Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

This article presents the syntheses, crystal structures, topological features and magnetic properties of two NiII/NaI coordination clusters (CCs) formulated [NiII3Na(L1)3(HL1 (MeOH)2] (1) and [NiII6Na(L1)5(CO3)(MeO (MeOH)3(H2O)3]·4(MeOH) 2(H2O) [2 4(MeOH) 2(H2O)] where H2L1 is the semi rigid Schiff base ligand (E)-2-(2-hydroxy-3 methoxybenzylideneamino)-phenol). Compound 1 possesses a rare NiII3NaI cubane (3M4-1) topology and compound 2 is the first example in polynuclear Ni/Na chemistry that exhibits a 2,3,4M7-1 topology

Carbodiimide modification of superhelical PM2 DNA: considerations regarding reaction at unpaired bases and the unwinding of superhelical DNA with chemical probes.

Superhelical PM2 DNA I can be modified with N-cyclohexyl-N'-beta-(4-methylmorpholinium)ethyl carbodiimide (CMC). The transition of the sedimentation coefficient uncorrected for buoyant density change (S20,*) vs. % reactivity in terms of base pairs shows the following characteristics. The S20,* increases by 4.5 S units upon 1% modification. There is a plateau in S20,* between 1 and 4% reactivity. The extent of reactivity was determined by buoyant density and 14C radioactive CMC binding measurements. Further reactivity was not explored since Pulleyblank and Morgan's (22) data of S20,* vs. % reactivity from 6 to 34% was previously published. The initial results obtained in this study are complementary to the cited results of the above authors. Consequently, both sets of data taken together represent a complete description of S20,* vs. % reactivity with CMC. It is shown that the model in which superhelical DNA is proposed to contain small intrastrand hairpin regions can be extended to account for the observed transitions in S20,* vs. reactivity

The search for cobalt single-molecule magnets: A disk-like (CoCo6II)-Co-III cluster with a ligand derived from a novel transformation of 2-acetylpyridine

International audienceThe initial employment of 2-acetylpyridine, (py)(Me)CO, in Co cluster chemistry is reported, and the synthesis, crystal structure, and full magnetic study of [Co-7(OH)(6)(L)(6)](ClO4)(3)center dot 1.6H(2)O (1.1.6H(2)O) are described: L- is the anion of 2-(pyridine-2-yl)pentane-2-ol-4-one, (py)(Me)C(CH2COCH3)(O)(-), formed in situ through a crossed-aldol reaction in acetone under strongly basic conditions. The reaction of Co(ClO4)(2)center dot 6H(2)O, (POMe)CO and (NBu4OMe)-O-II (1:1:1.2) in acetone at room temperature under aerobic conditions affords 1.1.6H(2)O in 35% yield. The mixed-valent cation possesses a wheel-shaped (or disk-like) structural motif comprising a central octahedral Co-III atom linked to six peripheral distorted octahedral Co-II atoms by six mu(3)-OII- groups: the six Co-II atoms on the rim are held together by six eta(1):eta(1):eta(1):mu(2).L- ligands and the oxygen atoms of the hydroxo groups. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1. The dc magnetic study of 1 shows a decline in the product chi(T)(M) with decreasing T. The observation of out-of phase (chi ''(M)) ac susceptibility signals below similar to 4 K suggests that the CoIIICo6II complex may be a single molecule magnet, and this was confirmed by single-crystal magnetization vs. dc field sweeps down to 0.04 K that exhibited hysteresis. The study reveals that each complex cation is a weak single-molecule magnet, but that there are also intermolecular interactions (also confirmed crystallographically) to create a 3D ordered lattice: this still gives some hysteresis at 5 K. (C) 2011 Elsevier Ltd. All rights reserved