Inorg. Chem. 1988, 27, 4750-4758
4750
Contribution from the Department of Chemistry, Monash University, Clayton, Victoria 3168, Australia, and Division of Applied Organic Chemistry, C S I R O , Lorimer Street, Fishermans Bend, Victoria 3207, Australia
Exogenous Bridging and Nonbridging in Copper(11) Complexes of a Binucleating 2,6-Bis( (N-methylpiperazino)methyl)-4-chlorophenolateLigand. Crystal Structures and Magnetic Properties of Bis(p-acetato), Dinitrito, and Bis(azido) Complexes. Possible Relevance to the Type 3 Depleted Laccase Active Site Karen Bertoncello,t Gary D. Fallon,+ Jonathan H. Hodgkin,t and Keith S . Murray*,’ Received M a y 12, I988 The syntheses and structural, spectral, magnetic, and redox properties of a range of binuclear copper(I1) complexes of a binucleating ligand, LH, are described where L H = 2,6-bis((N-methylpiperazino)~ethyl)-4-chlorophenol. The following exogenous ligands were incorporated into the complexes: hydroxo, [CuzL(OH)(HzO),] (C104),-H20 (la); pyrazolate, [Cu,L(pz)](C104), (lb); acetate, [ C U ~ L ( O A C ) ~ ] ( C ~ O ~(IC); ) . ~ Hnitrite, ~ O [Cu,L(NO,),(H,O),] (C104).H20 (ld); azide, [Cu,L(N,),] [ C U ~ L ( N ~ ) ~ ] ( C I O ~ ) . ~ H ~ O (le). Complexes la-c contain bridging exogenous groups while Id and le, which, like IC, contain at least two exogenous ligands, do not. Thus Id and l e possess “open” p-phenolate-only structures. The azide complex le shows the novel feature of crystallizing into a form that contains two different binuclear molecules in the asymmetric unit, each molecule having different numbers of azide groups as indicated in the molecular formula above. Infinite “strings” of binuclear molecules are formed via weak copper-azide intermolecular contacts. l a also contains two structurally different, but stoichiometrically identical, molecules (see ref 6). Crystal structure data at 20 OC: IC, monoclinic space group P2,/n with a = 20.127 (7) A, 6 = 14.480 (4) A, c = 11.263 (2) A, fi = 92.88 (3)O, and Z = 4; Id, orthorhombic space group P6ca with a = 20.654 (1) A, 6 = 20.087 (2) A, c = 13.873 (3) A, and Z = 8; le, triclinic space group P i with a = 91.250 (4) A, 6 = 13.405 (3) A, c = 12.873 (3) A, or = 121.77 ( 1 ) O , @ = 98.88 (1)O, y = 95.86 ( 1 ) O , and Z = 2. ICcontains two p-acetate and one p-phenolate bridging groups and thus provides another example of this rapidly growing class of compounds showing such a core unit. Like all of the other present complexes, it contains a distorted square-pyramidal geometry around each Cu. However, in contrast to la (and presumably lb), which displays approximate coplanarity of the two basal planes, there is a large dihedral angle between the basal planes of IC (91.5O), Id (83.7’), and l e (83.6O, molecule 1; 71.4’, molecule 2). The pphenolate (endogenous) oxygen atom “hinges” these basal planes together in all of the complexes, and despite the lack of coplanarity of the Cu, planes in l e e , it is still capable of providing a superexchange pathway leading to medium-strength antiferromagnetic exchange coupling. Correlations of this and of other geometric features with J values and with some features of the phenolate 0 Cu(I1) charge-transfer visible bands are described. Brief comments on possible relevance to recent findings on Cu-Cu biosites in the type 2 depleted (T2D) laccase enzyme are also included.
-
-
Introduction As p a r t of a wide study of t h e structure/magnetism/redox r e l a t i ~ n s l -in ~ binuclear copper(I1) complexes, we have employed a binucleating ligand, LH, obtained by a M a n n i c h reaction beOH
r?
Me-N \_/N-HzC
1
y
C
H
2
-
N
r? N-
*
CI
LH
tween a para-substituted phenol, formaldehyde, a n d N-methylp i p e r a ~ i n e . ~ . ’Molecular models showed t h a t simultaneous coordination of t h e phenol oxygen and t h e four piperazine nitrogen a t o m s t o t w o Cu(I1) ions, in t h e presence or absence of an exogenous bridging ligand, would be difficult in view of the sterically constrained ligand conformation. Nevertheless, a hydroxo-bridged complex, l a , was obtained a n d characterized by X - r a y crystalMe
Me
(c104)2
CI
X = OH- (la) X = pyrazolate (lb) Monash University !CSIRO.
lographic, spectral a n d magnetic la was found t o have one of the shortest Cu-Cu distances in p h y d r o x o complexes of this general type (viz. 2.87 A). This and other structural features of t h e bridging moiety were generally compatible with the weak ferromagnetic coupling observed via variable-temperature susceptibility studies.’V6 In attempting to insert other exogenous X groups, particularly those containing two or more atoms, we have obtained some unexpected and unusual results. W i t h X = pyrazolate t h e expected p p y r a z o l a t e complex, lb, was obtained. However, in t h e case of X = acetate, a triply bridged (p-phen) . ~was H~O oxo)bis(p-acetato) complex [ C U ~ L ( O A C ) ~ ] ( C ~ O ~(IC) obtained. This contrasts with the more usual type of mono(@acetato)copper(II) derivatives obtained with o t h e r related binuInterestingly, s i m i l a r b i s ( p c l e a t i n g ligand acetate)-bridged complexes of Fe(IIQ8 a n d MII(III)~have been reported since completion of t h e present syntheses, and this bridging unit h a s been proposed by Que et al.loat o be a thermodynamically favored core structure.lob Crystal structure data, (1) Murray, K. S . In Biological and Inorganic Copper Chemistry; Karlin, K. D., Zubieta, J., Eds.; Adenine: New York, 1986; Vol. 2, p 161. (2) Mazurek, W.; Berry, K.J.; Murray, K. S.;O’Connor, M. J.; Snow, M. R.; Wedd, A. G. Inorg. Chem. 1982,21, 3071. (3) Mazurek, W.; Kennedy, B. J.; Murray, K. S.;OConnor, M. J.; Rcdgers, M. J.; Snow, M. R.; Wedd, A. G.; Zwack, P. R. Inorg. Chem. 1985, 24, 3258. (4) Mazurek, W.; Bond, A. M.; Murray, K. S.; OConnor, M. J.; Wedd, A. G. Inorg. Chem. 1985,24, 2484. (5) Iliopulos, P.; Fallon, G. D.; Murray, K. S . J. Chem. Soc.,Dalton Tram. 1986,437. (6) Fallon, G. D.; Murray, K. S.;Spethmann, B.; Yandell, J. K.; Hodgkin, J. H.; Loft, B. C. J . Chem. SOC.,Chem. Commun. 1984,1561. ( 7 ) Hodgkin, J. H. Aust. J . Chem. 1984,37, 2371. (8) Murch, B. P.; Bradley, F. C.; Que, L., Jr. J . Am. Chem. SOC.1986,108, 5027. (9) (a) Diril, H.; Chang, H.-R.; Zhang, X.;Larsen, S . K.; Potenza, J. A.; Pierpont, C. G.; Schugar, H. J.; Isied, S . S.; Hendrickson, D. N. J . Am. Chem. SOC.1987,109,6207.(b) Buchanan, R. B.; Oberhausen, K. J.; Richardson, J. F. Inorg. Chem. 1988,27,911. (10) (a) Borovik, A. S.;Que, L., Jr.; Papaefthymiou, V.; Miinck, E.; Taylor, L. F.; Anderson, 0. P. J . Am. Chem. SOC.1988,110, 1986. (b) A Bis(r-benzoato)-bridgedCu(I1) complex of a type related to IC has just been reported: Nishida, Y . ;Tokii, T.; Mori, Y. J . Chem. SOC.,Chem. Commun. 1988. 675.
0020-1669/88/1327-4750$01.50/0 0 1988 American Chemical Society
Inorganic Chemistry, Vol. 27, No. 26, 1988 4751
Binuclear Cu(I1) Complexes
nitrite case, a lack of exogenous pazido bridging. Surprisingly, the crystals contain two different binuclear entities in the asymmetric unit, one containing three azides (per Cu2), the other containing two, with a perchlorate ion shared between them. Once more, the lack of 1,l- or 1,3-(pazido) bridging contrasts with that recently observed in other binuclear M-azido s y ~ t e m s . ' ~ - ~ ~ However, the present observations may well be relevant to a recent report by Spira-Solomon and Solomon, who have ascribed spectroscopic differences between azidohemocyanin (or azidotyrosinase) and azido T2D-laccase (type 2 depleted laccase) to the presence, or absence, of exogenous azido bridging2' Comments on the possible relevance to the type 3 protein sites, together with full preparative, structural, and magnetic characterization of complexes la-e are now described.
Me Me
Experimental Section CI IC
described below, show that the acetate groups in IC are not symmetrically bridging but, rather, adopt a semibridging mode. Use of nitrite, NO2-, as a potential exogenous bridge also led to the formation of a dinitrite complex, Id, but in this case X-ray (clod
CI
Id
crystallography shows that there is no exogenous bridging between the two Cu(I1) ions. This lack of nitrite bridging contrasts with the anticipated mono(pnitrito-O,N) bridging recently reported by Reed et al. in a related system.lI Complex Id provides another addition to the small group of binucleated compounds that are now known to possess only an endogenous phenolate (or alcoholate) bridging oxygen atom.12-16 Suzuki et al.12 and Urbach et a1.I6 have recently used the term "open" structure to describe this bridging mode and have attributed it to a less strained, more relaxed conformation of the binucleating ligand. Attempts to incorporate azide as the X group led to a number of products being formed, depending upon the precise reaction conditions used. Structural characterization of one such product, [ C U ~ L ( N [~C) ~U]~ L ( N ~ ) ~ ] ( C ~ O (le), ~ ) . ~showed, H ~ O as in the Me
Me
CI
Me
Me
~ 1 0 4 -
Synthesis of Complexes. Compound la was synthesized as described previously by reacting an ethanolic solution of copper(I1) perchlorate hexahydrate and ligand, LH, in the presence of sodium hydroxide.lS6 Compound Ib was obtained by mixing methanolic solutions of la (0.65 g, 0.87 mmol) and pyrazole (0.062 g, 0.87 mmol). The product, obtained as green crystals on evaporation of the solution, was recrystallized from methanol. Yield: 0.31 g, 48%. Anal. Calcd for C21H31C13C~2N609: C, 33.85; H, 4.16; N , 11.28; C1, 14.3; Cu, 17.0. Found: C, 33.73; H, 4.19; N, 11.58; CI, 14.4; Cu, 16.9. Compound IC. Copper(I1) acetate monohydrate (0.4 g, 2 mmol)was dissolved in warm aqueous ethanol (75 mL). Addition of ethanolic solutions of the ligand, L H (0.35 g, 1 mmol),and of sodium perchlorate (0.7 g, 5 mmol) led to the formation of a dark green solution. When concentrated, this solution yielded needle-shaped green crystals, which were recrystallized from aqueous ethanol. Yield: 0.57 g, 76%. Anal. Calcd for a monohydrate C22H36C12C~2N4010: C, 36.98; H , 5.04; N , 7.84; CI, 9.9. Found: C, 37.01; H, 5.03; N , 7.64; CI, 10.0. Compound Id. To an ethanolic solution containing ligand, L H (0.05 g, 0.144 mol), and copper (11) perchlorate hexahydrate (0.107 g, 0.288 mmol) was added a solution of sodium nitrite (0.023 g, 0.333 mmol) dissolved in ethanol. The resulting green powder was recrystallized from aqueous ethanol to yield green-black crystals of Id. Yield: 0.05 g, 53%. Anal. Calcd for C18H34C12C~2N6012: C, 29.84; H, 4.72; N , 11.60; CI, 9.8; Cu, 17.5. Found: C, 29.78; H , 4.98; N , 11.47; CI, 10.2; Cu, 18.0. Compound le. Method a. Sodium azide (0.02 g, 0.3 mmol) in water (2 mL) was added to a solution of la (0.1 g, 0.134 mmol) in methanol (20 mL). After addition of 2-propanol (50 mL) and slow evaporation for several days, dark green-black crystals were obtained. They had the formula [{CU~L(N~)~)(CU~L(N~)~~(CIO~)~~H~O] as determined by microanalysis and by the X-ray crystal structure determination. Yield: 0.013 g, 15%. Anal. Calcd for C36H60C13C~4N2308: C, 33.17; H, 4.63; N , 24.71; CI, 8.2. Found: C, 33.90; H, 4.20; N , 25.0; CI, 8.3. It was found that if the product was precipitated from methanol, without addition of 2-propano1, and then recrystallized from methanol/chloroform, crystals of [Cu2L(N3),]C104only were obtained. Anal. Calcd for C18H28C12CuN,oOS:C, 32.63; H, 4.23; N, 21.15. Found: C, 32.81; H , 4.86; N , 21.43. Method b. An aqueous solution of sodium azide (0.022 g, 0.34 mmol) was added to an aqueous ethanolic solution containing copper(I1) perchlorate hexahydrate (0.17 g, 0.29 mmol) and ligand, L H (O.O51g, 0.145 mmol), whereupon a brown solid of uncertain composition was deposited. After filtration and slow evaporation of the solution, dark green-black oblong-shaped crystals of [ C U ~ L ( N , ) ~ ] ( C I O were ~ ) formed as judged by the similarity of the IR spectrum to that of the analyzed sample, described above. A number of other reactions of sodium azide with mixtures of the ligand and copper(I1) salts, such as Cu(N03),.3H20 or C U ( C I O ~ ) ~ . ~ H ~ O , were attempted in the presence or absence of bases such as LiOH or KOH. Solid azido copper(I1) complexes could be obtained, but because
I CI
le (11) McKee, V.; Zvagulis, M.; Reed, C. A. Inorg. Chem. 1985, 24, 2914. Demura, Y . ;Murase, I. Bull. Chem. SOC. (12) Suzuki, M.; Kanatomi, H.; Jpn. 1984, 57, 1003. (13) Nishida, Y . ;Kida, S. J . Chem. SOC.,Dalion Trans. 1986, 2633. (14) Nishida, Y . ;Shimo, H.; Maehara, H.; Kida, S. J . Chem. SOC.,Dalion Trans. 1985, 1945. (15) McKee, V.; Smith, J. J . Chem. SOC.,Chem. Commun. 1983, 1465. (16) Maloney, J. J.; Glogowski, M.; Rohrbach, D. F.;Urbach, F.L.Inorg. Chim. Acta 1987, 127, L33.
(a) McKee, V.; Dagdigian, J. V.; Bau, R.; Reed, C. A. J . Am. Chem. SOC.1981, 103, 7000. (b) McKee, V.; Zvagulis, M.; Dagdigian, J. V.; Patch, M. G.; Reed, C. A. J . Am. Chem. SOC.1984, 106, 4765. (a) Boillot, M.-L.; Kahn, 0.;O'Connor, C. J.; Gouteron, J.; Jeannin, S.; Jeannin, Y .J . Chem. Soc., Chem. Commun. 1985, 178. (b) Mallah, T.; Boillot, M.-L.; Kahn, 0.; Gouteron, J.; Jeannin, S.; Jeannin, Y . Inorg. Chem. 1986, 25, 3058. Sorrell, T. N.; O'Connor, C. J.; Anderson, 0. P.; Riebenspies, J. H. J . Am. Chem. SOC.1985, 107, 4199. Karlin, K. D.; Cohen, B. I.; Hayes, J. C.; Farooq, A,; Zubieta, J. Inorg. Chem. 1987, 26, 147. Spira-Solomon, D. J.; Solomon, E. I. J . Am. Chem. SOC.1987, 109, 6421.
4152 Inorganic Chemistry, Vol. 27, No. 26, 1988
Bertoncello et al.
Table 1. Crystallographic Data IC formula fw cryst syst cryst habit cryst size, mm space group syst abs temp, ‘ C a, A b, 8,
Id
C U ~ C ~ ~ H ’ ~ N , C I ~ O ~ ‘ ~Cu2C18H32N6C1201 H~O I”2O 724.5 monoclinic orthorhombic acicular equant 0.21 X 0.10 X 0.04 0.11 X 0.11 X 0.19 m/n Pbca hOl, h I # 2n; OkO, k # 2n Okl, k # 2n; h01,l # 2n; hkO, h f 2n 20 20 20 20.127 (7) 20.654 (1) 19.250 (4) 20.087 (2) 13.405 (3) 14.480 (4) 13.873 (3) 12.873 (3) 11.263 (2) 90 121.77 (1) 90 90 98.88 (1) 92.88 (3) 90 90 95.86 (1) 4 8 2 2723 5756 3278 1.59 1.52 1.67 1.59 (1) 1.67 (1) 1.52 (1) Mo Ka; 0.7107 Cu Ka; 1.5418” Mo Ka; 0.7107 35.96 17.3 17.3 0.879, 0.586 0.852, 0.823 0.900, 0.815 Philips PW1100 Philips P W I 100 Philips PWI 100 0.05 0.04 0.05 f(0.65 0.2 tan 8) f(0.75 0.3 tan 8) f(0.75 0.2 tan 0) 750.7
+
c, A a,deg
0,deg T, deg
Z
v,A’
g cm-’ D m d rg cm-’ radiation; A, A p, cm-‘ transmissn factors: max, mint data collcn instrum scan speed, deg s-’ scan width, deg scan method collcn range, deg data collcd total no. of unique data no. of data used for refinement ( I 3 &Id,
34r))d no. of params refined R RwC*d
largest peak, e/A’
le CU4C’6H~6N2’C1’06’2H20 1303.7 triclinic acicular 0.27 X 0.1 1 X 0.06 P i (by successful refinement)
+
+
+
w
w
w
6
