Proton NMR spectroscopy and magnetic properties of a solution-stable dicopper(II) complex bearing a single mu-hydroxo bridge

The reaction of copper(II) perchlorate with the macrocyclic ligand [22]py4pz in the presence of base leads to formation of a dinuclear complex [Cu(2)([22]py4pz)(mu-OH)](ClO(4))(3)xH(2)O, in which two copper ions are bridged by a single mu-hydroxo bridge. Each copper ion is further surrounded by four nitrogen atoms of the ligand. The mu-hydroxo bridge mediates a strong antiferromagnetic coupling (2J = -691(35) cm(-1)) between the metal centers, leading to relatively sharp and well-resolved resonances in the (1)H NMR spectrum of the complex in solution. We herein report the crystal structure, the magnetic properties, and the full assignment of the hyperfine-shifted resonances in the NMR spectrum of the complex, as well as the determination of the exchange coupling constant in solution through temperature-dependent NMR studies.     

(infinity)(2)[Cu2(mu5-btb)(mu-OH)(mu-H2O)]: a two-dimensional coordination polymer built from ferromagnetically coupled Cu2 units (btb = benzene-1,2,3-tricarboxylate)

Hydrothermal reaction of Cu(NO(3))(2).3H(2)O, Cd(OH)(2) or Zn(OH)(2) with benzene-1,2,3-tricarboxylic acid (H(3)btb, hemimellitic acid) produced the 2D coordination polymer (MOF) [Cu(2)(mu(5)-btb)(mu-OH)(mu-H(2)O)] () and the 2D hydrogen-bonded complexes [Cd(H(2)btb)(2)(H(2)O)(4)].2H(2)O () and [Zn(H(2)O)(6)](H(2)btb)(2).4H(2)O () which are characterized by single-crystal X-ray diffraction, X-ray powder diffraction and thermoanalysis. Magnetic susceptibility measurements between 1.9-300 K for revealed three magnetic active exchange pathways that link the copper(ii) ions through a long mu-aqua bridge, an anti-syn carboxylate bridge [j(2) = 0.161(1) cm(-1)], and through a mixed mu-hydroxo + syn-syn carboxylate bridge [J = 83(1) cm(-1)]. At temperatures higher than 30 K the system behaves as isolated Cu(2) units with strong ferromagnetic Cu-Cu coupling through the mu-hydroxo and syn-syn carboxylate bridge. The strong ferromagnetic coupling is explained with Hoffmann's approach by means of the concept of counter-complementarity introduced by Nishida et al.[Chem. Lett., 1983, 1815-1818].     

Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: a description of the FeIV-oxo bond in the FeIII-O-FeIV dimer

Spectroscopic and electronic structure studies of the class I Escherichia coli ribonucleotide reductase (RNR) intermediate X and three computationally derived model complexes are presented, compared, and evaluated to determine the electronic and geometric structure of the FeIII-FeIV active site of intermediate X. Rapid freeze-quench (RFQ) EPR, absorption, and MCD were used to trap intermediate X in R2 wild-type (WT) and two variants, W48A and Y122F/Y356F. RFQ-EPR spin quantitation was used to determine the relative contributions of intermediate X and radicals present, while RFQ-MCD was used to specifically probe the FeIII/FeIV active site, which displayed three FeIV d-d transitions between 16,700 and 22,600 cm(-1), two FeIV d-d spin-flip transitions between 23,500 and 24,300 cm(-1), and five oxo to FeIV and FeIII charge transfer (CT) transitions between 25,000 and 32,000 cm(-1). The FeIV d-d transitions were perturbed in the two variants, confirming that all three d-d transitions derive from the d-pi manifold. Furthermore, the FeIV d-pi splittings in the WT are too large to correlate with a bis-mu-oxo structure. The assignment of the FeIV d-d transitions in WT intermediate X best correlates with a bridged mu-oxo/mu-hydroxo [FeIII(mu-O)(mu-OH)FeIV] structure. The mu-oxo/mu-hydroxo core structure provides an important sigma/pi superexchange pathway, which is not present in the bis-mu-oxo structure, to promote facile electron transfer from Y122 to the remote FeIV through the bent oxo bridge, thereby generating the tyrosyl radical for catalysis.     

Reactivity of bis(mu-hydroxo) divanadium site in gamma-H2SiV2W10O40(4-) with hydroxo compounds

The reactivity of divanadium-substituted silicotungstate, gamma-H2SiV2W10O40(4-) (I), with hydroxo compounds of alcohols, carboxylic acids, and water is reported. The reaction of the bis(mu-hydroxo) divanadium site in I with primary alcohols and formic acid smoothly proceeds to form corresponding monoesters and monoformate, respectively, and the crystal structures of the monomethyl and monoethyl esters and the monoformate of I are determined. The oxygen exchange between the hydroxo group and water proceeds easily. On the other hand, bulky compounds of 2-propanol, tert-butyl alcohol, and acetic acid hardly react with the bis(mu-hydroxo) divanadium site (equilibrium constant < 0.01) because of the steric crowding between the methyl groups and the polyoxometalate framework.     

Addition and metathesis reactions of zirconium and hafnium imido complexes

The zirconium and hafnium imido metalloporphyrin complexes (TTP)M = NArtPr (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; AriPr = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(mu-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of (TTP)Zr = NAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (mu-oxo)bis(mu-hydroxo)-bridged dimer [(TTP)Zr]2(mu-O)(mu-OH)2 (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction.     

Sterically controlled esterification on Bis(mu-hydroxo) dioxovanadium site in gamma-H2SiV2W10O40(4-)

The esterification of a bis(mu-hydroxo) dioxovanadium site in divanadium-substituted silicotungstate, gamma-H(2)SiV(2)W(10)O(40)(4)(-), with alcohols is sterically controlled: The secondary and tertiary alcohol esters are hardly formed (equilibrium constant < 0.01), and a large equilibrium constant of 75 is observed for the reaction with methanol.     

Structure and magnetic properties of a non-heme diiron complex singly bridged by a hydroxo group

The synthesis of the first singly bridged non-heme diiron complex with a mu-hydroxo bridging ligand, [{(salten)Fe}2(OH)][B(C6H5)4].(CH3CN)x.(H2O)y (1) [H2salten = 4-azaheptane-1,7-bis(salicylideneiminate)], is reported. The complex has been characterized with X-ray crystallography, FTIR, magnetic susceptibility measurements, and M?ssbauer spectroscopy. The data have been compared with the results of DFT calculations on both 1 and a model with an unsupported mu-oxo bridge (2) to verify the formulation of the complex as a mu-hydroxo-bridged species. The X-ray structure [Fe-O(H) = 1.997(1) A and Fe-O(H)-Fe = 159 degrees ] is consistent with the DFT-optimized geometry of 1 [Fe-O(H) = 2.02 A and Fe-O(H)-Fe = 151 degrees ]; the Fe-O(H) distance in 1 is about 0.2 A longer than the Fe-O separations in the optimized geometry of 2 (1.84 A) and in the crystallographic structures of diiron(III) compounds with unsupported mu-oxo bridges (1.77-1.81 A). The formulation of 1 as a hydroxo-bridged compound is also supported by the presence of an O-H stretch band in the FTIR spectrum of the complex. The magnetic susceptibility measurements of 1 reveal antiferromagnetic exchange (J = 42 cm(-1) and H(ex) = JS(1).S(2)). Nearly the same J value is obtained by analyzing the temperature dependence of the M?ssbauer spectra (J = 43 cm(-1); other parameters: delta = 0.49 mm s(-1), DeltaE(Q) = -0.97 mm s(-1), and eta = 0.45 at 4.2 K). The experimental J values and M?ssbauer parameters agree very well with those obtained from DFT calculations for the mu-hydroxo-bridged compound (J = 46 cm(-1), delta = 0.48 mm s(-1), DeltaE(Q) = -1.09 mm s(-1), and eta = 0.35). The exchange coupling constant in 1 is distinctly different from the value J approximately 200 cm(-1) calculated for the optimized mu-oxo-bridged species, 2. The increased exchange-coupling in 2 arises primarily from a decrease in the Fe-O bond length.     

Binuclear copper(II) complexes with N4O3 coordinating heptadentate ligand: synthesis, structure, magnetic properties, density-functional theory study, and catecholase activity

The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu 2(H 2L)(mu-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by mu-phenoxo and mu-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a mu-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (tau=0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (tau=0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (tau=0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di- tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat=29-37 h(-1).     

Dicopper(II) complexes of H-BPMP-type ligands: pH-induced changes of redox, spectroscopic ((19)F NMR studies of fluorinated complexes), structural properties, and catecholase activities

Substitution of the methyl group from the H-BPMP (HL(CH)3) ligand (2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol) by electron withdrawing (F or CF(3)) or electron donating (OCH(3)) groups afforded a series of dinucleating ligand (HL(OCH)3, HL(F), HL(CF)3), allowing one to understand the changes in the properties of the corresponding dicopper complexes. Dinuclear Cu(II) complexes have been synthesized and characterized by spectroscopic (UV-vis, EPR, (1)H NMR) as well as electrochemical techniques and, in some cases, by single-crystal X-ray diffraction: [Cu(2)(L(OCH)3)(muOH)][(ClO(4))(2)].C(4)H(8)O, [Cu(2)(L(F))(muOH)][(ClO(4))(2)], [Cu(2)(L(F))(H(2)O)(2)][(ClO(4))(3)].C(3)D(6)O, and [Cu(2)(L(CF)3)(H(2)O)(2)][(ClO(4))(3)].4H(2)O. Significant differences are observed for the Cu-Cu distance in the two mu-hydroxo complexes (2.980 A (R = OCH(3)) and 2.967 A (R = F)) compared to the two bis aqua complexes (4.084 A (R = F) and 4.222 A (R = CF(3))). The mu-hydroxo and bis aqua complexes are reversibly interconverted upon acid/base titration. In basic medium, new species are reversibly formed and identified as the bis hydroxo complexes except for the complex from HL(CF)3 which is irreversibly transformed near pH = 10. pH-driven interconversions have been studied by UV-vis, EPR, and (1)H NMR, and the corresponding pK are determinated. In addition, with the fluorinated complexes, the changes in the coordination sphere around the copper centers and in their redox states are evidenced by the fluorine chemical shift changes ((19)F NMR). For all the complexes described here, investigations of the catechol oxidase activities (oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone) are of interest in modeling the catecholase enzyme active site and in understanding aspects of structure/reactivity. These studies show the pH-dependence for the catalytic abilities of the complexes, related with changes in the coordination sphere of the metal centers: only the mu-hydroxo complexes from HL(CH)3, HL(F), and HL(OCH)3 exhibit a catecholase activity. Modification on R-substituent induces a drastic effect on the catecholase activity: the presence of an electron donating group on the ligand increases this activity; the reverse effect is observed with an electron withdrawing group.     

Unusual reactivity of molecular oxygen with pi-allylnickel(N-heterocyclic carbene) chloride complexes

One-pot preparation and characterization of the first reported nickel(II) complexes containing a single imidazol-2-ylidene ligand are reported. Subsequent treatment of these complexes with molecular oxygen at room temperature results in rapid formation of a mu-hydroxo dimer and alpha,beta-unsaturated carbonyl compounds. Mechanistic investigations indicate that this reaction proceeds via reversible oxygen binding followed by rate-limiting decomposition of the resulting metal-oxygen species.     

Synthesis of 2-pentafluorosulfanylnaphthalene

A three step synthesis of 2-pentafluorosulfanylnaphthalene is reported. Initial addition of SF₅Cl to benzobarralene was followed by elimination to form 2-pentafluorosulfanylbenzobarralene. Heating of this compound with 3,6-bis-(2-pyridyl)-1,2,4,5-tetrazine led to elimination of the ethylene bridge via a sequence of cycloadditions and retro-cycloadditions to form the title compound.     

Electronic structure of the Mn4OxCa cluster in the S0 and S2 states of the oxygen-evolving complex of photosystem II based on pulse 55Mn-ENDOR and EPR spectroscopy

The heart of the oxygen-evolving complex (OEC) of photosystem II is a Mn4OxCa cluster that cycles through five different oxidation states (S0 to S4) during the light-driven water-splitting reaction cycle. In this study we interpret the recently obtained 55Mn hyperfine coupling constants of the S0 and S2 states of the OEC [Kulik et al. J. Am. Chem. Soc. 2005, 127, 2392-2393] on the basis of Y-shaped spin-coupling schemes with up to four nonzero exchange coupling constants, J. This analysis rules out the presence of one or more Mn(II) ions in S0 in methanol (3%) containing samples and thereby establishes that the oxidation states of the manganese ions in S0 and S2 are, at 4 K, Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. By applying a "structure filter" that is based on the recently reported single-crystal EXAFS data on the Mn4OxCa cluster [Yano et al. Science 2006, 314, 821-825] we (i) show that this new structural model is fully consistent with EPR and 55Mn-ENDOR data, (ii) assign the Mn oxidation states to the individual Mn ions, and (iii) propose that the known shortening of one 2.85 A Mn-Mn distance in S0 to 2.75 A in S1 [Robblee et al. J. Am. Chem. Soc. 2002, 124, 7459-7471] corresponds to a deprotonation of a mu-hydroxo bridge between MnA and MnB, i.e., between the outer Mn and its neighboring Mn of the mu3-oxo bridged moiety of the cluster. We summarize our results in a molecular model for the S0 --> S1 and S1 --> S2 transitions.     

三氮唑取代杯[4]芳烃配位聚合物的合成与荧光性能

利用四[1-(1, 2, 4-三氮唑基)甲基]间苯二酚杯[4]芳烃配体(TTR4A)在溶剂热的条件下合成了两个配位聚合物,[[Zn₂(TTR4A)(L)₂]·DMF·4H₂O]_n(化合物1) (DMF = N, N-二甲基甲酰胺)和[[Co(TTR4A)Cl₂]·DMA·H₂O]_n (化合物2) (H₂L = 4, 4’-联苯二甲酸) (DMA = N, N-二甲基乙酰胺)。通过单晶X射线衍射方法对这两个配位聚合物的结构进行了确定。利用红外、元素分析、粉末X射线衍射(PXRD)和热重表征手段对化合物1和2进行了表征。在化合物1中,四个L配体连接着四个Zn(Ⅱ)离子形成了环状的Zn₄L₄结构单元,该结构单元进一步地被TTR4A链接形成了一维链状结构。在化合物2中,TTR4A的四个三氮唑基团各连接一个Co(Ⅱ)离子形成二维层状结构。此外,我们对化合物1的荧光性能进行了研究,荧光测定表明固态条件下化合物1发出很强的荧光,并能够选择性地对Fe³⁺、Cr₂O₇²⁻和硝基苯分子产生响应。     

Solid-state transformation of [Co(NCS)2(pyridine)4] into [Co(NCS)2(pyridine)2]n: from Curie-Weiss paramagnetism to single chain magnetic behaviour

Reaction of Co(NCS)(2) with pyridine (pyr) in aqueous solution at room temperature leads to the formation of the pyridine-rich 1:4 compound of composition [Co(NCS)(2)(pyridine)(4)] (1) reported recently. On heating, the pyridine-rich 1:4 compound transforms into its corresponding pyridine-deficient 1:2 compound of composition [Co(NCS)(2)(pyridine)(2)](n) (2), which decomposes on further heating. In the crystal structure of compound 2 the metal cations are coordinated by four N-atoms of two pyridine ligands and two N-bonded thiocyanato anions, each in mutually trans orientation, and by two S-atoms of two adjacent thiocyanato anions in a slightly distorted octahedral geometry. The thiocyanato anions bridge the metal cations forming one-dimensional polymeric chains. IR spectroscopic investigations on the pyridine-deficient 1:2 compound prepared in thermal decomposition are in accordance with bridging thiocyanato anions. Magnetic measurements of the pyridine-rich 1:4 compound and pyridine-deficient 1:2 compound reveal different behaviour with Curie-Weiss paramagnetism for compound 1 and single chain magnetic behaviour for compound 2, with a Mydosh-parameter φ = 0.12 and an effective energy barrier (-U(eff)/k(B)) of 62.5 K for the spin relaxation.     

A rare mu-hydroxo-bridged species. synthesis, structure, and properties of mu-hydroxo(tetraphenylporphyrinatomanganese(III))(phthalocyaninato(azido)chromium(III)), [(TPP)Mn-O(H)-CrPc(N3)

A novel ditetrapyrrolic, heteroleptic, and heterometallic (Mn-Cr) mu-hydroxo-bridged complex has been prepared, and its structural and general properties have been studied. The species mu-hydroxo(tetraphenylporphyrinatomanganese(III))(phthalocyaninato(azido)chromium(III)), [(TPP)Mn-O(H)-CrPc(N3)], isolated as a chloronaphthalene (ClNP) solvate, has been structurally characterized by single-crystal X-ray work. The two (TPP)Mn and CrPc(N3) fragments are held together by the bridging mu-hydroxo ion with long Mn-O [1.993(5) A] and Cr-O [1.976(5) A] bond distances and a Mn-O(H)-Cr angle of 163.7(3) degrees . The five-coordinate Mn center in the (TPP)Mn fragment is displaced from the TPP rigorously planar central N4 core by 0.128 A, and the environment is typical of a Mn(III) high-spin site. The six-coordinate Cr(III) in the CrPc(N3) moiety lies practically in the plane of the phthalocyanine macrocycle (displacement toward the azido group: 0.054 A). The average Mn-N(pyr) and Cr-N(pyr) bond distances are 2.011(6) and 1.982(6) A, respectively, and the Mn-Cr bond distance is 3.929(2) A. The porphyrin and phthalocyanine rings are in an almost eclipsed position [5.16(2) degrees ], and the mean planes of the two macrocycles form a dihedral angle of 5.79(4) degrees. Crystal data for [(TPP)Mn-O(H)-CrPc(N3)].2ClNP, C76H45CrMnN15O.2C10H7Cl: a = 16.645(3) A, b = 17.692(4) A, c = 25.828(5) A, alpha = 90 degrees , beta = 98.79(3) degrees , gamma = 90 degrees , space group P2(1)/c (No. 14), V = 7517(3) A(3), Z = 4, R1 = 0.086, and wR2 = 0.267. IR and UV-vis-near-IR spectral and room temperature magnetic susceptibility data of the [Mn-Cr] species are also presented.     

Theoretical interpretation of the line shape of the gaseous acetic acid cyclic dimer

A general quantum theoretical approach of the nu(X-H) IR line shape of cyclic dimers of weakly H-bonded species in the gas phase is proposed. In this model, the adiabatic approximation (allowing to separate the high frequency motion from the slow one of the H-bond bridge), is performed for each separate H-bond bridge of the dimer and a strong nonadiabatic correction is introduced into the model via the resonant exchange between the fast mode excited states of the two moieties. The present model reduces satisfactorily to many models in the literature dealing with more special situations. It has been applied to the cyclic dimers (CD(3)CO(2)H)(2) and (CD(3)CO(2)D)(2) in the gas phase. It correctly fits the experimental line shape of the hydrogenated compound and predict satisfactorily the evolution in the line shapes, to the deuterated one by reducing simply the angular frequency of the H-bond bridge and the anharmonic coupling parameter by the factor 1/ square root of 2.     

Studies on the enzyme immunoassay of bio-active constituents contained in oriental medicinal drugs. V. Preparation of bovine serum albumin conjugate and beta-galactosidase labelled antigen for enzyme immunoassay of 3 beta-(monoglucuron-1' beta-yl)-18 beta-glycyrrhetic acid

In order to prepare an immunogen for enzyme immunoassay of 3 beta-(monoglucuron-1'-beta-yl)-18 beta-glycyrrhetic acid (3MGA), which was isolated from a patient with glycyrrhizin-induced pseudoaldosteronisms, benzyl glycyrrhetate (3) was allowed to react with an acetobromosugar (2) in the presence of silver carbonate to give benzyl 3 beta-(methyl 2',3',4'-triacetyl-glucuron-1' beta-yl)-glycyrrhetate (5) and methyl 3',4'-diacetyl-alpha-1',2'-O-[1-(benzyl glycyrrhet-3 beta-yl)- ethylidene]-D-glucuronate (4). On the other hand, this reaction was carried out in the presence of mercuric cyanide in nitromethane to give compound 5, benzyl 3 beta-acetyl glycyrrhetate (6) and benzyl 11-oxo-A-neooleana-3(5),12-dien-3-oate (7). 4-Aminomethylcyclohexanecarboxylic acid and glycine were introduced as chemical bridges at C-30 of 3 beta-(tert-butylglucuron-1' beta-yl)-glycyrrhetic acid (11) derived from compound 5. The former bridge was used to prepare an immunogenic conjugate with bovine serum albumin, and the latter bridge was used for antigen labelled with beta-galactosidase.     

Synthesis, structure and heterogeneous catalytic activities of Cu-containing polymeric compounds: anion effect and comparison of homogeneous vs. heterogeneous catalytic activity

The structures of new polymeric compounds containing Cu(II) ions and btp (2,6-bis(N'-1,2,4-triazolyl)pyridine) ligands have been determined. The btp ligands bridge Cu(II) ions to form double zigzag chains, [Cu(ClO4)2(btp)2] 3 with perchlorate anions, and form single zigzag chains, [Cu(btp)(H2O)4](SO4).2H2O 4 with sulfate anions. The polymeric compound 3 was found to effectively catalyze the epoxide ring-opening reaction with methanol, while polymeric compound 4 was almost inactive with epoxides under the same conditions. The polymeric compound 3 showed an efficient catalytic activity and regioselective reactivity in the ring opening of epoxides and allowed reuse without a significant loss of activity through three runs with epoxides.     

The chemistry of dinuclear analogues of the anticancer drug cisplatin. A DFT/CDM study

The mechanism of the formation of dinuclear platinum(II) mu-hydroxo complexes from cisplatin hydrolysis products, their interconversion, decomposition, and reactions with biomolecules has been explored using a combined DFT/CDM approach. All activation barriers for the formation of [cis-{Pt(NH(3))(2)(X)}-(mu-OH)-cis-{Pt(NH(3))(2)(Y)}](n)()(+) (X, Y = Cl, OH(2), OH) via nucleophilic attack of a hydroxo complex on an aqua complex are lower than the activation barriers for cisplatin hydrolysis. Considering therapeutic Pt(II) concentrations in tumors, however, only the reaction between two molecules of cis-[Pt(NH(3))(2)(OH(2))(OH)](+) (E) yielding [cis-{Pt(NH(3))(2)(OH(2))}-(mu-OH)-cis-{Pt(NH(3))(2)(OH)}](2+) (5) remains kinetically superior to cisplatin hydrolysis. 5 is strongly stabilized by intramolecular hydrogen bonding between the terminal aqua and hydroxo ligands, resulting in an unusually high pK(a) of 5 and a low pK(a) of its conjugate acid. Unimolecular cyclization of 5 yields the dimers [cis-{Pt(NH(3))(2)}(mu-OH)](2)(2+) (7a with antiperiplanar OH groups and 7b with synperiplanar OH groups). The electronic structure of several diplatinum(II) complexes has been analyzed to clarify whether there are metal-metal interactions. The overall reactivity to guanine (Gua) and dimethyl sulfide (Met, representing the thioether functional group of methionine) increases in the order 5 < 7a approximately 7b < mononuclear complexes, whereas the kinetic selectivity to Gua relative to Met increases in the order 7a approximately 5 < 7b approximately monocationic mononuclear complexes < dicationic mononuclear complex. The results of this work (i) help assess whether dinuclear metabolites play a role in cisplatin chemotherapy, (ii) elucidate the toxicity and pharmacological inactivity of [cis-{Pt(NH(3))(2)}(mu-OH)](2)(2+), and (iii) suggest future investigations of dinuclear anticancer complexes that contain one mu-hydroxo ligand.