John C. Huffman

Can terdentate 2,6-bis(1,2,3-triazol-4-yl)pyridines form stable coordination compounds?

The first structurally characterized examples of the 1,2,3-triazole motif employed in a terdentate ligand display enhanced steric freedom and a facile receptivity towards a reversible aquation in the case of an electrogenerated Fe(III) state.

Single-Molecule Magnets: Characterization of Complexes Exhibiting Out-of-Phase AC Susceptibility Signals

Abstract The structures and characterization are described of complexes that exhibit an out-of-phase AC magnetic susceptibility x m” The dodecanuclear complexes [Mn12O12(O2CR)16(H2O)4]z contain 8MnIII, 4MnIV or MnII, 7MnIII, 4MnIV and possess ground state spins of S = 9 or 10 (z = 0) or S = 19/2 (z = −1). The distorted-cubane complexes [Mn4O3X(O2CR)3(dbm)3] contain 3MnIII, MnIV and have been prepared with a variety of X groups; in every case, the ground state is S = 9/2. The anion [Mn11O10X6(O2CPh)11(H2O)4]2− (9MnIII, 2MnIV; X = NCO−, N3 −) contains two [Mn4O3X] distorted-cubanes linked by a [Mn3O4]+ unit; the ground state is S = 5. The cation [V4O2(O2CEt)7(bpy)2]+ (4VIII) has a [V4O2]8+ butterfly core and a S = 3 ground state. All these complexes exhibit out-of-phase AC magnetic susceptibility signals at low temperatures (<8 K). These signals are indicative of slow relaxation of the magnetization, unable to keep in phase with the oscillating AC magnetic field, and are taken as evidence for single-molecul...

SYNTHESIS AND STUDY OF PHOSPHINES INCORPORATING 2-CYANOPHENYL GROUPS AND THE X-RAY STRUCTURE OF TRIS(2-CYANOPHENYL)PHOSPHINE

Abstract Both PhP(2-NCC6H4)2 and P(2-NCC6H4)3 have been synthesized from the carbanions generated from 2-bromobenzonitrile and dimethyl phenylphosphonite or triphenyl phosphite. The A1 υ(CO) bands for the Ni(CO)3L complexes of these two ligands along with that from the previously reported Ph2P(2-NCC6H4) have been recorded in dichloromethane solutions. The values (2073.0, 2076.4 and 2079.7 cm−1; decreasing number of Ph rings) reflect the electron-withdrawing nature of the ortho-positioned cyano groups. 31P chemical shifts of the L2PdCl2 complexes of these three ligands have been recorded, and all provide shifts of δ=24.1±1, approximately that for (PPh3)2PdCl2, δ=23.9. The molecular structure of P(2-NCC6H4)3, from X-ray crystallographic studies, is reported. A prominent feature of the structure is that the cyano groups are pointed in the general direction of the phosphorus lone pair. The average distances from phosphorus to cyano carbon and nitrogen atoms were found to be 3.03 and 3.23 A, respectively.

A single bond covalent radius for IrIII: crystal and molecular structure of fac-Ir(CH3)3(PMe2Ph)3

Abstract A low temperature (− 145°C) X-ray diffraction structure determination of crystalline fac-Ir(CH3)3(PMe2Ph)3 grown from CH2Cl2/pentane shows it to contain two independent molecules per unit cell with Ir—C = 2.160(9) and 2.158(9), and Ir—P = 2.3343(24) and 2.3307(26) A. Angles C—Ir—C are compressed to 83.4(4) and 83.3(4)°, and angles P—Ir—P are expanded to 99.99(8) and 99.83(8)°. An IrIII covalent radius of 1.40 A can be deduced from these data. Crystallographic data ( − 145°C): Space group R3c with a = b = 14.980(4), c = 41.732(12) A and Z = 12.

Reversible carbon-hydrogen bond oxidative addition across a W—W multiple bond

As previously reported, the reaction between W 2 (NMe 2 ) 6 and 2,2′-methylenebis(6- tert -butyl-4-methyl-phenol), HO-CH 2 -OH, in hydrocarbon solvents leads to W 2 ( μ -H)( μ -NMe 2 )( η 2 -O-CH 2 -O)( η 3 -O-CH-O)(HNMe 2 )(NMe 2 ), 1 , by oxidative cyclometallation to the ditungsten center. Upon heating 1 to greater than 60°C under dynamic vacuum W 2 (NMe 2 ) 2 ( η 2 -O-CH 2 -O) 2 , 2 , is formed with elimination of HNMe 2 . Compound 2 is proposed to have an ethane-like O 2 NW∖WO 2 N core based on NMR data. Addition of HNMe 2 to 2 at room temperature converts 2 to 1 . The addition of other neutral ligands (pyridine, PMe 3 ) to hydrocarbon solutions of 2 promotes the C-H oxidative addition to the W 2 center and the pyridine adduct W 2 ( μ -H)( μ -NMe 2 )(NMe 2 )(py)( η 2 -O-CH 2 -O)( η 3 -O-CH-O), 3 , has been fully characterized by an X-ray study. Addition of PMe 3 to 2 at low temperatures reveals that Lewis base association occurs prior to C-H activation. There is no evidence for an agostic interaction for 2 by NMR or IR spectroscopy.

Synthesis and preliminary characterization of new conducting salts derived from bis(ethylenedithio)tetraselenafulvalene (BETS)

Abstract Nine new conducting salts of BETS have been synthesized by electrocrystallization. The resistivities of these materials have been monitored to low temperatures. The resistivities of α-(BETS) 2 MHg(SCN) 4 (M = NH 4 and K), which are isostructural with well known BEDT-TTF (ET) compounds, decrease smoothly and monotonically from room temperature to 0.4 K, but neither are superconductors. X-ray structural data are reported.

Conducting salts of the new donor bis(ethylenedithio)tetrathionaphthalene (EDNA)

Abstract All radical cation-based superconductors are derived from tetrachalcogenafulvalene precursors. Bis(ethylenedithio) tetrathionaphthalene (EDNA) was designed and synthesized as a possible alternative to this limited set of starting materials. An electrochemical study of EDNA is discussed. The first radical cation salts of EDNA are reported. A variety of EDNA:anion stoichiometries are observed. Four-probe resistivity and room temperature ESR data are presented for three (EDNA)m(X)n salts (X= ClO4, SCN, I3). (EDNA)ClO4 and (EDNA)3(SCN)2 are semiconductors, but the room temperature resistivity of the perchlorate salt is 106 greater than that of the thiocyanate salt. (EDNA)2I3 is metallic to 220 K, where it undergoes a transition to a low activation energy (Ea = 88 meV) semiconductor.