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Chloranilate bridged sodium chains
MMUNICATIONS
ELSEVIER
Inorganic Chemistry Communications 1 (1998) 418-420
Chloranilate bridged sodium chains Christos Papadimitriou a9*,Panagiotis Veltsistas a, Jaromfr Marek b, Josef Novosad b, Alexandra M.Z. Slawin ‘, J. Derek Woollins ’ aDepartment ofChemistry, University of loannina, loanninu, Greece b Department of Chemistry, hiasaryk University, Kotiarska 2, 61137 Brtw, Czech Republic ‘Department of Chemistry, Loughborough Universiry, Loughborough, Leicestershire, L.E113TU, UK Received 24 August 1998
Abstract Slow crystallisation (in water glass) hasbeenused toobtainNk(ca) *3H,O (1) andNa,(ca)phen*2H,O (2) whichhavebeencharactetised b=8.472(1), c=9.816(1) A, cu=106.71(1), /3=92.04(l), by X-ray crystallography. 1: C12H120~a4014r triclinic a=6.567(1), 7=92.48(l)“, U=522 A3, P-l, Z= 1, F(OO0) =308, p(Mo-Ka) =0.72 mm-‘, 1700 observed [F>~.OV(F)] gave a final R=3.56%. 2: monoclinic, a= 10.754(l), b= 19.778(2), c= 13.681( 1) A, /3=98,55(l)“, U=2877 A3, P2,/c, Z=4, F(OO0) = 1328, p(Mo-KAY) =0.31 mm-‘, 2337 observed [F>4.0a(F)] gave a final R=5.73%. In both structures the chloranilate anions make use of chlorine atoms to 0 1998 Published by Elsevier Science S.A. All rights complete the six coordination of the sodium centres in the layer/chain systems. reserved. Keywords:
Cbloranilateanions; Layer/chain systems;Crystal structures; Sodium complexes
The coordination chemistry of catecholates/quinones is quite well established, with systems being capable of intramolecular-interligand or meta-ligand electron transfer [l41. Although numerous transition-metal complexes are known, few characterised complexes of alkali metals with quinones have been reported. Here we report the preparation and X-ray structure of sodium complexes of the chloranilate dianion. We obtained crystals of Na,( ca) *3H20 (1) from chloranilic acid and sodium acetate in silica gel ‘water glass’. Crystallisation of chloranilic acid, phenanthroline and sodium hydroxide in water glass gave [Na,(phen),(ca) *2H,O] (2) ; both compounds gave satisfactory microanalysis. In the X-ray structure of 1 ’ (Fig. 1) the chloranilate dianion coordinates to both Na+ counterions, in addition
* Corresponding author. Fax: + 30-651-44989 ‘Anal. Found: C, 24.05; H, 2.18; Na, 15.52. Calc.: C, 23.47; H, 1.97; Na, 14.98%. Crystal data: CIZH,204Na,0,4, triclinic a=6.567( 1). b=8.472(1), c=9.816(1) A, (~=106.71(1), /3=92.04(l), y= 92.48(l)“, U=522 A’, P-l, Z=l, F(OOO)=308, p(Mc-Ka)=O.72 mm-‘, 1826 reflections collected (2f3 range 3-500), R,.,=O.O78, 1700 observed [F>4.0u(F)] gave a final R=3.56% [4.62 all data]. 1387-7003/98/$ - see front matter 0 PZI S1387-7003(98)00109-9
there are three solvate water molecules. The coordination at Na( 1) consists of two oxygen atoms [ 0( 6) and 0( 7) -btidging water molecules to Na(2)], as well as a chelate [O( 1) and 0( 2) ] from the chloranilate and two additional oxygen atoms from adjacent chloranilate anions [ 0( 4) ] in the neighbouring layers on both sides of Na( 1). The Na( 2) centres are coordinated by the bridging water oxygen atoms, O(6) and O(7) bridging to Na( 1) as well as two, symmetry related, water molecules [ 0( 5) and 0( 5B) ] bridging to Na(2B), and are chelated by 0( 3) and Cl(2) of a chloranilate. The sodium centres are thus formally six coordinate and the chloranilate anions make use of all four oxygen centres and one chlorine atom for coordination. The chloranilate anions lie approximately in the UCplane of the lattice and, as mentioned above, adjacent layers are linked via 0( 4) (chloranilate) bridges and Na(2)05-05-Na(2B) bridges. The Na( l)...Na(2) and Na(2)...Na(2) distances are 3.50 and 3.47 A respectively. The surprising observation of the ‘coordination’ of the chloranilate chlorine in the ‘coordination sphere led us to synthesise another example to test if this observation was general. We obtained. [ N&phen( ca) - 2H,O] by the water glass method.
1998 Published by Elsevier Science S.A. All rights reserved.
C. Papadimittiou et al. /Inorganic Chemistry Communications 1 (1998) 418-420
419
OISAI .3Hz0 (1). Selected bondlengths (A) and angles (O): Cl( l)_c(l) 1.735(2), Cl(2)_c(4) 1*741(2), Cl(2)-Na(2) 2.9826(10). 0(1)--C(2) 1.246(2), O(l)-Na(1) 2.3576(114), 0(2)-C(3) 1.252(2), O(2)-Na(l) 2.400(2), 0(3)_~(5) 1.259(2),0(3)-Na(2) 2.34W2),0(4)-U6) 1.254(2), O(4)-Na(1) 2.3043(14), O(4)-Na(1) 2.675(2), C(l)-c(6) 1.397(3), C(l)-q2) 1.406(2), C(2M3) 1.542(2LC(3)-C(4) 1.400(3),C(4)X(5) 1.396(3),C(5)<(6) 1.541(2),Na(l)-O(4) 2.3044(14),Na(l)_0(6) 2.352(2),Na(l)_0(7) 2.567(2), Na(lW(4) 2.675(2). Na(l)-Na(1) 3.382(2), Na(l)-Na(2) 3.5040(12), Na(2)-0(6) 2.358(2), Na(2)_0(7) 2.392(2), Na(2)_0(5) 2.432.(2), Na(2)-0(5) 2.460(2), Na(WNa(2) 3.469(2), Na(Z)-Na(1) 3.5041(12), O(5)-Na(2) 2.460(2), O(6)-Na(2) 2.358(2), O(7)-Na(2) 2.392(2), O(7)-Na(1) 2.567(2). O(4)-Na(lW(6) 103.61(6), O(4)-Na(l)-O(l) 154.10(6), O(6)-Na(l)AB(l) 85.17(6), O(4)-Na(l)_0(2) 86.51(5),0(6)-Na(lPX2) 117.70(7),0(1)--Na(lW(2) 68.02(5),0(4)-Na(l)-0(7) 106.04(6),0(6)-Na(1)-0(7)83.26(6),0(1)-Na(l)-O(7) 99.11(6),0(2)-Na(lW(7) 152.88(6).0(4)-Na(1)-0(4)94.80(5),0(6)-Na(1)-0(4) 153,06(6),0(l)-Na(l)-O(4)86.71(5),0(2)-Na(l)a(4) 82.48(5)vO(7)-Na(l)~(4)72.74(5),0(3)-Na(2)-O(6) 167.45(7),0(3)-Na(2)-0(7) 103.74(7),0(6)-Na(2)-0(7)87.&j(6),0(3)-Na(2)~(5) 86.64(6), O(6)-Na(2)4(5) 86.64(6), 0(7)-W&O(5) 91.82(7), O(3)-Na(2)-0(5) 86.30(6), O(6)-Na(2)_0(5) 83.08(7), 0(7)_Na(2)_0(5) 169.91(7), O(5)-Na(2)+(5) 89.69(6), O(3)-NaW-CW 67.16(4), O(6)-Na(2)-C1(2) 120.49(5), O(7)-Na(2)_Cl(2) 87.56(5), 0(5)_Na(2)C1(2) 152.77(6), O(5)-Na(2)-C1(2) 95.64(5), Na(2)-0(5)-Na(2) 90.31(6), Na( 1)-O(6)-Na(2) 96.12(7), Na(2)-0(7)-Na( 1) 89.83(7).
fig. 1. Partoffie hfde
chainin the X-ray structureofNa,(ca)
Fig. 2. The x-ray smxtm of [NaAphenMca) .2H~01; part ofthe infinite chains. Selectedbond lengths (A) and angles (“): Na( l)-O( 1) 2.347(5), Na( l)O(2) 2.497(5), Na(lW(3) 2.384(5), Na(lW(4) 2.435(4), Na(l)-N(1) 2.459(7), Na(l)-N(10) 2.539(6), Na(2)-0(4) 2.421(5), Na(2)-0(6) 2.293(6),Na(2)-0(7) 2.393(6),Na(2)-N(la) 2.492(7),Na(2)-N(lOa) 2.494(7),Na(2)...Cl(l) 2.991(3),Na(l)...Na(2a) 4.003(4). O(l)-Na(l)O(2) 66.6(2), O(3)-Na(lW(4) 67.0(l), N(l)-Na(l)-N(l0) 67.1(2), O(6)-Na(2)-0(7) 84.1(2), N(la)-Na(2)-N(lOa) 66.6(2), O(4)Na(2) . ..Cl( 1) 66.0( 1).
420
C. Papadimitriou et al. /Inorganic
Chemistry Communications I (1998) 418-420
The X-ray structure of 2 ’ (Fig. 2) reveals each of the sodium centres to be coordinated by a l,lO-phenanthroline ligand. Na( 1) is also coordinated by four oxygens of two bridging chloranilate ligands resulting in severely distorted octahedral coordination geometry. In addition to the phenanthroline Na( 2) is coordinated by two water molecules as well as one oxygen of the chloranilate ligand [ 0( 4) shared with Na( 1) 1. Again this coordination mode results in close contacts with Cl(l) [Na...Cl 2.991(3) A] and Na(1) [Na( 1). . .Na( 2) 4.003(4) A]. The overall structure thus consists of Na( l)-chloranilate chains with Na(2) *2H20 as a ‘pendant’ group on the bridging chloranilate ligands. In 2 the IR spectrum 3 of the isolated crystals was identical with that of the bulk material. The results are similar to those reported for Ag,(ca) [S], [Pd(ca)(PPh3)2] -HZ0 [6], K,(ca)*H,O [7] and [Cu,(terpy),(ca)] [8]. The sharp
band of medium intensity at 3490 cm-’ is assigned to the V(O-H) stretching vibration of coordinated water molecules, and the very strong triplet at 1555,1545,1530 cm-’ as well as the medium band at 1380 cm- ’ are due to v(C-0) bond order of 1.5 [ 5-71. A third characteristic very strong band at 842 cm- ’ is assignable as a v(C-C~) stretching vibration
[&A. Acknowledgements Authors J.N. and J.M. wish to express their gratitude to the Grant Agency of the Czech Republic for the grants No. 203 / 95/1190 and No. 203/97/0955. References 111 R.M.
*Ad Found: C, 56.02; H, 3.36; N, 8.97; Na, 7.08. Calc.: C, 55.50; H, monoclinic 3.10; N, 8.63; Na, 6.97%. Crystal data: C,&,&O$la2C12, a=10.754(1), b=19.778(2), c=13.681(1) A, /3=98.55(l)“, U=2877 A’, P2,/c, Z=4, F(OOQ) = 1328, p(Mo-Kcr) =0.31 mm-‘, 5535 reflections collected (26 range 3-50”), 5067 independent ( Rinr= 4.48%), 2337 observed [F>4.0a(F)], gave a final R=5.73% [6.99% all data]. Both structures were solved by direct methods and refined against p using SHELXTL. 3 LR: 3585 w, 3490 m, 3380 tr, 1675 sh, 1625 s, db, 1545 vs, tr, 1485 m, db, 1380 w, 985 w, 842 vs. 570 s, 480 br, 365 w. Raman: 3060 s, db, 1612 vs - 1598 sh, 1505 m, 1460 m, 1425 vs. 1350 w, 1310 m, 1100 w, 1050 m, 850 w, 730 w, 555 w, 430 m, 360 w.
Buchanan, S.L. Kessel, H.H. Downs, C.G. Pierpont, D.N. Hendrickson, J. Am. Chem. Sot. 100 (1978) 7894. 121 S. Bhattacharya, C.G. Pierpont. Jnorg. Chem. 30 (1991) 1511. 131 C. Bemtelli, A. Dei, D. Gatteschi, L. Pardi, J. Am. Chem. Sot. 110 (1988) 6897. [41 S. Bhattacharya, S.R. Boone, G.A. Fox, C.G. Pierpont, J. Am. Chem. sot. 112 (1990) 1088. [51 P.E. Riley, S.F. Haddad, K.N. Raymond, Jnorg. Chem. 22 (1983) 3090. [61 W.Y. Yeong, R.A. Holwerda, Jnorg. Chem. 27 (1988) 2571. [71 W.Y. Yeong, R.A. Holwerda, Jnorg. Chem. 28 (1989) 2674. [81 J.V. Folgado, R. lbanez, E. Coronado, D. Beltran, J.M. Savariault, J. GaJy, Jnorg. Chem. 27 (1988) 19.
ELSEVIER
Inorganic Chemistry Communications 1 (1998) 418-420
Chloranilate bridged sodium chains Christos Papadimitriou a9*,Panagiotis Veltsistas a, Jaromfr Marek b, Josef Novosad b, Alexandra M.Z. Slawin ‘, J. Derek Woollins ’ aDepartment ofChemistry, University of loannina, loanninu, Greece b Department of Chemistry, hiasaryk University, Kotiarska 2, 61137 Brtw, Czech Republic ‘Department of Chemistry, Loughborough Universiry, Loughborough, Leicestershire, L.E113TU, UK Received 24 August 1998
Abstract Slow crystallisation (in water glass) hasbeenused toobtainNk(ca) *3H,O (1) andNa,(ca)phen*2H,O (2) whichhavebeencharactetised b=8.472(1), c=9.816(1) A, cu=106.71(1), /3=92.04(l), by X-ray crystallography. 1: C12H120~a4014r triclinic a=6.567(1), 7=92.48(l)“, U=522 A3, P-l, Z= 1, F(OO0) =308, p(Mo-Ka) =0.72 mm-‘, 1700 observed [F>~.OV(F)] gave a final R=3.56%. 2: monoclinic, a= 10.754(l), b= 19.778(2), c= 13.681( 1) A, /3=98,55(l)“, U=2877 A3, P2,/c, Z=4, F(OO0) = 1328, p(Mo-KAY) =0.31 mm-‘, 2337 observed [F>4.0a(F)] gave a final R=5.73%. In both structures the chloranilate anions make use of chlorine atoms to 0 1998 Published by Elsevier Science S.A. All rights complete the six coordination of the sodium centres in the layer/chain systems. reserved. Keywords:
Cbloranilateanions; Layer/chain systems;Crystal structures; Sodium complexes
The coordination chemistry of catecholates/quinones is quite well established, with systems being capable of intramolecular-interligand or meta-ligand electron transfer [l41. Although numerous transition-metal complexes are known, few characterised complexes of alkali metals with quinones have been reported. Here we report the preparation and X-ray structure of sodium complexes of the chloranilate dianion. We obtained crystals of Na,( ca) *3H20 (1) from chloranilic acid and sodium acetate in silica gel ‘water glass’. Crystallisation of chloranilic acid, phenanthroline and sodium hydroxide in water glass gave [Na,(phen),(ca) *2H,O] (2) ; both compounds gave satisfactory microanalysis. In the X-ray structure of 1 ’ (Fig. 1) the chloranilate dianion coordinates to both Na+ counterions, in addition
* Corresponding author. Fax: + 30-651-44989 ‘Anal. Found: C, 24.05; H, 2.18; Na, 15.52. Calc.: C, 23.47; H, 1.97; Na, 14.98%. Crystal data: CIZH,204Na,0,4, triclinic a=6.567( 1). b=8.472(1), c=9.816(1) A, (~=106.71(1), /3=92.04(l), y= 92.48(l)“, U=522 A’, P-l, Z=l, F(OOO)=308, p(Mc-Ka)=O.72 mm-‘, 1826 reflections collected (2f3 range 3-500), R,.,=O.O78, 1700 observed [F>4.0u(F)] gave a final R=3.56% [4.62 all data]. 1387-7003/98/$ - see front matter 0 PZI S1387-7003(98)00109-9
there are three solvate water molecules. The coordination at Na( 1) consists of two oxygen atoms [ 0( 6) and 0( 7) -btidging water molecules to Na(2)], as well as a chelate [O( 1) and 0( 2) ] from the chloranilate and two additional oxygen atoms from adjacent chloranilate anions [ 0( 4) ] in the neighbouring layers on both sides of Na( 1). The Na( 2) centres are coordinated by the bridging water oxygen atoms, O(6) and O(7) bridging to Na( 1) as well as two, symmetry related, water molecules [ 0( 5) and 0( 5B) ] bridging to Na(2B), and are chelated by 0( 3) and Cl(2) of a chloranilate. The sodium centres are thus formally six coordinate and the chloranilate anions make use of all four oxygen centres and one chlorine atom for coordination. The chloranilate anions lie approximately in the UCplane of the lattice and, as mentioned above, adjacent layers are linked via 0( 4) (chloranilate) bridges and Na(2)05-05-Na(2B) bridges. The Na( l)...Na(2) and Na(2)...Na(2) distances are 3.50 and 3.47 A respectively. The surprising observation of the ‘coordination’ of the chloranilate chlorine in the ‘coordination sphere led us to synthesise another example to test if this observation was general. We obtained. [ N&phen( ca) - 2H,O] by the water glass method.
1998 Published by Elsevier Science S.A. All rights reserved.
C. Papadimittiou et al. /Inorganic Chemistry Communications 1 (1998) 418-420
419
OISAI .3Hz0 (1). Selected bondlengths (A) and angles (O): Cl( l)_c(l) 1.735(2), Cl(2)_c(4) 1*741(2), Cl(2)-Na(2) 2.9826(10). 0(1)--C(2) 1.246(2), O(l)-Na(1) 2.3576(114), 0(2)-C(3) 1.252(2), O(2)-Na(l) 2.400(2), 0(3)_~(5) 1.259(2),0(3)-Na(2) 2.34W2),0(4)-U6) 1.254(2), O(4)-Na(1) 2.3043(14), O(4)-Na(1) 2.675(2), C(l)-c(6) 1.397(3), C(l)-q2) 1.406(2), C(2M3) 1.542(2LC(3)-C(4) 1.400(3),C(4)X(5) 1.396(3),C(5)<(6) 1.541(2),Na(l)-O(4) 2.3044(14),Na(l)_0(6) 2.352(2),Na(l)_0(7) 2.567(2), Na(lW(4) 2.675(2). Na(l)-Na(1) 3.382(2), Na(l)-Na(2) 3.5040(12), Na(2)-0(6) 2.358(2), Na(2)_0(7) 2.392(2), Na(2)_0(5) 2.432.(2), Na(2)-0(5) 2.460(2), Na(WNa(2) 3.469(2), Na(Z)-Na(1) 3.5041(12), O(5)-Na(2) 2.460(2), O(6)-Na(2) 2.358(2), O(7)-Na(2) 2.392(2), O(7)-Na(1) 2.567(2). O(4)-Na(lW(6) 103.61(6), O(4)-Na(l)-O(l) 154.10(6), O(6)-Na(l)AB(l) 85.17(6), O(4)-Na(l)_0(2) 86.51(5),0(6)-Na(lPX2) 117.70(7),0(1)--Na(lW(2) 68.02(5),0(4)-Na(l)-0(7) 106.04(6),0(6)-Na(1)-0(7)83.26(6),0(1)-Na(l)-O(7) 99.11(6),0(2)-Na(lW(7) 152.88(6).0(4)-Na(1)-0(4)94.80(5),0(6)-Na(1)-0(4) 153,06(6),0(l)-Na(l)-O(4)86.71(5),0(2)-Na(l)a(4) 82.48(5)vO(7)-Na(l)~(4)72.74(5),0(3)-Na(2)-O(6) 167.45(7),0(3)-Na(2)-0(7) 103.74(7),0(6)-Na(2)-0(7)87.&j(6),0(3)-Na(2)~(5) 86.64(6), O(6)-Na(2)4(5) 86.64(6), 0(7)-W&O(5) 91.82(7), O(3)-Na(2)-0(5) 86.30(6), O(6)-Na(2)_0(5) 83.08(7), 0(7)_Na(2)_0(5) 169.91(7), O(5)-Na(2)+(5) 89.69(6), O(3)-NaW-CW 67.16(4), O(6)-Na(2)-C1(2) 120.49(5), O(7)-Na(2)_Cl(2) 87.56(5), 0(5)_Na(2)C1(2) 152.77(6), O(5)-Na(2)-C1(2) 95.64(5), Na(2)-0(5)-Na(2) 90.31(6), Na( 1)-O(6)-Na(2) 96.12(7), Na(2)-0(7)-Na( 1) 89.83(7).
fig. 1. Partoffie hfde
chainin the X-ray structureofNa,(ca)
Fig. 2. The x-ray smxtm of [NaAphenMca) .2H~01; part ofthe infinite chains. Selectedbond lengths (A) and angles (“): Na( l)-O( 1) 2.347(5), Na( l)O(2) 2.497(5), Na(lW(3) 2.384(5), Na(lW(4) 2.435(4), Na(l)-N(1) 2.459(7), Na(l)-N(10) 2.539(6), Na(2)-0(4) 2.421(5), Na(2)-0(6) 2.293(6),Na(2)-0(7) 2.393(6),Na(2)-N(la) 2.492(7),Na(2)-N(lOa) 2.494(7),Na(2)...Cl(l) 2.991(3),Na(l)...Na(2a) 4.003(4). O(l)-Na(l)O(2) 66.6(2), O(3)-Na(lW(4) 67.0(l), N(l)-Na(l)-N(l0) 67.1(2), O(6)-Na(2)-0(7) 84.1(2), N(la)-Na(2)-N(lOa) 66.6(2), O(4)Na(2) . ..Cl( 1) 66.0( 1).
420
C. Papadimitriou et al. /Inorganic
Chemistry Communications I (1998) 418-420
The X-ray structure of 2 ’ (Fig. 2) reveals each of the sodium centres to be coordinated by a l,lO-phenanthroline ligand. Na( 1) is also coordinated by four oxygens of two bridging chloranilate ligands resulting in severely distorted octahedral coordination geometry. In addition to the phenanthroline Na( 2) is coordinated by two water molecules as well as one oxygen of the chloranilate ligand [ 0( 4) shared with Na( 1) 1. Again this coordination mode results in close contacts with Cl(l) [Na...Cl 2.991(3) A] and Na(1) [Na( 1). . .Na( 2) 4.003(4) A]. The overall structure thus consists of Na( l)-chloranilate chains with Na(2) *2H20 as a ‘pendant’ group on the bridging chloranilate ligands. In 2 the IR spectrum 3 of the isolated crystals was identical with that of the bulk material. The results are similar to those reported for Ag,(ca) [S], [Pd(ca)(PPh3)2] -HZ0 [6], K,(ca)*H,O [7] and [Cu,(terpy),(ca)] [8]. The sharp
band of medium intensity at 3490 cm-’ is assigned to the V(O-H) stretching vibration of coordinated water molecules, and the very strong triplet at 1555,1545,1530 cm-’ as well as the medium band at 1380 cm- ’ are due to v(C-0) bond order of 1.5 [ 5-71. A third characteristic very strong band at 842 cm- ’ is assignable as a v(C-C~) stretching vibration
[&A. Acknowledgements Authors J.N. and J.M. wish to express their gratitude to the Grant Agency of the Czech Republic for the grants No. 203 / 95/1190 and No. 203/97/0955. References 111 R.M.
*Ad Found: C, 56.02; H, 3.36; N, 8.97; Na, 7.08. Calc.: C, 55.50; H, monoclinic 3.10; N, 8.63; Na, 6.97%. Crystal data: C,&,&O$la2C12, a=10.754(1), b=19.778(2), c=13.681(1) A, /3=98.55(l)“, U=2877 A’, P2,/c, Z=4, F(OOQ) = 1328, p(Mo-Kcr) =0.31 mm-‘, 5535 reflections collected (26 range 3-50”), 5067 independent ( Rinr= 4.48%), 2337 observed [F>4.0a(F)], gave a final R=5.73% [6.99% all data]. Both structures were solved by direct methods and refined against p using SHELXTL. 3 LR: 3585 w, 3490 m, 3380 tr, 1675 sh, 1625 s, db, 1545 vs, tr, 1485 m, db, 1380 w, 985 w, 842 vs. 570 s, 480 br, 365 w. Raman: 3060 s, db, 1612 vs - 1598 sh, 1505 m, 1460 m, 1425 vs. 1350 w, 1310 m, 1100 w, 1050 m, 850 w, 730 w, 555 w, 430 m, 360 w.
Buchanan, S.L. Kessel, H.H. Downs, C.G. Pierpont, D.N. Hendrickson, J. Am. Chem. Sot. 100 (1978) 7894. 121 S. Bhattacharya, C.G. Pierpont. Jnorg. Chem. 30 (1991) 1511. 131 C. Bemtelli, A. Dei, D. Gatteschi, L. Pardi, J. Am. Chem. Sot. 110 (1988) 6897. [41 S. Bhattacharya, S.R. Boone, G.A. Fox, C.G. Pierpont, J. Am. Chem. sot. 112 (1990) 1088. [51 P.E. Riley, S.F. Haddad, K.N. Raymond, Jnorg. Chem. 22 (1983) 3090. [61 W.Y. Yeong, R.A. Holwerda, Jnorg. Chem. 27 (1988) 2571. [71 W.Y. Yeong, R.A. Holwerda, Jnorg. Chem. 28 (1989) 2674. [81 J.V. Folgado, R. lbanez, E. Coronado, D. Beltran, J.M. Savariault, J. GaJy, Jnorg. Chem. 27 (1988) 19.