240 Inorganic Chemistry, Vol. 10, No. 2, 1971 CONTRIBUTION FROM
BERTRAND, et al. BELL TELEPHONE LABORATORIES, IKC., MURRAY HILL,NEW JERSEY 07974, DEPARTMENT, GEORGIA INSTITUTE O F TECHNOLOGY, ATLANTA, GEORGIA
AND THE CHEMISTRY
Magnetic Exchange in Transition Metal Complexes. V.Ia Ferromagnetic Spin Coupling in a Tetranuclear Nickel(I1) Cluster BY J A B E R T R 4 X D 13 A P GINSBERG,* lo R I KAPLAS,'b C E KIRKIVOOD,'b R L hlARTIP\',ld A A D R C SHERWOODIG
Received March 20, 1970 Three-dimensional single-crystal X-ray data show the tetrameric clusters of tetrakis [pa-methoxo-2,4-pentanedionatomethanolcobalt(II)] to have the "cubane" type molecular structure. The compound crystallizes as red needles (a = 21.79 (4) A, b = 10.91 (2) if, c = 20.21 (4) if, and /3 = 121.7 (1)') of monoclinic space group CZ/c with 4 tetramer units per unit cell; the calculated density of 1.43 g:'cni3 agrees well with the experimental value of 1.40 ( 2 ) g,/cm3. A total of 1557 unique nonzero reflections were visually estimated f r o m precession camera photographs; least-squares refinement rFsulted in a conventional R value-of 0.10. The S i complex Ni4(0CH3)r(acac)a(CH30H)ais isostructural (a = 21.55 (4) A, b = 10.88 ( 2 ) -&, c = 20.00 (4) A, and /3 = 121.4 (1j o ) , The magnetic susceptibility of the Si complex has been measured from 296 down to 1.63'K1, and the field dependence of the susceptibility has been examined to l5,3 kOe a t several temperatures belorv 20'K. The results demonstrate that the eight eg electrons centered on the tetrad of nickel atoms are ferrotnagnetically coupled, the ground molecular spin state for the tetramer being S' = 4 ( i , e , ,eight spins parallel) and being fully populated by 21 OK. The magnitude of the intramolecular !Si-Xi coupling constant is J = 10' (-7 cm-lj. The tetramer molecules in their ground state exhibit an additional intermolecular ferromagnetic coupling which gives rise to a Weiss constant 0 = $0.8". This compound provides the second example of a polynuclear ferromagnet in which the level of niaximuni spin multiplicity has been fully populated by taking it to very low temperatures. I t is the first example of a cluster complex found to exhibit both intra- and intermolecular ferromagnetic spin coupling.
+
Introduction
pectation that the unpaired e6 electrons will couple ferromagnetically, in which event the ground state of the If potassium hydroxide in methanol is added to a tetramer should be associated with a "spin-only" solution of either cobalt(I1) or nickel(I1) acetylacemagnetic moment of peff = fiB M per Ni atom.4 tonate in boiling methanol, the tetrameric clusters &I4The first observation of ferromagnetic exchange in a (0CH8)4(acac)4(CH30H)d with i V = Co or Xi separate discrete, polynuclear cluster was reported by Ginsberg, from solution as large deep red or green crystals, reMartin, and Sherwoodlasbin trimeric nickel(I1) acetylspe~tively.~'3An X-ray single-crystal study3 of the soon after, concluded cobalt (11) tetramer, tetrakis [pa-methoxo-2,4-pentane- acetonate. Andrew and that intramolecular ferromagnetic exchange was ocdionatoinethanolcobalt(I1) 1, the details of which are curring in Schrauzer and Kohnle's8 "cubane"-type reported in the present paper, s h o w that the cobalt and tetramer Ni4(OCH3)4(salicyladehyde)4(CH30H)4,almethoxy oxygen atoms occupy the alternate corners of though they ivere unable to extend their magnetic meaa rather distorted cube-the so-called "cubane" arsurements below 80'K and so could not fully populate rangement (see Figure 3 ) . Each methoxide group the level of maximum spin multiplicity. We report bridges three Co atoms with Co-0-Co angles of 94.6here susceptibility data as a function of temperature 98.6 ( 5 ) One acetylacetone chelate and one methanol down to 1.G"K and as a function of field to 16.3 k0e for ligand complete a distorted octahedron of oxygen atoms the present nickel "cubane" tetramer which confirms around each Co atom, that the intramolecular Ni-Ni spin coupling is ferroThe nickel (11) tetramer, tetrakis [p3-methoxo-2.4-penmagnetic. The susceptibility measurements also demtanedionatomethanolnickel(II)]! is isostructural with onstrate the existence of an additional, much weaker, the cobalt complex and has a room-temperature maglattice ferromagnetism. Ni4(0CH3)4(acac)4(CH30H)4 netic moment peff = 3.3 BAT per Ni atom, a value thus becomes the first example of a cluster complex consistent vith octahedrally coordinated divalent found to exhibit both intra- and intermolecular ferronickel. Since all the nickel atoms appear to be in an magnetic spin coupling. orbitally nondegenerate ground state, the tetrameric cluster provides an interesting opportunity to study Theory spin-spin interactions in a crystal lattice composed of The magnetic properties of tetranuclear clusters Xi4 tetrahedra which are magnetically isolated from have been revien-ed elsewhere. For such compounds neighboring clusters by the peripheral ligands. The the spin-spin Hamiltonian presence of Ni-0-Xi angles near 90" leads to the ex* T o whom correspondence should be addressed. O,
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( C H S O H )between ~ 1.6 and 300°K are given in Table IV as X'A, the susceptibility expressed per Ni atom. A diamagnetic correction1' ( x d = -88.8 X 1 0 P cm3 gatom-') is included. Above 13"K, these measurements were made a t a field strength of 15.3 kOe. Below 13"K, the susceptibilities at 15.3 kOe were field dependent, and the values reported in Table IV were determined a t lower field strengths (less than 5kOe), a t which no field dependence could be detected. The and results are shown in Figure 4 as plots of ( X I * ) - ' perf = 2.8273 [x'AT]~'* VS. T . (11) P. W. Selwood, "Magnetochemistry," York, N. Y., 1956, pp 78,92.
2nd ed, Interscience, New
Inorganic Chemistry, Vol. 10, No. 2, 1971
244
BERTRAND, et al.
TABLE 111
6000!
ORECIPR3CRL SUSCEPTIBILITY PER G R B M ATCM NI
SELECTED INTRAMOLECULAR DISTANCES AND ANGLESIN CO~(OCH~)~(~~~C)~(CH~OH)~ Distance, %, Atoms Distance, & . 01-c1 1 . 4 1 (3) 3 , 1 6 (1) 1 . 4 6 (2) 02-c2 3 . 1 0 (1) 03-C3‘ 1.38(4) 3 . 1 2 (1) 04-C4 1.49 (3) 3.17(1) 12101-R1 C1 1 . 3 0 (3) 2.11 (1) RlC1-R1C4 1 . 3 9 (3) 2 . 0 6 (1) R1 C2-Rl C4 1 . 4 3 (3) 2 . 0 6 (1) 1 . 3 0 (2) R102-RlC2 2.04 (1) R1 C1-R1 C3 1 . 5 0 (3) 2.14 (1) RlC2-R1 C5 1.54 (4) 2 , l l (1) 1 . 2 6 (3) RZOl-R2Cl 2.15 (2) RZC1-RZC4 1 . 4 3 (3) 2.20 (2) RZC2-RZC4 1 . 3 6 (3) 2 . 0 5 (1) RZ02-RZC2 1 . 3 0 (3) 2.01 (2) 1.56 (4) RZC1-RZC3 2.00 (2) 1.55 (3) RZC2-RZC5 2 . 0 5 (2)
Atoms
Col-Col ‘ Col-co2 Col-Co2’ co2-Co2’ Col-01 Col-01’ Col-02 co2-02 co2-02’ co2-01 Col-03 c02-04 Col-R101 Col-R102 C02-R20 1 C02-R202 Atoms
Angle, deg
Col-01-Col’ co2-02-Co2’ c o 1-01-co2 c02-0l-c0l’ Col-02-co2 Col-02-C02’ 01-Col-01’ 01-Col-02 01’-Col-02 01-Col-R101 Ol-Col-Rl02 Ol’-C01-03 03-Col-Rl01 03-Col-Rl02 RlOl-C0l-R102 02-co2-02’ 02-co2-01 02’-C02-01 02’-C02-RZ01 02-C02-R201 02-c02-04 04-C02-R201
98.4 (6) 98,6( 5 ) 94.6 (5) 97.0 (5) 98.3 (5) 9 5 , s (5) 81.5(6) 8 2 . 5 (5) 84.5 (5) 9 3 , 5 (6) 100.4 (6) 88.9 (6) 9 5 , 5 (6) 89.1 ( 7 ) 89 9 (6) 81 0 ( 5 ) 83 3 (5) 81 5 ( 5 ) 100 3 (6) 97 6 (6) 86 9 (5) 88 4 (6)
Atoms
Angle, deg
04-Co2-RZ02 RZOl-Co2-RZ02
5600
c
*,K‘e~f’282731X~T)”2
48C
Y 9 ~ 142 4000
3 600 20 0
3 200 00
400
800
1200 1600 2000 TEMPERATURE (DEG K 1
2400
2800
3YODoo
Figure 4.-Temperature dependence of p e f i (BM) per Ni atom and 1 / x L for N ~ ~ ( O C H S ) ~ ( ~ C ~ ~ ) ~ ( C H ~ O H ) ~ . M A G N E T I Z A T ’ O N C U R V E S FOR 0 - I 6 3 O K DATA FULL C U R V E S
