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Maren Pink

Publications and source records attributed to Maren Pink.

48 records · Page 3Linked to original sources
PubMed2003

Dlf complexes with uniform coordination geometry: structural and magnetic properties of an LnNi2 core supported by a heptadentate amine phenol ligand.

The synthesis and physical characterization of a series of lanthanide (Ln(III)) and nickel (Ni(II)) mixed trimetallic complexes with the heptadentate (N(4)O(3)) amine phenol ligand H(3)trn [tris(2'-hydroxybenzylaminoethyl)amine] has been accomplished in order to extend our understanding of how amine phenol ligands can be used to coaggregate d- and f-block metal ions and to investigate further the magnetic interaction between these ions. The one-pot reaction in methanol of stoichiometric amounts of H(3)trn with NiX(2).6H(2)O (X = ClO(4), NO(3)) followed by addition of the corresponding LnX(3).6H(2)O salt, and then base, produces complexes of the general formula [LnNi(2)(trn)(2)]X.nH(2)O. The complexes were characterized by a variety of analytical techniques. Crystals of five of the complexes were grown from methanol solutions and their structures were determined by X-ray analysis: [PrNi(2)(trn)(2)(CH(3)OH)]ClO(4).4CH(3)OH.H(2)O, [SmNi(2)(trn)(2)(CH(3)OH)]NO(3).4CH(3)OH.2H(2)O, [TbNi(2)(trn)(2)(CH(3)OH)]NO(3).4CH(3)OH.3H(2)O, [ErNi(2)(trn)(2)(CH(3)OH)]NO(3).6CH(3)OH, and [LuNi(2)(trn)(2)(CH(3)OH)]NO(3).4.5CH(3)OH.1.5H(2)O. The [LnNi(2)(trn)(2)(CH(3)OH)](+) complex cation consists of two octahedral Ni(II) ions, each of which is encapsulated by the ligand trn(3)(-) in an N(4)O(2) coordination sphere with one phenolate O atom not bound to Ni(II). Each [Ni(trn)](-) unit acts as a tridentate ligand toward the Ln(III) ion via two bridging and one nonbridging phenolate donors. Remarkably, in all of the structurally characterized complexes, Ln(III) is seven-coordinate and has a flattened pentagonal bipyramidal geometry. Such uniform coordination behavior along the whole lanthanide series is rare and can perhaps be attributed to a mismatch between the geometric requirements of the bridging and nonbridging phenolate donors. Magnetic studies indicate that ferromagnetic exchange occurs in the Ni(II)/Ln(II) complexes where Ln = Gd, Tb, Dy, Ho, or Er.

Journal Article↗
PubMed2002

Insights into the Schrock 'chop-chop' reaction gained from density functional theory and preparation and structure of W2(mu-PhCCPh)(SC6H4-2-Me)6.

Computations employing density functional theory on the reactions between ethyne and the model compounds (HE)3M identical to M(EH)3, where M = Mo and W and E = O and S, predict that the alkyne adducts M2(mu-C2H2)(EH)6 are thermodynamically favored with respect to the metathesis products HC identical to M(EH)3 except when M = W and E = O; the reaction between (tBuO)3 W identical to CPh and 2-MeC6H4SH (> 3 equiv.) yields W2(mu-PhCCPh)(SC6H4-2-Me)6 consistent with expectations based on the calculations.

Journal Article↗
PubMed2002

Spin-state alteration from sterically enforced ligand rotation in bis(indenyl)chromium(II) complexes.

The rotational orientation of cyclopentadienyl rings usually has no effect on d-orbital energy levels and splitting in transition metal complexes. With related but less symmetrical carbocyclic ligands, however, the magnetic properties of the associated complexes can be altered by the alignment of the ligands. Examples of this effect are found in substituted organochromium(II) bis(indenyl) complexes. The monosubstituted compounds (1-RC(9)H(6))(2)Cr (R = t-Bu, SiMe(3)) are prepared from the substituted lithium indenides and CrCl(2) in THF; they are high-spin species with four unpaired electrons. Their spin state likely reflects that in the unknown monomeric (C(9)H(7))(2)Cr, which is calculated to have a high-spin (S = 2) ground state in the staggered configuration (180 degrees rotation angle). However, the analogous bis(indenyl) complexes containing t-Bu or SiMe(3) groups in both the 1 and 3 positions on the indenyl ligands ((1,3-R(2)C(9)H(5))(2)Cr) are low-spin compounds with two unpaired electrons. X-ray diffraction results indicate that [1-(t-Bu)C(9)H(6)](2)Cr exists in a staggered conformation, with Cr-C (av) = 2.32(4) A. In contrast, the average Cr-C distances in [1,3-(t-Bu or SiMe(3))(2)C(9)H(5)](2)Cr are 2.22(2) and 2.20(2) A, respectively, and the rings are in a gauche configuration, with rotation angles of 87 degrees. The indenyl conformations are sterically imposed by the bulk of the t-Bu and SiMe(3) substituents. The change from a staggered to a gauche indenyl orientation lowers the symmetry of a (C(9)H(7))(2)M complex and allows greater mixing of metal and ligand orbitals. Calculations indicate that previously nonbonding pi orbitals of the indenyl anion are able to interact with the chromium d orbitals, producing bonding and antibonding combinations. The latter remain unpopulated, and the resulting increase in the HOMO-LUMO gap forces the complexes to adopt a low-spin configuration. The possibility of using sterically imposed ligand rotation as a means of spin-state manipulation makes indenyl compounds a potentially rich source of magnetically adjustable molecules.

Journal Article↗
PubMed2002

An electron-excessive nitrosyl complex: reactivity of a ligand-centered radical leading to coordinated HNO.

The reaction of RuHCl(CO)L(2) (L = P(i)Pr(3)) with NO initially forms a 1:1 adduct, shown by DFT calculations and EPR spectroscopy (including the RuD isotopomer) to contain a bent ( 90 degree angle Ru-N-O = 143.9 degrees ) nitrosyl where the majority of the spin density is on the nitrosyl nitrogen. This radical adduct transforms further to give equimolar RuCl(NO)(CO)L(2) and RuHCl(HNO)(CO)L(2), the latter with hydride trans to the nitroxyl ligand HN=O. This is the first observation of the synthesis of coordinated HNO from NO itself. DFT calculations lead to the proposal that this H-atom transfer is effected by free NO, and the lifetime of RuHCl(HNO)(CO)L(2) is indeed qualitatively dependent on the presence of free NO.

Journal Article↗
PubMed2002

Linear trimer analogues of calixarene as chiral coordinating ligands: X-ray crystallographic and NMR spectroscopic characterization of chiral and achiral trisphenolates complexed to titanium(IV) and aluminum(III).

Achiral and chiral linear trisphenol analogues of calixarene (HOArCH(2)Ar'(OH)C(R)HArOH, Ar = 4,6-di-tert-butylphenyl; Ar' = 4-tert-butylphenyl; R = H (achiral), Me (chiral)) were prepared in anticipation of their adoption of a chiral conformation upon coordination to Lewis acidic metal centers. The trisphenols react with 1 equiv of Ti(OR')(4) (R' = i-Pr or t-Bu) to yield complexes with molecular formula Ti(2)(OArCH(2)Ar'(O)C(R)HArO)(2)(OR')(2) (R = H, Me; R' = i-Pr or t-Bu). An X-ray crystal structure of the titanium complex of the achiral trisphenol (R = H; R' = t-Bu) reveals that the trisphenolate ligand adopts an unsymmetrical (and therefore chiral) conformation, with eta(2)-coordination to one metal center and eta(1)-coordination to the second metal center. The chiral trisphenol, which contains a stereogenic center (indicated as C in the shorthand notation used above), coordinates titanium in an analogous fashion to produce only one diastereomer (out of four possible); therefore, the configuration of the stereogenic center controls the conformation adopted by the bound ligand. The reaction of achiral trisphenol with AlMe(3) produces a compound with molecular formula Al(2)(OArCH(2)Ar'(O)CH(2)ArO)(2). (1)H NMR spectroscopy and X-ray crystallography reveal that the trisphenolate ligand adopts an asymmetric, C(2) conformation in this complex, where the central phenolate oxygen bridges the aluminum centers and the terminal phenolate oxygens each coordinate a separate aluminum center. Because these trisphenolate ligands adopt chiral conformations when coordinated to metal centers, they may be useful for developing diastereo- or enantioselective catalysts and reagents.

Journal Article↗
PubMed2002

Tristhiolatomolybdenum nitrides, (RS)(3)Mo[triple bond]N where R = (i)Pr and (t)Bu, preparation, characterization and comparisons with related trialkoxymolybdenumnitrides.

The addition of thiols to ((t)BuO)(3)Mo[triple bond]N in toluene leads to the formation of (RS)(3)Mo[triple bond]N compounds as yellow, air-sensitive compounds, where R = (i)Pr and (t)Bu. The single-crystal structure of ((t)BuS)(3)Mo[triple bond]N reveals a weakly associated dimeric structure where two ((t)BuS)(3)Mo[triple bond]N units (Mo-N = 1.61 A, Mo-S = 2.31 A (av)) are linked via thiolate sulfur bridges with long 3.03 A (av) Mo-S interactions. Density functional theory calculations employing Gaussian 98 B3LYP (LANL2DZ for Mo and 6-31G* for N, O, S, and H) have been carried out for model compounds (HE)(3)Mo[triple bond]N and (HE)(3)MoNO, where E = O and S. A comparison of the structure and bonding within the related series ((t)BuE)(3)Mo[triple bond]N and ((t)BuE)(3)MoNO is made for E = O and S. In the thiolate compounds, the highest energy orbitals are sulfur lone-pair combinations. In the alkoxides, the HOMO is the N 2p lone-pair which has M-N sigma and M-O pi* character for the nitride. As a result of greater O p pi to Mo pi interactions, the M-N pi orbitals of the Mo-N triple bond are destabilized with respect to their thiolate counterpart. For the nitrosyl compounds, the greater O p pi to Mo d pi interaction favors greater back-bonding to the nitrosyl pi* orbitals for the alkoxides relative to the thiolates. The results of the calculations are correlated with the observed structural features and spectroscopic properties of the related alkoxide and thiolate compounds.

Journal Article↗
PubMed2002

Stereocontrolled [3 + 2] annulations with arene chromium tricarbonyl complexes: construction of spirocyclic compounds related to fredericamycin A.

[reaction: see text] An efficient method has been developed for the stereocontrolled construction of polycyclic and spirocyclic compounds, including the spirocyclic core of the antitumor agent fredericamycin A. The strategy involves a one-pot aldol addition/Brook rearrangement/cyclization sequence beginning from arene chromium tricarbonyl complexes and can formally be described as a [3 + 2] annulation.

Antibiotics, Antineoplastic↗
PubMed2001

5-chloro- and 5-bromobenzfurazan 1-oxide revisited.

At room temperature the two title compounds are isomorphous. Both have a disordered structure that includes a major component, one of the title compounds, and a minor component, the 6-halo isomer, occurring at the same site in the crystal. When the chloro compound is cooled to as low as 98 K, there is no change in the structure and no significant change in the degree of disorder. When the bromo compound is cooled, it undergoes a second-order phase transition at 282 K to a second polymorph, structurally very similar, but with two molecules in the asymmetric unit. In both isomorphs and both polymorphs the molecules occur in two-dimensional layers that are essentially the same. In the low-temperature form of the bromo compound the layers have shifted relative to each other by approximately 0.7 A in y. In the low-temperature form the disorder, which is still present after the transition, decreases as the temperature is lowered.

Journal Article↗
PubMed1997

Novel Alkali-Metal Coordination in Phenoxides: Powder Diffraction Results on C(6)H(5)OM (M = Li, Na, K, Rb, Cs).

We report the ab initio structure solutions of C(6)H(5)OM (M = K, Rb, Cs) by high-resolution powder X-ray diffraction. The compounds, which are of interest for reactions of the Kolbe-Schmitt type, are isostructural. The crystal structures are orthorhombic, space group Pna2(1), Z = 12, with lattice parameters (a, b, c in Å) 14.1003(1), 17.9121(1), and 7.16475(1) for the K compound, 14.4166(2), 18.2028(2), and 7.4009(1) for the Rb compound, and 14.8448(2), 18.5070(2), and 7.6306(1) for the Cs compound. They have a chain structure [M([6])] along the crystallographic c axis. This is a very unusual arrangement in which two different alkali-metal coordination spheres are observed: a distorted octahedron and a 3-fold oxygen coordination. In the latter, the 3-fold-coordinated unsaturated alkali metals additionally show weak interactions with phenyl rings. We also give powder patterns for the compounds with M = Li, Na. The former crystallizes in the monoclinic space group P2(1)/a with lattice parameters a = 22.594 Å, b = 4.7459 Å, c= 10.053 Å, and beta = 97.82 degrees with Z = 8, but no structure solution was possible. The powder pattern for the Na phenolate is in agreement with the earlier single-crystal structure.

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