Tuning the decay time of lanthanide-based near infrared luminescence from micro- to milliseconds through d-->f energy transfer in discrete heterobimetallic complexes

Inert and optically active pseudo-octahedral Cr(III)N6 and Ru(II)N6 chromophores have been incorporated by self-assembly into heterobimetallic triple-stranded helicates HHH-[CrLnL3]6+ and HHH-[RuLnL3]5+. The crystal structures of [CrLnL(3)](CF(3)SO(3))(6) (Ln=Nd, Eu, Yb, Lu) and [RuLnL3](CF3SO3)5 (Ln=Eu, Lu) demonstrate that the helical structure can accommodate metal ions of different sizes, without sizeable change in the intermetallic MLn distances. These systems are ideally suited for unravelling the molecular factors affecting the intermetallic nd-->4f communication. Visible irradiation of the Cr(III)N6 and Ru(II)N6 chromophores in HHH-[MLnL3]5/6+ (Ln=Nd, Yb, Er; M=Cr, Ru) eventually produces lanthanide-based near infrared (NIR) emission, after directional energy migration within the complexes. Depending on the kinetic regime associated with each specific d-f pair, the NIR luminescence decay times can be tuned from micro- to milliseconds. The origin of this effect, together with its rational control for programming optical functions in discrete heterobimetallic entities, are discussed.     

The first enantiomerically pure helical noncovalent tripod for assembling nine-coordinate lanthanide(III) podates

Decomplexation of the trivalent lanthanide, Ln(III), from the racemic bimetallic triple-stranded helicates [LnCr(L8)(3)](6+) provides the inert chiral tripodal nonadentate receptor [Cr(L8)(3)](3+). Elution of the latter podand with Na(2)Sb(2)[(+)-C(4)O(6)H(2)](2).5H(2)O through a cation exchange column allows its separation into its inert helical enantiomers M-(+)(589)-[Cr(L8)(3)](3+) and P-(-)(589)-[Cr(L8)(3)](3+), whose absolute configurations are assigned by using CD spectroscopy and exciton theory. Recombination with Ln(III) restores the original triple-stranded helicates [LnCr(L8)(3)](6+), and the associated thermodynamic parameters unravel the contribution of electrostatic repulsion and preorganization to the complexation process. Combining M-(+)(589)-[Cr(L8)(3)](3+) with Eu(III) produces the enantiomerically pure d-f helicate MM-(-)(589)-[EuCr(L8)(3)](CF(3)SO(3))(6).4CH(3)CN, whose X-ray crystal structure (EuCrC(113)H(111)N(25)O(21)S(6)F(18), monoclinic, P2(1), Z = 2) unambiguously confirms the absolute left-handed configuration for the final helix. The associated ligand-centered and metal-centered chiro-optical properties recorded for the complexes MM-[LnCr(L8)(3)](6+) and PP-[LnCr(L8)(3)](6+) (Ln = Eu, Gd, Tb) show a strong effect of helicity on specific rotary dispersions, CD and CPL spectra.     

Syntheses and crystal structures of dinuclear complexes containing d-block and f-block luminophores. Sensitization of NIR luminescence from Yb(III), Nd(III), and Er(III) centers by energy transfer from Re(I)- and Pt(II)-bipyrimidine metal centers

Mononuclear complexes [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] (bpym = 2,2'-bipyrimidine), in which one of the bipyrimidine sites is vacant, have been used as "complex ligands" to prepare heterodinuclear d-f complexes in which a lanthanide tris(1,3-diketonate) unit is attached to the secondary bipyrimidine site to evaluate the ability of d-block chromophores to act as antennae for causing sensitized near-infrared (NIR) luminescence from adjacent lanthanide(III) centers. The two sets of complexes so prepared are [Re(CO)(3)Cl(mu-bpym)Ln(fod)(3)] (abbreviated as Re-Ln; where Ln = Yb, Nd, Er) and [(F(3)C-C(6)H(4)-CC)(2)Pt(mu-bpym)Ln(hfac)(3)] (abbreviated as Pt-Ln; where Ln = Nd, Gd). Members of both series have been structurally characterized; the metal-metal separation across the bipyrimidine bridge is approximately 6.3 A in each case. In these complexes, the (3)MLCT (MLCT = metal to ligand charge-transfer) luminescences of the mononuclear [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] complexes are quenched by energy transfer to those lanthanides (Ln = Yb, Nd, Er) that have low-lying f-f states capable of NIR luminescence; as a result, sensitized NIR luminescence is seen from the lanthanide center following excitation of the d-block unit. In the solid state, quenching of the luminescence from the d-block chromophore is complete, indicating efficient d --> f energy transfer, as a result of the short metal-metal separation across the bipyrimidine bridge. In a CH(2)Cl(2) solution, partial dissociation of the dinuclear complexes into the mononuclear units occurs, with the result that some (3)MLCT luminescence is observed from mononuclear [Re(bpym)(CO)(3)Cl] or [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] present in the equilibrium mixture. Solution UV-vis and luminescence titrations, carried out by the addition of portions of Ln(fod)(3)(H(2)O)(2) or Ln(hfac)(3)(H(2)O)(2) to the d-block complex ligands, indicate that binding of the lanthanide tris(1,3-diketonate) unit at the secondary bipyrimidine site to give the d-f dinuclear complexes occurs with an association constant of ca. 10(5) M(-)(1).     

Hydrolytic synthesis and structural characterization of lanthanide-acetylacetonato/hydroxo cluster complexes--a systematic study

Lanthanide hydroxide cluster complexes with acetylacetonate were synthesized by the hydrolysis of the corresponding hydrated lanthanide acetylacetonates in methanol in the presence of triethylamine. Polymeric lanthanide hydroxide complexes based on diamond-shaped dinuclear repeating units of [Ln(2)(CH(3)CO(3))(2)](4+) (Ln = La, Pr) and discrete complexes featuring a tetranuclear distorted cubane core of [Ln(4)(μ(3)-OH)(2)(μ(3)-OCH(3))(2)](8+) (Ln = Nd, Sm) and a nonanuclear core of [Ln(9)(μ(4)-O)(μ(4)-OH)(μ(3)-OH)(8)](16+) (Ln = Eu-Dy, Er, Yb) were obtained. The dependence of the cluster nuclearity on the identity of the lanthanide ion is rationalized in terms of the influences of a metal ion's Lewis acidity and the sterics about the Ln-OH unit on the kinetics of the assembly process that leads to a particular cluster.     

Encapsulation of labile trivalent lanthanides into a homobimetallic chromium(III)-containing triple-stranded helicate. Synthesis, characterization, and divergent intramolecular energy transfers

The segmental bidentate-tridentate-bidentate ligand L2 reacts with M(II) (M = Cr, Zn) and Ln(III) (Ln = La, Eu, Gd, Tb, Lu) to give the heterotrimetallic triple-stranded helicates [MLnM(L2)3]7+. For M = Zn(II), the isolated complexes [ZnLnZn(L2)3](CF3SO3)7 (Ln = Eu, Tb) display only lanthanide-centred luminescence arising from the pseudo-tricapped trigonal prismatic LnN9 coordination site. For M = Cr(II), rapid air oxidation provides Cr(III) and leads to the isolation of inert [CrLnCr(L2)3](CF3SO3)9 (Ln = Eu, Tb) complexes, in which divergent intramolecular Ln --> Cr energy transfers can be evidenced. Taking [ZnEuZn(L2)3]7+ as a luminescent standard for Eu-centred emission, a quantitative treatment of the energy migration processes indicates that the rate constant characterizing the Eu --> Cr energy transfer is more efficient in the trimetallic system, than in the analogous simple bimetallic edifice. Particular attention is focused on potential control of directional energy transfer processes in Cr-Ln pairs.     

Solid state and solution studies of lanthanide(III) complexes of cyclohexanetriols, models of the coordination sites found in sugars

This report covers studies in trivalent lanthanide complexation by two simple cyclohexanetriols that are models of the two coordination sites found in sugars and derivatives. Several complexes of trivalent lanthanide ions with cis,cis-1,3,5-trihydroxycyclohexane (L(1)()) and cis,cis-1,2,3-trihydroxycyclohexane (L(2)()) have been characterized in the solid state, and some of them have been studied in organic solutions. With L(1)(), Ln(L)(2) complexes are obtained when crystallization is performed from acetonitrile solutions whatever the nature of the salt (nitrate or triflate) [Ln(L(1)())(2)(NO(3))(2)](NO(3)) (Ln = Pr, Nd); [Ln(L(1)())(2)(NO(3))H(2)O](NO(3))(2) (Ln = Eu, Ho, Yb); [Ln(L(1)())(2)(OTf)(2)(H(2)O)](OTf) (Ln = Nd, Eu). Lanthanum nitrate itself gives a mixed complex [La(L(1)())(2)(NO(3))(2)][LaL(1)()(NO(3))(4)] from acetonitrile solution while [La(L(1)())(2)(NO(3))(2)](NO(3)) is obtained using dimethoxyethane as reaction solvent and crystallization medium. With L(2)(), Ln(L)(2) complexes have also been crystallized from methanol solution [Ln(L(2)())(2)(NO(3))(2)]NO(3), (Ln = Pr, Nd, Eu). Single-crystal X-ray diffraction analyses are reported for these complexes. Complex formation in solution has been studied for several triflate salts (La, Pr, Nd, Eu, and Yb) with L(1 )()and L(2)(), respectively in acetonitrile and in methanol. In contrast to the solid state, both structures Ln(L) and Ln(L)(2) equilibrate in solution, as was demonstrated by low-temperature (1)H NMR and electrospray ionization mass spectrometry experiments. Competing experiments in complexing abilities of L(1)() and L(2)() with trivalent lanthanide cations have shown that only L(2)() exhibits a small selectivity (Nd > Pr > Yb > La > Eu) in methanol.     

Metal-to-ligand charge-transfer sensitisation of near-infrared emitting lanthanides in trimetallic arrays M2Ln (M=Ru, Re or Os; Ln=Nd, Er or Yb)

The new pro-ligand 4-methyl-4'-(carbonylamino(2-(tert-butoxycarbonylamino)ethyl))-2,2'-bipyridyl (L1) has been prepared and used to synthesise the complex fac-Re(I)Cl(CO)3(L1) 1 and the complex salts [M(II)(bipy)2(L1)](PF6)2 (M=RuII 8 or OsII 15). Deprotection with trifluoroacetic acid affords the amine-functionalised derivatives fac-Re(I)Cl(CO)3(L2) 2, [M(II)(bipy)2(L2)](PF6)2 (M=RuII 9 or OsII 16) which react with the dianhydride of diethylenetriamine pentaacetic acid (DTPA) to give the binuclear complex {fac-Re(I)Cl(CO)3}2(L3) 3 and the complex salts [{M(II)(bipy)2}2(L3)](PF6)4 (M = RuII 10 or OsII 17). The latter react with salts Ln(OTf)3 to afford a series of 12 heterotrimetallic compounds that contain a lanthanide (Ln) ion in the DTPA binding site; {fac-Re(I)Cl(CO)3}2(L3)LnIII (Ln=Nd 4, Er 5, Yb 6 or Y 7) and [{M(II)(bipy)2}2(L3)LnIII](PF6)(OTf)3 (M=RuII, Ln=Nd 11, Er 12, Yb 13 or Y 14; M=OsII, Ln=Nd 18, Er 19, Yb 20 or Y 21). All of these trimetallic species display absorption bands ascribed to metal-to-ligand charge-transfer (MLCT) excitations, and luminescence measurements show that these excited states can be used to sensitise near-infrared emission from LnIII (Ln=Nd, Er or Yb) ions. Single crystal X-ray structures of L1 and [RuII(bipy)2(L2H)](H2PO4)3.(CH3)2CO.0.8H2O were obtained, the latter revealing the presence of H2PO4- counter anions, the source of which is presumed to be hydrolysis of PF6- ions.     

Ru(ii) sensitized lanthanide luminescence: synthesis, photophysical properties, and near-infrared luminescent determination of alpha-fetal protein (AFP)

A series of dinuclear compounds of [Ru(bpy)(2)(tpphz)Ln(TTA)(3)](PF(6))(2) (tpphz = tetrapyrido[3,2-a:2',3'-c:3',2'-h:3',4'-j]phenazine; Ln = Er(iii), Nd(iii), Yb(iii) and Gd(iii); TTA = 2-thenoyltrifluoroacetone) have been prepared by attachment of a [Ln(TTA)(3)] fragment at the vacant diimine site of the luminescent mononuclear complex [Ru(bpy)(2)(tpphz)](PF(6))(2). In the solid state, in CH(2)Cl(2) solution and in Tris-HCl buffer solution of these dinuclear complexes , sensitized near-infrared (NIR) luminescence is observed from Nd and Yb centres following excitation of the d-block unit, which results from the effective Ru → Ln (Ln = Nd, Yb) energy transfer, but no Er-based NIR luminescence is produced. The (3)MLCT (MLCT = metal to ligand charge transfer) emission is partly quenched in the complex, slightly increased in the complex, and is not changed in the complex. Interestingly, alpha-fetal protein (AFP) tends to decrease the NIR luminescence intensity of the complex in Tris-HCl buffer solution. A novel NIR luminescent method for the determination of AFP was developed with a linear range of 0.5-18 ng mL(-1), and a detection limit of 0.2 ng mL(-1) based on 3 times the ratio of the signal-to-noise. Considering the attractive features, such as good selectivity, stability and rapidity, the proposed NIR luminescent method provides promising potential for AFP detection in clinical diagnosis and biomedical applications.     

A simple thermodynamic model for rationalizing the formation of self-assembled multimetallic edifices: application to triple-stranded helicates

Reaction of the bis-tridentate ligand bis[1-ethyl-2-[6'-(N,N-diethylcarbamoyl)pyridin-2'-yl]benzimidazol-5-yl]methane (L2) with Ln(CF(3)SO(3))(3).xH(2)O in acetonitrile (Ln = La-Lu) demonstrates the successive formation of three stable complexes [Ln(L2)(3)](3+), [Ln(2)(L2)(3)](6+), and [Ln(2)(L2)(2)](6+). Crystal-field independent NMR methods establish that the crystal structure of [Tb(2)(L2)(3)](6+) is a satisfying model for the helical structure observed in solution. This allows the qualitative and quantitative beta23 (bi,Ln1,Ln2)characterization of the heterobimetallic helicates [(Ln(1))(Ln(2))(L2)(3)](6+). A simple free energy thermodynamic model based on (i) an absolute affinity for each nine-coordinate lanthanide occupying a terminal N(6)O(3) site and (ii) a single intermetallic interaction between two adjacent metal ions in the complexes (DeltaE) successfully models the experimental macroscopic constants and allows the rational molecular programming of the extended trimetallic homologues [Ln(3)(L5)(3)](9+).     

Anion dependant self-assembly and the first X-ray structure of a neutral homoleptic lanthanide salen complex Tb4(salen)6

Reaction of H(2)salen (H(2)L) with Tb(OAc)(3).4H(2)O (3 : 2) in MeOH-MeCN under reflux gave homoleptic Tb(4)L(6) (1) in 40% yield; in contrast, similar reactions of Tb(NO(3))(3).6H(2)O and LnCl(3).6H(2)O (Ln = Tb, Nd and Yb) gave [TbL(NO(3))(MeOH)](2)(micro-H(2)L) (2) and [LnL(Cl)(MeOH)](2)(micro-H(2)L) (Ln = Tb (3), Nd (4) and Yb (5); H(2)L = N,N'-ethylenebis(salicylideneimine)).     

The first self-assembled trimetallic lanthanide helicates driven by positive cooperativity

The segmental tris-tridentate ligand L7 reacts with stoichiometric quantities of Ln(III) (Ln=La-Lu) in acetonitrile to give the complexes [Ln(2)(L7)(3)](6+) and [Ln(3)(L7)(3)](9+). Formation constants point to negligible size-discriminating effects along the lanthanide series, but Scatchard plots suggest that the self-assembly of the trimetallic triple-stranded helicates [Ln(3)(L7)(3)](9+) is driven to completion by positive cooperativity, despite strong intermetallic electrostatic repulsions. Crystallization provides quantitatively [Ln(3)(L7)(3)](CF(3)SO(3))(9) (Ln=La, Eu, Gd, Tb, Lu) and the X-ray crystal structure of [Eu(3)(L7)(3)](CF(3)SO(3))(9).(CH(3)CN)(9).(H(2)O)(2) (Eu(3)C(216)H(226)N(48)O(35)F(27)S(9), triclinic, P1, Z=2) shows the three ligand strands wrapped around a pseudo-threefold axis defined by the three metal ions rigidly held at about 9 A. Each metal ion is coordinated by nine donor atoms in a pseudo-trigonal prismatic arrangement, but the existence of terminal carboxamide units in the ligand strands differentiates the electronic properties of the terminal and the central metallic sites. Photophysical data confirm that the three coordination sites possess comparable pseudo-trigonal symmetries in the solid state and in solution. High-resolution luminescence analyses evidence a low-lying LMCT state affecting the central EuN(9) site, so that multi-metal-centered luminescence is essentially dominated by the emission from the two terminal EuN(6)O(3) sites in [Eu(3)(L7)(3)](9+). New multicenter equations have been developed for investigating the solution structure of [Ln(3)(L7)(3)](9+) by paramagnetic NMR spectroscopy and linear correlations for Ln=Ce-Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second-rank crystal-field parameters, obtained by LIS analysis, for the LnN(6)O(3) and LnN(9) sites with respect to the parameters extracted for Eu(III) from luminescence data, suggests that the geometry of the central LnN(9) site is somewhat relaxed in solution.     

Cyclic tetramers composed of rhodium(III), iridium(III), or ruthenium(II) half-sandwich and 6-purinethiones

Six new cyclic tetranuclear complexes [[M(Cp*)(L)](4)](4+) and [[Ru(II)(L)(cymene)](4)](4+) [Cp* = eta(5)-C(5)Me(5), cymene = eta(6)-p-MeC(6)H(4)Pr(i); M = Rh(III) and Ir(III); HL = 6-purinethione (H(2)put) and 2-amino-6-purinethione (H(2)aput)] were prepared in a self-assembly manner and characterized by NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray crystal structure analysis. The two crystal structures of [[Rh(Cp*)(H(0.5)put)](4)](CF(3)SO(3))(2) and [[Ir(Cp*)(Haput)](4)](CF(3)SO(3))(4) revealed that they have similar S(4) structures with an alternate chirality array of CACA, and all ligands adopt a mu-1kappaN(9):2kappa(2)S(6),N(7) coordination mode. The orientations of the four bridging ligands are alternately up and down, and they form a central square cavity. Interestingly, the cationic tetramers of the former are stacked up along the c axis, resulting in an infinite channel-like cavity. The driving force of this stacking is due to intermolecular double hydrogen bonds [N(1)-H...N(21) = 2.752(4) A] at both sides of the cavity. In the two Rh(III)- and Ru(II)-H(2)aput systems, it turned out that the dimeric species are dominantly formed in the reaction solutions but finally convert into the tetrameric species.     

Synthesis, characterization, and DNA-binding and -photocleavage properties of water-soluble lanthanide porphyrinate complexes

A series of cationic lanthanide porphyrinate complexes of the general formula [(Por)Ln(H(2)O)(3)](+) (Ln(3+)=Yb(3+) and Er(3+)) were synthesized in moderate yields through the interaction of meso-pyridyl-substituted porphyrin free bases (H(2)Por) with [Ln{N(SiMe(3))(2)}(3)]·x[LiCl(thf)(3)], and the corresponding neutral derivatives [(Por)Ln(L(OMe))] (L(OMe)(-)=[(η(5)-C(5)H(5))Co{P(=O)(OMe)(2)}(3)](-)) were also prepared from [(Por)Ln(H(2)O)(3)](+) by the addition of the tripodal anion, L(OMe)(-), an effective encapsulating agent for lanthanide ions. Furthermore, the water-soluble lanthanide(III) porphyrinate complexes--including [(cis-DMPyDPP)Yb(H(2)O)(3)]Cl(3) (cis-DMPyDPP=5,10-bis(N-methylpyridinium-4'-y1)-15,20-di(phenyl)porphyrin), [(trans-DMPyDPP)Yb(H(2)O)(3)]Cl(3) (trans-DMPyDPP=5,15-bis(N-methylpyridinium-4'-y1)-10,20-di(phenyl)porphyrin), [(TMPyP)Yb(L(OMe))]I(4), and [(TMPyP)Er(L(OMe))]I(4) (TMPyP=tetrakis(N-methylpyridinium-4-y1)porphyrin)--were obtained by methylation of the corresponding complexes with methyl iodide and unambiguously characterized. The binding interactions and photocleavage activities of the water-soluble lanthanide(III) porphyrinate complexes towards DNA were investigated by UV-visible, fluorescence, and near-infrared luminescence spectroscopy, as well as circular dichroism and gel electrophoresis.     

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.     

Synthesis and characterization of iron(III)-substituted, dimeric polyoxotungstates, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](n-) (n = 6, X = As(III), Sb(III); n = 4, X = Se(IV), Te(IV))

Interaction of the lacunary [alpha-XW(9)O(33)](9-) (X = As(III), Sb(III)) with Fe(3+) ions in acidic, aqueous medium leads to the formation of dimeric polyoxoanions, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)) in high yield. X-ray single-crystal analyses were carried out on Na(6)[Fe(4)(H(2)O)(10)(beta-AsW(9)O(33))(2)] x 32H(2)O, which crystallizes in the monoclinic system, space group C2/m, with a = 20.2493(18) A, b = 15.2678(13) A, c = 16.0689(14) A, beta = 95.766(2) degrees, and Z = 2; Na(6)[Fe(4)(H(2)O)(10)(beta-SbW(9)O(33))(2)] x 32H(2)O is isomorphous with a = 20.1542(18) A, b = 15.2204(13) A, c = 16.1469(14) A, and beta = 95.795(2) degrees. The selenium and tellurium analogues are also reported, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](4-) (X = Se(IV), Te(IV)). They are synthesized from sodium tungstate and a source of the heteroatom as precursors. X-ray single-crystal analysis was carried out on Cs(4)[Fe(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)] x 21H(2)O, which crystallizes in the triclinic system, space group P macro 1, with a = 12.6648(10) A, b = 12.8247(10) A, c = 16.1588(13) A, alpha = 75.6540(10) degrees, beta = 87.9550(10) degrees, gamma = 64.3610(10) gamma, and Z = 1. All title polyanions consist of two (beta-XW(9)O(33)) units joined by a central pair and a peripheral pair of Fe(3+) ions leading to a structure with idealized C(2h) symmetry. It was also possible to synthesize the Cr(III) derivatives [Cr(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)), the tungstoselenates(IV) [M(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)]((16)(-)(4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Hg(2+)), and the tungstotellurates(IV) [M(4)(H(2)O)(10)(beta-TeW(9)O(33))(2)]((16-4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)), as determined by FTIR. The electrochemical properties of the iron-containing species were also studied. Cyclic voltammetry and controlled potential coulometry aided in distinguishing between Fe(3+) and W(6+) waves. By variation of pH and scan rate, it was possible to observe the stepwise reduction of the Fe(3+) centers.     

Thermally inert metal ammines as light-inducible DNA-targeted agents. Synthesis,photochemistry, and photobiology of a prototypical rhodium(III)-intercalator conjugate

The recent discovery of the promising tumor cell kill by a novel platinum-acridine conjugate [Martins, E. T.; et al. J. Med. Chem. 2001, 44, 4492] has prompted us to explore the utility of analogous light-activatable rhodium(III) compounds as photocytotoxic agents. Here, the design and synthesis of [Rh(NH(3))(5)L](n)(+) complexes are described with L = 1,1,3,3-tetramethylthiourea (tmtu) or 1-[2-(acridin-9-ylamino)ethyl]-1,3,3-trimethylthiourea (2). The intercalator-based DNA-affinic carrier ligand 2 was synthesized from N-acridin-9-yl-N'-methylethane-1,2-diamine and dimethylthiocarbamoyl chloride and isolated as the hydrotriflate salt 2(CF(3)SO(3)). [Rh(NH(3))(5)(tmtu)](3+) (1) and [Rh(NH(3))(5)(2)](4+) (3) were obtained from the reactions of the trifluoromethanesulfonato complex [Rh(NH(3))(5)(OSO(2)CF(3))](CF(3)SO(3))(2) with the appropriate thiourea in noncoordinating solvents. All compounds were characterized by (1)H NMR and UV-vis spectroscopies and by elemental analyses. The single-crystal X-ray structures of 1(CF(3)SO(3))(3) x 2MeOH, 2(CF(3)SO(3)), and 3(CF(3)SO(3))(4) x H(2)O have been determined. Ligand-field photolysis of thermally inert 1 (lambda(max) = 378 nm) resulted in the aquation of 2 equiv of ammine ligand without noticeable release of sulfur-bound tmtu ((1)H NMR spectroscopy, NH(3)-sensitive electrode measurements). This was confirmed by (15)N[(1)H] NMR spectroscopy using (15)N-labeled [Rh((15)NH(3))(5)(tmtu)](3+) (1), which also indicated photoisomerization of the [RhN(5)S] moiety. Despite greatly accelerated ligand exchange, rhodium in 1 and 3 did not show light-enhanced formation of covalent adducts in calf thymus DNA. "Dark binding" levels of 3 in native DNA were slightly higher than for nontargeted 1, but significantly lower than those observed for analogous platinum-acridine. Agarose gel electrophoresis revealed photocleavage of supercoiled pUC19 plasmid DNA in the presence of hybrid 3 and its individual constituents 1 and 2. Simple 1 induced single-strand breaks while 3 produced complete degradation of the DNA after 24 h of continuous irradiation. Acridine 2 alone produced double-strand breaks. The extent of DNA damage observed for 1-3 correlates with the photocytotoxicity of the compounds in human leukemia cells, suggesting that DNA might be the cellular target of these agents.     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

Heteronuclear bipyrimidine-bridged Ru-Ln and Os-Ln dyads: low-energy 3MLCT states as energy-donors to Yb(III) and Nd(III)

The complexes [Ru((t)Bu(2)bipy)(bpym)X(2)] (X = Cl, NCS) and [M((t)Bu(2)bipy)(2)(bpym)][PF(6)](2) (M = Ru, Os) all have a low-energy LUMO arising from the presence of a 2,2'-bipyrimidine ligand, and consequently have lower-energy (1)MLCT and (3)MLCT states than analogous complexes of bipyridine. The vacant site of the bpym ligand provides a site at which [Ln(diketonate)(3)] units can bind to afford bipyrimidine-bridged dinuclear Ru-Ln and Os-Ln dyads; four such complexes have been structurally characterised. UV/Vis and luminescence spectroscopic studies show that binding of the Ln(III) fragment at the second site of the bpym ligand reduces the (3)MLCT energy of the Ru or Os fragment still further. The result is that in the dyads [Ru((t)Bu(2)bipy)X(2)(mu-bpym)Ln(diketonate)(3)] (X = Cl, NCS) and [Os((t)Bu(2)bipy)(2)(mu-bpym)Ln(diketonate)(3)][PF(6)](2) the (3)MLCT is too low to sensitise the luminescent f-f states of Nd(III) and Yb(III), but in [Ru((t)Bu(2)bipy)(2)(mu-bpym)Ln(diketonate)(3)][PF(6)](2) the (3)MLCT energy of 13,500 cm(-1) permits energy transfer to Yb(III) and Nd(III) resulting in sensitised near-infrared luminescence on the microsecond timescale.