Synthesis and characterization of a constricted and rigid ligand system for five-coordinate binuclear complexes

ELSEVIER

InorganicaChimica Acre263 (1997) 231-245

Synthesis and characterization of a constricted and rigid ligand system for five-coordinate binuclear complexes L i s h e n g C a i ~'*, W e n g e X i e a, H u s s e i n M a h m o u d a, Y i n g Hart C h a r l e s J. O ' C o n n o r b

a

D o n a l d J. W i n k ", S i c h u L i b,

a Department of Chemistry. The Universily oflllinois at Chicago. Chicago. IL 60607. USA b Department of Chermstry, The University of New Orleans. New Orleans, IA 70122. USA

Received5 February 1997;revised 7 April 1997;accepted6 May 1997

Abstract A generalized synthetic slrategy for a rigid ligand system for binuclear metal complexes has been developed. In the case of Co(H) and Cu (II), the ligand coordination environment forces the metal to adopt a trigonal bipyramidal configurationwith each of the axial bonds toward each other. The dicobalt complex crystallized from CH3CN/ether as a PIMPor E~N salt, and the dicopper cmnplex from CH3CN/ acetone as an Et4N salt. Single crystal X-ray analysis of [PIMP]2[Co2(/.t-OAe)L] (monoclinic, space gronp P21/c, a=!3.4308(2), b = 9.3747(2), c--45.9177(6)/~,/3 = 97.54( I )°, V= 573 !.5(2) ~3 Ri -- 0.0991, crystal dimensions 0.3 × 0.2 ×0.2 ram, Z=4,D,~ = 1.415 gcm- 3, F(000) = 2528 e, where L ==2,6-cresolate-N,N,N'3q'-tetramethylenecarboxylate) and [F.,I4N]2[Cu2(jr-OAt)L] ( lnonoclini~ group P2t, a=10.626(2), b=12.839(4), c=14.073(3) ~, ,8=104.15(2) °, V= !861.8(8) ~3 R!=0.0683, crystal dimensimm 0.4 × 0.3 × 0.2 mm, Z = 2, D ~ = !.448 g c m -3, F(000) ~- 856 e) reread that both metal ions adopt a five-coordinate Irigonal bipyranlid~

structure, each provided by the two carboxylic oxygens, one nitrogen, one bridging phenolate oxygen and the bt~'ging acetate gmep, whele the non-hydrogen atoms of acetate, the two metal ions and the atoms of the benzene ring adept a semi-coplanarconfiguration.The Selaratien between the two cobalt atoms is 3.505(5) ~ and the two C o O bonds (2.01(2) and 2.04(2) ]~) to the acetate ligand ate tilted lowmd each other, giving an O...O internuclear distance of ~ 2.2 ~. The separation between the two copper atoms is 3.550(5) ~ and the two ~ b o n d s ( 1.920(7) and 2.034(7) A) to the acetate ligand are tilted toward each other, giving an O.-.O internucleardistance of ~ 2.3 A. These m:sulB suggest that appropriate binuclear complexes of this ligand will favor coordinationore2, but not 02- or/.~-OH.V a r i a b l e t e ~ m a g n e t i c susceptibility measurements demonstrate weak antiferromagnetic (Zi/k= -7.8 K) and fen'onmgneticcoupling (2//k=20.58 K) for the cobalt and copper complexes, respectively. The magnetic behavior, electronic specmm~and eleetrochemistry oftbe derivatives suggest that the new rigid heptadentate ligand system should resist formation of #-oxo bridges between the complexed metal atoms. © 1997 Elsevier Science S.A. Keywords: Binuclearcomplexes;Coppercomplexes;Cobaltcompiexes;Oxo-bridgedcompiexes;~

1. Introduction

Binuclear B'ansition metal complexes have been demoBstrated or proposed in the active sites of oxyhemerythrin (Fe20) [ 1], rihonucleotide reduclase (Fe20) [2], methane monooxygenase (Fe20) [2,3], oxyhemGcyanin (CU202) [4 ], tyrosinase (Cu202) [5 ] and snperoxide dismulase (CuZn) [6]. In the efforts that have been made to model these sites, dimetallic complexes of several polypodal,binucleating ligand systems have been synthesized [7]. These hepmdenlate ligands incorporate a phenolate or an alkoxide bridge and 'also provide three additional donor sites to each metal ion. * Conespondingauthor. Tel.: 312 996 3161; fax: 312 996 0431. 0020-1693/97/$17.00 © 1997Elsevier Scie_qceS.A. All rights PII S0020-1693 (97) 05650-8

slmfmn~s;~

n,mnnLic

The bridge functions to maintain the two metal centers in close proximity under conditions where simple oxo-bridged complexes are known to dissociate [8]. Most of the ligands utilized to date are based on 2,6-[bis(substitutent)andnomethyi]-4-methyiphenol [9] and 1,3-di(substiment)amino2-propanol suucmml motifs [ 10]. Metalloprotein model complexes based on these muitidenlate ligands are chemically active, and have been shown in some instances to mimic the enzymes by reversibly binding oxygen [7b,10a,c,l I ] or by acting as oxygenation catalysts [9c,12]. Remarkably, the binuclem' complexes have been shown to be supcdorto their m o n ~ u d e a r cou.terpam [gc,d,13]. We are attempting to extend this advantage beyond the realm of enzymatic chemistry and into the binding

232

L. Caiet al. / lnorganica ChiraicaActa 263 (1997)231-245

and activation of small molecules in general, with dioxygen activation of particular interest. In doing so, we are not limited to polypodal ligands which mimic the coordination spheres of the various enzymes. Instead, we are interested in iigands having constricted and rigid geometry with which we can manipulate and control the properties of the metal binding sites. In examination ofligand systems which support transition metal activation of dioxygen, we found that formation of an additional/z-O or g-OH bridged species [9b,10¢,13c,f,14] typically blocks two coordination sites, preventing furtherO2 activation; moreover both metal centers in such models are often coordinatively seturated. The problem arises from the ability of the ligand to accommodate the short metal-metal distances required for #-O and p.-OH groups. Only a few examples of binuclear copper complexes based on 2,6[bis(substitutent)amino]-phenol have been documented to discourage such additional bridge formation [ 15]. Here we report the synthesis of a new ligand system designed to minimize the formation of/z-O or p~-OH bridged species and to accommodate a bridging O2 species, or even better, facilitate the splitting of 02 into two metal oxo groups. We also report the synthesis and characterization of its dicobalt and dicopper complexes with acetate as a bidentate bridging ligand where both metal centers are five-coordinate. Selection of metals is based on the probability of isolating dioxygen adducts as potential reactive intermediates (redox potential and the intrinsic stability of the metal oxo group are important considerations). Five-coordinate binuclear cobalt and copper complexes have been proposed to be the intermediates [ 16] in oxygenation reactions or as stable species [ 17] in solution with nitrogen-rich coordination environments. Examination of these species is our first attempt in this endeavor.

2. Experimental 2.1. Materials, methods and instrumentation

Chemicals were obtained from commercial suppliers and used as received unless otherwise stated. Air-sensitive materials were handled either in a Vacuum Atmospheres glove box or by using standard Schlenk techniques under nitrogen. Solvents used in the glove box were purified by standard methods. Elemental analyses were performed by either Galbraith Laboratories, Inc. or Midwest Microlab. tH NMR spectra were obtained on a Bruker AC 200 spectrometer and the chemical shifts were referenced to the residual solvent peaks. Electronic spectra were recorded on a Hewlett-Packard 8453 diode array spectrometer. IR spectra were obtained using an ATI Mattson Genesis Series FTIR instrument. 2.2. 2,6-Diamino-¢resol (2)

(a) 2,6-Dinitro-cresoi (MW = 198.15, 5.00 g, 25.2 mmol) was dissolved in 150 mi CH3OH in a 500 ml Schlenk flask,

and 10% Pd on carbon was added. The solution was dogassed by vacuum pumping and refilling with nitrogen gas. The last refilling was with hydrogen gas instead. The solution was kept under hydrogen overnight, The color of the solution changed from green to brown, and no heat was generated any longer. The catalyst was filtered in a glove box, and solvent was removed to afford the product (3.2 g, 92%), ~H NMR in CD3OD: 8 6.08 ( s, 2H, Ar-H); 2.10 ( s, 3H, -CH3). High resolution MS: M + found: 138.078992; eale.: 138.079312900; 138 (100%,M+), 121 (7.1%, [M-OH] +), 109 (15.7%, [ M - O H - C ] +). (b) 2,6-Dinitro-cresol (MW = 198.15,1.06 g, 5.32 mmol) was suspended in 25 ml concentrated HCI in a 200 ml Schlenk flask. The mixture was heated to reflux. SnCI2.2H20 (MW= 225.63, 20.1 g, 89.1 mmoi) in 25 mi concentrated HCI was added into the above solution over 5 rain by pipette. The solution was refluxed for ! h with the color of the solution changing from yellow to almost colorless. The solution was freeze-pump-thaw degassed. Degassed concentrated NH3" H2O (100 ml) was added into the above solution at -78°C to form a white suspension, which was transferred into a continuous liquid-liquid extractor under N2. Degassed ether (500 ml) was added, affording 472 mg product (64%) after 4 days. 2.3. N,N,N',N'-Tetrakis(sodium carboxylate methyl)2.6-diamino-cresol (3)

2,6-Diamino-cresol (MW= 138.19, 2.20 g, 15.9 mmol) was dissolved in 500 ml CH3OH. Then bromoacetic acid (MW=138.95, 10.6 g, 76.3 retool) and Na2CO3 (MW= 105.99, 18.0 g, 169.9 mmol) were added into the solution. Then t50 ml of H20 were injected into the solution. The mixture was refluxed overnight under N2. Upon removal of the solvent, the solid was extracted with CH3OH. Pumping off the solvent affords 6.6 g product (90%). ~H NMR in CD3OD: 8 6.71 (s, 2H, Ar-H); 3.56 (s, 8H, -CH2-); 2,15 (s, 3H, -CH3). 2.4. Lactone (4)

3 (MW =458.29, 2.00 g, 4.36 mmol) was dissolved in 10 m! efCH~OH. Acetic anhydride (MW = 102.1, 1.00 ml, 10.6 retool) was added into the solution. After stirring overnight, the solvent was removed. The solid was extracted with ethyl acetate, and the lactone was purified by silica gel cl':comatography using ether/hexane to afford 1.0 g product (yield 60%). tH NMR in CDCI3:8 6.14 (s, 1H, At-H): 5.95 (s, IH, At-H); 4.09 (s, 2H, -1CH2-); 3.96, 3.92 (s, 2H, --CHa-); 3,73 (s, 2H, --CH2-); 3.71 (s, 2H, -CH2-); 2.17 (s, 3H,-CH3). High resolution MS: M + found: 394.136464; calc.: 394.137615461; 394 (24.0%, M+), 366 (26.8%, [M-CO] +),335 (28.1%, [M-COOCH3] +),307 (100%, [M-CO-COOCH3] + ), 233 ( 14.7%, [ M - C O - C H 3 2COOCH3]+), 175 (23.1%, [M-CO-CH2COOCH32COOCH3] + ).

L. Caietal./Inorganica ChiraicaActa263 (1997)231-245 2.5. Sodium-N,N,N',N'-tetrakis(sodium carboxylate methyl)- 2, 6-diamino-c r esolat e (5) (a) 4 (MW -- 394.42,500 rag, 1.27 mmol) was suspended in water. Then NaOH (MW=40, 406 mg, 10.2 mmol) in water was added. The cloudy solution became clear after stirring for 0.5 h. The solution was stirred overnight. Upon removal of the solvent, the solid was washed with ethanol to get rid of excess NaOH to afford 460 mg product (80%). ~H NMR in D20:8 6.57 (s, 2H, At-H); 3.65 (s, 8H, --CH2-); 2.10 (s, 3H,--CH3). (b) 3 (MW=458.27, 1.00 g, 2.18 retool) was dissolved in 50 ml of CHaOH. Then NaOCH3 (MW = 54.03, 707 rag, 13.1 mmol) was added. After stirring at room temperature for 2 h, the solvent was removed. The solid was washed with ethanol to get rid of excess NaOCH3 to give 600 mg product

(60%). 2.6. Penta-tetraethylammonium-N,N,N',N'tetrakis(carboxylate methyl)-2, 6-diamino-cresolate (6) 4 (MW-- 394.42, 100 mg, 0.254 mmol) was suspended in methanol. Then Et4NOH (MW= 147.26, 165 rag, 1.12 retool) in water was added. The cloudy solution became clear after stirring overnight, The solvent was removed under vacuum to generate 6 in almost quantitative yield. IH NMR in CD3CN: 86.51 (s, 2H, Ar-H); 3.92 (s, 8H, --CH2-); 2.11 (s, 3H, -CH3); 3.27 (q, 3Jtm=7.3 Hz, 40I-t); 1.27 (dt, 3JHH= 6.9 Hz, 3JNH= 1.9 Hz, 60H).

2. Z Disodium t~-acetato-N,N,N ',N °-tetrakis(carboxylate methyl)-2,6-diamino-cresolate dicobalt (7) Co(OAt)2" 4H20 (MW = 249.11, 0.910 g, 3.65 retool) was dissolved in CH3OH. Then 5 (MW--458.27, 1.00 g, 2.18 mmol) in CH3OH was added dropwise. The solution was then stirred overnight. Upon removal of the solvent, the solid was extracted by ethanol to give 1.0 g product (80%). tH NMR in CD3OD: ~ 41.2 (brs, 4H, CH2, I-l~o or Hint); 26.1 (brs, 3H, -OCOCH3); 22.1 (brs, 2H,-Ar-H); 16.5 (brs, 3H, -Ar--CH3).

2.8. Di-tetraphenyl phosphonium it-acetato-N,N,N',N'tetrakis(carboxylate methyl)-2,6-diamino-cresolate dicobalt

7 (MW=529.14, !.00 g, 1.89 mmol) and Ph4PCI (MW=374.86, 0.64 g, 1.71 mmol) were dissolved in CH3OH/CH3CN ( I: I ) to give a purple solution. After stirring for 2 h, the solvent was removed. The solid was extracted with CH3OH/CH3CN ( 1:1), and the solvent from the filtrate was removed. The above extraction procedure was repeated for CH3OH/CHsCN (!:2) and CH3OH/CH3CN (!:4), respectively. Finally, the solid was extracted with CH3CN. Diffusing ether into the CH3CN solution provides 0.80 g reddish-pink rectangular block crystals (40%). ~H NMR in

233

CD3CN: 8 : 8 43.9 (brs, 4H, CH2, H~,o or Hi~); 31.5 (brs, 4H, CH2, He,~oor Hint); 23.5 (brs, 3H, --OCOCH3); 20.4 (brs, 2H,-Ar-H); 17.1 (brs, 3H,-Ar--CH3);7.68 (m,40H, PPh). Anal. Found: C, 63. ! 3; H, 4.68. Calc. for C65Hs6Co2N2OllP2: C, 63.94; H, 4.62%. 2.9. Di-tetraethyl ammonium p-acetato-N,N,N',N'tetrakis( carboxylate methyl)-2,6-diamino-cresolate dicobalt

7 (MW = 529.14, 500 mg, 0.945 mmol) was dissolved in 20 mi CHsOH. Then (CH3CH2),oNIF.xH20 (MW = 149.25198.50, 168 mg, 0.846-1.13 retool) in 10 ml CH3OH was added dropwise. Upon stirring for 2 h, the solvent was removed. The solid was extracted with CH3OH/CH3CN (1:!), and the solvent from the filtrate was removed. The above extraction procedure was repeated for CH3OH/ CH3CN (1:2) and CH3OH/CH3CN (1:4), respectively. Finally, the solid was extracted with CH3CN. Diffusing ether into the CH3CN solution provides 0.20 g reddish-pink rectangular block crystals (29%). tH NMR in CD3CN: 9:8 44.1 (brs, 4H, CH2, I-I~o or ['tint); 32.3 (brs, 4H, CH2, I-I~o or Hi,0; 23.6 (brs, 3H, --OCOCH3); 20.5 (brs, 2H,-Ar-H); 17.3 (brs, 3H, -Ar--CH3); 3.43 (q, 16H, NCH2); 1.31 (t, 24H, NCCH3). MS (positive FAB): 931 [M+Et4N] +, 803 [M+H] +,743 [ M - OAc] +,609 [ M - Et4N- OAcl +;MS (negative FAB): 672 [M-Et4N]-, 483 [ M - 2 E t ~ OAc] -.

2.10. Di-tetraethyl ammonium lz-acetato-N,N,N',N'tetrakis( carboxylate methyl)-2,6-diamino-cresolate dicopper (10) 6 (MW = 1016.75, 1.93 g, 1.90 retool) was dissolved in 20 ml CH3OH. Then Cu(OAc)2 (MW= 199.644, 713 rag, 3.60 mmol) in 10 ml CH3OH was added dropwise. Upon stirring overnight, the solvent was removed. The oily solid was washed with acetone to give a green powder. The solid was extracted with CH3CN and the solution was filtered to remove insoluble material. Removal of the solvent affords 486 mg of the copper complex. Yield 33%. X-my quality crystals were grown from vapor diffusion of acetone into an acetonitrile solution. ~H NMR in CD3CN: 1O: a 87J (brs, 4H, CH2, H~o or Him); 75.5 (la's, 4H, CH2, H w or I-I~-); 2.40 (brs, 3H, -OCOCH 3); 13.5 (Ins, 2H, -At-H); ! 7.2 (brs, 3H, -Ar-CH3); 3.65 (q, 16H, NCH2); 1.49 (t, 24H, NCCH3). Anal. Found: (2, 63.13; H, 4.68; N, 6.90. Calc. for C33H56Cu2N4On: C, 63.94; H, 4.62; N, 6.89%.

2,11. Collection and reduction of X-ray data for 8 Many attempts were made to crystallize the five-coordinate complexes. In a typical experiment the complexes were dissolved in acetonitrile in a glove box. The solution was divided into multiple small tubes ( !.5 ×4.5 cm), each of which was then placed in a vial ( 3 × 6 cm) containing 2 ml of ether,

234

L Cai et al. I lnorganica Chimica Acta 263 {1997) 231-245

Table I Crystal data and structure refinement for 8 and 10

Crystal data Empirical formula Color, habit Crystal size Crystal system Space group a(A) b(A) c (A) (°) ~C o) y (°) Volume (As) Z Formula weight Density (calc.) (Mg m -3) Absorptioncoefficient (mm - a) F(000) Data collection Diffractomoterused Radiation (A) Temperature (°C) 20 Range Scan speed (° rain- ~) Index range Total wflections Independent reflections Solution and refinement System used Solution Refinement method Data/restraints/parameters Weighting scheme Final R indices (!> 2o-(i) )

R indices (all data) Goodness-of-fiton F2 Max. and rain. differencepeaks (e A -s) Absolute structure parameter

Complex 8

Complex 10

C~Hs6CozN2OnP2 reddish-pink, rectangularblock

C33Hs6Cu2N,t Or, green blocks 0A×0.3×0.2 monoelioic P2~ 10.626(2) 12.839(,;) 14.073(3) 90 I04.15(2) 9O 1861.8(8) 2 811.90 1.448 1.204

0.3 x0.2× 0.2 monoelinic

P2Jc 13.4308(2) 9.3747(2) 45.9177(6) 90 97.54( I) 9O 5731.5(2) 4 1220.92 1.415

0.699 2528

856

Siemens SMART/CCD 0.71073 -60 1.78<20<52.36 1.2 in w

Enraf-NoniusCSD-4 0.71069 23 2.98 < 20<48.98 1.2-8.2 in m120

- 16
O ~ h < 12,0
SHELX93 direct n ~ o d s

SHELX93 direct methods full-matrix least-squares on F 2 3443/i/45 ! w-' = orZ(Fo2) + (0.1322P)2, Pffi [maX(Fo2.0)+ 2(FEZ)]/3 RI ffi 0.0fi84 RI =El IFol - IFcl I/~lFol, wR2= 0.1795, where wR2 ffi [Elw( Fo2- Fcz)2]lE[w( Foz)zl p/z RI = 0 0931, wR2=0.1989 i.130, where GOF= [~(w(FoZ-F~Z)z)/(n-p)] ~/2 and n and p denote the numberof data and parameters 0.973 and - 1.536 near C(32)

full-matrix least-squares on F z

11364/01739 w- i ffio.Z(FoZ)+ 36.9562(P), P= [max(F~,0) +2(F~2)]/3 RI ffi 0.0991

RI = E[ IFol - IFJ I/~1Fol, wR2= 0.1940, where wR2= [E[w( Fo2- F¢2)ZllE[w( Fo2)2]]ltz RI = 0.1082, wR2=0.2032 1.280, where GOF= [ Y(w(Foz -FcZ)2)l(n-p)] tj2 and n and p denotethe numberof dam and parameters !.743 and - t.881 near Co(2)

These vapor diffusion set-ups were sealed with plastic caps. Crystal formation was observed in 3--4 days in most cases. Rectangular block crystals were typically obtained for 8 andg. The quality of the crystals for 8 and 9 was not suitable for X-ray analysis by a conventional diffractometer like an EnrafNonius CAD-4. The crystal of 8 was transferred to a Siemens S M A R T / C C D three circle (X fixed at 54.65 °) diffractometer equipped with a cold stream of N2 gas and a graphite-monochromated Mo K a radiation source. Data collection was performed at - 60°C with an X-ray power of 2.2 kW. A total of 1321 frames of two-dimensional diffraction images was collected, each o f which was measured for 10 s. Crystallographic data for 8 are summarized in Table I.

- 0.01 ( 4 )

The raw data frames were processed to produce conventional intensity data by the program SAINT [ 18]. An initial background was determined from the first 12° of data. Integration was performed with constant spot sizes o f 1.75 ° in the detector plane and 0.9 ° in omega. The intensity data were corrected for Lorentz, polarization effects and absorption corrections.

2.12. Solution and refinement o f structure 8 The structure was solved by direct methods and standard difference Fourier techniques. Four independent binuclear cobalt molecules were found in the asymmetric unit cell. All final refinements was completed using SHELXL-93 [ 19].

L Cai et aL/Inorgonica ChimicaActa26311997)231-245

Table2 Atomiccoordinates( × 104) and equivalentisctropi¢displacementpatmw eters (~i.2X 103) for8

Table2 (continued)

Atom

x

Co(1) Co(2) P(100) P(200) O(I) O(11) 0(12) O(13) O(14) O(21) 0(22) 0(23) 0(24) O(31) 0(32) N(II) N(21) C(I) C(2) C(3) C(4) C(5) C(6) C(7) C(I1) C(12) C(13) C(14) C(21) C(22) C(23) C(24) C(31) C(32) C(101) C(102) C(103) C(104) C(I05) C(106) C(107) C(t08) C(109) C(IIO) C(Ill) C(I12) C(113) C(114) C(115) C(116) C(!17) C(118) C(119) C(120) C(121) C(122) C(123) C(124) C(201) C(202)

416(I) 297(I) 6004(I) 7037(i) 375(3) -690(3) -1390(3) 1706(3) 3169(4) -886(5) -1970(4) 1595(5) 2606(4) -67(3) 156(7) 969(4) 445(4) 726(4) 1042(4) 1394(4) 1442(4) 1131(5) 790(4) 1837(6) -707(4) 185(5) 2317(4) 1946(5) - 1212(6) -570(5) 1860(6) 1186(5) - 129(5) -493(7) 5272(5) 4403(5) 3830(5) 4106(6) 4963(7) 5548(6) 5298(4) 5712(5) 5187(6) 4243(6) 3832(5) 4365(5) 6297(4) 5505(5) 5687(6) 6655(6) 7443(5) 7268(5) 7115(4) 7832(5) 8646(5) 8733(5) 8025(5) 7209(5) 6084(4) 5170(5)

C(203) C(204) C(205) C(206) C{207) C(208) C(209) C(210) C(21t) C(212) C(213) C(214) C(215) C(216} C(217) C(218) C(219) C(220) C(221) C(222) C(223) C(224)

y

~4309(1) 1627(I) 7484(2) 691(2) 2302(4) 4856(6) 4656(6) 5293(5) 5423(8) 655(7) - 1171(7) 1042(5) -776(6) 5189(5) 3561(6) 3266(5) -436(5) 1346(6) 1763(6) 753(6) -686(6) -1086(6) -98(6) -1796(7) 4415(7) 3588(7) 4948(8) 3927(7) -472(9) -1076(7) -248(7) -1210(7) 4739(6) 5714(9) 7184(7) 6347(7) 6216(8) 6865(9) 7672(10) 7853(8) 8575(7) 8881(8) 9685(8) 10202(9) 9920(9) 9112(8) 5859(7) 5092(9) 3819(9) 3313(9) 4083(8) 5360(7) 8418(7) 7687(8) 8424(9) 9859(9) 10592(8) 9869(7) 1427(6) 740(8)

Ucq"

945(I) 24(I) i470(I) 47(I) 649(I) 31(I) 2513(I) 29(i) 1070(I) 32(I) 6,14(I) 47(I) 182(I) 50(I) 957(I) 45(1) 791(I) 68(2) 1584(!) 68(2) 1478(I) 72(2) 1688(I) 66(2) 1805(!) 58(1) 1301(I) 36(I) 1647(I) 95(3) 557(I) 27(I) 1251(I) 29(1) 889(1) 25(1) 627(I) 22(1) 447(1) 27(1) 523(!) 27(1) 788(I) 31(1) 973(1) 26(1) 328(I) 43(2) 383(!) 33(1) 307(1) 40(2) 780(1) 38(2) 532(2) 43(2) 1446(2) 48(2) 1221(1) 37(1) 1662(I) 42(2) 1456(I) 35(1) 1553(!) 34(1) 1769(2) 64(2) 297(1) 34(1) 269(2) 40(2) -!(2) 45(2) -240(2) 52(2) -223(2) 66(2) 48(2) 53(2) 868(1) 33(1) 156(1) 42(2) 1331(2) 47(2) 1227(2) 53(2) 943(2) 56(2) 759(2) 44(2) 849(I) 33(I) 937(2) 51(2) 1087(2) 60(2) 1157(2) 55(2) 1072(2) 51(2) 921(2) 41(2) 580(1) 32(!) 443(!) 38(I) 366(I) 45(2) 416(I) 45(2) 549(2) 49(2) 34(2) 39(2) 247(I) 31(I) 185(i) 39(I) (com~nued)

A~om

x

235

y 4416(5) 4602(6) 5516(7) 6254(5) 6692(5) 736~(6) 7135(7) 6225(8) 5571(7) 5801|5) 7193(4) 7212(5) 7405(5) 7587(6) 7549(6) 7355(5) 8195(4) 8750(5) 9630(5) 9923(5) 9353(5) 8480(5)

z 1345(9) 2593(9) 3257(9) 2678(8) 888(7) 449{8) 653(9) 1301(10) 1724(10) 1521(8) -1144(6) -1468(7) -2871(8) -3895(8) -3577(7) -2187(7) 1644(6) 1410(7) 2187(7) 3194(7) 3446(7) 2673(7)

• Ucqis definedas onethirdof the traceof the ~

U~* 1983(2) 1849(2) 1904(2) 2104(2) 2873(1) 3116(I) 3396(2) 3436(2) 3201(2) 2919(2) 2416(!) 2124(2) 2045(2) 2261(2) 2550(2) 2632(2) 500(1) 2271(!) 2264(2) 2475(2) 2697(2) 2708(!)

47(2) 56(2) 66(2) 51(2) 34(1) 45(2) 60(2) 68(3) 62(2) 43(2) 32(1) 38(!) 46(2) .q4(2) 53(2) 42(2) 30(I) 34(!) 42(2) 40(2) 41(2) 37(1)

U~tenor"

Refinement was carried out on F 2 for all reflections except for those with either very negative F or reflections flagged for potential systematic errors, normally for reflections besides strong ones. The relative large R factor (0.0991) may reflect the overall quality of the crystal, as witnessed by the difficulty to collect enough data from conventional X-ray diffractometer. Final non-hydrogen atomic positional and equivalent isotropic thermal parameters, and selected bond distances and angles for 8 are provided in Tables 2 and 3. Final anisotropic temperature factors and hydrogen positional parameters are given in Tables SI-$6, and a cell packing diagram is shown in Fig. S 1, see Section 5. 2.13. Collection and reduction of X-ray data for lO

Diffraction-quality crystals of the copper binuclear complex were obtained by diffusion of acetone into a solution of the compound in CH3CN. Crystals were mounted into a gluss capillary and sealed under N2 to avoid hydration of the crystal. A preliminary diffractometer search revealed moaoclini¢ symmetry. Systematic absences were observed which were consistent with the space group P2~. Diffraction data were collected at 293 K using graphite-mouochromafizedMo K a radiation on a Enraf-Nonins CAD-4 auton~ed diffractongter. Unit cell parameters were obtained by leust-squares refinement of the setting angles of 25 machine-centered reflections. The ~-20 scan technique was used to record intensifies. Peak counts were corrected for b a c k - ~ m d counts, which were obtained by extending the final scan by 25% at each end to yield net intensities, I, which were assigned standard deviations calculated with a conventional p factor of 0.01. Intensities of three standard reflections mow

236

L. Cai et aL / lnorganica Chbnica Acta 263 (19971231-245

Table 3 Selected bond lengths (A) and angles (°) for$ Co(I)-O(13) Co(1)-O(l) Co(I)-N(II) Co(21-O(211 Co{2)-O(321 O(I)-C(I) O(12)-C(11) O(14)-C(131 O(22)-(2"(211 O(241-C(23) O(32)-C(311 N(I1)-C(14) N{211-C(61 N(211-C(221 C(I)-C(6) C(31-C(41 C(41-C(71 C(ll)--C(12) C(21)-C(22) C(311-C(321

1,957(41 1,970(41 2.241(51 1.961(61 2,008(5) 1.346(6) 1.234(71 1.223(8) 1.236(91 1.227(91 1.229(81 1.469(8) 1.448(71 1.480(81 1.407(81 1.394(81 1.515(81 1,507(91 1.536(91 1.480(91

Co(l)-O(ll) Co(I)-O(31) Co(2)-O(I) Co(21-O{23) Co(2)-N(211 O(ll)-C(ll) O(131-C(131 O(211-C(21) O(231-C(23) O(311-C(31) N(tl)-C(2) N(ll)-C(12) N(211-C(241 C(11-C(21 C(2)-C(31 C(4)-C(5) C(5)-C(6) C(131--C(141 C(23)-~C(241

1,958(41 2.017(41 1,958(41 1,972(61 2,200(5) 1.265(71 1.268(81 1.280(10) 1.270(91 1.240(71 i.446(7) 1.484(7) 1.470(71 1.384(71 1,382(81 !.389(81 1.375(81 1.521(91 1,518(9)

O(13)-Co(I)-O(11) O(ll).-Co(l)-O(l) O(tl)-Co(11-O(31) O(13)-Co(I)-N(II) O(I)-Co(I)-N(II) O(1)-Co(2)-O(21) O(211~2o(21-O(23) O(211-Co(2).-O(321 O(1)-Co(21-N(21) O(23)-Co(21-N(21) C(I)-O(I)-Co(21 Co(2)-O(11-Co(I) C(13)-O(t3)-Co(1) C(231-O(231-Co(21 C(311--O(321-Co(21 C(2)-N(111-C(121 C(2)-N(II)--Co(1) C(12)-N(II)--Co(I) C(61-N(211-C(221 C(61-N(21)-Co(2) C(221-N(21)-Co(2) O(11-C(1)-C(6) C(31-C(21-C(I) C(I)-C(2)-N(II) C(51-C(41--C(3) C(3)-C(41--C(7) C(5)-C(61-C(11 C(I)-C(6)-N(2I) O(121-C(il)-C(12) N(II)-C(12)-C(il) O(14)-C(13).-C(141 N(11)-C(14)--C(13) O(22)-C(211-C(221 N(21)-C(22)-C(211 O(241-C(231-C(24} N(211-C(24)-C(23) O(321-C(31)-C(32)

118.9(21 114.1(21 99.8(2) 81.0(21 80.8(2) 123.0(21 115.4(31 100.8(31 80.6(2) 82.0(2) !15.4(31 126.1(21 120.4(41 I17.2(5) 135.1(51 113,0(51 105.5(31 104.5(31 113,8(4) 105.6(31 105.2(41 119.0(51 119.8(51 II6.8(51 118.2(5) 121.5(51 119.5(5) 115.9(51 117.0(6) !15.4(51 118.1(61 !14.6(51 !15.3(81 112.3(61 118,1(61 113.8{51 115.5(61

O(131-Co(I)-O(I) O(13)-Co(I)-O(311 O(I)~o(I)-O(31) O(l])-Co(I)-N(ll) O(3])-Co(l)-N(ll) O(11-Co(2)-O(23) O(I)-Co(2)-O(32) O(23)-Co(21-O(32) O(21)-Co(2)-N(21) O(32FCo(2)-N(21) C(I)-O(I)-Co(I) C(II)-O(i])--Co(I) C(21)-O(21).-Co(2) C(31)-O(31)-Co(I) C(2)-N(ll)-C(14) C(14)-N(il)-C(12) C(14)-N(II)-Co(I) C(61-N(21)-C(24) C(241-N(211-C(22) C(241-N(21)-Co(2) O(I)-C(I)~7(2) C(21-C(I)-C(6) C(3)-C(2)-N(II) C(2)-C(31--C(4) C(5)-C(41-C(7) C(61-C(51--C(4) C(51-C(61-N(21 ) O( 121-C( 11)--O( I I ) O(111-C(111-C(t2) O(141-C(13)-O(131 O(131-C(13)-C(14) O(22)-C(21)-O(21) O(211-C(211--C(221 O(24)-C(23)-O(231 O(231-C(23)-C(24) O(32)-C(311-O(31) O(311-C(31)--C(32)

120,1(21 99,3(2) 97.4(2) 81,6(2) [78.1(2) i14.5(2) 96.3(2) 99.7(3) 80,7(2) 176.8(21 115.5(31 120.0(41 119.2(51 133.2(41 113,2(5) 113.9(5) 105.6(41 113.9(51 113.4(51 103.7(31 121.3(5) 119.7(51 123.5(5) 121.3(51 120.2(51 121,5(5) 124.6(51 124.7(61 118.2(51 124.2(7) 117.6(51 127.8(81 116.8(61 123.6(71 118.2(61 125,4(6) !18.9(6)

itored every 97 reflections indicated no significant decay during the data collections. Corrections for Lorentz and polarization effects were applied. The absorption effect was checked by empirical 'psi'-sean methods, but was so insig-

nificant that correction was excluded. Assignment of space groups from statistics and systematic absences was confirmed by successful solutions and refinements of the structure. Crystallographic data for 10 are summarized in Table 1.

L Cai et al./inorganica ChimicaActa 263 (1997}231-245

Table4 Atomiccoordinates ( × 104) and equivalentisotropicdisplacementparameters (A-'X I03) for l0 Atom Cu(l) Cu(2) N(II) N(21) O(1) O(ll) O(12) O(13) O(14) O(21) 0(22) 0(23) 0(24) O(31) 0(32) C(I) C(2) C(3) C(4) C(5) C(6) C(7) C(II) C(12) C(13) C(14) C(21) C(22) C(23) C(24) C(31) C(32) N(100) N(200) C(101) C(102) C(103) C(104) C(105) C(106) C(107) C(108) C(201) C(202) C(203) C(204) C(205) C(206) C(207) C(208)

x

y 5703(I) 5844(I) 5188(8) 5246(7) 5195(8) 6912(8) 7931(10) 3909(11) 2206(11) 7616(7) 8613(9) 4548(10) 2754(12) 6355(9) 6432(10) 5145(9) 5096(9) 4950(11) 4865(14) 4992(11) 5115(10) 4678(23) 7103(12) 6234(13) 3294(14) 3884(15) 7645(11) 6317(11) 3743(15) 3990(11) 6560(11) 6958(15) 827(8) 9772(9) 204(14) 145(17) 89(13) - 1360(17) 865(12) 1526(19) 2175{11) 3083(14) 8882(39) 8966(21) 8910(49) 8551(74) 10694(59) 10226(41) 10421(58) 11377(55)

z

5974(I) 3952(I) 5921(I) 1458(I) 4509(7) 4347(5) 4461(7) 920(6) 5452(6) 2635(5) 5943(9) 523515) 4854(9) 6371(8) 6416(9) 4268(7) 5642(12) 4615(13) 5301(7) 1591(6) 4080(9) 939(7) 6439(7) 304(6) 5884(13) -786(9) 7289(6) 3553(6) 7275(7) 1968(7) 4418(8) 2625(7) 3867(7) 3476(6) 2781(8) 3445(8) 2247(8) 2577(9) 2788(8) 1747(8) 3854(8) 1781(7) 1084(11) 2527(11) 5057(10) 5667(8) 4182(!0) 5187(8} 5653(12) 4508(10) 4593(11) 4596(13) 4523(10) 1063(8) 4104(9) 490(7) 5726(13) - 134(9) 4598(11) 195(8) 7690(8) 2805(10) 8815(10) 2830(10) 7476(8) 1299(6) 2825(8) 3753(7) 8317(13) 1728(1t) 9376(13) 1167(12) 7220(11) 252(8) 6984(18) 138(15) 6541(12) 1982(10) 5577(12) 1723(12) 7747(11) 1221(9) 8056(14) 2187(!1) 3645(26) 3635(23) 4685(15) 3905(16) 1978(38) 3282(33) 1260(50) 3010(46) 3171(50) 3065(36) 2821(30) 5586(15) 2772(23) 4813(14) 2483(26) 3029(46)

U,.qa 41(I) 48(I) 39(2) 39(2) 47(2) 69(2) 88(3) 79(3) 140(6) 58(2) 76(3) 69(2) 118(4) 59(2) 68(2) 37(2) 35{2) 48(2) 59(3) 49(3) 39(2) 98(5) 54(3) 59(3) 68(4) 78(4) 51(3) 48(2) 75(5) 56(31 54(3) 68(3) 50(2) 53(2) 73(41 91(5) 64(3) 133(10) 68(4) 91(5) 59(3) 83(4) 199(18) 106(6) 340(42) 514(75) 389(54) 212(20) 339(40) 363(51)

u,~ is definedas one third of the traceof the orthogonalizedU,jtensor. 2.14. Solution and refinement of structures for 10

A three-dimensional Patterson synthesis was used to locate the copper positions, and a series of difference Fourier maps revealed the remaining non-hydrogen atorrs. Atomic scattering factors for the non-hydrogen ato~.~ were taken from International Tables for X-ray Crystallography [ 20] and those for

237

hydrogen atoms from Stewart et al. [ 21 ]. The final refinement were completed using SHELXL-93 [19]. Refinement was carried out on F 2 for all reflections except for those with either very negative F or reflections flagged for potential systematic errors. All non-hydrogen atoms except for one of the tetraethylammonium cations were refined anisotropically initially, Calculated, idealized hydrogen atom positions were included in the structure factor calculations. When convergence of the atomic positions was reached, the atoms of the remaining tetraethylammonium cation were given anisotropic thermal parameters and were added to the refinement. Care was taken to give the correct connectivity within the cation. Finally, calculated and ;.dcal;,zedhydrogen atom positions of the tetraethyl cation were added to the refinement. Three of the ethyl group of the tetraethylammonium cation gave imaginary thermal parameters in only one dimension and could not be fit with any reasonable disordered model. A final difference Fourier map revealed residue electron density near the methyl group of the bridging acetate. The final unweighted R factor was 0.0683. Large thermal motion in one of the tetraethylammonium groups apparently resulted in the high R factor. Final positional parameters for 10 are given in Table 4, and distances and angles within the coordination sphere of copper are tabulated in Table 5. Structure factors, thermal parameters, hydrogen atom positions, and ligand and cation distances and angles are included in Tables $ 7 SII, and a cell packing diagram is shown in Fig. $2, see Section 5.

2.15. Magnetic measurements

Magnetic susceptibility data were recorded with a Quantum Design MPMS-5S SQUID susceptometer. Measurement and calibration techniques have been reported elsewhere [22]. Magnetic data were recorded over the indicated temperature range at a magnetic field setting of I000 G on polycrystalline samples weighing 5-20 mg. The magnetic susceptibility, corrected for diamagnetism by using Pascal's constants, is listed in Tables S12-S 13, see Section 5.

2.16. Electrochemical measurements

Electrochemical measurements were performed under a dinitrogen atmosphere with use of an EG&G model 283 potentiostat. For cyclic voltammetry experiments, 1-10 mM solutions containing 0. l M Bu~NPF6 supporting electrolyte and a Pt micro disc working electrode were used. Potenfial~ were determined versus an AgCI/NaC! reference electrode. The stability of the reference electrode was checked by performing the same experiment with added Cp2_Ft;+PF6( E°l p. = 0.454 V).

238

L Cai et al. / lnorganica Chimica Acta 263 (1997) 231-245

Table 5 Selected bond lengths (A) and angles (°) for 10 Cu(l)-O(l) CB(I)~O(3t) Cu(l)--O(13) Cu(2)--O(23) Cu(2)--O(i) N(I1)--C(2) N(II)--C(14) N(21)--C(24) O(I)-C(I) O(12)-(:(!1) O(14)-C(13) O(22)--C(21) O(24)-C(23) O(32)-,-C(31) C(!)--C(2) C(3)-C(4) C(4)-C(7) C(!!)--C(12) C(21)--C(22) C(31)-C(32)

1.920(7) 1.959(8) 2.138(9) 1.970(9) 2.034(7) !.460(12) 1.51(2) 1.479(13) 1.328(13) 1.183(14) 1.20(2) !.224(14) 1.23(2) !.269(14) 1,403(13) 1.38(2) 1.51(2) !.51(2) 1.54(2) 1.50(2)

Cu(I)-O(ll) Cu(I)-N(II) Cu(2)--O(32) Cu(2)-O(21) Cu(2)-N(21) N(II)-C(12) N(21)--C(6) N(21)--C(22) O(II)--C(II) O(13)-C(13) O(21)-42(21) O(23)-C(23) O(31)-C(31) C(i)-C(6) C(2)--C(3) C(4)-C(5) C(5)-C(6) C(13)-C(14) C(23)--C(24)

1.943(7) 2.072(9) 1.925(9) 2.011(8) 2.063( 8) 1.473(14) 1.476(12) 1.487t13) 1.28(2) 1.27(2) 1.249(14) 1.30(2) 1.239(14) 1.385(13) 1.403(14) 1.39(2) 1.37(2) 1.49(2) 1.52(2)

O(1)-Cu(1)-O(ll) O(ll)-.Cu(l)-O(31) O(ll).-.Cu(I)-N(ll) O(l)-Cu(I)-O(13) O(31)-Cu(I)-O(13) G(32)--Cu(2)--O(23) O(23)-Cu(2)-O(21) O(23)--Cu(2)--O(I) O(32)--Cu(2)-N(21) O(21)-Cu(2)-N(21) C(2)-N(II)-C(12) C(12)-N(II)--C(14) C(12)-N(II)--Cu(1) C(6)-N(21)-C(24) C(24)-N{21)--C(22) C(24)-N(21)--Cu(2) C(1)-O(1)-Cu(1) Cu(1)-O(1)--Cu(2) C(13)-O(13),,.Cu(I) C(23)-O(23)-Cu(2) C(31)-O(32)-Cu(2) O(I)--C(1)-C(2) C(3)--C(2)--C(I) C(I)-C(2)-N(II) C(3)-C(4)-C(5) C(5)-C(4)-C(7) C(5)--C(6)-C(I) C(I)--C(6)-N(21) O(12)-C(11)-C(12) N(II)-C(12)-C(ll) O(14)--C(13)-C(14) C(13)--C(14)-N(il) O(22)-C(21)--C(22) N(21)-C(22)--C(21) O(24)-C(23)-C(24) N(21)--C(24)-C(23) O(31)-C(31)--C(32)

148.8(4) 94.8(4) 83.7(4) 103.8(4) 103,1(4) 95.8(4) 131.3(4) 117.6(4) 179.0(4) 82.6(3) I13.3(9) 112,8(10) 106.1(6) 112.3(8) 114.0(8) I06.9(7) 111.1(6) 127.7(4) 113.2(8) 113,6(9) 132.6(8) 120,3(8) 120,1(9) 115,0(8) 119.6(9) 119.6(11) 122.2(9) 116.1(8) 117.4(!1) 114.0(10) 112(2) 115.8(1t) 117.1(10) 111.9(8) 116(2) I12.4(I0) I19.1111)

O(1)--Cu(1)--O(31) O(I)-Cu(i)-N(II) O(31)--Cu(I)-N(II) O(ll)--Cu(l)-O(13) N(II)-Cu(I)-O(13) O(32)-Cu(2)--O(21) O(32)-Cu(2)-O(I) O(21)-Cu(2)--O(I) O(23)--Cu(2)-N(21) O(1)--Cu(2)-N(21) C(2)-N(II)--C(14) C(2)-N(II)--Cu(1) C(14)-N(II)-Cu(1) C(6)-N(21)--C(22) C(6)-N(21)--Cu(2) C(22)-N(21)-Cu(2) C(1)--O(1)-Cu(2) C(II)--O(II)--Cu(1) C(21)-0(21)-Cu(2) C(31)-O(31)-Cu(I) O(I)-C(1)-C(6) C(6)--C(I)-C(2) C(3)-C(2)-N(il) C(4)-C(3)-C(2) C(3)-C(4)-.C(7) C(6)-..C(5)-.C(4) C(5)--C(6)-N(21) 0(12)-C(11)-0(11) O(11)-C(11)-C(12) O(14)-C(13)-,,O(13) O(13)-C(13)--C(14) O(22)-C(21)-O(21) O(21)--C(21)--C(22) O(24)--C(23)-O(23) O(23)--C(23)-C(24) O(31)-C(31)--O(32) O(32)-C(31)-C(32)

93,4(3) 84.9(3) 173.9(3) 103.5(4) 83,0(4) 96.4(4) 96.2(3) 107,6(3) 85.0(4) 83.9(3) 110.9(9) I04.8(5) 108.3(7) 114.0(8) I05.2(6) 103.4(6) I07.9(6) 116.8(8) 114.8(7) 138.6(7) 121.6(9) 118.0(9) 124.9(9) 120.2(9) 120.7(11) 119.7(10) 121.7(9) 126.3(11) !16.2(10) 128.0(14) !!9.6(tl) 126.8(11) !16.0(9) 126(2) 1t8,7(12) 127,8(10) 113.1(11)

,.

L

Cal et aL IlnorganicaChimicaActa263 (1997)231-245

3. Results and discussion

distances and angles in the coordination sphere are presented in Table 3. The su'ucture of the anion is shown in Fig. 1. Another view to show the planarity of the benzene ring and its immediate surroundings is given in Fig. $3 (see Section 5). The thermal parameters for the acetate oxygen 0(32) on one of the dimensions are quite large (0.2291, 0.0324, 0.0232). This may explain the relatively large R1 (0.0991) value during the final refinement. Both cobalt atoms adopt a five-coordinate trigonal bipyramidal structure, each provided by the two carboxylic oxygens, one nitrogen, one bridging phenolate oxygen and the bridging acetate group. The coordination geomeb'y around the cobalt ions is almost identical, with each cobalt atom lying above the plane formed by the equatorial oxygen atoms toward the bridging acetate group by 0.30 + 0.01 .~. The bond angles around each cobalt above the equatorial plane ate uniformly greater than 90° (av. 99+4°), while the bond angles below the equatorial plane are uniformly smaller than 90° (av. 81 + i o). The bond angles between the axial bonds are very close to linear, 177 and 178°, respectively. Althongh the cobalt ions are not on the equatorial planes, the bond angles among the equatorial bonds are close to 12tY,on average 118 + 5°. The bond angles for the five oxygen atoms of the heptadentate ligand are about 120=1:6o, consistent with sp2 hybridization. This hybridization for the phenolate oxygen is quite interesting, with the lone pair on the p= mbital either conjugating with the benzene ring or overlapping with the partially filled d orbitals from Co(H). This may have significance in the observed magnetochemistryof these compounds (vide infra). The lone pairs from the two nitrogen atoms switch from conjugation with the benzene ring to coordinating with Co atoms. However, the sp2 hybridization of the oxygen atoms and the five.membered rings f~mxi around each Co atom force the adoption of a trigonal bipyr-

3.1. Ligand synthesis

The ligand was synthesized as shown in Scheme I. Reduction of the dinitro substrate 1 with SnC!2. 2H20 in concentrated HC! at 100°C for 2 h or Pal/C/H= in CH3OH at room temperature overnight gave the corresponding diamino compound 2 ( ~ 100% yield by =H HMR). The compound is stable in the solid state, but is sensitive to air in solution, owing to the conjugation of the two amino and one hydroxy group with the benzene ring. Subsequent reaction with BrCH2COOH in H20 and CH3OH ( 1:1) at reflux overnight gave amino acid crude ligand 3, which was precipitated by NaOCH 3 in CH3OH to get rid of excess BrCH=COONa. Excess NaOCH3 was washed out by ethanol to give pure ligand 3 ( > 60% yield), which can be used directly in the synthesis of metal complexes. If a purified synthetic intermediate is required, treatment of 3 with HCI or Ac20 at room temperature gives lactone 4 (40% yield after silica-gel column). Both 3 and 4 react with strong bases (NaOCH3 or NaOH) to give the penta-anion 5 (essentially quantitative yield), The relative ease of formation and hydrolysis of the ester group in 4 may indicate the auxiliary participation of the phenolate group during the processes. However. the lactone is air stable, which makes the purification and handling easier. 3.2. Structure of dinuclear complexes 3.2.1. Di-cobalt complex The dinuclear complexes were synthesized az shown in Scheme 2. Complex 8 crystallizes from acetonitrile--ether as reddish rectangular blocks. Crystal data are given in Table 1, final parameters are listed in Table 2, and significant bond

o OH

OH I-~1~1~

C~

1

C~ 3

2

:Oo °

ONa NaO O

8r~. zCOC3~ O ~ [ ~ ~ ~

02N~ NOt SnCl=.orp(lf.~.t~_ CH~

239

o%O

Q o..o

y CH3 6

Cl~

r-~3

4

S

SchemeI. Syntheticroutesforthe ligand.

~O

240

L. Cai et al. I lnorganica Chimica Acta 263 (1997) 231-245

O~ONa

NaOvO

-0

o o., o.:Of ~N~jN

0

O~ 0 O

0

Co(OAc)z

CH3

CH3 5

P = Na, 7 P = Ph4P.8 P : Et4N,9

Om~...,.~O"(Et4N)s "0....~.0 o~....0

"o~ T-,O

LL. j

(EI4N)2 M(OAc)2

e~a

OH3

L

M=Cu, 10 M=Co. 9

6

Scheme :2. Synthesisoftransition metal complexes.

~ C 31~

o 3 ~ ~ o~

ring with its immediate substitutent atoms (C(7), O(1), N( 11 ), N(21 ) ) consists era plane with 0.015 A r.m,s, deviation. The cobalt atoms are 0.103 and 0.444 A above the plane as defined by the benzene ring. The separation between the two cobalt atoms is 3.505(5)/~, larger than 3.1-3.2/~ in ligand systems consisting of a benzylamine (rather than a phenylamine) [t6a]. The two Co-O bonds (2.01(2) and 2.04(2) A) to the acetate are tilted toward each other, giving an O...O internuclear distance of 2.195 A (a value suitable for the coordination of O2, in favorable cases splitting 02 into two metal oxo groups, but unlikely for 02- or OH- ). Given the strong tendency for cobalt to form octahedral coordination spheres, the present five-coordinate binuclear cobalt complex is unique.

3.2.2. Di-copper complex

~cT Fig. i. Molecularstructure of compound8 with atomic numbering(ORTEP, 50% probabilityellipsoids, hydrogen atoms omitted for clarity).

amidal geometry, with a long Co-N bond ( ~2.2 ,~) compared with an average of 1.9 to 2.0 A in related binuclear cobalt systems [7c,16a,23]. The Co-O distances to nonbridging carboxylate arc shorter than those of the bridging acetate bonds, while the bridging Co-phenolat¢ bonds have intermediate values. Overall, those Co-O bonds are on the longer side of the average bond length in related systems [ 23b--e]. The bond angles around the nitrogen atoms involving the Co-N vector are around 105 + 1°, slightly tess than that of an idealized tetrahedron geometry for a nitrogen atom. The bond angles ,around the bridging carboxylate oxygen atom are 135 + I °, larger than that of an idealized sp2hybridization. This may relate to the difference in lability between the bridging and non-bridging carboxylates. The aromatic

Complex 10 crystallizes from acetonitrile/acetoneas green rectangular blocks. Crystal data are given in Table !, final parameters are listed in Table 4, and significant bond distances and angles in the coordination sphere are collected in Table 5. The structure of the anion is shown in Fig. 2. Another view to show the planarity of the benzene ring and its immediate surroundings is given in Fig. $4 (see Section 5), The thermal parameters for the methyl group on the aromatic ring and one of the tetraethylammonium cations are large. These may explain the relatively large RI value during the final refinement, Both copper atoms adopt a five-coordinate distorted trigonal bipyramidal structure, each provided by the two carboxylic oxygens, one nitrogen, one bridging phenolate oxygen and the bridging acetate group. Consistent with a trigonal bipyramidal configuration, the bond angles of the axial bonds, O(31)-Cu(I)-N(ll) and O(32)--Cu(2)N(21 ), are close to 180°, being 174 and 179°, respectively. The copper( I ) site deviates more from an idealized trigonal

L Cai et a l./lnorganica Chimica Acre 263 (1997) 231-245

o31

~

o

,

1

01S

geometry of the copper complex closely matches those of the cobalt complex described above. The aromatic ring with its immediate substitutent atoms (C(7), O( I ), N( ! ; ), N(21 ) ) consists of a plane with 0.045 A r.m.s deviation. The copper atoms are 0.371 and 0.475 ~, below the plane as defined by the benzene ring. Of the numerous binuclear copper complexes synthesized [24 ), only two other complexes have trigonal bipyramidal coordinated copper centers [7d,10f]. Only one of the compounds ([Cu2(L-Et) (OAt) ] [CIO412 (11), where HL-Et is the heptadentate binueleating iigand N,N,N',N'-tetrakis(2(1-ethylbenzimidazolyl))-2-hydroxy-l,3-diaminopropane)), resembles I0, involving alkoxide and acetate groups as bridges. Interestingly, both complexes possess only multiple five-membered chelate rings. The separation between the two copper atoms is 3.550 A,, comparable with that of the dicobalt complex described above (3.505 A), larger than that (,-, 3.0 A) in iigand systems consisting of a ben~lamine (rather than a phenylamine) [16a]. The two Cu---O bonds ( 1.959 and 1.925 ,~,) of the Cu to the acetate are tilted toward each other, giving an O-..O internuclear distance of 2.252 A, a value closely matching that of the di-eobalt complex. This supports ;he idea that the ligand, not the metal, controls the internuclear distances for the two complexes reported here.

2

023

0~4

0tt 0t**

0t') C12

022

Fig. 2. Molecular structure of compound 10 with atomic numbering (ORTEP, 50% probability ellipsoids, hydrogen atoms omitted for clarity).

bipyramidal configuration than the copper(2) site. On average, bond angles around Cu( I ) above the equatorial plane are 97+6 °, spanning a 10° range from 93 to 103°. Similar bond angles around Cu (2) give 96 + !° on average. However, bond angles below the equatorial plane are more convergent, an average of 84 + 1° at both sites. Among the bonds within the equatorial plane, the bond angles vary more dramatically, 126+13 o for the Cu(I) site ranging from 104 to 149°, ! 19-1-12° for the Cu(2) site ranging from 108 to 131°. This may reflect the tendency for copper to adopt a square pyram,idal configuration. The copper atoms lie 0.204 and 0.213 A above the equatorial plane for Cu(1) and Cu(2), respectively, toward the bridging acetate group. Overall, the other

.-. 2O01 150

24t

3.3. UV-Vis and IR studies of dinuclear complexes

The UV-Vis spectra for complexes 9 and 10 are presented in Fig. 3. Both complexes exhibit a medium phenolate --*metal (II) charge-transfer (CT) transition near 300 nm ( e = 4900 M - tcm - t for 9 and 2900 M - t era- t for lO) and much weaker d--d transitions at lower energy (9, hm~=551 am, e=423 M -x cm-t; 10, ~,,,~=861 am, e=125 M -t cm-'). Both complexes present interesting cases in which they have no CT features associated with the carboxylate ion; therefore, the phenolate CT band should be observed. However, previously reported five-coordinate p.-phenolato---cop-

,

,

,.-

0

v-X

0

500

600

7(10

8~

900

1000

Wavelength(rim) Fig. 3. Electronic spectra of 9 and l0 in acelonitrile solution. The insets show an expanded visible region of the spectra for 9 and 10.

L Caiet al. / lnorganicaChimicaActa263 (1997)231-245

242

~ let

CH2

CH2

120-

CI

I00.

CH2 CH2

40.

ii

80.

o

~

20- ~

OeOCH3

40,

CH

20

CH3

CH3

CH 0-

=

=

:-

. . . .

OCOCH3

,,

3.2

315

3~8

410

3.3

4.2

1iT x !o~ (K) Fig. 4. Temperature dependenciesof the isotropic shift~ of 8 in CD3CN solutim~at 240-300 K.

(1)

3.5. Magnetic properties of dinuclear complexes 3.5.1. Di-cobalt complex As shown in Fig. 6 (the experimental data are listed in Table S12, see Section 5), at low temperatures, the magnetic susceptibility exhibits a broad maximum consistent with short The signs of the contact shifts followfromthe relationshipA,=Opec where A, is ;he electron-nuclearcoupling constant of nuclei i, p"C is the spin densityin a Cp~"orbital, and Q-- QcH(negative) or Qcuo(postitve)-

319

411

4.3

0.06 0.05

0.04 o

0.03 II '~ 0,02

3.4. IH NMR studies of dinuclear complexes

(AH/Ho)~,= - [2~rAilh~/al [gl~uS(2S+ 1)/3kTl

317

I/Tx 103 (K) Fig. 5, Temperature dependenciesof the isotropicshifts of 10 in CD3CN solution at 240--300K,

per(II) dimers generally show a strong transition at lower energy (360-390 rim, 6 = 103 M -t cm -t) associated with the phenolate CT transition [25 ]. Moreover, Sorrell et al. [26] reported bands at 446 nm with an extinction coefficient of only 122 M - ~cm- ~.This is so far the highest energy band reported for the phenolate oxygen to metal CT transition.

Both complexes 8 and 10 show paramagnetic chemical shifts at room temperature. Differences in chemical shifts for Hint and Hcxo for both 8 (12.4 ppm) and 10 (12.0 ppm) support anisotropic contributions to the isotropic shifts (see Section 2). Neverthetheless, the temperature dependences of the isotropic shifts, displayed in Figs. 4 and 5, exhibit the I IT behavior of Eq. ( i ) for contact shifts of a Curie paramagnet with spin S; other symbols have their usual meanings t [27].

315

0.0l 0.00

~o

,oo lso 200 2~0 30o Temperature OK) Fig. 6. Plotof the correctedmolar magneticsusceptibility(in emu tool- ' ) for8 as a functionof temperature ( in K). The solidlinerepresentsthe result of the least-squaresfittingof the parameters of Eqs. (2) and (3) with the data. range antiferromagnetic coupling. The magnetic data were analyzc,J in the vicinity of the maximum using a model that assumes coupling of two S = 3/2 cobalt(II) centers. The isotropic coupling of these two centers gives the magnetic susceptibility equation (2). The magnetic data also required

X=

kT x

exp(2J/kT) + 5 exp(6J/kT) + 14 exp(IZI/kT) 1 +3 exp(2J/kT) + 5 exp(gJ/kT) + 7 exp( 12JIk~ (2)

L Cai et al. Ilnorganica ChimicaActa263 f1997)231-245

correction using the molecular field approximation due to secondary interactions, either from interdimer coupling, or from zero field splitting of the S = 3/2 multiplet. The secondary interactions were treated using the molecular field approximation as shown in Eq. (3), where X' is the magnetic susX' X

(3)

1 ~¢g2~ ceptibility of the material in the absence of the exchange field (Eq. (2)) and X is the molecular exchange field influenced magnetic susceptibility that is actually measured. The exchange field coupling parameter is zY, where z is the number of exchange coupled neighbors. The addition of the molecular field exchange correction resulted in a substantial improvement of the fit to the data. The magnetic susceptibility data of 8 were fit to Eq. (2) corrected by Eq. (3) and gave the following parameters g=2.00, J / k = -7.8 K (J=5.4 cm- ~), z J ' l k = - 2 . 4 4 K (J' = 1.69 cm-I), TIP (temperature independent paramagnetism) = 0.01. As a comparison, the molar magnetic susceptibility measured by Evan's method with the HMR measurements in CD3CN at room temperature (23°C) was 1.3 x 10 -2 versus 2.0X 10 -2 for the polycrystalline sample from a SQUID susceptometer. The temperature dependence of the isotropic shift of 8 is a!so consistent with the behavior of the magnetic susceptibility in the same temperature range. We believe that the coordination geometry of the ligand system offers the most logical explanation for the magnetic behavior. The argument rests on the notion that a strong magnetic interaction requires both good or orientation of the magnetic orbitals and good superexchange properties of the bridging atom(s) [28]. Neither condition is very well satisfied in the acetate complex. The trigonal bipyramidal stereochemistry dictates a (d,,y)I (d~, _,~) J(do) I ground state for a high-spin cobalt(It) center. The major lobes of the magnetic orbital (dz2) nwill be axially directed toward a single bridging ligand, the acetate (see Fig. 7). Only one lobe of (d~_~) 1 or (d,~) ! will point to the bridging phenolate oxygen atom, but not both orbitals. Of the bridging ligands found in this complex, phenolate is likely to be the best mediator of superexchange. With the large Co-O-Co angles in the present complex (near 127°) a strong antiferromagnetic superexchange can be expected by analogy m the/x-water dimers having similar Co--O-Co angles [29]. But ouly (d:_y2) t has the directionality of the magnetic orbitals appropriate for taking advantage of magr, etic exchange via the phenolate O

243

atom. There is no evidence that a single acetate group can function as a strong mediator of magnetic exchange. 3.5.2. Di-copper complex

A plot of X~a'~Tversus temperature for the solid di-copper complex is presented in Fig. 8. The X~" versus temperature plot is given in Fig. $5 and experimental data in Table S!3, see Section 5. The magnetic susceptibility of two interacting copper(H) ions may be described by Eq. (4) where 2,/is the X

Ng2p2 2 exp(2J/kT) kT 1 +3 exp(2J/kT)

(4)

separation of the singlet and triplet energy levels; a positive J value denotes a ground-state triplet. The line drown through the points in Fig. 8 is obtained by using Eq. (4) for the primary interaction and Eq. (3) for the secondary interactions treated by molecular field approximation and a temperatureindependent paramagnetism (TIP) of 0.0033 emu reel- t for the two copper(H) ions.To obtain thiscm've, the value ofg was not varied,while the restok'theparameters were allowed to change. The resultingvalues arc g = 2.I0, 2,11k= 20.58 K, z,r/k = - 0.345 K and TIP= 0.0030 emu reel- n. Structurally,compound I0 is similar to the/L-alkoxy-/~acetate copper dimer prepared by Reed and co-workers [ 10t']. That complex is reported to be ferromagneticallycow pied with J about + 12 cm- 1 although no detailed treatment has appeared. The alkoxy bridge was deemed to be the Wimary superexchange facilitator. The crystal structure for 10 suggests that the phenolate oxygen provides the likely pathway for coupling in this case since each copper is apparently trigonal bipyramidal and overlap with the d : _ .~ or d,~,orbital on each could allow a triplet ground state as shown in Fig. 7. However, the acetate group itself is able to promote anfiferromagnetic coupling bet may not contribute significantly in this case [30]. Obviously, the observed ferromagnetic interacdon suggests the localization o f an unpaired electron in the d~_~ or d~ orbital.Interestingly,of the two ferromagnefically coupled copper dime.r compounds observed, both involve Irigonalbipyramidal configurationsfor copper.

i.8 1.6 ~o 1.4 I

!.2 1.0 0.8

0

50

I~

150 200

250

300

T ~ Fig. 7. Schematicrepresentationof the orbitalorientationsin complexesS and 19 perpendicularto or alongthe benzeneplane.

Fig. 8. PI~ of the conected molar magneticsusceptibility ( in ema tnol-u ) for 10as a function of temperatme (in K). The solid line tepegsontsthe result of the least-sques fitting of the panuuetetsof Eqs. (4) aml (3) with the data.

244

L. Cai et ai./ lnorganica Chimiea Acta 263 (1997) 231-245

3.6. Electrochemical studies o f dinuclear complexes 3.6.I. Di-cobalt complex

Only an irreversible oxidation at 1.244 V is available for the dimer within the + 1.6 V range. This corresponds only to a moderate decrease in oxidation potential relative to C o ( H 2 0 ) ~ +, consistent with no observed reaction between this dimer and 02 or air. 3.6.2. Di-copper complex

One irreversible oxidation is observed with a minimum at 0.832 V, suggesting the ligand is not resistant toward oxidation by the resulting Cu 3 ÷ site. Irreversible reduction of the dimer only begins at - 1.209 V, a dramatic reduction in oxidativc power of Cu z *, compared with the aqueous Cu 2 ÷ at 0.13 V. Reduction of the Cu 2 + site probably initiates the departure of the bridging acetate, and the resulting complex is picked up by three oxidation peaks at - 0 . 3 6 3 , - 0 . 1 9 3 and 0.039 V, with none o f them stable enough within the time scale of the CV. The peak at - 0 . I 9 3 V corresponds to a multiple electron oxidation, which may be the degradation of the ]igand after departure of the metal. A cyclic voltammogram is shown in Fig. $6 (see Section 5).

4. Conclusions The rigidity of the structure and the separation of the two metal ions in this new ligand system may eventually allow for the activation of =-.roll molecules, like O2, and avoids the thermodynamic trap of a / z - O or t~-OH bridge which serves to block the coordination sites of the two metal centers 2 Evaluation of the reactivity and catalytic properties of 8-10 is in progress.

5. S u p p l e m e n t a r y m a t e r i a l Tables of atom coordinates, anisotropie thermal parameters, bond lengths, bond angle~, least-square planes, unit cell and packing diagrams, different orientations of the ORTEP diagrams, structure factor tables for 8 and 10, a different presentation of x~'r~T versus temperature, and a cyclic voltammogram of 10 (total 103 pages) are available from author L.C.

Acknowledgements We are grateful to Mr Brent Segal and Ms Christian Goddard at Harvard University for assistance with the X-ray structure determination, to Professor George Gould at UIC for 2The exact reason for th¢ cobalt to adopt the five coordination is unknown, considering the complex was synthesized from CH3OH and CH ~CN.both of coordinating solvems.

comments and suggestions, and to Drs Ulrich Welp and Vitali Methoshko at Argonne National Laboratory for experimental assistance. We also thank the Petroleum Research Fund, administered by American Chemical Society, and the University of Illinois at Chicago for financial support.

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