166 V4-V5 IC - 6450 Inorg. Chem. 1996, 35, 6450-6460...

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Tetranuclear and Pentanuclear Vanadium(IV/V) Carboxylate Complexes: [V 4 O 8 (NO 3 )(O 2 CR) 4 ] 2 - and [V 5 O 9 X(O 2 CR) 4 ] 2 - (X ) Cl - ,Br - ) Salts Gail B. Karet, ² Ziming Sun, Dwight D. Heinrich, ² James K. McCusker, Kirsten Folting, ² William E. Streib, ² John C. Huffman, ² David N. Hendrickson,* ,‡ and George Christou* Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405-4001, and Department of Chemistry-0358, University of California at San Diego, La Jolla, California 92093-0358 Recei V ed May 22, 1996 X The syntheses and properties of tetra- and pentanuclear vanadium(IV,V) carboxylate complexes are reported. Reaction of (NBzEt 3 ) 2 [VOCl 4 ]( 1a ) with NaO 2 CPh and atmospheric H 2 O/O 2 in MeCN leads to formation of (NBzEt 3 ) 2 [V 5 O 9 Cl(O 2 CPh) 4 ] 4a ; a similar reaction employing (NEt 4 ) 2 [VOCl 4 1b ) gives (NEt 4 ) 2 [V 5 O 9 Cl(O 2 - CPh) 4 4b ). Complex 4a MeCN crystallizes in space group P 2 1 2 1 2 1 with the following unit cell dimensions at - 148 ° C: a ) 13.863(13) Å, b ) 34.009(43) Å, c ) 12.773(11) Å, and Z ) 4. The reaction between (NEt 4 ) 2 [VOBr 4 2a ) and NaO 2 CPh under similar conditions gives (NEt 4 ) 2 [V 5 O 9 Br(O 2 CPh) 4 6a ), and the use of (PPh 4 ) 2 [VOBr 4 2b ) likewise gives (PPh 4 ) 2 [V 5 O 9 Br(O 2 CPh) 4 6b ). Complex 6b crystallizes in space group P 2 1 2 1 2 1 with the following unit cell dimensions at - 139 ° C: a ) 18.638(3) Å, b ) 23.557(4) Å, c ) 12.731(2) Å, and Z ) 4. The anions of 4a and 6b consist of a V 5 square pyramid with each vertical face bridged by a μ 3 -O 2 - ion, the basal face bridged by a μ 4 -X - (X ) Cl, Br) ion, and a terminal, multiply-bonded O 2 - ion on each metal. The RCO 2 - groups bridge each basal edge to give C 4 V virtual symmetry. The apical and basal metals are V V and V IV , respectively (i.e., the anions are trapped-valence). The reaction of 1b with AgNO 3 and Na(tca) (tca ) thiophene-2-carboxylate) in MeCN under anaerobic conditions gives (NEt 4 ) 2 [V 4 O 8 (NO 3 )(tca) 4 7 ). Complex 7 H 2 O crystallizes in space group C 2/ c with the following unit cell dimensions at - 170 ° C: a ) 23.606(4) Å, b ) 15.211(3) Å, c ) 23.999(5) Å, and Z ) 4. The anion of 7 is similar to those of 4a and 6b except that the apical [VO] unit is absent, leaving a V 4 square unit, and the μ 4 -X - ion is replaced with a μ 4 , η 1 -NO 3 - ion. The four metal centers are now at the V IV ,3V V oxidation level, but the structure indicates four equivalent V centers, suggesting an electronically delocalized system. Variable-temperature magnetic susceptibility data were collected on powdered samples of 4b , 6a , and 7 in the 2.00 - 300 K range in a 10 kG applied field. 4b and 6a both show a slow increase in effective magnetic moment ( μ eff ) from 3.6 - 3.7 μ B at 320 K to 4.5 - 4.6 μ B at 11.0 K and then a slight decrease to 4.2 μ B at 2.00 K. The data were fit to the theoretical expression for a V IV 4 square with two exchange parameters J ) J cis and J ) J trans ( H ˆ)- 2 JS i S j ): fitting of the data gave, in the format 4b / 6a , J )+ 39.7/ + 46.4 cm - 1 , J )- 11.1/ - 18.2 cm - 1 and g ) 1.83/1.90, with the complexes possessing S T ) 2 ground states. The latter were confirmed by magnetization V s field studies in the 2.00 - 30.0 K and 0.500 - 50.0 kG
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This note was uploaded on 01/20/2012 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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166 V4-V5 IC - 6450 Inorg. Chem. 1996, 35, 6450-6460...

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