Nuclear Quadrupole Coupling in Transition Metal Compounds by Shen-Dat Ing 'Ihesis submitted to the Graduate Faculty of the Virginia Polytechnic Institute and State Unlversity in partial fulfillment of the requirements for the degree of APPROVF.01 Thomas C. Ward M. McNair Doctor of Philosophy in Der.arlment of Chemistry Ray" F, 1 Tipswora' f November, 1971 B1acksburp,. I > - - "'
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Virginia Polytechnic Institute and State Unlversity...Nuclear Quadrupole Coupling in Transition Metal Compounds by Shen-Dat Ing 'Ihesis submitted to the Graduate Faculty of the Virginia
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Nuclear Quadrupole Coupling in
Transition Metal Compounds
by
Shen-Dat Ing
'Ihesis submitted to the Graduate Faculty of the
Virginia Polytechnic Institute and State Unlversity
in partial fulfillment of the requirements for the degree of
. . . Com'Pounds , . • , , • , , , , , . , • , . ' . . Experimental O~erved Frequencies Ratio and the AsYl1l!lletry Parameter Determined from
44
45
51
f.5
69
?4
Figure 22, • • • , • • , • , , • • • • • , • • ?8
v
Table XVIII
Table XIX
Table XX
Table XXI
Table XXII
Table XXIII
Table XXIV
Table XXV
Table XXVI
Table XXVII
Table XXVIII
Table XXIX
Table XXX
vi
NQR Data for Tin Compounds ••• • • • • • . . Orbital Populations in Fe(co)5 •••• , •••
Bond Direction of Cu-5 and Cu-Cl bonds w1 th Respect to x, y, z Axis System ••••••••
Angular Part of the Atomic Wave functions • •
Angular Contribution of One Electron in a Single Atomic Orbital ••••••••••••
The Total Contribution of One Electron in a
Page
80
83
93
94
96
Single Atomic Orbital • , •• , ••••• , , 97
The Contribution of a Single Electron in a Hybrid Orbital to the Z-EFG Tensor Component.
Estimated Orbital Population and Charge Density • • • • • • • , • • • • • • • • • • •
Ionic Contribution of Cl, Cu and S, to be qzz-EFG Tensor Component •••••••••••
Bond D1-rection of Cu-S, Cu-s Bonds with Respect to x, y, z Axis System ••••• . . . The Contribution of a Single Electron in a Hybrid Orbital to the Z-EFG Tensor Component,
Estimated Or.bital Population and Charge Densities , , •• , ••• • • f • • • • •
Cl2Sn(CHJ) 2 30.8 0.34 Cl2Sn, 2 '35.7! -a. Average for multiple resonances. b. T.L. Br01fll, P.A. l!Hwards, C.B, Harris and J.L. Kirsch, Inorg. Chem.,§., 763 (1969). c. J,D, Graybeal and P,J, Green, J. Phys, Chem,, Zl, 0000 (1969). d, J .D. Graybeal and B.A. Berta, Proceedings 2nd Materials Research Symposium, National Bureau
of Standards, 196?, p. 383. e. P,J. Green and J.D. Graybeal, J. Am, Chem. Soc,, !2.2,, 4305 (1967). f'. Assumed 'L • O. g, D.D. Spencer, J.J. Kirsch and T,L. Brown, J. Inorg, Chem., i, 237 (1970).
Ref,
b CX> 0
b
g
c
d
e
81
Sn-Cl bond and make it more available in the Sn-Co bond, (b) decrease
the net electron population of the Co atom, and (c) strengthen the C:O
bond. These effects will result in (a) an increase of the Co-Sn-Co-bond
angle, (b) an increase in e~zz(Co), and (c) an increase in the C-0
stretching frequency with increased Cl substitution. '!he first and third
points have been substantiated by Patmore and Graham35 while this w<>rk
confirms the second.
2. '!he replacement of a Co(CO\ group by a Cl atom show a
substantial increase in the coupling constant of cobalt atom further
confirming the concept of reduced electron density on the Co atoms due
to halogen inductive effect.
J, The value of e~zz(Cl) increases going from c12sn(Co(Co)4 ) 2
to Snc14 rather than decreases as one might expect if the Cl atom gained
electron density. 'lhis observed change indicates that the net electron
density change on the Sn atoms is relatively small and is insufficient
to provide any net increase of electron density on the Cl atoms in view
of increased competition of the large nwnber of Cl atoms,
4. Substitution of a phenyl group for the Co(Co)4, results in a
increase of e~ (Co) at the remaining cobalt atom, zz 47 BrOlnl has pointed
out that the substitution of a methyl group for a phenyl group has the
same effect on the remaining Co""8.tom. On the basis of the e2qq (Co) zz
values, the Co(co)4 group is a better electron withdrawing group than
either the phenyl or the methyl groups. 'lbe following series, in order
of decreasing electron withdrawing ability, can be established for
compounds of the type studied.
Cl )C Br > Co(C0)4 ) > CH 3
82
'lbe magnitude of the observed coupling constant can be ration-
alized on the basis of a simplified calculation of the EFG tensor
components and the use of an electronically analogous system to estimate
orbital electron populations. '!be molecular field gradient, qzz• can
be expressed in terms of the various type of Jd and 4p electrons by using
the relationship of the field gmdient to angular momentum. In either a
valence bond or molecular orbital approach, qzz arising from the Jd
and 4p electrons can be expressed in terms of atomic orbital populations,
The coupling constant is g1 ven by
e2Qqzz -= eQq320 [N 2 +1/2(Nd +Nd ) -dz x Yz z
(Nd +Nd 2 :) ] + e2Qq410 [ -(N +N ) + N ] x x -v PX Py (58) y .
2 p2
46 A,F. Schreiner has calculated the electron densities for Fe(CO) • 5
'lbese are given in '18.ble XX, 'Ibis is an isolectronic and iaostructural
compound to the bis(tetracarbonylcobalt)tin compounds, By using the
electron densities calculated by Schreiner, hydrogen-like wave functions
and an effective atomic number of Co given by Korol•kov and Makhanek23,
8'.3
TABLE XIX
Orbital Populations in Fe(co)5
Orbit.al Population Orbital Population
Jd 2 1,23 4p z 0,0? z
'.3d:xz • 3d 4p • 4n 0.17 yz x -y
3dxz• 3d x2-y2
4s O,Z?
84
the atomic coupling constant, e2Qq320 , is estimated to be 192 MHz. 'lhe 46 magnitude of ~10 is less than one-fifth that of q320 • 'lhe atomic
2 coupling constant e Qq410 , is estimated to be 12 MHz, 'lhe total coupling
constant as found by using ~uation 58 is 204MHz.
This calculated value is related to the observed value by
2 • (l-R) (e ~zz>calc,
where R is the Steinheimer shielding factor for an open-shell system,
Calculations to date show -0,J < R < 0.2. When onn considers that the
lOlfflr electronegati v!ty of tin, as compared to cnrhon, would probab1y
rAsul t in Nd 2 being largP,r in these compounds as compared to the l"omp lt'!te ly z
? symm.et~ic tY-re, the estim&te of e Qq_zz is re~sonable,
'fable XVI 11~ts the r-~erved frequencies of the CO!!!p·'.'i'mds
s+.urliP.d. A number of interest1 n17 ohservati ons re~rdinf" tliese observt-d
f.,.~queT1ctes can be made, 1) There is an:preciab1P variation amonp; the
observed f'requenc~es of those compounds which mi~ht be con::>Mered a~
belonging to an isomornhous series. 2) 'Ihe frequencies are in the
viclnity of the reported values for cu2o (26.02 MHz) and KCu(CN) 2
(JJ,468 MHz), 3) There are two absorption frequencies for the bis-
compounds of thiourea with copper halides and one frequency for the other
compounds, 4) The observed absorption frequencies for substituted thio-
urea complexes, in general, are higher than the thiourea complexes. 5)
There is a reversal of the order of the frequencies between the pair,
bis(thiourea)Copper(I) chloride and bromide and the pair, bis(ethylene-
thtourea)Copper(I)chlor1de and bromide,
8.5
2) Since all of the atomic orbitals to be considered fall into
groups having the same principal quantum numbers the radial parts are
common, and the angular and the radial parts are seperable, the radial
part is g1 van by an expression originally developed by Pa.ullng20 ,
- 2 z 3e e
where n • principal quantum number
1 • azimuthal quantum number
A0 • the Bohr radius
(60)
Ze • effective atomic charge • Z-s, s is the screening constant,
and the angular part,
3) The radial contribution is evaluated for Cu(I), which has
an electronic configuration 4s0 3d.10, by using the slater rules given by
Ka.uzmann20 in order to evaluate the necessary screening constant. The
screening constant is calculated to be 25.3, with the effective at~mic
charge being
Ze ~ 29 - 25.3 Q 3.7.
The radial contribution is then
, 2X(J.z)3 x 4,8 x 10-10 14 3 ~--'--) ----·- - ~ 8.56xlO esu cm-e rJ • 43 x (5.3 X 10-9)3 X (1+1)(2+1)
4) The angular part of the atomic were functions are given in
Table XXII, The angular contribution to qrs can be calculated as shown
by the following examples
86
Having enumerated the pertinent features regarding this work
possible explanations will now be considered, 1) The variations that
are observed among compounds such as Cu(etu) 2c1, Cu(etu) 2Br and
Cu(etu) 2No3 are of sufficient magnitude to indicate that there is an
appreciable anion effect operable. This is concluded since the magnitudes
of the differences are greater than normal differences due to non-equivalent
crystallographic sites.
2) The occurance of the observed resonance frequencies in the
vicinity of those of cu2o and KCu(CN) 2, lead one to conclude that the
bonding is probably similiar, Prior work on these compounds by other
investigators indicate predominantely covalent bondin8 in Cu2o and
predominant~ly covalent bonding in the Cu(CN)2- ion of KCu(CN) 2• This
evidence for covalent bonding forms the basis of later discussions of
the bonding,
3) The reason for the occurance of two frequencies for the
bis-compounds is different from that which gave rise to the two closely
Sl>IJ.Ced frequencies which were discussed in the cobalt compounds, For
the copper compounds their appearance is due to the occurance of two
distinctly inequivalent chemical sites and not to intermolecular inter-
actions or crystal pa.eking effects. This point is substantiated by
crystal structure studies on the bis(t~iourea)Copper(I) chloride, 'Ihe +
Cu(tu)2 species form infinite spiral chains with the Cu-CU separations
alternating between a long and a short internuclear distance with
accomp&nying "broad" and "sharp" Cu-S-CU aneles, This alternation of
bond distances along with that of the angles is a strong indication that
the coprer atoms are situation in two different chemical sites. On the
87
basis of the crystal study of the bis(thiourea)chloride and the observation
of two frequencies for each bis-compounds one is lead to conclude that all
of the bis-compounds h&ve structures similar to bis(thiourea)Copper(I)
chloride, 1,e, they form infinite spiral chains with the copper atoms
situated in tetrahedral sites with alternate broad and sharp angles. If
one accepts this conclusion, one would expect two frequencies for the
bis(thiourea)Copper(I) nitrate also. 'Ille experimental result however
shows only one frequency and therefore indicates one chemical site for
the copper atom. 'Ille reason for this is not known. A possible explanation
could be that the size of N03- ion is such that the compound cannot form
the same type structure as the halides and may possibly form a discret
structure similar to the tris(N,N'dimethylthiourea)copper(I) chloride.
4) '!he higher NQR resonance frequencies for the substituted
compounds ca.n be rationalized in terms of the inductive effect of the
substituents on the thiourea ligand. Figure 22 shows the resonance
forms of thiourea, ethylene thiourea and N,N•-dimethylthiourea. It was
pointed out by Dr. Philip Hall in a private discussion, that the o~er
of stability of the resonance form having charge separation are I II
III. On the basis of the resonance forms, one would expect that I will
contribute more electrons to the copper atom to form a complex than
either II or III. Consequently, the copper atom will have the least
p-electron defect if it forms complexes with I. Since the higher the
p-defect, the higher the frequency, the observed frequencies are then
in good agreement with this concept.
5) '!he reversal of the frequencies of the halogen complexes is
difficult to explain on the basts of the electronegativity of chlorine
88
FIGURE 23
Re;onance Forms of Various Ligands
89
or bromine, Since chlorine is more electronegative than bromine, one
would expect the chlorine atoa to withdraw electrons away froa the
copper atoa more than the bromide ion if the Cu-X bond were subtaintally
covalent, Consequently, the coupling constant or the resonance frequency
should be lower for the chlorine compound in both cases, For those
co11pounds whose structures have been determined the Cu-Cl bond length
is such that appreciable ionic character is indicated, An approxbiate
calculation, based on the assumption that all four compounds have the
same structural configuration as the bis(thiourea)copper(I)chloride,
1,e. the copper ato111 is situated at a tetrahedral site, with three
covalently bonded ligands at three corners of the tetrahedron and the
chloride or bromide ion at the fourth corner, shows that the contribution
to the EFG tensor component, q , varies with the internuclear distance zz between Cu and Cl as shown in Figure 23. At a particular internuclear
distance, q goes through a minimum. 'Ibis calculated minimum indicates zz that q can increase with either a decrease or an increasP. of the inter-zz nuclear distance of Cu-X, It is therefore believed that the electro-
negativity of the chlorine or bromine has relative little or no effect
on the reversal of the order of the coupling constants. '!be reversal is
probably due to the particular values of the Cu-X distances 1n the com-
p'>unds. In view of the lack of th'!'! crystal st:ructure data, the above
explanation at it best, a speculation.
Finally, the observed ?9Br and 81Br resonance at JB,828 and
46.588 MHz respectively, for bis(ethylenethiourea)eopper(I) bromide are
worth of mentioned. A simple Townes Dailey calculation using Br2 as a
base, shows that the Cu-Br bond with ?8% ionic character is in line with
the suggestions of AllUll8. and Knobler,
.0
N " I ~ ta H
::s c+
ID ~ c: 0 ..... i 11 ::z en i ::s 0 ct
~
~ :t ~ 0...,
Iii
N
-I .._
06
.0
N
N 0
91
. 6 65 1he pure quadrupole resonance frequencies of Jcu and Cu in
bis(thiourea.)copper(I)chloride were first reported by Sw1ger51 . 'Ihe
crystal structure revealed a pnlymeric chain of alternating copper at.m11s 48
and th1ourea molecules with chloride 1.nterper.::ed. AMma proposed a
dist~rted sp2-hybrjd bond s~~em~ for the Cu-S bonds and an ionic Cl.
!f this scheme is adopted for the his(tu}Cnpper(I}chloride, the bond
directions with respect to an arbitrary x, y, z axis eygtem, (Figure 24)
with +,he Cu-atom at thn or\v,1r. a.re given in Table XXI.
Following the m~thod described on page 28 • and assumtng a
plan~r configuration, the choice hybrid orbitals for Cu-S bonds can be
expressed in the following forms,
'/' l • 0.49358 + 0,8651 Px
4> 2 - 0.61559 - o.4255 Px
41') • 0,6215s - 0,4101 px
- 0.708lp y
+ 0.7055 p • y
These hybrid orbi ta.ls are both normalized and orthogonal. In order to
determine the values for this contribution of a single electron to the
principle z-EFG tensor component the EFG contribution due to one electron
in each atomic orbital must first be evaluated, This is done as followsa
1) The contribution due to one electron in an atomic orbital
described by a wave function, r n. is found by the conventional quantU!ll
mechanical average method,
2 '/' nl• II. ein e drd~
(59)
where fqrsJop is the EFG operation (!able VI.)
s . ...
92
I
....... '.,...... ..• ' --. s,
FIGURE 25
Orientation of Bonds in Cu(tu) 2c1
93
TABLE XX
Bond direction of eu-s and Cu-Cl bonds with respect to x, y, z axis system
x y z
Cu-Sl 90° 17° 107°
eu-s 2 29°29' 120° 95°
Cu-s3 30°19• 119°19• 87°
Cu-Cl 90° 90° 00
TABIE XXI
Angular part of the atomic wave functions
• ( ./3/2 ·hr ) cos e Pz
- /J/41t' sin 9 sin
- ./15/16T (sin 29 Cost/> )
•
• /3/4 Tr sin 9 Cos~ Py
d 2 z
d y
z
- ./5 /16 If ()Cos 2e-1)
• ./15/16"11 (sin 29 sinf' )
q xx
95
~ [3 sin 9 cos e -1J sin e sin ; sin9 ded; __3_1•1.br 2 2 2 2 Px • •
'!able XXIII sU11UD&rizes the angular contributions.
5) 'Ihe tota.l contribution of one electron in a single atomic
orbital is the product of the two individual contributions. 'Ihe values
are tabulated in Table XXIV.
(62)
6) 'Ihe values for the contributions of single electrons in each
hybrid orbital to the principal Z-EFG tensor component are calculated and
given in Table XXV.
7) It is estimated from the electronegativity difference between
the Cu and the S-e.toms that the ionicity of the Cu-S bond is 13.5%. Consequently, the S-atom would contribute 0.87 electron to the Cu-a.tom
if each of the three hybrid orbitals has an equal electron density, In
view of the recent detailed crystal structure analysis done by Amma48 ,
the change density on the Cu- and the S-atoms are estimated and tabulated
in Table XXVI, It was pointed out that one of the sulfur-a.toms forms a
three-center, two -electron-bridge bond with two Cu-a.toms while the other
two sulfur atoms each forms a Cu-S covalent bond with a Cu-atom. If one
assumes equal electron density for these two Cu-S hybrid orbitals, the
charge density on these two hybrid orbitals should be "11 = 0.87 and
l/12 ~ 0,87 electrons respectively. For the three-center, two electron
bridge hybrid, the S-atom must supply both electrons to form the bridge
bond, If this is indeed the case, the charge density of t;3 should be
0.4) electrons.
96
TABIE XXII
Angular contribution of one electron in a single atomic orbital
Atomic orbital q q q qxy qxz q xx yy zz yz
PX -0,8 -+o.4 -+o,4 0 0 0
p -+o.4 -o.a -+o,4 0 0 0 y
p i().4 -+().4 -0,8 0 0 0 z
Atomic orbital
4p y
4p z
TABLE XXtII
'!he total contribution of one electron in a single atomic orbital
-6.84 '3.42
+:3.42 -6.84
+J.42 3.42 -6.84
98
TABLE XXIV
'!he Contribution of a single electron in a Hybrid Orbital to the Z-EFG Tensor Component
Orbital q zz
"' 1
14 -3 2,22 x 10 esu cm
lli. -3 2.33 x 10 esu cm
99
TABLE XXV
Estimated Orbital Populations and Charge Density
No d1T - d...., Bonding D,,. - dr Bonding assumed
6161 0.87 o.87
'/J2 o.87 o.87
'PJ 0,41 0.43
JJ 1 0.5
11 2 0.5 s •cs1) 0.87 O.Y/ 1 •cs )
2 1.74 1.74
'•cs ) o.86 0.36 3
I -(Cl) -1.00 -1.00
j -(Cu) -1.17 -0.67
100
~v ~ 'Ihe (q ) for the Cu-a.tom is then calculated to be 4.94x10 zz -'3 14 -3 esu cm and 4. 08xl0 esu cm. for no d1r - d..- bonding and with d,.. - ~
bonding respectively. 'laking into consideration the shielding effect
for an open shell system, the observed (q )C is therefore expressed as zz u Cov
(q )ob zz
- 4.94 x (1 + 0,2)
14 -3 • J.95 x 10 esu cm
'!'he Sternheimer shielding constant for an open shell system, R00 , for + Cu is not known, The value R .. -0,2 is estimated from the calculated
co
value of the group IA elements. Since cu• is isoelectron with K+ and
(R co )K+ • -o .188, it is therefore reasonable to assume RoJcu + .. -0, 2,
8) We have so far neglected ionic contributions from the
chloride, sulfur and Cu-a.toms, By using the classical electrostatic
espress1on
( ) ionic = qr;z
e(Jcos29-l) r3 (64)
where r is the internuclear distance of Cu-X and 9 is the angle between
the Cu-X bond and the Z""8.Xis (X =Cl, S, Cu), '!he ionic·Z-EFG tensor
components were calculated and are tabulated in Table XXVII, The
observed EFG Z-component due to ions is related to the calculated value
by the Sternheimer shielding constant for a closed shell system, ( 00 , by
l' ;
(q )ionic • (q )ionic zz obs zz cal <1- r > 00
(65)
Cur
Cu II
S +cs > 1
J +cs2)
J •cs3)
J-(Cl)
Total
101
TABLE XXVI
Ionic Contribution of Cl, Cu and S to the qzz-EFG Tensor Component
with d - d assumption
-0,154 x 1014
-0.06 x io14
-0.15 x 1014
-0, 68 x 1014
-0.15 x 1014
-0,42 x 1014
-1,61 x 1014
without d - d assumption
-0.2:1 x io14 esu/cm3
-0.06 x 1014
-0,)4 x io14
-0,68 x 1014
14 -0,)4xJO
-0,42 x io14
-1.99 x 1014
102
The best calculated { 00 value for Cu+ is -17 .o57 • The calculated
nuclear quadrupole coupling constant due to both ionic and covalent
-10 -24 14 14 m 4.8xl0 x0.16xlO ((1.2)3.95xl0 -(18)xl.99xl0
6. 627xl0 -'Z?
• -36.o MHz
for no d1J'- d11" bonding and•30.53 MHz for the assumed d-r- d1"' bonding
case, It was also observed that there were two resonance frequencies
for the Cu-a.tom. Following the same procedure, the nuclear quadrupole
coupling constants for the Cu-atom having rCuCl • 3.16 were calculated
to be•J3.6 MHz and•28.03 MHz without d.,,. - d1'"' bonding and with
d1t'- d'fr bonding respectively. The experimentally oooerved values for
the Cu coupling constants are 44.28 and 40.22 MHz. In view of the
uncertainties of both the d.,.- d1Y bonding contribution and the Stern-
heimer effect, the calculated values are in good agreement with the
observed values. One must finally point out that the difference between
the calculated and observed values for two different sites are in excellent
agreement, and indicate that the model used is a reasonable one,
The resonance frequency for both eu63 and 65eu in tris(N•,N-
dimethylthiourea)copper(I)chloride were observed at 38.804 and 36.825 MHz.
The crystal structure has been determined by Amma 48 •49 , Figure 2.5. It
revealed a discreet tetrahedral structure with the Cu atom at the
tetrahedral site. The bond lengths of the Cu-S bonds are the same and 0 they form angles of 112 with the Cu-Cl bond, 'Ihe bond directions in
103
Figure 26
Structure of Bonds in Cu(dmtu)3c1
104
an arbitrary x, y, z axis are given in Table XX VIII, and shown in
Figure 26,
An sp3 hybrid scheme is adopted in evaluating the EFG tensor
com"Ponents at the Cu-a.tom in this system. The four hybrid orbitals
are obtained by em"Ploying the same method as was used for the bis{thiourea)-
Copper(I)chloride and are given by
tifJ l • 0,5 s + 0.866 Pz
'IJ 2 ... 0. 5 s + 0. 66 p - 0. 317 p x z d~ • 0.5s - 0.245 p + 0,707 p - 0.)17 p .... 3 x y z l/J4 - 0,5 s - 0,245 p - 0,707 p - 0,317 p x y z
The values for the contribution of a single electron to the principal
Z-EFG tensor component in each of the hybrid orbitals were calculated as
before and are given in Table xxrx. From the electronega.tivity differences, 'nle ionicity of the
Cu-S bond is estimated to be 13.5% and that of the Cu-Cl bond is
estimated to be 3~. Assuming an equal distribution of electron density
in each of the Cu-hybrid orbitals bonded to sulfur atoms, the charge
densities of the Cu and S-orbitals are estimated and given in Table XXX. cov
The (q ) for the Cu-atom is then calculated to be ' zz cu (-0.94) x io14 esu cm-3. Using the same Sterheimer shieldin~ constant
cov for the Cu-open shell system, the ob~~rverl (qzz)cu is e~~?"Pssed,
(q )Cov = ( ) Cov ( ) zz obs qzz cal 1 - Roo
14 -1 ~ 1.2 x (-0.04) ~ JO esu cm ·
.. -1 1.., , 014- "" ~ J •. ) x ,, .. Sil, cm
10.5
TABLE XXVII
Bond Direction of Cu-Sand Cu-Cl Bonds With Respect to x, y, z Axis System
x y z
eu-s1 98.54 109.5? 112°
Cu-52 98°.541 109° .571 112°
Cu-SJ 98°.541 109°.571 112.0
Cu-Cl 900 90° 00
106
FIGURE~
Orientation of Cu(dmtu)3c1
107
TABLE XXVIII
The Contribution of a Sin~le Electron in a Hybrid -orbital to the Z-EFG Tensor Component
Bond (orbital)
Cu-s1 (I/I 2)
cu-s2 (I/' 3)
eu-s3 ( , 4)
Cu-Cl ('11)
d yz d xy
0,7 x 1014 esu/cm'3
1. 24 x 1014
1.24 x io14
6 14 - .13 x 10 J4
2.32 x 10
14 -1.16 x 10
-1.16 x io14
108
TABLE xxrx Est1mated Orbital Populations and Charge Densities
No - d1r -dfJ'" bonding with cir - d'1'" bonding
'/' 1 0.87 0.87
.,,, 2 0,87 o.87
"' 3 0,87 o.87
'1'4 0.70 0,70
J •cs1) o.87 O.J?
J+(S ) 2
0.87 0.37
J +(s3) o.~7 -+o.J7
J-(Cl) -0.3 -0,3
J-(Cu) -2.31 -1.31
71'1 0,5
1i 2 0.5
109
Again, the ionic contr1bution of the sulfur and chlorine atoms
must be considered. The ionic contributions to q)zz are calculated by
using the same procedure used for Cu(tu)2c1 and are t~bulated in Table
XXXI.
The observed EFG-Z components due to ions is rel~ted to the
calculated value as followss ionic
Q.zz)obs ionic {
= qcal (l- a> )
= 18 x ( -0.764)
a -13.75 x 1014 esu/cm3 14 J For no d Tt - d 11"' and -7. 9 x 10 esu/cm for d,,. - d11' respectively. The
nuclear quadrupole coupling constant due to both ionic and covalent
contributions is 2 ionic cov
=e Qq ( qobs + qobs )
• 4.8 xlOlO x 0.16 x lo-24 (-13.71 6.6'2:1 x 10-'Z'l
·. • -17 .'2:1 MHz
- 1.1'3 )
for no d11' -d'Tt' and -10.45 NH~ for dw - dn respectively. These estimated
values are considerable lon~r than the experimentally observed value,
77.6 MHz. The reason for the difference is not yet known. Further in-
formation regarding the details of the crystal structure is needed
before any conclusions can be drawn.
C) Molybedenum Oxyhalides 95 Table XVII tabulated the observed frequencies for Mo or
Mo97 a.lonp; with the obst..:::·:cd. c135 frcc;,uencies for Mooc14 and Moo2c12.
For one of the Mo ~.&o<.opes, both of which have a nuclear spin, I=5/2,
J •cs2)
S •cs ) 3
A-(Cl)
d xy
d yz
d 2 z
Total
110
TABLE XXX
Ionic Contribution of Cl, S and Cu to q ) zz
w1 th no -d -d
14 3 -0 .186 x 10 esu/cm
14 3 -0.186 x 10 esu/cm
-0.186 x 1014 esu/cm3
14 1 -0,204 x 10 esu/cm
-f4,64 x 1014
-2.32 x 1014
14 .+4.64 x 10
-o. 764 x io14
with -d -d
-0,079 x 1014 esu/cm3
-0.079 x 1014
-0. 079 x 1014
-0,204 x 1014
+J,48 x 1014
-1.74 x 1014
14 -l.74xl0
-4, 64 x 1014
14 i4.64 x 10
-o.441 x 1014
111 2 the values of (e Qq)zz and ~were obtained from the experimental frequen-
cies by u~e of the series approximation for the transition frequencies 54 .
given in Table II. NMR studies hav~ shown the ~tic of the moments ,
Mo95; Mo97 to be equal to 9.J. From this ratio and the observed Mo fre-
quencies, one should expect to observe the other pair of frequencies
at either approximately 300 MHz or 3 MHz, both of which are beyond the
operating range of the spectrometer, The: assignment of the observed
frequencies to a particular isotopic species is therefore impossible
at the present time, We have also investigated a number of other Mo-
compound and were unable to observe any resonances, The limited number
of observation severely restrict the discussion of any relationships
of the observed frequencies to the bonding properties. We have, how-
ever opened up an interesting field for further studies,
·'
1.
2.
3.
4,
5. 6.
7.
8,
9.
10.
11.
12.
13.
14.
112
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