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.     

A copper(I) oxygenation precursor in the entatic state: two isomers of a copper(I) compound of a rigid tetradentate ligand

Oxygenation of [CuI(L1)(NC-CH3)]+ (L1 = dimethyl 2,4-bis(2-pyridinyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-on-1,5-dicarboxylate) leads to a relatively stable mu-peroxo-dicopper(II) product. The stability of this type of oxygenation product has been shown before to be the result of the square pyramidal geometry of L1; preorganization by a dinucleating ligand has been shown to increase the stability of the mu-peroxo-dicopper(II) compound. The structural data presented here indicate that destabilization of the copper(I) precursor is another important factor. There are two isomers of [CuI(L1)(NCCH3)]+; one is yellow, and the other is red. X-ray crystallography indicates that one pyridinyl donor is not coordinated in the yellow compound and that the red compound is 5-coordinate. In the light of the X-ray structure of the metal-free ligand and that of the corresponding copper(II) compound, it emerges that the ligand cavity is well suited for copper(II), whereas the copper(I) compounds are highly strained. This is supported by 1H NMR spectra of the copper(I) species where a fast dynamic process leads to line broadening and by electrochemical data, which indicate that the copper(II) products are exceptionally stable. Also presented are structural (copper(II)), electrochemical, and spectroscopic data (1H NMR, copper(I)) of the derivative [Cu(L2)(X)]n+ with a methyl substituent at the alpha-carbon atom of the two coordinated pyridinyl groups (L2 = dimethyl 2,4-bis(2-pyridinyl-6-methyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-on-1,5-dicarboxylate). There are two structural forms of [CuII(L2)(X)]n+ (X = NCCH3, Cl), which depend on the steric demand of the fifth donor X. For both, van der Waals repulsion leads to a destabilization of the copper(II) products, and this is also evident from an increase in the reduction potential (-110 mV vs. -477 mV, Ag/AgNO3).     

Trinuclear {M1}CN{M2}2 complexes (M1 = Cr(III), Fe(III), Co(III); M2 = Cu(II), Ni(II), Mn(II)). Are single molecule magnets predictable?

The reaction of the hexacyanometalates K3[M(1)(CN)6] (M(1) = Cr(III), Fe(III), Co(III)) with the bispidine complexes [M(2)(L(1))(X)](n+) and [M(2)(L(2))(X)](n+) (M(2) = Mn(II), Ni(II), Cu(II); L(1) = 3-methyl-9-oxo-2,4-di-(2-pyridyl)-7-(2-pyridylmethyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylic acid dimethyl ester; L(2) = 3-methyl-9-oxo-7-(2-pyridylmethyl)-2,4-di-(2-quinolyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylic acid dimethyl ester; X = anion or solvent) in water-methanol mixtures affords trinuclear complexes with cis- or trans-arrangement of the bispidine-capped divalent metal centers around the hexacyanometalate. X-ray structural analyses of five members of this family of complexes (cis-Fe[CuL(2)]2, trans-Fe[CuL(1)]2, cis-Co[CuL(2)]2, trans-Cr[MnL(1)]2, trans-Fe[MnL(1)]2) and the magnetic data of the entire series are reported. The magnetic data of the cyanide bridged, ferromagnetically coupled cis- and trans-Fe[ML]2 compounds (M = Ni(II), Cu(II)) with S = 3/2 (Cu(II)) and S = 5/2 (Ni(II)) ground states are analyzed with an extended Heisenberg Hamiltonian which accounts for anisotropy and zero-field splitting, and the data of the Cu(II) systems, for which structures are available, are thoroughly analyzed in terms of an orbital-dependent Heisenberg Hamiltonian, in which both spin-orbit coupling and low-symmetry ligand fields are taken into account. It is shown that the absence of single-molecule magnetic behavior in all spin clusters reported here is due to a large angular distortion of the [Fe(CN)6](3-) center and the concomitant quenching of orbital angular momentum of the Fe(III) ((2)T2g) ground state.     

Synthesis and reactivity of iridium complexes with pyridine and piperidine ligands: models for hydrodenitrogenation

The complexes [Ir(H)2(eta1-N-L)2(PPh3)2]PF6, L = py (1), iQ (2) and pip (3) (py = pyridine, iQ = isoquinoline, pip = piperidine) have been synthesized in high yields by hydrogenation of [Ir(cod)(PPh3)2]PF6 in the presence of the appropriate nitrogen compound. When hydrogen is bubbled through 1,2-dichloroethane solutions of 1 or 2, two new species were formed in each case by C-Cl bond activation of the solvent, Ir(H)2Cl(eta1-N-L)(PPh3)2 (L = py, 4; iQ, 5) and IrH(Cl)2(eta1-N-L)(PPh3)2 (L = py, 6; iQ, 7). Reaction of 3 with py or iQ yielded complexes 1 and 2, respectively, while under a slow stream of carbon monoxide the complex [Ir(H)2(eta1-N-pip)(CO)(PPh3)2]PF6 (8) was produced. Complex 3 also reacts with halide and 4-bromothiophenolate anions leading to the corresponding neutral species Ir(H)2(X)(eta1-N-pip)(PPh3)2, X = Cl (9), I (10) and 4-BrC6H4S (11), or with [MoS4]2- to yield the hetero-bimetallic complex [Ir(H)(PPh3)2(mu-S)2MoS2]- (13). All the new complexes were characterized by analytical and spectroscopic methods. The X-ray structures of , 2 and 8 consist of distorted octahedra with a mutually cis disposition of the two hydrides and mutually trans phosphines. Complexes 1, 2 and 3 and their derivatives are of interest as models for the chemisorption step in hydrodenitrogenation reactions on solid catalysts.     

Thiofunctional vanadium complexes

The neutral tetradentate ligand 1,6-bis(2'-pyridyl)-2,5-dithiahexane (N(2)S(2)), containing two thioether functions, reacts with [VX(2)L(4)] (X = Br, L(4) = 2 tmeda (tmeda = Me(2)NCH(2)CH(2)NMe(2)); X = I, L = tetrahydrofuran (THF)) and [VX(3)(THF)(3)] (X = Br, I) to form the complexes [VX(2)(N(2)S(2))] (1) and [VX(2)(N(2)S(2))]X (2), respectively. [V(2)(mu-Cl)(3)(THF)(6)]I and N(2)S(2) yield the V(IV) complex [VOCl(N(2)S(2)]I (3). The pentadentate, dianionic ligand 2,6-bis(2'-mercaptophenylthio)dimethylpyridine, NS(2)S'(2)(2-), which contains two thioether (S) and two thiophenolate (S') functions, reacts with [VBr(3)(THF)(3)] to afford [VBr(NS(2)S'(2))] (4). The complex [VO(Cl)S'NS'] (5; H(2)S'NS' is the Schiff base formed between o-mercaptoaniline and o-mercaptobenzaldehyde) is obtained by redox interaction between [VCl(3)(THF)(3)] and 2,2'-dithiodibenzaldehyde in the presence of o-mercaptoaniline. The crystal and molecular structures have been obtained for 3. THF, 4. THF, and 5. n-C(5)H(12). The relevance of these compounds and their formation for the interaction between vanadium and thiofunctional biomolecules is addressed.     

Coordination chemistry of chromium-Salen complexes studied by electrospray ionization mass spectrometry

The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positions has been studied in the presence of amines as ligands (propylamine and a series of diamines) under electrospray ionization conditions. The [Cr(III)(Salen)](+) complex formed stable five- and six-coordinated complex ions, [Cr(III)(Salen)(L)](+) and [Cr(III)(Salen)(L)(2)](+), respectively, where L = solvent molecule or amine. When diamines were used as ligands, abundant [Cr(III)(Salen)(L)](+) ions were observed in which two axial positions of the [Cr(III)(Salen)](+) species are occupied by the two amino groups of the diamine ligand. The relative abundances of ligated complex ions, fragment ions, and solvent adducts of fragment ions in the ESI mass spectra, were found to depend on the cone voltage used to record the spectrum. The ESI mass spectra of [Cr(III)(Salen)](+) in the presence of diamines as ligands, and experiments on ligand-pickup in the collision cell, clearly demonstrated that the [Cr(III)(Salen)(L)](+) complex ion is stable for 1,2-diaminoethane and 1,3-diaminopropane. The stability of [Cr(III)(Salen)(L)](+) ions gradually decreased from 1,4-diaminobutane to 1,6-diaminohexane, and then showed a slight increase for 1,7-diaminoheptane and 1,8-diaminooctane. The collision-induced dissociation spectra of [Cr(III)(Salen)(L)](+) ions support the above observations.     

Ni(P(Ph)2N(C6H4X)2)2]2+ complexes as electrocatalysts for H2 production: effect of substituents, acids, and water on catalytic rates

A series of mononuclear nickel(II) bis(diphosphine) complexes [Ni(P(Ph)(2)N(C6H4X)(2))(2)](BF(4))(2) (P(Ph)(2)N(C6H4X)(2) = 1,5-di(para-X-phenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; X = OMe, Me, CH(2)P(O)(OEt)(2), Br, and CF(3)) have been synthesized and characterized. X-ray diffraction studies reveal that [Ni(P(Ph)(2)N(C6H4Me)(2))(2)](BF(4))(2) and [Ni(P(Ph)(2)N(C6H4OMe)(2))(2)](BF(4))(2) are tetracoordinate with distorted square planar geometries. The Ni(II/I) and Ni(I/0) redox couples of each complex are electrochemically reversible in acetonitrile with potentials that are increasingly cathodic as the electron-donating character of X is increased. Each of these complexes is an efficient electrocatalyst for hydrogen production at the potential of the Ni(II/I) couple. The catalytic rates generally increase as the electron-donating character of X is decreased, and this electronic effect results in the favorable but unusual situation of obtaining higher catalytic rates as overpotentials are decreased. Catalytic studies using acids with a range of pK(a) values reveal that turnover frequencies do not correlate with substrate acid pK(a) values but are highly dependent on the acid structure, with this effect being related to substrate size. Addition of water is shown to dramatically increase catalytic rates for all catalysts. With [Ni(P(Ph)(2)N(C6H4CH2P(O)(OEt)2)(2))(2)](BF(4))(2) using [(DMF)H](+)OTf(-) as the acid and with added water, a turnover frequency of 1850 s(-1) was obtained.     

Redox-adaptable copper hosts. Pyridazine-linked cryptands accommodate copper in a range of redox States

A series of structurally characterized copper complexes of two pyridazine-spaced cryptands in redox states + (I,I), (II,I), (II), (II,II) are reported. The hexaimine cryptand L(I) [formed by the 2 + 3 condensation of 3,6-diformylpyridazine with tris(2-aminoethyl)amine (tren)] is able to accommodate two non-stereochemically demanding copper(I) ions, resulting in [Cu(I)(2)L(I)](BF(4))(2) 1, or one stereochemically demanding copper(II) ion, resulting in [Cu(II)L(I)()](BF(4))(2) 3. Complex 3 crystallizes in two forms, 3a and 3b, with differing copper(II) ion coordination geometries. Addition of copper(I) to the monometallic complex 3 results in the mixed-valence complex [Cu(I)Cu(II)L(I)](X)(3) (X = PF(6)(-), 2a; X = BF(4)(-), 2b) which is well stabilized within this cryptand as indicated by electrochemical studies (K(com) = 2.1 x 10(11)). The structurally characterized, octaamine cryptand L(A), prepared by sodium borohydride reduction of L(I), is more flexible than L(I) and can accommodate two stereochemically demanding copper(II) ions, generating the dicopper(II) cryptate [Cu(II)(2)L(A)](BF(4))(4) 4. Electrochemical studies indicate that L(A) stabilizes the copper(II) oxidation state more effectively than L(I); no copper redox state lower than II,II has been isolated in the solid state using this ligand.     

Dimetallic complexes of acyclic pyridine-armed ligands derived from 3,6-diformylpyridazine

A bis(pyridine-armed) acyclic Schiff base ligand L1 has been synthesised from 3,6-diformylpyridazine and two equivalents of 2-(2-aminoethyl)pyridine. Reduction of this ligand using NaBH(4) resulted in the formation of the amine analogue L2. Complexes of the form [M(2)L1(mu-X)]Y(2)ClO(4)[where: M = Cu(II), X = OH(-) and Y = ClO(4)(-) 1, Cl(-) 2, Br(-) 3 or I(-) 4; M = Co(II), X = OH(-) and Y = ClO(4)(-) 5; M = Ni(II), X = SCN(-) 6 or X = N(3)(-) 7 and Y = ClO(4)(-)], and [Cu(2)L2(mu-OH)](ClO(4))(3) 8 were prepared and characterised. The complexes 1 and 5-7 have been characterised by single-crystal X-ray diffraction. The acyclic L1 ligand provides three nitrogen donor atoms per metal centre, including a pyridazine bridge between the metal centres, and the anion X also bridges the two metal centres. As required, coordinating solvent molecules or additional anions make up the remainder of the coordination sphere. The two copper centres of 1 are very strongly antiferromagnetically coupled (2J=-1146 cm(-1))via the pyridazine and hydroxide ion bridges, whereas the competing antiferromagnetic pyridazine bridging pathway and ferromagnetic 1,1-bridging azide pathway resulted in the observation of weak antiferromagnetic exchange in the dinickel(II) complex 7 (2J=-14 cm(-1)). Electrochemical examination of L1, L2 and complexes 1 and 5-8 revealed multiple redox processes. These have been tentatively assigned to a mixture of metal centred and ligand centred redox processes on the basis of cyclic voltammetry and coulometry results and comparisons with literature examples.     

Platinum and palladium imido and oxo complexes with small natural bite angle diphosphine ligands

Treatment of L(2)MCl(2) (M = Pt, Pd; L(2) = Ph(2)PCMe(2)PPh(2) (dppip), Ph(2)PNMePPh(2) (dppma)) with AgX (X = OTf, BF(4), NO(3)) in wet CH(2)Cl(2) yields the dinuclear dihydroxo complexes [L(2)M(mu-OH)](2)(X)(2), the mononuclear aqua complexes [L(2)M(OH(2))(2)](X)(2), the mononuclear anion complexes L(2)MX(2), or mixtures of complexes. Addition of aromatic amines to these complexes or mixtures gives the dinuclear diamido complexes [L(2)Pt(mu-NHAr)](2)(BF(4))(2), the mononuclear amine complexes [L(2)M(NH(2)Ar)(2)](X)(2), or the dinuclear amido-hydroxo complex [Pt(2)(mu-OH)(mu-NHAr)(dppip)(2)](BF(4))(2). Deprotonation of the Pd and Pt amine or diamido complexes with M'N(SiMe(3))(2) (M' = Li, Na, K) gives the diimido complexes [L(2)M(mu-NAr)](2) associated with M' salts. Structural studies of the Li derivatives indicate association through coordination of the imido nitrogen atoms to Li(+). Deprotonation of the amido-hydroxo complex gives the imido-oxo complex [Pt(2)(mu-O)(mu-NAr)(dppip)(2)].LiBF(4).LiN(SiMe(3))(2), and deprotonation of the dppip Pt hydroxo complex gives the dioxo complex [Pt(mu-O)(dppip)](2).LiN(SiMe(3))(2).2LiBF(4).     

Electronic structure of bispidine iron(IV) oxo complexes

The electronic structure, based on DFT calculations, of a range of FeIV=O complexes with two tetra- (L1 and L2) and two isomeric pentadentate bispidine ligands (L3 and L4) is discussed with special emphasis on the relative stability of the two possible spin states (S = 1, triplet, intermediate-spin, and S = 2, quintet, high-spin; bispidines are very rigid diazaadamantane-derived 3,7-diazabicyclo[3.3.1]nonane ligands with two tertiary amine and two or three pyridine donors, leading to cis-octahedral [(X)(L)FeIV=O]2+ complexes, where X = NCCH3, OH2, OH-, and pyridine, and where X = pyridine is tethered to the bispidine backbone in L3, L4). The two main structural effects are a strong trans influence, exerted by the oxo group in both the triplet and the quintet spin states, and a Jahn-Teller-type distortion in the plane perpendicular to the oxo group in the quintet state. Due to the ligand architecture the two sites for substrate coordination in complexes with the tetradentate ligands L1 and L2 are electronically very different, and with the pentadentate ligands L3 and L4, a single isomer is enforced in each case. Because of the rigidity of the bispidine ligands and the orientation of the "Jahn-Teller axis", which is controlled by the sixth donor X, the Jahn-Teller-type distortion in the high-spin state of the two isomers is quite different. It is shown how this can be used as a design principle to tune the relative stability of the two spin states.     

Molybdenum 1,4-diazabuta-1,3-diene tricarbonyl solvento complexes revisited: from solvatochromism to attractive ligand-ligand interaction

Various complexes of the types [Mo(DAD)(CO)(3)L] (L = CO, MeCN, MeOH, THF, DMSO, DMF, Me(2)CO, EtOAc, THT, Im(H), Im(1), tBuNC, nBu(3)P), (ER(4))[Mo(DAD)(CO)(3)X] (ER(4) = NEt(4)(+); X(-) = Cl(-), Br(-), I(-), NCS(-), CN(-) and ER(4)(+) = PPh(4)(+); X(-) = N(3)(-)), and (ER(4))[{Mo(DAD)(CO)(3)}(2)(μ-X)] (ER(4)(+) = NEt(4)(+); X(-) = CN(-), OAc(-) and ER(4)(+) = PPh(4)(+); X(-) = N(3)(-); DAD = N,N'-bis(2,6-dimethylphenyl)butane-2,3-diimine) were prepared by ligand exchange from cycloheptatriene molybdenum tricarbonyl. A total of 19 crystal structures were determined, including unprecedented structural characterization of molybdenum(0) coordination by dimethyl sulfoxide (DMSO), methanol, ethyl acetate (EtOAc), acetone, and N,N-dimethylformamide (DMF). Correlation of (13)C NMR shifts with the complex geometry suggests a direct ligand-ligand interaction between DAD and O-bonded coligands with C═O and S═O double bonds, such as EtOAc, Me(2)CO, DMF, and DMSO. Unexpectedly, the solvatochromic properties of these tricarbonyl complexes [Mo(DAD)(CO)(3)L] are unfavorable for the determination of Kamlet-Taft parameters of the corresponding solvent L. Contrastingly, the UV/vis absorption of [Mo(DAD)(CO)(4)] is strongly correlated with the Kamlet-Taft parameter π*, which is shown for 22 solvents, including seven room temperature ionic liquids.     

Ligand effects in the syntheses and structures of novel heteroleptic and homoleptic bismuth(III) formamidinate complexes

Metathesis reactions of the alkali metal formamidinates M(RNC(H)NR), M = Li or K; R = C(6)H(3)-2,6-Pr(i)(2) (L(1)), C(6)H(3)-2,6-Et(2) (L(2)); C(6)H(2)-2,4,6-Me(3) (L(3)), C(6)H(3)-2,6-Me(2) (L(4)) or C(6)H(4)-2-Ph (L(5)), with BiX(3) (X = Cl or Br) gave a range of bismuth(iii) formamidinate complexes [Bi(L)Br(micro-Br)(thf)](2) (L = L(1), L(4)), [{Bi(L(1))Cl(2)(thf)}(2)Bi(L(1))Cl(2)], [Bi(L)(2)X] (L = L(2), L(5), X = Br; L = L(1), X = Cl), and [Bi(L)(3)] (L = L(2), L(3)). An analogous organometallic complex Bi(L(1))(2)Bu(n) was also isolated as a side product in one instance. Structural characterisation of the di-halide complexes show symmetrical dimers for X = Br, with two bromide bridges, and a coordinated thf molecule on each Bi atom, whereas for X = Cl a thf deficient species was crystallised, and has a weakly associated trinuclear array with two coordinated thf molecules per three Bi atoms. Complexes of the form Bi(L)(2)X (X = Br, Cl, Bu(n)) and Bi(L)(3) all have monomeric structures but the Bi(L)(3) species show marked asymmetry of the formamidinate binding, suggesting that they have reached coordination saturation.     

Reversible and irreversible vapor-induced guest molecule exchange in spin-crossover compounds

Spin-crossover (SCO) complex [Fe(tpa)(NCS)(2)] (tpa = tri(2-pyridylmethyl)amine) crystallized in two solvate forms, yellow [Fe(tpa)(NCS)(2)]·X [Fe:X = 1:1; X = n-PrOH (complex is named as n-PrOH), i-PrOH (i-PrOH), CH(2)Cl(2) (CH(2)Cl(2)), CHCl(3) (CHCl(3)), MeCN (MeCN)] and red [Fe(tpa)(NCS)(2)](2)·Y [Fe:Y = 2:1; Y = MeOH (MeOH), EtOH (EtOH)], respectively. Between the two forms, interesting solvent-vapor induced in situ reversible and irreversible guest molecule exchanges, [Fe(tpa)(NCS)(2)]·X ? [Fe(tpa)(NCS)(2)](2)·Y, occurred in the solid state followed by dramatic color changes as well as distinct structural and SCO behavior transformations. Comprehensive studies on structures and SCO behaviors associating guest exchanges have been conducted by X-ray single-crystal diffraction, PXRD, IR, elemental analysis, and magnetic measurements, respectively. This discrete molecular system shows unique solvent-dependent SCO behavior related to the nature of solvent molecules; the distinct color changes during guest exchange originate from the alternations of electronic states of the guest-sensitive Fe(II) centers, providing an effective route to fine-tune and optimize materials' properties by systematic structural perturbation, or serving for detection of toxic gases, such as CH(2)Cl(2) and CHCl(3).     

Anion-solvent dependence of bistability in a family of meridional N-donor-ligand-containing iron(II) spin crossover complexes

Five mononuclear spin crossover iron(II) bis-meridional ligand complexes of the general formula [Fe(L)(2)](X)(2).solvent, have been synthesized, where X = BF(4)- or ClO(4)-; L = 2-(1-pyridin-2-ylmethyl-1H-pyrazol-3-yl)-pyrazine (picpzpz) or 2-(3-(2-pyridyl)pyrazol-1-ylmethyl)pyridine) (picpypz); solvent = MeOH or EtOH. The magnetic and structural consequences of systematic variation of meridional ligand, solvent, and anion, including a desolvated species, have been investigated. The complex [Fe(picpzpz)(2)](BF(4))(2).MeOH, 1.MeOH, displays several unique properties including a two-step spin transition with a gradual higher-temperature step ((1)T(1/2) = 197 K) and an abrupt low-temperature step with hysteresis ((2)T(1/2) = 91/98 K) and a metastable intermediate spin state below 70 K with quench-cooling. Removal of the solvent methanol results in the loss of the abrupt step and associated hysteresis (T(1/2) = 150 K). The complexes [Fe(picpzpz)(2)](BF(4))(2).EtOH (1.EtOH), [Fe(picpzpz)(2)](ClO(4))(2).MeOH (2.MeOH), [Fe(picpzpz)(2)](ClO(4))(2).EtOH (2.EtOH), and [Fe(picpypz)(2)](BF(4))(2).MeOH (3.MeOH) all show gradual one-step spin transitions with T(1/2) values in the range 210-250 K. Photomagnetic LIESST measurements on 1.MeOH reveal a near-quantitative excitation of high-spin sites and a unique two-step relaxation process related to the two-step thermal spin transition ((1)T(LIESST) = 49 K and (2)T(LIESST) = 70 K). The structural consequences of the unusual spin transition displayed by 1.MeOH have been investigated by single-crystal X-ray diffraction structural analyses between 25 and 293 K. Detailed characterization of the unit cell parameter evolution vs temperature reflects both the gradual high-temperature step and abrupt low-temperature step, including the thermal hysteresis, observed magnetically.     

Heterometallic modular metal-organic 3D frameworks assembled via new tris-β-diketonate metalloligands: nanoporous materials for anion exchange and scaffolding of selected anionic guests

The modular engineering of heterometallic nanoporous metal-organic frameworks (MOFs) based on novel tris-chelate metalloligands, prepared using the functionalised β-diketone 1,3-bis(4'-cyanophenyl)-1,3-propanedione (HL), is described. The complexes [M(III)L(3)] (M=Fe(3+), Co(3+)) and [M(II)L(3)](NEt(4)) (M=Mn(2+), Co(2+), Zn(2+), Cd(2+)) have been synthesised and characterised, all of which exhibit a distorted octahedral chiral structure. The presence of six exo-oriented cyano donor groups on each complex makes it a suitable building block for networking through interactions with external metal ions. We have prepared two families of MOFs by reacting the metalloligands [M(III)L(3)] and [M(II)L(3)](-) with many silver salts AgX (X=NO(3)(-), BF(4)(-), PF(6)(-), AsF(6)(-), SbF(6)(-), CF(3)SO(3)(-), tosylate), specifically the [M(III)L(3)Ag(3)]X(3)·Solv and [M(II)L(3)Ag(3)]X(2)·Solv network species. Very interestingly, all of these network species exhibit the same type of 3D structure and crystallise in the same trigonal space group with similar cell parameters, in spite of the different metal ions, ionic charges and X(-) counteranions of the silver salts. We have also succeeded in synthesising trimetallic species such as [Zn(x)Fe(y)L(3)Ag(3)](ClO(4))((2x+3y))·Solv and [Zn(x)Cd(y)L(3)Ag(3)](ClO(4))(2)·Solv (with x+y=1). All of the frameworks can be described as sixfold interpenetrated pcu nets, considering the Ag(+) ions as simple digonal spacers. Each individual net is homochiral, containing only Δ or Λ nodes; the whole array contains three nets of type Δ and three nets of type Λ. Otherwise, taking into account the presence of weak Ag-C σ bonds involving the central carbon atoms of the β-diketonate ligands of adjacent nets, the six interpenetrating pcu networks are joined into a unique non-interpenetrated six-connected frame with the rare acs topology. The networks contain large parallel channels of approximate hexagonal-shaped sections that represent 37-48% of the cell volume and include the anions and many guest solvent molecules. The guest solvent molecules can be reversibly removed by thermal activation with retention of the framework structure, which proved to be stable up to about 270°C, as confirmed by TGA and powder XRD monitoring. The anions could be easily exchanged in single-crystal to single-crystal processes, thereby allowing the insertion of selected anions into the framework channels.     

An iron(II) dihydrogen hydrido complex containing the tripodal tetraphosphine ligand P(CH2CH2PMe2)3

The dihydrogen hydrido complex [FeH(H2)(PP3)]+ 1 (PP3 = P(CH2CH2PMe2)3 2) was formed by the protonation of the dihydrido complex FeH2(PP3) 3 with methanol or ethanol. The observation of H-D coupling in partially deuterated isotopomers of 1 and measurement of T1 relaxation times for the hydrido and dihydrogen resonances of 1 confirmed the presence of the eta2-dihydrogen ligand. Complex 1 shows dynamic NMR behaviour in both the 31P and 1H NMR spectra with facile exchange between the protons in the eta2-dihydrogen ligand and the eta1-hydrido ligand. The dihydrogen ligand of 1 is easily displaced by both anionic and neutral ligands to afford the corresponding hydrido complexes [FeHX(PP3)]+ (X = CO 11, X = PPh3 12) or FeHX(PP3)(X = Cl 13, X = Br 14, X = I 15, X = N3 16). Small quantities of the alkoxy hydrido complexes FeH(OR)(PP3)(R = Me 4; R = Et 5) are observed in methanol and ethanol solutions containing 1. In methanol solution, FeH(OMe)(PP3) 4 reacts to form the carbonyl hydrido complex [FeH(CO)(PP3)]+ 11 and isotopic labelling confirms that the carbonyl ligand of 11 is derived from the methanol solvent. The mechanism of methanol oxidation presumably proceeds through beta-hydride elimination from FeH(OMe)(PP3) to produce formaldehyde as an intermediate which is further dehydrogenated to form the carbonyl ligand. [FeH(H2)(PP3)]+ 1 and FeHCl(PP3) 13 react rapidly with paraformaldehyde to also form [FeH(CO)(PP3)]+ 11. Complex 11 also decarbonylates acetaldehyde to afford the methyl carbonyl complex [FeMe(CO)(PP3)]+ 17. The structure of 17 was confirmed by X-ray crystallography.     

Stepwise synthesis of [Ru(trpy)(L)(X)](n+) (trpy = 2,2':6',2' '-terpyridine; L = 2,2'-dipyridylamine; X = Cl-, H2O, NO2-, NO+, O2-). Crystal structure, spectral, electron-transfer, and photophysical aspects

Ruthenium-terpyridine complexes incorporating a 2,2'-dipyridylamine ancillary ligand [Ru(II)(trpy)(L)(X)](ClO(4))(n) [trpy = 2,2':6',2' '-terpyridine; L = 2,2'-dipyridylamine; and X = Cl(-), n = 1 (1); X = H(2)O, n = 2 (2); X = NO(2)(-), n = 1 (3); X = NO(+), n = 3 (4)] were synthesized in a stepwise manner starting from Ru(III)(trpy)(Cl)(3). The single-crystal X-ray structures of all of the four members (1-4) were determined. The Ru(III)/Ru(II) couple of 1 and 3 appeared at 0.64 and 0.88 V versus the saturated calomel electrode in acetonitrile. The aqua complex 2 exhibited a metal-based couple at 0.48 V in water, and the potential increased linearly with the decrease in pH. The electron-proton content of the redox process over the pH range of 6.8-1.0 was calculated to be a 2e(-)/1H(+) process. However, the chemical oxidation of 2 by an aq Ce(IV) solution in 1 N H(2)SO(4) led to the direct formation of corresponding oxo species [Ru(IV)(trpy)(L)(O)](2+) via the concerted 2e(-)/2H(+) oxidation process. The two successive reductions of the coordinated nitrosyl function of 4 appeared at +0.34 and -0.34 V corresponding to Ru(II)-NO(+) --> Ru(II)-NO* and Ru(II)-NO* --> Ru(II)-NO(-), respectively. The one-electron-reduced Ru(II)-NO* species exhibited a free-radical electron paramagnetic resonance signal at g = 1.990 with nitrogen hyperfine structures at 77 K. The NO stretching frequency of 4 (1945 cm(-1)) was shifted to 1830 cm(-1) in the case of [Ru(II)(trpy)(L)(NO*)](2+). In aqueous solution, the nitrosyl complex 4 slowly transformed to the nitro derivative 3 with the pseudo-first-order rate constant of k(298)/s(-1) = 1.7 x 10(-4). The chloro complex 1 exhibited a dual luminescence at 650 and 715 nm with excited-state lifetimes of 6 and 1 micros, respectively.     

Racemic monoperoxovanadium(V) complexes with achiral OO and ON donor set heteroligands: synthesis, crystal structure and stereochemistry of [NH3(CH2)2NH3][VO(O2)(ox)(pic)].2H2O and [NH3(CH2)2NH3][VO(O2)(ox)(pca)

Monoperoxovanadium(V) complexes, [NH3(CH2)2NH3][VO(O2)(ox)(pic)].2H2O (1) and [NH3(CH2)2NH3][VO(O2)(ox)(pca)] (2) [NH3(CH2)2NH3 = ethane-1,2-diammonium(2+), ox=oxalate(2-), pic=pyridine-2-carboxylate(1-), pca=pyrazine-2-carboxylate(1-)], were synthesized and characterized by X-ray analysis, IR and Raman spectroscopies. The five equatorial positions of the pentagonal bipyramid around the vanadium atoms are occupied by the eta2-peroxo ligand, two oxygen atoms of the ox, and the nitrogen atom of the pic or pca ligands, respectively. The oxo ligand and the oxygen atom of pic or pca are in the axial positions. Networks of X-HO (X=C, N or O) hydrogen bonds, and pi-pi interactions between aromatic rings in and anion-pi interactions in , determine the molecular packings and build up the supramolecular architecture. Three stereochemical rules for occupation of the donor sites in two-heteroligand [VO(O2)(L1)(L2)] complexes (L1, L2 are bidentate neutral or differently charged anionic heteroligands providing an OO, NN or ON donor set) are discussed. and crystallize as racemic compounds. The 51V NMR spectra proved that the parent complex anions of and partially decompose on dissolution in water to the monoperoxo-ox, -pic or -pca complexes.     

Molecular squares, cubes and chains from self-assembly of bis-bidentate bridging ligands with transition metal dications

The two new ligands L(fur) and L(th) consist of two chelating pyrazolyl-pyridine termini connected to furan-2,5-diyl or thiophene-2,5-diyl spacers via methylene groups. Reaction of these with a range of transition metal dications that prefer octahedral coordination affords a series of unusual structures which are all based on a 2M : 3L ratio. [M(8)(L(fur))(12)]X(16) (M = Co, Cu, X = BF(4); and M = Zn, X = ClO(4)) are octanuclear cubes with approximate D(4) symmetry in which two cyclic tetranuclear helicate M(4)L(4) units are connected by four additional 'pillar' ligands. In contrast [Ni(4)(L(fur))(6)](BF(4))(8) is a centrosymmetric molecular square consisting of two dinuclear Ni(2)L(2) units of opposite chirality that are connected by a pair of additional L(fur) ligands such that the four edges of the Ni(4) square are spanned by alternately two and one bridging ligands. [M(4)(L(th))(6)](BF(4))(8) (M = Co, Ni, Cu) are likewise molecular squares with similar structures to [Ni(4)(L(fur))(6)](BF(4))(8) with the significant difference that the two crosslinked double helicate M(2)L(2) units are now homochiral. The Cd(II) complexes both behave quite differently to the first-row metal complexes, with [Cd(L(fur))(BF(4))](BF(4)) being a simple mononuclear complex with a single ligand in which the furan oxygen atom is weakly interacting with the Cd(II) centre. In contrast, in {[Cd(2)(L(th))(3)](BF(4))(4)}(∞), where this quasi-pentadentate coordination mode of the ligand is not possible because thiophene is too poor an electron donor, the ligand reverts to bis-bidentate bridging coordination to afford a one-dimensional chain consisting of an infinite sequence of crosslinked, homochiral, Cd(2)(L(th))(2) double helicate units.