Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Macrocylic thioether-esters and thioether-thioesters and their palladium, platinum and silver complexes

Preparations by the high dilution method are reported for seven macrocyclic thioether-esters and thioether-thioesters (L1–;L7). Yields in these reactions between thiodiglycolyl dichloride and appropriate ,ω-diols or dithiols range from 10 to 51%. The compounds are characterized by ¹H and ¹³C NMR, IR and high resolution mass spectroscopy. They react with salts of Pd(II), Pt(II) and Ag(I) to form complexes of which MX₂·L2, (M = Pt, X = Cl; M = Pd, X = Cl, Br, I, SCN), [Pd(L2)₂][CF₃SO₃]₂·H₂O and [Ag(L5)₂][CF₃SO₃]·C₂H₅OH have been isolated and characterized by elemental analysis, IR and NMR spectroscopy. NMR spectra indicate reversible dissociation of the ligand occurs in dimethyl sulfoxide solvent for PdCl₂·L2 but not for the Pt analogue. For PtCl₂·L2, spectra indicate that the ligand is undergoing a conformational ‘wag’ about its pair of equivalent sulfurs. These remain bound to the metal while the unique sulfur moves from the apical position of the coordination sphere to a non-coordinated situation. Simultaneously, inversions at the bound sulfurs are occurring.     

Interactions between thiamine and large anions. Crystal structures of (H-thiamine)[Pt(SCN)4] · 3H2O and (H-thiamine)[Pt(SCN)6] · H2O

The reaction of thiamine with K₂Pt^IICl₄ and with Pt^IVCl₄ in the presence of excess NaSCN in aqueous solution gave thiamine salts, (H-thiamine)[Pt(SCN)₄] · 3H₂O (1) and (H-thiamine)[Pt(SCN)₆] · H₂O (2), respectively, structures of which have been determined by X-ray diffraction. The thiamine molecule adopts the usual F conformation in each salt. In 1, [Pt(SCN)₄]²⁻ ions act as large planar spacers in the crystal lattice and interact scarcely with thiamine, except for a hydrogen bonding with the terminal hydroxy O(5γ). Instead, water molecules form two types of host–guest-like interactions with the pyrimidine and the thiazolium moieties of a thiamine molecule, one being a C(2)–Hwaterpyrimidine bridge and the other being an N(4′)–Hwaterthiazolium bridge. In 2, despite the much larger ion size, octahedral [Pt(SCN)₆]²⁻ ions form a C(2)–Hanionpyrimidine bridge and an N(4′)–Hanionthiazolium bridge. An additional hydrogen bonding between the anion and the terminal O(5γ) of thiamine creates a hydrogen-bonded macrocyclic ring {thiaminium–[Pt(SCN)₆]²⁻}₂, a supramolecule.     

N,N′-Ethylene-bis(3-methoxysalicylideneimine) mononuclear (4f) and heterodinuclear (3d–4f) metal complexes: Synthesis, crystal structure and luminescent properties

The stepwise synthesis of mononuclear (4f) and heterodinuclear (3d–4f) Salen-like complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, reactions of ligand H₂L and Ln(NO₃)₃ · 6H₂O give rise to three mononuclear lanthanide complexes Ln(H₂L)(NO₃)₃ [H₂L = N,N′-ethylene-bis(3-methoxysalicylideneimine), Ln = Nd (1), Eu (2) and Tb (3)], in which N,N′-ethylene-bis(3-methoxysalicylideneimine) acts as tetradentate ligands with the O₂O₂ set of donor atoms capable of effective coordination. These species are fairly stable and have been isolated. Then, addition of Cu(Ac)₂ · H₂O to the mononuclear lanthanide complex yields expected heterodinuclear (3d–4f) complexes Cu(L)Ln(NO₃)₃ · H₂O [Ln = Nd (4) and Eu (5)] where the Cu(II) ion is inserted to the inner N₂O₂ cavity. Luminescent analysis reveals that complex 3 exhibits characteristic metal-centered fluorescence of Tb(III) ion. However, the characteristic luminescence of both Sm(III) and Eu(III) ions is not observed both in solution and solid state of the complexes.     

Structural determinations, magnetic and EPR studies of complexes involving the Cr(OH)2Cr unit

Five heterometallic compounds with formulae [Ba(H₂O)₄Cr₂(μ-OH)₂(nta)₂] · 3H₂O (I), [M(bpy)₂(H₂O)₂] [Cr₂(OH)₂(nta)₂] · 7H₂O, where M²⁺ = Zn, (II); Ni, (III); Co, (IV) and [Mn(H₂O)₃(bpy)Cr₂(OH)₂(nta)₂] · (bpy) · 5H₂O (V); bpy = 2,2′-bipyridine, (nta = nitrilotriacetate ion) have been prepared by reaction of I with the corresponding M^II-sulfates in the presence of 2,2′-bipyridine. Substances I–V have been characterized by magnetic susceptibility measurements, EPR and X-ray determinations. I represents a 2D coordination polymer formed by coordination of centrosymmetrical dimeric chromium(III) units and Barium cations. The 10-coordinate Ba polyhedron is completed by four water molecules. Compounds II–IV are isostructural and consist of non-centrosymmetric dimeric anions [Cr₂(μ-OH)₂(nta)₂]²⁻, complex cations [M^II(bpy)₂(H₂O)₂]²⁺ and solvate water molecules. The octahedral coordination of chromium atoms implies four donor atoms of the nta³⁻ ligands and two bridging OH groups. Multiple hydrogen bonds of coordinated and solvate water molecules link anions and cations in a 3D network. A similar [Cr₂(μ-OH)₂(nta)₂]²⁻ unit is found in V. The bridging function is performed by a carboxylate oxygen atom of the nta ligand that leads to the formation of a trinuclear complex [Mn(bpy)(H₂O)₂Cr₂(μ-OH)₂(nta)₂]. Experimental and calculated frequency and temperature dependences of EPR spectra of these compounds are presented. The fine structure appearing on the EPR spectra of compound V is analyzed in detail at different temperatures. It is established that the main part of the EPR signals is due to the transitions in the spin states of a spin multiplet with S = 2. Analyses of experimental and calculated spectra confirm the absence of interaction between metal ions (M^II) and Cr-dimers in complexes III and IV and the presence of weak Mn–Cr interactions in V. The temperature dependence of magnetic susceptibilities for I–V was fitted on the basis of the expression derived from isotropic Hamiltonian including a bi-quadratic exchange term.     

Hydride complexes of platinum(II) containing unsymmetrical di(phosphine) ligands: synthesis, characterization and evidence for pairwise addition of hydrogen based on parahydrogen induced polarization

Unsymmetrical di(phosphine) ligands (dpp)₂Rop (1a, b = bis(diphenylphosphino)-2-alkyl-3-oxapropane (alkyl = methyl and ethyl)) and (dpp)₂oCy (1c = trans-2-diphenylphosphinocyclohexyl diphenylphosphinite) and their Pt(II) dichloride complexes, PtCl₂((dpp)₂mop) (2a), PtCl₂((dpp)₂eop) (2b) and PtCl₂((dpp)₂oCy) (2c), have been synthesized and characterized by NMR spectroscopy. The crystal structures of 2b and 2c show that the geometry about the platinum centers is square planar. In 2b, the metal and di(phosphine) ligand chelate ring are in a chair conformation, whereas in 2c, the chelate ring conformation is a skewed boat. Initial reaction of sodium borohydride with 2a, b, c yields the monohydride monochloride complexes PtHCl((dpp)₂mop) (5a), PtHCl((dpp)₂eop) (5b) and PtHCl((dpp)₂oCy) (5c). At longer reaction times, fluxional dimeric species are obtained, [PtH((dpp)₂mop)]₂ (4a), [PtH((dpp)₂eop)]₂ (4b) and [PtH((dpp)₂oCy)]₂ (4c),and in the case of 4c two different isomers exist. The dihydride complexes PtH₂((dpp)₂mop) (3a), PtH₂((dpp)₂eop) (3b) and PtH₂((dpp)₂oCy) (3c), are prepared by further reaction of NaBH₄ and 2. Hydrogen cycling is facile in the dihydride complexes 3a, b, c, and oxidative addition of H₂ proceeds in a pairwise manner as determined by the observation of parahydrogen induced polarization (PHIP) in the ¹H NMR spectra. The reductive elimination of H₂ is also shown to be concerted by reaction of dihydride complexes with D₂. Crystal data: 2b (C₃₀H₃₂Cl₆OP₂Pt), monoclinic, space group P2₁/c (No. 14), a = 13.7040(1), b = 11.3430(7), c = 21.3880(9) Å, β = 97.923(9)°, V = 3292.9(2) ų and Z = 4; 2c (C₃₀H₃₀Cl₂OP₂Pt), monoclinic, space group P2₁ (No. 4), a = 11.7360(2), b = 8.4311(2), c = 14.2789(2) Å, β = 101.290(1)°, V = 1385.52(4) ų and Z = 2.     

Chemistry in environmentally benign media Part 1. Synthesis and characterization of 1,2-bis[bis(hydroxymethyl)phosphino]ethane (‘HMPE’). X-ray structure of [Pt{(HOH2C)2PCH2CH2P(CH2OH)2}2](Cl)2

The water-soluble bisphosphine, 1,2-bis(bis(hydroxymethyl)phosphino)ethane (1), was synthesized in near quantitative yield by the reaction of bisphosphine, H₂PCH₂CH₂PH₂, with an aqueous formaldehyde in the presence of K₂PtCl₄. The reaction of this water-soluble bisphosphine 1 with cis-Pt(COD)Cl₂ affords the mononuclear bischelate complex, [Pt{(HOH₂C)₂PCH₂CH₂P(CH₂OH)₂}₂](Cl)₂ (2), in near quantitative yield. The new ligand and complex have been characterized spectroscopically and the structure of the metal complex, 2, was determined by X-ray crystallography. The Pt(II) complex 2 crystallizes in the orthorhombic space group Pbca(a=14.623(1), B=16.216(2), C=9.319(4) Å) with Z=4. The final R value is 0.024.     

Synthesis and reactivity of diphosphino Pt(II) silanolate complexes as molecular models of the interaction of platinum particles with silica

A series of di- and monosubstituted cis-platinum(II) silanolate complexes, Pt(OSiR₃)₂(dppe) (R=Et, 1; R=Me, 2) and Pt(OSiR₃)Cl(dppe) (R=Et, 3; R=ⁱPr, 4) where dppe is 1,2-bis(diphenylphosphino)ethane, have been isolated and characterised spectroscopically. Complex 1 does not react with CO and H₂ under anhydrous conditions, but the complexes Pt{C(O)OCH₃)}₂(dppe) (6) and Pt(CO₃)(dppe) (7) have been isolated bubbling CO in methanol and CO₂ in moist benzene solutions of 1, respectively. The behaviour of 1 towards water or methanol is discussed on the basis of ¹H, and ³¹P{¹H} NMR spectroscopic data. The new complex Pt{S₂C(OSiEt₃)₂}(dppe) (8) has been isolated by reaction of 1 with CS₂ in benzene solution. This reactivity would suggest a high sensitivity towards water, but not towards H₂ or CO, of the bonding of slightly oxidised platinum particles with silanol groups of silica surface.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

Mixed anion lanthanide(III) crown ether complexes: crystal structures of [LaCl2(NO3)(12-crown-4)]2, [La(NO3)(OH2)4-(12-crown-4)]Cl2·CH3CN and [LaCl2(NO3)(18-crown-6)]

Reaction of LaCl₃·7H₂O containing small amounts of La(NO₃)₃·7H₂O as an impurity with 12-crown-4 or 18-crown-6 in 3:1 CH₃CN:CH₃OH resulted in the isolation of the mixed anion complexes [LaCl₂(NO₃)(12-crown-4)]₂, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN and [LaCl₂(NO₃)(18-crown-6)]. The nine-coordinate dimer, [LaCl₂(NO₃)(12-crown-4)]₂, has all of the anions in the inner coordination sphere and La³⁺ has a capped square antiprismatic geometry. It crystallizes in the orthorhombic space group Pbca with (at −150 °C) a = 12.938(6), B = 15.704(3), C = 13.962(2) Å, and D_calc = 2.08 g cm⁻³ for Z = 4. The second complex isolated from the same reaction, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN, has the bidentate nitrate anion in the inner coordination sphere but the two chloride anions are in a hydrogen bonded outer sphere. This complex is ten-coordinate 4A,6B-expanded dodecahedral and crystallizes in the monoclinic space group P2₁ with (at 20 °C) A = 7.651(2), B = 11.704(7), C = 11.608(4) Å, β = 95.11(2)°, and D_calc = 1.80 g cm⁻³ for Z = 2. The 18-crown-6 complex, [LaCl₂(NO₃)(18-crown-6)], has all inner sphere anions and has ten-coordinate 4A,6B-expanded dodecahedral La³⁺ centers. It crystallizes in the orthorhombic space group Pbca with (at 20 °C) a = 14.122(7), B = 13.563(5), C = 19.311(9) Å, and D_calc = 1.89 g cm⁻³ for Z = 8.     

Chemistry of vinylidene complexes XI. Synthesis of trinuclear MnFePt complexes by means of consecutive assembling out of mono- and dimetal vinylidene precursors

The dimetal μ-vinylidene complexes Cp(CO)₂MnPt(μ-C = CHPh)L₂ (L = tert.-phosphine or -phosphite), which have been obtained by coupling of the mononuclear complex Cp(CO)₂Mn=C=CHPh and unsaturated PtL₂ unit, add smoothly the Fe(CO)₄ moiety to produce trimetal MnFePt compounds. The μ₃-vinylidene cluster CpMnFePt(μ₃-C=CHPh)(CO)₆(PPh₃) was prepared in quantitative yields from the reactions of Cp(CO)₂MnPt(μ-C=CHPh)(PPh₃)L (L = PPh₃ or CO) with Fe₂(CO)₉ in benzene at 20 °C. The phosphite-substituted complexes Cp(CO)₂Mnpt(μ-C=CHPh)L₂ (L = P(OEt)₃ or P(OPrⁱ)₃) react under analogous conditions with Fe₂(CO)₉ to give mixtures (2:3) of the penta- and hexacarbonyl clusters, CpMnFePt(μ₃-C = CHPh)(CO)₅L₂ and CpMnFePt(μ₃-C = CHPh)(CO)₆L, respectively. The similar reaction of the dimetal complex Cp(CO)₂MnPt(μ-C = CHPh)(dppm), in which the Pt atom is chelated by dppm = Ph₂PCH₂PPhPin2 ligand, gives only a 15% yield of the analogous trimetal μ₃-vinylidene hexacarbonyl product CpMnFePt(μ₃-C = CHPh)(CO)(dppm), but the major product (40%) is the tetranuclear μ₄-vinylidene cluster (dppm)PtFe₃(μ₄-C = CHPh)(CO)₉. The IR and ¹H, ¹³C and ³¹P NMR data for the new complexes are reported and discussed.     

Molecular structure and reactions of azobenzene complexes with iron-lithium compounds

Reactions of azobenzene have been studied with heteronuclear iron-lithium compounds formed in the reaction of FeCl₃ with LiPh, one of the dinitrogen reducing systems of the Vol'pin type: Ph₄FeLi₄(OEt₂)₄ (1) and (H₂)FePh₄Li₄(OEt₂)₄ (2). The structures of the azobenzene complexes formed, (N₂Ph₂)₃FeLi₃(OEt₂)₃ (3) and (N₂Ph₂)₃FeLi₂(THF)₂ (4), as well as an ether-containing analog of the latter, (N₂Ph₂)₃FeLi₂(OEt₂)₂ (5), were determined by X-ray analysis of single crystals. Coordination of azobenzene at FeLi₃ and FeLi₂ clusters was shown to result in a sigificant elongation of the NN bond; partial cleavage of this bond on protolysis of the complexes resulted in the formation of hydrazobenzene and aniline. Magnetic susceptibility measurements and theoretic analysis of a similar model complex leads to the conclusion that the iron oxidation state in 3 may be considered between iron (I) and iron(III) (close to iron(I)), whereas in 4 and 5 it is close to iron(II).     

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.     

Facile and stereoselective condensation of acetone with ammonia ligands on cobalt(III): structure of a N-bonded cyanate complex containing the 2-methyl-2-amino-4-imino-pentane ligand

The complex [(NH₃)₅CoO₃SCF₃](CF₃SO₃)₂ reacts with excess NaNCO in warm acetone solution to give, stereoselectively, a Schiff base complex (40%) which has been characterized by standard NMR techniques as one of the six isomers of [Co{NH₂C(CH₃)₂CH₂C(CH₃)=NH}₂(NH₃)NCO](ClO₄)₂ · H₂O, confirmed by a single crystal X-ray structural analysis. Schiff base formation in non-basic conditions for kinetically inert Co(III) complexes is unprecedented. Also, this is only the second cyanate complex of pentaaminecobalt(III) to be structurally characterized (CoNCO: Co–N, 1.908 Å; N–C, 1.152 Å; C–O, 1.206 Å; Co–N–C, 170°; N–C–O, 177°).     

Diplatinum(III) complexes with bridging 1-methylcytosinate ligands and variable axial ligands, including guanine nucleobases

A series of diplatinum(III) complexes derived from cis-(NH₃)₂Pt^II and the model nucleobase 1-methylcytosine (1-MeC) has been prepared and X-ray structurally characterized, all of which contain two anionic base ligands (1-MeC⁻) in a head–tail (ht) arrangement: ht-cis-[(ONO₂)(NH₃)₂Pt(1-MeC⁻-N3,N4)₂Pt(NH₃)₂(ONO₂)](NO₃)₂·HNO₃·3H₂O (2b), ht-cis-[(NO₂) (NH₃)₂ Pt(1-MeC⁻-N3,N4)₂Pt(NH₃)₂(OH₂)](ClO₄)₃·3.5H₂O (3), ht-cis-[(OH₂)(NH₃)₂Pt(1-MeC⁻-N3,N4)₂Pt(NH₃)₂(OH₂)](ClO₄)₄·H₂O (4b), and ht-cis-[(9-EtGH-N7)(NH₃)₂Pt(1-MeC⁻-N3,N4)₂Pt (NH₃)₂(9-EtGH-N7)](NO₃)₄·9H₂O (7b) (9-EtGH=9-ethylguanine). Several other compounds, differing in the nature of the axial ligands, have been isolated and or observed in solution by ¹H and ¹⁹⁵Pt NMR spectroscopy. The chemistry of these diplatinum(III) compounds is dominated by facile substitution reactions of the axial ligands. Of particular interest in this context is the ready reaction of 2b or 3 with guanine nucleobases. Since similar compounds are not obtained with any of the other common nucleobases, 2b and 3 can be considered guanine-specific chemical probes.     

Syntheses, structures and magnetic properties of mono- and di-manganese inclusion compounds

Mono- and di-manganese inclusion compounds 1 and 2 are reported. Two mono-manganese molecules Mn(bpy)₂(NO₃)₂ (bpy=2,2′-bipyridine) and [Mn(bpy)₂(NO₃)(H₂O)]·NO₃ coexist in the mole ratio of 1:1 in the structure of 1, while two di-manganese molecules [Mn₂O(bpy)₂(phtha)₂(H₂O)₂]·(NO₃)₂ (phtha=phthalate) and [Mn₂O(bpy)₂(phtha)₂(NO₃)(H₂O)]·NO₃ in the structure of 2. Refluxing Mn(NO₃)₂/bpy/phthalic acid reaction mixtures in CH₃CN leads to the isolation of 1, further concentration of the reaction solution in raising temperature results in 2. The Mn₁ and Mn₂ units in the inclusion compounds 1 and 2 are similar to other reported Mn₁ and Mn₂ analogs, respectively. The Jahn–Teller distortion was observed to give rise to the elongation along the O_terminal---Mn---O_carboxyl axes for all the four Mn(III) sites in 2, leading to unexpected longer Mn(III)---O_aqua than Mn(II)---O_aqua in 1. Extensive hydrogen bonding interactions among H₂O, NO₃ ⁻ and COOH were observed in the two inclusion compounds. Cyclic voltammetry of 2 in DMF displays two quasi-reversible redox couples at +0.10/+0.22 and −0.43/−0.36 V assigned to the Mn(III)Mn(IV)/2Mn(III) and 2Mn(III)/Mn(III)Mn(II), respectively. Variable temperature magnetic susceptibilities of 1 and 2 were measured. The data were fit to a model including axial zero-field splitting term and a good fit was found with D=1.77 cm⁻¹, g=1.98 and F=1.48×10⁻⁵ for 1. For 2, the least-squares fitting of the experimental data led to J=2.37 cm⁻¹, g=2.02 and D=0.75 cm⁻¹ with R=1.45×10⁻³.     

Complexes of copper(II) dihalide with 2,2′-dipyridylamine. X-ray diffraction structures of the [dibromo-bis(dipyam)copper(II)]–water (1:2) and di[chloro-bis(dipyam)copper(II)]diiodide–acetonitrile (1:2) complexes

The formation of complexes between copper(II) halides and 2,2′-dipyridylamine (dipyam) has been studied systematically. Only complexes with a 1:1 and 1:2 metal-to-ligand ratio are formed. Some mixed chloro–iodide and halide–PF₆ compounds have also been isolated. The X-ray diffraction structures of the [Cu(dipyam)₂Br₂] · 2H₂O (I) and the [Cu(dipyam)₂Cl]₂I₂ · 2CH₃CN (II) complexes are reported. I is a rare example of an octahedral coordination among the copper(II) halide complexes of dipyam. The two bromo atoms, which occupy the apical positions, are H-bonded to the water molecules of crystallization. II is a dimer, where each copper forms a cationic chloro-complex of approximately trigonal bipyramidal geometry, the dimerization being due to hydrogen bonds formed by the NH group of one of the two dipyams coordinated to each metal atom with the chlorine atom of the centrosymmetric cationic complex. The iodide anions are hydrogen-bonded to the NH groups of the dipyams not involved in the dimerization.     

Molecular structures of Fe(II) complexes with mono- and di-protonated ethylenediamine-N,N,N′,N′-tetraacetate (Hedta and H2edta), as determined by X-ray crystal analyses

The molecular structure of the title complexes [Fe(H₂O)₄][Fe(Hedta)(H₂O)]₂ · 4H₂O (I) and [Fe(H[₂edta)(H₂O)] · 2H₂O (II) have been determined by single-crystal X-ray analyses. The crystal data are as follows: I: monoclinic, P2₁/n, A = 11.794(2), B = 15.990(2), C = 9.206(2) Å, β = 90.33(1)°, V = 1736.1(5) ų, Z = 2 and R = 0.030; II: monoclinic, C2/c, A = 11.074(2), B = 9.856(2), C = 14.399(2) Å, β = 95.86(1)°, V = 1563.3(4) ų, Z = 4 and R = 0.025. I is found to be isomorphous with the Mn^II analog reported earlier and to contain a seven-coordinate and approximately pentagonal-bipyramidal (PB) [Fe^II(Hedta)(H₂O]⁻ unit in which Hedta acts as a hexadentate ligand. The [Fe^II(H₂edta)(H₂O)] unit in II has also a seven-coordinate PB structure with the two protonated equatorial glycine arms both remaining coordinated, and thus bears a structural resemblance to the seven-coordinate [Co^II(H₂edta)(H₂O)] reported previously.     

Photoreactivity of buckminsterfullerene-bis(triphenylphosphite)platinum(0) induced by metal-to-ligand charge transfer excitation

The complex C₆₀Pt[P(OPh)₃]₂ displays C₆₀ ππ^* intraligand bands in the UV-Vis region and a long-wavelength absorption at λ_max = 770 nm which is assigned to a metal-to-ligand charge transfer (MLCT) transition from platinum to fullerene. The irradiation of the complex leads to the population of the reactive MLCT state and subsequently to the dissociation (C₆₀Pt[P(OPh)₃]₂ → C₆₀ + Pt[P(OPh)₃]₂) in the primary photochemical step. Product formation takes place by the interception of Pt[P(OPh)₃]₂ with suitable scavengers such as CHCl₃ or O₂.     

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).