Znorg. Chem. 1988, 27, 843-849
a43
Contribution from the Department of Chemistry, Washington S t a t e University, Pullman, Washington 99 164-4630
Magnetic and Structural Correlations in [(CSHsN)NH2]2Cu2C16and [(CSHSN)NH~I~CU~B~~*H~O Joan T. Blanchette and Roger D. Willett* Received October 23, 1987 The crystal structures of the title compounds, (3-aminOpyridiniUm),cU2cl6 and ( 3-aminopyridinium),Cu2Br6.H20, have been determined. The chloride dimer is monoclinic [a = 7.623 (1) A, b = 14.700 (2) A, c = 8.121 (1) A, j3 = 93.09 (1)O] and crystallizes in the space group PZ,/a, while the bromide dimer is monoclinic [a = 19.096 (5) A, 6 = 6.729 (1) A, c = 19.499 ( 5 ) A, /3 = 126.89 (1)O] and crystallizes in the space group C2/c. The two compounds contain similar species, with each copper ion having a distorted-trigonal-bipyramidalgeometry involving four halide ions and the amino nitrogen from the pyridinium ion. Pairs of copper(I1) ions are joined by two Cu-X-Cu (X = CI-, Br-) bridges to form the centrosymmetric dimer structures. The chloride dimer is symmetrically bibridged, while the bromide dimer is of the asymmetrically bibridged type. The latter contains a water of hydration, the structural effects of which are important magnetically. The copper ions in the chloride dimer show principally an angular distortion from trigonal-bipyramidal geometry, and the Cu-CI-Cu bridging angle in the dimer is 94.9 (1)'. In the bromide compound, the coordination is distorted more toward a 4 1 coordination eometry around each copper atom, with a Cu-Br-Cu bridging angle of 93.4 (1)" and an interdimer Br-Br distance of 3.728 The magnetic susceptibilities of the two compounds were measured between 2.0 and 280 K. The results have been interpreted in terms of ferromagnetic coupling within the chloride dimer (J,-,/k 30 K). A substantial antiferromagnetic coupling is observed for the bromide salt, and it is concluded that the magnetic dimer consists of copper ions from two adjacent structural dimers. The structural chemistry of five-coordinate copper(I1) chloride species is summarized, and it is concluded that the folded 4 + 1 coordination geometry is the favored geometry.
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1.
=
Introduction The study of t h e magnetostructural correlations is of interest not only in inorganic chemistry b u t also in fields ranging from solid-state physics to bioinorganic chemistry. Among solid-state physicists, t h e interest in t h e physics of low-dimensional magnetic systems has brought about a renewed interest in magnetic interactions in solids.' Many bioinorganic chemists are interested in t h e interactions of magnetically coupled metal ions in metalloproteins and metalloenzymes, as t h e study of these interactions could lead to an explanation of t h e role of these essential metal ions in t h e functioning of the protein or enzyme.* T h e work of t h e inorganic chemist is vital to t h e physicist's a n d biochemist's study of magnetic interactions in exchange-coupled systems. By synthesizing a n d characterizing various new types of magnetic systems, the inorganic chemist can provide models for magnetostructural correlations t h a t can then be. applied both to the more specific low-dimensional models of t h e solid-state physicists3 a n d to the often more complex magnetic systems in proteins and enzymes4 In our laboratory, t h e study of magnetostructural correlations has centered o n copper(I1) halide compound^.^ Copper(I1) compounds are spin'/2, so there is only one magnetic orbital per Cu atom, and t h u s the electronic properties of t h e single ion are easily described. I n compounds, however, t h e flexible coordination geometry of the copper(I1) and the existence of both "coordinated" a n d "semicoordinated" ligands have resulted in electronic structures t h a t a r e not well characterized and exist in a wide array of superexchange pathways.6 T h i s variety in the structure a n d magnetics of copper(I1) compounds makes copper(I1) systems a s interesting t o t h e inorganic chemist as they a r e to t h e physicist a n d t h e biochemist. One of t h e goals i n our laboratory, which is also of interest to solid-state physicists, is t h e design a n d isotropic (Heisenberg) ferromagnetic characterization of a spin linear-chain system.' Copper(I1) systems are also of interest t o ~
(1) Willett, R. D., Gatteschi, D., Kahn, 0. Eds. Magneto-Structural Correlation in Exchange Coupled Systems; NATO AS1 Series C140; D. Reidel: Dordrecht, The Netherlands, 1985. (2) Solomon, E. I.; Wilcox, D. E. in ref 1; p 463. (3) Bonner, J. C. J . Appl. Phys. 1978,49, 1299. De Jongh, L. J.; Miedena, A. R. Adu. Phys. 1974, 23, 1. Steiner, M.; Villain, J.; Windsor, C. G. Adu. Phys. 1976, 25, 87. (4) Vallee, B. L.; Williams, R. J. P. Proc. Natl. Acad. Sci. U.S.A. 1968, -59., 498 . .- . (5) Willett, R. D.; Grigereit, T.; Halvorson, K.; Scott, B. Proc.-Indian Acad. Sci., Chem. Sci. 1987, 98, 147. (6) Willett, R. D.; Geiser, U. Croat. Chem. Acta 1984, 57, 737.
0020-1669/88/1327-0843$01.50/0
the bioinorganic chemist because of t h e m a n y proteins and enzymes (e.g., hemocyanin, tyrosinase) t h a t contain copper(I1) magnetic interactions8 T h e project described i n this paper is a further study of t h e magnetostructural correlations in copper(I1) compounds by means of t h e synthesis, X-ray crystal structure determination, magnetic susceptibility measurements, and analysis of two new copper(I1) halide compounds. As a result of this project, we have discovered an unusual exchange p a t h w a y in copper( 11) halide dimers.
Materials and Methods Syntheses. (3AP)2Cu2C16. A 1.2-g sample of 3-aminopyridine was dissolved in an aqueous solution of 50% ethanol. A 4.0-g sample of CuCI2.2H2O was added with stirring. The solution was continuously stikred while 1 M HCI was added dropwise until the solution became clear. The solution was evaporated over low heat until crystals began to form. The red, plate-like crystals of (3AP)2Cu2C16(3AP 3-aminopyridinium) were recrystallized by temperature-gradient crystalli~ation.~ (3AP),Cu2Br6.H20.A 1.2-g sample of 3-aminopyridine was dissolved in 50% ethanol. To this was added 24 mL of 1 M CuBr2 (aqueous) and 24 mL of absolute ethanol. The solution was stirred continuously as 1 M HBr was added to make the solution clear. The dark violet, essentially opaque platelike crystals were grown and recrystallized as above. For both syntheses, it is necessary to avoid higher acid concentrations so as not to form the dicationic (3AP)CuX4 salts. X-ray Crystallography and Structure Solution. X-ray crystal structure data collections were performed on a Nicolet R3m/E diffractometer system.'" The crystal used for the chloride dimer had dimensions 0.40 X 0.40 X 0.05 mm. The system is monoclinic, P2,/a, with a = 7.623 (2) A, b = 14.700 (2) A, c = 8.121 (1) A, and p = 93.09 (1)' (A = 0.71069 A) with pEald = 1.94 g/cm3 for Z = 2. The structure solution and refinement were accomplished with use of the version 4.1 SHELX programs." A final value of R = xllFol - IFcll/CIFol = 0.029 and R, = ( X w ( F , - F,)2/XwIFo12)'/2= 0.044 was obtained. For the bromide dimer, the crystal used had dimensions 0.08 X 0.22 X 0.36 mm. This
(7) Groenendijk, H. A,; Blote, H. W. J.; Van Duyneveldt, A. J.; Gaura, R. M.; Landee, C. P.; Willett, R. D. Physica B+C (Amsterdam) 1981 Z06B+C, 45. Hoogerbeets, R.; Weigers, S. A. J.; Van Dugneveldt, A. J.; Willett, R. D.; Geiser, U. Physica B+C (Amsterdam) 1984, Z25B+C, 135. (8) (a) Solomon, E. I. In Copper Proteins, Spiro, T. G . , Ed.; Wiley-Interscience: New York, 1986; Chapter 2. (b) Dooley, D. M.; Scott, R. A,; Ellinghaus, E.; Solomon, E. I.; Gray, H. B. Proc Natl. Acad. Sci. U.S.A. 1978, 75, 3019. (9) Arend, H.; Huber, W.; Mischgofsky, F. H.; Richter-Van Leeuwen, G. K. J . Cryst. Growth 1978, 43, 213. (10) Campana, C. F.; Shepherd, D. F.; Litchman, W. M. Inorg. Chem. 1981, 20, 4039. (1 1) Sheldrick, G. SHELXTL, Version 4.1; Nicolet Analytical Instruments: Madison, WI, 1984.
0 1988 American Chemical Society
844 Inorganic Chemistry, Vol. 27, No. 5, 1988
Blanchette and Willett
Table I. X-ray Data Collection Parameters
bis( 3-aminopyridinium) hexachlorodicuurateU1) empirical formula mol wt diffractometer syst cryst class: space group: lattice consts a, A b, A c,
A
& deg
v.A3
F(OO0) radiation cryst size, mm3 abs coeff, cm-I Pcalcd, g/cm3 type of abs cor max transmissn min transmissn temp, OC data collcn technique scan range scan speed, deg/min check reflcns" tot. no. of reflcs 2O(max), deg no. of unique reflcns R for equiv reflcns hkl
C10H14C16CU2N4
C10H16Br6CU2N40
530.06 Nicolet R3m/E monoclinic PWa
814.78 Nicolet R3m/E monoclinic c2/c
7.623 (1) 14.700 (2) 8.121 (1) 93.09 (1) 908.6 (2) based on 25 reflcns in the range 350 < 20 < 400 1047.8 Mo K a with graphite monochromator 0.40 X 0.40 X 0.05 32.38 p = 1.94 (Z= 2) numerical 0.607 0.184 20 w scan 0.85 3.00 (min); 29.30 (max) l,l,O; 2,4,-1 3687 50 3601 with 3028 with F > 3 4 9
19.096 (5) 6.729 (1) 19.499 (5) 126.89 (1) 2002 (2) based on 25 reflcns in the range 260 < 28 < 270 1519.6 Mo Ka with graphite monochromator 0.08 X 0.22 X 0.36 140.9 p = 2.71 (2= 4) numerical 0.319 0.052 20 w scan 0.9 4.00 (min); 29.30 (max) 3,1,-4; 7,1,-5; 2,2,5 2038 50 1978 with 1448 with F > 3 4 7 ) 0.0229 O 4.1 A) Bra-Br contacts between dimers (listed in Table Vc). It is likely these pathways account for the observed magnetic behavior. In (NH3C2H4NH3)CuBr,,a short Br-Br contact of -3.8 A h a s led to an antiferromagnetic coupling of -68 K.39 The 3.728-A Br-Br contact can thus be unambiguously identified as the major exchange pathway in this system. Thus, the magnetic dimer consists
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Bencini, A,; Gatteschi, D. Inorg. Chim. Acta 1978, 31, 1 1 . Hatfield, W. E. In ref 1; p 5 5 5 . Laurent, J. P.; Bonnet, J . J.; Nepreu, F.; Astheimer, H.; Walz, L.; Haase, W. J . Chem. SOC.,Dalton Trans. 1982, 2433; Mikuriya, M.; Okawa, H.; Kida, S. Bull. Chem. SOC.Jpn. 1982, 55, 1086. Willett, R. D. In ref 1; p 389. O'Brien, S.; Gaura, R. M.; Landee, C. P.; Ramakrishna, B. L.; Willett, R.D. Inorg. Chim.Acta 1987, 1 4 1 , 83. Scott, B.; Willett, R. D. J. Appl. Phys. 1987, 61, 3289. Rubenacker, G. V.; Haines, D. N.; Drumheller, J. E.; Emerson, K. J. Magn. Magn. Mater. 1984, 43, 238. Halvorson, K.; Willett, R. D., submitted for publication in Acra Crystallogr.
Znorg. Chem. 1988, 27, 849-855
of copper atoms from adjacent structural dimers. Since N-H-sX interactions normally lead to ferromagnetic exchange, the J' coupling is likely due to intradimer coupling or to the longer interdimer Br...Br contacts. Acknowledgment. We acknowledge the support of NSF Grants DMR-8219430 a n d INT-8219425. In addition, t h e X-ray diffraction facility was established through funds supplied by NSF Grant CHE-8408407 and by The Boeing Co. Note Added in Proof. As noted in the paper, the local coordination geometries in (3AP)2CU2C& and ( g ~ a n i n i u m ) ~ C u ~ C are l , very ~ ~ , ~similar. Indeed, the gross molecular geometries are nearly identical. Yet the 3AP salt is ferromagnetic ( J / k = 30 K) while the latter is strongly antiferromagnetic ( J / k = -59 K).41 It is worthwhile to determine whether there is a structural explanation and, indeed, if an intradimer source for the difference exists (in contrast to the new interdimer inter-
Sundaralingam, M.; Carrabine, J. A. J . Mol. Biol. 1971, 61, 287. Declereq, J. P.; Debbaudt, M.; Van Meerssche, M.Bull. SOC.Chim. Belg. 1971, 80, 527. Drake, D. F.; Crawford, V. H.; Laney, N. W.; Hatfield, W. E. Znorg. Chem. 1974, 13, 1246. Villa, J. F. Znorg. Chem. 1973, 12, 2054.
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action in (3AP)2Cu2Br,.H20). In reference to Figure 1, the pertinent distances and angles in the 3AP and guaninium salts are as follows: Cu-C1(3), 2.496 vs 2.365 A; C1(2)Cu-Cl(la), 146.6 vs 134O; Cu-C1(2), 2.320 vs 2.288 A; Cu-C1(2a), 2.330 vs 2.447 A; Cu-C1(2)-Cu, 1 ..9 vs 98'. While many features are similar, two important differences exist. The longer Cu-Cl bond has switched orientation, and thus the orientation of the magnetic orbitals will have changed. However, this factor may not be too significant since, for these geometries, the unpaired electrons will be in a strongly mixed combination of d+z and d,z orbitals. Thus, the unpaired electron density at the bridging sites probably does not vary much for the two orientations. The more significant difference in this case would appear to be the bridging Cu-CI-Cu angles, which are 3.1' larger for the guaninium complex than for the 3AP complex. A decrease in the value of J / k by 25-30 K per degree of angular variation is not unreasonable. Thus, this effect is clearly capable of accounting for the bulk of the observed variations in J . Registry No. [(CSHSN)NH2]2C~2C16, 112196-26-6; [(CSHSN)NH.l,Cu,Brr-H,O. " . 112196-27-7.
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Supplementary Material Available: Tables of thermal parameters and derived hydrogen positions (3 pages); listings of calculated and observed structure factors for both compounds (31 pages). Ordering information is given on any current masthead page.
Contribution from the Dtpartement d e Chimie Mintrale, Analytique et Appliqute, and the Laboratoire d e Cristallographie, University of Geneva, 30 quai Ernest Ansermet, 121 1 GenEve 4, Switzerland
2,2'-Bis( 6-(2,2'-bipyridyl))biphenyl (TET), a Sterically Constricted Tetradentate Ligand: Structures and Properties of Its Complexes with Copper(1) and Copper(I1) Edgar Muller,*t Claude Piguet,t Gtrald Bernardinelli,* and Alan F. Williams' Received May 5, 1987 The synthesis of a new sterically constrained tetradentate N, ligand, 2,2'-bis(6-(2,2'-bipyridyl))biphenyl (C32H22N4= TET (I)), is presented. Its Cu(1) and Cu(I1) complexes have been prepared and characterized with the aid of crystal structure analyses, electrochemistry, and electronic spectroscopy. [Cu1(TET)]C1O4-2CH3CN(C32H22N4C~(C104).2C2H3N) (11) crystallizes in the triclinic system (PI)with a = 10.585 (2) A, b = 13.580 (3) A, c = 14.025 (2) A, a = 61.18 (1)O, 0 = 84.67 ( 1 ) O , y = 70.93 (1)O, and Z = 2. The pseudotetrahedral cation [Cul(TET)]+ shows a quasi-reversible Cu'/Cu" oxidation-reduction wave in the cyclic voltammogram at +0.94 V (NHE) in the noncoordinating solvent CH2CI2 (counterion CIO;) and has a strong metal-toligand charge-transfer absorption at 465 nm (e = 4400). In coordinating solvents (acetonitrile, tetramethylurea), the Cul/Cu" potential drops, indicating coordinative changes upon oxidation. A stability constant log K of 6.9 (1) was determined for the reaction TET Cu* F= [Cu(TET)]+ in acetonitrile. [Cu"(TET)CI]C10,.CH3CN (C32H22N4CuC1(C104)~C2H3N) (111) crystallizes in the monoclinic system (P2,lc) with a = 12.860 (2) A, b = 17.036 (3) A, c = 14.585 (2) A, a = y = 90°, = 96.33 (2)O, and Z = 4. The cation [Cul*(TET)C1]+is five-coordinate, showing a distorted trigonal-bipyramidal arrangement of the donor atoms. CI- occupies an equatorial position.
+
Introduction There is currently considerable interest in the synthesis of new ligands whose structure is such as to define quite precisely the stereochemistryof their complexationto a metal ion. In particular, in the chemistry of copper, which shows a variety of coordination geometries in both the +I and the +I1 oxidation state, the properties of the central ion are largely controlled via the imposed coordination environment. Diimine ligands, such as 2,2'-bipyridyl or 1,lO-phenanthroline and substituted derivatives thereof, are known to enhance the stability of the Cu(1) oxidation state relative to Cu(II),I especially when tetrahedral coordination is favored by the presence of bulky substituents, as in t h e cases of t h e 2,9disubstituted 1,lO-phenanthrolinesZor the 6,6'-disubstituted bipyridine^,^ or by use of cutenand type ligands." Another approach, recently reported for some Ni(I1) compounds, is to vary t h e distance between two bidentate subunits within a N4 macrocycle until strain effects in the bridges favor t h e adoption of a tetrahedral over t h e m o r e usual planar structure. Lippard and co-workers5 showed t w o aliphatic bridges of six CH2 groups between t w o diimine subunits t o be an optimal choice i n order to achieve a tetrahedral environment. In the case of t h e corresponding Cu(I1)
f
Ddpartement de Chimie Minerale, Analytique et Appliqute. Laboratoire de Cristallographie. 0020-1669/88/ 1327-0849$01.50/0
complexes, however, the 6,6 system was too flexible, and only a dinuclear species could be obtained.6 Our new approach, t h e open-chain ligand 2,2'-bis(6-(2,2'-bipyridy1))biphenyl (TET (I)), is also based upon a bridge of six carbon atoms joining t w o diimine subunits. In order t o limit flexibility, all a t o m s of the ligand a r e parts of a r o m a t i c sixmembered rings. Through intramolecular rotations around t h e single bonds joining the a r o m a t i c rings, t h e ligand may readily provide a pseudotetrahedral coordination geometry, but in no case a square-planar one. T h e use of twisted biphenyl "spacers" has recently been reported for a CuN,S, chromophore' and for a C u N , (1) James, B. R.; Williams, R. J. P. J . Chem. SOC.1961, 2007.
(2) Dietrich-Buchecker, C. 0.;Marnot, P. A.; Sauvage, J.-P.; Kirchhoff, J. R.; McMillin, D. R. J . Chem. Soc., Chem. Commun. 1983, 513. (3) (a) Burke, P. J.; McMillin, D. R.; Robinson, W. R. Znorg. Chem. 1980, 19, 1211. (b) Burke, P. J.; Henrick, K.; McMillin, D. R. Znorg. Chem. 1982, 21, 1881. (4) Albrecht-Gary, A.-M.; Saad, Z.; Dietrich-Buchecker, C. 0.;Sauvage, J.-P. J. Am. Chem. SOC.1985, 107, 3205. (5) Davis, W. M.; Roberts, M. M.; Zask, A.; Nakanishi, K.; Nozoe, T.; Lippard, S . J. J . Am. Chem. SOC.1985, 107, 3864. (6) (a) Davis, W. M.; Zask, A,; Nakanishi, K.; Lippard, S . J. Znorg. Chem. 1985, 24, 3737. (b) Davis, W. M.; Lippard, S. J. Inorg. Chem. 1985, 24, 3688. (7) Anderson, 0. P.; Becher, J.; Frydendahl, H.; Taylor, L. F.; Toftlund, H. J . Chem. Soc., Chem. Commun. 1986, 699.
0 1988 A m e r i c a n Chemical Society
