Organometallics 1983,2, 327-331 iminyl carbon and nitrogen atoms are bonded to different metal atoms. Structurally, these ligands show no unusual distortion^.^^ Each metal atom contains three linear terminal carbonyl ligands. The central s2os2(co)6 unit contains a "sawhorse" structure similar to that of ( ~ - s E t ) ~ F e ~ ( C The o ) ~di.~~ hedral angle between the Os(3)-0~(4)-S(l) and Os(3)Os(4)-S(2) planes is 102.4'. Overall, the molecule contains C2symmetry although this is not crystallographically imposed. The shortest intermolecular contacts were between the carbonyl oxygen atoms 0(8)-.0(10) = 3.04 (2) A and 0(5)-.0(18) = 3.07 (2) A. In order that all the metal atoms can achieve l&electron configurations, the sulfido ligands must serve as six-electron donors. This would include a formal donation of two electrons to both Os(1) and Os(6) and one electron to both 0 4 2 ) and Os(5). I t has been shown that sulfido ligands can play an important role in the synthesis of high nuclearity metal
327
carbonyl cluster c~mpounds.'-~Q'~'~ This is made possible to a large degree by their ability to serve as multicoordinate, multielectron bridging ligands and also engage in the wide variety of coordination environments I and IIa-IIe.
Acknowledgment. This work was supported by the Office of Basic Energy Sciences of the U S . Department of Energy under Contract No. DE-AC02-78ER04900 and the Alfred P. Sloan Foundation through a fellowship to R.D.A. We wish to thank Engelhard Industries for a loan of osmium tetroxide and Drs. I. T. Horvath and B. E. Segmiiller for helpful discussions. Registry No. IV, 84000-57-7. Supplementary Material Available: A listing of structure factor amplitudes (13 pages). Ordering information is given on any current masthead page. (25) Adams,R. D.; Golembeski, N. M. J. Am. Chem. 1979,101,2579. (26) Dahl, L. F.; Wei, C. H. Znorg. Chem. 1963, 2, 328.
Crystal and Molecular Structure of Hexaphenylcyclohexaarsine, CyclO -(ASP h)6 Arnold L. Rheingold' and Patrick J. Sullivan Department of Chemistty, Universiv of Delaware, Newark, Delaware 197 1 1 Received September 10, 1982
The crystal and molecular structure of hexaphenylcyclohexaarsine (1) has been determined in order to establish a standard for a "normal" As-As bond distance. The new structural determination represents a many-fold improvement in precision over a study performed 22 years ago. 1 crystallizes in the monoclinic s ace group ml/nwith a = 12.172 (1) A, b = 6.234 (1) A, c = 22.884 (3) A, /3 = 99.67 (l)', V = 1711.6 (3) and Z = 2. The final residuals are R = 4.45% and R, = 4.76%. The average As-As distance is 2.459 A. A discussion of trends in As-As bond distances in 26 compounds is included.
fi,
Table I. Crystal and Refinement Data for I
Introduction The extreme adaptability of arsenic, both naked and combined, as a bridging element in transition-metal cluster structures has prompted us recently to prepare and characterize crystallographically a series of novel structures containing arsenic-arsenic bonds. The wide ran e in the As-As bond distances that we observed, 2.3-2.8 caused us to search the existing literature for a reliable standard for a "normal" As-As single bond. The values most often cited as standards are (1) gaseous As4, 2.45 A,' (2) c(CH )5, (av) 2.428 (5) A: and (3) C-(C&&,h)6,(aV) 2.456 (5) .3 All of these standards have factors which limit their reliability: (1) the bond distance was determined 47 years ago by electron diffraction and the effects of strain caused by the 60" tetrahedral face angles is uncertain; (2) determined 25 years ago by X-ray crystallography with a 12.3% residual (all atoms isotropic, no absorption correction); and (3) determined 33 years ago by X-ray crystallography, no fiial residual reported, all atoms isotropic, no carbon atom parameters refined, and data limited to 482 observed reflections. We wish now to report the results of a redetermination of the crystallographic structure of c-(C&~AS)~ (I) and to
formula cryst system space group a, A
b, A
e, A
1,
P , deg v, A3
z
temp, "C
cryst dimens, mm
P
(1) Maxwell, L. R.; Hendricks, S.B.;Moseley, V. M. J.Chem. Phys. 1936, 3, 699. (2) Burns, J. H.; Waser, J. J. Am. Chem. Soc. 1957, 79, 859. (3) Hedberg, K.; Hughes, E. W.; Waser, J. Acta Crystallogr. 1961,14, 369. An 11-year delay occurred between data collection and refinement.
radiatn diffractometer abs coeff, cm-' scan speed, deg/min 20 scan range, deg scan technique
(I
data collected scan width, deg weighting factor, g 4 unique data unique data with (F,)' > 30(F0)' std rflns GOF R(F), % R(wF), % w = [ o Z ( F )+ gFZ]-'.
22.884 ( 3 ) 99.67 (1) 1711.6 ( 3 )
2 24 0.05 X 0.15 X 0.37 graphite-monochromated Mo Kor ( h = 0.710 73 A ) Nicolet R3 58.0 variable 3-15 3 < 20 < 55 e 120 ih, + k ,
+I
1.7 t A ( o , - a z ) 0.0012 3472 rflns (3931 collected) 2584 3/97 (no decay observed) 1.070 4.45 4.76
relate the new average As-As distance, 2.459 A, to others found in the literature.
0276-7333/83/2302-0327$01.50/0 0 1983 American Chemical Society
328 Organometallics, Vol. 2, No. 2, 1983
Rheingold and Sullivan
Table 11. Fractional Non-Hydrogen Atomic Coordinates for c-(AsC,H,), ~~
atom
Y
X
0.08499 (5) -0.11624 (5) -0.11971 (5) 0.0899 (5) 0.1345 (5) 0.1432 (6) 0.1108 (7) 0.0664 (6) 0.0552 (6) -0.171 5 (5) -0.2598 (5) -0.3035 (5) -0.2598 (7) -0.1717 (6) -0.1298 (6) -0.2836 (5) -0.3305 (6) -0.4450 (7) -0.5120 (6) -0.4649 (7) -0.3511 (6)
0.55289 (12) 0.51001 (12) 0.75289 (12) 0.4087 (12) 0.2075 (13) 0.1264 (14) 0.2455 (17) 0.4461 (16) 0.5279 (14) 0.7177 (11) 0.6477 (13) 0.7787 (15) 0.9739 (16) 1.0479 (14) 0.9207 (12) 0.7612 (11) 0.9595 (15) 0.9813 (15) 0.8104 (16) 0.6157 (19) 0.5884 (15)
z
0.09139 (3) 0.05552 (3) -0.02925 (3) 0.1683 (3) 0.1819 (3) 0.2381 (3) 0.2818 (4) 0.2698 (3) 0.2129 (3) 0.1079 (3) 0.1347 (3) 0.1741 (4) 0.1876 (4) 0.1617 (3) 0.1214 (3) -0.0490 (3) -0.0530 (5) -0.0664 (5) -0.0759 (4) -0.0726 (5) -0.0589 (5)
Figure 1. Thermal ellipsoid drawing of ~-(Asph)~, 1, with the current labeling scheme as viewed with the molecular orientation perpendicular to the crystallographicb axis.
%*
CRl
Experimental Section Preparation of Sample. 1 was prepared by the hypophosphorous acid reduction of benzene arsonic acid.4 Various techniques were attempted to grow diffraction grade crystals from a range of organic solvents, but all failed to yield either large enough crystals or ones with a melting point about 195 “C. Crystals of high quality were finally obtained by accident; cooling a partially reacted solution of 1 with CpMn(CO), in toluene in a sealed reaction tube from 140 OC to room temperature over a period of 2 days resulted in the formation of large, well-formed single crystals of 1, mp 210 OC. Collection of Diffraction Data. The parameters used during the collection of diffraction data are given in Table I. Epoxy cement was used to affm the crystal to the tip of a fine glass fiber. The original structural determination of 1 was carried out in the monoclinic space group P!&/c,~ but in order to take advantage of a less obtuse /3 angle, the nonstandard setting m l / n was used in the present analysis. The unit-cell dimensions were derived from the angular settings of 50 reflections with 28O I28 I35O. The data were corrected for absorption by an empirical procedure that employs six refined parameters to define a pseudoellipsoid used to calculate the correction^.^ A profile fitting procedure was applied to all intensity data to improve the precision of the measurement of weak reflections. Solution and Refinement of the Structure. A satisfactory structure solution was obtained from the atomic coordinates of the original determination3after application of the transformation matrix to convert E 1 / c to P2,/n. An all-isotropic model for the non-hydrogen atoms converged at R = 11.8%. With all nonhydrogen atoms refined anisotropically employing idealized hydrogen atom positions (d(C-H) = 0.96 A, thermal parameters equal 1.2 times the isotropic equivalent for the carbon atom to which it was attached) and a riding model that updated hydrogen atom positions after each cycle, the final residuals R(F) = 4.45% and R(wF) = 4.76% were obtained. A final difference Fourier synthesis showed only a diffuse background (maximum 0.37 e/A3). An inspection of F, vs. F, values and trends based upon sin 8, Miller index, or parity group failed to reveal any systematic errors in the data. A listing of atomic coordinates is provided in Table II. Tables 111s-VS (supplementary material) list the anisotropic thermal parameter, hydrogen atom coordinates, and the structure factors (F, vs. Fc), respectively.
Figure 2. Details of the As6ring environment in 1 revealing the highly puckered ring structure, [ (av) As-As-As angle = 91.0°], and the all-equatorial phenyl ring configuration.
Results and Discussion As is now well-known, 1 crystallizes as a discrete cyclohexamer containing an all-arsenic ring framework in a chair conformation with the phenyl groups in equatorial positions. Many aspects of the structure have been A thermal thoroughly described in earlier publi~ations.~*~ ellipsoid drawing is shown in Figure 1 with the current labeling scheme. The ring environment is more clearly seen in Figure 2. The packing of molecules in the crystalline lattice (Figure 3) produces a short intermolecular As-As contact [As(3) -As(3)” = 4.297 (1) AI7 which is shorter than the A s ( 3 ) 4 ~ ( 3 )intramolecular, ’ transannular distance 4.349 (1) 8. A space-fiing stereo diagram (Figure 4) reveals an absence of crowding not visible in “balland-stick” depictions. A table of selected bond distances and angles including torsional angles is provided in Table
VI. Of primary interest are the AsAs bond distances, both bonded and nonbonded. The three independent As-As distances are (1-2) = 2.464 (l),(2-3) = 2.456 (l),and (1-3) = 2.457 (1) A [ (av) = 2.459 A]; the previous determination of these parameters produced the values 2.457 (6), 2.456 (8),and 2.456 (9) A [(av) = 2.456 (5) A]. The previous observation that the As-As distances are all equal (within experimental error) should now be revised to take account of the current result that one As-As distance is slightly longer than the other two. The nonbonded, transannular As-As distances are of interest in an assessment of the role that across-ring, lone pair-lone pair interactions play in ring stabilization.8 The “1-3” distances are (1-3’) = 3.616 ~~
(4) Reesor, J. W. B.; Wright, G. F. J. Org. Chem. 1957,22, 382. (5) This program and all others used in the data collection and refmement are contained in the Nicolet program packages P3, SHELXTL (version 3.0), and XP and were executed on our in-house Data General Nova 4 computer.
‘
~~
(6) Donohue, J. Acta Crystallogr. 1962,15, 708. (7) Generated by the transformation -x, 2 - y , -2. (8) (a) Cowley, A. H.; Dewar, M. J. S.;Lattman, J.; Mills,J. L.; McKee, M. J. Am. Chem.SOC.1978,100,3349. (b) Cowley, A. H. In ”Homoatomic Rings, Chains and Macromolecules of Main-Group Elements”;Rheingold, A. L., Ed.; Elsevier: Amsterdam, 1977; p 59.
Organometallics, Vol. 2, No. 2, 1983 329
Hexapheny lcyclohexaarsine
Table VI. Selected Bond Distances, Bond Angles, and Torsion Angles for c-(AsC,H,),
As(2)-As(l)-As(3)’ As(l)-As(2)-As( 3) As(2)-As(3)-As(l)’ (av) As-As-As As( 2)-As(1)-C(11)
As(l)-As(2)-As(3)-As(l)’ As(2)-As(3)-As(l)’-As(2)‘ As(3)-As( 2)-As(l )-As(3) taw As-As-As-As C(11)-As( 1)-As( 2)-C(21) C(21)-As(2)-As(3)-C(31) C(31)-As(3)-As(1)-C(11)’ (av) C-As-As-C
(A) Bond Distances ( A ) 2.464 (1) As(1)-C(11) As( 2)-C(21) 2.456 (1) 2.457(1) As( 3)-C(31) (av) As-C 2.459 (B) Bond Angles (deg) 88.92(4) As( 3)‘-As(1)-C(11) 94.59(4) As( l)-As(2)-C(21) 89.82(4) As(3)-As(2)-C(21) As( 2)-As(3)-C(31) 91.1 As( 1)‘-As( 3)-C(31) 97.3(2) (av) As-As-C (C)Torsion Angles (deg) C(1l)-As(1)-As( 2)-As(3 ) 91.08(4) C(ll)-As( l)-As( 3)‘-As(2)’ 85.4(2) C(21)-As( 2)-As(3)-As(1) -90.31 (4) C(21)-As( 2)-As(1)-As(3)’ 188.91 C(31)-As(3)-As(2)-As( 1)’ 72.0 (3) C(31)-As(3)-As( 2)-As(1) -70.9 (3) (av) C-As-As-As -82.8(3) 175.21
(l), (2-3’)= 3.446(l), and (1-2’) = 3.468(1)A. The “1-4” distances are considerably longer: (1-1’) = 4.393(l), (2-2’) = 4.110(l), and (3-3’)= 4.349(1) A. The As-C distances were found to vary considerably in the earlier determination? 1.92-2.01A [ (av) = 1.97(2)A], a result surely due to the lack of refinement of carbon atom parameters. We find the range 1.959(7k1.971(6)A [ (av) = 1.966A] more reasonable and it in agreement with other aryl-As bond distances. The As-As-As bond angles agree almost identically to their earlier found values. Table VI1 provides least-squares planes with interrelating dihedral angles. An inspection of these data reveals a considerable variation in the dihedral angle relating the plane of the phenyl ring to the plane formed by the three arsenic atoms on which the phenyl ring is centered (and to the “best-fit” plane for all six As atoms). Whereas the rings attached to As(2) and As(3) are arranged very nearly perpendicularly, 91.5and 88.4’,respectively, the ring-As plane angle for As(1) shows a considerable tilt for perpendicularity, 75.4’. Since a minimization of steric crowding would be achieved by an all-perpendicular arrangement, it is reasonable to conclude that intramolecular steric factors are not prominent in determining the phenyl-ring tilt angle. The unusual tilt of the phenyl ring attached to As(1) is particularly evident in Figure 4 and is likely attributable to packing phenomena. A review of available As-As bond distance data reveals trends useful in correlating bond orders with bond distances. The Pauling covalent radius for arsenic is 1.21A (Dahl estimates its value as 1.22Ag),suggesting a ”normal” As-As single bond might fall in the range of 2.42-2.44A. A table of representative As-As bond distances obtained from a survey of the literature is provided in Table VIII. The values quoted range from 2.27to 2.75A and would roughly correspond to a range of bond orders from 2.0to 0.5. It is interesting to note that all of the shortest As-As bond distances (C2.4A) are found in transition-metal complexes in which bond orders greater than 1 may presumably be stabilized. Dahl has proposed that the apparent As=As bonds in 1-111 are the result of a back-donation of electrons from metal to the ?r* levels of A-As.lo The trend seen in these four compounds is exactly what (9) Campana,.C. F.; Lo, F. Y.-K.; Dahl, L. F. Inorg. Chem. 1979, 18, 3060. -...
(10)Foust,A. S.; Campana, C. F.; Sinclair, J. D.; Dahl, L. F. Inorg. Chem. 1979,18, 3047.
1.968(7) 1.959(7) 1.971 (6) 1.966 100.4(2) 98.5(2) 96.6(2) 94.5(2) 98.9(2) 97.7 169.4(2) -177.4(2) -169.7(2) 172.4(2) -180.0(2) -170.0 (2) 1173.2I
Table VII. Least-Squares Planesaib for c-(C,H,As), atoms dev atoms dev Plane I: 0.4934X- 0.8678Y- 0.05922- 2.7048= 0 0.6757 As(3)’ -0.6845 -0.7232 C11 -0.1784 ASP) 0.6845 C21 -0.0044 As(3) -0.2340 As(1): -0.6757 C31 ASP) 0.7232 Plane 11: 0.9145X+ 0.3984Y + 0.07042- 2.2583= 0 C(14) 0.0050 0.0017 C(11) C(15) 0.0032 0.0064 C(12) -0.0098 C(16) -0.0064 C(13) Plane 111: 0.6510X- 0.3885Y+ 0.65212+ 1.2449= 0 0.0073 C(24) 0.0030 C(21) 0.0084 C(25) 0.0039 CP2) -0.0135 C(23) -0.0091 C(26) Plane IV: -0.0587X- 0.0362Y+ 0.99762+ 0.5149= 0 0.0040 C(34) 0.0054 C(31) C(32) -0.0043 C(35) -0.0057 C(33) -0.0004 C(36) 0.0010 Plane V: -0.1885X+ 0.7711Y+ 0.60812- 3.6317= 0 As(1) 0 As(3) 0 As ( 2 ) C(21) 1.9215 Plane VI: 0.9854X+ 0.1438Y+ 0.09142+ 0.7794= 0 As ( 2 ) As(3)
0 0
As(1)’
C(31)
0
-1.9412
Plane VII: 0.0630X+ 0.6239Y- 0.77902- 0.7208= 0 0 As(3)’ 0 As(2) -1.9203 As(1) C(11) Dihedral Angles between Planes I1 I11 IV v VI 37.6 93.1 96.9 57.3 52.7 60.9 89.9 79.8 15.2 51.2 91.5 49.8 53.9 88.4 91.1
I I1 I11 IV V VI a Orthonormal coordinates. construct plane.
VI1 51.8 75.4 135.2 143.5 90.3 85.4 Italicized atoms used to
would be expected for the increasing basicity of the transition-metal moiety present in each. In IV and VII, a metal carbonyl group forms a threemembered ring with a RAsAsR group, Cr(CO)Sin IV, and
Rheingold and Sullivan
330 Organometallics, Vol. 2, No. 2, 1983
Figure 3. Stereoview of the unit-cell packing in 1 as viewed tilong the b axis. Table VIII. Representative Arsenic-Arsenic Bond Distances compd d(As-As),a structural comment
ref
I I1 I11
-.&=As -&=As -As=As
10,12 13 14
IV
one of the Cr(CO), groups is between and perpendicular to the As-As bond
15
V VI
VI1 VI11 IX X
[ 0 2 - ( ~ C , F , )1 ,[Fe(CO),I {p-[v'-catena(AsMe),] } [Fe(C0),I2 Ba3As14 CH,C(CH,As),
2.372 (5) 2.385 (3) 2.397 (3) 2.563 (2j 2.726 (3) 2.752 (3) 2.388 (7) 2.391 (7)[1,2] 2.399 2.432 2.498 2.405 (5) 2.422 (5) 2.422 (3) 2.428 (5)(av) 2.434 (7)(av)
16 17
As,Fe ring 4-membered chain bridging Fe(CO), groups tricyclic As, 3 -
18
As, ring
21
Ass chain bridging two
22 2 23
XI XI1 XI11
[p-(q'-AsMe)I [p-AsMel [Mn(CO),], c-(AsMe), {p-[ri4-catena(AsPr),]} [Mo(CO),],
XIV
} [CpMo(CO),], 2.434 (2)(av int) {~-[rl'-catena(AsMe),] 2.449 (2)(av term) [ P - ( s '-AsMe), I, [WCO), I, 2.442 (1) [ P -V "4AsMe l9 1 [ WCO l31, 2.445 (8)(av)
As, chain bridging two
[ ( p -q )-c-As )(triphos Co ), ]
As, ring
xv
XVI XVII XVIII XIX
xx
XXI XXII XXIII XXIV
xxv
+
c-(CF,As)4 [Cc-(v'-AsPh),1 [CpFe(CO),I, e-(AsPh), [~-(v'-AsHPh),l[CpMn(CO), I, Co As, (skutterudite) (PhC-AsPh), (As), (a-arsenic) As,%
2.45 (1)(av) 2.454 (1) 2.456 (2) 2.459 (av) 2.460 (1) 2.464 (2) 2.572 (2) 2.475 (1) 2.516 (1) 2.519 (3) 2.550 (3)
Fe(C0)4in VII. It is uncertain whether the best description for these complexes is as a three-membered heterocycle or as a q2(a)interaction; the former description requires an As-As single bond shortened by the effects of small ring formation and the latter, an As=As double bond elongated by the synergic combination of a (T donorla acceptor metal-ligand interaction.l0 In IV, R = C6H5,and in VII, R = C6F5. The effect of a more electron-withdrawing organic substituent in VI1 is to lengthen the &-As bond (2.371 A in IV and 2.388 (7) A in VII) and to restrict the donor capability of As in VII; in IV, but not in VII, two additional 16-electron Cr(C0)5groups are coordinated to the As atoms.
19 20
Mo(CO), groups
24
CpMo(CO), groups As, ring bridging two
a(co),P O U P S
a tetrasubstituted diarsine
25 26 27 28 29
this work 30
31 substituted 1,2-diarsacyclobutene two-dimensional nets of As, rings
32 33 34
In V and VI "naked" atoms form planar rings which in V are bonded to one C O ( C O ) group ~ and in VI, to two CpMo groups. In V the ring atoms form a single, symmetrical q3-As3ligand, whereas in V, the As5 ring may be partitioned into q2-As3and q2-As2ligands. The two longest As-As bonds in VI (2.726 (3) and 2.752 (3) A) connect the two ligands. These bond distances correspond to a bond order of -0.5 and are the longest accurately determined As-As distances we have been able to locate. Compounds VIII, XI, and XIII-XVI contain chains of RAs units bonded in various bridging geometries to metal carbonyl groups. The longest bonds in these As chain complexes are found a t the termini, but since bond lengths
Organometallics,Vol. 2, No.2, 1983 331
Hexaphenylcyclohexaarsine
Figure 4. Stereoview of a space-filling depiction of 1.
of uncoordinated As chains are not available for comparison, it is difficult to assess the full impact of coordination on As-As bond lengths in chains. It might be noted, however, that the terminal S-S bond distances in are longer than the interior distance, 2.074 vs. 2.061 A,ll by (11)Abrahams, S.C.; Bemstein, J. L. Acta Crystallogr., Sect. B 1969, B25, 2365. Tegman, R. Ibid. 1973,B29,1463. 1969. (12)Foust, A. S.;Foster, M. S.; Dahl, L. F. J. Am. Chem. SOC. 91,5633. (13)Sigwarth, F.; Zeolnai, L.; Berke, H.; Huttner, G. J. Organomet. Chem. 1982,226,C5. (14)Sullivan, P. J.; Rheingold, A. L. Organometallics 1982,1,1547. (15)Huttner, G.; Schmid, H.-G.; Frank, A.; Orama, 0. Angew. Chem., Znt. Ed. Engl. 1976,15,234. (16)Foust, A. S.;Foster, M. S.;Dahl, L. F. J. Am. Chem. SOC. 1976, 91.5631. (17)Rheingold, A. L.; Foley, M. J.; Sullivan, P. J. J.Am. Chem. SOC. 1982,104,4727. (18)Elmes, P. S.;Leverett, P.; West, B. 0. J. Chem. SOC., Chem. Commun. 1971,747. (19)Gatehouse, B. M. J. Chem. SOC.,Chem. Commun. 1969,948. (20)Schmettow, W.: von Schnerine. H.-G. Anaew. - Chem.. Znt. Ed. Engl. 1977,16,857. (21)Ellerman, J.; Schbssner, H. Angew. Chem., Int. Ed. Engl. 1974, 13,601. (22)Rbttinger, E.; Trenkle, A,; Miiller, R.; Vahrenkamp, H. Chem. Ber. 1980,113,1280. (23)Elmes,P.S.;Gatehouse, B. M.; Lloyd, D. J.; West, B. 0. J.Chem. SOC.,Chem. Commun. 1974,953. (24)Rheingold, A. L.; Churchill, M. R. J. Organomet. Chem., in press. (25)Cotton, F. A.; Webb, T. R. Inorg. Chim. Acta 1974,10,127. (26)Elmes, P.S.;Gatehouse, B. M.; Lloyd, D. J.; West, B. 0. J.Chem. SOC., Chem. Commun. 1974,953. (27)Di Vaira, M.; Midollini, S.; Sacconi, L. J. Am. Chem. SOC.1979, 101,1756. (28)Mandel, N.;Donohue, J. Acta Crystallogr., Sect. B 1971,B27,476. (29)Rheingold, A. L.;Sullivan, P. J. Organometallics 1982,1,1429. (30)Huttner, G.; Schmid, H.-G.; Lorenz, H. Chem. Ber. 1976,109, 3741. I .
’
a difference similar to that found in the As chain complexes. Compounds XII, XVIII, and XX contain single rings of monoorganoarsenic units. Because ring size and substitution varies so much among the rings, little value could derive from making comparisons. It is unusual that the stable allotrope of elemental arsenic (a-arsenic, XXIV) contains a “long” As-As bond, 2.516 (1)A. This may be attributed to interlayer bonding of the two-dimensional nets of As6 rings found in a-arsenic. A full consideration of representative data suggests that the range of a “normal” As-As single bond should be established as 2.43-2.46 A and that for an As-& double bond as 2.27-2.32 A. Distances outside these ranges are found in compounds in which special circumstances exert substantial bond compression or elongation effects.
Acknowledgment. This work was funded, in part, by a grant from the National Science Foundation, No. CHE 7911330. We are indebted to the authors of ref 32 who have allowed us to quote their work prior to its publication. Registry No. 1, 20738-31-2. Supplementary Material Available: Table IIIS,anisotropic thermal parameters, Table IVS, hydrogen atom coordinates, and Table VS, F, vs. F, (26 pages). Ordering information is given on any current masthead page. (31)Mandel, N.;Donohue, J. Acta Crystallogr., Sect. B 1971,B27, 2288. (32)Sennyey, G.;Mathey, F.; Fischer, J.; Mitachler, A,, submitted for publication. (33)Schiferl, D.; Barrett, C. S. J.Appl. Cryst. 1969,2,30. (34)Kutoglu, A. 2.Anorg. Allg. Chem. 1976,419,176.
