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In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on their excited state properties. Hence, a detailed analysis of the different synthetic pathways is presented; the photophysical properties were studied by using steady-state and time-resolved photoluminescence spectroscopy. We determined the absorption and emission spectra, the photoluminescence efficiencies, and the excited state lifetimes of the complexes in fluid solutions at room temperature and frozen glassy matrices at 77 K. Finally, a structure–property relationship was established, showing that the decoration of the bridging unit on the tridentate luminophores only marginally affects the excited state properties, whereas the double cyclometallation related to the tetradentate chelator prolongs the excited state lifetime and increases the photoluminescence quantum yield.

CoIn2 (Z. Metallkd. 1970, 61, 342–343) forms by reaction of the elements at 1470 K followed by annealing at 770 K for five days. The room temperature structure is orthorhombic (CuMg2 type, Fddd, a = 529.95(10), b = 940.49(13), c = 1785.8(3) pm, wR2 = 0.0563, 444 F 2 values, 17 variables) and shows a phase transition at 195(1) K (DSC data). The low-temperature modification crystallizes in the translationengleiche monoclinic subgroup C2/c and exhibits a new structure type (a = 933.7(7), b = 526.91(10), c = 1000.8(2) pm, β = 117.81(5)°, wR2 = 0.0374, 843 F 2 values, 30 variables). The structural phase transition is a consequence of a Peierls type distortion. The equidistant cobalt chains in HT-CoIn2 (270.1 pm, 175.2° Co–Co–Co) show pairwise dislocation in LT-CoIn2 with shorter (252.4 pm) and longer (284.1 pm) Co–Co distances. Each cobalt atom has coordination number 10 in the form of slightly distorted square antiprisms of indium, capped by cobalt on the rectangular faces. Density-of-states calculations reveal metallic behavior for both modifications. Integrated crystal orbital overlap populations featuring the bonding characteristics indicate a slightly higher intensity area for LT-CoIn2 along with a shift to lower energy, manifesting the stabilization by pair formation through Peierls distortion.

Phase analytical studies in the Sc–Cu–In system led to samples of the solid solutions ScCu1–x–y In1+x and ScCu2–x In which were studied by X-ray powder diffraction. At room temperature the compounds ScCu1–x–y In1+x crystallize with the ZrNiAl type, space group P 6 ‾ $\overline{6}$ 2m. Exemplarily, the structure of ScCu0.76In1.17 was refined from single crystal X-ray diffractometer data, revealing strong anisotropic displacements for the scandium atoms and a mixed occupied Cu/In site. Superstructure formation is observed at low temperatures. The ScCu0.78In1.14 and ScCu0.76In1.16 structures were refined from diffraction data recorded at 90 K. Both compounds adopt the HfRhSn type, space group P 6 ‾ $\overline{6}$ 2c, a klassengleiche subgroup of index 2; doubling of the subcell c axis. The Cu/In filled trigonal Sc6 prisms are strongly distorted in the superstructure, resulting from pairwise dislocation of the Cu/In atoms from ideal positions within an equidistant chain to shorter (311.0 pm) and longer (392.8 pm) Cu/In–Cu/In distances. Single crystal data of the Heusler phases ScCu1.95In and ScCu1.94In show small degrees of copper vacancies.

A series of Pd(ii) and Pt(ii) complexes bearing tetradentate ligands as dianionic luminophores were synthesized and their room-temperature photoluminescence in PMMA films as well as in mechanochromic crystalline phases was correlated with molecular structure.

The equiatomic metal-rich phosphide NbCrP shows a structural phase transition around 125 K. The structures of the high- and low-temperature modifications were refined from single crystal X-ray diffractometer data of an un-twinned crystal: TiNiSi type, Pnma, a = 619.80(2), b = 353.74(4), c = 735.24(6) pm, wR = 0.0706, 288 F 2 values, 20 variables at 240 K and P121/c1, a = 630.59(3), b = 739.64(4), c = 933.09(5) pm, β = 132.491(6)°, wR = 0.0531, 1007 F 2 values, 57 variables at 90 K. The structural phase transition is of a classical Peierls type. The equidistant chromium chain in HT-NbCrP (353.7 pm Cr–Cr) splits pairwise into shorter (315.2 pm) and longer (373.2 pm) Cr–Cr distances. This goes along with a strengthening of Cr–P bonding. The superstructure formation is discussed on the basis of a group–subgroup scheme. Electronic structure calculations show a lifting of band degeneracy. Protection of the non-symmorphic symmetry of space group Pnma is crucial for the phase transition. The estimated charge modulation is consistent with the interpretation as Peierls transition.

The equiatomic indide ScPtIn (ZrNiAl type, space group P 6 ‾ $‾{6}$ 2m) shows an extended solid solution Sc3Pt3–xIn3. Several samples of the Sc3Pt3–xIn3 series were synthesized from the elements by arc-melting and subsequent annealing, or directly in a high frequency furnace. The lowest platinum content was observed for Sc3Pt2.072(3)In3. All samples were characterized by powder X-ray diffraction and their lattice parameters and several single crystals were studied on the basis of precise single crystal X-ray diffractometer data. The correct platinum occupancy parameters were refined from the diffraction data. Decreasing platinum content leads to decreasing a and c lattice parameters. Satellite reflections were observed for the Sc3Pt3–xIn3 crystals with x = 0.31–0.83. These satellite reflections could be described with a modulation vector ( 1 3 , 1 3 , γ ) $\left(\frac{1}{3},\frac{1}{3},\gamma \right)$ ( γ = 1 2 $\gamma =\frac{1}{2}$ c* for all crystals) and are compatible with trigonal symmetry. The interplay of platinum filled vs. empty In6 trigonal prisms is discussed for an approximant structure with space group P3m1.

The structures of the equiatomic stannides RERhSn with the smaller rare earth elements Y, Gd-Tm and Lu were reinvestigated on the basis of temperature-dependent single crystal X-ray diffraction data. GdRhSn crystallizes with the aristotype ZrNiAl at 293 and 90 K. For RE = Y, Tb, Ho and Er the HP-CeRuSn type (approximant with space group R3m) is already formed at room temperature, while DyRhSn adopts the HP-CeRuSn type below 280 K. TmRhSn and LuRhSn show incommensurate modulated variants with superspace groups P31m(1/3; 1/3; γ) 000 (No. 157.1.23.1) (γ = 3/8 for TmRhSn and γ = 2/5 for LuRhSn). The driving force for superstructure formation (modulation) is a strengthening of Rh–Sn bonding. The modulation is expressed in a 119Sn Mössbauer spectrum of DyRhSn at 78 K through line broadening.

The scandium-rich indide Sc50Pt13.47In2.53 was obtained by induction melting of the elements and subsequent annealing. The structure of Sc50Pt13.47In2.53 has been refined from single-crystal X-ray diffractometer data: Fm 3 ¯ $\overline{3}$ , a = 1774.61(3) pm, wR2 = 0.0443, 1047 F2 values and 35 variables. Sc50Pt13.47In2.53 is isopointal with the intermetallic phases Sc50Co12.5In3.5, Sc50Rh13.3In2.7, Sc50Ir13.6In2.4, Ag7+xMg26−x and Ga4.55Mg21.85Pd6.6 (Pearson code cF264 and Wyckoff sequence ih 2 fecba). Two of the eight crystallographic sites in the structure show mixed occupancies: M1 (≡Pt20.70In10.30) and M2 (≡Pt30.76In20.24). The structure contains four basic polyhedra: M2@Sc8 cubes, Pt1@Sc10 sphenocorona and slightly distorted M1@Sc12 and In3@Sc12 icosahedra. The polyhedra are condensed via common scandium corners and edges. The various Sc–Sc distances range from 302–334 pm and are indicative of substantial Sc–Sc bonding, stabilizing the Sc50Pt13.47In2.53 structure.

The quaternary gallium-rich intermetallic phases RE 2Pt3Ga4In with RE = Y and Gd-Tm were synthesized by arc-melting of the elements and subsequent annealing. Small single crystals were obtained by high-frequency annealing of the samples in sealed tantalum ampoules. The polycrystalline samples were characterized through their X-ray powder patterns. The RE 2Pt3Ga4In phases crystallize with a site ordering variant of the orthorhombic Y2Rh3Sn5 type, space group Cmc 21. The structures of Gd2Pt3Ga4In, Dy2Pt3Ga4.14In0.86, Er2Pt3Ga4.17In0.83 and Tm2Pt3Ga4.21In0.79 were refined from single-crystal X-ray diffraction data. The single crystals reveal small homogeneity ranges RE 2Pt3Ga4±xIn1±x. The striking geometrical structural building units are slightly distorted trigonal prisms around the three crystallographically independent platinum atoms: Pt1@RE 4Ga2, Pt2@RE 2Ga4 and Pt3@RE 2Ga2In2. Based on these prismatic building units, the RE 2Pt3Ga4In structures can be described as intergrowth variants of TiNiSi and NdRh2Sn4 related structural slabs. Temperature dependent magnetic susceptibility studies of Gd2Pt3Ga4In and Tb2Pt3Ga4In show Curie-Weiss behavior and the experimental magnetic moments confirm stable trivalent gadolinium respectively terbium. Gd2Pt3Ga4In and Tb2Pt3Ga4In order antiferromagnetically at T N = 15.8(1) and 26.0(1) K. Magnetization curves at 3 K show field-induced spin reorientations.

Systematically twinned olivenite (Cu2(AsO4)OH) single crystals from Cap Garonne, Mine du Pradet, France, were studied by X-ray diffraction: P 21/n, a = 822.69(6) pm, b = 861.88(9) pm, c = 594.06(9) pm, β = 90.000(6)°, wR = 0.0224, 1621 F 2 values, 79 variables and a domain ratio of 0.501(1)/0.499(1). The temperature dependence of the magnetic susceptibility was well reproduced with a square-spin cluster model and an antiferromagnetic spin-exchange parameter of J/k B = 157(3) K.

The germanides Sr3Pd4Ge4 and BaPdGe were obtained from high-temperature reactions in sealed niobium ampoules and their structures have been determined from single-crystal X-ray diffraction data: a=444.2(1), b=438.1(1), c=2472.2(7) pm, space group Immm, U3Ni4Si4 type, wR2=0.0471, 576 unique reflections, 25 parameters for Sr3Pd4Ge4 and a=677.09(8), space group P213, LaIrSi type, wR2=0.0322, 409 unique reflections, nine parameters for BaPdGe. Both germanides have pronounced three-dimensional [Pd4Ge4] δ− and [PdGe] δ− polyanionic networks with Pd–Ge bonding interactions. This is confirmed by the density functional theory (DFT)-based electronic structure investigations, the trends of charge transfer and crystal orbital overlap population (COOP) analyses.

Three new complexes bearing the tridentate hydrazone-based ligand 2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)pyridine (L) were synthesized and structurally characterized. Biological tests indicate that the Zn(II) complex [ZnCl2(L)] is of low cytotoxicity against the hepatocellular carcinoma cell line HepG2. In contrast, the Cu(II) and Mn(II) complexes [CuCl2(L)] and [MnCl2(L)] are highly cytotoxic with EC50 values of 1.25 ± 0.01 μM and 20 ± 1 μM, respectively. A quantitative proteome analysis reveals that treatment of the cells with the Cu(II) complex leads to a significantly altered abundance of 102 apoptosis-related proteins, whereas 38 proteins were up- or down-regulated by the Mn(II) complex. A closer inspection of those proteins regulated only by the Cu(II) complex suggests that the superior cytotoxic activity of this complex is likely to be related to an initiation of the caspase-independent cell death (CICD). In addition, an increased generation of reactive oxygen species (ROS) and a strong up-regulation of proteins responsive to oxidative stress suggest that alterations of the cellular redox metabolism likely contribute to the cytotoxicity of the Cu(II) complex.

The YCrB4 type borides YTB4 (T = Mo, W, Re) were synthesized from the elements by arc-melting and subsequent annealing. The structures were refined from single crystal X-ray diffractometer data: Pbam, a = 602.84(8), b = 1164.5(1), c = 361.20(4) pm, wR2 = 0.0404, 624 F2 values, 26 variables for YMoB4, a = 603.00(7), b = 1165.1(1), c = 360.63(6) pm, wR2 = 0.0487, 474 F2 values, 26 variables for YWB4, and a = 596.67(6), b = 1154.4(1), c = 360.21(4) pm, wR2 = 0.0465, 544 F2 values, 26 variables for YReB4. The boron atoms build up planar networks which are a tessellation of slightly distorted pentagons and heptagons. Adjacent networks coordinate the transition metal and yttrium atoms in the form of pentagonal and heptagonal prisms, respectively. The four crystallographically distinct boron sites are differentiated by high-resolution 11B solid state isotropic magnetic shifts and nuclear electric quadrupolar coupling constants. Partial site assignments are possible based on comparisons with electric field gradient calculations using the WIEN2k code. 89Y MAS NMR spectroscopic studies suggest substantially weaker Knight shift contributions to the resonance frequencies when compared to other intermetallic yttrium compounds, including other ternary yttrium boride compounds measured previously.

Hydroalumination of H10C5N–N=C(Ad) with HAliBu2 yielded the hydrazide H10C5N–N(AliBu2)Ad (4; Ad = adamantyl, NC5H10 = piperidinyl). Compound 4 is monomeric and contains a highly strained AlN2 heterocycle formed by a donor–acceptor interaction between the Al atom and the β-N atom of the hydrazine. Two equivalents of the hydride afforded an adduct with an HAliBu2 molecule coordinated to 4 by an Al–N and a 3c–2e Al–H–Al bond (5). tBuN=C=O did not insert into the relatively weak AlN donor–acceptor bond of 4; instead, insertion into the shorter Al–N(amide) bond yielded five-membered AlN3C heterocycle 6 with an exocyclic C=O group. PhN=C=O showed a similar reaction, but the product 7 was dimeric in the solid state with two Al–O bonds. Reaction in a 1:2 ratio afforded a unique linear dimer of phenyl isocyanate, which is stabilised by the aluminium hydrazide (8). Isothiocyanates gave thiosemicarbazides 9–11, which have Al atoms coordinated in a chelating manner by formation of AlSCN heterocycles and show fascinating differences in their bonding situation.

6-(3,5-Dimethylpyrazol-1-yl)purine has recently been introduced as an artificial nucleobase for the specific recognition of canonical nucleobases via the formation of a metal-mediated base pair. We report here the synthesis and structural characterization by single crystal X-ray diffraction analysis of a series of metal complexes of the corresponding alkylated model nucleobases 9-methyl-6-(3,5-dimethylpyrazol-1-yl)purine 2 and 9-methyl-6-pyrazol-1-yl-purine 7. The sterically more demanding ligand 2 forms the Cu(2+) complexes [Cu(2)(NO3)2] and [Cu(2)Cl2] with a 1:1 stoichiometry of ligand and metal ion. In contrast, ligand 7 forms complexes [Cu(7)2(NO3)](NO3) and [Ag(7)2](ClO4) with a 2:1 stoichiometry. The molecular structures of [Cu(2)(NO3)2] and [Cu(2)Cl2] confirm the previously suggested coordination pattern, i.e. Cu(2+) is coordinated via the pyrazole nitrogen atom and the purine N7 position. The fact that different relative orientations of the two ligands in [Cu(7)2(NO3)](NO3) and [Ag(7)2](ClO4) are observed allows the prediction that the corresponding metal-mediated homo base pairs should be stable both in regular antiparallel-stranded and in the rare parallel-stranded double helices.

A CuII hydrazone complex has been synthesized that can be reduced in situ in boiling methanol to give the corresponding CuI complex. The latter complex readily activates dioxygen under ambient conditions, as was unambiguously shown by isotopic labeling studies. As a consequence of the dioxygen activation, the thienyl moiety appended to the hydrazone ligand is easily oxidized in β position (C–H C–O), finally leading to a change in the coordination environment of the central metal ion. All relevant complexes have been structurally characterized by single-crystal X-ray diffraction analyses. The hydrazone ligand applied in this study does not mimic a biologically relevant coordination motif in copper-containing oxygenases. Nonetheless, the reactivity of the CuI complex resembles that found in many oxygenases, indicating that hydrazone ligands may be well-suited for the generation of novel bioinspired oxidation catalysts.

Hydrogallation of the dialkynylbenzenes 1,3-(R2R′Si-C≡C)2C6H4 (3: R = Me, R′ = Ph; 4: R = Ph, R′ = Me) with dichlorogallane, H-GaCl2, afforded the corresponding dialkenylbenzenes 5 and 6, with GaCl2 groups geminal to the silyl substituents. Compound 6 was characterised by crystal structure determination, which revealed intramolecular bridging of both gallium atoms by two chlorine atoms as a new structural motif. Treatment of 5 and 6 with six equivalents of ethyllithium gave unprecedented heterocyclic digallanates 7 and 8, in which two four-coordinate gallium atoms were bridged by two 1,3-dialkenylbenzene spacer ligands. The obtained large heterocycles encapsulated two lithium counterions in their molecular cavities. The lithium atoms were coordinated in a cryptand-like fashion and showed a variety of short contacts to aromatic rings, alkenyl groups, and α-carbon atoms of terminal ethyl groups. They could be removed from the molecular cavity by coordination with chelating 1,2-dimethoxyethane ligands. Heating of digallanates 7 and 8 in toluene to more than 100 °C over a period of 5 h resulted in fascinating transformations with C–H bond activation and ortho-metallation. Five-membered GaC4 metallacycles were formed, which had a terminal R2R′Si-CH=CH- group resulting from the formal protolytic cleavage of an alkenyl–gallium bond by the ortho-hydrogen atom.

A family of five tridentate hydrazone-based ligands with an N,N,N-, N,N,O- or N,N,S-donor environment is reported. The tridentate ligands are derived from either 2-(1-methylhydrazinyl)pyridine or 2-hydrazinylpyridine and have been obtained by condensation with a series of aldehydes and ketones carrying one potential metal-binding site. To study their metal complexation behaviour, the five ligands and one of the bidentate precursor compounds have been reacted with ten different transition and main group metal ions. An interesting chromogenic behaviour has been found: ligands 1, 3 and H6 (with an N,N-, N,N,N- and N,N,O-donor environment) give very specific colour changes in the presence of Fe2+, whereas ligand H7 specifically forms a dark brown coloured complex with Co2+ only. All ligands form yellow to orange complexes with Pd2+. Three of these metal complexes were characterized by single-crystal X-ray diffraction analysis: the molecular structures of [Pd(1)Cl2], [Cu(1)Cl2]2, and [Cu(6)Cl] give an insight into the metal-binding behaviour of the ligands and nicely confirm the bidentate binding of ligand 1 and the tridentate binding of the deprotonated ligand 6−. It is proposed that the chromogenic behaviour of the ligands can be useful for the development of selective metal ion sensors.

The tetraalkyldigallium(II) compound R2Ga–GaR2 (1) [R = CH(SiMe3)2] reacted with amino and hydroxo functionalized carboxylic acids by retention of the Ga–Ga bond and release of CH2(SiMe3)2. New heterocyclic or cage-like compounds were formed with three, two, or six Ga–Ga bonds in a single molecule. The latter dodecagallium compounds encapsulated THF or dioxane molecules in their molecular cavities (carcerands), the other compounds have up to six THF molecules coordinated by N–H···O hydrogen bonds.

A versatile design strategy is presented towards new monoanionic pincer luminophores, showing that cyclometallating C^N^N ligands can yield phosphorescent Pt(II) complexes even if a neutral 1,2,3-triazole ring is inserted by click chemistry. The overall charge, intermolecular interactions and excited state properties can be manipulated and controlled by varying the nature of the ancillary ligand, and its effect on the structural and the triplet state characteristics can be thoroughly investigated and correlated by means of theory and spectroscopy.

Treatment of the tetraalkyldigallium compound R2Ga–GaR2 (1) [R = CH(SiMe3)2] with functionalized dicarboxylic acids (2,2′-bipyridyl-3,3′-dicarboxylic acid, 2,2′-iminodibenzoic acid, 2,2′-dithiodibenzoic acid) resulted in the formation of large heterocycles in which two Ga–Ga bonds were bridged by two dicarboxylato spacer ligands. Each Ga–Ga bond was bridged by two carboxylate groups in an almost ideal perpendicular arrangement that favors the formation of macrocyclic structures. The N–H groups of the imino-bridged compound pointed towards the center of the molecule and formed a network of hydrogen bonds through interactions with carboxylate oxygen atoms. Both disulfur groups of the dithio derivative adopted an ideal coplanar arrangement and came into relatively close contact, which might indicate a weak closed-shell bonding interaction between the sulfur atoms.

The bisimidazolium salt H2-1(PF6)2 featuring a bridging 1,4-phenylene group reacts with 0.5 equiv of [PdCl(allyl)]2 in the presence of Cs2CO3 to give the dinuclear complex [2](PF6)2, whereas the reaction of the same bisimidazolium salt with 0.5 equiv of [Ir(Cl)2(Cp*)]2 yields the mononuclear orthometalated complex [3]PF6 with one remaining imidazolium unit. The unreacted imidazolium group in complex [3]PF6, however, can also be metalated with RhIII to yield the doubly orthometalated heterobimetallic complex [4]. In complex [4], each MIII center (M = IrIII and RhIII) is coordinated by one NHC unit and orthometalates the central aryl ring of the ligand.

A new family of hydrazone-based nucleosides for use in metal-mediated base pairs was devised. The artificial nucleobases are derivatives of the papy ligand (papy = pyridinecarboxaldehyde-2′-pyridylhydrazone). By replacing the pendant pyridine moiety in papy by furan and thiophene, respectively, tridentate nucleosides with N, N, N-, N, N, O- and N, N, S-donor sites were obtained. As only a few transition metal complexes with pendant furan ligands have been reported, a model nucleobase for the N, N, O-donor nucleoside was synthesized. The molecular structures of its Cu2+, Ni2+, and Co2+ complexes are reported. In all complexes, only weak M–O(furan) bonding is observed. The Co2+ complex displays a pentagonal bipyramidal coordination arrangement. In general, the structures of the metal complexes suggest that the respective nucleosides can be applied in metal-mediated base pairs.

Reaction of 2-azidoethyl isocyanide 1, 2-azidophenyl isocyanide 2, or 2-nitrophenyl isocyanide 3 with complexes [Mo(CO)3(dppe)(py)] [4] or [W(CO)3(dppe)(N≡CCH3)] [5] yields the isocyanide complexes [Mo(CO)3(dppe)(C≡NR)] ([6]: C≡NR = 1; [12]: C≡NR = 2; [13]: C≡NR = 3) and [W(CO)3(dppe)(C≡NR)] ([7]: C≡NR = 1; [14]: C≡NR = 2; [15]: C≡NR = 3). Reduction of the nitro or azido groups attached to the isocyanide ligands by Zn/NH4Cl (azidoethyl or azidophenyl isocyanides) or Raney-nickel/hydrazine hydrate (nitrophenyl isocyanide) yields exclusively the complexes bearing the 2-amino-functionalized isocyanides. The normally unstable 2-amino-functionalized isocyanides are stabilized by M→C≡NR back-bonding, which deactivates the isocyanide carbon atom for an intramolecular nucleophilic attack by the primary amine.

The design of multinuclear metal complexes requires a match of the ligand-to-metal vectors and the preferred coordination geometries of the metal ions. Only a few ligands are known with a parallel orientation of N→M vectors that brings the metal ions into close proximity. We establish here the adenine derivative 1,N(6)-ethenoadenine (εA) as an ideal bis(monodentate) ligand. Scanning tunneling microscope images of alkylated εA on graphite surface clearly indicate that these ligands bind to Ag(I) ions. The molecular structures of [Ag2(1)2](ClO4)2 and [Ag2(2)2](ClO4)2 (1, 9-ethyl-1,N(6)-ethenoadenine; 2, 9-propyl-1,N(6)-propylenoadenine) confirm that dinuclear complexes with short Ag···Ag distances are formed (3.0256(3) and 2.984(1) Å, respectively). The structural motif can be extended to divalent metal ions, as was shown by determining the molecular structure of [Cu2(1)2(CHO2)2(OH2)2](NO3)2·2H2O with a Cu···Cu distance of 3.162(2) Å. Moreover, when introducing the 1,N(6)-ethenoadenine deoxyribonucleoside into parallel-stranded DNA duplexes, even dinuclear Ag(I)-mediated base pairs are formed, featuring the same transoid orientation of the glycosidic bonds as the model complexes. Hence, 1,N(6)-ethenoadenine and its derivatives are ideally suited as bis(monodentate) ligands with a parallel alignment of the N→M vectors for the construction of supramolecular metal complexes that require two metal ions at close distance.

Treatment of the tetraalkyldigallium(4) compound R2Ga–GaR2 [1; R = CH(SiMe3)2] with the highly functionalized acids 3- and 4-carboxyphenylthiourea, 7-azaindole-3-carboxylic acid, and 6-aminonicotinic acid afforded macrocyclic compounds in which two or four Ga–Ga bonds are bridged by the respective number of organic spacer ligands. In each reaction two equivalents of CH2(SiMe3)2 per formula unit of 1 were released. The Ga–Ga bonds of the products 2 to 5 are bridged by a carboxylato group and a chelating ligand containing two nitrogen donor atoms or the sulfur and nitrogen atoms of a thiourea group. The thiourea derivatives afforded different species with four or eight gallium atoms in the heterocycles (2 and 3) depending on their substitution patterns (1,3- versus 1,4-positions at the benzene rings). Supramolecular aggregates resulted that had up to 12 THF molecules encapsulated in the heterocycles or bonded to the surface of the molecules via hydrogen bonding or orthogonal dipolar interactions.

Metal-mediated base pairs can be used to insert metal ions into nucleic acids at precisely defined positions. As structural data on the resulting metal-modified DNA are scarce, appropriate model complexes need to be synthesized and structurally characterized. Accordingly, the molecular structures of nine transition metal complexes of N-methyl-2,2’-dipicolylamine (dipic) are reported. In combination with an azole-containing artificial nucleoside, this tridentate ligand had recently been used to generate metal-mediated base pairs (Chem. Commun. 2011, 47, 11041–11043). The PdII and PtII complexes reported here confirm that the formation of planar complexes (as required for a metal-mediated base pair) comprising N-methyl-2,2’-dipicolylamine is possible. Two HgII complexes with differing stoichiometry indicate that a planar structure might also be formed with this metal ion, even though it is not favored. In the complex [Ag2(dipic)2](ClO4)2, the two AgI ions are located close to one another with an Ag···Ag distance of 2.9152(3) A, suggesting the presence of a strong argentophilic interaction.

Treatment of diphenyl–diethynylsilanes, (H5C6)2Si(C≡C–R′)2 (R′ = –C6H5, –4-Me–C6H4), with two equivalents of dialkylaluminium hydrides, R2Al–H (R = –CMe3, –CH2CMe3), afforded the corresponding dialkenylsilanes (3–5) by hydroalumination. The mixed alkenyl–alkynyl compounds resulting from the reduction of only one C≡C triple bond occurred as intermediates. Two of these (1 and 2) were isolated and characterized by crystal structure determinations. They show close interactions of the α-carbon atoms of the ethynyl groups with the coordinatively unsaturated aluminium atoms and a cis arrangement of H and Al atoms across the C=C double bonds. cis/trans Rearrangement took place upon the formation of the dialkenyl species 3–5 with an all-trans configuration of the alkenyl groups. These compounds have two tricoordinate aluminium atoms and are ideally preorganized to be applied as chelating Lewis acids, as was shown with the chelating coordination of chloride ions (compound 6). Rearrangement and 1,1-carbalumination was observed upon heating of a mixed alkenyl–alkynylsilane (7). A silacyclobutene derivative (8) was isolated, which has a SiC3 heterocycle and an endo- and an exocyclic C=C double bond. Quantum chemical calculations give insight into the reaction mechanism.

Treatment of diphenyl-di(phenylethynyl)germane with two equivalents of di( tert -butyl)aluminum hydride afforded the corresponding dialkenyl derivative, Ph 2 Ge[C(Al t Bu 2 ) C(H)–Ph] 2 ( 1 ) by dual hydroalumination. The aluminum atoms of 1 are attached to the carbon atoms in α-position to germanium. They are coordinatively unsaturated and are able to act as chelating Lewis-acids and to coordinate donors such as chloride or bromide anions in a chelating manner ( 2 , 3 ). The analogous reaction of the corresponding silicon-centered dialkyne with two equivalents of dimethylaluminum hydride gave a mixture of unknown compounds. Interestingly, equimolar quantities of the hydride and the dialkyne resulted in dismutation and the formation of the unprecedented compound MeAl[C( CH–Ph)–SiPh 2 –C C–Ph] 2 ( 4 ). Compound 4 has two alkenyl groups bonded to the central aluminum atom and a terminal alkynyl group attached to each silicon atom. An attempt to reduce the remaining triple bonds by reaction with di( tert -butyl)aluminum hydride resulted in cleavage and isolation of the monoalkenyl compound t Bu 2 Al–C[ C(H)–Ph]–SiPh 2 –C C–Ph ( 5 ). The molecular structure of 5 showed a close interaction between the α-carbon atom of the triple bond and the coordinatively unsaturated aluminum atom.

The thermal decomposition of the hydrazine adducts R3AlNH2–N(H)CMe3 (1a, R = CMe3; 1b, R = Me) was investigated. Compound 1a afforded the hydrazide [(Me3C)2Al–N(H)–N(H)–CMe3]2 (2) upon heating to 155 °C. Compound 2 is dimeric in the solid state with a four-membered Al2N2 heterocycle in its molecular core. Heating of 2 to 190 °C gave the drum-like imidoalane [Me3CAlNH]6 (4) in which the Al and N atoms occupy the vertices of a hexagonal prism. This reaction is believed to proceed via the dimeric amide [(Me3C)2Al–NH2]2 (3) that was isolated in small quantities from a mixture obtained at a slightly lower temperature. Adduct 1b, which is sterically less shielded than 1a, decomposes readily at room temperature to yield an unprecedented Al–N cage compound, [Me2Al–N(H)–N(H)CMe3]2[MeAl–N(CMe3)–NH] (5), with a norbornane-like arrangement of three Al and four N atoms, and a hydrazinediido group in the bridging position. Heating of 5 gave, with the release of methane, the tetraaluminum compound [MeAlN(H)–NCMe3]4 (6) in which four hydrazinediide moieties are bridged by AlMe groups. Heating of 6 resulted in the gradual degradation of the N–N bonds and the formal release of 1 or 3 equiv. of nitrene, N–H, to give the unique cage compounds (MeAl)4[N(H)–NCMe3]3(NCMe3) (7) and (MeAl)4[N(H)–NCMe3](NCMe3)3 (8). The structures of compounds 6–8 may be derived from Al4N4 cubes in which a number of edges (four, three or one) are bridged by nitrogen atoms of hydrazinediido groups.

The coordination chemistry of 1-methyl-1H-1,2,4-triazole (1-mtri) with respect to the linearly coordinating metal ions silver(I) and mercury(II) has been established. The ligand serves as a model nucleobase for the artificial 1,2,4-triazole nucleoside. Solution studies show that 2:1 complexes are formed with both metal ions in water. Mercury(II) forms more stable complexes than silver(I), with a stability constant of log β 2 of 10.5 ± 2.5 vs. 4.3 ± 0.4 for the silver(I) complex. In the solid state, different types of cationic coordination polymers are formed. The silver complex [Ag(1-mtri)](ClO 4 ) (1) comprises a one-dimensional coordination polymer [Ag 2 -(1-mtri) 2 ] n 2n+ , showing a 1:1 ratio of ligand to metal. By contrast, the mercury complex [Hg(1-mtri) 2 ](ClO 4 ) 2 (2) retains a 2:1 stoichiometry while forming a two-dimensional coordination polymer. In compound 2, mercury(II) is coordinated in a distorted octahedral fashion, with two normal and four long bonds, resulting in a compressed octahedron.

Treatment of the tetraalkyldigallium compound R2Ga–GaR2 [R = CH(SiMe3)2] (1) with a large number of different functionalized carboxylic acids afforded dicarboxylatodigallium compounds R2Ga2(μ-O2C–R)2, in which two carboxylato ligands bridge the Ga–Ga bonds. The chelating ligands have additional nitrogen, oxygen or phosphorus donor atoms and may be suitable to act as Lewis-bases to yield supramolecular aggregates in future investigations. Four compounds have been characterized by crystal structure determinations. One gave unprecedented dimeric formula units in the solid state by Ga–N interactions. The similar reaction with isonicotinic acid resulted in the cleavage of the Ga–Ga bond. A tetragallium compound was formed in which four isolated metal atoms were bridged by four organic ligands to give a square molecular core.

Dialkylaluminum hydrides R2Al–H (R = Me, Et, iBu, CH2tBu, tBu), reacted with tert-butylethyne, H–CC–CMe3 ,b y hydroalumination and formation of the corresponding vinylic compounds, R2Al–C(H)=C(H)–CMe3. The products are dimeric in the solid state with the negatively charged vinylic carbon atoms in the bridging positions and adopt usually a centrosymmetric structure with the C=C double bonds on different sides of the central Al2C2 heterocycle. Only with R = Me the C2v structure with the cis arrangement of the alkenyl groups was found. Complicated mixtures of isomeric substances were detected in solution. Quantum-chemical calcu

The reactions of trialkyl-element compounds (E = Al, Ga) with hydrazines usually proceed by the intermediate formation of the simple adducts R3ENH2-N(H)-R′. However, only one adduct (1; R = iPr, E = Ga) could be isolated and characterized in the reactions of ER3 compounds bearing relatively small substituents with phenylhydrazine. In all other cases fast secondary processes gave directly the corresponding dimeric hydrazides [R2E–N(H)–N(H)-C6H5]2 (2 to 4; R = Me, Et; E = Al, Ga) by gas evolution below room temperature. In contrast, decomposition of the adduct 1 required boiling toluene to produce the hydrazide 5. Compounds 3 and 4 possess four-membered E2N2 heterocycles with two exocyclic N–N bonds in the solid state, while a five-membered Ga2N3 heterocycle with an endocyclic and an exocyclic N–N bond was found in the crystal structure of 5. These hydrazides exhibit a dynamic behavior in solution with a complicated equilibrium between four- and five-membered rings and cis-/trans-isomers. Further thermolysis of the hydrazides 2 and 4 inboiling toluene or at 200 °C afforded the cage compounds [(R)E–N(H)–N–C6H5]4 (6 and 7, E = Al, Ga) in which two six-membered E2N4 heterocycles with a boat conformation are connected by four Al–N bonds.

In recent investigations we found an easy access to dialkyl(alkynyl)aluminum compounds by the deprotonation of phenylethyne with di(tert-butyl)- and dimethylaluminum hydride with evolution of molecular hydrogen. In contrast, the reactions of the bulky hydride R2Al−H [R = CH(SiMe3)2] with different alkynes R−C≡C−H (R = CMe3, SiMe3, C6H5, H) yielded vinylic aluminum compounds, R2Al−CH═CH−R′, by hydroalumination. Due to the effective steric shielding of the bulky alkyl substituents, the products were monomeric even in the solid state, with the alkenyl groups bonded to coordinatively unsaturated, tricoordinated aluminum atoms. Quantum-chemical calculations verified that there was no interaction between the π-electrons of the C═C bond and the vacant p-orbital at the coordinatively unsaturated aluminum atoms.

The tetraindiumcluster In 4 [C(SiMe 3 ) 3 ] 4 1 reacted with phenylselenium bromide and phenyltellurium bromide by the insertion of InR groups into the chalcogen–bromine bonds. The oxidation state of the indium atoms increased from +1 to +3. Compounds were obtained in which the indium atoms bear three different substituents (alkyl groups, phenylchalcogenido ligands, and bromine atoms). The products form dimers in the solid state via In–Se–In and In–Te–In bridges, respectively, and the bromine atoms are in terminal positions.

We report the C-metalation of 6-furylpurine with Pt(2+), Pd(2+), and Hg(2+). The ligand binds the metal ions in a bidentate fashion, involving the N7 purine atom and one of the furyl carbon atoms. The regioselectivity is determined by the metal ion. Pt(2+) and Pd(2+) coordinate the furyl moiety in its β position and Hg(2+) in its electronically preferred α position.

A new artificial nucleoside 2 comprising 4-(2′-pyridyl)imidazole as the nucleobase was devised and incorporated into a series of DNA oligonucleotide duplexes. The propensity of 2 to form metal-mediated homo and hetero base pairs was investigated in various 13mer and 26mer duplexes. The artificial nucleoside readily forms Ag(I)-mediated homo base pairs of the type 2–Ag(I)–2, in which the Ag(I) ion resides in a [2 + 2] coordination environment. In addition, the combination with the previously established imidazole nucleoside 1 leads to the formation of Ag(I)-mediated hetero base pairs (2–Ag(I)–1 and 1–Ag(I)–2) with a [2 + 1] coordination environment. With an increase in the melting temperature of ΔT m = 21.8 °C upon the formation of a Ag(I)-mediated base pair, the 2–Ag(I)–1 pair with the 13mer duplex is the most stabilizing Ag(I)-mediated base pair so far. Generally, the impact of the formation of a metal-mediated base pair on the properties of the DNA duplex was found to be significantly more prominent for shorter, intrinsically less stable duplexes.

The artificial nucleobases 6-(2'-thienyl)-purine (6TP) and 6-(2'-furyl)-purine (6FP) have been investigated in terms of their applicability in metal-mediated base pairs. In principle, these nucleobases should be capable of providing an S,N- and O,N-coordination environment, respectively. Two metal complexes have been synthesized and structurally characterized, using the N9-methylated derivatives of 6TP and 6FP as model nucleobases. The silver(I) complex [Ag(9-Me6TP)(CH3CN)(NO3)]n is of polymeric nature. The thienyl substituent is not involved in metal binding. In contrast, the dinuclear copper(II) complex [Cu(9-Me6FP)Cl2(OH2)]2 clearly shows that the furyl substituent can participate in the coordination of the metal ion. Oligonucleotide double helices comprising a 6TP:6TP or a 6FP:6FP mispair are slightly stabilized in the presence of silver(I). However, a distinction between the formation of a metal-mediated base pair and an unspecific binding event cannot be finally made. Based on these studies, it is proposed that the formation of Hoogsteen-type metal-mediated base pairs should be the more promising alternative compared with the originally anticipated Watson-Crick-type metal-mediated base pairs.