The sodium salt of the double Keggin anion [Fe4Cu2Wlg07oH6]1(>-has been prepared from Na2W04-2H20, Fe(N03)3-9H20, and Cu(CH3C00)2-H20 in water and isolated in cystalline form as Na]0Fe4Cu2WlgO70H6-29H2O: monoclinic, P2,/n, a = 13.079 (3) A, b = 17.772 (4) A, c = 21.104 (7) A, ß = 93.46 (2)°, V = 4896 (2) A1 23, Z = 2, D(calcd) = 3.75 g cm'3 567. 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(II) sites, two octahedral Fe(III) sites, and two tetrahedral Fe(III) sites forming a Cu2Fe4D21 core. The cationic portion of the structure consists of two [Na5022]5+ 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.shows a 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.

The ammonium salts of [CoW17H4Na056F6]9" and [FeW,7H4Na056F6]8" have been isolated in crystalline form. X-ray powder patterns of the two compounds are identical. The crystals of (NH4)8(FeW17056F6NaH4)-8H20 belong to the space group Pnma, with a = 18.015 A, b = 17.743 A, c = 21.860 A, K = 6987 A3, Z = 4, Z)(calcd) = 4.283 g cm'3 4, and R = 0.113. FABMS and MS/MS, analytical, spectroscopic (visible, infrared), and X-ray evidence is presented which strongly indicates that the anions in the two isomorphous compounds have the Dawson structure, wherein one Fe3+ or Co2+ replaces one W6+ in the conventional X2W18O70 formulation. Polarograms of the new fluorinated anions have multiple electron addition steps with £1/2 for the first electronic addition -0.2 V relative to the standard calomel electrode. Tandem mass spectrometry is shown to be a useful technique for the characterization of large inorganic complexes.

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Magnetic exchange interactions in the heteropoly complexes [M4(H2O)2(PW9O3 4)2]10− [M=Co(II) and Cu(II)] J.Coupled pairs of differing magnetic spins in tungsto-heteropoly complexes have been investigated by studying the magnetic susceptibility over the temperature range 2-300 o K. The two sites of the magnetic ions are surrounded by oxygen ions in octahedral and tetrahedral coordinations with one oxygen ion in common. The ions studied were CoH, CoH, and Fe H in a total of six combinations on the two sites, offering a unique set of symmetries and ions for examining super-exchange effects. A closed form for the susceptibility has been obtained on assuming the spin Hamiltonian 3C ={J(gISI+g2S.) ·H-JSI· S2, allowing for the possibility of gl,e g2, Sl,e S2. Fitted values of J /k range from -6 to -70oK depending on the combinations of ions. The experimental agreement with the spin Hamiltonian for all cases studied is satisfactory for this system.

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