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Modeling of the Chemistry of the Active Site of Galactose Oxidase.

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isolated species and the widened angle (148 ) that has been
experimentally found.[221
The energy of the molecular Irr, level
(compared to E F )is extremely sensitive to the size of the C-B-C
angle. thus stressing the importance of the bending vibration for
the appearance of superconductivity.
Superconducting boride carbides such as Y B,C, with
T, = 3.6 Klz4I and La,B,C, with T, = 6.9 K r z s 1have been
known for a long time. Recently a lot of interest has focused on
boride carbides with the composition LnNi,B,C (T'(max) =
16.6 K ) . [ ? h - ? Y I The bonding is complicated in all of these
phases: YBzCz contains B-C networks, in La,B2C,
( = La,Cz(CBC),) there are CBC and C 2 anions, and in LnNi,B,C the bands carry contributions from all atoms at the
Fermi edge. In comparison, the bondingconditions in the superconductor La,Br,(CBC), are fairly clear. The "fingerprint" for
superconductivity is similarly present for the compound
La,Br,(CBC), .Lslwhich is structurally closely related. There are
bands with large and negligible dispersions about 0.5 eV above
and below E, . Attempts to change E, by substitution of La3+
are currently in progress.
Receiked: Februar) 28. 1996 [28879 I€]
German version. Aii,?c% Chwi. 1996. IflX. 1805- 1807
-
Keywords: carbide borides halides
structures * superconductivity
- lanthanides
*
solid-state
Siilioii. i l i i y c l l . C / i c j i j , 1987. Y Y , 602. .?ii~q"i. C h j . /!I/. €d € f i x / . 1987. 26.
579
[2] A Simon. ( ' / i m i C w Zcii 1988. 22. 1.
131 A Simon. H Mattausch. R. Eger. R. K . Kremer, Angm,. Choir. 1991. 103.
1209: A/i,ycii C%mir I/?/ E d EtigI. 1991. 30. 1188.
[4] A . Simon. A Yoshiasii. M . Backer. R . W. Henn. C. Felser. R . K . Kremer. H.
Mattausch. %. .qii(ir,q. A//,q CIIPIII.1996. 622. 123.
[5] H M,ittausch. A . Simon. A ? i p i , . Chwi 1995. 107. 1764: A i i g w . Cherfi./irr
E d .Fly/. 1995. 34. 1633.
r .
.S/ii//,ym/. (1996) The lattice
[6] H M,ittauscli. A. Simon. J h d ~ ~.WP/-FKI.:
c ~ i i i t i i i i t s iitoniic
.
parameters. and details of the crystal structure analysis ma>
be iihtiiined fro111 the Fachinformations7entruni Karlsruhe. D-76344 Eggenstein-Lcopoldsh~ifen.o i i quoting t h e depositot-y number CSD-404168.
[7] Thc T t i atnpoulc\ wcrc filled with atarting muterial (ca. 7 g). welded under a n
;irgoii prcssurc of I atin. sealed into quartz glass ampoulea. heated at 1460 K
(Cc,,Bi-,(CHC'),. I dn!. 30% yield). a t 1700 K (La,l,(CBC),. 1 day. X-ray
purc). i i t 1460 K (L;i,Br,(CBC),: 7days. X-ray pure). a n d then quenched to
trooiii tenipci-arui-e. The quantitative synthesis o f the samples (especiall)
B c' = 1 : 7 ) pro\cs the correct atomic assignment from the X-ra! analysis [9]
nthesis and handling of the starting material. see ref [HI
oirmann. R Egei-. R K. Kremer. A. Simon. Z Aiior,?.
,!/I3 C ' h i j i 1994. 620. 18x9
il intensit! ine~isurenients
o n it four-circle diffractometer (CAD4.
€.nrciS-hoiiiii\) \ v i t I i Agk, I-adiation Setniempirtcal absorption correction ($I
\c;iiil t iill-m;itrix Ieasi-squares refinement o n F' [lo]. Ce,Br,(CBC),. P ~ I I I I I I I :
1i=12'~35(.:)./,=380.4(1).~ =781.h(I)pm.Cel:0.5094(1),
14.0.1970(2):
Cc.2- I 4. I -1. 0.5475(3). Ce3: 0.5956(1). I 4. 0.9135(2): Ce4: 0.3056(1).I 4.
0951017). ( ' c 5 0.632911). 1 4. 0.350212). B r l . 0.5481(1).1 4. 0.5747(3). Br2(1.34Slil). I J.O.?25X(3). B r 3 : 3 4. 14.0.787j(5):C1:0.6241(7).3 4.0.136(3):
C3 0 7037(Sj. 3 4. (I 728(3): C 3 : 0.4561(7).1 4. 0.973(31. B1: 0.5794(9). 3 4.
0 11914). B2, I 4. <. 4. 0.776(5). RI = 0.069. n R 2 = 0.135 for 1463 independent ~ r e l l c c t i ~ ~ nL'i,Br,(CBC),:
s
P i i i i i r n . LI = 3319(2). h = 385 3(1). < =
790 01.3) pi11 La1 0 5093il). I 4. 0.1973(2): La?. 1 4. I 4. 0.5464(3). La3.
0 j Y 5 9 ( I ) . I 4. 0.91 1312): La4: 0.3054(1). 1 4.0.9543(2). La5. 0.6330(1). 1 4.
0 131.X2): H r l 0 5481(1). I 4. 0.5728(3): Br2- 0.3480(1). 1 4. 0 3276(3): Br3.
3 J. I 4. 0 7X5Xl5). CI 0.62537). 3 4.0.137(3). C 2 - 0.294017). 3 4. 0.726(3):
c'3 0 456617). I 1.0.977(3). B1 0 579( I).3 4. 0.144(4): B3. I 4. 3 4.0.774(4)
RI = 1) 053. i i R2 = 0 103 for 1097 independent rcllectiona. Thecorrect assigniiieiit 01' H a n d c' is clzarl! visible from the R ~ a l u e and
s
the corresponding
displacement parmieters Isotyptc IS La,l,(CBC), with (I = 3385.7(4).
I) = ?94.XI(4).( = X21.8(1) pin. Furtlierdetailsofthecryst;ilstructuresnia~be
oht~iincil11-om the tacliinli~rn~ationszenti-uni
Karlst-uhe. D-76344 EggensteinLcopiild\lialcn (German) ). upon quoting the depositot-y numbers: CSD404170 (LLi~~Hi-JCBCl,).
CSD-404708 (LaJG(CBC)5). and CSD-404169
(Cc.,Hr,(c'BC'),)
[ I O ] C;. XI. Sheldrtck. SIIELXTL-PLL'S. Gottinsen. 1992 and SH€LXL-Y3.
Ghttingcn. I993
[ I I ] E. DOM
I ) . .A TO 1I.S /,I,- Wfiidoii,\.Version 3 1. Shape Software. Kingsport. T N
3766.:. I995
[I] A
The structtire I, closely related to thc onr: ofLa,Br,,(CBCI, 151. The lowered Br
content of Ce,Br,(CBC), leads t o a stronger corrug;i!io~i of the sheets.
Q C P E program E H M A C C by M.-H. Whangbo. M.Ev,iin. T Hughbanks. M
Kerteaz. S. Wijeyesekera. C. Wilkrr. C Zheng. ; ~ i i d R Hoffmann.
Parametrization 'iccording to S. Al\,are7
The iiiiignetic susceptibilities were measured a i 10 G u i t h i i n M P M S Quantum
Design S Q U I D niagnetonieteiL J. \ a n der Pauw. Philips Re\. RcJp 1958. 13. I
Program TB-LMTO-ASA 4.7 (tight btnding-linear nitiffit1 ttn orbital-atomic
spheres a p p r o r ~ m a t i o n )1171 by G. Kricr. 0.
Jepsen. A. B~II-khardt.
and 0 . K.
Andersen.
0. K. Andersen. Phi 5 R r v . B 1975. 1 2 , 3 0 6 0 . 0 . K Aiiderwi. 0.
Jepsen. P/II \ .
Rev. L w 1984. 53. 2571.
The conventional orbital repi-esentation is obtained h) c\changing the .\-and :
directions.
L. S. Bartell. J Uwr. Eihu 1968. 45. 754
R. G.Peiirson. J A m . Choir. Sot,. 1969. Y1. 4947.
A D F 1.1.4. Department of Theoretical Chcmistr). Vrije Uni\ersiteit. Ainsterdam. E. J. Baerends. D. E. Ellis. P. Ros. Ciioii Phi.,? 1973. 2. 41 : G. te Velde.
t J Barrend\. J Cow/>.P/iy.\. 1992. 99. 84.
We h a w performed q u a n t u m mechanical optimtrations (triple-zeta basis sets
including two polarizition functions for all valence orbitdla. local density functional) of the bridging angles o f CBC"- molecular ion>. with ;I fixed C B
distance (151 pin). The calculation, are model-like because of the Coulomb
explosions that ma) be expected for such high charges. I),,,s>mnietr) i s only
found for CBC' and CBC'.. wheieac C B C = a n d CBC" adopt ( i 2 >synimetry with angles of 121 ;u]d 1 i0 . Test cnlculations on SO1 \how these ciilculations to be better than 7 . and they stt-ongly faboi- the LDA with respect to
gradient-corrected ftinctionals.
Pi-ogt-am CACAO bk C. Mealli. D. Proserpto. J. C h i i . E d i i ~ .1990. 67. 399
T. Sakai. G:Y. A d x h i . J. Shiokawa. J L ~ ~ \ , \ - C f j i i i i i i ~W(,/.
j j i . 1982. 84. 107.
J Batter. O Bars. J. L<,\.\-Ciiiii~ii~iii
. W P ~ 1983.
.
9.5. 267.
R. J. Ca\a. H. T q a k i . H. W. Zandbergen. J J. Kraijcw*.kt. W. E Peck. T.
Siegriat. B Batlogg. R. B. viin Dover. R. J Felder. K . Miriih;ishi. J 0 Lee, H.
Eisakt. S. Ucliida. .Vo/iire 1994. 367. 252.
[27] T. Siegrist. H . W. Zandbergen. R J Caw. 1. J. Ki-ajewski. W. F. Peck. .Yti/ilre
1994,367. 254.
[ X I T. Sicgrist. R 1 Cava. W F. Peck. J. .41/0j.\ Coiiip 1994. 216. 135.
[29] W. R. Pickctt. D. J. Singh. P/i!..\. RPV.L P / / .1994. 27. 3702
Modeling of the Chemistry of the Active Site of
Galactose Oxidase**
Jason A. Halfen, Victor G. Young, Jr., and
William B. Tolman*
Arrays consisting of organic free radicals proximate to metal
centers recently have been identified as important components
of active sites in enzymes that catalyze multielectron redox reactions.['] An intriguing example of a functionally significant
metal-radical pair is found in galactose oxidase (GAO),"] a
fungal enzyme containing a monocopper active site that effects
the two-electron oxidation of primary alcohols to aldehydes.
Extensive biophysical studies[". 31 including X-ray structures[4'
have resulted in the elucidation of the topology of the active site
(Fig. 1, inset) and an electronic structural description of the
functionally competent form. This form (structure A, Fig. 1 ) is
postulated to contain a Cu" ion tightly coupled to a radical
localized on an equatorial, covalently S-cys-modified tyrosinato
['I
[*'I
Prof. W. B Tolman. J. A. Halfen. Dr V. G. Young. J r
Department of Chemistry
University of Minnesota
207 Plcas;int Street S. E.. Minneapolia. M N 55455 ( U S A )
Fax: I n t code +(612)624-7029
e-mail : tolnianio chcinsun.cliem.umn.edu
Thiswroi-k wassupported by grants from theNationa1 fnstitute\ofHealth ( G M
47365). the National Science Foundation (National Younf Inwstigator Award
to W. B. T.). the Alfred P.Sloan a n d Camille and Henry Dre>fus Foundations
(fellowships to W. B. T.). and the University of Minnesotn (Dissertation Fellow'ship to J. A. H ). O n e of the dtffractometers used wi;is purchased in part
from funds from the N S F (CHE-9413114).
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B
Fig 1 Schematic drawings of the crystallographically characterized actibe slte of gitlactose 0x1dase at pH 7.0 (inset. from Ref. [4]) and the proposed mechanism for alcohol oxidation by the
enzyme (from Ref. [ 2 ] ) .
ligand and stabilized by n-stacking interactions with a nearby
tryptophan residue (not shown). Poised to perform two-electron redox chemistry. the free- radical-coupled copper complex
A has been proposed to yield intermediate adduct B upon deprotonation of the alcohol substrate by the axial tyrosinato
ligand.['"] The subsequent alcohol oxidation has been suggested
to occur by initial hydrogen atom abstraction by the appended
tyrosyl radical,i51 followed by electron transfer to copper to
afford the aldehyde and the reduced Cu' active site (Fig. 1).[61
Two-electron oxidation by 0, completes the hypothetical catalytic cycle.
We wish to assess the viability of this interesting mechanism
by examining appropriate synthetic model complexes. Previous
modeling studies have demonstrated the feasibility of phenolato-Cu" units found in the inactive form of GAO (one-electron
reduced form of A)[71 and the functional competence of freeradical-coupled copper compounds to oxidize alcohols, albeit
with an abiological radical cofactor (2,2,6,6-tetramethyl-l -piperidinyloxy, TEMPO) .I8] Here we report the identification of
synthetic analogs of A and a novel mixed alcoholato -phenolat0
complex of Cu" that models reduced B. Moreover, we find that
one-electron oxidation of B induces aldehyde production.
Reasoning that any attempt to generate a functional pair
consisting of a phenoxyl radical aiid a Cu" ion would be thwarted by inactivation reactions at the ortl7o and p v c i positions of
the arene ring, we prepared
the protected monophenolato ligands L' and L2.Deprotonation with NaH followed by treatment with the
L': R = CH,
appropriate anhydrous Cu"
YNUN,f L2: RzC(CH3)3 salt yielded the deep purple
I
I
complexes
[LCuX] (1 :
L = L'. x = c1: 2: L = L*.
X = C1; 3: L = Lz, X = O,SCF,), one of which (1) was structurally characterized by X-ray crystallography (Fig. 2. top).[''
The complex adopts a square-pyramidal geometry["' with the
chloro and phenolato ligands in cis-equatorial positions: spectroscopic comparisons implicate a similar arrangement in 2 and
Fig. 2. X-ray crystal structures of 1 (top) and 4 (bottom). Selected bond lengths
1: C u l - 0 1 1.916(5). C u l L N l 2069(5). Cul N4 2.148(6).
Cul -N7. 2.291(6).Cul -CII. 2.286(2);ClI-CuI-0I 90.3(2).Cll-Cul-N1 171.4(2),
CII-Cul-N4 92 4(2). CII-Cul-N7 102 7(2). 01-Cul-NI 92.8(2), 01-Cul-N4
167.4(2). OI-Cul-N7 109 3(2). NI-Cul-N4 X3.0(2). Nl-CuLN7 83.9(3). N4-CulN7 8 2 4 2 ) Selected bond distances [A] and angles [ ] for 4: C u l - 01 1.893(1).
Cul - - 0 2 I.931(1). Cul -NI 2.082(2). Cul N4 2397(2), Cul N7 2 140(2). N1Cul-N4 80.45(6). NI-Cul-N7 82.89(6). N4-Cul-N7 82.29(6). N1-Cul-01
169 80(6). N I - C u l - 0 2 92.88(6). OI-Cul-N7 88.23(6). 0 1 - C u l - 0 2 Y4.85(6). 01Cul-N4 103 39(6). N4-Cul-02 107.94(6). N7-Cul-02 IhX.Zl(6).
[A] and angles [ - ] for
3.["] The stabilizing effect of the the tevt-butyl groups[''] is
manifested in the unique electrochemical behavior of 2 and 3,
both of which exhibit reversible one-electron oxidation waves
in their cyclic voltammograms (CVs) obtained with 0.25 M
Bu,NPF, in CH,CI, (2: E l , , = 0.59 V, AEp = 86 mV; 3:
E l : 2= 0.72 V, AEp = 96 mV; both vs. SCE at 100 mVs-').
One-electron oxidation of purple, EPR-active 3 could be accomplished at -40 ' ~ Celectrochemically by controlled potential
electrolysis at 1 .O V vs. SCE or chemically by treatment with
equimolar (NH,),[Ce(NO,),] in CH,CN. Both procedures resulted in the production of a new green species. Consistent with
the electrochemical reversibility evident in the CV of 3, reaction
of stoichiometric amounts of ferrocene [Cp,Fe] with the green
complex resulted in the quantitative regeneration of 3 and the
production of [Cp2Fe]+.The green, oxidized species lacks an
EPR signal and exhibits an optical absorption feature at 410 nm
( i : = 4000 M
cm- I ) similar to that observed in active GAO
(445 nni, I: = 5400 M - cm- ')[I3] and many 2,4,6-trisubstituted
phenoxyl radicals."41 These results support assignment of the
green oxidized species (3") as a magnetically coupled phenoxyl-Cu" radical complex akin to GAO species A.
In an approach toward modeling substrate interactions
with the enzyme we treated 2 with NaOCH,Ph to yield
[L'Cu(OCH,Ph)] (4) as green crystals suitable for X-ray crystallographic characterization (Fig. 2. bottom) .[', ''I The cis-equatorial arrangement of the alcoholato and phenolato ligands in
the square-pyramidal ' I o 1 complex mimics the proposed disposi-
+
+
+
~
'
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tion of these groups in GAO during enzyme turnover. Additional noteworthy features of 4 are the short Cu"-alcoholato bond
length [ C u l - 0 1 = 1.893(1) and a 2.36 8, distance between a
benzylic hydrogen (HIOA) and the phenolate oxygen ( 0 2 ) that
implicates an 0 .. . H-C interaction of possible functional iniportance."'' insofar as such an arrangement may be viewed as
necessary for the hypothesized hydrogen atom abstraction that
is the first step in alcohol oxidation. Indeed. the cyclic voltammogram of 4 exhibits an irreversible oxidation wave
(Eva = 0.37 V vs. SCE in CH,CN) and upon bulk electrolysis
at +0.5 V. 0.9+0.1 e - mol-' was abstracted from thecomplex
concomitant with bleaching of its EPR and U V W s features.
' H N M R and GC'MS analysis of the resulting solution (after
removal o f copper-containing species) revealed the production
of benzaldehyde (46 O h based on 4) and small amounts of 1.4-diisopropyl-1.4.7-triazacyclononane~'
'1 and 4.6-di-rert-butyl-2formylphenol (Scheme 1).
A]
+
L' : A solutioii of the M m n i c h base of 1 . 4 - d 1 i ~ o p r o p ~ 1 - 1 . i . ~ - r i - i ; i ~ a c ~ c l o n ~ ~ i i ~ i n c
(4.95 mmol) [I71 and 1.4-dimethylphenol (5.16 minol) iierc iic;ited a t i r l l u x in
methanol for 12 h according to ref. [ I S ] . Addition o f water lo thc i-e:iction iiii\tui-c
caused the deposition of a colorless oily mass. which cr!stallized 011 standing. Yield:
(s. l H ) . 0 6 0 ( \ . l H ) . 3 7 3 ( ~ .
L21g(71'%1) ' H N M R ( ~ O O M H Z . C D C I , )=6.XI
:~
2 H ) . 3 0 2 - 2 . 9 6 ( i n . 4 H ) . 2 8X(sept.J = 6.5 H2. 2 H ) . 2.67(1.J = 5 !) 117. 4 H 1 . 2 43
(s. 4 H ) . 7-19 IS. 3 H ) . 2.17 (5. i H ) . 0.95 (d. J = h . j H r . 1 2 t l ) : " C : ' H ; N M R
(125MHz.CDCI,):ii=154.2. 1300. 116.8. 1264. 1245. 111.9.608. 548. 5 3 6 .
53.4. 52 Y. 20.4. 1X.3. 15.6. An analogous procedure \*;is used t o prcpire Lz froin
2.4-di-ir,-r-hut~lphrnolin 90% jield Data for L'- ' H Y M R !.XI!) MHz. CIXI,).
i i = 7 . 1 7 ( d . J = 2 4 H z . I H ) . 6 X 1 (d. J = 2 . 4 H r . I H ) . 3 . 7 6 ( > . 2 H ) .3.04 2.85
(overlapping inultiplet a n d septet.6H). 2.68 ( t . J = 4.8 Hz. 4 H ) . 2.46 ( \ . 4 H ) . 1.42
( s . 9 H ) . 1 2X(s.YH).0.97(d../= 6.6 Hr. 12H): "CI'H: Y M R i 7 5 M H z . C I X 1 3 ) :
ri=1550.139~h.13S3.123.7.11?4.122.1.61.5.54.6.541.~.~7.53.1.3J~.34l.
.3l.7.29 6. 1x4.
1 3: Thc sodium salt of L' (prepared by the reaction of L' (0 21 g. (1.60 inniol) with
N a H i n T H F ) and anhydrous CuCI, (0OX1 g. 0 60 niniol) \!we h r e d in T H F
( 5 mL)for 1 h. The mixture was then filtered through a pad ofcclite. m d the Iiitr'ite
evaporated under reduced pressure. Recrystallirntion of the i-e\idiic from CH,CI
pentane yielded 1 a s purple crystals suitable for a single-cr)\i,il X-I-a) iinalys
0 1x9 g (70"4,).An analogous method was wed to p r e p u c 2 from L' snd CuCI,
X6"h !ieid: complex 3 wiih prepired similarly tising L' and CLI!O,SCF,)~
in Y5':c~
!ield
4:A solution o f 2 (0.163 g. 0 31 minol) and NaOCH,Ph (0.062 g. 0.JX mniol) werr
stirred in THF ( 5 niL) for 1 h. Pentane (IOinL) was then addcd. and the green
niixture liltered through a pad of celite. Concentration o f t h c filtrate and stoi-agc '11
-20 C for m e r a l da!scaused the deposition ofsmall green cr!\tal\ o f t h c producl.
0.050 g ( 2 7 % ) Recrystallization from toluene pentiine .it - 2 0 C !ielded crystals
oC4-0 5 toluene suitable for ii single-crystal X-I-a! anal!\is
v
8
vs. SCE
Rcceive~t-Iiiiiuarj I I . 14196
Rebised \iersioii March I X . 1996 [Z87161E]
Gerinan ver5ion .Aii~qiw C/wiii 1996. IIIX. 1x32 1835
Keywords: copper compounds - galactose oxidase
. radicals
46 %
Scheme I . SCE
=
4
5%
< 5 Yo
\aturated calomel electrodc
The overall reaction whereby one-electron oxidation of 4
yields benzaldehyde and. presumably. Cu' coproduct(s) parallels that promoted by GAO. By analogy to the electrochemical
behavior exhibited by 2 and 3. we suggest that electrolysis of 4
generates 4". a reactive Cu" complex with coupling between the
free radical and the copper center that binds the substrate.
analogous to enzyme intermediate B. Hydrogen atom abstraction (cf. HlOA) by the phenoxyl oxygen ( 0 2 ) would initiate
benzaldehyde generation. while abstraction from the activated
benzylic position of the phenoxyl group would afford the byp r o d ~ c t s . [ ' ~InterI
or intramolecular paths are possible. although we view internal delivery of a hydrogen atom from the
benzyl alcoholate to the phenoxyl oxygen as a particularly attractive alcohol oxidation route in view of the 0 . .. H - C interaction identified by crystallography for 4.
In sum. we have obtained chemical precedents for key intermediates hypothesized in alcohol oxidation catalyzed by the
unique active site of GAO comprising a monocopper center
coupled to a free radical. Important findings include the identification of species derived from one-electron oxidation of phenolato-Cu" compounds that model the active form of the
enzyme ( A ) . structural characterization of a mixed phenolatoalcohoiato complex that models the reduced enzyme-substrate
adduct (reduced B). and aldehyde evolution from the phenolato-alcoholato compound upon its one-electron oxidation. a
reaction that mimics GAO function.
. oxidations
[ l ] a ) J. A. Stuhbe. Annir. Rev. B i o i h f i 1989. 58. 757 2XS. hl 1. Z. Ped
Fina7zi-Agro. FEBS Lcr.. 1993. 325. 53-5s.
[2] a ) 1.W Whittaker in . W ~ ~ ~ o / / o c i i ~l i i l~o /ir~i iii ~, q(Aiiiiiio A i id Ri,$ii/iw i i i i r l Rr/iiii,il
Rm/ico/.\. I?>/. 30 (Ed.; : H Sigel. A. Sigel). Marcel Dekkcr. We\* Yoi-k. 1994.
pp. 115 360: b) P F. Knowles. N . I t o i n P i v y w i ~ i i wiii h - i i i o r , y i i i i i c Chviii s m , , Lid. 2. J'ii Press LTD. London. 1994. pp. 207- 244
[3] 'I) A J. Baron. C. Srccens. C Wilinot. K . D. S e n e \ x ~ t i i e .V Blnkele?. D. M.
Dooley. S E V.Phillips. P. F Knowles. M . J. McPherson. .I Em/. Chiif. 1994.
269. 25095- 25105: h ) P. F. Knowles. R. D. Bro\\n 111. S H Koenig. S Wang.
R A Scott. M. A. McCiiirl. D E Brown. D M.Doole!. hoi-q C h i i 1995.
34. 3x95-3902.
[4] a ) N Ito. S E. V. Phillips. C. Ste\ens. 2 B. Ogel. M ..I McPher\oii. J N
Keeln. K . D S. Yadnv. P. F. Knowlcs. ,Vorirrc 1991. .W/. X7 -90: h ) N. Ito.
S. E V. Phillips. C. Stevens. 2. B. Ogel. M. J. McPhci-son. 1 U.Keen. K . D.S.
Yiidav. P R. Knowlcs. F ( i r d ( y Di.\m\.\.1992. 93. 75 8-1. c ) N. Ito. S. E V.
Phillips. K . D . S Y i i d a ~ .P F. Knowles. J .tlo/ R i d 1994. ?3X. 794 814.
IS] An alternative routc involving deprotonation h! t h e stacked tr)ptophan
residue ;iko has been suggested [4b]
[6] a ) B. P.Branchaud. M. P Montague-Smith. D. J. Kosmaii. F R. McLaren. J
,Aiii Ciimi Soc 1993. l f j . 798 -800:b) K. Clark. J E. Penncr-Hahn. M.M .
Whittaker. J W. Whittaker. ;hid. 1990. /I.?.6433 6434. c I R c1. Wachter. B.
P. Branchaud. J. .4iii C'/iwii. S o , . 1996. 118. 2 7 x 1 27SY.
[7] i i ) U. Rnjrndran. R Viswanathan, M. Palaniitnda\ar. M. 1 ak\hinin~ira?anan.
J. Cliciii. S o i . D d f o i i k i i i \ . 1992. 3563 3564. b) R Uim. R. Visuniiathan. M.
Paluiiiaiidiivar. M L;ikshininara);iiiaii. .I C/iwi. . S i r lldioii P(iii\. 1994.
I l l 9 1216: c) H Adam,. N A Bailey. D E Fenton. 0 He. fiioip. C/im
. 4 i i r t 1994.213. 1 3. d ) H. . A d a m Y.A. Bale). C 0 R de Barhiit-in. D E.
Fenton. Q -Y He. J Chnii. Snc. Diilroii Truii\ 1995. 232: 2331 : e ) M Whittaker. Y. Chuang. 1. Whittaker. .I ,4171, Cheiii. So(.1993. / / ;. 10029 10035. i')
N Kitajiina. K Whang. Y Moro-oka. A. Uchida. Y. S ' I ~ ; I.I. <'/iCi71 S o ( .
Ciicni. Coiiiiiiiiii. 1986. 1504. 1505: g ) M.M Whitlakei-. \\: R 1)unc:iii. 1. W.
Whittaker. 1iiiwy. C h i i 1996. 35. 3x2 3x6
[ 8 ] J L'iugiei. J - M Latour. A C'ineschi. P. Re!. liioi-x C h i i 1991. 3 1 . 4474
4477
[Y] X-m! cr)stal structure u i i a l k s i s o f 1 purple block c i - ! d ( 0 5 0 x 0 50 x
0 10 mm): CL,H,3,CICuN,0. .M,= 445.53. monoclinic. rpacc group PI, L.
u = I 5 . 1 X ( 4 ) A . h = 7 . 5 ? X ( I ) ~ . i ~ = 2 0 . 5 X ( ~ j ~ . / 1 = 1 0I 9( I ) .I =2225(X)Ai.
2 = 4 iit 2913(2) K . [ I ~ , , , ~I, .330
,
gem '. 20 ,",, = 50.00 . 11,,,. = I1. I 0 ciii ' The
structui-c \%a\\ol\ed by direct methods: hydrogen dtoiii\ \\ere placed a t calcaiI'irzd posilioiis b u t CIpre not refined. A semicmpiiicnl ah\orptioii correction
(DIFABS) was applied T h e fiiiiil cycle of full-ni,iirixlca\i-\qiiarcs i-elincmcnt
( o n F ) . bxed on 4319 reflections [ / > 2 n ( l ) ] and 245 \ari;ihle pnranictcr\. conLcrped .II R = 0 071 xnd 1 1 R = 0 0% ( m i x i i i i i i ic5idu,il cIcctroii den\it> !) 7 2
~
- 1.03 e - k').
Data were collected on an Enraf-Nonius C A D 4 diffractometei-. and calculations were performed with the TEXSAN software package. X-ray crystal structure analysis of 4.0.5toluene: green block crystal
M = 647.42. monoclinic. space
(0.50 x 0.50 x 0.25 mm): C,, ,,,H,,CuN,O,.
group P2,'ii. 0=17.5316(4)!% h=9.3694(3),& ( = 22.1187(S)A. / I =
91.444(1), V=3632.1(2)A3. Z = 4 at 173(2) K: (I,,,,,,=I.lX4gcm-'.
20,,,,, = 50.18 :pMS= 6.36 cm-'. The structure was solved by direct methods:
non-hydrogen atoms were refined aiiisotropically. and hydrogen atoms were
placed at calculated positions and refined as riding atoms with individual
isotropic displacement parameters. A semiempirical absorption corrcctioii was
applied. A disordered toluene molecule was located on a n inber$ion center: the
occupancies of its atoms were fixed at 0.5 to account for the disorder. The final
cycle of full-matrix least-quai-es refinement (on F ' ) . based on 6402 reflections
[ I > 2 r i ( / ) ] and 495 variable parameters. converged at R1 = 0.0359, and
I I R2 = 0.0865 (max min residual electron density 0.264 - 0.369 e A -').
Data were collected on a Siemens SMART system and calculations were
performed using the SHELXTL V5.0 suite of prograins Crystallographic
data (excluding structure factors) for the sti-ucturcs reported in this paper have
been deposited with the Cambridge Crystallographic Data Centre as supplementary publications no. CCDC-179.44. Copies of the data can be obtained
free of charge on application to The Director. CCDC. 12 Union Road.
Cambridge CB2 IEZ UK (Telefax: Int. code +(l223) 336-033: e-inail:
techedict cliemcrys.cam.ac.uk)
For 1 and 4,T = 0.07 and i = 0.03, respectively. where values of 0 or I . respcclively. refer to ideal square-pyramidal or trigonal-bipyramidal geometries as
described in A. W. Addison. T. N. Rao. J. Reedijk. J van Rijn. G. C. Verschoor.
J. Chmi. Soc. Doiroii ? h i . \ . 1984, I349 - 1356.
I : EPR ( I : I CH,CI;toluene.
77 K. 9.46 GHz): ~q = 2.25. A = 152 G .
t L = 2.03. UV Vis (CH,CI,)- i,,,,,( I : ) = 340 (3 I x l o J ) . 520 ( 1 . 5 ~lo3).
710 nin (sh. 440). 2: EPR ( 1 - 1 CH2CI2:toluene.77 K. 9.46 GHz): ,q = 3.26.
A = 153 G. g L = 2.04: UV Vis (CH,CI,): j,,,4x
( I : ) = 350 ( 3 . 0 x 10'). 526
(1.2xIO'). 720nm(sh,400).3: E P R ( I : I CH,CI,:toluenc. 77K.9.46GHz):
4 = 2.25. A = 151 G. g A= 2.03. UV VIS (CH,CI,): i,,,,( I : ) 328 (3 3 x 10').
S32(1 1 xlO3).696iim(sh.450).4.EPR(l:lTHFtoluene.77K.Y.46GH7)
g,=2.26. A,=153G,~,=2.03.~~'=102:
UVVis(THF) ;
._,,x ( i : ) = 4 3 6
(700). 760 nm (130)
Oxidation of 1 was irreversible ( & = + 0 71 V vs. SCE at 100mVsC' with
0 . 2 Bu,NPF,
~
in CH2CI,).
M. M. Whittaker. J. W. Whittaker. J Biol. C l i w i i . 1988, 263. 6074- 6080.
E. R. Altwicker. Chcnl. R E V .1967. 67 , 475-531
Report describing species in which phenoxyl radicals are coordinated to iron:
J. Hockertz. S. Steenken, K . Wieghardt. P. Hildebrandt. J. A m . CIWJI So(
1993, 115. 11222-11230.
T Steiner. W. Saenger. J Ain. Cliem. Soc. 1993, 115.4540 -4547. and references
cited therein
R. P. Houser. J. A. Halfen. V. G. Young, Jr.. N J Blackburn. W. B. Tolman. J.
Am. Cliein. Soc. 1995. 117, 10745- 10746.
D. A. Moore, P.E. Fanwick. M .J. Welch. / I I < J ~ ~Cliiwi
.
1989. 28. 1504 - 1506
(6,3)-connected net with spacious interconnected cavities that
enclose large amounts of unusually well-ordered solvent and
anions."] The cyanozinc derivative [Zn3(tpt),(CN)3(N0,)3]~
solvate, which is also cubic, consists of two infinite networks of
a previously unknown topology which interpenetrate so as to
produce extraordinarily large but completely sealed-off chambers capable of enclosing of the order of twenty mofecules
of solvent (e.g. ca. 18CHC1, + 4 C H 3 0 H per chamber o r
9 C,H,CI, + 9 C H 3 0 H per chamber)-essentially
minute
droplets of liquid imprisoned in microscopic cells.rz1 A zinc
hexafluorosilicate derivative (also cubic) consists of multiply
interpenetrating enantiomorphic (10,3)a
Recently a different type of ( 1 0 3 net, namely Wells's (10,3)b net, was reported by Moore et. al. in a coordination polymer of Ag' ions with
the related trigonal building block 1.3.5-tris(4-ethynylbenzonitrile)ben~ene.[~I
We report here yet another highly symmetrical
coordination polymer of tpt that consists of two independent
and interpenetrating cubic nets, producing large, solvent-filled
cavities.
Diffusion of a solution of [Cu(CH,CN),]CIO, in acetonitrile
into a solution of tpt in chloroform/l , I ,2,2-tetrachloroethane
gave very dark red, almost black crystals of solvated
[Cu,(tpt),](CIO,), whose structure was determined from singlecrystal X-ray diffraction data collected at 110 K. All tpt units
are equivalent and are attached to three copper centers at the
corners of an equilateral triangle (edge length 12.898(3) A). All
copper centers are equivalent and are coordinated by four tptderived pyridine donors in a distorted tetrahedral arrangement
(N-Cu-N, 111.0(3) and 106.415)"). This results in an infinite
(3,4)-connected three-dimensional network with (63)4(6284), top ~ l o g y . ' ~A] repeated structural motif immediately apparent in
the network comprises six copper centers a t the corners of a
regular octahedron. with tpt units occupying alternate triangular faces of the octahedron. These octahedral chambers are
large: the diametrically opposed copper atoms are separated by
18.241(4) A (a unit cell length). Each copper atom is shared by
two such units as shown in Figure 1. The tpt units are signifi-
A Cubic (3,4)-Connected Net with Large
Cavities in Solvated [Cu,(tpt),](ClO,),
(tpt = 2,4,6-Tri(4-pyridyl)-1,3,5-triazine)* *
Brendan F. Abrahams, Stuart R. Batten, Hasan Hamit,
Bernard F. Hoskins, and Richard Robson*
Early studies suggest that the simple trigonal building block
2,4,6-tri(4-pyridyl)-1,3,5-triazine(tpt) may provide coordination polymers with diverse structures; examples known to date
reveal high symmetry, unusual topology and, as a result of the
large size and rigidity of the ligand, large intraframework
spaces. The mercury(l1) complex [Hg(tpt),](CIO,), .6C2H,C1,
has a highly symmetrical cubic structure involving a new type of
[*I
[**I
Dr. R. Robson, Dr. B. F. Abrahams, S. R. Batten. H. Hamit. Dr. B. F. Hoskins
School of Chemistry. University of Melbourne
Parkville. Victoria 3052 (Australia)
Fax: Int. code +(3)347-5180
e-mail: richard- rohson(ir muwayf-unimelbedu.au
This work was supported by the Australian Research Council. We thank Dr.
K. Nugent of theSchool of Physics. University of Melbourne for measuring the
UV Vis spectrum.
Fig. I Two iidjiicenl chambers in the structure of [Cu,(tpt),](C10,),~solvate. Each
chamber comprises six Cu' centers (the larger circles) at the corners of a regular
octahedron and tpt units occupy alternate triangular faces. Smaller circles represent
C and N . Cu N.2.014(9) A.
cantly bowed away from the center of the chamber. one consequence of which is to allow the coordination geometry of the
copper atom to approach more closely the tetrahedral ideal.
These chambers can be imagined to be derived from the
adamantanoid cages of a diamond net by replacing the four
3-connecting centers of the adamantane unit by four trigonal
nodes.
Every chamber is connected by its six copper vertices to six
others whose centers are arranged octahedrally around the first.
An infinite cubic collection of chambers is thereby produced as
shown schematically in Figure 2. At the center ofeach collection
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