The stnwture of the heteronuclear iron acetate [Fe2CoO(CH3COO)6(3-CI-Py)3].I/4.3-CI-Pyx. 1/4(CH3)2C0.1/2H20 was determined by X-ray sttT~cture analysis.
Journal of Stru~tuml Chemistry. Vol. 40, No. 6. 1999
STRUCTURE, IR AND MOSSBAUER SPECTRA, AND MAGNETIC PROPERTIES OF [Fe2CoO(CH3COO)6(3-CI-PY)31- 1/4. 3CI-Py. 1/4(CH3)2CO- 1/2H20 T. C. Jovmir, C. I. Turta, S. G. Shova, Yu. A. Simonov, M. Gdaniec, I. I. Bulgac, I. G. Cadelnie, and G. Fiioti
U DC 548.736:546.72:539.194
The stnwture o f the heteronuclear iron acetate [Fe2CoO(CH3COO)6(3-CI-Py)3].I/4.3-CI-Pyx 1/4(CH3)2C0.1/2H20 was determined by X-ray sttT~cture analysis. The crystal has a molecular stt~cture and is monoclinic with lattice parameters a = 21.034(4). b = 8.398(2), c = 23.360(5) ,4, 6= 98.28(3)% R = 0.0656. space group P2I/c. The tHnuclear complex- [Fe2CoO(CH3COO)6(H20)3] has a structure ~_pical for iron(Ill) Hr compounds with iron atoms lying at the vertices of the equilateral oiangle centered by an o.~'gen atom. The metal atoms are each cooldinated to four o.v3'gen atoms of the four bridging carbo.D, groups, the blidging oaTgen atom ([t3-O ), and the coordinated 3-chloropylidine molecule which is trans relative to the latter atom. According to Mi~ssbauer spectroscopy data, the iron(Ill) ions are in the high-spin state. The value of (p-~f)rnole / P'3 at room temperature and its temperature dependence suggest that the resulting magnetic exchange interaction between the paramagnetic centers of the cluster is attt~felromagnetic.
INTRODUCIION The classical trinuclear transition metal carboxylate complexes (basic carboxylates) remain to be interesting objects for both modern preparative chemistry and X-ray structure analysis. O f special interest among these are iron la3-oxocarboxylates. Recently. they were proposed as models of active centers in iron-containing proteins (ferritin, hemerythrin, etc.) [!-3]. Studies of the magnetic properties of homo-trinuclear systems unambiguously indicate that the iron atoms are involved in a magnetic exchange interaction of antiferromagnetic type [4]. However. the mechanism as well as the factors governing the character of the exchange interaction have not been studied in full detail. The results of magnetic measurements reported in [5-8] indicate that the parameters of the exchange interaction between the three paramagnetic centers in the complex are nonequivalent. This may be caused by the insignificant differences in the geometry of the environment (bond lengths and angles) of the complexing ions. Thus it is assumed that the geometry of the b'ridging fragments (p.3-O or syn-syn-carboxy groups) is the major factor governing the character of exchange in the cluster. This problem may only be discussed based on sufficiently exact structural data for a large number of complexes of this class. H eterometallic trinuclear complexes are of particular interest [9-13]. Investigations of magnetic properties for a number of iron-containing carboxylates showed that the exchange interaction between the iron ions in such compounds is stronger than in complexes with a Fe30 nucleus. The structure of acetate complexes of this class differing in the composition of the central part was reported in the literature: Cr2FeO [14, 15], CrFe20 [16], Fe2CoO [17], and FellFeI~ [18, 19]. In all of these works, the molecular nucleus was reported to have approximately D3h symmetry. The Institute of Chemistry, Academy of Sciences, Moldova Republic, Kishinev. Institute of Applied Physics, Academy of Sciences, Moldova Republic, Kishinev. A. Mickiewicz University, Poznan, Poland. National Institute of Physics o f Materials, Bucharest, Romania. Translated from Zhumal Stmkturnoi Khimii, Vol. 40, No. 6, pp. 1116-1127, November-December, 1999. Original article submitted September 4, 1998. 0022-4766/99/4006-0905522.00 9 1999 Kluwer Academic/Plenum Publishers
905
centers in the trimer have not been unambiguously assigned to the metal ions. This is explained by two factors. The first reason is an equiprobable arrangement of metal atoms at three positions in the trinuclear cluster. The second reason is methodological. As a rule, metals in the trinuclear cluster differ in the atomic number by 1 or 2 units. This hinders their unambiguous interpretation based on X-ray diffraction data. The above references do not give site assignments of cations in the cluster. It seems that this problem may be solved by creating certain conditions, for example, by choosing a certain ligand providing the same orientation of heterometallic clusters in the crystal. In the framework of our systematic studies of basic iron carboxylates [20-24] we investigated a trinuclear complex with a Fe,CoO nucleus. This paper reports on the structure and properties of the trinuclear carboxylate complex [Fe2CoO(CH 3COO)6 • (3-CI-Py)3] - 1/4- 3-C1-Py- 1/4(CH3)2CO - 1/2H20.
EXPERIMENTAL Synthesis. To a suspension of [Fe2CoO(CH3COO)6(H20)3] - 2H20 (1.5 g, 2.4 mmole) [251 in acetone (40 ml) was added 3-C1-Py (1.5 ml, 16 mmole). The mixture was heated on a water bath tbr 20-30 rain. The resulting dark brown solution was filtered off and left overnight tor crystallization. The crystalline precipitate which settled the next day was filtered off and washed with acetone. Yield 1.10 g (50c~). The metal content was determined by means o f atomic absorption spectroscopy. Found for C29H33.5CI3.25CoFe2N3.25OI3.75. %: Fe 11.9, Co 5.7, C 35.1, H 3.8, N 4.5. Calculated for C29H33.5CI3.25CoFe2N3.250 13.75, %: Fe 11.24, Co 5.92, C 35.63, H 3.37, N 4.58. Crystals suitable for an X-ray diffraction analysis were prepared by a similar procedure using more dilute solutions. In this case, elongated prismatic crystals settled in a few days and were stored in the mother solution because of quick degradation in air. X-Ray diffraction analysis. For an X-ray diffraction experiment we used a single crystal with dimensions 0.2)< 0.2)< 0.4 m m sealed in a capillary with the mother solution vapor to provide crystal stability throughout the X - r a y experiment. The data were collected on a Kuma KM-4 diffractometer (graphite monochromator, MoKc~ radiation). Lattice p a r a m e t e r s were determined by the least squares method using 25 reflections in the range of angles 15 241)] R factor (for all data collected) Maximal peaks in the difference synthesis, e- ~-3
21.034(4) 8.398(2) 23.360(5) 98.28(3) 4083(2) 4 1.513 1.377 1884 0.2x 0.2x 0.4 0.98 to 24.05 ~
-24< It< 23,0< k< 9 , 0 < 1< 26 6562 6398 [R (int)= 0.0755] Full-matrix least-squares 4770 / 24 / 494 1.104 R l = 0.0656. wR2= 0.1879 R 1 = 0.2330. wR2 = 0.3052 0.676 and -0.705
TABLE 2. Coordinates of Basic Atoms (x 104) and Equivalent Isotropic Thermal Parameters (A2x 103) (Ueq= I/3Z,Z Utja, aaa~aj) T Atom / x y z Ueq Atom _v v z Ueq 1
Fe(1) Fe(2) Co CI(1) C1(2) C1(3) CI(G) O(1) O(IA) O(2A) O(IB)
O(2B) O(IC) O(2C) O(1D) O(2D) O(IE) O(2E) O(IF) O(2F) O(S1) W(1)
2
7909( 1) 6870(1) 8398(l) 8368(3) 4269(3) 9769(2) 5137(19) 7721(3) 8105(4) 7076( 4 ) 7899(4) 6873(4) 8678(4) 8982(4) 8514(4) 8845(4) 6701(4) 7363(4) 6450(4) 7190(4) 6220(29) 5677(26)
3
3469(2) 1871(2) 1976(2) 9098(6) 1160(16) 3109(5) 2181(45) 2439( 8) -305(9) -298(10) 2808( 1O) 28O3(10) 2051(10) 1013(10) 5118(9) 4131(9) 821(10) 2007(10) 3960(9) 5110(9) 4447(70) 3656(64)
4
6381(1) 7127(I) 767O( 1) 5072(2) 6101(4) 9931(2) 4902(19) 7056(3) 7841(4) 7481(4) 8305(3) 7934(3) 6268(3) 7147(3) 6791(3) 7669(3) 6331(3) 5811(3) 6823(4) 6355(3) 5011(20) 5197(22)
5
38( 1) 37(1) 4l(1) 120(2) 293(7) 96( 1) 258(19) 35(2) 53(2) 57(2) 54(2) 50(2) 53(2) 56(2) 48(2) 56(2) 51(2) 54(2) 52(2) 51(2) 141(32) 112(16)
6
C(IC) C(2C) C(1D) C(2D) C(IE) C(2E) C(IF) C(2F) C(21) C(31) C(41) C(51) C(61) C(22) C(32) C(42) C(52) C(62) C(23) C(33) C(43) C(53)
7
9029(5) 9490(6) 88O6(5) 9165(6) 6958(6) 6710(9) 6669(5) 6280(7) 8171(6) 8262(6) 8270(6) 8215(7) 8145(6) 5441(6) 4823(8) 4634(7) 5075(8) 5690(6) 9271(5) 9728(6) 10137(6) 10081(6)
8
1116(13) 115(14)
5208(13) 6729(13) 995(15) -124(20) 5111(13) 6656(15) 6265( 15 ) 7087(16) 6219(22) 4655(20) 3908(16) 1273(19) 774(25) 52(20) -48(19) 529(18) 2370(14) 1988(14) 741(18) -I23(17)
9
6614(5) 6385(5) 7301 (5) 7462(5) 589(/(5) 5399(6) 6559(5) 6518(7) 5562(5) 5057(6) 4564(6) 4574(6) 5093(6) 6732(7) 6718(8) 7208(8) 7672(8) 7653(7) 8863(5) 9318(5) 9294(5) 8812(7)
10 43(3) 58(4) 39(3) 57(3) 46(3) 98(6) 40(3) 76(4) 55(3) 6l(4). 73(4) 67(4) 61(4) 71(4) 104(6) 86(5) 90(6) 73(4) 46(3) 48(3) 59(4) 68(4) 907
TABLE 2 Continued) 1
2
W(2) N(1) N(2) N(3) N(G) C(IA) C(2A) C(IB) C(2B)
3
4
5491(34) 3137(90) 8O96(4) 4715(12) 5863(4) 1146(12) 9198(4) 1513(11) 6483(18) 5427(46) 7579(6) -940(13) 7525(7) -2657(14) 7326(6) 3093(13) 7157(6) 3805(18)
4463(33) 5565(4) 7163(4) 8382(4) 4953(19) 7728(5) 7905(6) 8321(5) 887O(5)
5
158(24) 47(2) 48(3) 43(2) 90(17) 40(3) 69(4) 43(3) 69(4)
6
7
C(63) C(2G) C(3G) C(4G ) C(5G) C(6G) C(SI) C($2) C($3)
8
9585(6) 6084(18) 5650(14) 5641(22) 6060( 25 ) 6477(18) 6123(19) 5524(25) 6580(29)
9
271(15) 4352(46) 3579(35) 3959(56) 5084(62) 5797(45) 4730(44) 4540( 117 5338(109)
8363(6) 5099(14) 4693(14) 4120(14) 3972(16) 4407(20) 4520(20) 4144(26) 4175(31)
10
54(3) 163(70) 121(34) 114(35)
133(30) 88(22) 77(17) 119(32) 139(34)
TABLE 3. Bond Lengths d (A) and Angles o) (deg) Bond
d
Bond
d
Bond
1
2
3
4
5
Fe( 1)-O(1) Fe( 1)-O(1D) Fe(I)-O(2E) Fe(I)-O(2F) Fe( 1)-O(IC) Fe( 1)-N( 1) O( IC)-C(1C) O( 1D)-C(1D) O(2E)-C(IE) O(2F)-C(1F) C(IC)-C(2C) C(ID)-C(2D) N(1)-C(21) N(1)-C(61) C(21)-C(31) C(31)-C(41) C(41)-C(51) C(51)-C(61) CI(1)-C(31) Angle Fe( 1)-O( l)-Co O( 1)-Fe(I)-O(1C) O( 1)-Fe( 1)-O(1D) O( l)-Fe(1)-O(2E) O( 1)-Fe(I)-O(2F) O( 1D)-Fe( 1)-O(IC) O( 1D)-Fe(I)-O(2F) O(2E)-Fe(I)-O(2F) O(2E)-Fe( 1)-O(IC) O( ID)-Fe(I)-O(2E) O (2F)-Fe( 1)-O(IC) O( l)-Fe( I)-N(1) O( IC)-Fe( 1)-N(1) O( 1D)-Fe( I)-N(1) O (2E)-Fe( I)-N(1) O (2F)-Fe( I)-N(1) C(1C)-O(IC)-Fe(1) 908
1.891(6) 2.026(8) 2.O40(8) 2.041(8) 2.056(8) 2.258(9) 1.28(1) 1.26( 1)
1.24(1) 1.26(1) 1.44(2) 1.50(2) 1.31(2) 1.31(1) 1.40(2) 1.36(2) 1.32(2) 1.39(2) 1.70( 1)
Fe(2)-O(1) Fe(2)-O(2A) Fe(2)-O(2B) Fe(2)-O(1E) Fe(2)-O(IF) Fe(2)-N(2) O( IE)-C(IE) O( 1F)-C(1F) O(2A)-C(IA) O(2B)-C(IB) C(1E)-C(2E) C(IF)-C(2F) N(2)-C(22) N(2)-C(62) C(22)-C(32) C(32)-C(42) C(42)-C(52) C(52)-C(62) C1(2)-C(32)
1.882(7) 2.021(8) 2.041(8) 2.043(8) 2.045(8) 2.217(9) 1.24(1) 1.27(1) 1.25(1) 1.24(1) 1.52(2) 1.53(2) 1.25(2) 1.35(2) 1.36(2) 1.40(2) 1.32(2) 1.39(2)
1.75(2)
03
Angle
co
119.8(4) 96.0(3) 96.3(3) 95.9(3) 95.1(3) 90.3(3) 87.9(3) 92.4(3) 87.0(3) 167.7(3) 168.8(3) 178.0(3) 85.7(3) 84.8(3) 83.0(3) 83.2(3) 131.8(7)
Fe(2)-O( l)-Fe(1) O(I)-Fe(2)-O(2A) O(I)-Fe(2)-O(2B) O( I )-Fe(2)-O(IE) O( l)-Fe(2)-O(IF) O( 1E)-Fe(2)-O (IF) O(2A)-Fe(2)-O(2B) O(2A)-Fe(2)-O(1E) O(2B)-Fe(2)-O(IF) O(2B)-Fe(2)-O(1E) O(2A)-Fe(2)-O(1F) O(1)-Fe(2)-N(2) O(IE)-Fe(2)-N(2) O(IF)-Fe(2)-N(2) O(2A)-Fe(2)-N(2) O(2B)-Fe(2)-N(2) C(IA)-O(2A)-Fe(2)
120.4(4) 96.5(3) 96.2(3) 94.1(3) 96.9(3) 92.5(3) 89.8(4) 89.O(3) 86.3(3) 169.7(3) 166.3(3) 176.9(3) 82.7(3) 83.2(3) 83.5(3) 86.9(3) 133.9(7)
Co-O(1) Co-O(2C) Co-O(2D) Co-O(IB) Co-O(1A) Co-N(3) O( 1A)-C(1A) O( 1B)-C(IB) O(2C)-C(IC) O(2D)-C(ID) C(IA)-C(2A) C(IB)-C(2B) N(3)-C(23) N(3)-C(63) C(23)-C(33) C(33)-C(43) C(43)-C(53) C(53)-C(63) C1(3)-C(33) Angle Fe( 1)-O( l)-Co O( l)-Co-O (IA) O( l)-Co-O (IB) O(1)-Co-O(2C) O(1)-Co-O(2D) O( 1B)-Co-O (1A) O( 2C)-Co-O (IA) O(2C)-Co-O(2D) O(2D)-Co-O(IB) O(2C)-Co-O(1B) O(2D)-Co-O(IA) O(I)-Co-N(3) O(1A)-Co-N(3) O(IB)-Co-N(3) O(2C)-Co-N(3) O(2D)-Co-N(3) C( 1B)-O( 1B)-Co
d 6
1.910(7) 2.023(7) 2.039(8) 2.059(8) 2.069(8) 2.224(9) 1.22(1) 1.23( 1)
1.27(1) 1.24(1) 1.51(2) 1.50(2) 1.32(1) 1.33(1) 1.36(2) 1.36(2) 1.33(2) 1.41(2) 1.71(1) 09 119.9(3) 97.1(3) 94.0(3) 94.6(3) 96.5(3) 88.8(3) 88.3(3) 91.9(4) 89.0(4) 171.2(3) 166.4(3) 178.2(3) 84.7(3) 85.9(3) 85.5(3) 81.8(3) 133.4(8)
TABLE 3 (Continued) 1
2
3
4
5
6
C( 1D)-O( 1D)-Fe(1) C( 1E)-O(2E)-Fe(1) C( IF)-O(2F)-Fe(1) O(2C)-C( IC)-O(IC) O( IC)-C(IC)-C(2C) O( 2C)-C(1C)-C(2C) O(2D)-C( 1D)-O(ID) O( 1D)-C(ID)-C(2D) O(2D)-C(ID)-C(2D) C(61)-N( l)-Fe(1) C(2 I)-N( 1)-Fe(1) C(61)-N(1)-C(21) N(1)-C(21)-C(31) C(41)-C(31)-C(21) C(41)-C(31)-CI(1) C(21)-C(31)-C1(1) C(51)-C(41)-C(31) C(41)-C(51)-C(61) N(1)-C(61)-C(51)
132.5(7) 130.6(7) 132.3(7) 123(1) 119(1) 119(1) 126(1) 117(1) 118(1) 121.0(9) 120.0(8) 119(1) 122( 1) 118(1) 122(1) 120(1) 120( 1) 119(1) 122(1)
C(IB)-O(2B)-Fe(2) C( IE)-O(1E)-Fe(2) C( 1F)-O ( 1F)-Fe(2) O(2E)-C( IE)-O(IE) O( IE)-C(1E)-C(2E) O(2E)-C(IE)-C(2E) O(2F)-C( IF)-O(IF) O( 1F)-C(1F)-C(2F) O(2F)-C(IF)-C(2F) C(22)-N(2)-Fe(2) C(62)-N(2)-Fe(2) C(22)-N(2)-C(62) N(2)-C(22)-C(32) C(22)-C(32)-C(42) C(22)-C(32)-C1(2) C(42)-C(32)-C1(2) C(52)-C(42)-C(32) C(42)-C(52)-C(62) N(2)-C(62)-C(52)
130.4(7) 131.8(8) 130.9(7) 127( 1) 114(1) 119(1) 126(1) 117(1) 118(1) 121.3(8) 120.8(9) 118(1) 124(2) 120(2) 119(2) 121(1) 117(1) 120(2) 122(2)
C( IA)-O( IA)-Co C( IC)-O(2C)-Co C( ID)-O(2D)-Co O( IA)-C(IA)-O(2A) O( IA)-C(IA)-C(2A) O(2A)-C(IA)-C(2A) O( IB)-C(IB)-O(2B) O( 1B)-C(1B)-C(2B) O(2B)-C(IB)-C(2B) C(23)-N(3)-Co C(63)-N(3)-Co C(23)-N(3)-C(63) N(3)-C(23)-C(33) C(43)-C(33)-C(23) C(43)-C(33)-C1(3) C(23)-C(33)-C1(3) C(53)-C(43)-C(33) C(43)-C(53)-C(63) N(3)-C(63)-C(53)
130.3(8) 135.0(8) 131.6(7) 126(1) 117(1) 117(1) 126(1) 117(1) 117(1) 121.5(8) 120.9(8) 117(1) 121(1) 122(1) 120( 1) 118(1) 118(1) 118(1) 124( 1)
Bond angles in outer-spheric molecules
Bond lengths in outer-spheric molecules Bond
d
N(G)-C(2G) 1.310(9) N(G)-C(6G) 1.311(9) C(3G)-C(4G) 1.374(9) C(3G)-C(2G) 1.380(9) C(3G)-CI(G) 1.71(1)
Bond C(5G)-C(4G) C(5G)-C(6G) OS1-CS1 CSI-CS2 CS1-CS3
d
Angle
1.37(1) O(S1)-C(SI)-C(S2) 1.38(1) O(SI)-C(SI)-C(S3) 1.23(1) O($2)-C(S1)-C($3) 1.435(9) C(2G)-N(G)-C(6G) 1.435(9) C(4G )-C( 3G )-C( 2G ) C(4G)-C(3G)-CI(G)
Angle
O)
C(2G)-C(3G)-CI(G) C(4G)-C(5G)-C(6G) C(5G)-C(4G)-C(3G) N(G)-C(6G)-C(5G) N(G)-C(2G)-C(3G)
120.6(8) 119(1) 119(1) 122(1) 122( 1)
Magnetic measurements. Magnetic susceptibility was measured by the Guye method in the temperature range 300-120 K. The sample temperature was measured with a copper--constantan thermocouple. The temperature was maintained to an accuracy of + 1.5 K. The emf of the thermocouple (sample temperature-ice melting temperature) was measured with a PP-63 potentiometer. Co[Hg(NCS)4] was used as a reference. Effective molar magnetic moments were determined by the formula (p_eff)/mole= ~r~,. 8T. The value of X' was taken with allowance tor diamagnetic corrections [281.
DISCUSSION OF RESULTS In the range 3700-3300 cm- 1 of the IR spectrum of the complex one can observe very broad absorption bands relating to the stretching vibrations V(OH) of the crystallization water molecules. The presence of a weak band at 1720 cm- I points to a carbonyl-containing compound. The low intensity of this band (Vco) is the result of the low content of acetone in the complex. The latter is consistent with XRD data on the statistical distribution of H20 and (CH3)2CO solvate molecules in the crystal. The spectrum also exhibits very intense bands at 1630 and 1600 cm- 1 referring to the stretching vibrations of the pyridine ring [29]. Intense absorption bands characteristic of acetate groups are observed at 1575 and 1440 cm- 1. They relate to Vas(COO-) and vs(COO-), respectively [30]. In the region of 650 cm- l there is medium-intensity band assigned to the vibrations 8(OCO). The modes belonging to the M30 fragment [Vas(Fe30)] [30] are observed at 710-550 cm-1 as medium-intensity bands. Spectroscopic data are in fair agreement with the structure of the complex obtained by X-ray diffraction 909
c(42) c1(2)
c(52),
32)
c(62)
c(22)
O(2a)
I
O(le)
) C(2e) ~C(2f) 0(19
c C(lb 9
Jl
O(2f)
O(lb o(3) Fe(1; 0(2c) O(lc)j
c(61) c(51 )
c(: Cll
c(33
O(2d)~
~C(l' d0)( l d )
C(21) C(31
C(53) c(43) ~C(2d,~ Fig. 1. Structure of [Fe2CoO(CH3COO)6(3-CI-PY)3].
Fig. 2. Fragment of the crystal structure.
910
CI
analysis (Fig. 1). The crystal has a molecular structure consisting of neutral complexes [Fe~Icono(cH3COO)6(3-CI PY)3] Sol, where the solvent molecules 3-CI-Py, H20, and acetone occupy statistical voids tormed by the bulky neutral clusters (Fig. 2). No contacts which could be attributed to intermolecular hydrogen bonds were found in the structure. In the neutral trinuclear cluster [Fe2CoO(CH3COO)6(3-CI-Py)3], three metal atoms are united into a nearly regular triangle by the lu3-oxo and acetate bridges. The distances between the metal ions are as follows: Fe(1)-Fe(2) 3.274 A, Fe(l)-Co(3) 3.288 A, Fe(2)-Co(3) 3.282 A. The M-Ia3-O distances are 1.891(6), 1.882(7), and 1.910(7) ,~. As mentioned above, an analysis of interatomic distances in the bt3-O fragment of homo- and heteronuclear complexes (neutral molecules) does not always allow an unambiguous interpretation of the type of metal. The metaI-O(la 3) distances are 1.899, 1.915, and 1.908 /~ in [Fe30(C6HsCOO)6(CH3OH)2(H20)]- C6H5COO. C2HsOH• CH3OH [31]; 1.87(2), 1.90(2), and 1.91(2) .2t in [Fe30(CH3COO)6(H20)31NOy 4H20 [201; 1.891(6), 1.892(7), and 1.899(7) /1~ in [FeCr20(CH3COO)6(H20)3]NO 3- CH3COOH 1141: 2.010(4) and 1.856(7) a, (at 163 K) and 1.953(5) and 1.879(2) & (at 298 K) in [FenFelllo(cH3coo)6(4-Et-py)3114-Et-py) [191. According to the data of [32], the ionic radii of the high-spin Fem and Co It are 0.79 and 0.89 k,, respectively, differing by 0.10 .&. In our case, the distances M-O(bl3) and the average distances M - O c o O and M-N tot the three coordination polyhedra are 1.891, 2.041, 2.258; 1.882, 2.038. 2,217; 1.910. 2.048, 2.224 A. respectwely. In view of the systematic lengthening of metal-oxygen bonds tor the third position of metal in the cluster, one can tentatively assume that the Co(II) cations predominantly occupy this position. The metal-nitrogen distance is considerably affected by the steric interactions between the carboxy oxygens and the 3-CI-Py hydrogens in the 2 and 6 positions of the pyridine ring. In the title heterotrinuclear complex, the metal ions are linked with each other not only by the ~t3-O bridge but also by six syn-syn-carboxy bridging groups [331. The mean distances metal-carboxy oxygen for Fe(1), Fe(2), and Co(3) are 2.041, 2.038, and 2.048 A,, respectively (Table 3). The deviations of the metal atom toward the bt3-oxo oxygen atom are 0.208, 0.210, and 0.198 A for Fe(1), Fe(2), and Co(3), respectively. The 3-Cl-pyridine molecule is in the trans-position to p.3-O; it is coordinated via the nitrogen atom with distances from nitrogen to the 1-3 positions of the metal 2.258(9), 2.217(9), and 2.224(9) A (Table 3). These distances are close to those found in the structures with coordinated pyridine or its derivatives [18, 19]. The core of the molecule has approximately D3,~ symmetry distorted by the orientation of the 3-Cl-pyridine ligands relative to the 113-O fragment. The plane of the 3-Cl-pyridine molecule (Fig. 1) defined by the N(1)-C(61) atoms makes a dihedral angle of 79.3~ with the planar Fe-,CoO fragment; the same angle is 7.1 ~ for the N(2)-C(62) plane and 75.7 ~ for the N(3)-C(63) plane. Evidently, the rotation of the aromatic rings around the metal-nitrogen bond results from the intra- and intermolecular nonvalent interactions. In the carboxylate ions, the electron density in the O ' " C ' " O bridging fragment is delocalized. The mean distances are C:-:'O 1.25 A and C-C 1.50 A; the OCO angle is 126~ In the planar 3-CI-Py fragment, the mean distances are N-C 1.31 A, C-C 1.37 A, and C-CI 1.72 A. In Table 4, one can trace the variation of the M6ssbauer parameters of the trinuclear g3-oxo iron acetates with an iron ion replaced by the cobalt(ll) ion and with water molecules substituted by the nitrogen-containing ligand (3-CI-Py) in the heteronuclear clusters, It can be seen that substitution of the Co(II) ion for the Fe~III) ion dramatically increases quadrupole splitting but slightly reduces the isomer shift. This change in the M6ssbauer parameters of iron(Ill) ions indicates that the total s-electron density around the iron nucleus slightly increases. Simultaneously, the symmetry of the electron cloud around the M6ssbauer nucleus is lowered. Probably, in the iron(Ill) acetate heterotrinuclear complex, the MO system of the complex is such that the occupations of the iron 3d-AOs decrease (the screening is decreased). Moreover, the reduction is nonequivalent for orbitals oriented along the z axis and those oriented along
TABLE 4. M6ssbauer Spectral Parameters of Selected la3-Oxo-Acetates of [Fe2MO(CH3COO)6L3]X- nSolv Type
•Fe.
Substance
T, K
[Fe2CoO(CHCOOH)6(3-CI. Py)3]l/4(3-CIRy)x 1/4(CH3)2CO-1/2H20 [Fe2CoO (CH 3OO)6(H 20)3]- 2H20 [Fe30(CH3OO)6(H20)3]NOy 4H20
300
0.42
0.89
300 300
0.43 0.49
0.78 0.58
Note. The accuracy for & AEQ, 1- = + 0.02 mm/s.
mm/s
AEo., mm/s F t / Fr, mm/s
l
Ref.
0.30/0.27
This work
0.36/0.38
[34] [20]
911
TABLE 5. Molar Magnetic Susceptibility and Effective Magnetic Moment per Mole [(~teff)/mole] of the Complex in the Temperature Range 300-120 K Parameter
T = 300
285
270
230
200
185
~(mole, cm3/mole ([Lteff)mole/~[3
0.008737 4.58
0.009012 4.53
0.009313 4.48
0.010193 4.33
0.010960 4.18
0.011423 4.11
Parameter
T = 170
155
140
130
120
7whole, cm3/mole
0.012028 4.04
0.012688 3.97
0.013442 3.88
0.014020 3.82
0.014697 3.76
(~eff) mole/~[3
the x and v axes. Replacement of H20 by 3-CI-Py molecules does not change the total s-electron density in the region of the iron nucleus but slightly increases the quadruple splitting (QS) in agreement with the literature data [34]. This is an expected result since in the 3-C1-Py-containing cluster the local symmetry of the environment of iron (FeO 6 --> FeO5N) decreases, increasing the electric field gradient around the M6ssbauer nucleus. The magnetic measurement data for the complex in the range 300-120 K are given in Table 5. The effective magnetic moment per mole of substance (~teff)/mole at room temperature is 4.58 BM, which is substantially lower than the spin value (7.2 BM) tbr the trinuclear cluster if the spin of the cobalt(II) ions is taken into account (S = 3/2). As the temperature is lowered to 120 K, (~teff)/mole decreases to 3.76 BM. Both the value of (~teff)/mole at room temperature and its temperature dependence suggest that the overall magnetic exchange interaction between the paramagnetic centers in the cluster is antiferromagnefic.
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912
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