2934 zyxwvutsr zyxwvutsrqpo zyxwvu zyx zyxw zyxwvutsrq zyxwvu Inorg. Chem. 1987, 26, 2934-2939 Contribution from the Departments of Chemistry, Delaware State College, Dover, Delaware 19901, University of Delaware, Newark, Delaware 19716, and State University of New York, Plattsburgh, New York 12901 Preparation, Structure, and Magnetic Properties of Na,oFe4Cu2W18070Hs~29820, Containing the Double Keggin Anion [ F e 4 C U 2 W 1 8 0 7 0 H ~ ] ’ ~ Sadiq H. Wasfi,*la Arnold L. Rheingold,*Ib Gerald F. Kokoszka,*lc and Alan S. Goldsteinlc Received February 19, 1987 The sodium salt of the double Keggin anion [Fe4C~2W18070H6] Io- has been prepared from Na2W0,.2H20, Fe(N03),.9H20, and C U ( C H ~ C O O ) ~ . Hin~ water O and isolated in cystalline form as NaloFe4Cu2W18070H6~29H20: monoclinic, P2,/n, a = 13.079 (3) A, b = 17.772 (4) A, c = 21.104 (7) A, p = 93.46 (2)O, V = 4896 (2) A’, 2 = 2, D(ca1cd) = 3.75 g cmW3.This is the first polytungstate ion to contain six paramagnetic centers and the first with four paramagnetic centers bridged by a single oxygen atom. The anion contains two octahedral Cu(I1) sites, two octahedral Fe(II1) sites, and two tetrahedral Fe(II1) sites forming a Cu2Fe402,core. The cationic portion of the structure consists of two [Na502,15+oxygen-bridged structures draping the anion in necklace fashion. The magnetic susceptibility of the salt was determined for the temperature range 4-374 K; it exhibits strong antiferromagnetic interaction at low temperature. xMTshowsa pronounced decrease at about 100 K and approaches a constant value at 20 K. The EPR spectrum in the 77-300 K range consists of a broad feature (1000 G) with little structure centered at about g = 2.2 and a weaker second line at about g = 4.4. The broad line suggests that the six central metal ions participate in the magnetism in this temperature range. Introduction Heteropolyoxoanions of groups 5 and 6 form a large class of complexes with an extraordinary array of interesting properties.* To a large extent, these discrete inorganic complexes m a y be viewed as fragments of close-packed metal oxide lattices, and they provide well-defined models for examining many of the properties of such lattices, including magnetic interaction, electron delocalization, and heterogeneous catalysis. The study of spin-spin interactions with multinuclear centers is gaining increasing att e n t i ~ n . Several ~ systems of coupled spins have been reported. These systems include pair^,^,^ and some finite chains* with similar and dissimilar spins and g values. In 1972, Baker9 e t al. reported six heteropoly complexes in which a pair of paramagnetic centers of different spins and g values are coupled. The double Keggin structure anion’0.” we now report, [ F ~ ~ C U ~ W I ~lo-,O provides ~ O H ~ ]a well-characterized system to study t h e magnetic interaction of four Fe(II1) sites (two tetrahedral, two octahedral) and two Cu(I1) sites (octahedral) in an oxygen-bridged network. Such systems a r e analogous to the redox center of t h e cytochrome oxidase molecule.” Experimental Section Preparation of Na,oFe4Cu2W,8070H6~29H20. A solution of 17 g (42.1 Table I. Crystal and Data Collection Parameters (a) Crystal Parameters NaloFe4Cu2W 18070H6.29H20 5536.13 monoclinic P2,ln a, 8, 13.079 (3) b, 8, 17.772 (4) c, 8, 21.104 (7) deg 93.46 (2) v, A3 4896 (2) Z 2 color brown cryst dimens, mm 0.21 X 0.21 X 0.43 temp, OC 23 F , cm-l 234.2 D(calcd), g cm-3 3.75 D(obsd), g 3.70 F(000) 4966 formula fw cryst syst space group P 3 (b) Data Collection diffractometer radiation wavelength, 8, monochromator scan limits, deg scan technique scan speed, deg min-l no. of reflcns collcd no. of unique data no. of unique data, F, 3 3a(F0) std reflcns decay mmol) of Fe(N03),.9H20 in 200 mL of distilled water was combined with 30 m L of a saturated sodium acetate solution and added to a solution containing I O g (50.1 mmol) of CU(CH,COO)~.H~O in 100 mL of distilled water. The resulting solution containing Cu2+ and Fe” was Nicolet R3 Mo Koc 0.71073 oriented graphite 4 c 20 c 45 w zyxwvutsr (1) (a) Delaware State College. (b) University of Delaware. (c) State University of New York, Plattsburgh. (2) (a) Baker, L. C. W. In Advances in the Chemistry of Coordination Compounds; Kirshner, S . , Ed.; Macmillan: New York, 1961; p 608. (b) Evans, H. T., Jr. Perspect. Struct. Chem. 1971, 4 . (c) Weakley, T. J. R. Struct. Bonding (Berlin) 1974, 18, 131. (d) Day, V. W; Klemperer, W. G . Science (Washington, D.C.)1985, 228, 533. ( e ) Pope, M . T. Heteropoly and Isopoly Oxometalates; Springer-Verlag: New york, 1983. (f) Kokoszka, G.; Padula, F.; Siedle, A. In Biological and Inorganic Copper Chemistry; Karlin, K., Zubieta, J. Eds.; Adenine: Guilderland, NY, 1985. (3) Magnetostructural Correlations in Exchange Coupled Systems; Willet, R. D., Gatteschi, D., Kahn, A., Eds.; NATO-AS1 Series; D. Reidel: Boston, 1986. (4) (a) Bleaney, B.; Bowers, K. D. Proc. R. SOC.London, A 1952, 214,451. (b) Weltner, W., Jr. Magnetic Atoms and Molecules; Van Nostrand Reinhold: New York, 1983. (5) Smart, J. S. Treatise Mod. Theory Matter 1963, 3, 63. (6) (a) Kambe, K. J . Phys. SOC.Jpn. 1950,5,48. (b) Orgenstern-Badarau, E.; Wickman, H. H. Inorg. Chem. 1985, 24, 1889. (7) Viet. R.: Girard, J.-J.; Kahn, 0.;Robert, F.; Jeannin, Y. Inorg. Chem. 1986, 25, 4175. (8) (a) Figgis, B. N.; Lewis, J. Prog Inorg. Chem. 1964,6, 37. (b) Hatfield, W. In Biological and Inorganic Copper Chemistry; Karlin, K., Zubieta, J. Eds.; Adenine: Guilderland, NY, 1985. (9) Baker, L. C. W.; Baker, V . E. S . ; Wasfi, S. H.; Candela, G. A,; Kahn, A. H. J , Chem. Phys. 1972, 6, 4917. (10) Weakley, T. J. R.; Evans, H. T., Jr.; Showelle, J. S.; Tourne, G. F.; Tourne, C. M. J . Chem. Soc., Chem. Commun. 1973, 139. (11) Keggin, J. F. Proc. R . Soc. London, A 1934, 144, 75. (12) Powers. L.; Chance, B. J . Inorg. Biochem. 1985, 23, 207. 0020-1669/87/1326-2934$01.50/0 T n l a x l Tmax ow-] 4-10, variable 6670 6140 4944 3 std/197 reflcns <1% I .53 zyxwv (c) Refinement RF,% 6.87 GOF R ~ FYc, 7.32 g“ No/’% 7.6 N o = 2 a (Fa)+ g F 2 . 1.373 0.0025 0.054 added dropwise to a solution of 112 g (339.6 mmol) of sodium tungstate, Na2W04.2H20,in 500 mL of distilled water. After the completion of the addition, the solution was boiled for 1 h and left to cool to room temperature. After filtration, the filtrate was left to crystallize; crystals of NaloFe4Cu,W,8070H6~29H20 formed overnight. Fe was determined by precipitation as Fe20,, Cu by precipitating it as Cu-benzoin oxime, and W by precipitation either as tungstic acid or cinchonin tungstate followed by conversion to tungstic oxide by ignition at 750 0C.13,14Sodium and H,O (Karl Fischer) were determined by Galbraith Laboratories, Knoxville, Tn. Anal. Calcd for Na,oFe4Cu2W,8070H6~29H20: Na, 4.15; Fe, 4.03; Cu, 2.29; W, 59.78; H 2 0 , 10.09. Found: Na, 4.95; Fe, 3.41; Cu, 2.34; W, 57.05; H20, 10.17. ( 1 3) Vogel, A. 1. Quantitatiue Inorganic Analysis, 2nd ed.; Longmans, Green and Co.: London, 1951; p 430. (14) Willard, H. H.; Diehl, H. Advanced Quanritatiue Analysis; Van Nostrand: New York, 1943; p 218. 0 1987 American Chemical Society zyxw zyx zy zyxwvutsrqp zyxwvutsr zyxwvutsrqp Inorganic Chemistry, Vol. 26, No. 18, 1987 2935 Na ,,Fe,Cu2W 8070H6*29H20 Table 11. Atomic Coordinates (X104) and Isotropic Thermal Parameters X Y Z ua -1711 (1) 5545 (1) 9472 (1) 7110 ( i j -4470 (1j 10637 (1) -4446 (1) 6880 (1) 7793 (1) -2601 (1) 7009 (1) 10670 (1) 4610 (1) -2784 (1) 10840 (1) -2564 (1) 6731 (1) 7819 (1) 4428 (1) -2794 (1) 8330 ( I ) 5612 (1) -3658 (1) 6686 (1) 6069 (1) -3652 (1) 12043 (1) -4643 (2) 4616 (2) 11897 (3) 5593 (2) -5380 (2) 10504 (3) 4251 (2) -6270 (2) 10627 (3) 3020 (7) -608 (8) 9601 (11) 1826 (8) -3812 (8) 9426 (12) 1824 (8) 878 (7) 9690 (10) 2870 (6) -2508 (7) 9620 (10) 964 (7) 2286 (8) 11395 (11) 4979 (12) -1743 (12) 10602 (17) 5212 (9) -2915 (10) 9492 (15) 5627 (10) -731 (12) 9420 (1 7) 6061 (10) -1976 (11) 8363 (17) 6240 (10) -1996 (11) 10366 (16) 4798 (10) -1787 (10) 8485 (16) -3428 (1 1) 7535 (IO) 10786 (18) 6376 (9) -3636 (10) 10484 (13) 7184 (8) -4332 (11) 9180 (17) -4247 (1 3) 6867 (9) 12028 (16) 6510 (11) -5196 (11) 10458 (16) 7785 (11) -4980 (12) 10955 (19) 7245 (11) -3401 (11) 7530 (16) 3853 (9) -6395 (11) 11870 (15) -4799 (12) 3660 (12) 11927 (16) 6401 (11) -4215 (12) 6511 (17) -4154 (29) 1381 (21) 11099 (33) 7503 (11) -4905 (12) 7288 (18) -2598 (1 1) 7066 (9) 9244 (15) (A2X 10)) X ~~ 11963 (15) 11000 (19) 10796 (15) 9670 (15) 11638 (17) 11786 (17) 7411 (17) 6646 (16) 8501 (17) 7286 (14) 7510 (15) 5421 (18) 7116 (17) 13353 (18) 11707 (20) 10642 (1 5) 13224 (16) 10538 (20) 10914 (17) 9690 (17) 8265 (18) 9791 (23) 8178 (22) 7911 (28) 9729 (17) 10605 (18) 8218 (22) 11496 (20) 7899 (18) 9930 (23) 9539 (19) 10887 (24) 11124 (26) 6876 (19) 7195 (34) 8525 (28) Y -2791 (12) -1882 (13) -3769 (1 2) -2568 (IO) -2988 (10) -2486 (12) -1819 (12) -2727 (13) -3764 (12) -2999 (10) -2506 (1 1) -3551 (14) -4501 (12) -3612 (15) -4458 (1 1) -5335 (10) -3952 (12) 554 (12) -1590 (13) -575 (12) -1506 (12) -630 (14) 263 (19) -3434 (16) -2481 (13) -3612 (13) -3367 (14) 1326 (13) 667 (14) 315 (16) 2086 (18) 2748 (16) 3293 (20) 4459 (13) 5624 (21) 4035 (23) Z ua 6688 (9) 7534 ( 1 1 ) 4452 (10) 4056 (9) 5404 (10) 4151 (11) 7202 (1 1) 6202 (12) 4311 (9) 5017 (9) 3770 (1 1) 5336 (10) 5222 (11) 6050 (10) 5577 (11) 4684 (10) 4659 (11) 2892 (1 1) 3066 (1 1) 1917 (1 1) 2883 (12) 4090 (1 3) 3197 (18) 915 (16) 1710 (11) 2816 (11) 2538 (17) 1697 (13) 1638 (13) 719 (13) 1044 (14) -68 (13) 1660 (18) 670 (18) 75 (19) 1065 (15) 56 (7) 78 (9) 61 (7) 51 (7) 61 (7) 63 (8) 67 (8) 76 (9) 63 (8) 51 (7) 60 (7) 74 (9) 67 (8) 75 (9) 72 (9) 55 (7) 64 (8) 72 (9) 72 (9) 70 (8) 72 (9) 95 (11) 125 (15) 116 (14) 73 (9) 71 (9) 106 (13) 83 (10) 82 (10) 96 (11) 99 (12) 98 (12) 125 (15) 113 (14) 154 (19) 128 (16) zyxwvutsrqp zyxwvutsrqpo "Equivalent isotropic U defined as one-third of the trace of the orthogonalized U , tensor. 03' 03' 033 031' Figure 1. Anion structure and labeling scheme. A center of symmetry relates the labeled and unlabeled atoms. zyxwvutsrqp zyxwvuts zy zyxwvutsrqpo zyxwvut 2936 Inorganic Chemistry, Vol. 26, No. 18, 1987 Wasfi et al. Table 111. Selected Interatomic Distances (A) and Angles (deg) for Na,oFe4CuzW,,070H6.29Hz0 (a) W-0 Anion Distances (h0.02 (i) Axial Exterior 1.75 W(6)-O(26) 1.72 W( 7)-O( 30) 1.71 W(8)-0(3 1 ) 1.73 W(9)-O(33) 1.70 (ii) Axial Interior' 2.25 W(6)-O( 14) 2.15 W(7)-0(2) 2.22 W(8)-O( 14) 2.28 W(9)-0(8) 2.25 (iii) Equatorial 1.96 W(5)-O(23) 1.93 W( 5)-O( 24) 1.89 W(6)-0(4) 1.98 W(6)-O( 13) 2.06 W(6)-O( 19) 1.94 W (6)-O( 27) 1.96 W(7)-0(6) 1.81 W(7)-O(23) 1.90 W(7)-0(28)b 2.05 W (7)-O( 29) 1.95 W(8kOf 16) 1.81 Wt8j-Oi27j 1.97 W(8)-O(29) 1.84 W(8)-0(32). I .88 W(9)-O(10) 1.89 W(9)-O(20) 2.04 W(9)-O(24) 1.78 W(9)-0(34)a (b) Fe-0 Anion Distances (k0.02 Fe(l)-O(l1) 1.97 Fe(l)-0(35a) Fe(l)-0(34) 2.27 Fe(2)-0( 14) Fe(l)-0(35) 1.94 Fe(2)-O(35) Fe(l)-0(22a) 2.29 Fe(2)-0(2a) Fe(l)-0(28a) 2.01 Fe(2)-0(8a) cu-O( 15) cu-O(22) C~-0(34) 1.76 1.78 I .73 1.72 2.27 2.19 2.14 2.18 1.91 1.95 1.93 1.89 1.95 1.87 1.96 2.01 1.76 1.94 1.96 2.07 1.92 1.73 1.99 101 73 171 160 75 164 75 I68 102 158 160 101 74 161 101 74 0(2)-W(7)-0(6) 0(2j-w(7 j-oi23) 0(2)-W(7)-0(30) 0(6)-W(7)-0(28) 0(23)-W(7)-0(29) 0(28)-W(7)-0(30) 0(16)-W(8)-0(29) O( 16)-W(8)-0( 31 ) 0(16)-W(8)-0(14a) 0(27)-W(8)-0(32) 0(27)-W(8)-0(14a) 0(31)-W(8)-0(32) 0(31)-W(8)-0(14a) 0(8)-W(9)-0(10) 0(8)-W(9)-0(20) 0(8)-W(9)-0(33) O( lO)-W(9)-0(24) 0(20)-W(9)-0(34) O( 24)-W(9)-0( 33) 0(33)-W(9)-0(34) 75 74 168 160 163 104 159 101 74 162 73 105 165 72 73 164 161 162 101 103 zyxwvu zyxwvuts 2.02 1.89 1.81 A) (d) Na-0 Cation Distances (f0.03 A) Na(l)-O(37) 2.42 Na(3)-O(49) Na(1)-O(38) 2.45 Na(3)-O(50) Na(l)-0(39) 2.34 Na(3)-0(2a) Na(l)-O(40) 2.37 Na(4)-O(23) Na(1)-O(41) 2.26 Na(4)-0(38) Na( 1)-O(42) 2.47 Na(4)-O(40) Na(2)-0( 17) 2.51 Na(4)-O(44) Na(2)-O(43) 2.68 Na(4)-O(45) Na(2)-O(44) 2.41 Na(4)-O(46) 2.55 Na(5)-O(47) Na(2)-O(45) Na(2)-O(46) 2.38 Na(5)-0(50) Na(2)-0(12a) 2.36 Na(5)-0(51) Na(3)-O(37) 2.52 Na(5)-O(52) Na(3)-O(39) 2.59 Na(5)-0(25a) Na(3)-O(47) 2.52 Na(5)-0(36a) Na(3)-O(48) 2.38 2.02 1.89 1.90 1.85 1.91 (e) Nonbonded Distances 3.120 (5) Fe(2)...Cu 3.257 (6) 2.58 2.71 2.44 2.50 2.37 2.51 2.46 2.35 2.46 2.30 2.47 2.39 2.36 2.44 2.63 (m) Anion-0-Cation Angles (kl") W(2)-0(12)-Na(2a) 136 W(7)-0(23)-Na(4) W(4)-0(21 )-Na(3a) 144 W(5)-0(25)-Na(5a) W(5)-0(23)-Na(4) 126 Cu-O(36)-Na(Sa) 3.399 (6) (f) 0-W-0 Anion Angles with Greater than IO" Deviations from O( 1 )-W( 1)-0(4) 0(2)-W( I )-0(3) 0(2)-W( 1)-O(6) O(3)-W( 1)-0(5) 0(5)-W( 1 )-0(6) 0(7)-W(2)-0(8) 0(7)-W(2)-0(11) 0(8)-W(2)-0(10) 72 164 103 160 73 (g) 0-Cu-0 and 0-Fe-0 Anion Angles (*I0) with Greater Than 10' Deviations from Octahedral Symmetry (Cu and Fe(1)) and Tetrahedral Symmetry (Fe(2)) 0(1l)-Fe(l)-0(35) 168 0(28a)-Fe(l)-0(35a) 166 0(35)-Fe(l)-0(35a) 78 (h) W-0-W Anion Bond Angles (*I0) W( I)-O(l)-W(5) 114 W(2)-0(10)-W(9) 113 96 W(3)-0(14a)-W(6) W( 1 )-0(2)-W(5) 97 98 W( 1 )-0(2)-W(7) 97 W(3)-0(14a)-W(8) 98 W(5)-0(2)-W(7) 122 W(6)-0(14a)-W(8) 114 W( 1)-0(4)-W(6) 151 W(3)-0(16)-W(8) W( 1)-0(5)-W(4) 151 W(4)-O( 19)-W(6) 155 W(l)-0(6)-W(7) I15 W(4)-0(20)-W(9) 1 I7 W(2)-0(7)-W(4) 117 W(5)-0(23)-W(7) 114 150 W(2)-0(8)-W(4) 98 W(5)-0(24)-W(9) W(2)-0(8)-W(9) 99 W(6)-0(27)-W(8) 116 150 W(4)-0(8)-W(9) 97 W(7)-0(29)-W(8) W(2)-0(9)-W(3) 152 (i) W-0-Cu Anion Angles (f 1 ") Cu-O( 15)-W(3a) 138 Cu-O(2a)-W(8a) 140 I32 Cu-O(22)-W( 5 ) (j)W-0-Fe Anion Angles (*lo) W(2)-0(1l)-Fe(l) 143 W(7a)-0(2a)-Fe(2) 1I8 W(5a)-0(22a)-Fe(l) 133 W(2a)-0(8a)-Fe(2) 1 I8 122 W(7a)-0(28a)-Fe( 1 ) 145 W(4a)-0(8a)-Fe(2) W( 1 a)-0(2a)-Fe(2) 123 W(9a)-0(8a)-Fe(2) 1 I9 W(5a)-0(2a)-Fe(2) 122 (k) Cu-0-Fe Anion Angles (&lo) Cu-O(22)-Fe( 1 a) 91 Cu-O(35)-Fe(la) 101 Cu-O(34)-Fe( 1 ) 91 Cu-O(35)-Fe(2) 118 Cu-O(35)-Fe( I ) 102 (1) Fe-0-Fe Anion Angles (*lo) Fe( 1)-O(35)-Fe(la) 102 Fe(2)-0(35)-Fe(la) 1 I6 (c) Cu-0 Anion Distances (k0.02 A) 2.04 Cu-O(35) 2.06 2.13 CU-O(36) 2.13 2.08 Cu-O( 32a) 2.01 Fe( 1). .Cu Fe(l)...Fe(2) 0(16)-W(3)-0(14a) o(i8j-wi3j-oi14aj O( 18)-W(3)-0(15a) 0(5)-W(4)-0(7) 0(7)-W(4)-0(8) 0(7)-W(4)-0(21) 0(8)-W(4)-0(20) O(8)-W(4)-0(2 1) 0(19)-W(4)-0(20) O( 1 )-W(5)-0(2) O(I)-W(5)-0(22) 0(2)-W(5)-0(22) 0(2)-W(5)-0(25) 0(22)-W(5)-0(25) 0(23)-W(5)-0(24) 0(4)-W(6)-0(3) O( 13)-W(6)-0(26) 0(13)-W(6)-0(14a) O( 19)-W(6)-0( 27) 0(2)-W(6)-0(27) 0(27)-W(6)-0(14a) Octahedral Angles (&lo) 164 0(8)-W(2)-0(12) 168 0(9)-W(2)-0(10) 73 0(9)-W(2)-0(12) 103 O(Il)-W(2)-0(12) 161 0(9)-W(3)-0(16) 72 0(9)-W(3)-0(18) 161 0(13)-W(3)-0(14a) 74 0(13)-W(3)-0(15a) 166 158 101 103 158 101 72 162 (n) Na-0-Na Anion Angles (&lo) Na( 1)-0(37)-Na(3) 96 Na(2)-0(45)-Na(4) Na( 1)-0(38)-Na(4) 90 Na(2)-0(46)-Na(4) Na( I)-0(39)-Na(3) 96 Na(3)-0(47)-Na(5) Na(l)-0(40)-Na(4) 88 Na(3)-0(50)-Na(5) Na(2)-0(44)-Na(4) 82 (0)0-Na-0 1I 5 139 130 81 83 107 97 Anion Angles (*lo) with Greater Than IOo IDeviations from Octahedral Symmetry 0(37)-Na(l)-0(38) 105 0(43)-Na(2)-0(45) 155 0(37)-Na(l)-0(40) 159 0(43)-Na(2)-0(12a) 107 0(38)-Na( l)-0(42) 167 0(44)-Na(2)-0(12a) 165 0(39)-Na( 1)-O(42) 103 0(37)-Na(3)-0(39) 73 O( 17)-Na(2)-0(43) 1 16 0(37)-Na(3)-0(47) 79 O( 17)-Na(2)-0(46) 161 0(37)-Na(3)-0(48) 119 0(43)-Na(2)-0(44) 79 0(37)-Na(3)-0(49) 131 zyxwvutsr zyxw zyx zyx zyxwvutsrqpo NaloFe4Cu2Wle070H6.29H20 Inorganic Chemistry, Vol. 26, No. 18, 1987 2937 Table I11 (Continued) 0(37)-Na(3)-0(50) 0(39)-Na(3)-0(47) 0(39)-Na(3)-0(49) 0(39)-Na(3)-0(50) 0(39)-Na(3)-0(21a) 138 109 71 147 133 0(47)-Na(3)-0(48) 0(47)-Na(3)-0(50) 0(47)-Na(3)-0(21a) 0(48)-Na(3)-0(21a) 0(49)-Na(3)-0(50) 162 74 102 79 76 0(49)-Na(3)-0(2 1a) 0(50)-Na(3)-0(21a) 0(23)-Na(4)-0(46) 0(38)-Na(4)-0(45) 0(40)-Na(4)-0(45) 149 75 104 101 168 0(44)-Na(4)-0(46) 0(47)-Na(5)-0(51) 0(47)-Na(5)-0(36a) O(5 l)-Na(5)-0(52) 79 151 73 105 “Forms link to Cu. bForms link to Fe(1). CAllform links to Fe(2). Table IV. Magnetic Susceptibilities of Na,oFe4Cu2Wl,070H6~29H20“ T,K 106x. 106YMc 373 350 323 300 279 250 210 180 140 110 90 75 60.4 50.9 40.4 30.3 20.4 10.65 7.20 5.10 4.59 3.18 3.23 3.27 3.35 3.39 3.50 3.66 3.90 4.35 5.04 5.61 6.28 7.44 8.51 10.23 13.19 19.03 35.92 53.04 76.62 84.53 18 776.2 19055.7 19 279.3 19 726.5 19950.1 20 565 21 459 22 801 25 317 29 174 32 360 36 105 42 590 48 571 58 186 74732 107377 201 793 297494 429306 473523 The Fe and C u sites were crystallographically unambiguous; the visible and EPR spectra indicated tetragonal sites for Cu(I1) and TXMc 7.00 6.67 6.23 5.92 5.56 5.14 4.5 1 4.10 3.54 3.20 2.91 2.70 2.51 2.47 2.35 2.26 2.19 2.14 2.14 2.19 2.17 (xMc)-’ t h e strong antiferromagnetic coupling indicated the placement 53.25 52.47 5 1.86 50.69 50.13 48.62 46.60 43.86 39.49 34.28 30.90 27.69 23.48 20.59 17.19 13.38 9.31 4.95 3.36 2.33 of the two Fe(II1) sites. The pattern and degree of oxygenation about each W(V1) site is precisely known by crystallography. T h e anion charge is completed by six H+ ions, the locations of which a r e unknown. T h e 10 Na+ ions were crystallographically confirmed. The assignment of 29 “waters of hydration” is confirmed zyxwvutsrqp by Karl Fischer titration d a t a a n d by crystallographic location of otherwise unassigned oxygen atoms. Overall, the composition Nalo[Fe4Cu2W18070H6].29H20 is supported by the close agreement between the calculated (3.75 g ~ m - and ~ ) experimental (3.70 g ~ m - densities. ~ ) Structure of Na,oFe4Cu2W,8070H,~29H20. The anionic and cationic portions of the structures are interlinked through five bridging oxygen atoms ( 0 ( 1 2 ) , 0 ( 2 1 ) , 0 ( 2 3 ) , 0 ( 2 5 ) , and O(36)) to form an infinitely extended three-dimensional array. Figure 1 shows the [Fe4CU2W18070H6]~*anion in a ball-and-stick representation with its labeling scheme. A stereoview is given in Figure 2. T h e anion structure is essentially that of a doubled showed t h a t the atomic ratio for t h e metals, Cu:Fe:W, is 1:2:9. and interpenetrating Keggin ion structure,’’ the halves being related by a crystallographic inversion center. Linking of the halves occurs through Cu-0 bridges at the octahedrally coordinated Fe(1) and Fe( 1’) sites as shown in Figure 3. The Fe( 1) octahedron is distorted by elongation of the O(34)-Fe( 1)-O(22’) axis whose Fe-0 bonds average 2.28 (2) 8, compared t o an equitorial plane average of 1.98 (2) 8,. All six Fe(1)-0 bonds form links to other oxymetalate polyhedra. T h e structure is closely related t o t h a t reported b y W e a k l e y f o r t h e anion (P2C0qW18070H4)~*.~~~~~ The six oxygen atoms a t C u ( 1) form a fairly regular octahedral coordination site with an average C u - 0 distance of 2.08 (2) A; one of t h e six oxygen atoms, 0 ( 3 6 ) , is a water molecule (cf., the average Cu-0 distance in C U ~ M Oof~ 2.05 O ~ 8, ~ and in N a C u (OH)(Mo04) of 2.13 AI7). T h e Fe-0 distances and angles a t Fe(2) show a relatively undistorted tetrahedral environment but with F e - 0 distances (average 1.89 (2) 8,)considerably shorter than those a t Fe(1); all four bonds t o Fe(2) a r e linking. The bond parameters of the nine independent W(V1) octahedra surrounding the Cu2Fe4011core are within normal ranges2d,2efor individual bond types as grouped in Table 111. The cationic portion of the salt (Figure 4) consists of five Na+ ions linked by oxygen atoms of water molecules to form a nearly semicircular cradle around each end of the anion with oxygen links t o t h e cradled anion and also to adjacent anions. The structure is completed by six lattice water molecules for each double anion, which form many hydrogen-bonded contacts, the shortest being either t o each other, e.g., O(90)-O(92) = 2.39 (4) A, or t o the cationic structure, e.g., O(90)-O(41) = 2.27 (5) A. The magnetic susceptibility measurements (Figure 5) show a strong antiferromagnetic coupling of the spins. However, a t the highest temperature (374 K ) some spin-spin coupling remains, while in the lower range t h e product XT approaches a constant value (see Table IV). The magnetic moment in the temperature region below about 20 K may be estimated from the equation of I.L = 2 . 8 4 ( ~ , T ) ’ / ~and produces a result of about 3.2. T h e value is approximately that for two unpaired electrons per formula unit. T h e lowest state would seem to be paramagnetic and the excited spin states depopulated by 2 0 K. Spin-spin coupling constants of 10-100 K would not seem unreasonable in view of the simple bridging geometry found in the central metal core (see Figure 3). T h e paramagnetism t h a t remains below 20 K is not understood (15) Selwood, P. Mugnetochemistry, 2nd ed.;Interscience: New York, 1956; p 78. (16) Klemm, W. 2. Anorg. Allg. Chem. 1940, 244, 377; 1941, 246, 347. (17) Moini, A,; Peascoe, R.; Rudolf, P. R.; Clearfield A. Inorg. Chem. 1986, 25, 3782 “Units: 2.1 1 xg,cm3 g-I; xM,cm3 mol-’. Visible spectra were recorded on a Perkin-Elmer Lambda 3 spectrophotometer. X-ray Structural Determination. Table I contains crystal data and the parameters of data collection and refinement. Crystals suitable for an X-ray diffraction structural determination were obtained directly from the reaction mixture. The unit-cell parameters were obtained from the least-squares fit of the angular settings of 25 well-centered reflections (20’ 6 20 6 28’). The space group was uniquely assigned from systematic absences. A profile fitting procedure was used to improve the accuracy of the intensities of weak reflections. An empirical absorption correction was applied to the intensity data (256 data, six-parameter pseudoellipsoid). The structure was solved by direct methods (SOLV),and completed by a series of difference Fourier syntheses. The identities of the three independent, first-row metal atoms was confirmed by site occupancy ( K ) refinement. If an Fe site was misassigned to Cu, K was 0.90 (1); if a Cu site was misassigned to Fe, K was 1.12 (1). All current assignments yielded K = 1 .OO (1). The final model included anisotropic contributions for all non-hydrogen atoms. No attempt was made to include hydrogen atom contributions. The final difference map was devoid of chemically relevant peaks although a background “noise” level of 1.2-1.6 e A-’ was present in the vicinity of the W atoms. All computations and sources of scattering factors are contained in the SHELXTL (4.1) program library (Nicolet Corp., Madison, WI). Atomic coordinates are provided in Table 11, and bond distances and angles are provided in Table 111. Additional crystallographic data are available (see paragraph regarding supplemental material at the end of this paper). Magnetic Measurements. Susceptibility measurements were determined by the SQUID method (superconducting quantum interference detector) between the He(l) temperature -4 K and 374 K. The diamagnetic corrections were those given by Selwood based on work by Klemm.15,16The results are summarized in Table IV. EPR spectra were obtained at the X-band with a reflection cavity spectrometer in the temperature range 77-300 K. The broad features were centered below DPPH, which was used as an internal standard. zyxwvutsrqp Results and Discussion Determination of the Composition of Na,o[Fe4CuzW,,070- H6]29H20.Analytical and crystallographic characterization zyxwvutsrqp zyxwvutsr 2938 Inorganic Chemistry, Vol. 26, No. 18, 1987 W a s f i et al. Figure 2. Stereoview of the unit-cell packing. I , I 1 I I 1 uuu 100 T IW Figure 5. Plot of the inverse of the molar magnetic susceptibility vs. absolute temperature. 2u0 Figure 3. Central temperature range. A half-field line was also observed. From the measured crystallographic data a linewidth estimate can be made. The Van Vleck isotropic approximation is core of the anion. + 1)11/2(d/m) H,, = 4.72 x 104[s(s 017 R 051 io2 0 041 Figure 4. [NaS(H20)22]S+ cation association. but might be associated with spins predominantly on the two Cu(I1) ions. Such a possibility would be consistent with the observed g values in the E P R spectrum and the low temperature X T product. Moreover, it would imply fairly strong antiferromagnetic Fe(II1)-Fe(II1) couplings in the Cu2Fe,Oz2core as found in the crystallography. It is expected that the magnetic interaction will be quite complex and unique because all six paramagnetic centers are within reasonable distances for exchange interaction (see Table IV). The four bridged Fe+3 ions lie closer to each other than the bridged paramagnetic centers reported by Baker, et. a]., of 3.3 A.9 The longest distance between two Fe+3 ions in the present complex anion is Fe(1')-Fe(2) = 3.259 A. The EPR spectra are consistent with the magnetic susceptibility data. A broad asymmetric peak centered about g = 2.2 with a width of nearly 1000 G was the major feature in the 77-300 K where d is the density, m is the molecular weight and S is taken as 5 for convenience in the calculation. This produces a line width of about 150 G, which is considerably smaller than the measured value. The observed line width may be associated with unresolved fine structure and possibly the superposition of various spin states. DipoleAipole interactions within the cluster remains a possibility down to the lowest measured temperature. The visible spectrum of a 5.69 X M aqueous solution of the sodium salt of the anion is characterized by a wide absorption maximum around 830 p m ( ~ 1 2 9 4 8cm-I) with an extinction coefficient of 80. A review of the spectra of copper(I1) in different geometries indicates a tetragonal geometry for Cu(I1). The hexaaquocopper(I1) ion has a single, broad maximum at 12 000 cm-l with an extinction coefficient of about 12, but it is clear that the envelope contains more than one transition.'* Regular tetragonal derivatives of Cu(I1) are very common. In general, tetragonal copper(I1) derivatives, if approximately regular, are expected to give a broad band (at room temperature) with a weak extinction c ~ e f f i c i e n t . ' ~However, spin-spin interactions can add appreciable intensity due to the magnetic dipolar transition probability supplementing the unusual electric dipolar mechanism. In Cu(I1) in 11:l and 17:2 heteropoly complexes, Tourne2' found the absorption band with a maximum a t 10690 cm-I for (GeCuWI1O4)*-,11 240 cm-I for (PCuWIIOa)'-, and 11 230 cm-' for (P2CuW,,0,,)10-. The molar absorptivities for each of the complexes increased by a factor of 4 over that of [ C U ( H ~ O ) ~ ] ~ + . The increase in intensity is attributed to the deformation of the zyxwv (18) Lewis, J.; Wilkins, R. G.Modern Coordination Chemistry; Interscience: New York, 1960; p 287. (19) Podler, D. Physica (Amsrerdam) 1942, 9, 709. (20) Simmon, V. E. Doctoral Dissertation, Boston University, 1965; p 320. (21) Tourne, C. C. R. Seances Acad. Sci., Ser. C. 1968, 266, 702. zyxwvut zyxwvut zyxwvu zyxwv 2939 Inorg. Chem. 1987, 26, 2939-2943 C u 0 6 octahedronZoas well as the enhancement due to increased magnetic dipole transition probability. The latter observation supports our contention that the metal ions are exchange coupled. Acknowledgments. S.H.W. thanks Dr. George A. Candela of the National Bureau of Standards for lending his expertise in the magnetic susceptibility measurements, A.L.R. thanks N S F for supporting the purchase of the diffractometer, and G.F.K. acknowledges the donors of the Petroleum Research Fund, ad- ministered by the American Chemical Society, for partial support of this work. Registry No. Nalo[Fe4Cu2W,80,0H,].29H20, 109466-62-8;Fe(NO&, 10421-48-4;Cu(CH3C00),, 142-71-2;Na,WO,, 13472-45-2. Supplementary Material Available: Tables 2S-4S, listing bond distances and angles and anisotropic thermal parameters (7 pages); Table lS, listing observed and calculated structure factors (29 pages). Ordering information is given on any current masthead page. zyxwv Contribution from the Laboratoire de Spectrochimie des Elements de Transition, UA No. 420, Universit6 de Paris-Sud, 9 1405 Orsay, France, and Departament de Cristal.lografia i Mineralogia, Universitat de Barcelona, 08007 Barcelona, Spain Magnetic Interaction and Spin Transition in Iron( 11) Dinuclear Compounds. Crystal Structure of (~-2,2'-Bipyrimidine)bis[ (2,2'- bipyrimidine)bis( thiocyanato)iron( II)] Jacqueline Antonio Zarembowitch,'" Olivier Received March 13, 1987 zyxwvuts zyxwvutsrq zyxw Kahn,*la and Xavier Solanslb Three iron(1I) dinuclear compounds of genera! formula [FeL(NCS),],bpym have been synthesized. Bpym is the bridging ligand 2,2'-bipyrimidine. L is bpym (l),bpy (2,2'-bipyridine; 2). or bzp (bromazepan; 3). The crystal structure of 1 has been solved. 1 crystallizes in the triclinic system, space group Pi,with a = 11.622 ( 3 ) A, b = 9.138 (2) A, c = 9.241 (2) A, a = 118.74 ( 2 ) O , 0 = 74.39 ( 2 ) O , y = 99.85 (2)', and Z = 1. The structure consists of centrosymmetric dinuclear units with two NCS groups in a cis position, a terminal bpym, and two nitrogen donors of the bridging bpym around each iron. The magnetic properties of 1-3 have been investigated down to 4.2 K. In 1 and 2, the iron(I1) ions are high spin in the whole temperature range and interact in an antiferromagnetic fashion with J = -4.1 cm-' in 1 and -4.9 cm-I in 2 (% = -JSA-SB).In 3, a gradual and incomplete spin transition occurs around 235 K. Below the transition, the compound consists of roughly 52% of the diamagnetic S S species, 40% of the antiferromagnetically coupled QQ species, and only 8% of the electronically dissymmetric SQ species ( S = local singlet, Q = local quintet). Introduction The renewed interest brought to spin transitions is due, among other reasons, to the fact that this phenomenon is one of the most T h e first report by Cambi on a metal complex exhibiting a spectacular examples of bistability in inorganic chemistry. The high-spin transition appeared temperature-induced low-spin spin transition may be very abrupt-the total conversion may occur more than half a century ago.2 Nevertheless, this field remains within less than 1 K-and may exhibit a n hysteresis. It follows very a ~ t i v e , and ~ , ~ great strides have been made in the last few that a spin transition system could potentially be utilized as an years. T h e mechanism of the phenomenon is today reasonably element of a molecular device able to store information. In other well understood, at least q~alitatively.4~~ In particular, it has been words, if we consider the low-spin/high-spin transformation conclusively pointed out that the abruptness of the transition is related to the cooperativity of the phenomenon within the crystal LS HS 1- x X lattice.6 Slichter and Drickamer have proposed a thermodynamic approach to an understanding of the spin transition in which this which is assumed to be abrupt, where x is the molar fraction of cooperativity is accounted for by an interaction Gibbs free enhigh-spin form a t a given temperature, the x vs. T plot (or the ergye6g7 This approach, similar to that utilized for the regular x M T vs. T plot, xMbeing the molar magnetic susceptibility) solutions, may fairly well reproduce the more or less abrupt nature schematized in Figure 1 may be seen as a signal, in the general of the transition, as well as the eventual hysteresis e f f e ~ t . ~ q ~ * ~sense of the term. Another recent break-through in this area is the discovery of the A difficulty, however, arises along this line. For a mononuclear LIESST (light-induced excited-spin-state trapping) phenomenon; spin transition compound, the low-spin phase is always the stable Decurtins et al. have shown that it was possible to convert optically phase below the critical temperature T,. This situation may be the low-spin phase into the high-spin phase in the very low temunderstood on the basis of very simple thermodynamical considperature range where the low-spin phase is thermodynamically erations. At the temperature T,, we have stable.'0%" AG = AH - T,AS = 0 (2) - zyxwv - (1) (a) Universitd de Paris-Sud. (b) Universitat de Barcelona. (c) On leave from the Department of Inorganic Chemistry, University of Valencia, Suain. Cimbi, L.; Cagnasso, A. Atti Accad. Naz. Lincei, Cl. Sci. Fis. Mat. Nar., Rend. 1931, 13, 809. Giitlich, P. Struct. Bonding (Berlin) 1981, 44, 8 3 . KBnig, E.; Ritter, G.; Kulshreshtha, S . K. Chem. Reu. 1985, 85, 219. Rao, C. N. R. Internat. Rev. Phys. Chem. 1985, 4 , 19. Slichter, C. P.; Drickamer, H. G. J . Chem. Phys. 1972, 56, 2142. Drickamer, H. G.; Frank, C. W. Electronic Transitions and the High Pressure Chemistry and Physics of Solids; Chapman and Hall: London, 1973. Zarembowith, J.; Claude, R.; Kahn, 0. Inorg. Chem. 1985, 24, 1576. Purcell, K. F.; Edwards, M. P. Inorg. Chem. 1984, 23, 2620. Decurtins, S.; Giitlich, P.; Kohler, C. P.; Spiering, H.; Hauser, A. Chem. Phys. Lett. 1984, 105, 1. Decurtins, S.; Giitlich, P.; Hasselbach, K. M.; Hauser, A.; Spiering, H. Inorg. Chem. 1985, 24, 2174. 0020-1669/87/1326-2939$01.50/0 where the variations of Gibbs free energy AG = GHS- GLS, of = H H S - HLS and Of entropy = SHS - sLS refer to the transformation (1). AS is Dositive. Indeed. the electronic degeneracy and hence the electroiic entropy are higher in the HS phase than in the L S phase. Moreover, in the HS phase, the metal-ligand bond lengths are, on average, longer, so that the internal vibrational entropy, which is the main component of the total vibrational e n t r ~ p y is , ~also higher in this phase than in the LS phase. Since AS is positive, from (2) AH is positive too. Below T,, AG is positive and the LS phase is stable; above T,, the reverse situation holds. To sum up this point, we can say that with a mononuclear compound exhibiting a spin transition, the most likely type of signal is that schematized in Figure 1; above Tc,we have a strong response and below T,, a weak response. An exception would be possible with a compound presenting either two spin as zyx 0 1987 American Chemical Society