Source:http://linkedlifedata.com/resource/pubmed/id/11942833
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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
15
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pubmed:dateCreated |
2002-4-10
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pubmed:abstractText |
Tetranuclear complexes [Zn(4)(bdmap)(2)(OOCR)(6)] 1 (R = Me) and 2 (R = Et), where Hbdmap = 1,3-bis(dimethylamino)-2-propanol, were prepared from zinc carboxylates and Hbdmap in tetrahydrofuran (THF). The solid-state structures of isomers 1a and 2a consist of two pairs of zinc atoms, each bridged by two mu-1,2 and one mu-1,1 carboxylate ligands. Two pairs are connected by two tridentate bdmap ligands with oxygen acting as a bridging donating atom. The complexes retain the tetranuclear structure in solution and two dynamic processes are observed from variable-temperature (1)H and (13)C NMR spectra. A low-temperature process (LT dynamics) observed already below 200 K is a coalescence of the mu-1,2 and the mu-1,1 resonances to a single resonance. An additional dynamic process (HT dynamics) is observed above 247 K (1) and 263 K (2), leading to a coalescence of two dimethylamino resonances. Both dynamic processes are rationalized by a mechanism involving changes in the carboxylate coordination mode termed as carboxylate shift. The LT dynamics is ascribed to interconversions of a single mu-1,2 and a single mu-1,1 carboxylate ligation by rotations of 60 degrees. The interconversions involve all carboxylate ligands in 1 and 2. The HT dynamics is ascribed to the exchange of the coordinating geometries of two carboxylate-bridged zinc atoms. We propose a mechanism that starts with a cleavage of the Zn-N coordination bond. The resulting coordinatively unsaturated zinc atom acquires an additional oxygen donor atom by carboxylate shift of mu-1,2 carboxylate to mu-1,1 mode. The activation parameters (DeltaH values in kilocalories per mole, DeltaS values in calories per mole per kelvin) were determined by line-shape analysis of VT NMR spectra: for 1 in THF-d(8), DeltaH(LT) = 8.1(3), DeltaS(LT) = -12(2), DeltaH(HT) = 17.9(2), DeltaS(HT) = 14(1); for 1 in CDCl(3), DeltaH(HT) = 13.6(5), DeltaS(HT) = 3(3); for 1 in CD(2)Cl(2), DeltaH(HT) = 9.9(3), DeltaS(HT) = -8(2); for 2 in THF-d(8), DeltaH(LT) = 11(1), DeltaS(LT) = -5(3), DeltaH(HT) = 19.6(5), DeltaS(HT) = 18(3). Polymeric [Zn(4)(bdmap)(2)(OOCMe)(6)](n) 1-catena crystallizes from a dichloromethane solution of 1. In 1-catena, the zinc atoms are linked into a chain through mu-1,2 and mu-1,1 acetate alternated by mu-1,2 acetate and bdmap.
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pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/Carboxylic Acids,
http://linkedlifedata.com/resource/pubmed/chemical/Organometallic Compounds,
http://linkedlifedata.com/resource/pubmed/chemical/Oxygenases,
http://linkedlifedata.com/resource/pubmed/chemical/Ribonucleotide Reductases,
http://linkedlifedata.com/resource/pubmed/chemical/Zinc,
http://linkedlifedata.com/resource/pubmed/chemical/methane monooxygenase,
http://linkedlifedata.com/resource/pubmed/chemical/ribonucleotide reductase R2 subunit
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pubmed:status |
MEDLINE
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pubmed:month |
Apr
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pubmed:issn |
0002-7863
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:day |
17
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pubmed:volume |
124
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
3951-8
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pubmed:dateRevised |
2008-11-21
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pubmed:meshHeading |
pubmed-meshheading:11942833-Carboxylic Acids,
pubmed-meshheading:11942833-Cold Temperature,
pubmed-meshheading:11942833-Crystallography, X-Ray,
pubmed-meshheading:11942833-Magnetic Resonance Spectroscopy,
pubmed-meshheading:11942833-Molecular Conformation,
pubmed-meshheading:11942833-Molecular Structure,
pubmed-meshheading:11942833-Organometallic Compounds,
pubmed-meshheading:11942833-Oxygenases,
pubmed-meshheading:11942833-Ribonucleotide Reductases,
pubmed-meshheading:11942833-Spectrophotometry, Infrared,
pubmed-meshheading:11942833-Temperature,
pubmed-meshheading:11942833-Thermodynamics,
pubmed-meshheading:11942833-Zinc
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pubmed:year |
2002
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pubmed:articleTitle |
Variable-temperature nuclear magnetic resonance spectroscopy allows direct observation of carboxylate shift in zinc carboxylate complexes.
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pubmed:affiliation |
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, SI-1000 Ljubljana, Slovenia. alojz.demsar@uni-lj.si
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pubmed:publicationType |
Journal Article,
Research Support, Non-U.S. Gov't
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