Determination of the perpendicular magnetic parameters for Cu(II) EPR spectra from angular anomalies

I

Volume 93. number

CHCbllCAL PHYSICS LLlTLRS

DETERMINATION FROM ANGULAR

Reccwcd

2 June

OF THE PERPENDICULAR ANOMALIES

1982,

in tiwl

form

6 Scpwmbcr

MAGNETIC

IV Novcmbcr I982

PARAMETERS

FOR Cu(H) EPR SPECTRA

1982

A method IS outlmcd to obtam accurate values ofgl and Al tn EPR spectra ofCu(il) compounds, provldcd thal an c\or absorption peak due to an angular anon1~1~ GUIcwly be rccogmzcd Tlus method turns out to bc uehl cspccwUy WI tltc USC of low rcsolut~on and III the prcscncc of a supcritypcrfinc pattern due to tbc @nds

1. Introduction

ultcractions due to hgands compbcatc pattern of the copper nucleus.

The annlysis of powder complexes

is often

EPR spectra

complicated

part that IS not well resolved tsmty

In the h&-field

presence

of extra

anomahes

of coppcr(Il)

by a perpendicular Moreover,

the unccr-

pararnetcrs

by the

tosc-oxldase

region ts increased

absorptton

peaks, due to angular

of t9F-

procedures

perturbation

and Kosman

theory

based both on second-order

and exact diagonahzatlon

of the

[3] used the appearance

IO assign unambiguously for the EPR spectra

of

the spectral

of copper

and Its modtficatrons

galac-

upon the addltron

Ions or Imidazolc.

The purpose

[ 1.21.

Stmulallon

Bcrcman an overshoot

the four-kne

of this note IS to show that In some

cases the proper

ldentlficatton

could glvc another

ofan

angular

way of cvaluatmggl

anomaly

and A,

that

spin hamdtonian matnx, have been developed. Even though simulation methods are powerful rechmques

IS faster and as rehablc as IIIC simulaltoa procedure self. On the other hand the values of the ImagnetIc

for the interpretation of the EPR spectra, II IS well known that they are Ime-consummgtrial-and-error procedures,due to the number of parameters to be

paranletcrsobtamd from the study of the angular anormhcsare the best ulput parametersfor attempltng

varied,

among

which

the hncwidth

a sirnulatron

of the expenmental

it-

spectrum.

plays an Important

role. The conditions can be expected

for wluch

an extra

in an experimental

absorption spectrum

peak

2. Experimental

have

been studted for the case of complexes with S = l/3 and havmg axial symmetry [3]. The conclusion of

EPR data wcrc collcctcd tronat X-band spcctromcter

that analysissuggeststhat when an overshoot K easdy recognizedin a copper(H)spectrum. Its field value

wttl~ B standard

low-temperature

case of solution

spectra,

can provide

anol were used tn order to obtain

out accurate the resolution

additional

mformatron

values ofg,

and A,,

In order to work especially

when

IS very low and when superhyperfine

02.75 0 1982 North-Holland

mixtures

apparatus.

In the

of water and netltgood glasses. In the

case of nuxed complexes a slight excess of the dranton was used to be sure that copper(U) a ternary

0 009-2614/82/0000-0000/S

at 120 K with a conven(Bruker 200-D) cqurpped

Ion was present

as

species only. 99

Volu~nr93. number

I

CllChllCAL

PHI XS

19 Novcmbcr 1982

LLTTCRS

3. Results AS explamed In ref. 121 the study of the transition field JS CIfunclion of tlw polar ariglc showed that mplor

depend

nnomohcs

ratlog,,,/g,,

nlmost exclus~vcly

on the g anisotropy.

nanwly

on the Moreover

.

they arf P $cuhrlty of the angula depcndencc of the ttr, = -3/Z resowmcc field For the other nuclear qumtuln numbers the transition field behaves monotonically

with

respect lo the polar angle, thclr eyes-

tcnce bcmg confined only to unrcahstlcg,. and A, volucs (I c. at Y = 9 050 CHz,g; = I! 400 nnd A= =

A3

0.0170

H mT)

cm-’

, the m1 = -l/2

aogular anomdly 1s cx-

peclcd only for g,,, nearly equal togto rcro)

Hcncc, tilclr contribution

the nx~alspectra of coppcr(ll) glcctcd.

As a consequence

extra peak is generally

and A,,,

near

to extra p&ks

complexes

m

can be ne.

of thcsc consldcratlons

the lughcst field fcaturc

the

of the

Assummg that gu and A, can easdy be ob-

spectrum

tamed directly once known

from the cxpcrmlcntal spectrum, and the field vnlur of the extra absorptron

equation (I) tn ref. [2] for the transltioii ficld can bc solved IO give the values ot,n, and A~.

peak, the

A non-lmcar

starch was employed

arc prcsumcd

to be. An approximate

used whlc

Uly

startmg from a

WIIICII the values ofg,

range of values within

and A,

value ofg,

1s ml-

the search IS made along the A, dlrcc-

tlon, the value ofgl

Tllr. I Pol)w)‘sldlhnc fustdcrwatnc EPR spcclrum of Cuz+dopcd CaCd034,COO)~ 6H20 (3). frozen solutmn CPR spectrum of coppcr(ll)-tluodhccta:c sgstcm (b). m waler-methanol mhturc 31 110 K

IS then refined by a search along untd

lntcd from the angular anomaly at 3 19.5 f 0.2 mT Thry sl~ow rcaknble ngrcenrent even though second-

sopl~sl1c3tcd nicthods are not ncccssary in tlus case,

order cffecrs surely affect the values ofgl and A, obtatncd from tlx spectrum. Startmg rrom diffcrcnr

the gl thrcctlon convcrgncc

bul of course

,md the cntirc process rcpcatcd IS obralncd. We vcrlfied t1mt more many

solve the problem,

simtbr

leclmtques

dcpcndmg

sic.? and computrng

on the rcqurred

ror in ..I I is +-0 0002 cm-’

values ofgL with in A,, so that the er-

_

6H,O

pound

14-71

doped with copper(l1)

In fact many srudw

have shown

km with lughly-resolved portions

mtcnsc extra nbsorptlon trum of this compound a comparison directly

100

on ISIS com-

the search always converges to-

value ofgl

with an error of *O.OOZ,

wl~dethe A, value IS affected cm -t.

Moreover

those obtnmed

by an error of +0.0007

the computed

values agree with

by means of smgle.crystal

spcctruni.

liavmg a very

peak. The powder EPR

spcc-

IS shown m fog. la. In table I thcg,

ward apphcatlon a solution

of this method

of copper(l)

specrrum of wluch

parallel and pcrpcndtcular

is made among

obtained

of the prew

that It IS J perfect axial sys.

of the cxpcrimcnlal

and A,,

studies [6,7].

The second example we choose as a straightfor-

Ions was chosen ;IS a test for the valrdity ous awxtions.

ranges ofgl

words a umquc

the field value of the extra peak

is not very scnsltlvc to variation

CaCd(CH3COO),

precl-

fac~l~ms.

Whlc 11 IS very easy to obtain an error of +0.002,

can be used to

and A, values

from the spectrum and those calcu-

was the spectrum

thiochacetate

complex,

IS shown m fig. lb [9]

WC there IS no resolution

m thegl

of

the

_As one

can

region. The perpen-

dtcular parameters dcduccd with the usual methods are obvrously less realistic than those calculated taking the angular anomaly mto account (see table I). Bcmg mvolvcd in a study of the coordmation propertrcs of the copper ion in a series of rnalonate dramens and the mlxcd complexes with 2,2’-bipyndyl,

Volume 93, numbci

I

CIICSIICAL

19 Nclvenibcr 1982

PHYSICS LITTERS

l?g 2 rrozcn solu11on CPR spectra of coppcr(ll) s)‘slcn~ (a) and coppcr(ln-malonatc-2,2’-blpyridyl (b) ,n wax-nwthnol m~\turc 31 120 ii

nlalon;ltc syncm

WC noted that the spcctrd of these complexes frcqucntly appeared wtll on overshoot due to an angular

srlornaly. malonatc

scntcd

111 figs. 2n and 3s the spectra of Cuand Cu-dlburylnwlonatc syswms JrC prc-

The spin IxmnltunKm

tcnls arc rcportcd

paramlcrs

of thcsc sys-

in table I. Fogs 3b and 3b show the

frozen soluhon

EPR spectra

Cu(hlAL)(bpy)

and Cu(DBu-blAL)(bpy)(whcrc

MAL,

DBu-MAL

of the

mlucd con~plcucs

and bpy arc the abbrevlatlons

rnalonatc, dlbutylmalonatc

and 1,~‘-blpyndyl,

for respcc-

one can see the perpendicular part IScomphcated by overlapping hnes due to the -3/2 parallel line of the copper nucleus hyperfinc interaction and lrnes coming from the intcractron of the odd electron with “N nuclei of the bpy molecule. In this case, whde It 1svery ample to grvc WIUCSof t~vcly). As

g,,A

,, , A:

and A? bccausc of the good rcsolutlon

of these spectra, it is not possible to draw out drrcctly

from the spectra anyg,, andAl values. These spcclra

need to be carefully

simulated In order to achieve rch101

Volume 93, number

CHthllCAL

I

PHYSICS

LLI-TCRS

19 Novcmbcr

and 3b), even If comphcated pattern

due to two

used to compute In conclusion, P

its field

the g1 and A,

peaks due to angular

of the transition

function

ande

of the polar

aid lo obtain

value can be

values.

ahes m the behavlour as a dqnostrc

*II

by the superhypcrfine

14N nuclei, the extra

1982

could

anom-

field as a

be successfully

used

the spin hamdtoman

parameters for a complrcated spectrum of a copper (II) compound. The method only requrres careful recognition of the extra peak in the expcnmcntal spectrum and whenever possible It should be used to

g,, ;‘;:I;

obtain

first-approxmlntion

later by a simulation

parameters

to be relined

procedure.

H ImTl

References b

ru: 3 I-rorcn solution EPR spcctm of coppcr(ll)-dlbutylrn.don~lc syslcm (3) and copper(dibutylmslon~tc-2.2’dtp>nd>

I s, stem (b)

an \\;lxcr--n,ctl,c,n.,l

able values of the pcrpcndlculJr IS complxatcd

paramctcrs an cvtra

I07

m~..turc at 120 K.

paramctcrs.

by the need for suilable

Imewrdth

Also III ~IIIS cwz, smcc the spectra peak (dcslgnatcd

by an astcrlsk

Thus task show

m figs. 2b

[I ] J V. Ovchinndov and V.N son. 3?. (1978) 179

Konstantmov. J hlagn Rc-

121 R P. Bonomo and r Rgg~, Lcttcrc Nuovo Cuncnto 30 (1981) 304. (31 R D. Bcrcman and DJ Kosmsn, J. Am Chcm. Sot 99 (1977) 7322 [4] R. Adams, R. Cnun. R. Repowskl and C. Rokoska, Phys Lcttcrs 49A (1974) I1 (51 A.K Cregson and S hlltra, J. Chcm. Phys 50 (1969) 2021. [6J D G Billing, B J Hathaway and P. Nlcholk., J. Chem.

Sot. A (1970) 1877 171 FE hlabbsand W.R. Small, J.Chcm.Soc. 1716.

A(1970)

181 J R. Pdbrow and hl C. Wmticld, hlol. Phys 25 (1973) 1073 [9J R P. Bonomo. C R~zmclh. S. Sammartzmo and F Rrgl. lnorg Chrm Acta 43 (1980) 11