Control of Intramolecular Magnetic Interaction by the Spin Polarization

Sabrina Turba , Olaf Walter , Siegfried Schindler , Lars Preuss Nielsen , Alan Hazell , Christine J. McKenzie , Francesc Lloret , Joan Cano and Miguel...
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3294

J. Phys. Chem. 1995,99, 3294-3302

Control of Intramolecular Magnetic Interaction by the Spin Polarization of d, Spin to plC Orbital of an Organic Bridging Ligand Hiroki Oshio**i$'and Hikaru Ichida' Department of Applied Molecular Science, Institute for Molecular Science, Okazaki 444, Japan, and Department of Chemistry, The University of Tokyo, 7-3-1 Hongo, Tokyo 113, Japan Received: August 2, 1994; In Final Form: November 12, 1994@

Multinuclear metal complexes have been designed with ferromagnetic interactions between the metal centers by considering the topological network of d, spin to the bridging ligand. The four complexes [Cu3(tpa)3(3), and [Cu2(bpmx)(NCS)d (ta)l(C104)3*4H20(l),[Fedbpepm)(NCShI (2), [Fe2(bpmar)(H20)41(N03)4*3H20 (4), with tpa = tris(2-pyridylmethyl)amine, H3ta = trimesic acid, bpepm = 4,6-bis[(bis(2'-pyridylethyl)amino)methyl]pyrimidine, and H2bpmar = 4,6-bis[(N~-bis(2'-pyridylmethyl)amino)methyl]-2-methylresorcinol, have been synthesized, and crystal structures of 1 and 2 have been determined. Magnetic properties have been investigated in the 2-270 K temperature range. Central metal ions in each complex are cupric for 1 and 4, high-spin ferrous for 2, and high-spin femc species for 3, respectively. Magnetic susceptibility measurements for 1, 2, and 4 showed antiferromagnetic behavior, and the Weiss constants for the data above 100 K are -3.26, -3.86, and -2.09 K, respectively. Magnetic data for 3 have been quantitatively studied above 10 K and have revealed that 3 exhibits ferromagnetic coupling with a magnetic exchange coupling constant of J = +0.65(3) cm-' (where H = -2JSjS2). The measurement of magnetization (M) versus the field (H) for 3 has shown that the quantum number of the total angular momentum (J)at 4.0 and 8.5 K is larger than J = 4, where the expected value (J) in absence of ferromagnetic interaction is 5/2. The ferromagnetic interaction in 3 was interpreted by the spin polarization of d, spin to the ligand p, orbital. 0 monoclinic, space group C2/c, a = 36.228(8) A, b = 19.565Crystal data: [Cu3(tpa)3(ta)](ClO4)3*4H2(l), (3) A, c = 26.341(6) A, p = 122.07(1)', V = 15821(6) A3, 2 = 8, R = 0.090 (R, = 0.096) for 4992 data points with lFol > 3a(F0); [Fez(bpepm)(NCS)4] (2), monoclinic, space group C2/c, a = 42.28(1) A, b = 13.467(4) A, c = 15.527(3) A, p = 94.83(2)", V = 8810(4) A3, Z = 8, R = 0.050 (R, = 0.048) for 2676 data points with IFo[ > 3a(F0).

Introduction The evolution of molecular-level techniques applicable to solid state is having an increasingly profound impact on the fundamental understanding of solid state chemistry. Some organic solids, which were designed by the accumulation of knowledge about molecules, have been proven to be molecular ferromagnets or superconductors. However, interaction or cooperation of d, electrons on metal centers with p, electrons of an organic ligand has been understood to be indispensable in improving physical properties. Metal complexes with organic ligands can be used to examine the possibility of the d, and p, mixing. Recently, some molecular-based ferromagnets have been reported. The charge transfer complexes [Fe(C~Mes)z](TCNE),',2[Mn(C5Me5)2](TCNQ),3and [V(TCNE),]y(CH2C12)4 (C5Me5 = pentamethylcyclopentadienyl,TCNE = tetracyanoethylene, and TCNQ = tetracyanoquinone) have proved to be molecular ferromagnets. In the complex [Fe(C5Me5)2][TCNEl, the origin of the ferromagneticinteraction is due to an exchange effect between the negative spin density on the Cp ring and the positive spin density on the neighboring [TCNE- unit.5 Strong antiferromagnetic interactions between paramagnetic centers with different spin multiplicities can stabilize the highest spin multiplicity in compounds. Kahn et al. have reported spontaneous magnetization in their oxamato-bridged Mn(I1)-Cu(I1)

'Institute for Molecular Science.

Present address: Department of Chemistry, Faculty of Science, Tohoku University, Aoba-Ku, Sendai 980, Japan. = The University of Tokyo. Abstract published in Advance ACS Abstracts, February 1, 1995. 8

@

complexes.6-s Some low-dimensional Mn(I1) complexes, which have a nitronyl nitroxide as a bridging ligand, show magnetic ordering at 7.6 Ke9-" On the other hand, the orthogonality of d, and d, spins was used to obtain ferromagnetic interactions in oxalato-bridged Cr(1II)-Ni(II) and Cr(II1)-Cu(II) complexes which show magnetic ordering below 20 K.I2.l3 Cr(II1)-Ni(111) cyanide was reported to show ferromagnetic ordering at 90 K.I4 The origin of the ferromagnetism in these compounds is the spin or degenerate orbitals of the metal ions. Recently, some pure organic compounds, Cm*TDAEI5andp-NFW"N6(Ca = fullerene, TDAE = tetrakis(dimethylamino)ethylene, and p-NPNN = p-nitrophenylnitronyl nitroxide), have been characterized as ferromagnets. In the compounds mentioned above, a three-dimensionalmagnetic interaction, which determines the transition temperature, successfully or accidentally produces the highest spin multiplicity in the ground state. However, a successful strategy for the synthesis of a ferromagnetically interacting molecular assembly has not been established. The control of the magnetic interaction in the multinuclear system is essential in order to build a molecular-based ferromagnet if strategies found successful for the intramolecular magnetic interaction are extended to intermolecular interactions. Some strategies for incorporation of ferromagnetic interactions in organic multiradical compounds have been propo~ed.'~-~' A spin polarization mechanism, Le., topological symmetry of the n electron network, was applied to design high-spin organic molecules using carbenes as the paramagnetic center^.^'-'^ An intramolecular ferromagnetic interaction between radicals is obtained in the polycarbene system if the radicals are connected to the aromatic ring in the meta-positions (see below).

0022-365419512099-3294$09.00/0 0 1995 American Chemical Society

Control of Intramolecular Magnetic Interaction

J. Phys. Chem., Vol. 99, No. IO, 1995 3295 TABLE 1: Crystallographic Data for [Cu~(tpah(ta)l(Cl04)3~4HzO (1) and [Fez(bpepm)(NCSkl (2)

1

1

.t

: Radical

t

Is it possible to apply the spin polarization mechanism to designing multinuclear complexes with an intramolecular ferromagnetic interaction? In this study, multinuclear metal complexes, in which the metal ions are connected to aromatic rings in the meta-position, were prepared and their magnetic properties were studied. The ligands used in this study are trimesic acid, 4,6-bis[(bis(2'-pyridylethyl)amino)methyl]pyrimidine, and 4,6-bis[(N,N-bis(2'-pyridylmethyl)amino)methyl]-2methylresorcinol, which are abbreviated as Hsta, bpepm, and Hzbpmar, respectively. Molecular design by considering the spin polarization of the metal spin on the ligand n orbital, that is, construction of a topological network, makes the magnetic interaction controllable. Part of this work was preliminarily reported.26 Experimental Section Syntheses. All chemicals used were commercially available and used without further purification. Ligands used in this work are depicted below.

formula

Fw

temperature ("C) crystal system spafe group a

b

(4)

(4)

c (A)

PCO,

v (A3)

Z

D,(g ~ m - ~ )

radiation (Mo K,) (A) P (Mo K d (cm-') transmission coeff R" RWb

C ~ ~ H ~ ~ C I 2~ 0CI 8 U ~ N CX I J - ~ S F ~I 2S4 ZN 1639.27 902.734 22 22 monoclinic monoclinic c2/c c2tc 36.228(8) 42.280( 12) 19.565(3) 13.467(4) 26.341(6) 15.527(3) 122.07(1) 94.83(2) 8810(4) 1582l(6) 8 8 1.361 1.376 0.71073 0.71073 10.1 9.01 0.936-0.946 0.870-0.908 0.090 0.050 0.096 0.048

a R = E(IFol- lFcl)/ZIFol.Rw = IEw(lF0l - I~cl)z/C~I~01211'2; w = (uc2 (0.030~1F1)~)-' for 1; w = (02 (0.015~1F1)~)-~ for 2.

+

H3ta

CH3

Hlbpmar

Tris(2-pyridylmethy1)amine (tpa). The ligand tpa was prepared by the literature method.27 To 2-aminomethylpyridine (216.3 mg, 2 mmol) was added 2-(chloromethy1)pyridine(502.3 mg, 4 mmol), and the mixture was stirred for 1 h. The mixture was dissolved in water, followed by addition of saturated aqueous Na2C03. The organic layer was extracted with chloroform. The extract was dried with Na2S04, followed by evaporation in vacuo, and the compound was separated by gelpermutation chromatography (eluting with chloroform). 4,6-Bis(bromomethyl)pyrimidine. A mixture of 2,4-dimethylpyridine (3 g, 10 mmol) and N-bromosuccinimide (5.1 g, 28.6 mmol) in dry C c 4 (200 mL) was refluxed for 30 min, and then benzoyl peroxide (30 mg) was added. The mixture was refluxed for another 5 h, and then the succinimide was filtered off. The CCL solution was concentrated and chromatographed on a silica gel column with CHCl3-MeOH (92:8) to give white crystals (3.5 g, 30% yield). 'H NMR (400 MHz, CDCl3, standard SiMe4): 6 4.47 (s, 4H, CHz-pyrimidine),7.61 (s, lH, pyrimidine ring), and 9.06 (s, lH, pyrimidine ring).

+

4,6-Bis[ (N,"-bis(2'-pyridylethyl)amino)methyl]pyrimidine (bpepm). A mixture of N,N-bis(2-pyridylethyl)amine (0.20 g, 1 mmol) and Na2C03 (0.53 g, 5 mmol) in freshly distilled acetonitrile (300 mL) was heated to reflux, and a solution of 4,6-bis(bromomethyl)pyrimidine(0.133 g, 0.5 mmol) in acetonitrile (100 mL) was added dropwise over 2 h with stirring, followed by refluxing for another 6 h. After cooling to room temperature, the insoluble solid was filtered off and the filtrate was evaporated. Gel-permutation chromatography of the residue eluting with chloroform gave bpepm (0.68 g, 45% yield). 'H NMR (400 MHz, CDCl3): 6 2.98 (td, J = 8.55 and 5.80 Hz, 16H, CHzCH2-pyridine), 3.79 (s, 4H, CH2-pyrimidine), 7.04 (d, 4H, J = 6.72 Hz, pyridine ring), 7.05 (s, lH, pyrimidine ring), 7.07 (td, 4H, J = 4.73 and 4.89 Hz, pyridine ring), 7.51 (td, 4H, J = 7.64 and 1.83 Hz, pyridine ring), 8.48 (d, 4H, J = 4.01 Hz, pyridine ring), and 8.99 (d, lH, J = 3.97 Hz, pyrimidine ring). 4,6-Bis[(N,iV-bis(2'-pyridylmethyl)amino)methyl]3-methylresorcinol (Hzbpmar). NJV-Bis(2-pyridylmethy1)amine (1 g, 5 mmol) was added to formalin (1.32 g, 16.2 m o l ) in MeOH (5 mL) at 0 "C under argon. Then 2-methylresorcinol (0.31 g, 2.5 mmol) in MeOH (8 mL) was added dropwise. The solution was allowed to warm to room temperature and treated with HOAc (6 mL). After the mixture was allowed to stir for 48 h, the solvent was removed in vacuo, neutralized with dilute NaOH, and extracted with CH3C1. Gel-permutation chromatography of the dried (Na2S04) extract eluted with chloroform gave Hzbpmar (0.36 g, 26% yield). 'H NMR (400 MHz, CDC13): 6 2.55 (s, 3H, Me-resorcinol), 3.69 (s, 4H, CH2resorcinol), 3.84 (s, 8H, CH2-pyridine), 6.59 (s, lH, Hresorcinol), 7.12 (td, 4H, J = 6.1 1 and 1.22 Hz, pyridine ring), 7.32 (d, 4H, J = 7.93 Hz, pyridine ring), 7.60 (td, 4H, J = 7.63 and 1.83 Hz, pyridine ring), and 8.55 (d, 4H, J = 3.97 Hz, pyridine ring). [Cu3(tpa)~(ta)](C104)3.4Hz0(1). To a mixture of Cu(C104)2.6H20(370 mg, 1 m o l ) and tpa (290 mg, 1 m o l ) in MeOH (50 mL) was added trimesic acid (70 mg, 0.33 mmol), and then piperidine (255 mg, 3 mmol) was slowly added. The blue precipitate was filtered and washed with cold MeOH. Slow evaporation of the methanol solution gave a blue crystalline solid which was subjected to the X-ray analysis. Anal. Calcd for C63H&13Cu3N12022: C, 46.16; H, 4.00; N, 10.25. Found: C, 46.24; H, 4.11; N, 10.10. [Fez(bpepm)(NCS)4] (2). Na(NCS) (162 mg, 2 mmol) in water (10 mL) was added to a water-methanol solution (60

HoocvcooH COOH

2

3296 J. Phys. Chem., Vol. 99, No. 10, 1995

Oshio and Ichida

TABLE 2: Positional (x lo4) and Equivalent Isotropic Thermal Parameters (A2)for [Cu3(tpa)3(ta)](C104)34H20 (1) X

Y

Z

Be,"

X

Y

Z

3918(1) 6084(1) 3693(1) 3176(2) 1243(3) 7054(2) 4277(4) 3771(4) 5679(4) 5544(4) 3997(4) 4533(4) 3601(5) 3780(4) 4415(5) 3440(5) 6519(4) 6546(4) 6262(4) 5647(5) 33 19(5) 3223(5) 4153(5) 3483(6) 4419(5) 4808(5) 5035(5) 4910(5) 4521(6) 4262(6) 4 125(5) 5441(6) 4345(6) 3265(7) 3903(7) 3385(7) 3485(6) 3356(8) 3540(7) 3857(7) 3973(6) 4320(6) 4595(8) 4968(8) 5099(7) 4794(6) 3 198(6) 2790(6) 2664(7) 2921(7) 3315(6) 6737(7)

6345(1) 3592(1) 1547(1) 1091(3) 1029(4) 1141(3) 5559(5) 4858(6) 3513(6) 4652(6) 2388(5) 1967(6) 7254(7) 6340(7) 70 18(7) 6153(7) 3581(8) 42 15(7) 2555(7) 3775(8) 691(7) 1927(8) 928(7) 1502(9) 4380(7) 4484(8) 3922(8) 3263(8) 3169(8) 3720(8) 496 l(8) 4070(9) 2454(9) 7 198(10) 7796(9) 7360(9) 6787(9) 6877( 11) 6464( 1 1) 5998(10) 5935(9) 7650(9) 8 184(11) 8007( 12) 7300(11) 6830( 10) 6703( 10) 6696( 11) 6064( 12) 5491(11) 5534(9) 4237( 11)

6501(1) 6494(1) 643 1(1) 2462(3) 5351(3) 5445(3) 6650(5) 6573(6) 6755(5) 6640(6) 6622(6) 6541(7) 6323(6) 7154(6) 6660(7) 5622(6) 6219(6) 7155(6) 6637(7) 5584(6) 6233(8) 6605(7) 7086(8) 5530(8) 6700(8) 67 13(7) 6712(8) 6706(7) 6683(7) 6679(7) 6648(8) 6689(8) 66 18(9) 6496(9) 6652(9) 5674(9) 7096(8) 7501(10) 7998(9) 8092(9) 7668(9) 6645(9) 6651(12) 6661(13) 6744( 11) 6708(8) 5343(9) 4742(9) 445 3( 10) 4739(9) 5334(9) 6387(9)

4.0 4.0 5.7 8.5 9.4 8.9 4.2 4.6 4.4 4.7 5.1 6.5 4.1 4.0 4.6 4.4 4.3 3.6 4.6 5.3 5.9 5.4 6.1 7.5 3.0 3.2 3.1 3.1 3.7 3.6 3.5 4.3 4.9 5.7 5.3 6.6 4.5 6.7 6.7 5.5 5.3 5.2 8.4 9.2 7.5 5.3 5.3 5.5 7.2 6.2 4.9 6.4

6833(7) 6293(6) 6839(7) 7201(7) 7235(6) 6929(6) 6580(6) 66 13(6) 6764(8) 6550(8) 6203(8) 6066(7) 5861(6) 5636(7) 5196(8) 4974(7) 5193(7) 3082(7) 3612(7) 2956(8) 2933(7) 2584(7) 2520(7) 2799(7) 3 164(7) 4008(7) 4277(8) 4709(8) 4841(7) 4558(6) 3 179(8) 3012(8) 3 166(8) 3480(8) 3615(8) 3504(7) 3309(9) 2976( 10) 2828( 10) 1611(8) 1070(8) 1228(11) 1252(11) 6833(7) 6846(7) 7123(8) 7507(7) 4835(7) 4183(9) 7970(8) 5854(13)

3023( 10) 3468( 12) 4424(9) 4857( 11) 5049(11) 4814(10) 4400(9) 24 19(10) 1770(12) 1234(12) 1363(11) 2044( 10) 3793( 10) 4049( 11) 4223( 11) 4202( 11) 396 1(10) 719(11) 89(11) 699( 12) 1458(10) 1624(12) 2237( 12) 2768(14) 2587( 10) 272(10) -222( 11) -20(13) 662( 11) 1106(10) 984( 11) 810(12) 1198(13) 1759(14) 1914(13) 1348(11) 494( 12) 1513(12) 761( 19) 845(15) 534(14) 902(21) 1673(13) 1062(9) 799(9) 1791(9) 798(13) 1912(14) 252(17) 1496(15) 1903(16)

6513(9) 5570(8) 702 l(9) 7422(10) 7937(10) 8068(9) 7650(8) 6580(9) 6626( 10) 67 10(11) 6792( 11) 6723(10) 5273(8) 4680( 10) 4406(10) 4737( 10) 5330(9) 6570(12) 6405(11) 5568(11) 6556( 10) 6606( 11) 6682( 1 1) 6758(11) 6709(11) 6995( 10) 7446(13) 7988(13) 8066( 12) 7604(10) 5219(12) 4622(11) 4315(11) 465 1(12) 5226(11) 2450(11) 2707(12) 2583(16) 1972(13) 5774( 14) 5574(12) 4886( 12) 5491( 16) 4812(9) 5680(9) 5601(9) 5707(11) 5704( 12) 65 l(12) 274( 17) 4928(14)

5.8 6.2 5.2 6.7 6.3 5.2 4.1 5.6 7.5 8.5 8.3 6.4 5.1 6.7 7.1 6.6 6.3 8.0 9.0 9.2 6.7 7.5 8.1 8.6 7.0 6.4 9.1 9.7 8.4 6.1 8.o 8.9 8.7 9.8 8.5 16.0 17.3 24.0 25.0 21.4 17.7 28.1 24.0 12.3 11.7 14.2 16.4 19.3 22.3 26.1 29.3

a The equivalent isotropic temperature factor is calculated using the expression B , = (4/3)C,z,a;a,&, where ai's are the unit cell edges in direct space.

mL, 1:2) of FeS04*7Hz0 (278 mg, 1 m o l ) and bpepm (279 mg, 0.5 mmol). After standing overnight, red crystals were formed, and one of them was subjected to an X-ray structural analysis. Anal. Calcd €or C ~ S H ~ S F ~ ~C,N50.56; I ~ S ~H,: 4.24; N, 18.62. Found: C, 50.56; H, 4.34; N, 18.49. [Fe~(bpmar)(H~O)d(N0&.3H20 (3). All procedures were carried out under an argon atmosphere. To a hot EtOH solution (30 mL) of Fe(N03)3*9HzO(404 mg, 1 mmol) was added a hot ethanol solution (30 mL) of Hzbpmar (273 mg, 0.5 mmol), and then piperidine (85 mg, 1 mmol) was added slowly. After standing overnight, the precipitate was filtered off and washed with cold ethanol. Recrystallization from hot ethanol gave a dark blue microcrystalline. Anal. Calcd for C33H47FezN100 2 1 : C, 38.43; H, 4.59; N, 13.58. Found: C, 38.26; H, 4.61; N, 13.39. FABMS (fast atom bombardment mass spectrometry): mle 655 (calcd for [Fez(bpmar)I4+ = 656.4).

[Cu2(bpmar)(NCS)2] (4). All procedures were done under an argon atmosphere. A hot methanol solution (20 mL) of Hzbpmar (273 mg, 0.5 mmol) was added to the hot methanol solution (20 mL) of CuC12-2H20 (170 mg, 1 mmol). After stirring for 1 h, addition of NaNCS (81 mg, 1 mmol) and piperidine (85 mg, 1 mmol) gave a precipitate of the product. Red microcrystals were obtained by recrystallization from hot methanol. Anal. Calcd for C35&1Cu2N&&: C, 48.83; H, 4.80; N, 13.01. Found: C, 49.08; H, 4.85; N, 12.78. Magnetic Measurement. Temperature dependent magnetic susceptibilities of the complexes were measured using an Oxford Faraday type magnetic balance system equipped with a superconducting magnet. Data were collected from 2 to 270 K at 10 kG for 1, 2, and 4 and 2 to 300 K at 1 kG for 3. Pascal's28 constants were used to estimate the diamagnetic correction. X-ray Crystallography. A single crystal for 1 and 2 was

Control of Intramolecular Magnetic Interaction mounted on a glass fiber with epoxy resin. Diffraction data were collected on a Rigaku 5 four-circle diffractometer with graphite-monochromatized Mo K a radiation. The general procedure has been described p r e v i o u ~ l y .Corrections ~~ were applied for Lorentz polarization and absorption effects, but not for extinction. The lattice constants for compounds 1 and 2 were optimized from a least-squares refinement of the settings of 40 carefully centered Bragg reflections in the range 25" < 28 < 30", respectively. Crystallographic data are collected in Table 1. The structures were solved by conventional heavy atom methods and Fourier techniques and refined by a blockdiagonal least-squares approach. All non-hydrogen atoms of the cation were readily located and refined with anisotropic thermal parameters, and hydrogen atoms were located from difference Fourier maps and refined with isotropic thermal parameters. Atomic scattering factors and anomalous scattering corrections were taken from the l i t e r a t ~ r e . ~Final ~ atomic parameters and equivalent isotropic thermal parameters for nonhydrogen atoms are listed in Tables 2 and 3. All calculations were carried out with the Universal CrystallographicComputation Program System UNICS-III.~' Electrochemical Measurement and UV-Vis Spectra. Cyclic voltammetry (CV) and constant-potential electrolysis (CPE) were accomplished with a three-electrode potentiostat (Hokuto Denko HA501G potentiostatlgalvanostat and HB-105 function generator, and HA- 105 potentiostatlgalvanostat and HF201 digital coulometer, respectively). The internal resistance drop was compensated with a Hokuto HI-203 IR compensation instrument for CV. The electrochemical measurements were performed at 25 "C by the use of a normal three-electrode configuration consisting of a highly polished glassy carbon working electrode (area 0.28 cm3; BAS Ltd.), a platinum-wire auxiliary electrode, and an Ag-Ag+ reference electrode containing 0.01 M AgNO3 and 0.1 M tetrabutylammonium perchlorate-acetonitrile solution (BAS Ltd.) in a microcell. A platinum mesh for both working and auxiliary electrodes was used for CPE. The working and auxiliary electrode was used for CPE. The working and auxiliary compartments contained a 0.1 M solution of the supporting electrolyte. Spectral grade acetonitrile (Dojin Lab.) was used without further purification. The supporting electrolyte NEkPF6 (Fluka Chemie AG Industries) was recrystallized two times from ethanol and water and dried under vacuum in an oven at 80 "C for 12 h. The compartment of the cell was bubbled with solvent-saturated argon to deaerate the solution. Ferrocene was used as an internal standard. Potentials for the compound are reported vs corrected Ag-Ag+(aq). The half-wave potential of the ferroceneferricenium under the conditions employed was 0.12 V (A = 170 mV) vs Ag-Ag+. The electronic spectrum was recorded on an Hitachi U-3400 spectrophotometer. Molecular Orbital Calculation. The MNDO was used for the molecular orbital calculation on organic molecules.

Results and Discussion Description of the Structure: [Cu3(tpa)3(ta)l(C104)3.4Hz0 (1). An ORTEP representation of the structure is presented in Figure 1, and selected interatomic distances and angles are listed in Table 4. In complex 1, the copper atoms, which are bridged by trimesic acid, are coordinated by four nitrogen atoms (one from tertiary amine and three from pyridine) and one carboxylate oxygen atom. The three copper units and bridging ligands are nearly planar with three copper atoms displaced by 0.456(3), 0.588(3), and 0.450(3) A, respectively, from the benzene ring. The

J. Phys. Chem., Vol. 99, No. IO, 1995 3297 TABLE 3: Positional (for Iron xlOs and Others xlv) and Equivalent Isotropic Thermal Parameters (A2)for [Fez(bpepm)(NCSkl (2) X

Y

Z

33928(3) 40418(3) 2668(1) 3212(1) 4459( 1) 4436(1) 3449(1) 2969(1) 3863(2) 3938(1) 4501(1) 3529(1) 3652(1) 3871( 1) 3153(2) 3373(2) 4166( 1) 4134( 1) 3173(2) 2850(2) 2793(2) 2573(2) 2525(2) 2701(2) 2919(2) 3742(2) 3802(2) 4000(2) 4295(2) 4457(3) 4330(3) 4032(2) 41 65(2) 4499(2) 4642(2) 491 l(2) 5036(2) 4898(2) 4632(2) 36 lO(2) 3503(2) 3355(2) 3042(2) 2917(2) 3082(2) 3392(2) 3472(2) 3979(2) 3774(2) 3629(1) 3723(2) 3851(2) 2955(2) 3302(2) 4287(2) 426 l(2)

38042(9) -2192(9) 6280(2) 2870(2) -2627(3) 2635(2) 378 l(5) 2885(4) 4530(5) - 1147(4) -48(5) -374(4) 2406(4) 867(4) 5096(5) 3321(5) - 1354(5) 945(5) 4258(6) 4096(7) 3 lOO(6) 2445(7) 1544(7) 1327(6) 2012(6) 4314(7) 5253(6) 5068(6) 5470(7) 5312(8) 4757(9) 4358(7) -1996(6) - 1820(7) -811(7) -666(7) 264(8) 1064(7) 855(6) -1542(6) -1955(6) -1 173(6) -1262(6) -519(7) 305(6) 339(6) 2731(6) -478(6) 1785(5) 207 l(5) 1135(6) 532(5) 5578(6) 3 136(5) - 1896(6) 1645(6)

4645(8) -4463(7) -569(3) -2554(2) -2301 (2) -1843(2) 1976(4) 744(4) 432(4) 743(4) 321(3) -947(4) 851(3) 487(3) 171(5) -828(4) - 1248(4) - 1277(3) 2352(6) 1836(5) 1414(5) 1668(6) 1238(6) 569(6) 336(5) 2308(6) 1838(6) 1076(6) 1058(7) 346(8) -315(8) -258(6) 880(5) 633(5) 768(5) 1340(5) 1430(5) 1006(5) 448(5) 679(5) -209(6) -784(5) -1137(6) - 1660(7) -1826(6) - 1450(5) 2265(5) 1515(4) 310(4) 1661(4) 1903(4) 1300(4) -120(6) -1539(5) - 1684(5) - 15lO(4)

Be0

6.3 5.2 13.5 8.9 13.4 8.7 6.7 6.2 7.5 6.0 6.0 5.5 4.8 4.7 9.3 7.2 6.6 6.0 8.2 8.1 6.6 8.0 8.7 8.0 7.0 7.9 8.9 7.8 10.1 13.2 13.2 9.1 8.0 8.1 6.9 8.1 9.0 8.1 6.5 7.4 7.3 6.6 8.8 10.6 8.1 6.0 6.1 6.0 4.5 4.4 5.1 5.1 8.1 6.1 6.6 5.5

coordination geometry about each copper center is described as a trigonal bipyramid. The shortest bond distance among Cu-N and Cu-0 is Cu-O(carboxy1ate) (Cu(1)-O(1) = 1.92(l), Cu(2)-0(3) = 1.93(2), and Cu(3)-O(5) = 1.89(1) A). The O(carboxy1ate)-Cu-N(tertiary amine) angles are close to 180" (0(l)-Cu( l)-N( 1) = 171.4(7), 0(3)-C~(2)-N(5) = 174.8(6), and 0(5)-Cu(3)-N(9) = 174.2(8)"). The coordination angles about Cu atoms in the plane defined by Cu(1)-N(2)N(3)-N(4), CU(~)-N(~)-N(~)-N(S),and Cu(3)-N(10)N( 11)-N( 12) deviate slightly from 120". In order to understand the electronic structure of the five-coordinate copper complex, a qualitative analysis of the trigonality of the coordination geometry around copper atoms is required. The distortion of the five-coordinate complex from ideal trigonal-bipyramidal or

3298 J. Phys. Chem., Vol. 99, No. 10, 1995

Oshio and Ichida

Figure 1. ORTEP drawing of [Cu3(tpa)3(ta)I3+ with 50% probability.

TABLE 4: Selected Bond Lengths (A) and Bond Angles ((leg) for [Cu3(tpa)3(ta)l(C104)3.4H~O(1) Cu( 1)-O( 1) CU(1)-N(2) CU(1)-N(4) Cu(2)-N(5) Cu(2)-N(7) Cu(3)-0(5) C~(3)-N(10) Cu(3)-N( 12)

O( 1)-Cu( 1)-N(l) O( I)-Cu(l)-N(3) N( 1)-Cu( 1)-N(2) N( 1)-Cu( 1)-N(4) N(2)-Cu( 1)-N(4) 0(3)-Cu(2)-N(5) 0(3)-C~(2)-N(7) N(5)-Cu(2)-N(6) N(5)-Cu(2)-N(8) N(6)-Cu(2)-N(8) 0(5)-Cu(3)-N(9) 0(5)-Cu(3)-N(ll) N(9)-Cu(3)-N( 10) N(9)-Cu(3)-N( 12) N( lO)-Cu(3)-N( 12)

1.92(1) 2.03(2) 2.06(1) 2.05(2) 2.10(1) 1.89(1) 2.12(2) 2.07(2) 171.4(7) 92.5(6) 80.6(7) 82.2(5) 120.9(7) 174.8(6) 94.5(7) 82.6(7) 81.5(7) 130.6(6) 174.2(8) 101.1(5) 80.9(7) 83.2(8) 114.4(7)

CU(1)-N( 1) CU(1)-N(3) C~(2)-0(3) Cu(2)-N(6) Cu(2)-N(8) Cu(3)-N(9) C~(3)-N(11) O( 1)-Cu( 1)-N(2) O(1)-Cu( 1)-N(4) N(l)-Cu(l)-N(3) N(2)-Cu(l)-N(3) N(3)-Cu(l)-N(4) 0(3)-C~(2)-N(6) 0(3)-Cu(2)-N(8) N(5)-Cu(2)-N(7) N(6)-Cu(2)-N(7) N(7)-Cu(2)-N(8) 0(5)-Cu(3)-N(10) 0(5)-Cu(3)-N(12) N(9)-Cu(3)-N( 11) N( IO)-Cu(3)-N(I 1) N(ll)-C~(3)-N(12)

2.03(1) 2.09(2) 1.93(2) 2.05(1) 2.09( I ) 2.04(2) 2.04(1) 105.6(6) 99.0(6) 79.3(6) 114.0(6) 117.4(7) 100.2(6) 99.5(7) 80.3(7) 112.7(5) 110.1(6) 93.3(7) 98.6(7) 82.0(6) 114.4(8) 125.5(8)

square-pyramidal geometries can be estimated by an index t introduced by Addison et al.,35 which is defined as {[O(carboxy1ate)-Cu-N(tertiary amine)] - [N(pyridine)-Cu-N(pyridine)]}/60.0. The coordination geometry deviates from the trigonal-bipyramid to square-pyramid as the index z changes from unity to zero. The average t values for Cu(l), Cu(2), and Cu(3) chromophores are 0.90,0.95, and 0.94, respectively. Thus, the coordination geometries for each chromophore are trigonalbipyramidal, where the axis O(carboxy1ate)-Cu-N(tertiary amine) is the principal axis of the trigonal bipyramid. An unpaired electron of the copper atoms resides in the dz2 orbital which is directed at the bridging ligand. [Fez(bpepm)(NCS)41 (2). An Ortep view of 2 is shown in Figure 2, and selected bond distances and angles are listed in Table 5. The complex consists of two six-coordinate iron chromophores, and the two crystallographically independent iron

ions are bridged by a pyrimidine. The coordination geometry about each iron center is a distorted octahedron. Each iron atom is coordinated by the nitrogen atoms of tertiary amine, two pyridines, pyrimidine, and two thiocyanates. Two thiocyanates are in cis-positions in the equatorial plane. The Fe-N(tertiary amine) bond lengths (Fe( 1)-N(l) = 2.339(6) and Fe(2)-N(4) = 2.302(6) A) are longer than the Fe-N(pyridine or pyrimdine) lengths (Fe(l)-N(2) = 2.252(6), Fe(l)-N(3) = 2.222(7), Fe(1)-N(7) = 2.235(6), Fe(2)-N(5) = 2.203(6), Fe(2)-N(6) = 2.250(6), and Fe(2)-N(8) = 2.222(6) A). The long Fe-N bond lengths are due to the constraining nature of the bpepm ligand. The Fe-N(thiocyanate) bond lengths (Fe(1)-N(9) = 2.047, Fe(l)-N(lO) = 2.105, Fe(2)-N(11) = 2.067, and Fe(2)-N(12) = 2.087 A) are the shortest among the Fe-N bonds. Spectroscopic and Electrochemical Properties of [Fez(bpmar)(Hz0)4](N03)4.3H20 (3). Electronic spectra of 3 in methanol show intense bands at 250 nm ( E = 29 900 M-I cm-I) and 330 nm ( E = 13 400 M-' cm-') and a moderately intense band at 580 nm ( E = 3000 M-I cm-I). Ferric complexes with phenol or catechol ligands have been extensively studied as model compounds of nonheme iron ~ x y g e n a s e . Fe(II1)~~ (EDDHA)- (EDDHA = ethylenediamine bis[(o-hydroxyphenyl)acetate] exhibits a broad band near 475 nm ( E = 4000 M-' cm-') which was assigned to a ligand (pz) to metal (d,.) charge transfer (LMCT) band by the excitation profile experiment of resonance Raman ~pectra.~'Ferric complexes with catechol [Fe(III)L(DBC)] (DBC = 3,5-di-tert-butylcatecholate and L = tetradentate tripodal ligand) exhibit two LMCT bands in the 400-900 nm spectral region with moderate i n t e n ~ i t i e s . ~ ~ Hence, the band at 580 nm of 3 can be assigned to a LMCT (p,-d,*) band, and the band at the high-energy region is likely due to ligand n-n* transition. The redox property of 3 was studied by cyclic voltammetry and controlled-potential electrolysis. The cyclic voltammogram (Figure 3) of 3 shows a quasi-reversible wave for which Epc and EPaare at -0.03 and -0.28 V vs Ag-Ag+, respectively. Such a redox wave was not observed in the cyclic voltammogram of the free bpmar ligand. On the basis of the controlled-

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P

I3 Figure 2. ORTEP drawing of [Fez(bpepm)(NCS)4]with 50% probability.

TABLE 5: Selected Bond Lengths (A) and Bond Angles (deal for [Fedbpepm)(NCS)d (2) Fe( 1) -N( 1) 2.339(6) Fe( 1)-N(3) 2.222(7) Fe( 1)-N(9) 2.047(7) Fe(2)-N(4) 2.302(6) Fe(2)-N(6) 2.250(6) Fe(2)-N(ll) 2.067(6) N( 1)-Fe( 1)-N(2) 79.3(2) N( 1)-Fe( 1)-N(7) 73.3(2) N( 1)-Fe( 1)-N( 10) 160.9(3) N(2) -Fe( 1)-N(7) 82.2(2) N( 2) -Fe( 1) -N( 10) 92.6(2) N(3)-Fe( 1)-N(9) 92.9(3) N(7)-Fe( 1) -N( 9) 177.3(3) N(9)-Fe( 1)-N( 10) 94.1(3) N(4)-Fe( 2)-N( 6) 89.1(2) N(4)-Fe(2)-N(ll) 99.0(2) N(5)-Fe(2)-N(6) 167.5(2) N(5)-Fe(2)-N(ll) 98.4(2) N( 6)-Fe( 2)-N( 8) 86.0(2) N( 6)-Fe( 2)-N( 12) 94.6(2) N( 8)-Fe(2)-N( 12) 89.8(2)

Fe( 1)-N(2) Fe( 1)-N(7) Fe( 1)-N( 10) Fe(2)-N(5) Fe(2)-N( 8) Fe(2)-N( 12) N( 1)-Fe( 1)-N(3) N( 1)-Fe( 1)-N(9) N(2)-Fe( 1)-N(3) N(2)-Fe( 1)-N(9) N(3)-Fe( 1)-N(7) N(3)-Fe( 1)-N( 10) N(7)-Fe( 1)-N( 10) N(4)-Fe(2)-N(5) N(4)-Fe(2)-N(8) N(4)-Fe(2)-N( 12) N(5)-Fe(2)-N(8) N(5)-Fe(2)-N( 12) N(6)-Fe(2)-N(ll) N(8)-Fe(2)-N(ll) N(l l)-Fe(2)-N(12)

2.252(6) 2.235(6) 2.105(6) 2.203(6) 2.222(6) 2.087(6) 90.8(2) 104.0(3) 167.4(2) 97.0(3) 87.6(2) 9433) 88.6(2) 80.9(2) 75.0(2) 164.0(2) 84.2(2) 93.1(2) 90.5(2) 173.1(2) 96.5(2)

E / V (vs. Ag/AgCI)

Figure 3. Cyclic voltammogram of 1 mM [Fez(bpmar)(HzO)& (N03)4.3&0 in acetonitrile at a scan rate of 100 mV SKI.

potential electrolysis experiment carried out at -0.28 V, this wave was shown to correspond to a two-electron transfer. These results lead us to conclude that 3 has two redox active centers, that is, two iron ions in the molecule.

Individual redox potentials (E11/2and @1/2 in eq 1) for the multistep electron transfer process can be estimated by Taube's method.39 E' 112 and @ I D values were respectively estimated to be -0.06 and -0.26 V by using measured Epcand EPavalues.

Magnetic Properties Cryogenic magnetic susceptibilities of the complexes were measured down to liquid helium temperature, and the xmT vs temperature plots, where xrnis the molar magnetic susceptibility, are depicted in Figure 4. The temperature dependence of the product of xrnand temperature T values can be informative about the magnetic interaction between magnetic centers. If the xmT values decrease as temperature decreases, an antiferromagnetic interaction is indicated, while an increase of xrnTvalues as the temperature decreases indicates a ferromagnetic interaction. Electronic configurations of the each metal center in [Cu3(tpa)3(ta)l(ClO4)3*4H20 (l), [Fe2(bpepm)(NCS)41 (21, [Fez(bprnar)(H20)41(N03)4.3H~O (31, and [Cu2(bpmar)(NCS)21.4H20 (4) are cupric d9 for 1 and 4, high-spin ferrous d6 for 2, and high-spin ferric d5 for 3. Curie and Weiss constants, which were calculated from the magnetic susceptibility data above 100 K, are listed in Table 6. The xrnT values for 1 and 4 do not show any change above 20 K with sudden decreases below 20 K, and this behavior can be interpreted as the existence of weak antiferromagnetic interactions between the copper centers. The xrnTvalues for 2 do not show significant change (about 7.4 emu mol-' K) above 50 K, and the values are typical for high-spin iron(I1) (S = 2 state). On the other hand, the xrnTvalues below 50 K show a rapid decrease, and this behavior might be due to a zero-field splitting for the S = 2 state. The magnetic interaction between two metal centers in 2 is concluded to be negligible. The temperature dependence of the xrnTvalues for 3 is quite different from those of the other three complexes. The xrnTvs T plot shows a gradual increase as the temperature decreases with a maximum xrnTvalue (11.888 emu mol-' K) being reached at 7.0 K. This magnetic behavior indicates a ferromagnetic interaction between iron centers. An abrupt decrease of the xmT value below 7.0 K might be due to an intermolecular antiferromagnetic interaction. The magnetic

Oshio and Ichida

3300 J. Phys. Chem., Vol. 99, No. 10, 1995

'

4

60

1

50

-J

1

I

I

I

1

-

. ;

-

7

at-.

za

E

1

40-

+ & 5 K X 4.0 K

3

d

-J=3

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c1 40

1

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I

J = 4

2

I

e

30

u

5

20

I

?$ ;lo 0

2000 H n (kG

0

4000

K')

" I

0

5

10

15

H/TxlO"

Figure 4, Temperature dependences of xmTfor (A) [Cu,(tpa)3(ta)](Ci0&-4H20, ( 0 ) [Fe~(bpepm)(NCS)41,( x 1 [Fe~(bpmar)(H20)41(N03)4*3H20,and (A)[C~~(bpmar)(NCS)~]. I

TABLE 6: Curie and Weiss Constants for the Complexes Curie constant Weiss (emu atom-' K) constant (K) [Cu3(tpa)3(TA)I(C104)3.4Hz0(1) 0.44 -3.26 [Fe2(bpepm)(NCS)41(2) 3.11 -3.86 [Fe2(bpmar)(H20)41(N03)4.3H20 (3) 4.30 +0.47 [Cu2(bpmar)(NCS)2].4H~O (4) 0.44 -2.09 susceptibility data above 10 K were analyzed by using the van Vleck equation ( 2 )

55 11

+

+ 30x" + 1 4 ~+' 5x24 ~ + x28 + 7 x ' * + 5x24+ 3x28+ 9X'O

X3O

(where the spin Hamiltonian is defined as H = -US)&) for the S = 5/2 dinuclear system, where g is the g factor, is the Bohr magneton, N is Avogadro's number, k~ is the Boltzmann constant, x = exp(-J/k7'), and J is the coupling constant. The best fit parameters are J = +0.65(3) cm-' and g = 1.953(4), where the origin of the small g value is not understood yet. Magnetization as a function of applied field up to 7 T at 4.0 and 8.5 K was measured, and plots of magnetization (M) vs temperature-normalizedfield strength (H/V are shown in Figure 5. The theoretical magnetization curves (solid lines) are given by the Brillouin function [BJ(x)],with J = S = 3,4, and 5. The magnetization is expressed as

M = M,B,(x) x = Jgp,H/k,T

where M , is the saturation magnetization and J is the quantum number of the total angular momentum. In this calculation, the g value was fixed to 1.953, which was estimated from the magnetic susceptibility measurement. The experimental magnetization values at both 4.0 and 8.5 K are greater than the values predicted by the Brillouin function for J = 5 / 2 . If a ferromagnetic interaction does not exist, the magnetization values should

20

25

30

(kG f')

Figure 5. Plots of magnetization (M) vs field strength (HIT) for [Fez(bpmar)(H20)4](N03)4-3H20 at 4.0 K ( x ) and 8.5 K (+). Solid lines are given by the Brillouin function with J = 3, 4, and 5. be equal to or lower than the values for the femc high-spin species ( J = 5/2). Experimental magnetization data does show that the quantum number J, as the result of the ferromagnetic interaction, is greater than J = 4.

Discussion High-spin organic molecules are accessible when nonbonding molecular orbitals are present due to the symmetry of the alternate hydrocarbons. Some polycarbene systems, in which the radicals on meta-positions of a benzene ring, have shown fairly strong ferromagnetic interactions.2'-24 The ferromagnetic interaction in a polycarbene system can be explained by polarized pn spin over the whole molecule, which forms a topological network. We have applied this strategy to multinuclear metal complexes bridged by an organic molecule in order to have ferromagnetic interactions between the metal centers. Bridging ligands were designed to have the d, spin of the metal ion topologically networked. In [Cu3(tpa)3(ta)](C104)3.4H20(l),three copper(II) atoms are connected to the benzene ring in the meta-position through carboxylate groups. The X-ray crystallographic study reveals that the coordination geometry about copper atoms in 1 is trigonal-bipyramidal with the O(carboxy1ate)-Cu-N(tertiary amine) bond as the principal axis. The magnetic orbitals of the copper atoms are dZ2 orbitals which are directed at the coordinating carboxylates of the bridging ligand such that a strong magnetic interaction is expected. A very weak antiferromagnetic interaction was observed for 1. MNDO molecular orbital calculation for the trimesic acid (Figure 6a) showed that there are doubly degenerate orbitals ("HOMOS: next-next HOMO) which consist mainly of p, orbitals of the carbon and oxygen atoms. If the copper atom can induce spin on any carboxylate group through either the u or n pathway, this leads to the propagation of magnetic interactions. The u pathway results in an antiferromagnetic interaction, while the n pathway

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J. Phys. Chem.. Vol. 99, No. 10, 1995 3301

4 27

(c) resorcinol

'\, *.

-

HOMO : 2.0 BV 7

"HOMO

: 0.78 eV

0 43

-0

(a) trimesic acid 0.67

-033 0 24

-____ HOMO :-10.4 eV

046

(b) pyrimidine

Figure 6. MNDO diagrams of (a) trimesic acid, (b) pyrimdine. and ( c ) resorcinol.

is expected to result in an ferromagnetic interaction. The copper(I1) does not have dz spin because of its electronic configuration (d9), and the mixing of the d, orbital of the copper atoms and px orbitals of trimesic acid is not allowed because of a different symmetry of their orbitals. Hence, there is a negligible magnetic interaction in 1. It is apparent from the viewpoint of the symmetry that the metal should have d, spin in order to interact or mix with the organic pn orbital. In [ F e r (b~epm)(NCS)~] 2 the iron atoms are in the ferrous high-spin state with S = 2; hence the iron atoms have d, spins. Furthermore, two iron atoms are coordinated to the pyrimidine ring in meta-positions, so a ferromagnetic interaction is expected. Magnetic susceptibility measurements on 2 showed a fairly weak antiferromagneticbehavior. Simple perturbation theory predicts that two orbitals can strongly interact only if the orbitals have the same symmetry and are comparable in energies. The iron has d, spin, which is symmetry-allowed for the mixing with px orbitals of the bridging ligand. A MNDO calculation for the pyrimidine ligand (Figure 6b) shows the HOMO at -10.04 eV. The energy level of the d, orbitals of the iron is not known; however, the HOMO of the pyrimidine might be too low in energy for the d, spin to be polarized onto the bridging ligand. In order to have strong electronic interactions between d, and pn orbitals of metals and organic molecules, respectively, the energy level of the two orbitals should be close. It is expected that the energy level of the dz orbitals is higher than pn orbitals of the organic molecule. There are two ways to have strong interactions between two orbitals. First, a metal ion, of which the energy level of the d, orbital is comparable with that of the px orbital of the organic bridges, should be selected. Second, bridging ligands, whose HOMO has a higher energy, should he available for this purpose. We took the second way for the following reasons. The d orbitals of the first-row transition metal ions are the lowest in energy among the transition metal ions, and the iron ion has a d, orbital at rather lower energy than the other first-row transition metal ions?O Thus, the iron ion is expected to have ad, orbital which

is closer in energy to the pn orbitals of the organic molecule. On the other band, the bridging ligands, of which the HOMO has relatively high energy, can be prepared by chemical modifications of organic bridging ligands. The HOMO of an organic molecule can be stabilized by the introduction of electron-attracting groups like halogen atoms, while the introduction of electron-donating groups or negative charges to a molecule results in the destabilization of the HOMO. Resorcinol, which is the bridging group of [Fez(bpmar)(H20)nl(NO,)c3H20 (3). has two negative charges: hence it has a destabilized HOMO (2.00 eV: Figure 6c). It is expected that the d, orbitals of the irons will easily mix with px orbitals of the resorcinol. The magnetic susceptibility and magnetization experiments reveal a ferromagnetic interaction between iron centers ( J = +0.65 cm-'). Propagation of the ferromagnetic interaction results from two factors. The ferric iron ions in 3 are in the high-spin state, so the iron ions have both d, and d, spin. The iron ions can interact with both n and u pathways through the bridging ligands. The two iron atoms are separated by two oxygen and three (or four) carbon atoms. This makes a direct overlap of the magnetic orbitals (the d, orbitals on the iron atoms) negligible, which leads to the absence of antiferromagnetic exchange interactions through the u pathway. The second contribution is the propagation of the ferromagnetic interaction due to the spin polarization of the dz spin to the pn electrons on the organic ligand. If we assume an a spin on the iron, a fi spin on the carbon atom is induced through the pn electrons of the coordinating oxygen atom. This p spin is polarized as an a spin on the adjacent carbon atoms, and so on. Finally an a spin on the other side of the iron atom is induced; that is, a ferromagnetic interaction between the two iron centers is propagated (Figure 7). [Cu2(hpmar)(NCSh14H20 (4), with the same bridging ligand as 3, in which copper ions do not have any d, spin, does not show a ferromagnetic interaction. It should be noted from this experiment that the dx spin in 3 plays an important role leading to ferromagnetic interactions.

3302 J. Phys. Chem., Vol. 99, No. 10, 1995

Figure 7. Spin polarization scheme in [Fe2(bpmar)(H20)41(N0~)4.3HzO.

Conclusions Multinuclear metal complexes with intramolecular ferromagnetic interaction were successfully designed and prepared by considering three points. (i) Central metal ions should have d, spin. (ii) Organic bridging ligands should have destabilized HOMOS which are close in energy to the magnetic orbitals of the metal ions. (iii) A topological network concerning the d, spin to the ligand p, orbitals must exist. Molecular-based ferromagnets may well be realized by expanding this intramolecular strategy to intermolecular interactions.

Acknowledgment. We appreciate editing of this manuscript by Professors F. Wudl (Univ. of California, Santa Barbara) and T. P. Fehlner (Univ. of Notre Dame). This work was supported in part by Grand-in-Aid for Scientific Research on Priority Area “Molecular Magnetism” (Area No. 228/06218203) and No. 05453039 from the Ministry of Education, Science and Culture, Japan. Supplementary Material Available: Tables listing X-ray data collection parameters, derived hydrogen positions, thermal parameters, bond distances and angles, and magnetic susceptibility data (15 pages); listing of observed and calculated structure factors (18 pages). Ordering information is given on any current masthead page. References and Notes (1) Miller, J. S.; Calabrese, J. S.; Rommelmann, H.; Chittipeddi, S. R.; Zhang, J. H.;Reiff, W. M.; Epstein, A. K. J . Am. Chem. SOC. 1987, 109, 769. (2) Miller, J. S.; Epstein, A. K.; Reiff, W. M.; Epstein, A. K. Chem. Rev. 1988, 80, 201. (3) Broderick, W. E.; Thompson, J. A,; Day, E. P.; Hoffmann, B. M. Science 1990, 249, 401. (4) ,Manriquez, J. M.; Yee, G. T.; McLean, R. S.; Epstein, A. J.; Miller, J. S. Science 1991, 252, 1415. ( 5 ) Kollmar, C.; Couty, M.; Kahn, 0. J . Am. Chem. SOC. 1991, 113,

7994. (6) Pei, Y.; Kahn, 0.; Nakatani, K.; Codjovi, E.; Mathonikre, C.; Sletten, J. J . Am. Chem. SOC. 1991, 113, 6558. (7) Nakatani, K.; Camat, J. Y.; Journaux, Y.; Kahn, 0.; Lloret, F.; Renard, J. P.; Pei, Y.; Sletten, J.; Verdaguer, M. J. Am. Chem. SOC. 1989, 111,5739.

Oshio and Ichida (8) Kahn, 0.; Pei, Y.; Verdaguer, M. J . Am. Chem. SOC. 1988, 110, 782. (9) Caneschi, A.; Gatteschi, D.; Renard, J. P.; Rey, P.; Sessoli, R. lnorg. Chem. 1989, 28, 1676, 2940. (10) Caneschi, A.; Gatteschi, D.; Rey, P.; Sessoli, R. Acc. Chem. Res. 1989, 22, 392. (11) Caneschi, A.; Gatteschi, D.; Renard, J. P.; Rey, P.; Sessoli, R. lnorg. Chem. 1988, 27, 1756. (12) Zhong, 2. J.; Matsumoto, N.; Okawa, H.; Kida, S. Chem. Lett. 1990, 87. (13) Matsumoto, N.; Sakamoto, M.; Tamaki, H.; Okawa, H.; Kida, S. Chem. Lett. 1990, 853. (14) Gadet, V.; Mallah, T.; Castro, I.; Verdaguer, M.; Villet, P. J . Am. Chem. SOC.1992, 114, 9213. (15) Allemand, P. M.; Khemani, K. C.; Koch, A,; Wudl, F.; Holczer, K.; Donovan, S.; Griiner, G.; Thompson, J. D. Science 1991, 253, 301. (16) Kinoshita, M.; Tureck, P.; Tamura, M.; Nozawa, K.; Shiomi, D.; Nakazawa, Y.; Ishikawa, M.; Takahashi, M.; Awaga, K.; Inabe, T.; Maruyama, Y. Chem. Lett. 1992, 1225. (17) McConnel, H. M. J . Chem. fhys. 1963, 31, 299. (18) Mataga, N. Theor. Chim. Acta 1968, 10, 372. (19) Ovchinnikov, A. A. Theor. Chim. Acta 1978, 47, 297. (20) Itoh, K. Pure Appl. Chem. 1978, 50, 1251. (21) Breslow, R.; Juan, B.; Kluttz, R. Q.; Xia, C. Z. Tetrahedron 1982, 38,863. (22) Itoh, K. Chem. Phys. Lett. 1967, 1 , 235. (23) Sugawara, T.; Bandow, S.; Kimura, K.; Iwamura, H.; Itoh, K. J. Am. Chem. SOC.1986, 108, 368. (24) Sugawara, T.; Tsukada, H.; Izuoka, A,; Murata, S.; Iwamura, H. J . Am. Chem. SOC. 1986, 108, 4272. (25) Fujita, I.; Teki, Y.; Takui, T.; Kinoshita, T.; Itoh, K.; Miko, F.; Sawaki, Y.; Iwamura, H.; Izuokia, A,; Sugawara, T. J. Am. Chem. SOC. 1990, 112, 4074. (26) Oshio, H. J. Chem. SOC.,Chem. Commun. 1991, 240. (27) Karlin, K. D.; Hayes, J. C.; Shi, J.; Hutchinson, J. P.; Zubieta, J. lnorg. Chem. 1982, 21, 4106. (28) Hatfield, W. E. In Theory and Application of Molecular Paramagnetism; Boudreaux, E. A., Mulay, L. N., Eds.; Wiley and Sons, Inc.: New York, 1976; pp 491-495. (29) Oshio, H.; Nagashima, U. lnorg. Chem. 1990, 29, 3221. (30) lnrernational Tables for X-ray Crystallography; Kynoch Press: Birmingham, England; Vol. IV. (31) Sakurai, T. K.; Kobayashi, K. Sci. Rep. Instrum. Chem. fhys. Res. (Jpn.) 1979, 55, 69. (32) Thiel, W. Q C f E 1978, 11, 353. (33) Beppu, Y.; Ninomiya, I. QCPE 1981, 14, 409. (34) Sasaki, Y.; Takaghi, A.; Tanaka, A,; Tokura, R. Bull. Computation Center Osaka Univ. 1985, 14, 103. (35) Addison, A. W.; Rao, T. N.; Reedijk, J.; Rijin, J.; Verschoor, G. C. J. Chem. SOC.Dalton Trans. 1984, 1349. (36) Que, L., Jr. Adv. Inorg. Biochem. 1983, 5, 166. (37) Gaber, B. P.; Miskowski, V.; Spiro, T. G.J . Am. Chem. SOC.1973, 96, 6968. (38) Cox, D. D.; Benkovic, S. J.; Bloom, L. M.; Bradley, F. C.; Nelson, M. J.; Que, L., Jr. J . Am. Chem. SOC. 1988, 110, 2026. (39) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20, 1278. (40) Yamaguchi, K.; Nakano, M.; Namimoto, H.; Fueno, T. Jpn. Appl. Phys. 1998, 27, L1835.

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