Novel platinum(II) ammine hydroxamate and hydroximate complexes and the platinum-assisted hydrolysis of hydroxamic acids

The 2-pyridinecarboxylate (2-pyca) platinum(IV) complex [2-pycaH2][PtCl4(2-pyca)].H2O, 1, has been synthesised from K2[PtCl4] following the hydrolysis of 2-pyridinehydroxamic acid (2-pyhaH) in the presence of H2O2, and directly from K2[PtCl6] and picolinic acid. Structural characterisation of 1 reveals octahedral geometry about platinum(IV) consisting of a (N,O)-bidentate pyridinecarboxylate ligand and four chloride ligands. A mechanism for the hydrolysis of 2-pyridinehydroxamic acid to 2-pyridinecarboxylic acid is proposed. Two novel coordination modes of hydroxamic acids to platinum(II) are also reported. The dinuclear platinum ammine hydroximato complex, [{cis-Pt(NH3)2}2(mu-2-pyhaH(-1))](ClO4)2.H2O, 3, has been synthesised where the two platinum(II) centres are bridged via(O,O) and (N,N) coordination. The latter coordination mode is via the hydroximate nitrogen and the pyridine nitrogen. The corresponding mononuclear platinum(II) pyridinehydroxamate complex, [cis-Pt(NH3)2(2-pyha)]ClO4, 4, has been synthesised. Spectroscopic studies indicate that the coordination mode is through the pyridine nitrogen and hydroxamate oxygen atoms (N,O).     

A trinuclear heterobimetallic Ru(II)/Pt(II) complex as a chemodosimeter selective for sulfhydryl-containing amino acids and peptides

A trinuclear heterobimetallic Ru(II)/Pt(II) complex, cis-{Ru(phen)2[CN-Pt(DMSO)Cl2]2} (phen = 1,10-phenanthroline), is able to function as a "switch-on" luminescent chemodosimeter for sulfhydryl-containing amino acids and peptides via specific binding of the amino acids/peptides with the Pt(II) centers and the subsequent cleavage of the Ru(II)-Pt(II) cyano-bridge.     

New heterobimetallic and polymeric selenocarboxylates derived from [M(SeC{O}Ph)4]- (M = Ga and In) as molecular precursors for ternary selenides

(Et3NH)[In(SeC{O}Ph)4].H2O (1) along with heterobimetallic and polymeric metal selenocarboxylates, namely [NaGa(SeC{O}Ph)4] (2), [K(MeCN)2Ga(SeC{O}Ph)4] (3), [NaIn(SeC{O}Ph)4] (4), [K(MeCN)2In(SeC{O}Ph)4] (5), [(Ph3P)2CuIn(SeC{O}Ph)4].CH2Cl2 (6), and [(Ph3P)2AgIn(SeC{O}Ph)4].CH2Cl2 (7), have been synthesized by incorporating either alkali metal ions (Na+ and K+) or group 11 metal ions (Cu(I) and Ag(I)) into the [M(SeC{O}Ph)4]- anion. Crystal structures determined by X-ray crystallography indicate that 3 and 5 have one-dimensional coordination polymeric structures while 6 and 7 have an M(mu-Se)2In (M = Cu, Ag) core. The thermal decomposition of these compounds except 4 lead to the formation of the corresponding metal selenides as confirmed by thermogravimetric analysis and in some cases by powder X-ray diffraction studies.     

Tetranuclear copper(II) complexes bridged by alpha-D-glucose-1-phosphate and incorporation of sugar acids through the Cu4 core structural changes

Tetranuclear copper(II) complexes containing alpha-D-glucose-1-phosphate (alpha-D-Glc-1P), [Cu4(mu-OH){mu-(alpha-D-Glc-1P)}2(bpy)4(H2O)2]X3 [X = NO3 (1a), Cl (1b), Br (1c)], and [Cu4(mu-OH){mu-(alpha-D-Glc-1P)}2(phen)4(H2O)2](NO3)3 (2) were prepared by reacting the copper(II) salt with Na2[alpha-D-Glc-1P] in the presence of diimine ancillary ligands, and the structure of 2 was characterized by X-ray crystallography to comprise four {Cu(phen)}2+ fragments connected by the two sugar phosphate dianions in 1,3-O,O' and 1,1-O mu4-bridging fashion as well as a mu-hydroxo anion. The crystal structure of 2 involves two chemically independent complex cations in which the C2 enantiomeric structure for the trapezoidal tetracopper(II) framework is switched according to the orientation of the alpha-D-glucopyranosyl moieties. Temperature-dependent magnetic susceptibility data of 1a indicated that antiferromagnetic spin coupling is operative between the two metal ions joined by the hydroxo bridge (J = -52 cm(-1)) while antiferromagnetic interaction through the Cu-O-Cu sugar phosphate bridges is weak (J = -13 cm(-1)). Complex 1a readily reacted with carboxylic acids to afford the tetranuclear copper(II) complexes, [Cu4{mu-(alpha-D-Glc-1P)}2(mu-CA)2(bpy)4](NO3)2 [CA = CH3COO (3), o-C6H4(COO)(COOH) (4)]. Reactions with m-phenylenediacetic acid [m-C6H4(CH2COOH)2] also gave the discrete tetracopper(II) cationic complex [Cu4{mu-(alpha-D-Glc-1P)}2(mu-m-C6H4(CH2COO)(CH2COOH))2(bpy)4](NO3)2 (5a) as well as the cluster polymer formulated as {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-m-C6H4(CH2COO)2)(bpy)4](NO3)2}n (5b). The tetracopper structure of 1a is converted into a symmetrical rectangular core in complexes 3, 4, and 5b, where the hydroxo bridge is dissociated and, instead, two carboxylate anions bridge another pair of Cu(II) ions in a 1,1-O monodentate fashion. The similar reactions were applied to incorporate sugar acids onto the tetranuclear copper(II) centers. Reactions of 1a with delta-D-gluconolactone, D-glucuronic acid, or D-glucaric acid in dimethylformamide resulted in the formation of discrete tetracopper complexes with sugar acids, [Cu4{mu-(alpha-D-Glc-1P)}2(mu-SA)2(bpy)4](NO3)2 [SA = D-gluconate (6), D-glucuronate (7), D-glucarateH (8a)]. The structures of 6 and 7 were determined by X-ray crystallography to be almost identical with that of 3 with additional chelating coordination of the C-2 hydroxyl group of D-gluconate moieties (6) or the C-5 cyclic O atom of D-glucuronate units (7). Those with D-glucaric acid and D-lactobionic acid afforded chiral one-dimensional polymers, {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-D-glucarate)(bpy)4](NO3)2}n (8b) and {[Cu4{mu-(alpha-D-Glc-1P)}2(mu-D-lactobionate)(bpy)4(H2O)2](NO3)3}n (9), respectively, in which the D-Glc-1P-bridged tetracopper(II) units are connected by sugar acid moieties through the C-1 and C-6 carboxylate O atoms in 8b and the C-1 carboxylate and C-6 alkoxy O atoms of the gluconate chain in 9. When complex 7 containing d-glucuronate moieties was heated in water, the mononuclear copper(II) complex with 2-dihydroxy malonate, [Cu(mu-O2CC(OH)2CO2)(bpy)] (10), and the dicopper(II) complex with oxalate, [Cu2(mu-C2O4)(bpy)2(H2O)2](NO3)2 (11), were obtained as a result of oxidative degradation of the carbohydrates through C-C bond cleavage reactions.     

Chelating or bridging Pd(II) and Pt(II) metalloligands from the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine. New heterometallic Pd(II)/Pt(II) and Pt(II)/Au(I) complexes

The reaction of two equivalents of the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine Ph2PNHC=NNCHS (2) with [PdCl2(NCPh)2] in the presence of NEt3 gives the neutral, P,N-chelated complex cis-[Pd(Ph2PN=CNN=CHS)2] ([Pd(2-H)2], 3b), which is analogous to the Pt(II) analogue cis-[Pt (Ph2PN=CNN=CHS)2] ([Pt(2-H)2], 3a) reported previously. These complexes function as chelating metalloligands when further coordinated to a metal through each of the CH-N atoms. In the resulting complexes, each endo-cyclic N donor of the thiadiazole rings is bonded to a different metal centre. Thus, the heterodinuclear palladium/platinum complexes cis-[Pt(Ph2PN=CNN=CHS)2PdCl2]([Pt(2-H)2·PdCl2], 4a) and cis-[Pd(Ph2PN=CNN=CHS)2PtCl2]([Pd(2-H)2·PtCl2], 4b) were obtained by reaction with [PdCl2(NCPh)2] and [PtCl2(NCPh)2], respectively. In contrast, reaction of 3a with [AuCl(tht)] occurred instead at the P-bound N atom, and afforded the platinum/digold complex cis-[Pt{Ph2PN(AuCl)=CNN=CHS}2] ([Pt(2-H)2(AuCl)2], 5). For comparison, reaction of 4a with HBF4 yielded cis-[Pt(Ph2PNH=CNN=CHS)2PdCl2](BF4)2([H24a](BF4)2, 6), in which the chelated PdCl2 moiety is retained. Complexes 3b, 4a·CH2Cl2, 4b·0.5C7H8, 5·4CHCl3 and 6 have been structurally characterized by X-ray diffraction.     

Pt(II)-promoted [2 + 3] cycloaddition of azide to cyanopyridines: convenient tool toward heterometallic structures

The [2 + 3] cycloaddition reactions (which are greatly accelerated by microwave irradiation) of the di(azido)platinum(II) compounds cis-[Pt(N(3))(2)(PPh(3))(2)] (1) with cyanopyridines NCR (2) (R = 4-, 3-, and 2-NC(5)H(4)) give the corresponding bis(pyridyltetrazolato) complexes trans-[Pt(N(4)CR)(2)(PPh(3))(2)] (3) [R = 4-NC(5)H(4) (3a), 3-NC(5)H(4) (3b), and 2-NC(5)H(4) (3c)]. Compound 3c has been characterized as the N(1)N(2)-bonded isomer in the solid state by X-ray crystallography and represents the first bis(tetrazolato) complex of this kind. Complexes 3a and 3b have been used as metallaligands to generate heteronuclear coordination polymers in the presence of copper nitrate. A one-dimensional supramolecular architecture was obtained as the exclusive product, {trans-[Pt(2)(N(4)CR)(4)(PPh(3))(4)Cu](n)(NO(3))(2n).nH(2)O (4.nH(2)O) (R = 4-NC(5)H(4)), when 3a was employed, whereas with 3b the heteronuclear square complex trans-[Pt(N(4)CR)(2)(PPh(3))(2)Cu(NO(3))(2)(H(2)O)](2) (5) (R = 3-NC(5)H(4)), composed of Pt/Cu ions, was obtained. All the isolated complexes were characterized by IR, elemental, and (for 3b, 3c, 4, and 5) X-ray structural analyses. Complexes 3 were additionally characterized by (1)H, (13)C, and (31)P {(1)H} NMR spectroscopies.     

Magneto-structural studies on heterobimetallic malonate-bridged M(II)Re(IV) complexes (M = Mn, Co, Ni and Cu)

The mononuclear Re(IV) compound of formula (PPh(4))(2)[ReBr(4)(mal)] (1) was used as a ligand to obtain the heterobimetallic species [ReBr(4)(μ-mal)Co(dmphen)(2)]· MeCN (2), [ReBr(4)(μ-mal)Ni(dmphen)(2)] (3), [ReBr(4)(μ-mal)Mn(dmphen)(2)] (4a), [ReBr(4)(μ-mal)Mn(dmphen)(H(2)O)(2)]·dmphen·MeCN·H(2)O (4b), [ReBr(4)(μ-mal)Cu(phen)(2)]·1/4H(2)O (5) and [ReBr(4)(μ-mal)Cu(bipy)(2)] (6) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline, phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine). The structures of 2 and 5 (single-crystal X-ray diffraction) are made up of neutral [ReBr(4)(μ-mal)M(AA)] dinuclear units [AA = dmphen with M = Co (2) and AA = phen with M = Cu (5)] where the metal ions are connected through a malonate ligand which exhibits simultaneously the bidentate [at the Re(IV)] and monodentate [at the M(II)] coordination modes. The carboxylate-malonate group in them adopts the anti-syn conformation with intramolecular ReM separation of 5.098(8) (2) and 4.947(2) ? (5). The magnetic properties of 1-6 were investigated in the temperature range 1.9-295 K. The magnetic behaviour of 1 is the expected for a magnetically isolated Re(IV) complex with a large value of the zero-field splitting (2D ca. -70 cm(-1)) whereas weak antiferromagnetic interactions between Re(IV) and M(II) are observed in the heterobimetallic compounds 2 (J = -0.63 cm(-1)), 3 (J = -1.37 cm(-1)), 4a (J = -1.29 cm(-1)), 5 (J = -1.83 cm(-1)) and 6 (J = -0.26 cm(-1)). Remarkably, 4b behaves as a ferrimagnetic chain with regular alternating Re(IV) and Mn(II) cations (J = -2.64 cm(-1)).     

A family of alkynylgold(III) complexes [AuI(mu-{CH2}2PPh2)2Au(III)(C triple bond CR)2] (R = Ph, tBu, Me3Si): facile and reversible comproportionation of gold(I)/gold(III) to digold(II)

The symmetric digold(II)dichloride bis(ylide) complex [Au2Cl2(mu-{CH2}2PPh2)2] reacts with acetylides to form the asymmetric heterovalent gold(I)/gold(III) complexes [AuI(mu-{CH2}2PPh2)2AuIII(CCR)2] [R = Ph, tBu, and SiMe3], the phenyl analogue of which was characterized by X-ray crystallography. These compounds represent the first examples of gold(III) complexes containing two acetylide ligands. [AuI(mu-{CH2}2PPh2)2AuIII(CCPh)2] undergoes a reversible comproportionation reaction upon treatment with [Ag(ClO4)tht] to give the symmetric digold(II) cationic complex [Au2(tht)2(mu-{CH2}2PPh2)2](ClO4)2. If this complex is treated with phenylacetylene in the presence of base, the heterovalent gold(I)/gold(III) complex is re-formed. This reversible interconversion between binuclear gold(I)/gold(III) and digold(II) bis(ylide) complexes is unprecedented.     

Copper-complex-linked polytungsto-bismuthate (-antimonite) chain containing sandwich Cu(II) ions partially modified with imidazole ligand

Two sandwich-type complexes Na9n(Cu(im)4(H2O)2)1.5n(Cu(im)4(H2O))n[{Cu(im)4}{Na(H2O)2}3{Cu3(im)2(H2O)}(XW9O33)2]2n .(xH2O)n (im=imidazole, X=Bi (1), Sb(2), x=42.5 (1), 40 (2)) have been synthesized and structurally characterized. Basic frameworks of 1 and 2 are built from sandwich-type [{Na(H2O) 2} 3{Cu3(im)2(H2O)}(XW9O33)2](9-) (X=Bi or Sb) anions and [Cu(im) 4](2+) cations. The Cu(2+) and Na(+) ions in the central belt are coordinated by alpha-[XW9O33](9-) units, im, and water molecules to form {CuO4(im)}, {CuO4(H2O)}, and {NaO4(H2O)2} groups in which Cu (2+) ions are partially modified with im ligands. These groups connect alternately forming a six-membered ring including six alpha-[XW9O 33](9-) units. Neighboring anions are further linked by [Cu(im) 4](2+) cations to display an unprecedented anionic chain, which is first observed in sandwich-type tungsto-bismuthate (-antimonite) system. Two kinds of isolated copper complexes and sodium ions are located as counterions, which cause three-dimensional packings of 1 and 2 to present interesting cage structures. The magnetic properties for 1 and 2 both indicate dominant antiferromagnetic interactions among trinuclear Cu(II) clusters.     

Preparation and reactivity of penta- and tetracoordinate platinum(II) hydride complexes with P(OEt)3 and PPh(OEt)2 phosphite ligands

The pentacoordinate [PtH{P(OEt)3}4]BF4 (1) hydride complex was prepared by allowing the tetrakis(phosphite) Pt{P(OEt)3}4 to react with HBF4.Et2O at -80 degrees C. Depending on the nature of the acid used, however, the protonation of the related Pt{PPh(OEt)2}4 complex yielded the pentacoordinate [PtH{PPh(OEt)2}4]BF4 (3) or the tetracoordinate [PtH{PPh(OEt)2}3]Y (4) [Y = BF4- (a), CF3SO3- (b), Cl- (c)] derivatives. Neutral PtHClP2 (7,8) [P = P(OEt)3, PPh(OEt)2] hydride complexes were prepared by allowing PtCl2P2 to react with NaBH4 in CH3CN. The tetrakis(phosphite)[Pt{P(OEt)3}4](BF4)2 (2) derivative was also synthesised and then characterised spectroscopically and by an X-ray crystal structure determination. Reactivity with aryldiazonium cations of all the hydrides was investigated and found to proceed only with the PtHClP2 complex to yield the aryldiazene [PtCl(ArN=NH)P2]BF4[P = PPh(OEt)2] derivative. The hydrazine [PtCl(NH2NH2){PPh(OEt)2}2]BPh4 complex was also prepared by allowing PtHClP2 to react first with AgCF3SO3 and then with hydrazine.     

Nitrile-amidine coupling at Pt(IV) and Pt(II) centers. An easy entry to imidoylamidine complexes

Treatment of trans-[PtCl4(RCN)2] (R = Me, Et, Ph, NEt2) with 2 equiv of the amidine PhC(=NH)NHPh in a suspension of MeCN (R = Me), CHCl3 (R = Et, Ph), or in CHCl3 solution (R = NEt2) results in the formation of the imidoylamidine complexes trans-[PtCl4{NH=C(R)N=C(Ph)NHPh}2] (1-4) isolated in good yields (66-84%). The reaction of soluble complexes 3 and 4 with 2 equiv of Ph3P=CHCO2Me in CH2Cl2 (40 degrees C, 5 h) leads to dehydrochlorination resulting in a chelate ring closure to furnish the platinum(IV) chelates [PtCl2{NH=C(R)NC(Ph)=NPh}2] (R = Ph, 5; R = NEt2, 6), accordingly, and the phosphonium salt [Ph3PCH2CO2Me]Cl. Treatment of 5 with 3 equiv of Ph3P=CHCO2Me at 50 degrees C for 5 d resulted in only a 30% conversion to the corresponding Pt(II) complex [Pt{NH=C(NEt2)NC(Ph)=NPh}2] (15). The reduction can be achieved within several minutes, when Ph2PCH2CH2PPh2 in CDCl3 is used. When the platinum(II) complex trans-[PtCl2(RCN)2] is reacted with 2 equiv of the amidine, the imidoylamidinato complexes [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) and [PhC(=NH)NHPh] x HCl (7) are formed. The reaction of trans-[PtCl2(RCN)2] with 4 equiv of the amidine under a prolonged reaction time or treatment of [PtCl(RCN){NH=C(R)NC(Ph)=NHPh}] (8-11) with 2 more equiv of the amidine yields the complex bearing two chelate rings [Pt{NH=C(R)NC(Ph)=NHPh}2] (12-15). The treatment of cis-[PtCl2(RCN)2] (R = Me, Et) with the amidine gives ca. 50-60% yield of [PtCl2{NH=C(R)NHC(Ph)=NHPh}] (16 and 17). All of the platinum compounds were characterized by elemental analyses; FAB mass spectrometry; IR spectroscopy; 1H, 13C{1H}, and 195Pt NMR spectroscopies, and four of them (4, 6, 8, and 15) were also characterized by X-ray crystallography. The coupling of the Pt-bound nitriles and the amidine is metal-mediated insofar as RCN and PhC(=NH)NHPh do not react in the absence of the metal centers in conditions more drastic than those of the observed reactions. The nitrile-amidine coupling reported in this work constitutes a route to the synthesis of imidoylamidine complexes, some of them exhibiting luminescent properties.     

Synthesis of acetimino complexes of Pt(II) and Pt(IV) and the first heteronuclear mu-acetimido complexes

The reactions of [Ag(NH=CMe2)2]ClO4 with cis-[PtCl2L2] in a 1:1 molar ratio give cis-[PtCl(NH=CMe2)(PPh3)2]ClO4 (1cis) or cis-[PtCl(NH=CMe2)2(dmso)]ClO4 (2), and in 2:1 molar ratio, they produce [Pt(NH=CMe2)2L2](ClO4)2 [L = PPh3 (3), L2= tbbpy = 4,4'-di-tert-butyl-2,2'-dipyridyl (4)]. Complex 2 reacts with PPh3 (1:2) to give trans-[PtCl(NH=CMe2)(PPh3)2]ClO(4) (1trans). The two-step reaction of cis-[PtCl2(dmso)2], [Au(NH=CMe2)(PPh3)]ClO4, and PPh3 (1:1:1) gives [SP-4-3]-[PtCl(NH=CMe2)(dmso)(PPh3)]ClO4 (5). The reactions of complexes 2 and 4 with PhICl2 give the Pt(IV) derivatives [OC-6-13]-[PtCl3(NH=CMe2)(2)(dmso)]ClO4 (6) and [OC-6-13]-[PtCl2(NH=CMe2)2(dtbbpy)](ClO4)2 (7), respectively. Complexes 1cis and 1trans react with NaH and [AuCl(PPh3)] (1:10:1.2) to give cis- and trans-[PtCl{mu-N(AuPPh3)=CMe2}(PPh3)2]ClO4 (8cis and 8trans), respectively. The crystal structures of 4.0.5Et2O.0.5Me2CO and 6 have been determined; both exhibit pseudosymmetry.     

NMR studies on the novel heterobimetallic complexes [M(dppm)(Ph(2)PCH(2)PPh(2)PPPP) {Pt(PPh3)2}]OTf (M = Rh, Ir) derived from the stepwise activation of white phosphorus

The solution structures of the novel heterobimetallic complexes [Ir(dppm)(Ph(2)PCH(2)PPh(2)PPPP){Pt(PPh(3))2}]OTf and [Rh(dppm)(Ph(2)PCH(2)PPh(2)PPPP){Pt(PPh(3))(2)}]OTf derived from the reaction of Rh and Ir--P(5) precursors with [Pt(C2H4)(PPh3)2] have been unambiguously assigned on the basis of 1H NMR and 31P{1H} NMR data. The results are in agreement with the regio-selective insertion of the {Pt(PPh3)2} moiety resulting in a new pentaphosphorus topology which agrees with the formal formation of a unique phosphonium(+)-tetraphosphabutadienide(2-) ligand.     

Influence of solvent and weak C-H...O contacts in the self-assembled [Pt2M4{CC(3-OMe)C6H4}8] (M = Cu, Ag) clusters and their role in the luminescence behavior

New alkynyl complexes [Pt2M4{CC(3-OMe)C6H4}8] (M = Ag 1, Cu 2) have been synthesized and their structures and properties compared to those of related [Pt2M4(CCPh)8] compounds. For the Pt-Ag derivatives, the X-ray structures of the discrete yellow solvate monomer, [Pt2Ag4{CC(3-OMe)C6H4}8].2THF ([1.2THF]), and the dark garnet unsolvated polymeric form, [Pt2Ag4{CC(3-OMe)C6H4}8](infinity) ([1](infinity)), are presented. The yellow form ([1.2THF]) exhibits a distorted octahedral geometry of the metal centers with the platinum atoms mutually trans and the four silver atoms in the equatorial plane. Pairs of Ag atoms are weakly bridged by THF molecules [mu-Ag2...O(THF)]. The garnet form ([1](infinity)) has an unprecedented infinite stacked chain of octahedral clusters linked by short Pt...Pt bonds (3.1458(8) A). In both forms, different types of weak C-H...O (OMe) hydrogen bonds are observed. For comparative purposes, we have also provided the crystal structures of the yellow monomer form, [Pt2Ag4-(CCPh)8].CHCl3, and the red dimer form, [Pt2Ag4(CCPh)8]2 (Pt-Pt 3.221(2) A). These clusters display intense photoluminescence in both solution and the solid state, at room temperature and 77 K. The emission observed for the yellow form [1.2THF] in the solid state is assigned to a 3MLM'CT [Pt(d)/pi(CCR) --> Pt(p(z))/Ag(sp)/pi(CCR)] state modified by Pt...Ag, Ag...Ag, and Ag...(THF) contacts. However, in the garnet form [1](infinity) and in 2, the emissions are related to the axial Pt-Pt bonds and are assigned as phosphorescence from a metal-metal-to-ligand charge-transfer (3MMLCT) excited state ([1](infinity)), or an admixture of a metal-metal (Pt-Pt) centered 3(dsigmap(z)sigma) and 3MMLCT excited state (2). For 1, a remarkable quenching and a shift to higher energies in the emission is observed on changing from CH2Cl2 to THF, and for both 1 and 2, the emission spectra at 77 K varies with the concentration, showing their tendency to stack even in glass.     

Supramolecular isomerism of 2,2'-bipyrazine complexes with cis-(NH(3))(2)Pt(II): ligand rotational state and sequential orientation determine the 3D shape of metallacycles

2,2'-Bipyrazine (2,2'-bpz) reacts with cis-(NH(3))(2)Pt(II) in water to give a variety of products, several of which were isolated and characterized by X-ray analysis: cis-[Pt(NH(3))(2)(2,2'-bpz-N4)(2)](NO(3))(2)·3H(2)O (1), [{cis-Pt(NH(3))(2)(2,2'-bpz-N4,N4')}(3)]-(PF(6))(5)NO(3)·7H(2)O (2a), [{cis-Pt(NH(3))(2)(2,2'-bpz-N4,N4')}(3)](BF(4))(2)-(SiF(6))(2)·15H(2)O (2b), and [{cis-Pt(NH(3))(2)(2,2'-bpz-N4,N4')}(4)]-(SO(4))(4)·22H(2)O (3). In 1, 2b, and 3 the 2,2'-bpz ligands adopt approximately C(2h) symmetries, hence the two pyrazine halves are in trans orientation, whereas in 2a all three 2,2'-bpz bridges are approximately C(2v) symmetric, with the pyrazine halves cis to each other. The topologies of the two triangular complexes 2a and 2b are consequently distinctly different, but nevertheless both cations act as hosts for anions. In 2a a PF(6)(-) and a NO(3)(-) anion are associated simultaneously with the +6 cation, whereas in 2b it is a BF(4)(-) anion and a water molecule, which are trapped in its cavity. There is no anion inclusion in case of the metallasquare 3. In principle, 3 can exist in a large number of stereoisomers, depending on the rotational states of the bridging 2,2'-bpz ligands. Isolation of a single rotamer form of 3 with C(2h) symmetric 2,2'-bpz ligands and an overall meso form is proposed to be a consequence of a highly efficient self-assembly process that starts from the precursor 1 and reaction with two cis-(NH(3))(2)Pt(II) units. This process leads to the isolated rotamer of 3 regardless of whether two cations 1 in head-head form react with two cis-(NH(3))(2)Pt(II), or whether the Δ enantiomer of the chiral head-tail form of 1 combines with its Λ enantiomer through two cis-(NH(3))(2)Pt(II) entities.     

Hydrothermal reaction of Cu(II)/pyrazine-2,3,5-tricarboxylic acid and characterization of the copper(II) complexes

Four copper(II) complexes [Cu3(PZHD)2(2,2'-bpy)2(H2O)2].3H2O (1), [Cu3(DHPZA)2(2,2'-bpy)2] (2), [Cu(C2O4)phen(H2O)].H2O (3), and [Cu3(PZTC)2(2,2'-bpy)2].2H2O (4) were synthesized by hydrothermal reactions, in which the complexes 1-3 were obtained by the in situ Cu(II)/H3PZTC reactions (PZHD3- = 2-hydroxypyrazine-3,5-dicarboxylate, 2,2'-bpy = 2,2'-bipyridine, DHPZA3- = 2,3-dihydroxypyrazine-5-carboxylate, C2O42- = oxalate, phen = 1,10-phenanthroline, and H3PZTC = pyrazine-2,3,5-tricarboxylic acid). The Cu(II)/H3PZTC hydrothermal reaction with 2,2'-bpy, without addition of NaOH, results in the formation of complex 4. The complexes 1-4 and transformations from H3PZTC to PZHD3-, DHPZA3-, and C2O4(2-) were characterized by single-crystal X-ray diffraction and theoretical calculations. In the complexes 1, 2, and 4, the ligands PZHD3-, DPHZA3-, and PZTC3- all show pentadentate coordination to Cu(II) ion forming three different trinuclear units. The trinuclear units in 1 are assembled by hydrogen-bonding and pi-pi stacking to form a 3D supramolecular network. The trinuclear units in 2 acting as building blocks are connected by the carboxylate oxygen atoms forming a 2D metal-organic framework (MOF) with (4,4) topology. While the trinuclear units in 4 are linked together by the carboxylate oxygen atoms to form a novel 2D MOF containing right- and left-handed helical chains. The theoretical characterization testifies that electron transfer between OH- and Cu2+ and redox of Cu 2+ and Cu+ are the most important processes involved in the in situ copper Cu(II)/H3PZTC reactions, forming complexes of 1-3.     

Synergistic effect of Ni(II) and Co(II) ions on the sulfite induced autoxidation of Cu(II)/tetraglycine complex

The synergistic effect of Ni(II) and Co(II) on the sulfite induced autoxidation of Cu(II)/tetraglycine was investigated spectrophotometrically at 25.0 degrees C, pH = 9.0, 1 x 10(-5) mol dm(-3) < or = [S(IV)] < or = 8 x 10(-5) mol dm(-3), [Cu(II)]= 1 x 10(-3) mol dm(-3), 1 x 10(-6) mol dm(-3) < or = [Ni(II)] or [Co(II)] < or = 1 x 10(-4) mol dm(-3), [O2] approximately 2.5 x 10(-4) mol dm(-3), and 0.1 mol dm(-3) ionic strength. In the absence of added nickel(II) or cobalt(II), the kinetic traces of Cu(III)G4 formation show a large induction period (about 3 h). The addition of trace amounts of Ni(II) or Co(II) increases the reaction rate significantly and the induction period drastically decreases (less than 0.5 s). The effectiveness of Cu(III)G4 formation becomes much higher. The metal ion in the trivalent oxidation state rapidly oxidizes SO3(2-) to SO3*-, which reacts with oxygen to produce SO5*-. The strongly generated oxidants oxidize Cu(II)G4 to Cu(III).     

Kinetics and mechanism for reversible chloride transfer between mercury(II) and square-planar platinum(II) chloro ammine, aqua, and sulfoxide complexes. Stabilities, spectra, and reactivities of transient metal-metal bonded platinum-mercury adducts

The Hg2+aq- and HgCl+aq-assisted aquations of [PtCl4]2- (1), [PtCl3(H2O)]- (2), cis-[PtCl2(H2O)2] (3), trans-[PtCl2(H2O)2] (4), [PtCl(H2O)3]+ (5), [PtCl3Me2SO]- (6), trans-[PtCl2(H2O)Me2SO] (7), cis-[PtCl(H2O)2Me2SO]+ (8), trans-[PtCl(H2O)2M32SO]+ (9), trans-[PtCl2(NH3)2] (10), and cis-[PtCl2(NH3)2] (11) have been studied at 25.0 degrees C in a 1.00 M HClO4 medium buffered with chloride, using stopped-flow and conventional spectrophotometry. Saturation kinetics and instantaneous, large UV/vis spectral changes on mixing solutions of platinum complex and mercury are ascribed to formation of transient adducts between Hg2+ and several of the platinum complexes. Depending on the limiting rate constants, these adducts are observed for a few milliseconds to a few minutes. Thermodynamic and kinetics data together with the UV/vis spectral changes and DFT calculations indicate that their structures are characterized by axial coordination of Hg to Pt with remarkably short metal-metal bonds. Stability constants for the Hg2+ adducts with complexes 1-6, 10, and 11 are (2.1 +/- 0.4) x 10(4), (8 +/- 1) x 10(2), 94 +/- 6, 13 +/- 2, 5 +/- 2, 60 +/- 6, 387 +/- 2, and 190 +/- 3 M-1, respectively, whereas adduct formation with the sulfoxide complexes 7-9 is too weak to be observed. For analogous platinum(II) complexes, the stabilities of the Pt-Hg adducts increase in the order sulfoxide < aqua < ammine complex, reflecting a sensitivity to the pi-acid strength of the Pt ligands. Rate constants for chloride transfer from HgCl+ and HgCl2 to complexes 1-11 have been determined. Second-order rate constants for activation by Hg2+ are practically the same as those for activation by HgCl+ for each of the platinum complexes studied, yet resolved contributions for Hg2+ and HgCl+ reveal that the latter does not form dinuclear adducts of any significant stability. The overall experimental evidence is consistent with a mechanism in which the accumulated Pt(II)-Hg2+ adducts are not reactive intermediates along the reaction coordinate. The aquation process occurs via weaker Pt-Cl-Hg or Pt-Cl-HgCl bridged complexes.     

7-Methylguanine: protonation, formation of linkage isomers with trans-(NH3)2Pt(II), and base pairing properties

Three protonated forms of 7-methylguanine (7-MeGH, 1) with different counter ions, [7-MeGH(2)]X (X = NO(3), 1a; ClO(4), 1b; BF(4), 1c) and two Pt(II) complexes, trans-[Pt(NH(3))(2)(7-MeGH-N9)(2)](ClO(4))(2) (4) and trans-[Pt(NH(3))(2)(7-MeGH-N9)(7-MeGH-N3)](ClO(4))(2)·3H(2)O (5) are described and their X-ray crystal structures are reported. 1a-1c form infinite ribbons via pairs of intermolecular hydrogen bonds between N1H···O6 and N3···N2H(2) sites, with anions connecting individual ribbons, thereby generating extended sheets. 4 and 5 do not display unusual features, except that 5 represents a rare case of a bis(nucleobase) complex of Pt(II) in which linkage isomers occur. Unlike in a previously reported compound, [Pt(dien)(7-MeGH-N9)](NO(3))(ClO(4)), the Pt coordination planes and the 7-MeGH planes are not coplanar in 4 and 5. The hydrogen bonding behaviour of 7-MeGH, free and when platinated at N9 (complex 4), was studied in Me(2)SO-d(6). It revealed the following: (i) there is no detectable self-association of 1 in Me(2)SO solution. (ii) 1 and 1-methylcytosine (1-MeC) form Watson-Crick pairs. (iii) 4 does not self-associate. (iv) 4 associates with 1-MeC in the Watson-Crick fashion. (v) 4 and 1 interact in solution, but no model can be proposed at present. (vi) Remarkable interaction shifts between 4 and 1 occur when NH(3) is liberated from trans-(NH(3))(2)Pt(II) to give NH(4)(+) in Me(2)SO-d(6). Feasible models, which imply the presence of deprotonated 7-MeG(-) species are proposed. Finally, DFT calculations were carried out to qualitatively estimate the effect of 7-MeGH acidity in [Pt(dien)(7-MeGH-N9)](2+) in dependence of the dihedral angle between the Pt coordination plane and the nucleobase.     

Single-molecule magnet behavior in heterometallic M(II)-Mn(III)(2)-M(II) tetramers (M(II) = Cu, Ni) containing Mn(III) salen-type dinuclear core

The linear-type heterometallic tetramers, [Mn(III)(2)(5-MeOsaltmen)(2)M(II)(2)(L)(2)](CF(3)SO(3))(2) x 2H(2)O (MII = Cu, 1a; Ni, 2a), where 5-MeOsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene) bis(5-methoxysalicylideneiminate), and H(2)L = 3-{2-[(2-hydroxy-benzylidene)-amino]-2-methyl-propylimino}-butan-2-one oxime, have been synthesized and characterized from structural and magnetic points of view. These two compounds are isostructural and crystallize in the same monoclinic P2(1)/n space group. The structure has a [M(II)-NO-Mn(III)-(O)(2)-Mn(III)-ON-M(II)] skeleton, where -NO- is a linking oximato group derived from the non-symmetrical Schiff-base complex [M(II)(L)] and -(O)(2)- is a biphenolato bridge in the out-of-plane [Mn(2)(5-MeOsaltmen)(2)](2+) dimer. The solvent-free compounds, 1b and 2b, have also been prepared by drying of the parent compounds, 1a and 2a, respectively, at 100 degrees C under dried nitrogen. After this treatment, the crystallinity is preserved, and 1b and 2b crystallize in a monoclinic P2(1)/c space group without significant changes in their structures in comparison to 1a and 2a. Magnetic measurements on 1a and 1b revealed antiferromagnetic Mn(III)---Cu(II) interactions via the oximato group and weak ferromagnetic Mn(III)---Mn(III) interactions via the biphenolato bridge leading to an S(T) = 3 ground state. On the other hand, the diamagnetic nature of the square planar Ni(II) center generates an S(T) = 4 ground state for 2a and 2b. At low temperature, these solvated (a) and desolvated (b) compounds display single-molecule magnet behavior modulated by their spin ground state.