Synthesis and crystal structure of tetranuclear copper(I) and silver(I) complexes bridged by 2-amino-1,3,4-thiadiazole (atdz): [Cu4(atdz)6](ClO4)4·2CH3OH and [Ag4(atdz)6](ClO4)4

Two novel tetracopper(I) and tetrasilver(I) complexes [Cu₄(atdz)₆](ClO₄)₄·2CH₃OH (1) and [Ag₄(atdz)₆](ClO₄)₄ (2), have been prepared using 2-amino-1,3,4-thiadiazole (atdz), and their crystal structures and properties have been determined. On each tetranuclear complex, two Cu or Ag atoms (M) are bridged by two atdz ligands to form a six-membered N₂M₂N₂ framework. The two N₂M₂N₂ frameworks are in parallel linked by another atdz ligand to provide the tetranuclear structure with a rectangular M₄ core. The four Cu or Ag atoms possess a trigonal-square geometry. The two adjacent MM separations are (3.096(1) and 3.412(1) Å) and (3.316(2) and 3.658(2) Å) for 1 and 2, respectively. On both tetranuclear complexes there are two species of hydrogen bonds between the ClO₄ ⁻ anions and the NH₂ group of atdz ligands. It is proposed that the hydrogen bonds are related to the stabilization of the tetranuclear structure during the crystallization process.     

Catalytic and electrochemical properties of new manganese(III) compounds of 2-(2′-hydroxyphenyl)-oxazoline (Hphox or HClphox). Molecular structures of [Mn(Clphox)2(MeOH)2](ClO4) and [Mn(phox)2(MeOH)2][Mn(phox)2(ClO4)2](H2O)2

New manganese(III) complexes of Hphox (2-(2′-hydroxyphenyl)-oxazoline) and HClphox (2-(5′-chloro-2′-hydroxyphenyl)-oxazoline) have been synthesised. The X-ray structures of [Mn(phox)₂(MeOH)₂][Mn(phox)₂(ClO₄)₂](H₂O)₂ and [Mn(Clphox)₂(MeOH)₂](ClO₄) show the manganese(III) ions to be octahedrally coordinated with methanol or perchlorate at the axial coordination sites. The cyclic voltammograms of the complexes, with the exception of [Mn(phox)₂(acac)] (Hacac=2,4-pentanedione), show an irreversible reduction wave of manganese(III) to manganese(II). After addition of an excess of 1-methylimidazole (1-Meim), the reduction process shifts towards lower potentials and becomes (quasi-) reversible, indicating that the presence of 1-Meim affects the catalytic efficiency of the complexes. The complexes catalyse the epoxidation of styrene by dihydrogen peroxide. The cumulative turnover numbers towards styrene oxide obtained after 15 min. vary from 16 for [Mn(Clphox)₂(MeOH)₂](ClO₄) to 26 for [Mn(phox)₂(acac)]. Ligand degradation appears to be the limiting factor for obtaining higher turnover numbers.     

DNA binding and cleavage activity of [Ru(NH3)4(diimine)]Cl2 complexes

The interaction of a series of mixed ligand complexes of the type [Ru(NH₃)₄(diimine)]Cl₂, where diimine=2,2^′-bipyridine (bipy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 4,7-dimethyl-1,10-phenanthroline (4,7-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp), 3,4,7,8-tetra-methyl-1,10-phenanthroline (Me₄phen), with calf thymus DNA has been studied using absorption, emission and circular dichroic spectral measurements and viscometry and electrochemical techniques. On interaction with DNA the complexes show hypochromism and red-shift in their MLCT band suggesting that the complexes bind to DNA. The magnitude of the binding constant (K_b) obtained from absorption spectral titration varies depending upon the nature of the diimine ligand: Me₄phen > 5,6-dmp > 4,7-dmp > phen suggesting the use of diimine ‘face’ of the octahedral complexes in binding to DNA. The interaction of phen complex possibly involves phen ring partially inserted into the DNA base pairs. In contrast, the methyl-substituted phen complexes would involve hydrophobic interaction of the phen ring in the grooves of DNA, which is supported by hydrogen bonding interactions of the ammonia ligands with the intrastrand nucleobases. Also the shape and size of the phen ligand as modified by the methyl substituents determine the DNA binding site sizes (0.12-0.45 base pairs). The relative emission intensities (I/I₀) of the DNA-bound complexes parallel the variation in K_b values. Almost all the metal complexes exhibit induced CD bands on binding to B DNA, with the 4,7-dmp and Me₄phen complexes inducing certain structural modifications on the biopolymer. DNA melting curves obtained in the presence of metal complexes reveal a monophasic melting of the DNA strands, the Me₄phen complex exhibiting a slightly enhanced tendency to stabilize the double-stranded DNA. There were slight to appreciable changes in the relative viscosities of DNA, which are consistent with enhanced hydrophobic interaction of the methyl-substituted phen rings. Upon interaction with CT DNA, the Me₄phen, 4,7-dmp and 5,6-dmp complexes, in contrast to bipy, phen and 2,9-dmp complexes, show a decrease in anodic peak current in their cyclic voltammograms suggesting that they exhibit enhanced DNA binding. DNA cleavage experiments show that all the complexes induce cleavage of pBR322 plasmid DNA, the Me₄phen and 5,6-dmp complexes being remarkably more efficient than other complexes.     

Synthesis and properties of the dichloro [tetramethyl (trifluoromethyl)cyclopentadienyl]ruthenium dimer: X-ray structure of [M2(η-C5Me4CF3)2Cl2(μ-Cl)2] (M=Ru, Rh)

The reaction of RuCl₃(H₂O), with C₅Me₄CF₃J in refluxing EtOH gives [Ru₂(η⁵-C₅Me₁CF₂)₂ (μ-Cl₂] (20 in 44% yield. Dimer 2 antiferromagnetic (−2J=200 cm¹). The crystal structures of 2 (rhombohedral system, R3 space group, Z=9, R=0.0589) and [Rh₂(η⁵-C₅Me₄CF₃(₂Cl₂(μ-Cl)₂] (3) (rhombohedral system. space group, Z = 9, R = 0.0641) were solved; both complexes have dimeric structures with a trans arrangement of the η⁵-C₅Me₄CF₄ rings. Comparison of the geometry of 2 and 3 with those of the corresponding η⁵-C₅Me₅ complexes shows that lowering the ring symmetry causes significant distortion of the M₂(μ-Cl)₂ moiety. The analysis of the MCl₃ fragment conformations in 2 and 3 and in the η⁵-C₅ME₅ analogues shows that they are correlated with the M---M distances. The Cl atoms are displaced by Br on reaction of 2 with KBr in MeOH to give the diamagnetic dimer [Ru₂(η⁵-C₅Me₄CF₃)₂Br₂ (μ-Br₂] (4). Complex 2 reacts with O₂ in CH₂Cl₂ solution at ambient temperature to form a mixture of isomeric η⁶-fulvene dimers [Ru₂(η⁶-C₅Me₃CF₃ = CH₂)₂Cl₂(μ-Cl)₂] (5). Reactions of 5 with CO and allyl chloride give Ru(η⁵-C₅Me₃CF₃CH₂Cl)(CO)₂Cl (6) and Ru(η⁵-C₅Me₃CF₃CF₃CH₂Cl)(η³-C₃H₅)Cl₂ (7) respectively.     

Mixed-metal butterfly acetamidediato clusters derived from a highly reactive ruthenium oxo cluster: synthesis and characterization of [(PPh3)2N][MRu3(CO)12(η-μ3-NC(μ-O)CH3)], (M = Mn or Re)

Analogy with the isolable oxo cluster [Fe₃(CO)₉(μ₃-O)]²⁻, which is structurally interesting and synthetically useful, prompted the present attempt to synthesize its ruthenium analog. Although the high reactivity of [Ru₃(CO)₉(μ₃-O)]²⁻ (I) prevented its isolation, the reaction of this species with [M(CO)₃(NCCH₃)]⁺, where M = Mn or Re, yields [PPN][MRu₃(CO)₁₂(η²-μ₃-NC(μ-O)CH₃]⁻. The high nucleophilicity of the oxo ligand in [Ru₃(CO)₉(μ₃-O)]²⁻ (I) appears to be responsible for the conversion of acetonitrile to an acetamidediato ligand and for the instability of I. The crystal structure of [PPN][MnRu₃(CO)₁₂(η²-μ₃-NC(μ-O)CH₃)]] reveals a hinged butterfly array of metal atoms in which the acetamidediato ligand bridges the two wings with μ₃-N bonding to an Mn and two Ru atoms, and μ-O bonding to an Ru atom.     

Copper(II) complexes with (2-hydroxybenzyl-2-pyridylmethyl)amine–Hbpa: syntheses, characterization and crystal structures of the ligand and [Cu(II)(Hbpa)2](ClO4)2·2H2O

Copper(II) complexes were synthesized and characterized by means of elemental analysis, IR and visible spectroscopies, EPR and electrochemistry, as well as X-ray structure crystallography. The group consists of discrete mononuclear units with the general formula [Cu(II)(Hbpa)₂](A)₂·nH₂O, where Hbpa=(2-hydroxybenzyl-2-pyridylmethyl)amine and A=ClO₄ ⁻, n=2 (1), CH₃COO⁻, n=3 (2), NO₃ ⁻, n=2 (3) and SO₄ ²⁻, n=3 (4). The structures of the ligand Hbpa and complex 1 have been determined by X-ray crystallography. Complexes 1–4 have had their UV–Vis spectra measured in both MeCN and DMF. It was observed that the compounds interact with basic solvents, such that molecules coordinate to the metal in axial positions in which phenol oxygen atoms are coordinated in the protonated forms. The values were all less than 1000 M⁻¹ cm⁻¹. EPR measurements on powdered samples of 1–3 gave g/A values between 105 and 135 cm⁻¹, typical for square planar coordination environments. Complex 4·3H₂O exhibits a behaviour typical for tetrahedral coordination. The electrochemical behaviour for complexes 1 and 2 was studied showing irreversible redox waves for both compounds.     

Mixed anion lanthanide(III) crown ether complexes: crystal structures of [LaCl2(NO3)(12-crown-4)]2, [La(NO3)(OH2)4-(12-crown-4)]Cl2·CH3CN and [LaCl2(NO3)(18-crown-6)]

Reaction of LaCl₃·7H₂O containing small amounts of La(NO₃)₃·7H₂O as an impurity with 12-crown-4 or 18-crown-6 in 3:1 CH₃CN:CH₃OH resulted in the isolation of the mixed anion complexes [LaCl₂(NO₃)(12-crown-4)]₂, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN and [LaCl₂(NO₃)(18-crown-6)]. The nine-coordinate dimer, [LaCl₂(NO₃)(12-crown-4)]₂, has all of the anions in the inner coordination sphere and La³⁺ has a capped square antiprismatic geometry. It crystallizes in the orthorhombic space group Pbca with (at −150 °C) a = 12.938(6), B = 15.704(3), C = 13.962(2) Å, and D_calc = 2.08 g cm⁻³ for Z = 4. The second complex isolated from the same reaction, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN, has the bidentate nitrate anion in the inner coordination sphere but the two chloride anions are in a hydrogen bonded outer sphere. This complex is ten-coordinate 4A,6B-expanded dodecahedral and crystallizes in the monoclinic space group P2₁ with (at 20 °C) A = 7.651(2), B = 11.704(7), C = 11.608(4) Å, β = 95.11(2)°, and D_calc = 1.80 g cm⁻³ for Z = 2. The 18-crown-6 complex, [LaCl₂(NO₃)(18-crown-6)], has all inner sphere anions and has ten-coordinate 4A,6B-expanded dodecahedral La³⁺ centers. It crystallizes in the orthorhombic space group Pbca with (at 20 °C) a = 14.122(7), B = 13.563(5), C = 19.311(9) Å, and D_calc = 1.89 g cm⁻³ for Z = 8.     

Solution and crystal structure of the dihydrogen complex [Ru(H2)(H)(PMe2Ph)4]PF6, an active alkyne hydrogenation catalyst

The complex [Ru(H₂)(H)(PMe₂Ph)₄]PF₆ (1) has been prepared by reaction of [Ru(H)(PMe₂Ph)₅] FP₆ (2) in THF with 1 atm H₂ and characterised by variable temperature ³¹P and ¹H NMR. It undergoes four distinct fluxional processes listed in order of decreasing activation energy: (i) exchange of H₂ in solution with the dihydrogen ligand above 273 K; (ii) isomerisation of cis and trans isomers of 1 above 230 K; (iii) exchange of H atoms between H₂ and hydride in trans-1 above 180 K; (iv) rapid H₂/hydride exchange in cis-1 to below 180 K. A single crystal X-ray diffraction study of 1 at 173 K shows that the complex has the cis geometry in the solid state but does not clearly reveal the positions of the hydrogen ligands. Complex 1 starts out as a catalyst of high activity for the selective hydrogenation of 1-alkynes to 1-alkenes (RC≡CH; R=¹¹Bu, Ph) but it is rapidly deactivated, possibly because of formation of the enynyl complex [Ru(η³RC₃CHR)(PMe₂Ph)₄]⁺. Complex 1 efficiently catalyzes the hydrogenation of internal alkynes (3-hexyne, 2-pentyne) to internal cis-alkenes with little deactivation, although some isomerisation of the alkene produced is observed. These observations are consistent with those of Nkosi, Coville, Albers and Singleton who reported that complex 2 must dissociate one PMe₂Ph ligand to produce the species active for alkyne hydrogenation. Complex 2 catalyses these hydrogenations with slower initial rates than complex 1 but deactivates less readily. In contrast to 1, complex 2 does not appear to cause the isomerisation of internal alkenes.     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.     

Comparison in halide binding ability between the unsaturated clusters [Pd3(μ-dppm)3(CO)] and [PdPtCo(μ-dppm)2(CO)3(CNBu)] (dppm = Ph2PCH2PPh2)

The trinuclear clusters [Pd₃(μ-dppm)₃(CO)]²⁺ and [PtPdCo(μ-dppm)₂(CO)₃(CN^tBu)]⁺ exhibit a large and a small cavity, respectively, formed by the phenyl rings of the bridging diphosphine ligands. Their binding constants (K₁₁) with halide ions (X⁻) were obtained by UV-Vis spectroscopy. The binding ability varies as I⁻ > Br⁻ > Cl⁻, and [Pd₃(μ-dppm)₃(CO)]²⁺ > [ptPdCo(μ-dppm)₂-(CO)₃(CN^tBu)]⁺. The MO diagram for the related cluster [Pd₂Co(μ-dppm)₂(CO)₄]⁺ has been addressed theoretically in order to predict the nature of the lowest energy electronic bands. For this class of compounds, the lowest energy bands are assigned to charge transfers from the Co center to the Pd₂ centers.     

The ReH6[P(C6H5)3]2 ion as a ligand: complexes with M(CO)3 fragments (M = Cr, Mo, W)

The reactions of [(H₅C₆)₃P]₂ReH₆⁻ with (CH₃CN)₃Cr(CO)₃, (diglyme)Mo(CO)₃ or (C₃H₇CN)₃W(CO)₃ led to the formation of [(H₅C₆)₃P]₂ReH₆M(CO)₃⁻ (M = Cr, Mo, W) complexes. These have been characterized by IR and NMR spectroscopies, as well as elemental analyses. A single crystal X-ray diffraction study has also been carried out for the M = Cr complex as a K(18-crown-6)⁺ salt. The complex crystallizes as a THF monosolvate in the monoclinic space group P2₁/n with a = 22.323(6), B = 9.523(2), C = 27.502(5) Å, β = 104.98(2)⁰ and V = 5648 ų for Z = 4. The Re---Cr separation is 2.5745(12) Å, and the two phosphine ligands are oriented unsymmetrically. Although the hydride ligands were not found, the presence of three bridging hydrides and a dodecahedral coordination geometry about rhenium could be inferred. Low temperature ¹H and ³¹P NMR spectroscopic studies did not reveal the low symmetry of the solid state structure.     

The synthesis of the tripodal phosphine CH3C{CH2P(m-CF3C6H4)2}3 and its rhodium coordination chemistry

The new tripodal phosphine CH₃C{CH₂P(m-CF₃C₆H₄)₂}₃, CF₃PPP, was prepared by reacting CH₃C(CH₂Br)₃ with Li⁺P(m-CF₃C₆H₄)₂⁻, the latter being best obtained by adding Li⁺NⁱPr₂⁻ to PH(m-CF₃C₆H₄)₂. The rhodium complexes [RhCl(CO)(CF₃PPP)], [Rh(LL)(CF₃PPP)](CF₃SO₃) (LL = 2 CO or NBD), [RhX₃(CF₃PPP)], [RhX(MeCN)₃(CF₃PPP)](CF₃SO₃)₂ (X = H and Cl), [RhCl₂(MeCN)(CF₃PPP)](CF₃SO₃) and [Rh(MeCN)₃(CF₃PPP)](CF₃SO₃)₃ were prepared and characterized. The X-ray crystal structure of [Rh(NBD)(CF₃PPP)](CF₃SO₃) is reported. The lower oxygen sensitivity of the CF₃PPP rhodium(I) complexes, relative to the corresponding species with the parent ligand CH₃C(CH₂PPh₂)₃, is attributed to the higher effective nuclear charge on the metal centers caused by the presence of the six CF₃ substituents on the terdentate phosphine. A similar effect may be responsible for the easier hydrolysis of the CF₃PPP-containing, cationic rhodium(III) complexes relative to the corresponding compounds of the parent ligand.     

First- and second-order mechanisms for oxidative addition for bound methyl disulfide in the complex W(CO)3(phen)(MeSSMe)

The rate of oxidative addition of methyl disulfide in the complex W(CO)₃(1,10-phenanthroline) (MeSSMe) in methylene chloride has been studied. The dominant reaction pathway is second order in metal complex and inhibited by excess methyl disulfide. Formation of a dinuclear complex [W(CO)₃(phen)]₂(MeSSMe) is proposed to lead to the transition state for cleavage of the sulfur-sulfur bond in the second-order mechanism. In neat methyl disulfide, or in concentratred solutions of methyl disulfide at low metal complex concentrations, the reaction occurs at reduced rate and follows a first-order mechanism. Addition of Mo(CO)₃(1,10-phenanthroline) (MeSSMe) to the corresponding tungsten complex results in a ten-fold increase in the rate of oxidative addition of the tungsten complex and production of Mo(CO)₄(1,10-phenanthroline) as the sole molybdenum-containing product. The faster rate of reaction in the presence of the molybdenum complex is attributed to the faster formation of the heteronuclear dinuclear intermediate by initial loss of MeSSMe from the molybdenum versus tungsten center. Additional kinetic/mechanistic studies are described using a new flow-through FT-IR/microscope reaction system designed to allow convenient monitoring of small quantities of sensitive/hazardous reactants.     

Ligand connected metal clusters. The molecular structures and solid state packing of {Ru3(CO)11}2(bis(diphenylphosphino)ethane) and {Ru3(CO)11}2(1,4-bis(diphenylphosphino)benzene)

The preparation and structural characterization of {Ru₃(CO)₁₁}₂(1,4-bis(diphenylphosphino)benzene), a modified synthesis of 1,4-bis(diphenylphosphino)benzene, and the structural characterization of {Ru₃(CO)₁₁}₂(bis(diphenylphosphino)ethane) are reported. In both compounds two metal cluster units are connected through ditertiary-phosphine ligands. Both molecules consist of centrosymmetric units in which the diphosphine ligands are largely covered by the triangular ruthenium clusters. No direct interaction between the two cluster units occurs within individual molecules. Molecular packing in the solid state is dominated by interactions between sets of carbon monoxide ligands in motifs that were previously identified in the solid state structure of the parent cluster, Ru₃(CO)₁₂.     

Syntheses and structures of palladium(II) and platinum(II) complexes with tridentate (Ph2PCH2CH2CH2)2S and its arsenic analogue

A series of square-planar complexes [MLCl]ClO₄ (M = Pd(II), Pt(II); L = bis(3-(diphenylphosphino)propyl)sulfide (psp), bis(3-(diphenylarsino)propyl)sulfide (asa)) have been prepared and characterized. The X-ray crystal structures of two of them have been determined: [Pd(psp)Cl]ClO₄, P2₁/c, A = 12.519(2), B = 15.766(2), C = 16.501(2) Å, β = 105.22(1)°, Z = 4; and [Pt(asa)Cl]ClO₄, P2₁/c, a = 12.583(5), B = 16.007(6), C = 16.549(6) Å, β = 104.89(3)°, Z = 4. In both structures, there is a conformational disorder between the chair and skew-boat orientation in one of the two six-membered chelate rings. The C---H…O hydrogen bond between the hybrid ligand and the perchlorate counter ion that induces the conformational disorder is discussed.     

Variation of DNA photocleavage efficiency for [(TL)2Ru(dpp)]Cl2 complexes where TL=2,2'-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

The complexes [(bpy)₂Ru(dpp)]Cl₂, [(phen)₂Ru(dpp)]Cl₂, and [(Ph₂phen)₂Ru(dpp)]Cl₂ (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Ph₂phen = 4,7-diphenyl-1,10-phenanthroline) have been investigated and found to photocleave DNA via an oxygen-mediated pathway. These light absorbing complexes possess intense metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum. The [(TL)₂Ru(dpp)]²⁺ systems populate ³MLCT states after visible light excitation, giving rise to emissions in aqueous solution centered at 692, 690, and 698 nm for TL = bpy, phen, and Ph₂phen respectively. The ³MLCT states and emissions are quenched by O₂, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph₂phen)₂Ru(dpp)]²⁺ > [(phen)₂Ru(dpp)]²⁺ > [(bpy)₂Ru(dpp)]²⁺. The presence of the polyazine bridging ligand will allow these chromophores to be incorporated into larger supramolecular assemblies.     

The new enneanuclear nickel carbonyl anion [Ni9(CO)16] and its relationships with the [Ni12(CO)21] and [Ni6Rh3(CO)17] clusters

The reaction of [N(PPh₃)₂]₂[Ni₆(CO)₁₂] with Cu(PPh₃)_xCl (x=1, 2), as well as the degradation of [N(PPh₃)₂]₂[H₂Ni₁₂(CO)₂₁] with PPh₃, affords the new and unstable dark orange–brown [N(PPh₃)₂]₂[Ni₉(CO)₁₆].THF salt in low yields. This salt has been characterized by a CCD X-ray diffraction determination, along with IR spectroscopy and elemental analysis. The close-packed two-layer metal core geometry of the [Ni₉(CO)₁₆]²⁻ dianion is directly related to that of the bimetallic [Ni₆Rh₃(CO)₁₇]³⁻ trianion and may be envisioned to be formally derived from the hcp three-layer geometry of [Ni₁₂(CO)₂₁]⁴⁻ by the substitution of one of the two outer [Ni₃(CO)₃(μ−CO)₃]²⁻ layers with a face-bridging carbonyl group.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.     

Studies of the oxovanadium(IV)—oxalate system: syntheses and crystal structures of binuclear (Ph4P)2[(VO)2(H2O)2(C2O4)3]·4H2O and of the one-dimensional chain material, (Ph4P)[VOCl(C2O4)]

The hydrothermal reactions of (Ph₄P)[VO₂Cl₂] and H₂C₂O₄ at 150 and 125°C yield (Ph₄P)₂[V₂O₂(H₂O)₂(C₂O₄)₃]·4H₂O (1) and (Ph₄P)[VOCl(C₂O₄)] (2), respectively. The structure of the molecular anion of 1 consists of a binuclear unit of oxovanadium(IV) octahedra bridged by a bisbidentate oxalate group. The VO₆ coordination geometry at each vanadium site is defined by a terminal oxo group, an aquo ligand, and four oxygen donors — two from the bisbidentate bridging oxalate and two from the terminal bidentate oxalate. The structure of 2 consists of discrete Ph₄P⁺ cations occupying regions between [VOCl(C₂O₄)]⁻_∞ spiral chains. The structure of the one-dimensional anionic chain exhibits V(IV) octahedra bridged by bisbidentate oxalate groups. Crystal data: 1·4H₂O, monoclinic P2₁/n, A = 12.694(3), B = 12.531(3), C = 17.17(3) Å, β = 106.32(2)°, V = 2621.3(13) ų, Z = 2, D_calc = 1.501 g cm⁻³, structure solution and refinement converged at a conventional residual of 0.0518; 2, tetragonal P4₃, A = 12.145(2), C = 15.991(3) Å, V = 2358.7(12) ų, Z = 4, R = 0.0452.     

Isolation of a thermodynamically unfavorable [Ni(DACO)2] complex and its isomer: syntheses, characterization, crystal structures and theoretical study (DACO=1,5-diazacyclooctane)

Two Ni^II complexes of 1,5-diazacyclooctane (DACO), [Ni(DACO)₂]Br₂ (I) and [Ni(DACO)₂]Br·ClO₄ (II) have been newly synthesized and characterized. Single crystal X-ray diffraction analysis of DACO and both Ni^II complexes reveals that DACO takes boat/chair conformation in the solid state and its Ni^II complexes. In complex I, Ni^II ion is at the center of symmetry, which is four-coordinated by nitrogen donors of DACO. However, in complex II, an unexpected coordination mode of [M(DACO)₂]²⁺ (M=Cu^II and Ni^II) was found, in which two DACO ligands are related to each other by a mirror plane and the coordination sphere of Ni^II is a distorted planar geometry. Furthermore, complexes I and II form quite different packing patterns (macrocycle or chain) through hydrogen bonds, which may be a key role to stabilize the crystals. The results of theoretical calculation indicate that complex I has thermodynamic stability, while II has chemical stability. Therefore, both of them have the probability to be obtained from different reaction processes or conditions.