by four Cl atoms and one S atom and additionally forms a long Hg...Cl contact.     

Structural Studies of [V_2S_6O_2(CuPPh_3)_4(CuMeCN)_2]·2CH_2Cl_2·2PrOH

ＳｔｒｕｃｔｕｒａｌＳｔｕｄｉｅｓｏｆ［Ｖ_２Ｓ_６Ｏ_２（ＣｕＰＰｈ_３）_４（ＣｕＭｅＣＮ）_２］·２ＣＨ_２Ｃｌ_２·２ＰｒＯＨＺＨＡＮＧＨａｎ－Ｈｕｉ；ＹＵＸｉｕ－Ｆｅｎ；ＹＡＮＧＲｏｎｇ－Ｓｈｅｎｇ；ＺＨＥＮＧＦａ－Ｋｕｎ；ＨＵＡＮＧＬｉａｏ－Ｙｕ...     

Spectral studies, cyclic voltammetry and synthesis of cobalt(II) and ruthenium(III) complexes with symmetric and asymmetric ring containing membered N2S2, N4, and N5 donor macrocyclic ligands

Reaction of divalent cobalt(II) and trivalent ruthenium(III) salts (NO3, SCN and SO4) with macrocyclic ligands L1, L2 and L3 having N2S2, N4 and N5 core, have been designed and carry out. All these three macrocyclic ligands and their complexes were obtained in pure form. Their structures were investigated by using microanalytical analyses, IR, mass, magnetic moments, electronic and EPR spectral studies. The redox properties of the complexes were also examined by cyclic voltammetry. An interesting feature of complexes is that the relatively large rings of macrocyclic ligands prevent the macrocyclic rings from approaching the metal center as closely as they would, if they were not constrained. So the Ru-N distances are longer than expected due to ring size. Electrochemical studies show that the macrocyclic ligand L1 is more effective electron donors to ruthenium than of L2 and L3. Electronic spectral properties also show that the sulphur donor atom of L1 weakens the ligand field with respect to ligand-to-metal charge-transfer band. However it is expected that second-row transition metal-ligand bonds tend to be weaker than third-row transition metal-ligand bonds. There are well-established examples of reactions in which decreased of reactivity down a triad of transition metals is not observed. These novelties are usually attributed to pi-bonding effects for ligands such as carbon monoxide, solvent effects, or a change in mechanism.     

Synthesis, structure and dioxygen reactivity of a bis(micro-iodo)dicopper(I) complex supported by the [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine ligand

The air-sensitive bis(micro-iodo)dicopper(I) complex 1 supported by [N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N,N-di-(2-pyridylmethyl)]amine (L) has been prepared by treating copper(I) iodide with L in anhydrous THF. Compound 1 crystallizes as a dimer in space group C2/c. Each copper(I) center has distorted tetrahedral N2I2 coordination geometry with Cu-N(pyridyl) distances 2.061(3) and 2.063(3) A, Cu-I distances 2.6162(5) and 2.7817(5) and a Cu...Cu distance of 2.9086(8) A. Complex 1 is rapidly oxidized by dioxygen in CH2Cl2 with a 1 : 1 stoichiometry giving the bis(micro-iodo)peroxodicopper(II) complex [Cu(L)(micro-I)]2O2 (2). The reaction of 1 with dioxygen has been characterized by UV-vis, mass spectrometry, EPR and Cu K-edge X-ray absorption spectroscopy at low temperature (193 K) and above. The mass spectrometry and low temperature EPR measurements suggested an equilibrium between the bis(micro-iodo)peroxodicopper(II) complex 2 and its dimer, namely, the tetranuclear (peroxodicopper(II))2 complex [Cu(L)(micro-I)]4O4 (2'). Complex 2 undergoes an effective oxo-transfer reaction converting PPh3 into O=PPh3 under anaerobic conditions. At sufficiently high concentration of PPh3, the oxygen atom transfer from 2 to PPh3 was followed by the formation of [Cu(PPh3)3I]. The dioxygen reactivity of 1 was compared with that known for other halo(amine)copper(I) dimers.     

Synthetic and structural studies on [Fe2(SR)2(CN)x(CO)6-x](x-) as active site models for Fe-only hydrogenases.

A series of models for the active site (H-cluster) of the iron-only hydrogenase enzymes (Fe-only H2-ases) were prepared. Treatment of MeCN solutions of Fe2(SR)2(CO)6 with 2 equiv of Et4NCN gave [Fe2(SR)2(CN)2(CO)4](2-) compounds. IR spectra of the dicyanides feature four nu(CO) bands between 1965 and 1870 cm(-1) and two nu(CN) bands at 2077 and 2033 cm(-1). For alkyl derivatives, both diequatorial and axial-equatorial isomers were observed by NMR analysis. Also prepared were a series of dithiolate derivatives (Et4N)2[Fe2(SR)2(CN)2(CO)4], where (SR)2 = S(CH2)2S, S(CH2)3S. Reaction of Et4NCN with Fe2(S-t-Bu)2(CO)6 gave initially [Fe2(S-t-Bu)2(CN)2(CO)4](2-), which comproportionated to give [Fe2(S-t-Bu)2(CN)(CO)5](-). The mechanism of the CN(-)-for-CO substitution was probed as follows: (i) excess CN(-) with a 1:1 mixture of Fe2(SMe)2(CO)6 and Fe2(SC6H4Me)2(CO)6 gave no mixed thiolates, (ii) treatment of Fe2(S2C3H6)(CO)6 with Me3NO followed by Et4NCN gave (Et4N)[Fe2(S2C3H6)(CN)(CO)5], which is a well-behaved salt, (iii) treatment of Fe2(S2C3H6)(CO)6 with Et4NCN in the presence of excess PMe3 gave (Et4N)[Fe2(S2C3H6)(CN)(CO)4(PMe3)] much more rapidly than the reaction of PMe3 with (Et4N)[Fe2(S2C3H6)(CN)(CO)5], and (iv) a competition experiment showed that Et4NCN reacts with Fe2(S2C3H6)(CO)6 more rapidly than with (Et4N)[Fe2(S2C3H6)(CN)(CO)5]. Salts of [Fe2(SR)2(CN)2(CO)4](2-) (for (SR)2 = (SMe)2 and S2C2H4) and the monocyanides [Fe2(S2C3H6)(CN)(CO)5](-) and [Fe2(S-t-Bu)2(CN)(CO)5](-) were characterized crystallographically; in each case, the Fe-CO distances were approximately 10% shorter than the Fe-CN distances. The oxidation potentials for Fe2(S2C3H6)(CO)4L2 become milder for L = CO, followed by MeNC, PMe3, and CN(-); the range is approximately 1.3 V. In water,oxidation of [Fe2(S2C3H6)(CN)2(CO)4](2-) occurs irreversibly at -0.12 V (Ag/AgCl) and is coupled to a second oxidation.     

High-frequency, high-field EPR; magnetic susceptibility; and X-ray studies on a ferromagnetic heterometallic complex of diethanolamine (H2L), [Cu4(NH3)4(HL)4][CdBr4]Br2.3dmf.H2O

The novel heterometallic complex [Cu(4)(NH(3))(4)(HL)(4)][CdBr(4)]Br(2).3dmf.H(2)O has been prepared in the reaction of zerovalent copper with cadmium oxide in the air-exposed solution of ammonium bromide and diethanolamine (H(2)L) in dimethylformamide (dmf). The compound is monoclinic, with space group P2(1)/c, a = 14.876(3) A, b = 33.018(6) A, c = 11.437(2) A, beta = 108.182(3)(o), and Z = 4. The crystal lattice consists of [Cu(4)(NH(3))(4)(HL)(4)](4+) cations, [CdBr(4)](2)(-), Br(-) anions, and uncoordinated dmf and water molecules. In the cation, four independent Cu atoms occupy vertexes of a distorted tetrahedron with bridged Cu...Cu distances in the range 3.127(2)-3.333(3) A and other Cu...Cu separations being 3.445(3)-3.503(2) A. The magnetic susceptibility and the EPR spectra were measured over the temperature ranges 1.8-300 and 3-300 K, respectively. The magnetic moment was found to increase with decreasing temperature to reach a maximum of 2.60 muB per one copper atom at ca. 10 K and was found, subsequently, to diminish slightly at lower temperatures owing to zero-field and Zeeman splitting of the S = 2 ground state. The temperature dependence of the magnetic susceptibility was fitted to the spin Hamiltonian H = J(ab)S(a)S(b) + J(bc)S(b)S(c) + J(cd)S(c)S(d) + J(ad)S(a)S(d) + J(ac)S(a)S(c) + J(bd)S(b)S(d) with the exchange integrals J(ab) = J(bc) = J(cd) = J(ad) = -65(3) cm(-1) and J(ac) = J(bd) = +1(3) cm(-1). High-field, high-frequency (95-380 GHz) EPR spectra due to an S = 2 ground state were simulated with g(x) = 2.138(1), g(y)) = 2.142(1), g(z) = 2.067(1), D = -0.3529(3) cm(-1), and E = -0.0469(8) cm(-1). Calculations based on the X-ray structure indicate a negligible contribution of the magnetic dipole-dipole interactions to the zfs parameters D and E. A discussion of the isotropic and anisotropic exchange interactions and their effect on the zfs parameters is also given.     

Synthesis, crystal structures and magnetic properties of cyanide- and phenolate-bridged [M(III)NiII]2 tetranuclear complexes (M=Fe and Cr)

The binuclear complex NiII2L(H2O)2(ClO4)2(1) and the neutral tetranuclear bimetallic compounds [{M(III)(phen)(CN)4}2{NiII2L(H2O)2}].2CH3CN with M=Fe (2) and Cr (3)[H2L=11,23-dimethyl-3,7,15,19-tetraazatricyclo[19.3.1.1(9,13)]hexacosa-2,7,9,11,13(26),14,19,21(25),22,24-decaene-25,26-diol] have been synthesized and the structures of and determined by single crystal X-ray diffraction. and are isostructural compounds whose structure is made up of centrosymmetric binuclear cations [Ni2(L)(H2O)2]2+ and two peripheral [M(phen)(CN)4]- anions [M=Fe (2) and Cr (3)] acting as monodentate ligands towards the nickel atoms through one of their four cyanide nitrogen atoms. The environment of the metal atoms in 2 and 3 is six-coordinated: two phen-nitrogen and four cyanide-carbon atoms at the iron and chromium atoms and a water molecule, one cyanide-nitrogen and two phenolate-oxygens and two imine-nitrogens from the binucleating ligand L2- at the nickel atom build distorted octahedral surroundings. The values of the FeNi and CrNi separations through the single cyanide bridge are 5.058(1) and 5.174(2)A respectively, whereas the Ni-Ni distances across the double phenolate bridge are 3.098(2)(2) and 3.101(1) A (3). The magnetic properties of have been investigated in the temperature range 1.9-290 K. The magnetic behaviour of corresponds to that of an antiferromagnetically coupled nickel(II) dimer with J=-61.0(1) cm-1, the Hamiltonian being defined as H=-J S(A).S(B). An overall antiferromagnetic behaviour is observed for and with a low-lying singlet spin state. The values of the intramolecular magnetic couplings are J(Fe-Ni)=+17.4(1) cm-1 and J(Ni-Ni(a))=-44.4(1) cm-1 for and J(Cr-Ni)=+11.8(1) cm-1 and J(Ni-Ni(a))=-44.6(1) cm-1 for [H=-J(M-Ni)(S(M).S(Ni)+S(Ma).S(Nia))-J(Ni-Nia)S(Ni)S(Nia)]. Theoretical calculations using methods based on density functional theory (DFT) have been employed on in order to analyze the efficiency of the exchange pathways involved and also to substantiate the exchange coupling parameters.     

Synthesis, X-ray structure, polarized optical spectra and DFT theoretical calculations of two new organic-inorganic hybrid fluoromanganates(III): (bpaH2)[MnF4(H2O)2]2 and (bpeH2)[MnF4(H2O)2]2

Two new fluoromanganates(III) of 1,2-bis(4-pyridyl)ethane (bpa) and trans-1,2-bis(4-pyridyl)ethylene (bpe), LH(2)[MnF(4)(H(2)O)(2)](2) (L = bpa or bpe), have been prepared and their structure have been solved by single-crystal X-ray diffraction. The [MnF(4)(H(2)O)(2)](-) anion displays an octahedral geometry with a strong Jahn-Teller tetragonal distortion along the H(2)O-Mn-OH(2) axis. The equatorial metal-ligand distances (Mn-F 1.827(1)-1.859(2) A) are shorter than the axial ones (Mn-O 2.203(2)-2.234(2) A). Three polarized absorption bands at 22,500, 18,300 and 14,500 cm(-1) are observed in the optical spectra of (bpaH(2))[MnF(4)(H(2)O)(2)](2). Finally, we present theoretical calculations on the equilibrium bond distances as well as the crystal-field electron structure using density functional methods. The calculated Mn-F bond distances (1.85 A) are in agreement with the experimental data but the obtained Mn-O distances (2.53-2.56 A) are higher than the experimental one as usually found in similar Jahn-Teller distorted systems. The calculated d-d transition energies are compared with experimental energies derived from the optical spectra. The variation of the HOMO energy and transition energies against the Mn-O distance is also shown.     

Dynamic structures of horse liver alcohol dehydrogenase (HLADH): results of molecular dynamics simulations of HLADH-NAD(+)-PhCH(2)OH, HLADH-NAD(+)-PhCH(2)O(-), and HLADH-NADH-PhCHO.

Molecular dynamics simulations of the oxidation of benzyl alcohol by horse liver alcohol dehydrogenase (HLADH) have been carried out. The following three states have been studied: HLADH.PhCH(2)OH.NAD(+) (MD1), HLADH.PhCH(2)O(-).NAD(+) (MD2), and HLADH.PhCHO.NADH (MD3). MD1, MD2, and MD3 simulations were carried out on one of the subunits of the dimeric enzyme covered in a 32-A-radius sphere of TIP3P water centered on the active site. The proton produced on ionization of the alcohol when HLADH.PhCH(2)OH.NAD(+) --> HLADH.PhCH(2)O(-).NAD(+) is transferred from the active site to solvent water via a hydrogen bonding network consisting of serine48 hydroxyl, ribose 2'- and 3'-hydroxyl groups, and Hist51. Hydrogen bonding of the 3'OH of ribose to Ile269 carbonyl maintains this proton in position to be transferred to water. Molecular dynamic simulations have been employed to track water1287 from the TIP3 water pool to the active site, thus exhibiting the mode of entrance of water to the active site. With time the water1287 accumulates in two different positions in order to accept the proton from the ribose 3'-OH and from His51. There can be identified two structural substates for proton passage. In the first substate the imidazole Ne2 of His51 is adjacent to the nicotinamide ribose C2'-OH and hydrogen bonding distances for proton transfer through the hydrogen bonded relay series PhCH(2)OH...Ser48-OH...Ribose2'-OH...His51...OH(2) (path 1) average 2.0, 2.0, and 2.1 A and (for His51...OH(2)) minimal distances less or equal to 2.5 A. The structure for path 1 is present 20% of the time span. And in the second substate, there are two possible proton passages: path 1 as before and path 2. Path 2 involves the hydrogen-bonded relay series PhCH(2)OH...Ser48-OH...Ribose2'-OH...Ribose3'-OH...His51.OH(2) with the average bonding distances being 2.0, 2.0, 2.1, and 2.0 A and (for His51...OH(2)) minimal distances less or equal to 2.5 A (20% probability of the time span), respectively. During the molecular dynamics simulation the NAD(+) ribose conformations have stabilized at the C2'-endo-C3'-exo or the C2'-endo conformations. With the C2'-endo conformation the first and second substates are able to persist for different time spans, while with the C2'-endo-C3'-exo conformation the only possible pathway involves the first substate. For both first and second substates the fluctuation of the distances between the ribose-OH protons and N epsilon 2 of His51 imidazole ring is partially contributed by the "windshield wiper" motion of the His51 imidazole ring. Since the imidazole of His-51 contributes only about 10-fold to activity, as estimated from the decrease in activity upon substitution with a Gln, there must be an alternate route for the proton to pass to solvent without going through this histidine. A third pathway involves ribose C3'-OH and Ile-269. In MD2, near attack conformers (NACs) for hydride transfer from PhCH(2)O(-) to NAD(+) represent approximately 60% of E.S conformers. The molecular dynamic study of MD3 at mildly basic pH reveals that reactive ground state conformers (NACs) for hydride transfer from NADH to PhCHO amount to 12 mol % of conformers. In MD3, anisotropic bending of the dihydronicotinamide ring of NADH (average value of alpha(c) = 4.0 degrees and alpha(n) = 0.5 degrees, respectively) is observed.     

Cadmium(II) and mercury(II) complexes of an NO2S2-donor macrocycle and its ditopic xylyl-bridged analogue

The NO2S2-donor macrocycle (L1) was synthesised from the ring closure reaction between Boc-N-protected 2,2'-iminobis(ethanethiol) (3) and 2,2'-(ethylenedioxy)bis(benzyl chloride) (4) followed by deprotection of the Boc-group. alpha,alpha'-Dibromo-p-xylene was employed as a dialkylating agent to bridge two L1 to yield the corresponding N-linked product (L2). The X-ray structure of L2 (as its HBr salt) is described. A range of Cd(II) and Hg(II) complexes of L1 (6-9) and L2 (10-12) were prepared and characterised. Reaction of HgX2 (X = Br or I) with L1 afforded [Hg(L1)Br]2[Hg2Br6].2CH2Cl2 6 and [Hg(L1)I(2)] 7, respectively. For 6, the Hg(II) ion in the complex cation has a distorted tetrahedral coordination environment composed of S2N donor atoms from L1 and a bromo ligand. In 7 the coordination geometry is highly distorted tetrahedral, with the macrocycle coordinating in an exodentate manner via one S and one N atom. The remaining two coordination sites are occupied by iodide ions. [Hg(L1)(ClO4)]ClO4 8 was isolated from the reaction of Hg(ClO4)2 and L1. The X-ray structure reveals that all macrocyclic ring donors bind to the central mercury ion in this case, with the latter exhibiting a highly distorted octahedral coordination geometry. The O2S2-donors from the macrocyclic ring define the equatorial plane while the axial positions are occupied by the ring nitrogen as well as by an oxygen from a monodentate perchlorato ion. Reaction of Cd(NO3)(2).4H2O with L1 afforded [Cd(L1)(NO3)2](.)0.5CH2Cl2 9 in which L1 acts as a tridentate ligand, binding exo-fashion via its S2N donors. The remaining coordination positions are filled by two bidentate nitrate ions such that, overall, the cadmium is seven-coordinate. Reactions of HgX2(X = Br or I) with L2 yielded the isostructural 2 : 1 (metal : ligand) complexes, [Hg2(L2)Br4] 10 and [Hg2(L2)I(4)] 11. Each mercury ion has a distorted tetrahedral environment made up of S and N donors from an exodentate L2 and two coordinated halides. Contrasting with this, the reaction of L2 with Cd(NO3)(2).4H2O yielded a 1-D coordination network, {[Cd2(L2)(NO3)4].2CH2Cl2}n 12 in which each ring of L2 is exo-coordinated via two S atoms and one N atom to a cadmium ion which is also bound to one monodentate and one bidentate nitrate anion. The latter also has one of its oxygen atom attached to a neighboring cadmium via a nitroso (mu2-O) bridge such that the overall coordination geometry about each cadmium is seven-coordinate. The [Cd(L2)0.5(NO3)2] units are linked by an inversion to yield the polymeric arrangement.     

Cis‐ and trans‐influences in [PtCl2(SPh2)2]

Both cis‐ and trans‐di­chloro­bis­(di­phenyl ­sulfide)­platinum(II), [PtCl₂(C₁₂H₁₀S)₂], crystallize as mononuclear pseudo‐square‐planar complexes. In the cis compound, the Pt—Cl distances are 2.295 (2) and 2.319 (2) Å, and the Pt—S distances are 2.280 (2) and 2.283 (2) Å. In the trans compound, Pt is located on a centre of inversion and the Pt—Cl and Pt—S distances are 2.2786 (15) and 2.3002 (12) Å, respectively.     

Extra large macrocycle: 40-membered macrocycle via 2:2 cyclization and its dimercury(II) complex

A large 40-membered N(4)O(4)S(4) macrocycle (L(2)) was obtained through a 2:2 cyclization of the corresponding dithiol and dichloride as a minor product during the preparation of a 20-membered N(2)O(2)S(2) macrocycle (L(1), 1:1 cyclization product). Each macrocycle was successfully separated from the mixed products and identified. The larger macrocycle L(2) allowed the preparation of its dimercury(II) complex, adopting a one-dimensional (1D) stairway-like polymeric chain linked with the anion. A monomercury(II) complex of the smaller macrocycle L(1) was also prepared. Both complexes and the larger macrocycle L(2) were structurally characterized by the single crystal X-ray analysis.     

Macrocyclic nickel(II) complexes coligated by hydrosulfide and hexasulfide ions: syntheses, structures, and magnetic properties of [NiII2L(mu-SH)]+ and [(LNiII2)2(mu-S6)]2+

The borohydride complex [Ni(II)2L(mu-BH4)]+ (3) where L(2-) represents a sterically demanding hexaaza-dithiophenolate ligand reacts rapidly with elemental sulfur in acetonitrile at ambient temperature to produce the cationic complexes [Ni(II)2L(mu-SH)]+ (4) and [(Ni(II)2L) 2(mu-S6)]2+ (6). Both complexes were isolated as ClO4(-) or BPh4(-) salts and characterized by IR and UV/vis spectroscopy and X-ray crystallography. Complex 4 (also accessible from [Ni(II)2L(ClO4)]+ (5) and Na2S.9H2O) features an unprecedented N3Ni(II)(mu-SR)2(mu-SH)Ni(II)N3 core structure, the hydrosulfide ligand being deeply buried in the binding-cavity of the bowl-shaped [Ni(II)2L]2+ complex. In 6, a helical S6(2-) chain, with a structure reminiscent to that of plastic sulfur, is almost completely encapsulated by two [Ni(II)2L]2+ subunits. In contrast to other triply sulfur-bridged N3Ni(II)(SR)3Ni(II)N3 structures whose ground states are typically of S = 0, 4 reveals an S = 2 ground-state which is attained by a ferromagnetic exchange interaction between the two Ni(II) (S = 1) ions ( J = 18 cm (-1), H = -2JS1S2). Intradimer ferromagnetic exchange interactions are also present in 6 ( J = 23 cm (-1)). A qualitative explanation for this difference is offered.     

Magnetic properties and crystal structure of a one-dimensional phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II)

A new crystalline polymorphic phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II) was obtained by direct synthesis, in space group P2(1)/n. The copper coordination is in a slightly distorted square pyramidal geometry with an intramolecular Cu...Cu distance of 2.6494(8) angstroms. The Cu-O distances of the two copper in a dimer are different, giving different chemical environments for each Cu ion. The crystal structure is built up of well-separated stacking columns oriented along the b-axis, with units uniformly spaced, producing a one-dimensional (1-D) zigzag chain through Cu(II)-S...S-Cu(II) interdimer interactions [S...S separation: 3.975(2) angstroms]. Magnetization measurements in the range 2-300 K indicate two magnetic orderings, at low temperature (T < 10 K) a weak ferromagnetic ordering is observed, and above this temperature an antiferromagnetic behavior takes place. ESR spectra at 300 and 77 K of a polycrystalline sample show the characteristic signal of zero-field with D = 0.354 cm(-1), consistent with a ferromagnetic Cu...Cu exchange interaction at low temperature.     

1-Ethylthio-2-[2-thienyltelluro]ethane (L) a new (Te, S) ligand: Synthesis and complexation with Ag(I), Cu(I), Pd(II) and Pt(II) – Single crystal structures of [PdCl2(L)] and bis(thienyl) tellurium(IV) chloride

Lithium 2-thienyltellurolate, generated from 2-thienyl lithium, reacts at −78 °C in THF with chloroethyl ethyl sulfide to give a (Te, S) ligand 1-ethylthio-2-[2-thienyltelluro]ethane (L) as a red oil. The complexes [PdCl₂(L)] (1), [PtCl₂(L)] (2), [Ag(L)₂][ClO₄] (3) and [CuBr(L)]₂ (4) were synthesized. The complex [HgCl₂(L)] on crystallization decomposed giving Th₂TeCl₂ (5) [where Th = 2-thienyl], which was characterized by X-ray diffraction on its single crystals. The ligand L and complexes 1–4 exhibit proton and carbon-13 NMR spectra, which are characteristic. The coordination through Te in 1–4 is indicated by downfield coordination shifts in the position of the TeCH₂ signal of L. Complex 1 was characterized by X-ray diffraction on its single crystals. The geometry around Pd is square planar. The Pd–Te, Pd–S and Pd–Cl bond lengths are 2.5040(4), 2.273(1) and 2.322(1)/2.380(1) Å, respectively. There are intermolecular interactions between Te (coordinated to Pd) and Cl, and sulfur and Cl. The Te–Cl and S–Cl distances, 3.401 and 3.488 Å, respectively, are shorter than the sum of the van der Waal’s radii (3.81 and 3.55 Å, respectively). The Pd–Pd distance between the two molecules is 3.4156(6) Å, greater than the sum of van der Waal’s radii (3.26 Å). The structure of 5 is typical of that of a tellurium(IV) compound (saw-horse type). The two Te–Cl bond lengths are identical, 2.480(1) Å. The geometry around Te in 5 can be best described as pseudo tetrahedral (trigonal bipyramidal with a lone pair on one corner of the triangle).     

Vapochromic behavior of {Ag2(Et2O)2[Au(C6F5)2]2}n with volatile organic compounds

The vapochromic behaviors of {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1), Me2CO (2), THF (3), CH3CN (4)) were studied. {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1)) was synthesized by the reaction of [Bu4N][Au(C6F5)2] with AgOClO3 in 1:1 molar ratio in CH2Cl2/Et2O (1:2). 1 was used as starting material with THF to form {Ag2L2[Au(C6F5)2]2}n (L = THF (3)). 3 crystallizes in the monoclinic space group C2/c and consists of tetranuclear units linked together via aurophilic contacts resulting in the formation of a 1D polymer that runs parallel to the crystallographic z axis. The gold(I) atoms are linearly coordinated to two pentafluorophenyl groups and display additional Au...Ag close contacts within the tetranuclear units with distances of 2.7582(3) and 2.7709(3) A. Each silver(I) center is bonded to the two oxygen atoms of the THF molecules with a Ag-O bond distance of 2.307(3) A. TGA analysis showed that 1 loses two molecules of the coordinated solvent per molecular unit (1st one: 75-100 degrees, second one: 150-175 degrees C), whereas 2, 3, and 4 lose both volatile organic compounds (VOCs) and fluorinated ligands in a less well defined manner. Each complex loses both the fluorinated ligands and the VOCs by a temperature of about 325 degrees C to give a 1:1 gold/silver product. X-ray powder diffraction studies confirm that the reaction of vapors of VOCs with 1 in the solid state produce complete substitution of the ether molecules by the new VOC. The VOCs are replaced in the order CH3CN > Me2CO > THF > Et2O, with the ether being the easiest to replace. {Ag2(Et2O)2[Au(C6F5)2]2}n and {Ag2(THF)2[Au(C6F5)2]2} n both luminesce at room temperature and at 77 K in the solid state. Emission maxima are independent of the excitation wavelength used below about 500 nm. Emission maxima are obtained at 585 nm (ether) and 544 nm (THF) at room temperature and at 605 nm (ether) and 567 nm (THF) at 77 K.     

Structural characterization and luminescence behavior of a silver(I) 1D polymeric chain constructed via a Bridge with unusual 4,5-diazospirobifluorene and perchlorate

A new polymeric silver complex, [Ag(2)(L(2))(ClO(4))(2)] (L = 4,5-diazospirobifluorene), has been synthesized and shown to exhibit interesting luminescence properties in a single crystal. Structural analysis reveals a one-dimensional chain, which contains a [Ag(2)(L(2))](2+) dimer bridged with ClO(4)(-). The Ag...Ag distances are 2.776(1) and 4.575(1) A incorporated by two L ligands and by a ClO(4)(-) bridge, respectively.