Inorganic Chemistry, Vol. 16, No. 5, 1977 1119
u vs. P Bonding in Tetrahedral Zinc(I1) Complexes
which contains no 0-H stretch or Mn-OH deformation in its infrared spectrum. The addition of H 2 0 to this material dissolved in an appropriate organic solvent gives a compound similar to Mn( 5-NOzSALDPT)(OH). Preliminary analytical and spectroscopic evidence suggests that a peroxo species is the initial pr~duct.’~Consequently we propose the tentative mechanistic scheme given by eq 1-4 recognizing that eq 4 is Mn’+L + 0, -+ LMn’+O;
(1)
LMn3+0; + Mn’+L-+LMn’+(-0-O-)’-Mn’+L LMn3+(-0-O-)’-Mn3+L + 2H,O 2LMn3+-OH t H,O,
(2) (3)
LMn3+-OH + [ O ] L’Mn’+-OH
(4)
-+
-+
significant in the early stages only for Mn(XSALDPT) and that L’ corresponds to an oxidized product of XSALDPT. In summary, evidence has been presented which shows the irreversibility of the reaction between O2 and Mn(I1) complexes containing a pentadentate OzN3ligand field. In the majority of cases reaction with O2 does not stop with conversion to Mn(II1) but continues with oxidation of the ligand even under strictly anhydrous conditions. Oxidized products from nonanhydrous reactions are isolated for the nitro-substituted complexes which have the formulation Mn(5N02SALDPT)(OH) and Mn(5-N02SALMeDPT)(OH). Acknowledgment. This research was supported by NIH Research Grant 21844-01 from the National Institute of General Medical Sciences. Registry No. Mn(5-CISALDPT),61916-28-7;Mn(S-BrSALDPT), 61 916-1 1-8; M n ( 5 - N 0 2 S A L D P T ) , 61916-12-9; Mn(3CH30SALDPT),6 1916- 13-0; Mn(5-BrSALMeDPT), 6 1951-29-9; Mn(5-N02SALMeDPT),61916-14-1; Mn(SALPrDPT), 61916-15-2; Mn(SALPhDPT), 61 916- 16-3; M n ( 5 - N 0 2 S A L D P T ) ( O H ) ,
61967-10-0; Mn(5-N02SALMeDPT)(OH), 61 91 6-17-4; Mn(3CH30SALDPT)(OH), 6 1916-18-5; Mn(SALDPT), 15378-52-6; Mn(SALMeDPT), 6 1916-19-6.
References and Notes (1) 8. B. Keele, J. M. McCord, and I. Fridovich, J. Biol. Chem., 245,6176 (1970). (2) M. Calvin, Reu. Pure Appl. Chem., 15, 1 (1965). (3) K. B. Wiberg, Oxid. Org. Chem., Part A (1965). (4) G.W. K. Canham and A. P. B. Lever, Inorg. Nucl. Chem. Lett., 9,513 (1974). (5) L. H. Vogt, A. Zalkin, and D. H. Templeton, Inorg. Chem., 6,1725 (1967). (6) H. S. Maslen and T. N. Waters, J. Chem. Sac., Chem. Commun., 760 (1973). (7) T. Matsushita, T. Yarino, I. Mosuda, T. Shomo, and K. Shinra, Bull. Chem. Sot. Jpn., 46, 1712 (1972). (8) B. M. Hoffman, C. J. Weschler, and F. Basolo, J. Am. Chem. SOC.,98, 5473 (1976). (9) J. T. Braunholtz and F. C. Mann, J . Chem. Sot., 1817 (1953). (10) W. Coleman, M.S. Thesis, Virginia Polytechnic Institute and State University, 1970. (1 1) S. J. Ebbs, M.S.Thesis,Virginia Polytechnic Institute and State University, 147
nonhydrogen atoms. The structures were then refined using full-matrix 2.000(I) were considered reliable and were used in the structure least-squares calculations with isotropic and then anisotropic thermal analysis. The intensity data were reduced to a set of structure parameters. At this point a difference Fourier synthesis was calculated amplitudes by the usual application of Lorentz-polarization corrections. to determine the positions of the hydrogen atoms, which were included In all three cases the initial choice of the centric space group was based in the final three cycles of least-squares calculatons but were not on calculated intensity statistics and was confirmed by the successful refined. The refinement was terminated when the indicated shifts structure analysis. The relevant crystal data for each of the compounds in positional parameters were less than one-fourth of their estimated are given in Table I. standard deviation. The scheme of refinement and the R index at For ZnC12(4-ac-py)2, a preliminary set of intensity data was various stages, where R = CllFol- IFcl/CIFol,are given in Table 11. collected u’sing the method described above but with Cu Ka!radiation The quantity minimized in the least-squares calculations was (A 1.5418 A) and a 28 range of 0-60°. However, the values of m and xw[llFol - lFClll2where w 1 / 2= F0(F1,, if F, < Flow,w1/2= 1 if Flow y calculated from the least-squares fit of 15 reflections deviated by 5 F,,5 Fhigh, and W1’2 = Fhlsh/F0If Fhish < F,. The Values Of Flow 0.15 and 0.12O, respectively, from the ideal value of 90°. Therefore, and Fhwfor each of the three compounds are given in Table 11. The this data set was of questionable reliability and was used for the scattering factors for the zinc, chlorine, carbon, nitrogen, and oxygen calculation of the Patterson function, the Fourier syntheses, and the atoms were taken from Hanson, Herman, Lea, and Skillmann;” those isotropic least-squares refinement but not for the anisotropic leastfor the hydrogen atom were taken from Stewart, DavidBon, and squares refinement. Of the 1200 reflections measured in this preSirnpson.l4 All scattering factors are uncorrected for the real and liminary data set, the 1042 reflections with I > 2.00a(I) were imaginary parts of the anomalous dispersion. The final atomic considered reliable and were used in the structure analysis. A second parameters for the nonhydogen atoms are given in Tables 111-Y; the set of intensity data was measured using Mo Km radiation and was hydrogen atom parameters are given in Tables VI-YIII. Tables of used for the anisotropic least-squares refinement. The values listed observed and calculated structure factor amplitudes are a~ailab1e.l~ in Table I for ZnC12(4-ac-py)2 are for the second set of data. Results and Discussion Solution and Refinement of Structures. All three structures were The approximately tetrahedral nature of the three complexes solved by the heavy-atom method. The zinc atom position was determined by use of a Patterson function; the other atoms in the can be seen in Figures 1-3 which also give the atomic
+
+
1122 Inorganic Chemistry, Vol. 16, No. 5, 1977
W. L. Steffen and Gus J. Palenik
Table V. Final Parameters of Nonhydrogen Atoms in ZnC1,(4CN-py),a ~~
Atom
Zn W1) Cl(2) N(1a) C(2a) C(3a) C(4a) C(5a) C(6a) C(7a) N(8a) N(1b) C(2b) C(3b) Ci4b) USb) C(6b) C(7b) N(8b)
Y
X
24 605 (5) 1 6 8 5 (1) 2 085 (1) 3 113 (3) 3 535 (5) 4 019 (4) 4 044 (4) 3 588 (4) 3 131 (5) 4 562 (5) 5 001 (4) 3 249 (4) 3 360 (5) 3 885 (5) 4 287 (5) 4 180 (6) 3 640 (5) 4 818 (6) 5 244 (5)
5924 (11) -1431 (3) 3141 (3) -721 (9) 188 (9) -617 (11) -2476 (11) -3441 (10) -2536 (8) -3359 (13) 4 0 2 7 (12) 1388 (8) 375 (11) 905 (12) 2455 (10) 3491 (13) 2886 (11) 3072 (12) 3568 (13)
Z
P1 I
12 769 (3) 1 6 7 5 (1) 851 (1) 649 (2) 269 (3) -142 (3) -152 (3) 228 (3) 622 (3) -559 (4) -870 (3) 1 9 2 4 (2) 2 417 (3) 2 860 (3) 2 788 (4) 2 282 (4) 1 864 (3) 3 252 (4) 3 596 (4)
417 (4) 52 (1) 59 (1) 35 (2) 44 (4) 38 (3) 32 (3) 48 (3) 47 (4) 44 (3) 63 (3) 44 (3) 49 (4) 43 (4) 37 (4) 58 (5) 59 (4) 49 (4) 74 (4)
P22
1247 (17) 192 (4) 136 (4) 162 (16) 141 (15) 193 (16) 212 (20) 146 (15) 111 (14) 264 (22) 348 (24) 137 (13) 186 (18) 222 (24) 193 (17) 263 (21) 237 (20) 232 (20) 368 (25)
~~
118 (2) 20 ( 0 ) 18 (0) 12 (1) 15 (2) 16 (1) 15 (1) 20 (2) 18 (2) 23 (2) 31 (2) 14 (1) 17 (2) 16 (2) 17 (2) 25 (2) 19 (2) 24 (2) 38 (2)
013
P12
P33
-77 (16) -50 (4) 31 (3) 6 (12) -13 (12) 18 (14) 39 (12) 12 (13) -13 (11) 44(16) 105 (16) -57 (11) 4 0 (16) -7 (16) -25 (13) -109 (19) -95 (16) -31 (16) -78 (17)
P23
-86 -3 -11 -11 -8 -7
(3) (1) (1) (3) (4) (3) -8 (4) -5 (4) -13 (4) -7 (4) 12 (4) -7 (3) -12 (4) -14 (4) -10 (5) -20 (6) -19 (5) -19 (6) -57 (6)
-21 (10) 13 (2) 4 (2) 6 (8) 5 (8) 1(10) -19 (9) -19 (9) 0 (8) -7 (12) -19 (11) 1(7) 11 (10) -1 (10) -20 (10) 24 (13) 21 (10) 3 (12) -6 (13)
a All values are X l o 4 , except those for Zn, which are X lo5. The estimated standard deviati6ns are given in parentheses. The temperature factor is of the form exp[-(pl,h2 + &,k2 t p 3 J 2 + p12hk+ p13hl+ &#)].
Table VI. Final Parameters of the Hydrogen Atoms in ZnC1, ( 4 - ~ i n - p y ) , ~
Table VIII. Final Parameters of the Hydrogen Atoms in ZnC1, ( 4 - c N - p ~ ) ~ ~
Distance, Atom
X
Y
z
B,A2
A
X
Y
z
B,A2
Distance, A
H(2a) H(3a) H(5a) H(6a) H7(7a) H8(8a) H9(8a) H(2b) H(3b) H(5b) H(6b) H7(7b) H8(8b) H9(8b)
174 306 229 79 431 460 308 -162 -34 504 377 217 508 619
141 24 -501 -320 -183 496 -605 -200 -302 -201 -77 -394 446 -317
74 -64 81 202 -155 -173 -36 421 568 430 300 672 677 588
7.1 8.1 8.5 7.8 10.6 12.7 12.7 7.1 7.9 8.7 7.8 10.7 12.4 12.4
1.14 1.12 1.18 1.12 1.35 1.32 1.40 1.24 1.19 1.10 1.13 1.36 1.33 1.13
365 435 353 285 303 400 468 389
162 51 491 -345 -102 33 460 323
26 4 2 26 87 243 334 215 128
4.5 4.8 4.7 4.5 5.5 5.2 6.8 5.7
1.08 1.20 1.10 1.00 1.18 1.17 1.24 1.40
The positional parameters are X lo3. The number in parentheses is the number of the carbon atom to which the hydrogen is bonded at a distance given in the last column. CL i2I
The positional parameters are X 10’. The number in parentheses is the number of the carbon atom to which the hydrogen is bonded at a distance given in the last column. Table VII. Final Parameters of the Hydrogen Atoms in ZnC1,(4-a~-py),~
c
1
Distance, Atom H(2a) H(3a) H(5a) H(6a) H7(8a) H8(8a) H9(8a) H(2b) H(3b) H(5b) H(6b) H7(8b) H8(8b) H9(8b)
X
Y
z
B,A’
A
469 569 496 411 627 671 652 260 157 183 271 62 55 72
445 381 192 225 332 355 262 318 351 581 536 583 542 610
23 -87 24 109 -216 -129 -224 -96 -257 -151 53 -456 -295 -341
5.8 6.1 8.0 8.7 9.7 9.7 9.7 7.8 6.5 7.4 5.7 10.0 10.0 10.0
1.00 1.05 0.93 1.13 1.00 1.09 1.01 1.16 1.03 1.13 1.05 0.96 1.08 0.90
The positional parameters are X l o 3 . The number in parentheses is the number of the carbon atom to which the hydrogen is bonded at a distance given in the last column.
numbering. The bond lengths and angles in the coordination sphere are given in Table IX. The dimensions of the pyridine ligands together with the least-squares planes data are a~ailab1e.I~ These three complexes together with ZnC12(py)21 and ZnC12(4-CH3-py)212form a series of ZnClz(4-R-py)z
153,
Figure 1. ORTEP drawing of dichlorobis(4-~inylpyridine)zinc(11) showing the thermal ellipsoids and atomic numbering.
complexes in which the substituent in the 4 position has been systematically varied. The basicity of the pyridine in aqueous solution (pKb)I6varies with the substituent in the order CH3 (7.97) > vin (8.38) > H (8.80) > ac (10.49) > CN (12.12). Therefore, we have a series in which the steric properties of the ligand are approximately constant while the donor properties vary. A plot of the average Zn-Cl and Zn-N distances in the five complexes vs. the ligand pKbis shown in Figure 4. In the case of the Zn-N distances a linear relationship Zn-N(av) = [2.004 (1) 0.0050 (5)(p&)] A can be obtained by a least-squares pr0~edure.l~The point for the ac complex was assigned a weight of ’ I 2because the esd‘s for the Zn-N bond were approximately twice those of the other complexes. The relationship illustrated in Figure 4 of the Zn-N bonds has
+
a vs.
?r
Inorganic Chemistry, Vol. 16, No. 5, 1977 1123
Bonding in Tetrahedral Zinc(I1) Complexes
Table IX, Bond Lengths (A) and Angles (deg) in the Coordination Sphere for the ZnC12(4-R-py), Complexes R Acetyl
Vinyl
Cyano .4
Zn-CKl) ZnC1( 2) Zn-N( la) Zn-N( 1b)
Lengths 2.214 (2) 2.204 (2) 2.054 ( 5 ) 2.040 ( 5 )
2.216 (3) 2.206 (3) 2.061 (9) 2.042 (9)
2.207 2.218 2.059 2.069
C1( l)-ZnC1(2) C1( 1)-Zn-N(1a) C1( 1)-Zn-N( 1b) C1(2)-Zn-N( 1a) C1(2)-Zn-N( l b ) N(l a)-Zn-N(l b)
Angles 118.7 (1) 106.9 (2) 110.8 (2) 110.7 (2) 106.6 (2) 101.9 (2)
123.6 (1) 105.7 (3) 104.5 (3) 107.9 (3) 105.7 (3) 109.0 (4)
125.7 (1) 106.9 (2) 107.8 (2) 105.5 (2) 104.3 (2) 105.0 (2)
(2) (2) (5) (6)
2241 223t
$222
2
4E.
i
P
I
80
90
100
11 0
12 0
13 0
LIGAND pKb
L 121
2.071 0 4
8'
E9 H
0206-
f
Figure 2. ORTEP drawing of dichlorobis(4-acetylpyridine)zinc(II) showing the thermal ellipsoids and atomic numbering. LIGAND pKb
Figure 4. Average Zn-Cl and Zn-N bond distances in ZnC12(4-R-py)2 complexes vs. the ligand pKb values. Abbreviations: CH3, methyl; vin, vinyl; ac, acetyl; C N , cyano; H, unsubstituted complex.
were significant, then we might have anticipated that the Zn-N distance would not be linearly dependent on the pKb value of the ligand. Therefore, we conclude that ?r bonding in these ZnC12L2complexes must be minimal. The variation in Zn-C1 bond distances with pKb as shown in Figure 4 is somewhat more complicated. If we exclude the point for pyridine (H), the relationship Zn-Cl(av) = [2.199 (2) 0.0011 (4) (pKb)] 8, can be derived. The pyridine complex packs differently from the others, vide infra, which can explain the deviation of that point. The variation in Zn-€1 distance with the p& is so small that the average bond lengths are virtually independent of pKb. In fact, the average bond lengths for the CH, case (2.207 8,) are not significantly different from those found in the CN complex (2.212 A) using the usual test.'* The zinc(I1) ion presumably does not transmit changes in the a-donor abilities of the pyridine ligands to the chloride ion. Consequently, a phenomenon analogous to the trans effect in square-planar c o m p l e ~ e sdoes ' ~ not appear to exist for the ZnC12(4-R-py)2series. Far-Infrared Studies. The infrared frequencies in the region 500-190 cm-I observed for the five complexes are given in Table X. The Zn-C1 and Zn-N stretching frequencies were assigned by comparison with those reported for other ZnC12(R-py)2c ~ m p l e x e s ~ * *as" follows ~~ (cm-I): VZn-N 255, 240, and 199 for CH3, 243 and 196 for vin, 222 and 203 for H, 245 and 202 for ac, 216 and 199 for CN; v ~ 335~ and304 for CH3, 329 and 304 for vin, 330 and 297 for H, 337 and 302 for ac, 340 and 302 for CN. Plots of the average Zn-Cl and Zn-N stretching frequencies vs. ligand p& are shown in Figure 5. There is no systematic change of either Zn-C1 or Zn-N with pKb of the ligand. The,
+
Figure 3. ORTEP drawing of dichlorobis(4-cyanopyridine)zinc(II) showing the thermal ellipsoids and atomic numbering.
important implications regarding the nature of the bonding in these tetrahedral ZnC12 complexes. The ligand pK{s can be viewed as a measure of the strength of the interaction of the pyridine with a hydrogen ion. A smaller pKb indicates a stronger pyridine-hydrogen interaction. Since there is no possibility for ?r bonding to a hydrogen ion (via a ?r* orbital of the pyridine), the pKb can be viewed as an indication of the u-donor strength of the pyridine. Consequently, the variation of the Zn-N distance with pKb can be interpreted as being strictly a a-bond effect. If, as has been suggested: ?r bonding
~
~
W. L. Steffen and Gus J. Palenik
1124 Inorganic ~~~~~~~~y~V d . 16, Noe 5, 1937 Table X. Infrared Spectra in the Region 500-190 crn-’ for Some ZnC1, (4-R-py), and ZnRr, ( 4 - W - p ~Complexesn )~
Gornpd
Absorption peaks, em‘’
, W, 358 V J , 335 S, 304 S, ZnCl,(4CH3-py), 494 s p , 489 ~ p 388 255 m, 240 m, 199 s Zn61I2(4-vin-py), 466 br, 452 br, 329 s, 304 s, 243 w, 196 s ZnCl,(py), 424 sp, 418 s p , 330 s, 297 s, 2 2 2 rn, 203 w ZnCl2(4-ac-py), 429 rn, 388 br, 337 s, 302 s, 245 rn, 202 m ZnC12(4-CN-py), 391 sp, 384 sp, 340 s, 302 s, 216 m, 199 s ZnBr,(py), 425 sp, 417 sp, 256 5, 222 s, 185 rn ZnBr2(4CN-py), 390 sp, 387 sp, 272 s, 214 s, 205 w, 190 m a Relative intensities: s, strong; m,moderate; w, weak; br, broad; sp, sharp.
3’0
t
Figure 6. Packing diagram for the dichlorobis(4-vinylpyridine)zinc(II) complex. so
80
10.0
11.0
12.0
13.0
LIGAND P K ~
ac
H
I 1 210
CN
I 00
90
100
11 0
12 0
13 0
LIGAND P K ~
Figure 5. Average Zn-Cl and Zn-N stretching frequencies in some ZnC12(4-R-py)2complexes vs. ligand pKb values. The abbreviations are the same as in Figure 4.
A, mode for the Zn-C1 stretch at about 300 cm-’ and the B, mode at about 330-340 cm-l are virtually independent of the ligand pP(b in agreement with our structural studies. The Zn-N frequencies show a bit more scatter and are not as constant as a function of pKb. The symmetric stretch, A,, shows some tendency to decrease with pKb although the value for the 4-ac derivative is higher than might be expected. The asymmetric stretch at about 196-204 cm-I appears to be virtually independent of p&,. A calculation was made to correct for the difference in mass of the various derivatives2’ but it did not reveal any variations with p&,* .4 normal~ , ~shown ~ coordinate analysis of the ZnC12(py)*~ o m p l e xhas that there is little or no coupling between the Z n 4 l and Zn-N stretching modes which might affect the correlation of the frequencies with ligand pKb. The earlier study of the ZnC12(py), momplex4assigned values of 219.2 and 152.6 cm-’ to the Zn-N stretche4The lower value
was particularly important in their arguments regarding substituent effects. Our measurements of 222 and 203 cm-’ for Zn-N in Z r ~ C l ~ ( p yare ) ~ in agreement with the values reported by others: 222.4 and 203.9,23222,24221,20and 220 cm-1.25Consequently, it appears that the earlier conclusions4 may have been based on an incorrect assignment of the Zn-N frequencies. Packing Effects. The plot of the average Zn-G1 distances vs. ligand pKb given in Figure 4 shows that the four substituted pyridines fall on a straight line. However, a much longer Zn-Cl distance was found in the unsubstituted case (point H) which appears to be related to the unique packing arrangement found in the ZnC12(py)2complex. The packing diagrams for the vin, ac, and CN complexes are given in Figures 6-8 while similar diagrams are available for the py” and CH3I2complexes. In the py case one set of rings (the “a rings”) are stacked across a center of symmetry to give a dimerlike unit. The inter-ring distances of 3.7-3.8 h; are about the shortest found in the ZnC12L2series. The dimerlike units have longer contacts between the “b rings” of about 4.2 h; with the rings tipped by about 25 “C relative to each other. When there is a bulky substituent in the 4 position, the dimerlike pair is prevented from forming because of steric factors and the rings are much further apart, 4.8-5.2 A. For example in the vin complex, Figure 7, although the a and b rings appear to stack across centers of symmetry, the rings are displaced along the a axis so that the ring centers are very far apart. The intramolecular H . 4 1 contacts in the pyridine case also appear to be slightly different from the substituted complexes. The H 4 1 contacts (Table XI) usually consist of one short contact of about 2.8 h; and a long contact of greater than 3.1 h; for each ring. For comparison, the van der Waals radii for H and C12*give a nonbonded contact of about 3.0 A. The difference in the two contacts of a given ring simply represents a rotation about the Zn-N bond. These rotations about the Zn-N bond of the individual molecules can also be seen in Figures 1-3. Presumably, the significantly different packing arrangement in the ZnC12(py)2complex causes small rotations in the pyridine rings and a slight weakening of the Zn-Cl bond distances. The fact that the Zn-N distances are a function of pKb also suggests that a-bonding arguments are not im-
Inorganic Chemistry, Vol. 16, No. 5, 1977 1125 Table XI. Comparison of the C1, 421 and C1+ -H Intramolecular Contacts (in A) for the ZnC12(4-R-py), Complexes R
C1(1)**4 3 2 ) H(a1.a G(1) H(a). * Cl(2) H(b). *Cl(l) H(b)***C1(2)
-
CH,'
vin
H
ac
CN
3.86 3.12 2.86 2.98 3.11
3.80 2.85 3.85 3.89 2.77
3.87 3.26 3.01 3.05 3.05
3.90 3.17 3.18 3.39 2.83
3.94 2.87 3.23 3.10 3.24
Calculated from the data in ref 12.
Figure 7. Packing diagram for the dichlorobis(4-acetylpyridine)zinc(II) complex.
+
+ Figure 8. Packing diagram for the dichlorobis(4-cyanopyridine)zinc(II) complex. Only the two cyano groups have been labeled but the A denotes the a ring and B the b ring.
portant and that the longer Zn-C1 distances in the py derivative are a result of crystal-packing effects. Comparison of ZnC12(4-R-py)2Structures with Those of Other ZnClzL2Complexes. The Zn-N and Zn-C1 distances in a number of ZnCI2L2complexes where L is a nitrogen donor are given in Table XII. The entries are arranged in order
of increasing pKb values of the ligand. The Zn-C1 distances fall within a comparatively narrow range of 2.228-2.198 A if the ZnC12(NH3)231 and ZnC12(imid)232 (imid = imidazole) cases are excluded. The ZnC12(NH3)zstructure is rather old and should probably be redone. In this complex the existence of N-H...Cl hydrogen bonds could easily account for the long Zn-C1 bonds. There are N-HO-Cl hydrogen bonds in the Z ~ ~ C l ~ ( i mstructure i d ) ~ and the Zn-C1 bonds are a bit longer than might be expected. In the remaining cases the Zn-C1 distances are only slightly dependent on the ligand pKb. The dependence of the Zn-N distance on the ligand pKb is more pronounced but again we see small changes due to steric effects. The dmphen vs. phen is a particularly interesting example where the Zn-N distance is increased sli htly due to steric factors. The Zn-N distance of about 2.00!f appears to be a lower limit, but as noted above, the ZnC12(NH3)2data are not up to modern standards. In conclusion, we see that in tetrahedral ZnC12Lzcomplexes with L as a nitrogen donor the Zn-N distances roughly parallel the ligand pKb values with small perturbations due to steric effects. The reported Zn-N and Zn-Cl stretching frequencies for various ZnClzL2 complexes with L as a nitrogen donor are given as a function of the ligand pKb in Table XIII. A perusal of the various values does not reveal any obvious trends in the two stretching frequencies as a function of ligand pKb. The lack of a correlation is not too surprising since even in our limited series, as seen in Figure 5, there was no obvious relationship between the stretching frequency and p&. Presumably, the packing effects are sufficient to mask any small changes in the frequencies. Consequently, spectroscopic data alone may not be sufficient to interpret trends in bonding of molecular complexes. Structures of the Three Pyridine Ligands. Although the various pyridine rings are planar (see supplementary material15), the dimensions, as expected, do not correspond to those of a regular hexagon. The C-N bonds average 1.335 (4) A4' compared to the value in gaseous pyridine of 1.340 (1) A42or of 1.330 A in the glucitol-pyridine complex.43 The C-C distances average 1.375 (3) A4' compared to the value of 1.394 (1) A in gaseous pyridine and 1.367 A in the glucitol complex. The shorter C-C bonds may be related to libration effects. The average C-N-C, N-C-C, and C-C-C angles of 117.8 (3), 122.7 (3), and 118.9 (3)' are very similar to the values of 116.8, 123.9, and 118.5' observed in gaseous pyridine. Consequently, there appears to be very little change in the pyridine ring dimensions which is reasonable if the Zn-N bonding is nearly pure u with very little H interaction. This observation is in agreement with our earlier discussion. The structure of uncomplexed 4-cyanopyridine has been reported44and the pyridine distances and angles are virtually identical with the average values found in our studies. Furthermore, the C-C distance of 1.439 (8) A and the C-N distance of 1,137 (8) %I in the uncomplexed ligand are virtually identical with the corresponding values of 1.449 (1 1) and 1.135 (12) A observed in the ZnC12 complex. If H effects were important, then the C-N-ring interactions might be altered and the CN dimensions would be different in the complexed
W. L. Steffen and Gus J. Palenik
1126 Inorganic Chemistry, Vol. 16, No. 5, 1977
Table XII. Comparison of Zn-N and Z n C l Bond Distances in Some Tetrahedral ZnCl,L, Complexes, Where L is a Nitrogen Donor Compda
PKb
Ref
ZnC1, A
Zn-N,A 2.01 1.995 2.046 2.059 2.040 2.052 2.050 2.042 2.069
2.30 ( l l ) , 2.020 (11) 2.258 (3), 2.239 (3) (5), 2.042 (5) 2.211 (2), 2.204 (2) ( l l ) , 2.074 (9) 2.204 (3), 2.219 (3) (5), 2.054 (5) 2.204 (2), 2.214 (2) (6), 2.046 (5) 2.228 (2), 2.215 (2) ( 7 ) , 2.072 (7) 2.207 (3), 2.198 (3) (9), 2.061 (9) 2.216 (3), 2.206 (3) (6), 2.059 (5) 2.218 (2), 2.207 (2) a imid is imidazole; dmphen is 2,9-dimethyl-l,lO-phenanthroline; phen is 1,lO-phenanthroline. ZnC1, (NH a), ZnC1, (imid), ZnC1, (4-CH3-py), ZnC1, (drnphen)a ZnCl2(4-vin-py), ZnC1,(PY)z ZnCl,(phen)a ZnCl2(4-ac-py), ZnC1, (4-CN-py),
4.74 7.01 7.97 8.15 8.38 8.80 9.04 10.49 12.12
29 16 16 16 30 16 16 16 16
Ref 31 32 12 6 This work 11 33 This work This work
Table XIII. Comparison of Zn-N and Zn-Cl Stretching Frequencies in Some Tetrahedral ZnCl,L, Complexes, Where L is a Nitrogen Donor ZnC1, (NH, ), ZNC1, (2-CH3-imid) ZnCl,(N-CH,-imid), ZnCl,(imid), ZnC1, (4-CH3-py), ZnC1,(2-CH3-py), ZnCl,( 3-CH3-py), ZnC1, (4-vin-py), ZnC1, (4-CH2OH-py), ZnC1, (Ph-hyd), ZnCl,(py), ZnCl2(3,4-xyld), ZnC1, @-told), ZnCl,(rn-told), ZnCl,(anil), ZnC1, (2,s-xyld) , ZnC1, (o-told), ZnC1, (2,6-xyld), ZnCl,(p-Cl-anil), ZnCl2(4-Br-py), ZnCl2(4-ac-py), ZnC1, (rn-C1-ad), ZnC1, (4-CONH2py), ZnC1,(4-COOCH3-py) , ZnC1, (4-CN-py), ZnC1, (2-C1-py), a
4.74 6.14 6.75 7.01 7.97 8.04 8.30 8.38 8.59 8.80 8.80 8.83 8.92 9.29 9.42 9.47 9.60 10.05 10.05 10.25 10.49 10.55 10.57 10.76 12.12 13.51
29 16 16 16 16 16 16 30 2 16 16 30 16 16 16 30 16 16 16 16 16 16 2 2 16 30
422 240 235 253, 231 255,240, 199 224,209 204 243, 196 233,173 394, 376 222,203 413 417, 39Sb 417, 385b 402, 362 386b 411, 390b 390, 357b 411, 396 223 245, 202 420,391 227, 210 230, 204 216, 199 210
Ph-hyd is phenylhydrazine; xyld is 3,4-xylidine; told is toluidine; ani1 is aniline.
and uncomplexed states. Consequently, the indications, once again, support the postulate of mainly a u interaction between the Zn atom and pyridine base. The dimensions of the acetyl and vinyl groups are not particularly remarkable. The C = C distance in the vinyl group of 1,195 A is short, but the thermal parameters are large and libration and/or disorder could account for these apparently short distances.
Summary The structural data on ZnC12(4-R-py)2complexes have been correlated with the pKb of the pyridine ligand. The average Zn-N distance varies linearly with the ligand pKb. Since the ligand pKb is strictly a u-bond effect, the importance of ?r bonding in the above series must be minimal. When R is a bulky group, the Zn-C1 distances appear to be independent of the ligand pKb, again suggesting a minimum *-type interaction. Finally, the dimensions of the various ligands are consistent with the a-bond model. The ZnC12(py)2complex is anomalous because the small H atom in the 4 position permits a significantly different packing arrangement. Our conclusions are the opposite of other reports which emphasize the importance of T bonding in the above series. The far-infrared data for ZnC12L2complexes, where L is a nitrogen donor, do not appear to be dependent upon the ligand pKb in any simple way. Presumably, mass differences, crystal packing, and coupling of modes can produce small effects which obscure the changes due to the ligand pKb. In
286 302,287 306,285 301,289 335, 304 318, 297 329, 284 329, 304 311, 294 297 330,297 307,294 298 303 294 315,295 303,285 315 304 324,298 337, 302 308,298 328, 294 329,298 340, 302 321, 308
34 35 36 34 This work 21 20 This work 4 37 This work 38 38 38 39 38 38 38 40 21 This work 40 4 4 This work 21
Listed as "other modes".
addition, the problem of the correct bond assignment is always present. Therefore, one should use the results of infrared studies cautiously in discussing the nature of the bond in ZnC12L2complexes and, by extension, in other systems as well.
Acknowledgment. We wish to thank the Center for Instructional and Research Activities, University of Florida, for a grant of computer time and Professor A. J. Cary, University of Waterloo, for measuring the infrared spectra in the 500190-cm-' region. Registry No. ZnC12(4-vin-py)2, 17501-34-7; ZnC12(4-ac-py)2, 19234-45-8; ZnClz(4-CN-py),, 19234-43-6; ZnCI2(4-CH3-py),, 13869-84-6; ZnC12(py)2, 6843-20-5; ZnBr2(py),, 14024-88-5; ZnBrz(4-CN-py),, 418 15-87-6. Supplementary Material Available: Tables of the interatomic distances and angles and least-squares planes for the pyridine rings, together with the observed and calculated structure factors (26 pages). Ordering information is given on any current masthead page.
References and Notes (1) Abstracted in part from a dissertation by W.L.S. to the Graduate School, University of Florida, in partial fulfillment of the requirements for the Ph.D. degree, Aug 1975. (2) P. T. T. Wong and D. G. Brewer, Can. J . Chem., 46, 131 (1968). (3) P. T. T. Wong and D. G. Brewer, Can. J . Chem., 46, 139 (1968). (4) P. T. T. Wong and D. G. Brewer, Can. J . Chem., 47, 4589 (1969). (5) M. Mathew and G. J. Palenik, Znorg. Chim. Acta, 5, 349 (1971). (6) H. S. Preston and C . H. L. Kennard, J . Chem. SOC.A , 1956 (1969). (7) S. Tazuke and S. Okamura, J . Polym. Sci. Polym. Chem. Ed., 5, 1083 (1967).
Inorganic Chemistry, Vol. 16, No. 5, 1977 1127
Binuclear Complexes (8) R. S.Nyholm, Proc. Chem. Soc., London, 273 (1961). F. A. Cotton and F. Zingales, J . Am. Chem. Soc., 83, 351 (1961). D. G. Brewer and P. T. T. Wong, Can. J . Chem., 44, 1407 (1966). W. L. Steffen and G. J. Palenik, Acta Crystallogr.,Sect. E, 32,298 (1976). H. Lynton and M. C. Sears, Can. J . Chem., 49, 3418 (1971). H. P. Hanson, F. Herman, J. D. Lea, and S.Skillman, Acta Crystallogr.,
(9) (10) (I 1) (12) (1 3)
17, 1040 (1964) (14) R. F. Stewart, E. R. Davidson, and W. T. Simpson, J . Chem. Phys., 42, 3175 (1965). (15) Supplementary material. (16) D. D. Perrin, “Dissociation Constants of Organic Bases in Aqueous Solution: Supplement 1972”, Butterworths, London, 1972. (17) P. R. Bevington, “Data Reduction and Error Analysis for the Physical Sciences”, McGraw-Hill, New York, N.Y., 1969, pp 92-118. (18) D. W. J. Cruickshank and A. P. Robertson, Acta Crystallogr., 6, 698 (1953). (19) T. G. Appleton, H. C. Clark, and L. E. Manzer, Coord. Chem. Rev., 10, 335 (1973). (20) J. Burgess, Spectrochim. Acta, Part A , 24, 277 (1968). (21) N. S.Gill and H. J. Kingdon, Aust. J . Chem., 19, 2197 (1966). (22) I. S.Ahuja and R. Singh, J . Inorg. Nucl. Chem., 36, 1505 (1974). (23) Y Saito, M. Cordes,and K. Nakamoto, Spectrochim. Acta, Part A , 28, 1459 (1972). (24) C. W. Frank and L. B. Rogers, Inorg. Chem., 5, 615 (1966). (25) R. J. H. Clark and C. S. Williams, Inorg. Chem., 4, 350 (1965). (26) The Zn-N stretching frequencies for ZnC12(4-CH py)*have been reported as 238.2 and 192.4 cm-’ and as 254 and 238 cm-i-. Thus, the three bands at 255,240, and 199 cm-I have been included in the assignment for uzn+
for ZnC12(4-CHz-py)z (27) J. R. Dyer, “Applications of Absorption Spectroscopy of Organic Compounds”, Prentice-Hall, Englewood Cliffs, N.J., 1965, p 24.
(28) L. Pauling, “The Nature of the Chemical Bond’’, Cornell University Press, Ithaca, N.Y., 1960, p 260. (29) D. A. Skoog and D. M. West, “Fundamentals of AnalyticalChemistry”, Holt. Rinehart and Winston. New York, N.Y., 1969, D 817.(30) D. D. Perrin, “Dissociation Constants of Organic Bases in Aqueous Solution”, Butterworths, London, 1965. (31) C. H. MacGillavry and J. M. Bijovet, 2.Kristallogr., Kristallgeom., Kristallphys., Kristallchem., 94, 249 (1936). (32) B. K. S.Lundberg, Acta Crystallogr., 21, 901 (1966). (33) C. W. Reimann, S.Block, and A. Perloff, Inorg. Chem., 5, 1185 (1966). (34) C. Perchard and A. Novak, Spectrochim. Actd, Part A , 26,871 (1970). (35) D. M. L. Goodgame, M. Goodgame, and G.W. Rayner-Canham, Inorg. Chim. Acta, 3, 399 (1969). (36) D. M. L. Goodgame, M. Goodgame, and G. W. Rayner-Canham, Inorg. Chim. Acta, 3, 406 (1969). (37) L. U. Konovalov, I. S.Maslennikova,and V. N. Shemyakin, Zh. Obshch. Khim.. 40. 2443 (19701.
I. S. Ahuja, D. H.’Brown, R. H. Nuttall, and D. W. A. Sharp, J . Inorg. Nucl. Chem., 27, 1625 (1965). I. S.Ahuja, D. H. Brown, R. H. Nuttall, and D. W. A. Sharp, J . Inorg. Nucl. Chem., 27, 1105 (1965). I. S. Ahuja and P. Rastogi, J . Chem. SOC.A , 1893 (1969).
The value quoted is the unweighted average of the appropriate bonds in the three complexes. The esd of the mean value (2 = xpxt/N)is [ L Y X , - X ) 2 / w - 1)1”*. (42) B. Bak. L. Hansen-Nvnaard. and J. RastruDAndersen. J. Mol. SDectrosc, *-
. , 2, 361 (1958).
(43) H. S.Kim,G.A. Jeffrey, and R. D. Rosenstein, Acta Crystallogr., Sect. E , 27, 307 (1971). (44) M. Laing, N. Sparrow, and P. Sommerville, Acta Crystallogr., Sect. E , 27, 1986 (1971).
Contribution from the Center for Molecular Structure, Department of Chemistry, University of Florida, Gainesville, Florida 3261 1
Binuclear Complexes. Synthesis and Characterization of the Binuclear Ligand 1,4-DihydrazinophthalazineBis(2’-pyridinecarboxaldimine) and the Nickel Complex p-Chloro-tetraaqua[1,4-dihydrazinophthalazine bis(2’-pyridinecarboxaldimine)]dinickel( 11) Chloride Dihydrate DOUGLAS A. SULLIVAN and GUS J. PALENIK’
Received September 10, 1976
AIC606775
The synthesis and characterization by x-ray diffraction techniques of a binuclear ligand and its corresponding dinickel complex are described. The ligand dhphpy, 1,4-dihydrazinophthaIazinebis(2’-pyridinecarboxaldimine), is formed by the reaction of pyridinecarboxaldehyde with the 1,4-dihydrazinophthalazine, dhph, in the presence of the Ni(I1) ion. The protonated ligand H2dhphpy(N03)2-2H20(I) forms monoclinic crystals with unit cell dimensions of a = 20.480 (3), b = 11.166 (2), and c = 10.704 (2) 8, with p = 102.99 (2)’. The space group is C2/c and, with 4 molecules per cell, the ligand I lies on a twofold axis. The structure was solved by direct methods and refined to an R value of 0.050. The dinickel complex I1 also forms monoclinic crystals (green) with the space group C/2c. With 8 dinuclear units per cell, no symmetry is required; however, there is in essence a twofold axis in the complex. The unit cell dimensions are a = 15.016 (6), b = 15.527 (6), and c = 28.704 (17) 8, with p = 115.78 (3)’. The final R was 0.048. The main differences between the ligand I and the dinickel complex I1 are the angles in the “hydrazone arms” which change slightly after complex formation. The magnetic moment in solution of the dinickel complex is 2.74 pB,slightly lower than the spin-only value. Since the cations are well separated in the crystal and presumably in solution, the lowering of the moment must represent a nickel-nickel interaction. Both the ligand I and the dinickel complex I1 (excluding the axial water molecules) are remarkably planar and show extensive delocalization. Therefore, the preparation of binuclear ligands from dhph and various aldehydes appears to be virtually limitless.
Introduction Multidentate ligands which incorporate two metal atoms are useful in studying the magnetic interactions between metal ions. The binuclear complexes themselves are of interest as models of metalloenzymes and in applications to catalysis. Ligands which yield binuclear complexes are not common2and have generally involved either substituted dif~rmylphenols,~-~ or 1,4-dihydrazinophthala~ine~~~ although a few heptatri~nes,~,’
other examples are known.’OJ1 However, in the majority of cases the bridging groups are determined by the geometry of the ligand and cannot be altered. Therefore, we decided to prepare a binuclear ligand where only the bridging atom was undefined and could presumably be varied. The reaction of 1,4-dihydrazinophthalazine with appropriate aldehydes should yield hydrazones with six donor atoms arranged in a manner which would favor the formation of bi-
