Mechanistic analysis of reductive nitrosylation on water-soluble cobalt(III)-porphyrins

The reactions of NO and/or NO2- with three water-soluble cobalt porphyrins [Co(III)(P)(H2O)2]n, where P = TPPS, TCPP, and TMPyP, were studied in detail. At pH < 3, the reaction with NO proceeds through a single reaction step. From the kinetic data and activation parameters, the [Co(III)(P)(NO)(H2O)]n complex is proposed to be the primary product of the reaction with NO. This complex reacts further with a second NO molecule through an inner-sphere electron-transfer reaction to generate the final product, [Co(III)(P)(NO-)](n-1). At pH > 3, although a single reaction step is also observed, a systematic study as a function of the NO and NO2- concentrations revealed that two reaction steps are operative. In the first, NO2- and NO compete to substitute coordinated water in [Co(III)(P)(H2O)2]n to yield [Co(III)(P)(NO)(H2O)]n and [Co(III)(P)(NO2-)(H2O)](n-1) as the primary reaction products. Only the nitrite complex could be detected and no final product formation was observed during the reaction. It is proposed that [Co(III)(P)(NO)(H2O)]n rapidly reacts with NO2- to form the nitrite complex, which in the second reaction step reacts with another NO molecule to generate the final product through an inner-sphere electron-transfer reaction. The reported results are relevant for the interaction of vitamin B(12a) with NO and NO2-.     

Cobalt(III) complexes of [3(5)] adamanzane, 1,5,9,13-tetraazabicyclo[7.7.3]nonadecane. Report of an inert, chelate hydrogen carbonate ion

Three cobalt(III) complexes of the macrocyclic tetraamine [3(5)]adamanzane (1,5,9,13-tetraazabicyclo[7.7.3]nonadecane) were isolated as salts. The X-ray crystal structures were solved for the compounds [Co([3(5)]adz)(CO(3))]AsF(6) (1b), [Co([3(5)]adz)(HCO(3))]ZnBr(4).H(2)O (2a), and [Co([3(5)]adz)(SO(4))]AsF(6).H(2)O (3a). The coordination geometry around the cobalt(III) ion is a distorted octahedron with the inorganic ligands at cis-positions. Complex 2 is the second example of a cobalt(III) complex for which the X-ray structure shows a chelate binding mode of the hydrogen carbonate entity. The pK(a) value of the [Co([3(5)]adz)(HCO(3))](2+) ion (2) was determined spectrophotometrically to be 0.27 (25 degrees C, I = 5.0 M). The protonation appears to occur at the noncoordinated carbonyl oxygen atom of the carbonate group, with hydrogen bonding to the crystal water molecule. Evidence is presented for this oxygen atom as the site of protonation in solution as well. In 5.0 M CF(3)SO(3)H a slow reaction of the carbonato complex, quantitatively yielding the [Co([3(5)]adz)(H(2)O)(2)](3+) ion, was observed. k(obs) = 7.9(1) x 10(-)(6) s(-)(1) at 25 degrees C.     

Syntheses of 8-quinolinolatocobalt(III) complexes containing cyclen based auxiliary ligands as models for hypoxia-activated prodrugs

New ligands H(2)L2-H(2)L6 comprise the cyclen macrocycle which is N,N'-dialkylated at the 1,7-nitrogen atoms by three- and four-carbon alkyl chains bearing terminal sulfonic (C(3) H(2)L2), phosphonic (C(3) H(2)L3, C(4) H(2)L4) or carboxylic acid (C(3) H(2)L5, C(4) H(2)L6) groups, and HL7 is N-monoalkylated by a four-carbon sulfonic acid group. The ligands were prepared by alkylation of a bridged bisaminal intermediate. The syntheses of cobalt(III) complexes containing a tetradentate cyclen, N,N'-1,7-Me(2)cyclen, cyclam or L2-L7 ligand together with the bidentate 8-quinolinato (8QO(-)) ligand, of interest as it is a model for a more potent cytotoxic analogue, were investigated. Coordination of ligands (L) cyclen, N,N'-1,7-Me(2)cyclen or cyclam to cobalt(III) was achieved using Na(3)[Co(NO(6))] to form [Co(L)(NO(2))(2)](+). HOTf (trifluoromethansulfonic acid) was used to prepare the triflato complexes [Co(L)(OTf)(2)](+), followed by substitution of the labile triflato ligands to yield [Co(L)(8QO)](ClO(4))(2) isolated as the perchlorate salts. One further example containing cyclam and the 5-hydroxymethyl-8-quinolinato ligand was also prepared by this method. Complexes containing the pendant arm ligands L2-L6 were prepared from the cobalt precursor trans-[Co(py)(4)Cl(2)](+). Reaction of this complex with H(2)L2·4HCl and 8QOH produced [Co(L2)(8QO)] in one step and contains two deprotonated sulfonato pendant arms. The reaction of H(2)L3·4HBr with [Co(py)(4)Cl(2)](+) gave [Co(L3)]Cl in which L3 acts as a hexadenate ligand with the three-carbon phosphonato side chains coordinated to cobalt. H(2)L5·4HCl bearing three-carbon carboxylic acid pendant arms gave a similar result. The four-carbon ligands were coordinated to cobalt by reaction of [Co(py)(4)Cl(2)](+) with H(2)L4·4HBr or H(2)L6·4HCl to give [Co(HL4)Cl(2)] or [Co(H(2)L6)Cl(2)]Cl, which in turn with 8QOH gave the 8QO(-) complexes [Co(L4)(8QO)] bearing anionic phosphate pendant arms or [Co(H(2)L6)(8QO)]Cl(2) containing neutral carboxylic acid side chains. The reaction of Na(3)[Co(CO(3))(3)] with the mono-N-alkylated ligand HL7·4HCl and then HOTf gave [Co(L7)(CO(3))] and then in turn [Co(L7)(OTf)(2)]. The carbonato complex [Co(L7)(CO(3))] with [8QO](2)[SO(4)] produced [Co(L7)(CO(3))]. All complexes containing L7 bear an anionic sulfonato group on the side chain. The synthesis and characterisation of the six new ligands based on N-alkylated cylen ligand and the cobalt complexes outlined above are described, along with cyclic voltammograms of the 8QO(-) complexes and the molecular structures determined by X-ray crystallography of [Co(cyclen)(H(2)O)(2)](OTf)(3) (formed by aquation of the triflato complex), [Co(cyclen)(8QO)](ClO(4))(2), Co(L2)(8QO)·2H(2)O, Co(L4)(8QO)·6H(2)O and [Co(H(2)L6)Cl(2)]Cl·H(2)O. These demonstrate the coordination of the cyclen ligand in the folded anti-O,syn-N configuration with the N-alkylated nitrogens occupying apical positions.     

Metal Chelates of N‐(2‐pyridylmethyl)iminodiacetate(2‐) Ion (pmda). Part II. Ternary pmda Chelates with M = Co,Cu or Zn and Creatinine as Auxiliary Ligand

The compounds [Cu(pmda)(crea)]·H₂O ( 1 ), [Zn(pmda)(crea)]·H₂O ( 2 ) and [Co(pmda)(crea)(H₂O)]·H₂O ( 3 ) were prepared and characterized by thermal, spectral and X‐ray diffraction methods. In compounds 1 and 2 the M^II coordination is of type 4+1 and approaches to a trigonal bipyramid (71.85 and 86.18 %, respectively) with rather linear N(pmda)‐M^II‐N(crea) trans‐apical angles, but with different longest coordination bond (Cu‐O(pmda) or Zn‐N(apliphatic, pmda), respectively). Both compounds are isotypic and one intra‐molecular interligand N‐H···O interaction reinforces the molecular recogniton crea‐M^II(pmda) chelate. In contrast, the compound 3 exhibits an octahedral coordination, imposed by the 3d⁷ electronic configuration of the cobalt(II) atom, and the crea‐chelate recognition involves the Co‐N(crea) coordination bond and one intramolecular ‘bifurcated’ H‐bonding interaction between one N‐H(crea) bond and one O(pmda) plus the O(aqua) atoms as ‘acceptors’.     

Environmental control of solution speciation in cobalt(II) 2,2':6',2'-terpyridine complexes: anion and solvent dependence

In methanol or chloroform/methanol solutions, reactions of Cltpy or MeOtpy (Rtpy = 4'-R-2,2':6',2'-terpyridine) with CoX(2)·xH(2)O (X(-) = Cl(-), [OAc](-), [NO(3)](-) or [BF(4)](-)) result in the formation of equilibrium mixtures of [Co(Rtpy)(2)](2+) and [Co(Rtpy)X(2)]. A study of the solution speciation has been carried out using (1)H NMR spectroscopy, aided by the dispersion of signals in the paramagnetically shifted spectra; on going from a low- to high-spin cobalt(II) complex, proton H(6) of the tpy ligand undergoes a significant shift to higher frequency. For R = Cl and X(-) = [OAc](-), increasing the amount of CD(3)OD in the CD(3)OD/CDCl(3) solvent mixture affects both the relative proportions of [Co(Cltpy)(2)](2+) and [Co(Cltpy)(OAc)(2)] and the chemical shifts of the (1)H NMR resonances arising from [Co(Cltpy)(OAc)(2)]. When the solvent is essentially CDCl(3), the favoured species is [Co(Cltpy)(OAc)(2)]. For the 4'-methoxy-2,2':6',2'-terpyridine, the speciation of mono- and bis(terpyridine)cobalt(II) complexes depends upon the anion, solvent and ligand:Co(2+) ion ratio. The (1)H NMR spectrum of [Co(MeOtpy)(2)](2+) is virtually independent of anion and solvent. In contrast, the signals arising from [Co(MeOtpy)X(2)] depend on the anion and solvent. In the case of X(-) = [BF(4)](-), we propose that the mono(tpy) complex formed in solution is [Co(MeOtpy)L(n)](2+) (L = H(2)O or solvent, n = 1-3). The formation of mono(tpy) species has been confirmed by the solid state structures of [Co(Cltpy)(OAc-O)(OAc-O,O')], [Co(MeOtpy)(OAc-O)(OAc-O,O')], [Co(MeOtpy)(NO(3)-O)(2)(OH(2))] and [Co(MeOtpy)Cl(2)]. The single crystal structure of the cobalt(III) complex [Co(Cltpy)Cl(3)]·CHCl(3) is also reported.     

Chirality transfer from guest chiral metal complexes to inorganic framework: the role of hydrogen bonding

The structure elucidation of a new zinc phosphate [Co(II)(en)(3)][Zn(4)(H(2)PO(4))(3)(HPO(4))(2)(PO(4))(2 H(2)O)(2)] (1) reveals that the racemic cobalt complex templates the zinc phosphate framework in such a way that the local C(2) point symmetry of the structural motif of the inorganic framework conforms with that of the cobalt complex pairing with it, in essence transferring its chirality to the inorganic host. An analysis of hydrogen bonding between the guest molecules and the inorganic host framework reveals that hydrogen bonding is responsible for the stereospecific structural arrangement. Upon examining previously reported chiral metal-complex-templated structures of metal phosphates, it is revealed that such hydrogen bonding is the common origin for inducing chirality transfer in metal-phosphate frameworks templated with chiral metal complexes. Crystal data of 1: orthorhombic, Pbcn (no. 60), a=10.4787(8) A, b=20.0091(14) A, c=14.9594(10) A, and Z=2.     

Interligand interactions controlling the mu-N7,N9-metal bonding of adenine (AdeH) to the N-benzyliminodiacetato(2-) copper(II) chelate and promoting the N9 versus N3 tautomeric proton transfer: molecular and crystal structure of [Cu2(NBzIDA)(2)(H2O)(2)(mu-N7,N9-Ade(N3)H)].(3)H2O

The reaction in water of the N-benzyliminodiacetate-copper(II) chelate ([Cu(NBzIDA)]) and the adenine:thymine base pair complex (AdeH:ThyH) with a Cu/NBzIDA/AdeH/ThyH molar ratio of 2:2:1:1 yields [Cu(2)(NBzIDA)(2)(H(2)O)(2)(mu-N7,N9-Ade(N3)H)].3H(2)O and free ThyH. The compound has been studied by thermal, spectral, and X-ray diffraction methods. In the asymmetric dinuclear complex units both Cu(II) atoms exhibit a square pyramidal coordination, where the four closest donors are supplied by NBzIDA in a mer-tridentate conformation and the N7 or N9 donors of AdeH, which is protonated at N3. The mu-N7,N9 bridge represents a new coordination mode for nonsubstituted AdeH, except for some adeninate(1-)-[methylmercury(II)] derivatives studied earlier. The dinuclear complex is stabilized by the Cu-N7 and Cu-N9 bonds and N6-H(exocyclic)...O(carboxyl) and N3-H(heterocyclic)...O(carboxyl) interligand interactions, respectively. The structure of the new compound differs from that of the mononuclear compound [Cu(NBzIDA)(Ade(N9)H)(H(2)O)].H(2)O, in which the unusual Cu-N3(AdeH) bond is stabilized by a N9-H...O(carboxyl) interligand interaction and where alternating benzyl-AdeH intermolecular pi,pi-stacking interactions produce infinite stacked chains. The possibility for ThyH to be involved in the molecular recognition between [Cu(NBzIDA)] and the AdeH:ThyH base pair is proposed.     

Synthesis, crystal structure, and luminescence of a new complex [Co(6,6′-Bpbc)(Phen)(H2O)] · 2EtOH

A novel complex constructed with [Co(6,6′-Bpbc)(Phen)(H₂O)] · 2EtOH (6,6′-Bpbc = 2,2′-bipyridine-6,6′-dicarboxylic acid, Phen = 1,10-phenanthroline) has been successfully synthesized and characterized by X-ray diffraction, and elementary analysis. The photoluminescence properties of this complex were also studied. In the crystal, the cobalt(II) ion adopts the formation of a heptacoordination environment, and the structure units aggregate together to give birth to the infinite 1D chains, 2D-networks, and 3D-frameworks through either hydrogen bonding or π···π-stacking interaction between the aromatic rings.     

Nonclassical titanocene silyl hydrides

The titanocene silyl hydride complexes [Ti(Cp)2(PMe3)(H)(SiR3)] [SiR3=SiMePhCl (6), SiPh2Cl (7), SiMeCl2 (8), SiCl3 (9)] were prepared by HSiR3 addition to [Ti(Cp)2(PMe3)2] and were studied by NMR and IR spectroscopy, X-ray diffraction (for 6, 8, and 9), and DFT calculations. Spectroscopic and structural data established that these complexes exhibit nonclassical Ti-H-Si-Cl interligand hypervalent interactions. In particular, the observation of silicon-hydride coupling constants J(Si,H) in 6-9 in the range 22-40 Hz, the signs of which we found to be negative for 8 and 9, is conclusive evidence of the presence of a direct Si-H bond. The analogous reaction of [Ti(Cp)2(PMe3)2] with HSi(OEt)3 does not afford the expected classical silyl hydride complex [Ti(Cp)2(PMe3)(H)[Si(OEt)3]], and instead NMR-silent titanium (apparently TiIII) complex(es) and the silane redistribution product Si(OEt)4 are formed. The structural data and DFT calculations for the compounds [Ti(Cp)2(PMe3)(H)(SiR3)] show that the strength of interligand hypervalent interactions in the chlorosilyl complexes decreases as the number of chloro groups on silicon increases. However, in the absence of an Si-bound electron-withdrawing group trans to the Si-H moiety, a silane sigma complex is formed, characterized by a long Ti-Si bond of 2.658 A and short Si-H contact of 1.840 A in the model complex [Ti(Cp)2(PMe3)(H)(SiMe3)]. Both the silane sigma complexes and silyl hydride complexes with interligand hypervalent interactions exhibit bond paths between the silicon and hydride atoms in Atoms in Molecules (AIM) studies. To date a classical titanocene phosphane silyl hydride complex without any Si-H interaction has not been observed, and therefore titanocene silyl hydrides are, depending on the nature of the R groups on Si, either silane sigma complexes or compounds with an interligand hypervalent interaction.     

Cobalt chemistry with mixed aminotroponiminate salicylaldiminate ligands: synthesis, characterization, and nitric oxide reactivity

A new class of mixed aminotroponimine salicylaldimine ligands and their corresponding cobalt(II) complexes are reported. This work expands the family of cobalt(II) aminotroponiminato complexes to include salicylaldiminate and derivatized fluorescein moieties. The H2iPrSATI-n (n = 3, 4) ligands 3 and 4, respectively, contain an aminotroponimine moiety and a salicylaldimine fragment connected with an alkyl linker. In the H2iPrFATI-n (n = 3, 4) ligands 5 and 6, a derivatized fluorescein replaces the salicylaldimine fragment. The cobalt(II) complexes [Co(iPrSATI-3)] (7) and [Co2(iPrSATI-4)(2)] (9) were prepared and structurally characterized. The reaction of NO with both complexes ultimately results in the formation of a dinitrogen-containing species. The mononitrosyl, [Co(iPrSATI-3)(NO)] (8), was isolated and characterized. The reactivity of [Co(iPrFATI-3)] (10) and [Co(iPrFATI-4)] (11) with NO mimics that observed for the salicylaldimine derivatives, as monitored by solution IR spectroscopy. When followed by fluorescence spectroscopy, reaction of 11 with NO evoked a 3-fold increase in emission intensity after 22 h.     

From {Bi22O26} to chiral ligand-protected {Bi38O45}-based bismuth oxido clusters

The reaction of [Bi(22)O(26)(OSiMe(2)tBu)(14)] (1) in THF with salicylic acid gave [Bi(22)O(24)(HSal)(14)] (2) first, which was converted into [Bi(38)O(45)(HSal)(22)(OH)(2)(DMSO)(16.5)]·DMSO·H(2)O (3·DMSO·H(2)O) after dissolution and crystallization from DMSO. Single-crystal X-ray diffraction analysis and ESI mass spectrometry associated with infrared multi-photon dissociation (IRMPD) tandem MS experiments confirm the formation of the large and quite stable bismuth oxido cluster 3. The reaction of compound 2 with the butoxycarbonyl(BOC)-protected amino acids phenylalanine and valine (BOC-PheOH and BOC-ValOH), respectively, resulted in the formation of chiral [Bi(38)O(45)(BOC-AA)(22)(OH)(2)] (AA=deprotonated amino acid), as shown by a combination of different analytical techniques such as elemental analysis, dynamic light scattering, circular dichroism spectroscopy, and ESI mass spectrometry.     

Cobalt(II)-(dpyo)-dicarboxylate networks: unique H-bonded assembly and rare bridging mode of dpyo in one of them [dpyo = 4,4'-dipyridyl N,N'-dioxide

Polymeric networks, {[Co(dpyo)(ox)]}(n) (1), {[Co(dpyo)(fum)(H(2)O)(2)]}(n) (1) and {[Co(dpyo)(tp)(H(2)O)(2)] x [Co(H(2)O)(6)] x (tp) x (H(2)O)}(n) (3) [ox = oxalate dianion, fum = fumarate dianion, tp = terephthalate dianion and dpyo = 4,4'-dipyridyl N,N'-dioxide] have been synthesized and characterized by single crystal X-ray diffraction analyses. The structural determination reveals 1 and 2 are covalent bonded 2D networks of 4,4 topology and of these, complex 2 undergoes a H-bonding scheme resulting in a 3D supramolecular architecture. Complex 3 is a 1D coordination polymer built up by almost collinear hexacoordinated Co(ii), doubly bridged by a tp carboxylate group and a dpyo oxygen, which in combination with lattice [Co(H(2)O)(6)](2+), tp and water molecules shows an unprecedented 3D supramolecular network through H-bonding. In the polymer the dpyo shows novel mu-4,4 bridging mode towards the cobalt ion. Low temperature magnetic interaction reveals antiferromagnetic coupling in all of the complexes.     

Synthesis, structure and magnetic properties of chiral and nonchiral transition-metal malates

Carboxylate-bridged complexes of transition metals, M(II)=Mn(II), Fe(II), Co(II), Ni(II), Zn(II), were synthesised by reaction of M(II) salts with dl-malate and L-malate under hydrothermal conditions. These complexes form four series of compounds, which have been fully characterised structurally, thermally and magnetically. The crystal structures of the new chiral compounds, [Mn(L-mal)(H(2)O)] (1), [Fe(L-mal)(H(2)O)] (2), [Co(L-mal)(H(2)O)] (3) and [Zn(L-mal)(H(2)O)] (4) as well as those of the bimetallic analogues [Mn(0.63)Co(0.37)(L-mal)(H(2)O)] (5) and [Mn(0.79)Ni(0.21)(L-mal)(H(2)O)] (6) have been solved by single-crystal X-ray diffraction. The six L-malate monohydrates crystallise in the chiral space group P2(1)2(1)2(1) and consist in a three-dimensional network of metal(II) centres in octahedral sites formed by oxygen atoms. These structures were compared to those of the chiral trihydrate compounds [Co(L-mal)(H(2)O)]2 H(2)O (7), [Ni(L-mal)(H(2)O)]2 H(2)O (8) and [Co(0.52)Ni(0.48)(L-mal)(H(2)O)]2 H(2)O (9), which exhibit helical chains of M(II) centres, and those of dl-malate dihydrates [Co(dl-mal)(H(2)O)]H(2)O (10) and [Ni(dl-mal)(H(2)O)H(2)O (11) and trihydrate [Mn(L-mal)(H(2)O)]2 H(2)O (12) highlighting the great flexibility of the coordination by the malate ligand. UV/Vis spectroscopic results are consistent with octahedral coordination geometry of high-spin transition-metal centres. Extensive magnetic characterisation of each homologous series indicates rather weak coupling interaction between paramagnetic centres linked through carboxylate bridges. Curie-like paramagnetic, antiferromagnetic, ferromagnetic or weak ferromagnetic behaviour is observed and discussed on the basis of the structural features. The bimetallic compounds 5 and 6 represent new examples of chiral magnets.     

Influence of tetraazamacrocyclic ligands on the nitric oxide reactivity of their cobalt(II) complexes

The reactions of cobalt(II) complexes of tetraazamacrocyclic tropocoronand (TC) ligands with nitric oxide (NO) were investigated. When [Co(TC-5,5)] was allowed to react with NO(g), the {CoNO}(8) mononitrosyl [Co(NO)(TC-5,5)] was isolated and structurally characterized. In contrast, a {Co(NO)(2)}(10) species formed when [Co(TC-6,6)] was exposed to NO(g), and the nitrito [Co(NO(2))(TC-6,6)] complex was structurally and spectroscopically characterized from the reaction mixture. The {Co(NO)(2)}(10) species was assigned as the bis(cobalt dinitrosyl) complex [Co(2)(NO)(4)(TC-6,6)] by spectroscopic comparison with independently synthesized and characterized material. These results provide the first evidence for the influence of tropocoronand ring size on the nitric oxide reactivity of the cobalt(II) complexes.     

The mechanism of alkene addition to a nickel bis(dithiolene) complex: the role of the reduced metal complex

The binding of an alkene by Ni(tfd)(2) [tfd = S(2)C(2)(CF(3))(2)] is one of the most intriguing ligand-based reactions. In the presence of the anionic, reduced metal complex, the primary product is an interligand adduct, while in the absence of the anion, dihydrodithiins and metal complex decomposition products are preferred. New kinetic (global analysis) and computational (DFT) data explain the crucial role of the anion in suppressing decomposition and catalyzing the formation of the interligand product through a dimetallic complex that appears to catalyze alkene addition across the Ni-S bond, leading to a lower barrier for the interligand adduct.     

Dinuclear complexes of chiral tetradentate pyridylimine ligands: diastereoselectivity, positive cooperativity, anion selectivity, ligand self-sorting based on chirality, and magnetism

The synthesis and coordination chemistry of two chiral tetradentate pyridylimine Schiff base ligands are reported. The ligands were prepared by the nucleophilic displacement of both bromides of 1,3-bis(bromomethyl)benzene (2) or 3,5-bis(bromomethyl)toluene (3) by the anion of (S)-valinol, followed by capping of both amine groups with pyridine-2-carboxaldehyde. Both ligands react with CoCl(2) and NiCl(2) to give [M(2)L(2)Cl(2)](2+) complexes. Remarkably, neither fluoride nor bromide ions can act as bridging ligands. The formation of [Co(2)((S)-3)(2)Cl(2)](2+) is highly diastereoselective, and X-ray crystallography shows that both metal centers in the [Co(2)((S)-3)(2)Cl(2)](CoCl(4)) complex adopt the lambda configuration (crystal data: [Co(2)(C(31)H(40)N(4)O(2))(2)Cl(2)](CoCl(4)).(CH(3)CN)(3), monoclinic, P2(1), a = 11.595(2) A, b = 22.246(4) A, c = 15.350(2) A, V = 3705(1) A(3), beta = 110.643(3) degrees, Z = 2). Structurally, the dinuclear complex can be viewed as a helicate with the helical axis running perpendicular to the [Co(2)Cl(2)] plane. The reaction of racemic 2 with CoCl(2) was shown by (1)H NMR spectroscopy to yield a racemic mixture of Lambda,Lambda-[Co(2)((S)-2)(2)Cl(2)](2+) and delta,delta-[Co(2)((R)-2)(2)Cl(2)](2+) complexes; that is, a homochiral recognition process takes place. Spectrophotometric titrations were performed by titrating (S)-3 with Co(ClO(4))(2) followed by Bu(4)NCl, and the global stability constants of [Co((S)-3)](2+) (log beta(110) = 5.7), [Co((S)-3)(2)](2+) (log beta(120) = 11.6), and [Co(2)((S)-3)(2)Cl(2)](2+) (log beta(110) = 23.8) were calculated. The results revealed a strong positive cooperativity in the formation of [Co(2)((S)-3)(2)Cl(2)](2+). Variable-temperature magnetic susceptibility curves for [Co(2)((S)-2)(2)Cl(2)](BPh(4))(2) and [Co(2)((S)-3)(2)Cl(2)](BPh(4))(2) are very similar and indicate that there are no significant magnetic interactions between the cobalt(II) centers.     

Metallosupramolecular chemistry with bis(benzene-o-dithiolato) ligands

The bis(benzene-o-dithiol) ligands H(4)-1, H(4)-2, and H(4)-3 react with [Ti(OC(2)H(5))(4)] to give dinuclear triple-stranded helicates [Ti(2)L(3)](4)(-) (L = 1(4)(-), 2(4)(-), 3(4)(-)). NMR spectroscopic investigations revealed that the complex anions possess C(3) symmetry in solution. A crystal structure analysis for (PNP)(4)[Ti(2)(2)(3)] ((PNP)(4)[14]) confirmed the C(3) symmetry for the complex anion in the solid state. The complex anion in Li(PNP)(3)[Ti(2)(1)(3)] (Li(PNP)(3)[13]) does not exhibit C(3) symmetry in the solid state due to the formation of polymeric chains of lithium bridged complex anions. Complexes [13](4)(-) and [14](4)(-) were obtained as racemic mixtures of the Delta,Delta and Lambda,Lambda isomers. In contrast to that, complex (PNP)(4)[Ti(2)(3)(3)] ((PNP)(4)[15]) with the enantiomerically pure chiral ligand 3(4)(-) shows a strong Cotton effect in the CD spectrum, indicating that the chirality of the ligands leads to the formation of chiral metal centers. The o-phenylene diamine bridged bis(benzene-o-dithiol) ligand H(4)-4 reacts with Ti(4+) to give the dinuclear double-stranded complex Li(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the (1)H NMR spectrum of (Ph(4)As)(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] ((Ph(4)As)(2)[(16]) reveal C(2) symmetry for the anion [Ti(2)(4)(2)(mu-OCH(3))(2)](2)(-). For a comparative study the dicatechol ligand H(4)-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H(4)-4, was prepared and reacted with [TiO(acac)(2)] to give the dinuclear complex anion [Ti(2)(5)(2)(mu-OCH(3))(2)](2)(-). The molecular structure of (PNP)(2)[Ti(2)(5)(2)(mu-OCH(3))(2)] ((PNP)(2)[17]) contains a complex anion which is similar to [16](2)(-), with the exception that strong N-H...O hydrogen bonds are formed in complex anion [17](2)(-), while N-H...S hydrogen bonds are absent in complex anion [16](2)(-).     

Cobalt(III) complexes of monodentate N9-bound adeninate (ade-), [Co(ade-kappaN9)Cl(en)2]+ (en = 1,2-diaminoethane): syntheses, crystal structures, and protonation behaviors of the geometrical isomers

In acidic aqueous solution, a cobalt(III) complex containing monodentate N(9)-bound adeninate (ade(-)), cis-[Co(ade-kappaN(9))Cl(en)(2)]Cl (cis-[1]Cl), underwent protonation to the adeninate moiety without geometrical isomerization or decomposition of the Co(III) coordination sphere, and complexes of cis-[CoCl(Hade)(en)(2)]Cl(2) (cis-[2]Cl(2)) and cis-[Co(H(2)ade)Cl(en)(2)]Cl(3) (cis-[3]Cl(3)) could be isolated. The pK(a) values of the Hade and H(2)ade(+) complexes are 6.03(1) and 2.53(12), respectively, at 20 degrees C in 0.1 M aqueous NaCl. The single-crystal X-ray analyses of cis-[2]Cl(2).0.5H(2)O and cis-[3]Cl(2)(BF(4)).H(2)O revealed that protonation took place first at the adeninate N(7) and then at the N(1) atoms to form adenine tautomer (7H-Hade-kappaN(9)) and cationic adeninium (1H,7H-H(2)ade(+)-kappaN(9)) complexes, respectively. On the other hand, addition of NaOH to an aqueous solution of cis-[1]Cl afforded a mixture of geometrical isomers of the hydroxo-adeninato complex, cis- and trans-[Co(ade-kappaN(9))(OH)(en)(2)](+). The trans-isomer of chloro-adeninato complex trans-[Co(ade-kappaN(9))Cl(en)(2)]BF(4) (trans-[1]BF(4)) was synthesized by a reaction of cis-[2](BF(4))(2) and sodium methoxide in methanol. This isomer in acidic aqueous solution was also stable toward isomerization, affording the corresponding adenine tautomer and adeninium complexes (pK(a) = 5.21(1) and 2.48(9), respectively, at 20 degrees C in 0.1 M aqueous NaCl). The protonated product of trans-[Co(7H-Hade-kappaN(9))Cl(en)(2)](BF(4))(2).H(2)O (trans-[2](BF(4))(2).H(2)O) could also be characterized by X-ray analysis. Furthermore, the hydrogen-bonding interactions of the adeninate/adenine tautomer complexes cis-[1]BF(4), cis-[2](BF(4))(2), and trans-[2](BF(4))(2) with 1-cyclohexyluracil in acetonitrile-d(3) were investigated by (1)H NMR spectroscopy. The crystal structure of trans-[Co(ade)(H(2)O)(en)(2)]HPO(4).3H(2)O, which was obtained by a reaction of trans-[Co(ade)(OH)(en)(2)]BF(4) and NaH(2)PO(4), was also determined.     

Homochiral column structure of rac- and lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate in crystal structures and cation-anion association in aqueous solution

rac- and Lambda-tris(ethylenediamine)cobalt(III) cyclotriphosphate dihydrate with the chemical formulas rac-[Co(en)(3)]P(3)O(9).2H(2)O (1) and Lambda-[Co(en)(3)]P(3)O(9).2H(2)O (2) were synthesized, and their crystal structures were determined by single-crystal X-ray analyses. In 1, the cationic complex molecule [Co(en)(3)](3+) with the Delta or Lambda enantiomer and cyclotriphosphate anion are alternately arrayed and connected by multiple hydrogen bonds to form a homochiral column structure. Adjacent homochiral columns with different chirality for 1 are connected by intercolumn hydrogen bonds through P(3)O(9)(3)(-) anions, as the bridging groups, to form a tetrameric cyclic cylindrical structure, while the adjacent columns with the same chirality are connected for 2 to form the cyclic cylindrical structure. All 6 amino groups per [Co(en)(3)](3+) participate in the formation of 12 hydrogen bonds, in which 8 hydrogen bonds contribute to the construction of a homochiral column and the remaining 4 hydrogen bonds contribute to the intercolumn interactions. The circular dichroism spectrum of the aqueous solution of Lambda-[Co(en)(3)](3+) changes drastically when excess P(3)O(9)(3)(-) is added, and this change is explained by ion-pair formation. The thermodynamic association constant of [Co(en)(3)](3+) with P(3)O(9)(3)(-), calculated from the conductivity data, was log K = 4.26 at 25 degrees C.