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Study of the mutual influence of ligands in cobalt(II) complexes containing thiocyanate and imidazole derivatives
ELSEVIER
htorganicaChimicaActa 255 t 1997) .343-349
Study of the mutual influence of ligands in cobalt(Ii) complexes containing thiocyanate and imidazole derivatives Anna Maslejova a,,, Stanislava Uhrinova a Jerzy Mroziriski b, Bogumita :Zurowska b.., Mad Carmen Munoz c, Miguel Julve d.. ~LDepartment of Inorganic Chemistry, Slovak Technical University. 81237 Bratislava. Slovakia b Faculty of Chemistry. University of Wroclaw, 50383 Wroclaw. Poland Departamento de Fisica Aplicada, Universidad PoliMcnica de Valencia. Camino de Vera s/n, 46071 Valencia, Spain a Departament de Quimica inorganica, Facultat de Quhnica de la Universitat de Valencia. Dr. Moliner 50, 46100 Burjassot (Valencia). Spain
Received6 February 1996; revised24 May 1996
Abstract The cobalt(ll) complexes of formula [Co(NCS)2L,~] and [Co(NCS)2L'4] (L=imidazole (iz) derivatives, l-Meiz (1), 2-Meiz (2), 2Etiz (3), 2-1sopropiz (4), 2-Pheniz (5), 1,2-Me2iz (6), Biz (7), 2-Mebiz (8), 2-Etbiz (9); L' = iz (10), l-Meiz (11) ) have been synthesized and characterized by spectroscopic methods and magnetic measurements, The crystal and molecular structures of complexes 6 and 11 have been determined by X-ray diffraction methods, Complex 6 crystallizes in the orthorhombic space group Pnma with cell constants a = 9.209(3), b = 12.462(5), c = 14.851(3) A; V= 1704.3(9) A 3, D (calc., Z = 4 ) = 1,43 g c m -3, /14,=367.35, F(000) =640, h(Mo Kt~) =0.71079 A, /z = 11.2 cm- ~and T= 293 K. Complex 11 crystallizes in the monoclinic space group P211n with cell constants a = 7,689(2), b--- 11.095( 1 ), c = 14.156(2) A, fl=93.46(2)°; V= 1205.4(3) A 3, D (calc., Z = 2 ) = 1.39 g cm -3, M,= 503.51, F(000) =534. A(Mo Kt~) =0.71079 ,A, /~= 8.56 cm- t and T= 293 K. 2553 (6) and 2485 ( I1 ) reflections were collected over the range I _<0_< 25; from these, 1571 (6) and I977 ( 11 ) ( independent and with ! > 3o'(I) ) were used in the structural analysis. The final value of the Rw residual was 0.077 and 0.042 for 6 and 11, respectively. The structure of 6 is built up by [ Co(NCS) 2( 1,2-Meaiz) 2] mononuclearunits where the metal atom exhibits an approximately tetrahedral configuration: the Co-N bond distances and N--Co-N bond angles vary in the range !.958(8)-!.922(8) ,~ and I14,7(3)108,3(3) °, respectively. The structure of 11 consists of [Co(NCS)2( l-Meiz)4] monomeric units where two N-coordinated thiocyanate groups in trans position and four l-methylimidazole ligands build a slightly distorted CoN6 octahedral environment. The Co-N bond lengths lie in the range 2.158(2)-2,135(3) A being significantly longer than the related ones observed in 6. Keywords: Cobalt(!!) comptexes;Crystal sWdctures;Thiocyanatecomplexes:Imidazolecomplexes:Magneticproperties
1. Introduction Some years ago, Darby and Vallarino [ 1 ] investigated the electronic and vibrational spectra of cobalt(II) complexes with methyl-substituted pyridines in order to establish a general relationship between the electronic steric requirements of the ligands and the stoichiometry, stereochemistry and stability of the resulting species. The main conclusions from their work are as follows: (i) the limiting stoichiometry of the complexes is dictated by the sterie requirements of the substituted pyridine, the maximum number of coordinated ligands being four, two and one for the unhindered, monohindered and doubly-hindered pyridines, respectively; (ii) the geometry of the Co(II) ion results from a fine balance of * Conespondingauthors. 0020-1693/97/$17.00 © 1997ElsevierScienceS.A. All rights reserved Pll S0020- i 693( 96 )05 387-X
several factors, among which the crystal field stabilization energy and the ionic lattice energy play a predominant role. Smaller aromaticity and thus longer bonds in the case of imidazole compared with pyridine shift the substituent into the a-position, so that for thiocyanato-nickel(ll) complexes with imidazole and its derivatives it does not exhibit sufficient steric effect [2]. Thiocyanato-containing nickel(ll) complexes with 2-methyl- and 2-ethylbenzimidazole, with both positions around the donor atom substituted, show an asqaare-planar arrangement o f donor groups around N i ( l l ) , in contrast to complexes with other substituted imidazoles which exhibit a pseudooctahedral geometry. In this framework it appeared to be interesting to study the conditions of the formation of thiocyanate-containing cobalt(lI) complexes with imidazole derivatives and to investigate the influence of steri¢ properties on the stoichi-
344
A. Maslejovaet aL / lnorganica ChimicaActa 255 (1997)343-349 (10 mmol, 10 cm 3) and KNCS (20 mmol, 30 cm 3) under continuous stirring. Complexes 1-7 separated immediately as polycrystalline products, which were filtered off, washed with diethyl ether and dried over KOH in a dessicator, Blue parallelepiped single crystals of 6 were grown from its mother liquor by slow evaporation at room temperature. Compounds 8 and 9 were prepared in a similar manner but using ethanolic solutions of C o ( N C S ) 2 (10 mmol dissolved in a minimum amount of solvent) and methanolic solutions of either 2-Mebiz (8) or 2-Etbiz (9) (20 mmol, 20 e l 3 ) .
ometry as well as on the stereochemistry of the resulting species. We now report the preparation, spectroscopic and magnetic characterization of a series of complexes of general formulae [ C o ( N C S ) : L , ] and [Co(NCS)2L'41 where L = i m i d a z o l e (iz) derivatives, l-Meiz (1), 2-Meiz (2), 2Etiz (3), 2-Isopropiz (4), 2-Pheniz (5), 1,2-Me2iz (6), Biz ( 7 ) , 2-Mebiz (8), 2-Etbiz (9) and L ' = i z (10), 1-Meiz (11). The crystal and molecular structures of the complexes 6 and 11 are also reported herein.
2. Experimental
2.2.2. Complexes [Co(NCS)2L'4] (10 and 11) These complexes were prepared as follows. An ethanolic solution of L' (60 mmol, 20 cm 3) was added to an ethanolic solution of C o ( N C S ) 2 ( 10 mmol dissolved in a minimum amount of EtOH). 10 and 11 separated immediately as pink crystalline solids which were filtered off, washed with diethyl ether and dried over KOH in a d~'~s.icator. Prismatic single crystals of 11 were grown from the mother liquor by slow evaporation at room temperature,
2.1. Reagents Imidazole and its derivatives were purchased from commercial sources and used as received. Ethanolic solutions of C o ( N C S ) 2 were prepared by reaction of stoichiometric amounts of C o ( N O 3 ) ~ - 6 H 2 0 and KNCS dissolved in the minimum volume of ethanol. The white precipitate of KNO3 was removed by filtration. Elemental analysis (C, H, N) was performed on an automatic Carlo Erba elemental analyzer. The cobalt content was determined chelatometrically using murexide as indicator. The formula, color and analytical data of the isolated complexes are given in Table !.
2.3. Physical measurements IR spectra were taken on a Philips analytical PU 9800 FTIR spectrometer as KBr pellets in the 4000--200 c m - ' region and the electronic spectra were recorded as diffuse reflectance on a Beckman UV 5240 spectrophotometer in the region 25 000-4000 c m - J using MgO as reference. X-band EPR spectra on polycrystalline samples were obtained on a Brtiker ER 200E-SRC spectrometer in the temperature range 77-300
2.2. Synthesis 2.2.1. Complexes [Co(NCS)2Lz] (1-9) Compounds 1-7 were prepared by adding a methano!ic solution of the corresponding imidazole l igand (20 mmol, 20 cm 3) to an aqueous solution containing C o ( N O 3 ) 2 . 6 H 2 0 Table I Analytical data of thiocyanatocobalt(II) complexes with imidazole (1-11) Compound
MW Color
%C calc. found
%H calc. found
%N calc. found
%Co calc. found
1
Co(NCS)2(I-Meiz) 2
2
Co(NCS)2(2-Meiz) 2
3
Co(NCS):(2-Etiz)2
4
Co ( NCS ).,( 2- lsopropiz).,
5
Co(NCS)2(2-Pheniz)_
6
Co(NCS)2(1,2-Me2iz) 2
7
Co(NCS)2(Biz) z
8
Co(NCS)2(2-Mebiz)2
9
Co(NCS)2(2-Etbiz)2
339.32 blue 339.32 blue 367.36 blue 395.42 blue 463.46 blue 367.36 blue 41 !.38 blue 439.42 blue 467,48 blue 447,42 pink 503.54 pink
35.40 35.32 35.40 35.34 39.23 39.37 42.53 41.50 51.83 51.50 39.23 39.15 46.7 i 47.18 49.20 49.16 51.39 50.7 ! 37.58 36.74 42.94 41.70
3.57 3.50 3.57 3.56 4.39 4.34 5.10 5.00 3.48 3.45 4.39 4,36 2.94 2.88 3.67 3.61 4.31 4,32 3.61 3.83 4.81 4.70
24.76 24.74 24.76 24.98 22.88 22.61 21.25 20.69 18.13 18. I I 22.88 22.67 20.43 20.18 19.13 19.11 17.98 17.65 31.24 31.50 27.82 27.80
17.37 17. I0 17.37 17.35 16.04 !6.01 14.90 14.58 12.72 12.65 16.04 15.84 14.33 14.10 13,41 13.10 12.61 12.45 13.17 13. i 0 I 1.70 11,90
Compound no.
10
Co(NCS)5(iz)4
11
Co(NCS)~( i-Meiz)4
A. Maslejova et al. /hwrganica ChimicaAcre 255 (1997) 343-349
345
Table 2 Crystallographic data for ICo(NCS)+.( 1,2-Me2iz)~_[ (6) and ICo(NCS)_+(l-Meiz)4] (I1)
Chemical formula Formula weight Crystal system a (A) b (,~) c (A) /3 (°) V (/~3) Z Space group T (°C) D~,~ (gcm- ~) Radiation, A (,~) F(000) /.~(cm- ' ) Scan method Scan speed (° min-L) Scan range (°) No. collected reflections Cutoff observed data No. observed reflections No. refined parameters R a = R, ~
6
11
C12Hl~N6CoS+. 367.35 orthorhombic 9.209(3) 12,462(5) 14.851(3) 90.0 1704.3(9) 4 Prima 20 1.43 graphite monochromatedMe Ka. 0.71079 640 11.2
C,,H~N,~CoS+ 503.54 monoclinic 7.689(2) 11.095( I ) 14.156(2) 93.46(2) 1205.4(3) 2 P2, / n 20 1.39 graphite monochromated Me Ka, 0.7!079 534 8.56 0>-20 547 2 <20~50 2485 3o {I ) 1977 144 0,042
'1 R = E( I IF.I - IF~I I ) / E ( IFol ).
"R, = unit weight was used.
K and 0--I T magnetic field range. Solid DPPH was used as an external standard. Magnetic susceptibility measurements in the temperature range 8 0 - 3 0 0 K were carried out by using the Gouy m e t h o d on a sensitive Cahn RM-2 electronic balance at a magnetic field strength of 9.9 kOe. The apparatus was calibrated with mercury tetrakis(thiocyanato)cobaltat¢ ( I I ) , for which the magnetic susceptibility was taken as 1 6 . 4 4 × 10 -6 c m ~ g - t [3]. Corrections for the diamagnetism of the constituent atoms were made by the use o f Pascal constants [ 4]. The effective magnetic m o m e n t for the complexes is calculated through the expression/.~fr = 2.83 (xmT) t/2 ( B M ) using 4 3 0 x 10 -6 c m ~ m o l - i as the value of the temperature-independent paramagnetism per C o ( I I ) in a tetrahedrai field.
2.4. X-ray structure determination o f complexes 6 and 11 Crystals o f 6 and 11 of approximate dimensions 0.1 x 0 . 2 × 0 . 2 and 0.1 × 0 . 1 × 0 . 2 m m , respectively, were m o u n t e d on an Enraf-Nonius C A I M diffractometer and used for data collection. Information concerning crystallographic data collection and refinement o f the structures is given in Table 2. T h e unit cell parameters of 6 and 11 were determined from least-squares refinement of the setting angles o f 25 reflections in the range 0 8-14 °. Three standard reflections, which were measured every 2 h as orientation and intensity control, showed no significant variations during data collection. T h e 2 0 range for data collection was 2 - 5 0 °, the index
ranges o f data collection being 0 < h < 14, 0 < k < 10 and 0 ~ l < 17 (6) and 0 < h < 9 , 0 _ < k < 13 and - 1 6 < l _ < 1 6 (11). Intensities were corrected for Lorentz and polarization effects but not for absorption. Th~ structures were solved by standard Patterson m e t h o d s and subsequently completed by Fourier recycling. All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were located from a difference synthesis and Table 3 Final atomic coordinates for non-hydrogen atoms and equivalent isotropic displacement parameters b for complex 6 Atom
xla
ylb
zlc
U~q
Co( l ) S( I ) S(2) N( 1) N(2) N(3) C( l ) C(2) C(3) C(4) C(5) C(6)
0.0337(i ) 0.1 ]90(3) 0.5234(3) 0.0560(9) 0.2277(9) -0.0741(8) -0.2366(7) 0.0807(9) 0.351 I(10) -0.1707(7) -0.2190( ! 1) -0.3532(7) -0.1505(12)
C(7)
- 0.0629(14)
0.25000 0.25000 0.25000 0.25000 0.25000 0.3724(6) 0.4937(5) 0.25000 0.25000 0.4306(6) 0.4365(9) 0.5648(6) 0.4613(I0) 0.3958(8 )
0.02635(8) -0.2845(2) 0.1019(2) -0.1023(5) 0.0804(5) 0.0745(7) 0.1100(8) -0.1798(6) 0.0902(5) 0.0648(6) -0.0396(4) 0.1189(5) 0.1999(6) 0.1803(6)
00562(5) 0.0774(8) 0.0798(8) 0.078(2) 0.081(2) 0.124(3) 0.129(4) 0.060(2) 0.062(2) 0.084(2) 0.119(4) 0.081(2) 0.I 12(3) 0.112(3)
N(4)
a E.s.d.s are given in parentheses. U values for anisotmpically refined atoms ~ given in the form of the isotropic equivalent thermal parameter U~ = !/3( U, t + U_ + U33).
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A. Maslejova et al. I lnorganica Chimica Acta 255 (I997) 343-349
refined with an overall isotropic thermal parameter using a riding model for computed atoms. The final fullmatrix least-squares refinement minimizing the function Ew( tFol - IF~i )2 (iFol and IF~I are the observed and calculated structure factors), each reflection being assigned a unit weight, converged at R = R~ indices of 0.077 and 0.042 for all observed reflections. Maximum and minimum peaks in the final difference synthesis were 0.86 and - 0.57 e A, - 3 Table 4 Final atomic coocdinatesfor non-hydrogen atoms and equivalentisotropie displacementparameters b for complex 11 Atom
x/a
y/b
z/c
U~
Co(I) S(1) N(i) N(2) N(3) N(4) N(5) C(I) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9)
0.00000 0.3265(2) 0.1661(3) 0.2792(3) 0.1412(3) 0.3587(3) 0,1751(4) 0.3112(4) 0,3819(4) 0.1510(4) 0.3058(5) 0,1104(4) 0.2458(4) 0.2934(4) 0.5270(5) 0.2388(4)
0.00000 0.3382(I) -0,0204(2) 0.0047(2) -0.1414(2) -0.2377(2) 0.1294(2) -0.0927(3) -0,0774(3) 0.0358(3) 0.0517(4) -0.2620(3) -0.3222(3) -~.1303(3) -0.2598(4) 0.2]53(3)
0.00000 -0.1187(1) 0.1274(2) 0,2731(2) -0.0647(2) -0.1232(2) -0.0530(2) 0.1409(2) 0.2304(2) 0.2084(2) 0.3688(2) -0,0621(2) -0.0989(2) -0.1024(2) -0.1657(3) -0.0802(2)
0.0386(3) 0.0904(6) 0.0445(8) 0.0514(8) 0.0427(8) 0.0523(8) 0.0550(8) 0.0541(9) 0.0576(9) 0.0494(8) 0.0713(9) 0.0491(8) 0.0565(9) 0.0525(9) 0,0832(9) 0.0462(8)
E.s.d.s are given in parentheses. h U values for anisotropically refined atoms are given in the form of the isotropic equivalentthermal parameter U~q= 1/a f U~~+ U2~+ U3.~). Table 5 Bond distances (/~) and angles (°) for complex6 ~
Table 6 Bond distances (/~) and angles (°) for complex 11 a Cobalt environment Co(I)-N(i) Co( 1)-N(3)
2.158(2) 2.135(3)
Co(I)-N(5)
2.145(2)
N( I)-.Co(I)-N(3) N( I)--Co( I )-N(5)
89.5(1) 99.6(1)
N(3)-Co( I )-N(5)
89.8(I)
l-Meiz ligand N( 1)-C( I ) C( ! )-C(2) C(2)-1"(2) N(2)-CI4) N(2)-C(3) C(3)-N(I)
1.378(4) 1.358(4) 1.370(4) 1.455(4) 1.349(4) 1.318(4)
N(3)-C(5) C(5)-C(6) C(6)-N(4) N(4)-C(8) N(4)-C(7) C(7)-N(3)
1.359(4) 1.366(47 1.337(47 1.479(4) 1.333(4) 1.321(4)
C(3)-N( ! )-C( I ) N( I)-C( 1)-C(2) C( I )-C(2)-N(2) C(2)-N(2)-C(4) C(2)-N(2)-C(3) C(4)-N(2)-C(3) N(2)-C(3)-N(I)
105.5(2) 109.4(3) 106.6(3) 126,6(3) 106.7(2) 126.6(3) 111.7(3)
C(7)-N(3)-C(5) N(3)-C(5)-C(6) C(5 )-C~6)-N(4) C(6)-N(4)-C(7) C(6)-N(4)-C(8) C(8)-N(4)-C(7) N(4)-C(7)-N(3)
105.3(3) 109.4(3) 106.1(3) 108.1(3) 125.9(3) 126.0(30) 111.1(3)
Thiocyanateiigand S(!)-C(9) S( I )-C(9)-N(5)
1.629(3) 179.2(3)
C(9)-N(5) Co(I )-N(5)-C(9)
1.149(4) 165.1(3)
E.s.d.s are given in parentheses. for 6 and 0.78 and - 0 . 5 6 e • - 3 for 11. Max, shift/e.s.d is 0.1. f , f ' and f ' were taken from Ref. [5]. All calculations were performed by using the SHELX-86 [6] and SHELX76 [7] programs. The molecular plots were drawn using the SCHAKAL [ 8] program. The final atomic coordinates for non-hydrogen atoms with isotropic temperature factors and bond lengths and angles for complexes 6 and 11 are listed in 'Fables 3-6.
Cobalt environment Co( I )-N( 1) Co( I )-N(2)
1.922(8) 1.958(8)
Co(I)-N(3)
1.955(7)
3. Results a n d d i s c u s s i o n
N(I)-Co(I)-N(2) N(I)--Cotl)-N(3)
108.1(3) 114.7(3)
N(3)---Co(1)-N(2)
108.3(3) 102.5(3)
3. i. Description o f the structures
N(3)-Co(I)-N(3i) h
1,2-Me~izligand N(3)-C(3) C(3)-C(4) C(3)-N(4) N{4)-C(5)
1.16(1) 1.61(1) 1.20(1) 1.398(9)
N(4)-C(6) C(6)-C(7) C(7)-N(3)
1.60( I ) 1.18(I) 1.60( i )
C(7)-N(3)-C(3) N(3)--C(3)-N(4) N(3)-C(3)-C(4) C(4)-C(3)-N(4) C(3)-N(4)-C(5)
93.3(8) 137.0(1) 111.0{9) 111.6(9) 149.0(9)
C(3)-N(4)-C(6) C(5)-N(4)-C(6) N(4)-C(6)--C(7) C~)--C(f)-N(3)
92.9(8) 117.4(9) 107.8(9) 108.8(9)
Thiocyan~eligand S(i)-C(ll C(I)-N(I)
1.595(9) 1,17(i)
S(2)-C(2) C(2)-N(2)
1.596(9) 1.15(I)
S(i)-C(I)-N(I) Co(1)-N(I)-C(I)
178.4(9) 174.9(8)
S(2)-C(2)-N(2) Co(I)-N(2)-C(2)
178.8(8) 163.2(8)
a E.s.d.s we given in parentheses. hi=x, 0.5-y, z.
3.1.1. [Co(NCS)z( I,2-Me2i: ~zl (6) The structure of complex 6 consists of discrete [Co(NCS)2(1,2-Me2iz)2] mononuclear units (Fig. l) which are held together by van der Waais forces. The coordination of the cobalt atom is very nearly tetrahedral with four nitrogen atoms, two from monodentate thiocyanate groups and the other two from two 1,2-dimethylimidazol¢ ligands, building the CoN 4 chromoph.~rc. The largest deviation from the tetrahedral angle is 7.0 ° at the N ( 3 ) C o ( I ) - N ( 3 i) ( i = x , 0 . 5 - y , z) angle. A mirror plane contains the metal atom and the two thiocyanate groups, the whole molecule having a Cs symmetry. The C o N(thioeyanate) bond distances are slightly different ( 1 , 9 2 2 ( 8 ) and 1,958 A for Co( 1 ) - N ( 1 ) and Co( 1 ) - N ( 2 ) , respectively) but they agree well with those observed in the structurally characterized tetrakis (thiocyanato) cobaltate (II) complexes ( C o - N mean bond lengths from !.958(12) to
A. Maslejova et al. / Inorganica Chimica Acta 255 (1997) 343-349
347
N(thiocyanate) bond (2.145 (2) A for Co( I ) - N ( 5 ) ) is also longer than that observed in 6 as expected. The bond distances and bond angles within l-methylimidazole can he considered as normal and are very close to those observed in 6 for 1,2dimethylimidazole. The imidazole skeleton is planar as expected and the dihedral angle between adjacent imidazole planes is 94.4 °. As far as the thiocyanate lignnd is concerned, it is practically linear (179.2(3) ° for N ( 5 ) - C ( 9 ) - S ( 1 ) ) and a significant bending is observed in the Co-N-C(S) linkage (165.1(3) ° for C o ( 1 ) - N ( 5 ) - C ( 9 ) ) as in the preceeding structure. The shortest intermolecular metabmetal separation (Co( 1)-..Co(li), i = 0.5 +x, 0.5 - y , 0.5 + z ) is 9.561 ~,. Fig. I. Perspective drawing oflhe complex [Co(NCS)2( 1.2-Me2iz),.] (6), showing the atom numbering. Hydrogen atoms were omitted for the sake of
3. 2. Infrared and electronic spectra
clarity. 1.967(4) A) [9]. The Co-N(disubstituted imidazole) bond distance is 1,955(7) A, a value which is very close to that observed in other imidazole-containing cebait(II) complexes with the metal atom in a tetrahedral surrounding [ 10-15 ]. The imidazole rings are planar as expected (the largest deviation from the mean plane is 0.023/~ at C(3) atom) and they form a dihedral angle of 87.37 °. Bond lengths and angles within the imidazole rings are in good agreement with the parameters reported for the structure of imidazole itself'determined at - 150°C [ 16] and will therefore not he discussed in detail here. The NCS groups are almost linear (178.4(9) and 178.8 (8)° for S( 1)-C( 1 )-N( 1 ) and S(2)-C( 2 ) - N ( 2 ) , respectively), whereas a significant bending is displayed by the Co-N-C(S) linkages (174.9(8) and 163.2(8)° for Co( I ) - N ( l)--C( 1) and Co( I ) - N ( 2 ) - C (2), respectively). The shortest intermolecular metal-metal separation (Co(1)--.Co(li), i = - x , - y , - z ) is 6.311/~. o
3.1.2. [Co(NCS)2(I-Meiz)4] (11) The structure of complex 11 is made up of neutral and centrosymmetric [Co(NCS)2( l-Meiz)4] monom~fic entities (Fig. 2) which are linked by van der Waals interactions. The cobalt is six-coordinate with two thiocyanate-nitrogen atoms in trans positions and four l-Meiz-nitrogens building an almost undistorted octahedral CoN6 polyhedron. The CoN(imidazole) bonds (2.158(2) and 2.135(3) A) are significantly longer than that reported for 6 and other tetrahedral Co--N(imidazole) distances [ 10-15] but they are closer to octahedral Co-N(imidazole) bonds [15,17-22]. The C o -
Fig. 2. Perspective drawing of the complex [Co(NCS)2( l-Meiz)4l (11), showing the atom numbering. Hydrogen atoms were omitted for clarity.
In the con,plexes studied (Table I ) the asymmetric stretchmg vibration of yen was observed in the range 2058-2112 cm- ~ as an intensive, very strong band sometimes expressively split or rarely with a shoulder. The bands ofcG~nplexes with substituted imidazoles are broader and for complexes with a-substituted ligands an expressive splitting of tim band yen into two peaks was observed. The value of this splitting decreases in the order Co(NCS)2(2-Meiz)2 (39 cm- ~) > Co(NCS) z(Pheniz)2 (22 cm- ~) > Co(NCS)z(2Mebiz) 2 ( 19 cm- ~) > Co (NCS) 2( 1,2-Meziz):t ( 18 cm- l). The more the steric hindrance increases, the higher is the value of this splitting. Considering the position of the band VcN it may be assumed that the thiocyan~.te group is endbonded by its nitrogen atom [23]. In the region of the symmetric stretching vibration Vcs band, out-of-plane deformation vibrations of the C-H band in iraidazole are also found and they can interfere. The band belonging to the Vcs vibration in the interval 770-853 erawas determined using the value [24] of band frequency of the combined vibration ~'cn + ~'cs as indicated in the nitrogen bonded NCS group [25 ]. The values of wavenumber may exclude S-coordination for all rite complexes. The band belonging to the deformation vibration ig~cswas found in range 465-496 eraThe absorptions in the 400-200 cm-~ region have been assigned toCo-NCS and Co-N(L) vibrations (Table 7).For the pseudotetrahedral (C~,) complexes, Co(NCS)zL2, two IR active metal-thiocyanate stretching vibrations are expected in far-IR region [26] and two are indeed observed. Of the two expected Co N(L) stretching vibrations, bowever, only one is observed. Electronic spectral data are given in Table 8. To calculate Dq and B the transition energies are based on the centers of intensity of these bands, The ligand field spectra of the Co(NCS)2L2 complexes are typical for pseudoteta'ahedral ligand arrangements around Co(H). In each of the spectra two sets of bands can be distinguished, one in the visible and the other in the near-IR region. The former multiple absorption appears between 16 800 and 17 100 cm - t and may be attributed to the 4A2 - , 41",(P) wansition. Splitting of the band is probably due
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A. Maslejova et aL / hwrganica Chimica Acta 255 (1997) 343-349
Table 7 Infrared spectra of thiocyanatocobalt(I1) complexes with imidazole
Compound
Ucr~
l'cs
t~NCS.
PC~F-NCS
I'~Ct~N(L)
Co(NCS)2( I-MeizL, Co(NCS)_,(2-Meiz)_, Co(NCS),(2-Etiz)_, Co( NCS ),_(2-1sopropiz) ~ Co ( NCS),, (2-Pheniz) =, Co(NCS)-,( 1,2-Me,iz)2 Co( NCS),(Biz) z Co(NCS)_~( 2-Mebiz)_, Co(NCS)2(2-EtbizL, Co ( NCS )., ( iz )4 Co(NCS):( l-Meiz).,
2070 2105. 2068 2097, 2081 2089, 2089 2080. 2058 2076, 2058 2095, 2078 2092, 2073 2095, 2078 2105, 2100sh 2086, 2078sh
843 841 853 831 849 843 843 841 835 845 843
476 478 475 496 475 482 480 482 476 469 475
301,324 280-320 sp 299, 316 300-304 sp 287. 316 301. 324 294, 322 311,327 291,322 249 243
274 260 278 282 268 278 289 289 282 235 223
Table 8 Electronic spectral data of thiocyanatocobalt (ll) complexes with imidazole Compound
Band positions v ( 10-~cm- ~)
Co(NCS)2( l-Meiz)2 Co ( NCS)-, ( 2-Meiz ) =, Co(NCS), (2-Etiz)_~ Co( NCS)_,( 2-1sopropiz ); Co ( NCS )-,( 2- Pheniz) 2 Co(NCS),( 1.2-Me2iz)2 Co(NCS),(Biz)2 Co( NCS )~.(2-Mebiz) • Co( NCS)~ (2-Etbiz), Co(NCS):(iz)4 Co(NCS)~(I-Meiz)4
8.30, 8.20, 8.30, 8.15, 8.05. 8.20, 8.30, 8.30, 8.30. 9.70, 9.50,
16.80 17.10 17.10 17.00 !6.90 17.00 17.10 16.95 16.90 19.00sh, 20.80 19.20sh 20.80
Q~ D
C --, T
Dq (cm- ~)
B (cm- ')
24.3 21.7sh, 23.8 22.2 21.7sh, 24 Ash 22.0 21.9sh 21.7, 23.5 24. I
31.0 32.2 32.05 32.25 31.25 31.9 30.2 31.25 31.7
487 481 486 477 471 480 486 487 487 1092 1069
698 726 721 722 721 720 721 710 706 821 836
0.72 0.75 0.74 0.74 0.74 0.74 0.74 0.73 0.73 0.85 0.86
Table 9 Magnetic data and EPR parameters of thiocyanatocobalt (ti) complexes with imidazole Compound
Curie constant C (cm ~ tool - ~K)
Weiss constant 69 (K)
Magnetic susceptibility I 0~× Xra ( c m~ tool - ~)
t~.~t-(BM) average (77-300 K)
Spectl oscopic splitting factor g (77 K) no line 2.696 ~ 3.72 2.954 3.390 4.055 ~ 7.24 no line 3.145
(r.t.)
Co ( NCS ), ( 1-Meiz) 2 Co(NCS),(2-Meiz), Co(NCS).,(2-Etiz)., Co ( NCS ) ~(2-1sopropiz): Co ( NCS ), (2-Pheniz) 2 Co(NCS)~( 1,2-Me,_iz)~ C,:,. NCS)~(Biz), Co(NCS) 2( 2-Mebiz ) 2 Co(NCS),(2-Etbiz) 2 Co ( NCS ) 2( iz )4 Co(NCS)2( I-Meiz)4
2.36
10.4
2.25 2.55 1.9 ! 2.17 2.1 ! 2.52
il.3 6.1 10.4 12.9 12.4 8.2
8060 8020 8950 6620 7460 7550 8680
2.21
5.7
7510
2.20 2.76 3.07
10.7
7560
4.48 4.37 4.60 4.04 4.33 4.27 4.60 4.28 4.33
- 7.0 - I I. I
8910
4.55
3.866
9840
4.76
3.809
to interaction with the d o u b l e t state through spin-orbit coupling [27 ]. T h e near-IR bands are perceptibly b r o a d e n e d and m o s t o f them s h o w a long tail towards lower wavenuv:bers, Their c o m p l e x i t y is c a u s e d b y the c o m p o n e n t s o f the 4T, ( F ) level, which b e c o m e allowed transitions in C2,, oymmetry [281. T h e electronic spectra o f the c o m p o u n d s C o ( N C S ) 2 L 4 ' exhibit bands c o r r e s p o n d i n g to the transition 4T,g(F) --, 4T2~ at 9 7 0 0 or 9 5 0 0 c m - ~ , respectively, and to the transition
4Tig ( F ) ~ 4Tig ( P ) at 20 800 e r a - ' and a s h o u l d e r at 18 9 0 0 or 19 200 c m j , respectively, being a c o n s e q u e n c e o f s p i n orbit coupling in the state e f ' ~ l ' ~ ( P ) and indicating a pseudooctahedral configuration [ 2 9 ] . The results indicate a greater distortion o f the tetrahedral configuration c o m p a r e d with the o c t a h e d r ~ form. The values o f the D q and B parameters o f C o ( N C S ) 2 ( 2 M e i z ) 2 and C o ( N C S ) 2 ( B i z ) z c o r r e s p o n d with the values o f these parameters calculated using the data for the c o m p l e x e s
A. Ma,¢lejova et al. / Inorganica Chimica Acta 255 (1997) 343-349
[Co(NCS)4] 2-, [301.
[Co(2-Meiz)4] 2+ and [Co(Biz)4l 2÷
3.3. Magnetic properties The effective magnetic moments (Table 9) indicate that the complexes are of the high-spin type. The values for Co(NCS)z(iz)4 and Co(NCS)2(I-Meiz)4 correspond to octahedral structures [31 I. The magnetic moments for Co(NCS)2(2-Etiz).~ 'rod Co(NCS).,(Biz)2 lie in the range 4.4-4.8 BM normally observed for tetrahedral cobalt(U) complexes [ 32]. For the remaining complexes Co(NCS) 2L2, the #e,' values are in accord with tetrahedral stereochemistries, although the /.L,.crvalues lie at the lower end of the overlap region lbr the tetrahedral environment or are lower (below 4.4 BM) than those normally found for tetrahedral complexes. The low magnetic moments observed for Co(NCS)2L 2 (L=2-Mebiz, 2-Etbiz, 2-lzopropiz, 1,2Me2iz) were attributed to superexchange coupling of the cobalt atoms by means of the short symmetrical N-C-N chains which form part of a mobile rr-electron system [33,34].
4. Conclusions From the above results it follows that the same reason non-substituted t~-position ~ leads to the formation of octahedral complexes of the composition Co(NCS)2L4'. If the imidazole derivative has its nitrogen donor atom sterically hindered, the lbrmed compounds have the composition Co(NCS)2L2 with tetrahedral configuration.
5. Supplementary material Tables of thermal parameters, hydrogen coordinates, leastsquares planes (6 pages), and a listing of observed and calculated structure factors (21 pages) are available from the authors on request.
Acknowledgements Financial support from the Slovak Ministry of Education, the State Committee for Scientific Research (Warsaw, Poland) and Spanish DGICYT (Project PB94-1002) is gratefully acknowledged.
349
References [I] W.L. Darby and L.M. Vallarino, inorg. Chim. Acto,48 (1981) 215. [2] A. Maslejova and I. Kovacik, Z Anorg, Allg. Chem.. 604 ( 1991 ) 151. [31 B.N. Figgis and RC. Nyholm, J. Chem, Soc.,(1958) 4190. [4 ] E. K0nig, Magnetic Properlies of CenTrdinatioa and Organometallic Trart~ition Metal Comtnmnds, Springer, Berlin, 1966. [5] International Tables for X-ray Crystallography, Vol. IV, Kynoch, Birmingham, UK, 1974, pp. 99--I lO, 149. [6] GM. Sheldrick, SHEL,Y-86, a computer program for the crystal structure determination, University of G6ttingen, Gernmny, 1986, [7] G.M. Sheldriek, SHELX-76, a computer program for the crystal structure determination, University of Cambridge, UK, 1976. [81 K. Keller, SCHAKAL, a FORTRAN progr~n for the graphic representation of molecular and crystallographic models, University of Freiburg, Germany, 1987. [9l (a) K. Me~itner and A. Preisinger, Acta CrystaUogr., Sect. C, 44 (1988) 1178; (b) J.S. Wood and R.K. McMullan, Acta Crystallogr., Sect. C, 40 (1984) 1803: (c) K. Mereimer and A. Preisiager, Acta Crystallogr., Sect. B, 38 (1982) 1084: (d) M.G.B. Draw and A.H. bin Othman, Acta Crystallogr., Sect. B, 31 (1975) 613. [ 10] A. Gadet, C.R. Acad. Sci., Set. C, 272 ( 1971 ) 1299. [ i i ] C.J. Antti and B.K.S. Lundberg, Acta Chem. Scand., 26 (1972) 3995. [ 12] M. Sturm, F. Brandl, D. Engel and W. Hoppe, Acta Crystaltogr., Sect. B, 31 (1975) 2369. [ 13] A. l..aidoudi, N. Kheddar and M.L. Brians6, Acta Crysrallogr., Sect. B, 34 (1978) 782. [ 14] W.D. Horrocks, J.H. lshley and R.R. Whittle, lnorg. Chem.,21 (1982) 3265. [ 15] W.D. Horrocks, J.H. Ishley and R.R. Whittle, Inorg. Chem., 21 (1982) 3270. [ 16] S. Martfnez-Carrera,Acta C~stallogr., 20 (1966) 783. [ 17] E. Baraniak, H.C. Freeman, J.M. James and C.E. Noc,kodls, J. C/tern. Soc. A. (1970) 2558. [ 18] R. Strandberg and B.K.S. Lundberg, Acta Chem. Scand., 25 ( 1971 ) 1767. [ 19] A. Gadet, C.R. Acad Sci.. Set. C. 274 [ I972) 263. [20] F. Akhtar, F. Heq and A C. Skapski. J. Chem. Sac., Dalton Trans., (1972) 1353. [21 ] R.G. Little, Acta Crystallogr.. Sect. B, 35 (1979) 2398. [22] R.A.J. Dries.sen, F.B. Httlsbergen, W.J, Vermin andJ. Ree~jk, inorg. Chem., 21 (1982) 3594. [23] A.H. Norbury, Adv. lnorg. Chem. Radiochem., 5 (1975) 17, [24] C.I~. Donker, J.G. Haasnoot and W.L. Groeneveld, Transition Met. Chem., 5 (1980) 368. [25] R.J.H. Clark and C.S. Williaras, Spectrochim. Acta, 22 ( 1966~t 1081. [ 26] G. Marcolrigiaao, L. Menabue and G.C. Pellacani, !norg. Clam. Acta, 26 (1978) 57. [27] F.A. Cotton mad M. Goodgame, J. Am. Chem. Soc., 83 ( 196t ) 1777. [28] A.B.P. Lever and S.M, Nelson, J. Chem. So,-. A, (1966) 859, [ 29] AB,P. Lever, I.M. Walker and P.J. McCarthy, fnorg. Chim. Acta. 39 (1980) 81, [30]A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Ar~terdam, 2nd edn,, 1984, pp. 742. 743, [311F.E. Mabbs and DJ. Machin, Magnetism and Transition Metal Complexes, Chapman and Hall, London, 1973. (32] B.N. Figgis and J. Levis, Prog. !norg. Chem., 6 (1964) 37, [331 W.J. Eiibeck, F. Holmes and A.E. Underhitl, J. Chen~ Sac. A, (1967) 757. [ 34] W,J. Eilbeck. F. Holmes, C.E. Taylor and A.E, Unded~ill, £ Chem. .':oc. A, (1968) 128.
htorganicaChimicaActa 255 t 1997) .343-349
Study of the mutual influence of ligands in cobalt(Ii) complexes containing thiocyanate and imidazole derivatives Anna Maslejova a,,, Stanislava Uhrinova a Jerzy Mroziriski b, Bogumita :Zurowska b.., Mad Carmen Munoz c, Miguel Julve d.. ~LDepartment of Inorganic Chemistry, Slovak Technical University. 81237 Bratislava. Slovakia b Faculty of Chemistry. University of Wroclaw, 50383 Wroclaw. Poland Departamento de Fisica Aplicada, Universidad PoliMcnica de Valencia. Camino de Vera s/n, 46071 Valencia, Spain a Departament de Quimica inorganica, Facultat de Quhnica de la Universitat de Valencia. Dr. Moliner 50, 46100 Burjassot (Valencia). Spain
Received6 February 1996; revised24 May 1996
Abstract The cobalt(ll) complexes of formula [Co(NCS)2L,~] and [Co(NCS)2L'4] (L=imidazole (iz) derivatives, l-Meiz (1), 2-Meiz (2), 2Etiz (3), 2-1sopropiz (4), 2-Pheniz (5), 1,2-Me2iz (6), Biz (7), 2-Mebiz (8), 2-Etbiz (9); L' = iz (10), l-Meiz (11) ) have been synthesized and characterized by spectroscopic methods and magnetic measurements, The crystal and molecular structures of complexes 6 and 11 have been determined by X-ray diffraction methods, Complex 6 crystallizes in the orthorhombic space group Pnma with cell constants a = 9.209(3), b = 12.462(5), c = 14.851(3) A; V= 1704.3(9) A 3, D (calc., Z = 4 ) = 1,43 g c m -3, /14,=367.35, F(000) =640, h(Mo Kt~) =0.71079 A, /z = 11.2 cm- ~and T= 293 K. Complex 11 crystallizes in the monoclinic space group P211n with cell constants a = 7,689(2), b--- 11.095( 1 ), c = 14.156(2) A, fl=93.46(2)°; V= 1205.4(3) A 3, D (calc., Z = 2 ) = 1.39 g cm -3, M,= 503.51, F(000) =534. A(Mo Kt~) =0.71079 ,A, /~= 8.56 cm- t and T= 293 K. 2553 (6) and 2485 ( I1 ) reflections were collected over the range I _<0_< 25; from these, 1571 (6) and I977 ( 11 ) ( independent and with ! > 3o'(I) ) were used in the structural analysis. The final value of the Rw residual was 0.077 and 0.042 for 6 and 11, respectively. The structure of 6 is built up by [ Co(NCS) 2( 1,2-Meaiz) 2] mononuclearunits where the metal atom exhibits an approximately tetrahedral configuration: the Co-N bond distances and N--Co-N bond angles vary in the range !.958(8)-!.922(8) ,~ and I14,7(3)108,3(3) °, respectively. The structure of 11 consists of [Co(NCS)2( l-Meiz)4] monomeric units where two N-coordinated thiocyanate groups in trans position and four l-methylimidazole ligands build a slightly distorted CoN6 octahedral environment. The Co-N bond lengths lie in the range 2.158(2)-2,135(3) A being significantly longer than the related ones observed in 6. Keywords: Cobalt(!!) comptexes;Crystal sWdctures;Thiocyanatecomplexes:Imidazolecomplexes:Magneticproperties
1. Introduction Some years ago, Darby and Vallarino [ 1 ] investigated the electronic and vibrational spectra of cobalt(II) complexes with methyl-substituted pyridines in order to establish a general relationship between the electronic steric requirements of the ligands and the stoichiometry, stereochemistry and stability of the resulting species. The main conclusions from their work are as follows: (i) the limiting stoichiometry of the complexes is dictated by the sterie requirements of the substituted pyridine, the maximum number of coordinated ligands being four, two and one for the unhindered, monohindered and doubly-hindered pyridines, respectively; (ii) the geometry of the Co(II) ion results from a fine balance of * Conespondingauthors. 0020-1693/97/$17.00 © 1997ElsevierScienceS.A. All rights reserved Pll S0020- i 693( 96 )05 387-X
several factors, among which the crystal field stabilization energy and the ionic lattice energy play a predominant role. Smaller aromaticity and thus longer bonds in the case of imidazole compared with pyridine shift the substituent into the a-position, so that for thiocyanato-nickel(ll) complexes with imidazole and its derivatives it does not exhibit sufficient steric effect [2]. Thiocyanato-containing nickel(ll) complexes with 2-methyl- and 2-ethylbenzimidazole, with both positions around the donor atom substituted, show an asqaare-planar arrangement o f donor groups around N i ( l l ) , in contrast to complexes with other substituted imidazoles which exhibit a pseudooctahedral geometry. In this framework it appeared to be interesting to study the conditions of the formation of thiocyanate-containing cobalt(lI) complexes with imidazole derivatives and to investigate the influence of steri¢ properties on the stoichi-
344
A. Maslejovaet aL / lnorganica ChimicaActa 255 (1997)343-349 (10 mmol, 10 cm 3) and KNCS (20 mmol, 30 cm 3) under continuous stirring. Complexes 1-7 separated immediately as polycrystalline products, which were filtered off, washed with diethyl ether and dried over KOH in a dessicator, Blue parallelepiped single crystals of 6 were grown from its mother liquor by slow evaporation at room temperature. Compounds 8 and 9 were prepared in a similar manner but using ethanolic solutions of C o ( N C S ) 2 (10 mmol dissolved in a minimum amount of solvent) and methanolic solutions of either 2-Mebiz (8) or 2-Etbiz (9) (20 mmol, 20 e l 3 ) .
ometry as well as on the stereochemistry of the resulting species. We now report the preparation, spectroscopic and magnetic characterization of a series of complexes of general formulae [ C o ( N C S ) : L , ] and [Co(NCS)2L'41 where L = i m i d a z o l e (iz) derivatives, l-Meiz (1), 2-Meiz (2), 2Etiz (3), 2-Isopropiz (4), 2-Pheniz (5), 1,2-Me2iz (6), Biz ( 7 ) , 2-Mebiz (8), 2-Etbiz (9) and L ' = i z (10), 1-Meiz (11). The crystal and molecular structures of the complexes 6 and 11 are also reported herein.
2. Experimental
2.2.2. Complexes [Co(NCS)2L'4] (10 and 11) These complexes were prepared as follows. An ethanolic solution of L' (60 mmol, 20 cm 3) was added to an ethanolic solution of C o ( N C S ) 2 ( 10 mmol dissolved in a minimum amount of EtOH). 10 and 11 separated immediately as pink crystalline solids which were filtered off, washed with diethyl ether and dried over KOH in a d~'~s.icator. Prismatic single crystals of 11 were grown from the mother liquor by slow evaporation at room temperature,
2.1. Reagents Imidazole and its derivatives were purchased from commercial sources and used as received. Ethanolic solutions of C o ( N C S ) 2 were prepared by reaction of stoichiometric amounts of C o ( N O 3 ) ~ - 6 H 2 0 and KNCS dissolved in the minimum volume of ethanol. The white precipitate of KNO3 was removed by filtration. Elemental analysis (C, H, N) was performed on an automatic Carlo Erba elemental analyzer. The cobalt content was determined chelatometrically using murexide as indicator. The formula, color and analytical data of the isolated complexes are given in Table !.
2.3. Physical measurements IR spectra were taken on a Philips analytical PU 9800 FTIR spectrometer as KBr pellets in the 4000--200 c m - ' region and the electronic spectra were recorded as diffuse reflectance on a Beckman UV 5240 spectrophotometer in the region 25 000-4000 c m - J using MgO as reference. X-band EPR spectra on polycrystalline samples were obtained on a Brtiker ER 200E-SRC spectrometer in the temperature range 77-300
2.2. Synthesis 2.2.1. Complexes [Co(NCS)2Lz] (1-9) Compounds 1-7 were prepared by adding a methano!ic solution of the corresponding imidazole l igand (20 mmol, 20 cm 3) to an aqueous solution containing C o ( N O 3 ) 2 . 6 H 2 0 Table I Analytical data of thiocyanatocobalt(II) complexes with imidazole (1-11) Compound
MW Color
%C calc. found
%H calc. found
%N calc. found
%Co calc. found
1
Co(NCS)2(I-Meiz) 2
2
Co(NCS)2(2-Meiz) 2
3
Co(NCS):(2-Etiz)2
4
Co ( NCS ).,( 2- lsopropiz).,
5
Co(NCS)2(2-Pheniz)_
6
Co(NCS)2(1,2-Me2iz) 2
7
Co(NCS)2(Biz) z
8
Co(NCS)2(2-Mebiz)2
9
Co(NCS)2(2-Etbiz)2
339.32 blue 339.32 blue 367.36 blue 395.42 blue 463.46 blue 367.36 blue 41 !.38 blue 439.42 blue 467,48 blue 447,42 pink 503.54 pink
35.40 35.32 35.40 35.34 39.23 39.37 42.53 41.50 51.83 51.50 39.23 39.15 46.7 i 47.18 49.20 49.16 51.39 50.7 ! 37.58 36.74 42.94 41.70
3.57 3.50 3.57 3.56 4.39 4.34 5.10 5.00 3.48 3.45 4.39 4,36 2.94 2.88 3.67 3.61 4.31 4,32 3.61 3.83 4.81 4.70
24.76 24.74 24.76 24.98 22.88 22.61 21.25 20.69 18.13 18. I I 22.88 22.67 20.43 20.18 19.13 19.11 17.98 17.65 31.24 31.50 27.82 27.80
17.37 17. I0 17.37 17.35 16.04 !6.01 14.90 14.58 12.72 12.65 16.04 15.84 14.33 14.10 13,41 13.10 12.61 12.45 13.17 13. i 0 I 1.70 11,90
Compound no.
10
Co(NCS)5(iz)4
11
Co(NCS)~( i-Meiz)4
A. Maslejova et al. /hwrganica ChimicaAcre 255 (1997) 343-349
345
Table 2 Crystallographic data for ICo(NCS)+.( 1,2-Me2iz)~_[ (6) and ICo(NCS)_+(l-Meiz)4] (I1)
Chemical formula Formula weight Crystal system a (A) b (,~) c (A) /3 (°) V (/~3) Z Space group T (°C) D~,~ (gcm- ~) Radiation, A (,~) F(000) /.~(cm- ' ) Scan method Scan speed (° min-L) Scan range (°) No. collected reflections Cutoff observed data No. observed reflections No. refined parameters R a = R, ~
6
11
C12Hl~N6CoS+. 367.35 orthorhombic 9.209(3) 12,462(5) 14.851(3) 90.0 1704.3(9) 4 Prima 20 1.43 graphite monochromatedMe Ka. 0.71079 640 11.2
C,,H~N,~CoS+ 503.54 monoclinic 7.689(2) 11.095( I ) 14.156(2) 93.46(2) 1205.4(3) 2 P2, / n 20 1.39 graphite monochromated Me Ka, 0.7!079 534 8.56 0>-20 547 2 <20~50 2485 3o {I ) 1977 144 0,042
'1 R = E( I IF.I - IF~I I ) / E ( IFol ).
"R, = unit weight was used.
K and 0--I T magnetic field range. Solid DPPH was used as an external standard. Magnetic susceptibility measurements in the temperature range 8 0 - 3 0 0 K were carried out by using the Gouy m e t h o d on a sensitive Cahn RM-2 electronic balance at a magnetic field strength of 9.9 kOe. The apparatus was calibrated with mercury tetrakis(thiocyanato)cobaltat¢ ( I I ) , for which the magnetic susceptibility was taken as 1 6 . 4 4 × 10 -6 c m ~ g - t [3]. Corrections for the diamagnetism of the constituent atoms were made by the use o f Pascal constants [ 4]. The effective magnetic m o m e n t for the complexes is calculated through the expression/.~fr = 2.83 (xmT) t/2 ( B M ) using 4 3 0 x 10 -6 c m ~ m o l - i as the value of the temperature-independent paramagnetism per C o ( I I ) in a tetrahedrai field.
2.4. X-ray structure determination o f complexes 6 and 11 Crystals o f 6 and 11 of approximate dimensions 0.1 x 0 . 2 × 0 . 2 and 0.1 × 0 . 1 × 0 . 2 m m , respectively, were m o u n t e d on an Enraf-Nonius C A I M diffractometer and used for data collection. Information concerning crystallographic data collection and refinement o f the structures is given in Table 2. T h e unit cell parameters of 6 and 11 were determined from least-squares refinement of the setting angles o f 25 reflections in the range 0 8-14 °. Three standard reflections, which were measured every 2 h as orientation and intensity control, showed no significant variations during data collection. T h e 2 0 range for data collection was 2 - 5 0 °, the index
ranges o f data collection being 0 < h < 14, 0 < k < 10 and 0 ~ l < 17 (6) and 0 < h < 9 , 0 _ < k < 13 and - 1 6 < l _ < 1 6 (11). Intensities were corrected for Lorentz and polarization effects but not for absorption. Th~ structures were solved by standard Patterson m e t h o d s and subsequently completed by Fourier recycling. All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were located from a difference synthesis and Table 3 Final atomic coordinates for non-hydrogen atoms and equivalent isotropic displacement parameters b for complex 6 Atom
xla
ylb
zlc
U~q
Co( l ) S( I ) S(2) N( 1) N(2) N(3) C( l ) C(2) C(3) C(4) C(5) C(6)
0.0337(i ) 0.1 ]90(3) 0.5234(3) 0.0560(9) 0.2277(9) -0.0741(8) -0.2366(7) 0.0807(9) 0.351 I(10) -0.1707(7) -0.2190( ! 1) -0.3532(7) -0.1505(12)
C(7)
- 0.0629(14)
0.25000 0.25000 0.25000 0.25000 0.25000 0.3724(6) 0.4937(5) 0.25000 0.25000 0.4306(6) 0.4365(9) 0.5648(6) 0.4613(I0) 0.3958(8 )
0.02635(8) -0.2845(2) 0.1019(2) -0.1023(5) 0.0804(5) 0.0745(7) 0.1100(8) -0.1798(6) 0.0902(5) 0.0648(6) -0.0396(4) 0.1189(5) 0.1999(6) 0.1803(6)
00562(5) 0.0774(8) 0.0798(8) 0.078(2) 0.081(2) 0.124(3) 0.129(4) 0.060(2) 0.062(2) 0.084(2) 0.119(4) 0.081(2) 0.I 12(3) 0.112(3)
N(4)
a E.s.d.s are given in parentheses. U values for anisotmpically refined atoms ~ given in the form of the isotropic equivalent thermal parameter U~ = !/3( U, t + U_ + U33).
346
A. Maslejova et al. I lnorganica Chimica Acta 255 (I997) 343-349
refined with an overall isotropic thermal parameter using a riding model for computed atoms. The final fullmatrix least-squares refinement minimizing the function Ew( tFol - IF~i )2 (iFol and IF~I are the observed and calculated structure factors), each reflection being assigned a unit weight, converged at R = R~ indices of 0.077 and 0.042 for all observed reflections. Maximum and minimum peaks in the final difference synthesis were 0.86 and - 0.57 e A, - 3 Table 4 Final atomic coocdinatesfor non-hydrogen atoms and equivalentisotropie displacementparameters b for complex 11 Atom
x/a
y/b
z/c
U~
Co(I) S(1) N(i) N(2) N(3) N(4) N(5) C(I) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9)
0.00000 0.3265(2) 0.1661(3) 0.2792(3) 0.1412(3) 0.3587(3) 0,1751(4) 0.3112(4) 0,3819(4) 0.1510(4) 0.3058(5) 0,1104(4) 0.2458(4) 0.2934(4) 0.5270(5) 0.2388(4)
0.00000 0.3382(I) -0,0204(2) 0.0047(2) -0.1414(2) -0.2377(2) 0.1294(2) -0.0927(3) -0,0774(3) 0.0358(3) 0.0517(4) -0.2620(3) -0.3222(3) -~.1303(3) -0.2598(4) 0.2]53(3)
0.00000 -0.1187(1) 0.1274(2) 0,2731(2) -0.0647(2) -0.1232(2) -0.0530(2) 0.1409(2) 0.2304(2) 0.2084(2) 0.3688(2) -0,0621(2) -0.0989(2) -0.1024(2) -0.1657(3) -0.0802(2)
0.0386(3) 0.0904(6) 0.0445(8) 0.0514(8) 0.0427(8) 0.0523(8) 0.0550(8) 0.0541(9) 0.0576(9) 0.0494(8) 0.0713(9) 0.0491(8) 0.0565(9) 0.0525(9) 0,0832(9) 0.0462(8)
E.s.d.s are given in parentheses. h U values for anisotropically refined atoms are given in the form of the isotropic equivalentthermal parameter U~q= 1/a f U~~+ U2~+ U3.~). Table 5 Bond distances (/~) and angles (°) for complex6 ~
Table 6 Bond distances (/~) and angles (°) for complex 11 a Cobalt environment Co(I)-N(i) Co( 1)-N(3)
2.158(2) 2.135(3)
Co(I)-N(5)
2.145(2)
N( I)-.Co(I)-N(3) N( I)--Co( I )-N(5)
89.5(1) 99.6(1)
N(3)-Co( I )-N(5)
89.8(I)
l-Meiz ligand N( 1)-C( I ) C( ! )-C(2) C(2)-1"(2) N(2)-CI4) N(2)-C(3) C(3)-N(I)
1.378(4) 1.358(4) 1.370(4) 1.455(4) 1.349(4) 1.318(4)
N(3)-C(5) C(5)-C(6) C(6)-N(4) N(4)-C(8) N(4)-C(7) C(7)-N(3)
1.359(4) 1.366(47 1.337(47 1.479(4) 1.333(4) 1.321(4)
C(3)-N( ! )-C( I ) N( I)-C( 1)-C(2) C( I )-C(2)-N(2) C(2)-N(2)-C(4) C(2)-N(2)-C(3) C(4)-N(2)-C(3) N(2)-C(3)-N(I)
105.5(2) 109.4(3) 106.6(3) 126,6(3) 106.7(2) 126.6(3) 111.7(3)
C(7)-N(3)-C(5) N(3)-C(5)-C(6) C(5 )-C~6)-N(4) C(6)-N(4)-C(7) C(6)-N(4)-C(8) C(8)-N(4)-C(7) N(4)-C(7)-N(3)
105.3(3) 109.4(3) 106.1(3) 108.1(3) 125.9(3) 126.0(30) 111.1(3)
Thiocyanateiigand S(!)-C(9) S( I )-C(9)-N(5)
1.629(3) 179.2(3)
C(9)-N(5) Co(I )-N(5)-C(9)
1.149(4) 165.1(3)
E.s.d.s are given in parentheses. for 6 and 0.78 and - 0 . 5 6 e • - 3 for 11. Max, shift/e.s.d is 0.1. f , f ' and f ' were taken from Ref. [5]. All calculations were performed by using the SHELX-86 [6] and SHELX76 [7] programs. The molecular plots were drawn using the SCHAKAL [ 8] program. The final atomic coordinates for non-hydrogen atoms with isotropic temperature factors and bond lengths and angles for complexes 6 and 11 are listed in 'Fables 3-6.
Cobalt environment Co( I )-N( 1) Co( I )-N(2)
1.922(8) 1.958(8)
Co(I)-N(3)
1.955(7)
3. Results a n d d i s c u s s i o n
N(I)-Co(I)-N(2) N(I)--Cotl)-N(3)
108.1(3) 114.7(3)
N(3)---Co(1)-N(2)
108.3(3) 102.5(3)
3. i. Description o f the structures
N(3)-Co(I)-N(3i) h
1,2-Me~izligand N(3)-C(3) C(3)-C(4) C(3)-N(4) N{4)-C(5)
1.16(1) 1.61(1) 1.20(1) 1.398(9)
N(4)-C(6) C(6)-C(7) C(7)-N(3)
1.60( I ) 1.18(I) 1.60( i )
C(7)-N(3)-C(3) N(3)--C(3)-N(4) N(3)-C(3)-C(4) C(4)-C(3)-N(4) C(3)-N(4)-C(5)
93.3(8) 137.0(1) 111.0{9) 111.6(9) 149.0(9)
C(3)-N(4)-C(6) C(5)-N(4)-C(6) N(4)-C(6)--C(7) C~)--C(f)-N(3)
92.9(8) 117.4(9) 107.8(9) 108.8(9)
Thiocyan~eligand S(i)-C(ll C(I)-N(I)
1.595(9) 1,17(i)
S(2)-C(2) C(2)-N(2)
1.596(9) 1.15(I)
S(i)-C(I)-N(I) Co(1)-N(I)-C(I)
178.4(9) 174.9(8)
S(2)-C(2)-N(2) Co(I)-N(2)-C(2)
178.8(8) 163.2(8)
a E.s.d.s we given in parentheses. hi=x, 0.5-y, z.
3.1.1. [Co(NCS)z( I,2-Me2i: ~zl (6) The structure of complex 6 consists of discrete [Co(NCS)2(1,2-Me2iz)2] mononuclear units (Fig. l) which are held together by van der Waais forces. The coordination of the cobalt atom is very nearly tetrahedral with four nitrogen atoms, two from monodentate thiocyanate groups and the other two from two 1,2-dimethylimidazol¢ ligands, building the CoN 4 chromoph.~rc. The largest deviation from the tetrahedral angle is 7.0 ° at the N ( 3 ) C o ( I ) - N ( 3 i) ( i = x , 0 . 5 - y , z) angle. A mirror plane contains the metal atom and the two thiocyanate groups, the whole molecule having a Cs symmetry. The C o N(thioeyanate) bond distances are slightly different ( 1 , 9 2 2 ( 8 ) and 1,958 A for Co( 1 ) - N ( 1 ) and Co( 1 ) - N ( 2 ) , respectively) but they agree well with those observed in the structurally characterized tetrakis (thiocyanato) cobaltate (II) complexes ( C o - N mean bond lengths from !.958(12) to
A. Maslejova et al. / Inorganica Chimica Acta 255 (1997) 343-349
347
N(thiocyanate) bond (2.145 (2) A for Co( I ) - N ( 5 ) ) is also longer than that observed in 6 as expected. The bond distances and bond angles within l-methylimidazole can he considered as normal and are very close to those observed in 6 for 1,2dimethylimidazole. The imidazole skeleton is planar as expected and the dihedral angle between adjacent imidazole planes is 94.4 °. As far as the thiocyanate lignnd is concerned, it is practically linear (179.2(3) ° for N ( 5 ) - C ( 9 ) - S ( 1 ) ) and a significant bending is observed in the Co-N-C(S) linkage (165.1(3) ° for C o ( 1 ) - N ( 5 ) - C ( 9 ) ) as in the preceeding structure. The shortest intermolecular metabmetal separation (Co( 1)-..Co(li), i = 0.5 +x, 0.5 - y , 0.5 + z ) is 9.561 ~,. Fig. I. Perspective drawing oflhe complex [Co(NCS)2( 1.2-Me2iz),.] (6), showing the atom numbering. Hydrogen atoms were omitted for the sake of
3. 2. Infrared and electronic spectra
clarity. 1.967(4) A) [9]. The Co-N(disubstituted imidazole) bond distance is 1,955(7) A, a value which is very close to that observed in other imidazole-containing cebait(II) complexes with the metal atom in a tetrahedral surrounding [ 10-15 ]. The imidazole rings are planar as expected (the largest deviation from the mean plane is 0.023/~ at C(3) atom) and they form a dihedral angle of 87.37 °. Bond lengths and angles within the imidazole rings are in good agreement with the parameters reported for the structure of imidazole itself'determined at - 150°C [ 16] and will therefore not he discussed in detail here. The NCS groups are almost linear (178.4(9) and 178.8 (8)° for S( 1)-C( 1 )-N( 1 ) and S(2)-C( 2 ) - N ( 2 ) , respectively), whereas a significant bending is displayed by the Co-N-C(S) linkages (174.9(8) and 163.2(8)° for Co( I ) - N ( l)--C( 1) and Co( I ) - N ( 2 ) - C (2), respectively). The shortest intermolecular metal-metal separation (Co(1)--.Co(li), i = - x , - y , - z ) is 6.311/~. o
3.1.2. [Co(NCS)2(I-Meiz)4] (11) The structure of complex 11 is made up of neutral and centrosymmetric [Co(NCS)2( l-Meiz)4] monom~fic entities (Fig. 2) which are linked by van der Waals interactions. The cobalt is six-coordinate with two thiocyanate-nitrogen atoms in trans positions and four l-Meiz-nitrogens building an almost undistorted octahedral CoN6 polyhedron. The CoN(imidazole) bonds (2.158(2) and 2.135(3) A) are significantly longer than that reported for 6 and other tetrahedral Co--N(imidazole) distances [ 10-15] but they are closer to octahedral Co-N(imidazole) bonds [15,17-22]. The C o -
Fig. 2. Perspective drawing of the complex [Co(NCS)2( l-Meiz)4l (11), showing the atom numbering. Hydrogen atoms were omitted for clarity.
In the con,plexes studied (Table I ) the asymmetric stretchmg vibration of yen was observed in the range 2058-2112 cm- ~ as an intensive, very strong band sometimes expressively split or rarely with a shoulder. The bands ofcG~nplexes with substituted imidazoles are broader and for complexes with a-substituted ligands an expressive splitting of tim band yen into two peaks was observed. The value of this splitting decreases in the order Co(NCS)2(2-Meiz)2 (39 cm- ~) > Co(NCS) z(Pheniz)2 (22 cm- ~) > Co(NCS)z(2Mebiz) 2 ( 19 cm- ~) > Co (NCS) 2( 1,2-Meziz):t ( 18 cm- l). The more the steric hindrance increases, the higher is the value of this splitting. Considering the position of the band VcN it may be assumed that the thiocyan~.te group is endbonded by its nitrogen atom [23]. In the region of the symmetric stretching vibration Vcs band, out-of-plane deformation vibrations of the C-H band in iraidazole are also found and they can interfere. The band belonging to the Vcs vibration in the interval 770-853 erawas determined using the value [24] of band frequency of the combined vibration ~'cn + ~'cs as indicated in the nitrogen bonded NCS group [25 ]. The values of wavenumber may exclude S-coordination for all rite complexes. The band belonging to the deformation vibration ig~cswas found in range 465-496 eraThe absorptions in the 400-200 cm-~ region have been assigned toCo-NCS and Co-N(L) vibrations (Table 7).For the pseudotetrahedral (C~,) complexes, Co(NCS)zL2, two IR active metal-thiocyanate stretching vibrations are expected in far-IR region [26] and two are indeed observed. Of the two expected Co N(L) stretching vibrations, bowever, only one is observed. Electronic spectral data are given in Table 8. To calculate Dq and B the transition energies are based on the centers of intensity of these bands, The ligand field spectra of the Co(NCS)2L2 complexes are typical for pseudoteta'ahedral ligand arrangements around Co(H). In each of the spectra two sets of bands can be distinguished, one in the visible and the other in the near-IR region. The former multiple absorption appears between 16 800 and 17 100 cm - t and may be attributed to the 4A2 - , 41",(P) wansition. Splitting of the band is probably due
348
A. Maslejova et aL / hwrganica Chimica Acta 255 (1997) 343-349
Table 7 Infrared spectra of thiocyanatocobalt(I1) complexes with imidazole
Compound
Ucr~
l'cs
t~NCS.
PC~F-NCS
I'~Ct~N(L)
Co(NCS)2( I-MeizL, Co(NCS)_,(2-Meiz)_, Co(NCS),(2-Etiz)_, Co( NCS ),_(2-1sopropiz) ~ Co ( NCS),, (2-Pheniz) =, Co(NCS)-,( 1,2-Me,iz)2 Co( NCS),(Biz) z Co(NCS)_~( 2-Mebiz)_, Co(NCS)2(2-EtbizL, Co ( NCS )., ( iz )4 Co(NCS):( l-Meiz).,
2070 2105. 2068 2097, 2081 2089, 2089 2080. 2058 2076, 2058 2095, 2078 2092, 2073 2095, 2078 2105, 2100sh 2086, 2078sh
843 841 853 831 849 843 843 841 835 845 843
476 478 475 496 475 482 480 482 476 469 475
301,324 280-320 sp 299, 316 300-304 sp 287. 316 301. 324 294, 322 311,327 291,322 249 243
274 260 278 282 268 278 289 289 282 235 223
Table 8 Electronic spectral data of thiocyanatocobalt (ll) complexes with imidazole Compound
Band positions v ( 10-~cm- ~)
Co(NCS)2( l-Meiz)2 Co ( NCS)-, ( 2-Meiz ) =, Co(NCS), (2-Etiz)_~ Co( NCS)_,( 2-1sopropiz ); Co ( NCS )-,( 2- Pheniz) 2 Co(NCS),( 1.2-Me2iz)2 Co(NCS),(Biz)2 Co( NCS )~.(2-Mebiz) • Co( NCS)~ (2-Etbiz), Co(NCS):(iz)4 Co(NCS)~(I-Meiz)4
8.30, 8.20, 8.30, 8.15, 8.05. 8.20, 8.30, 8.30, 8.30. 9.70, 9.50,
16.80 17.10 17.10 17.00 !6.90 17.00 17.10 16.95 16.90 19.00sh, 20.80 19.20sh 20.80
Q~ D
C --, T
Dq (cm- ~)
B (cm- ')
24.3 21.7sh, 23.8 22.2 21.7sh, 24 Ash 22.0 21.9sh 21.7, 23.5 24. I
31.0 32.2 32.05 32.25 31.25 31.9 30.2 31.25 31.7
487 481 486 477 471 480 486 487 487 1092 1069
698 726 721 722 721 720 721 710 706 821 836
0.72 0.75 0.74 0.74 0.74 0.74 0.74 0.73 0.73 0.85 0.86
Table 9 Magnetic data and EPR parameters of thiocyanatocobalt (ti) complexes with imidazole Compound
Curie constant C (cm ~ tool - ~K)
Weiss constant 69 (K)
Magnetic susceptibility I 0~× Xra ( c m~ tool - ~)
t~.~t-(BM) average (77-300 K)
Spectl oscopic splitting factor g (77 K) no line 2.696 ~ 3.72 2.954 3.390 4.055 ~ 7.24 no line 3.145
(r.t.)
Co ( NCS ), ( 1-Meiz) 2 Co(NCS),(2-Meiz), Co(NCS).,(2-Etiz)., Co ( NCS ) ~(2-1sopropiz): Co ( NCS ), (2-Pheniz) 2 Co(NCS)~( 1,2-Me,_iz)~ C,:,. NCS)~(Biz), Co(NCS) 2( 2-Mebiz ) 2 Co(NCS),(2-Etbiz) 2 Co ( NCS ) 2( iz )4 Co(NCS)2( I-Meiz)4
2.36
10.4
2.25 2.55 1.9 ! 2.17 2.1 ! 2.52
il.3 6.1 10.4 12.9 12.4 8.2
8060 8020 8950 6620 7460 7550 8680
2.21
5.7
7510
2.20 2.76 3.07
10.7
7560
4.48 4.37 4.60 4.04 4.33 4.27 4.60 4.28 4.33
- 7.0 - I I. I
8910
4.55
3.866
9840
4.76
3.809
to interaction with the d o u b l e t state through spin-orbit coupling [27 ]. T h e near-IR bands are perceptibly b r o a d e n e d and m o s t o f them s h o w a long tail towards lower wavenuv:bers, Their c o m p l e x i t y is c a u s e d b y the c o m p o n e n t s o f the 4T, ( F ) level, which b e c o m e allowed transitions in C2,, oymmetry [281. T h e electronic spectra o f the c o m p o u n d s C o ( N C S ) 2 L 4 ' exhibit bands c o r r e s p o n d i n g to the transition 4T,g(F) --, 4T2~ at 9 7 0 0 or 9 5 0 0 c m - ~ , respectively, and to the transition
4Tig ( F ) ~ 4Tig ( P ) at 20 800 e r a - ' and a s h o u l d e r at 18 9 0 0 or 19 200 c m j , respectively, being a c o n s e q u e n c e o f s p i n orbit coupling in the state e f ' ~ l ' ~ ( P ) and indicating a pseudooctahedral configuration [ 2 9 ] . The results indicate a greater distortion o f the tetrahedral configuration c o m p a r e d with the o c t a h e d r ~ form. The values o f the D q and B parameters o f C o ( N C S ) 2 ( 2 M e i z ) 2 and C o ( N C S ) 2 ( B i z ) z c o r r e s p o n d with the values o f these parameters calculated using the data for the c o m p l e x e s
A. Ma,¢lejova et al. / Inorganica Chimica Acta 255 (1997) 343-349
[Co(NCS)4] 2-, [301.
[Co(2-Meiz)4] 2+ and [Co(Biz)4l 2÷
3.3. Magnetic properties The effective magnetic moments (Table 9) indicate that the complexes are of the high-spin type. The values for Co(NCS)z(iz)4 and Co(NCS)2(I-Meiz)4 correspond to octahedral structures [31 I. The magnetic moments for Co(NCS)2(2-Etiz).~ 'rod Co(NCS).,(Biz)2 lie in the range 4.4-4.8 BM normally observed for tetrahedral cobalt(U) complexes [ 32]. For the remaining complexes Co(NCS) 2L2, the #e,' values are in accord with tetrahedral stereochemistries, although the /.L,.crvalues lie at the lower end of the overlap region lbr the tetrahedral environment or are lower (below 4.4 BM) than those normally found for tetrahedral complexes. The low magnetic moments observed for Co(NCS)2L 2 (L=2-Mebiz, 2-Etbiz, 2-lzopropiz, 1,2Me2iz) were attributed to superexchange coupling of the cobalt atoms by means of the short symmetrical N-C-N chains which form part of a mobile rr-electron system [33,34].
4. Conclusions From the above results it follows that the same reason non-substituted t~-position ~ leads to the formation of octahedral complexes of the composition Co(NCS)2L4'. If the imidazole derivative has its nitrogen donor atom sterically hindered, the lbrmed compounds have the composition Co(NCS)2L2 with tetrahedral configuration.
5. Supplementary material Tables of thermal parameters, hydrogen coordinates, leastsquares planes (6 pages), and a listing of observed and calculated structure factors (21 pages) are available from the authors on request.
Acknowledgements Financial support from the Slovak Ministry of Education, the State Committee for Scientific Research (Warsaw, Poland) and Spanish DGICYT (Project PB94-1002) is gratefully acknowledged.
349
References [I] W.L. Darby and L.M. Vallarino, inorg. Chim. Acto,48 (1981) 215. [2] A. Maslejova and I. Kovacik, Z Anorg, Allg. Chem.. 604 ( 1991 ) 151. [31 B.N. Figgis and RC. Nyholm, J. Chem, Soc.,(1958) 4190. [4 ] E. K0nig, Magnetic Properlies of CenTrdinatioa and Organometallic Trart~ition Metal Comtnmnds, Springer, Berlin, 1966. [5] International Tables for X-ray Crystallography, Vol. IV, Kynoch, Birmingham, UK, 1974, pp. 99--I lO, 149. [6] GM. Sheldrick, SHEL,Y-86, a computer program for the crystal structure determination, University of G6ttingen, Gernmny, 1986, [7] G.M. Sheldriek, SHELX-76, a computer program for the crystal structure determination, University of Cambridge, UK, 1976. [81 K. Keller, SCHAKAL, a FORTRAN progr~n for the graphic representation of molecular and crystallographic models, University of Freiburg, Germany, 1987. [9l (a) K. Me~itner and A. Preisinger, Acta CrystaUogr., Sect. C, 44 (1988) 1178; (b) J.S. Wood and R.K. McMullan, Acta Crystallogr., Sect. C, 40 (1984) 1803: (c) K. Mereimer and A. Preisiager, Acta Crystallogr., Sect. B, 38 (1982) 1084: (d) M.G.B. Draw and A.H. bin Othman, Acta Crystallogr., Sect. B, 31 (1975) 613. [ 10] A. Gadet, C.R. Acad. Sci., Set. C, 272 ( 1971 ) 1299. [ i i ] C.J. Antti and B.K.S. Lundberg, Acta Chem. Scand., 26 (1972) 3995. [ 12] M. Sturm, F. Brandl, D. Engel and W. Hoppe, Acta Crystaltogr., Sect. B, 31 (1975) 2369. [ 13] A. l..aidoudi, N. Kheddar and M.L. Brians6, Acta Crysrallogr., Sect. B, 34 (1978) 782. [ 14] W.D. Horrocks, J.H. lshley and R.R. Whittle, lnorg. Chem.,21 (1982) 3265. [ 15] W.D. Horrocks, J.H. Ishley and R.R. Whittle, Inorg. Chem., 21 (1982) 3270. [ 16] S. Martfnez-Carrera,Acta C~stallogr., 20 (1966) 783. [ 17] E. Baraniak, H.C. Freeman, J.M. James and C.E. Noc,kodls, J. C/tern. Soc. A. (1970) 2558. [ 18] R. Strandberg and B.K.S. Lundberg, Acta Chem. Scand., 25 ( 1971 ) 1767. [ 19] A. Gadet, C.R. Acad Sci.. Set. C. 274 [ I972) 263. [20] F. Akhtar, F. Heq and A C. Skapski. J. Chem. Sac., Dalton Trans., (1972) 1353. [21 ] R.G. Little, Acta Crystallogr.. Sect. B, 35 (1979) 2398. [22] R.A.J. Dries.sen, F.B. Httlsbergen, W.J, Vermin andJ. Ree~jk, inorg. Chem., 21 (1982) 3594. [23] A.H. Norbury, Adv. lnorg. Chem. Radiochem., 5 (1975) 17, [24] C.I~. Donker, J.G. Haasnoot and W.L. Groeneveld, Transition Met. Chem., 5 (1980) 368. [25] R.J.H. Clark and C.S. Williaras, Spectrochim. Acta, 22 ( 1966~t 1081. [ 26] G. Marcolrigiaao, L. Menabue and G.C. Pellacani, !norg. Clam. Acta, 26 (1978) 57. [27] F.A. Cotton mad M. Goodgame, J. Am. Chem. Soc., 83 ( 196t ) 1777. [28] A.B.P. Lever and S.M, Nelson, J. Chem. So,-. A, (1966) 859, [ 29] AB,P. Lever, I.M. Walker and P.J. McCarthy, fnorg. Chim. Acta. 39 (1980) 81, [30]A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Ar~terdam, 2nd edn,, 1984, pp. 742. 743, [311F.E. Mabbs and DJ. Machin, Magnetism and Transition Metal Complexes, Chapman and Hall, London, 1973. (32] B.N. Figgis and J. Levis, Prog. !norg. Chem., 6 (1964) 37, [331 W.J. Eiibeck, F. Holmes and A.E. Underhitl, J. Chen~ Sac. A, (1967) 757. [ 34] W,J. Eilbeck. F. Holmes, C.E. Taylor and A.E, Unded~ill, £ Chem. .':oc. A, (1968) 128.