摘要:

J. CHEM. SOC. DALTON TRANS. 1987 2555 In memory of S. M. Nelson Formation of a (4 + 4) Schiff-base Macrocyclic Ligand by a Template Rearrangement. Crystal and Molecular Structures of Two Tetranuclear Manganese@) Complexes t Sally Brooker, Vickie McKee," and William B. Shepard Chemistry Department, University of Canterbury, Christchurch, New Zealand Lewis K. Pannell Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, MD 20892, U.S.A. Two tetranuclear manganese( it) complexes (2) and (3) have been obtained by Schiff-base condensation of 1,3-diamino-2- hydroxypropane and 2,6-diacetylpyridine in the presence of Ba2+, followed by transmetallation using Mn2+. The complexes have been characterised by analytical, spectroscopic, 252Cf plasma desorption mass spectroscopic, and single-crystal X-ray diffraction methods.Complex (2) contains a 40-membered macrocycle formed by a ( 4 + 4) Schiff-base condensation of four molecules of 1,3-diamino-2- hydroxypropane with four molecules of 2,6- diacetylpyridine. The macrocycle is wrapped around a cubane-like Mn,(alkoxide), core. Complex (3) is dimeric. The asymmetric unit contains two binuclear, 20-membered macrocycles each formed by a (2 + 2) Schiff-base condensation reaction. This complex contains five geometrically distinct thiocyanate groups. Routes for the formation of (3) are discussed and the possible significance of the compounds as models for the photosynthetic water-splitting system is noted. There is much current interest in the nature of the manganese cofactor of photosystem I1 which is thought to be the active site for the photosynthetic water-splitting For some time it has been accepted that the natural system must involve at least two magnetically coupled manganese centres probably bridged by oxygen donors.' The properties of many binuclear synthetic systems have been investigated as models for the photosynthetic site.3 A tetranuclear cluster has also been proposed to account for the properties of the various inter- mediates (S-states, oxidation levels) in the water-splitting cycle: particularly their complex e.s.r.chara~teristics.~,~ As yet, however, few tetranuclear model compounds involving oxidation states 11, 111, or IV have been characterised.6 Consequently, low molecular weight model systems involving either bi- or poly-nuclear manganese complexes are potentially of great value in contributing to the understanding of the photosynthetic process.The (2 + 2) macrocyclic ligand H,L was chosen for an investigation of the general properties of binuclear manganese systems having endogenous oxygen bridging. It is large enough, and has enough donor atoms, to bind two transition-metal ions and hold them close together. The macrocycle has six imine- type nitrogen donors and two pendant alcohol groups which have the potential to deprotonate and form alkoxide bridges. Bridging is not enforced however, as the ligand has sufficient flexibility for the alcohol groups to twist away from the central cavity. This flexibility means that the ligand can, to some extent, adjust to suit the stereochemical preferences of the co- ordinating metal ions.The ligand H,L can be prepared in good yield by a template reaction involving condensation of two molecules of 2,6-di- acetylpyridine with two molecules of 1,3-diamino-2-hydroxy- ~~~ t Supplementary data available (No. SUP 56675, 7 pp.): mass spectra and assignments. See Instructions for Authors, J. Chem. SOC., Dalton Trans., 1987, Issue 1, pp. xvii-xx. Non-S.I unit employed: 1 a.m.u = 1.6602 x lP2' kg. 7 0 2 1 3<N N OH N I H ~ L '2556 J. CHEM. SOC. DALTON TRANS. 1987 Table 1. Atomic co-ordinates ( x lo4) for [Mn4(L’)(C10,),J~2H,0 (2) and [Mn,(HL)(L)(NCS),]NCS (3) X 5 850(1) 4 946( 1) 6 509( 1) 6 6 0 3 1) 5 475(1) 4 499( 1) 4 296(1) 5 743( 1) 6 486( 1) 6 878(2) 7 296(2) 7 330(2) 6 929( 1) 6 972(1) 7 462(2) 6 632( 1) 6 249( 1) 6 018(1) 5 236( 1) 5 451(2) 4 688(1) 4 407(2) 3 920(2) 1 605(1) 1 545(1) 825( 1) 1600(2) 1206(2) 1124(2) 1952(3) 2 122(4) 2 466(4) 2 232(4) 2 254(4) 2 532(4) 2 036(3) 2 005(4) 1852(3) 2 091(4) 1955(3) 2 060(4) 2 330(4) 1 946(4) 2 014(4) 1917(4) 1 748(4) 1 681(4) 1768(3) 1513(3) 1498(4) 1409(3) 1271(4) 1 104(4) 1 113(4) 1592(3) 1490(4) 790(3) 789(4) 694(4) 1 Oll(1) 1 100(2) 1 900(4) 2 399(4) 1434(3) 1391 Y 3 837(1) 2 242(1) 4 924(2) 3 127(2) 796(2) 1153(2) 2 945(2) 5 275(2) 5 824(2) 6 509(2) 6 241(2) 5 310(2) 4 655(2) 3 614(2) 3 232(3) 2 108(2) 1738(2) 736(2) 65(2) -929(2) 256(2) -440(2) - 167(2) 259(2) 2 628(2) 3 219(2) 1 894(2) 1361(8) 1405(8) 1606(7) 3 289(8) - 7 14( 10) - 1 023(12) -1 586(13) -1 796(14) - 1 505(13) - 961( 12) - 620( 12) - 941( 15) -58(10) 367( 13) 1 395(12) 2 207( 12) 3 069(10) 3 970( 13) 4 348(14) 4 629(13) 5 656( 15) 6 114(15) 5 559(13) 4 556(12) 4 097(10) 3 815(11) 4 058( 15) 2 161(12) 1 404(12) 298( 12) 3 005(9) - 76( 10) - 677( 1 1) - 1 052(13) 4 143(10) 5 157(13) 5 796(15) 1495 z 2 462(1) 1 663(1) 1995(1) 1 806(1) 1 776(1) 973(1) 884( 1) 2 967( 1) 2 188(1) 1 906(1) 1410(2) 1 225(1) 1537(1) 1439(1) 967(2) 1816(1) 2 400( 1) 2 263( 1) 1 500(1) 1622(2) 1009(2) 612(2) 162(2) 1 295(1) 1 184(1) 476( 1) 539(4) 1268(4) - 202(4) 530(4) 1956(6) 2 491(7) 2 919(8) 2 813(8) 2 274(7) 1838(7) 1232(7) 1031(9) 925(6) 312(7) 256(7) 534(8) 791(5) 862(7) 620(8) 1282(7) 1417(8) 1882(8) 2 211(8) 2 038(7) 1 587(6) 2 361(7) 3 006(8) 2 062(5) 2 316(7) 1810(7) 2 079(7) 2 128(5) 2 556(7) 3 076(7) -518(1) -1 372(6) -1 328(7) -1 855(8) 186 X 3 745(2) 4 050( 1) 3 945(1) 3 485(2) 4 296(1) 4 882(1) 4 732(1) 6 022(1) 5 927(2) 5 690(1) 2 481(1) 5 002( 1) 2 122( 1) 2 100(1) 2 598(1) 3 108(1) 5 768(1) 5 702( 1) 5 908( 1) 5 159(1) 6 299(1) 7 766(2) 618(5) 619(4) 680(4) 5 13(4) 1013(4) 712(3) 898(4) 529(4) 473(4) 359(4) 6(4) 47(4) 704(4) 799(3) 753(4) 157(4) 410(3) 255(3) 323(4) 585(3) 85(4) 674(3) 1028(4) 969(3) 1 086(4) 889(4) 891(5) 498(3) 246(4) 1467(3) 1692(3) - 102( 1) 2 018(1) 1354(3) 1 247(4) 1091(1) 1 llO(4) 868(4) 524(1) 1922(3) 2 019(3) 2 146(1) Y 768(2) 1424(2) 2 462(2) 2 869(3) 3 967(2) 4 342(2) 5 335(2) 6 003(2) 6 990(2) 2 317(1) 3 750(1) 3 966( 1) 3 597(2) 3 812(2) 4 957(2) 3 480(2) 2 905(1) 2 463(2) 3 889(2) 2 785(2) 2 465(2) 347(4) 5 289(17) 4 250(16) 3 680(13) 2 534(14) 2 165(10) 1959(16) 1124(11) 765(11) 280(10) - 138(12) - 296( 12) - 1 423(13) -239(14) 252( 13) 402( 14) 1465(14) 1258(10) 1863(12) 2 969(12) 3 175(10) 3 725( 15) 4 169(12) 4 200( 12) 4 890( 10) 5 102(12) 5 558(13) 6 672( 15) 2 738(10) 2 988(13) 3 326(5) 3 409(11) 3 477( 12) 3 538(4) -1 172(11) - 1 800(15) - 2 682(4) - 1 388(14) - 1 386(15) - 1 441(4) 1 627(10) I532(12) 1385(4) Z 1 10( 1) 520(1) 483(1) -21(2) 865(1) 1 275( 1) 1 502(1) 2 737(1) 2 973(2) 2 518(1) 1 825(1) 1758(1) 2 335(1) 1 678(1) 1811(1) 590( 1) 1 202(1) -38(1) 39U) - 407( 1) - 378(1) 3 17(2) - 2 428( 10) - 2 457( 10) - 1 922(8) -1 889(8) -1 351(6) - 2 440(9) -1 201(7) -631(7) - 308(7) 87(6) 297(7) 212(8) 998(7) 1330(8) 1355(8) 732(6) 1056(7) 1012(7) 888(5) 1086(9) 738(7) 748(7) 389(6) 700(7) - 272(5) - 674(8) - 589(9) - 408(6) - 657(7) - 999(4) - 676(6) - 822(7) - 1 043(2) 91 l(6) 1 170(8) 1514(3) -1 389(7) -1 721(8) - 2 200(3) 1898(5) 2 425(7) 3 175(2)J.CHEM. SOC. DALTON TRANS. 1987 2557 Table 2. Selected bond lengths (A) and angles (”) for [Mn,(L’)- Mn( 1)-N( I ) Mn( 1)-N(6) Mn( 1 )-O( 2) Mn( 1)-O( 14’) Mn(2)-N(4) Mn(2)-0( 1) Mn(2)-0( 1’) N( 1)-Mn( 1)-N(2) N(2)-Mn( 1)-N(6) N(2)-Mn( 1)-O( 1) N(1 1 N(6)-Mn( 1)-0(2) N(1)-Mn( 1)-O(2’) N(6)-Mn( 1)-O(2’) O(2)-Mn( 1)-O(2’) N(2)-Mn( 1)-O( 14’) O( 1 )-Mn( 1 )-O( 14’) 0(2’)-Mn( 1)-O( 14‘) N(3)-Mn(2)-N(5) N(3)-Mn(2)-0( 1) N(5)-Mn(2)-0(1) N(4)-Mn(2)-0(2) O(1 )-Mn(2)-0(2) N(4)-Mn(2)-0( 1 ’) O( 1 )-Mn(2)-0( 1 ’) Mn( 1 )-O( 1 )-M n( 2) Mn( 1)-O( 1 )-Mn(2‘) Mn(l)-0(2)-Mn(l’) - 2.267(2) 2.309(2) 2.142(2) 2.6 1 O(2) 2.279(2) 2.297( 2) 2.143(2) 69.4( 1) 136.6( 1) 72.3( 1) 1O4.4( 1) 104.3(1) 139.8(1) 71.4(1) 77.7( 1) 73.3( 1) 84.0( 1) 103.3(1) 135.6( 1) 70.9( 1 ) 151.3(1) 1 4 1 4 1) 78.8( 1) 106.7( 1) 77.q 1) 95.7( 1) 1 0 0 3 1) 101.9(1) Mn( 1)-N(2) Mn(l)-O( 1) Mn( 1)-O(2’) Mn(2)-N(3) Mn(2)-N(5) Mn(2)-O(2) Mn(2)-O(21) 2.291(2) 2.19 3( 2) 2.287(2) 2.328(2) 2.286(2) 2.177(2) 2.728(2) 69.3( 1) 141.7( 1) 146.8( 1) 98.q 1) 81.9( 1) 150.7( 1) 78.4( 1) 84.4( 1) 89.8( 1) 165.3(1) 68.7( 1) 69.1(1) 139.2(1) 146.6( 1) 72.7( 1) 1O4.3(1) 100.6(1) 82.0( 1) 102.0( 1) 100.9( 1) 96.6( 1) * Atoms marked ’ are related by a two-fold rotation axis to those given in Table 1.They have co-ordinates 1 -x, y, 4-2. propane in the presence of Ba2+.’ The resulting complex, [Ba( H2L)(H20),] [ClO,] (l), undergoes facile transmetalla- tion reactions in which the barium ion can be replaced by two transition-metal ions; this reaction is generally accompanied by deprotonation of one or both of the alcohol groups.We have previously reported the structure and properties of a binuclear, singly-bridged copper(I1) complex of the monodeprotonated ligand HL-.’v8 A number of binuclear complexes of iron(m) with L2- have also been prepared; these contain seven-co- ordinate iron bridged by both alkoxide groups.’ In this paper we report the preparation and structures of two tetranuclear manganese(I1) complexes derived from H,L. One of these is a dimer, [Mn,(HL)(L)(NCS),]NCS (3) while the second is a complex of the larger macrocycle H,L’, with stoicheiometry [Mn,(L’)(C10,),]~2H20 (2).The structure of the latter complex has been communicated previously,” the ligand has the same connectivity as H2L but the ring has been expanded to twice the size. The mechanism by which the (4 + 4) macrocycle H,L’ is formed, and the potential of the complexes as models for the photosynthetic system are discussed. Results and Discussion Synthesis ofthe Complexes.-The (2 + 2) macrocycle H,L was synthesised as the barium(I1) complex [Ba(H,L)(H,O),]- [CIO,], (1) in ca. 75% yield uiu a Ba2+ ion template reaction from 2,6-diacetylpyridine and 1,3-diamino-2-hydroxypropane. The identity of this complex was established from i.r.7 13C n.m.r., and mass spectral data; an X-ray structural determination has also been carried out.’ When methanol or ethanol solutions of (1) were treated with an excess of Mn(C104)2.6H,07 the single Ba2+ ion of the precursor could be replaced by manganese(r1) ions yielding the perchlorate complex.Addition of excess NaNCS to the refluxing solution gave the corresponding Table 3. Selected bond lengths (A) and angles (”) for CMn,(HL)(L)(NCS),INCS (3) Mn( 1)-O( 1) Mn(l)-N( 1) Mn( 1)-N(6) Mn(1 jN(80) M n( 2)-O( 2) M n (2)-N (3) Mn(2)-N(5) Mn(3)-O(3) M n (3)-N (7) Mn(3)-N(12) Mn(3)-N(60) Mn(4)-O(3) Mn(4)-N(9) Mn(4)-N(ll) O( 1 )-Mn( 1)-0(2) O(2)-Mn( 1)-N( 1) 0(2)-Mn(l)-N(2) OU)-Mn(l)-N(6) N( 1 FMn( 1 b”6) 0 ( 1 )-Mn( 1 )-N(70) N( 1)-Mn( 1)-N(70) N(6)-Mn( 1)-N(70) O(2)-Mn( 1)-N(80) N(2)-Mn( 1)-N(80) N( 70)-M n( 1 )-N (80) O(ltMn(2)-0(4) O(1 )-Mn(2W(3) 0(4)-Mn(2)-N(3) 0(2)-Mn(2)-N4) N(3)-Mn(2)-N(4) 0(2)-Mn(2)-N(5) N(3)-Mn(2)-”5) O(l)-Mn(2)-N(80) 0(4)-Mn(2)-N(80) N(4)-Mn( 2)-N(80) 0(3)-Mn(3)-0(4) 0(4)-Mn(3)-N(7) 0(4)-Mn(3)-N(8) 0(3)-Mn(3)-N( 12) N(7)-Mn( 3)-N( 12) 0(3)-Mn(3)-N(50) N(7)-Mn( 3)-N( 50) N( 12)-Mn(3)-N(50) 0(4)-Mn(3)-N(60) N(8 )-Mn(3)-N(60) N( 50)-Mn( 3)-N( 60) 0(2tMn(4F0(4) 0(2tMn(4)-N(9) 0(4)-Mn(4)-“9) 0(3)-Mn(4)-N( 10) N(9)-Mn(4)-N(10) 0(3)-Mn(4)-N( 1 1) N(9)-Mn(4)-N( 1 1) 0(2)-Mn(4)-N(50) 0(4)-Mn(4)-N( 50) N( 1 O)-Mn(4)-N( 50) Mn( 1)-O( 1)-Mn(2) Mn( 1)-0(2)-Mn(4) Mn( 1 )-0(2)-Mn(2) Mn(2)-0(2)-Mn(4) 2.244( 11) 2.241(12) 2.264( 14) 2.461( 12) 2.247( 10) 2.304(14) 2.288( 13) 2.242( 10) 2.277( 13) 2.289( 13) 2.163( 15) 2.238(11) 2.304( 13) 2.322( 14) 73.0(4) 140.6(4) 143.6(4) 146.0(4) 69.7(5) 110.1(4) 87.7( 5 ) 8 5.3 ( 5 ) 81.7(4) 86.0(4) 168.7(4) 94.1(3) 72.8(4) 104.5(4) 1 44.3 ( 5 ) 68.6(5) 75.0(4) 134.8(4) 81.8(4) 167.6(4) 92.7(4) 14 1.7(4) 142.4(4) 148.3( 4) 69.5(5) 79.0(4) 9 1.4(4) 94.9(5) 74.7(4) 102.4(4) 97.2(5) 170.9( 5 ) 83.2(3) 94.8(4) 146.9(5) 139.0(4) 69.3(5) 142.6(4) 1 3 8.5( 5) 166.2(4) 83.3(4) 92.1(4) 87.8(4) 128.6(4) 86.8(3) 96.1(4) Mn( 1)-0(2) Mn( 1)-N(2) Mn( 1)-N(70) Mn(2)-0( 1) M n( 2)-0 (4) M n(2)-N(4) Mn(2)-N(80) Mn( 3)-0(4) Mn( 3)-N(8) Mn(3)-N( 50) Mn(4)-0( 2) Mn(4)-O(4) Mn(4)-N( 10) Mn(4)-N( 50) O( 1)-Mn( 1)-N( 1) O(1)-Mn( 1)-N(2) N( 1)-Mn( 1)-N(2) O(2)-Mn( 1)-N(6) N(2)-Mn( 1)-N(6) 0(2)-Mn(l)-N(70) N(2)-Mn( 1 )-N(70) O( 1 )-Mn( 1)-N(80) N( 1 )-Mn( 1 )-N(80) N(6)-Mn( 1)-N(80) O( 1 kMn(2)-0(2) 0(2)-Mn(2)-0(4) 0(2)-Mn(a-N(3) 0(1)-MnWN(4) 0(4FMn(a-N(4) O(1 )-Mn(a-N(5) 0(4)-Mn(2)-N(5) N(4kMn(2)-N(5) 0(2)-Mn(2)-N(80) N(3)-Mn(2)-N(80) N( 5)-Mn(2)-N(80) O( 3)-Mn(3)-N( 7) 0(3)-Mn(3)-N(8) N(7)-Mn( 3)-N( 8) 0(4)-Mn(3)-N( 12) N(8)-Mn(3)-N( 12) 0(4)-Mn(3)-N( 50) N(8)-Mn( 3)-N( 50) 0(3)-Mn(3)-N(60) N(7)-Mn(3)-N(60) N(12)-Mn(3)-N(60) 0(2)-Mn(4)-0( 3) 0(3)-Mn(4)-0(4) 0(2)-Mn(4)-N( 10) 0(4)-Mn(4)-N( 10) 0(2)-Mn(4)-N( 1 1) 0(4)-Mn(4)-N( 1 1) N( 10)-Mn(4)-N( 1 1) 0(3)-Mn(4)-N(50) N(9)-Mn(4)-N( 50) N(l 1)-Mn(4)-N(50) Mn( 3)-O( 3)-Mn(4) Mn(2)-0(4)-Mn(4) M n( 3)-0(4)-Mn(4) 0(3tMn(4)-N(9) Mn(2)-0(4)-Mn(3) 2.3 14( 10) 2.323( 15) 2.242( 14) 2.277(11) 2.229(9) 2.251 (13) 2.388(12) 2.300( 10) 2.333( 13) 2.44 1 ( 14) 2.251(10) 2.237( 14) 2.4 1 O( 12) 138.3(4) 71.3(4) 70.0(5) 73.9(4) 139.6(4) 1 O4.0(4) 94.5(5) 80.8(4) 8 1.9(4) 87.0(4) 73.7(4) 82.9( 3) 146.0(4) 14 1.3( 5) 97.7(4) 145.0(4) 97.2(4) 69.5(5) 84.8(4) 8 5.5 (4) 80.2(4) 14 1.0(4) 72.2(4) 68.8(5) 73.6(4) 136.8(4) 8 1.6(4) 75.2(5) 94.1 ( 5 ) 90.3 ( 5 ) 94.0(5) 94.1(3) 75.7(4) 71.5(4) 100.5(4) 143.7(5) 102.5(4) 73.3(4) 70.6(5) 79.8(4) 94.9(4) 76.3(4) 88.8(4) 95.4(4) 125.8(5) 87.1 (3) 2.21 l(8) thiocyanate complex. The macrocyclic products all showed a band at ca.1 620 cm-’ in their i.r. spectra attributed to the imine bonds. The disappearance of the carbonyl signal at ca. 1700 cm-’ was taken as an indication of the formation of a closed macrocyclic ring rather than an open chain system. Description of the Structures.-Crystals of [Mn,(L’)(ClO,),]* 2H,O (2) and [Mn,(HL)(L)(NCS),]NCS (3) were obtained2558 J. CHEM. SOC. DALTON TRANS.1987 Figure 1. The structure of complex (2). Dotted lines represent the long Mn-OClO, bonds Figure 3. The structure of complex (3); the ionic thiocyanate has been omitted. The dotted line represents the hydrogen bond Figure 2. The cubane core of complex (2) in the same orientation as Figure 1 from acetonitrile solution and their X-ray crystal structures have been determined. Atomic co-ordinates are listed in Table 1 and selected bond lengths and angles are given in Tables 2 and 3. The structure of (2) contains the (4 + 4) ligand co-ordinated to four manganese centres and utilising all 16 potential donor atoms (Figure 1). The alcohol groups have been deprotonated and each one bridges three manganese centres, forming a central cubane-type structure with stoicheiometry Mn,(alkoxide), (Figure 2).Alternatively, this structure may be viewed as two interpenetrating tetrahedra [Mn, and (alkoxide),] but the Mn- Mn separations [3.33( 1)-3.45( 1) A] suggest that there are no metal-metal bonds. The macrocycle is able to wrap itself around this cluster by virtue of the flexible propane links which permit a 90" twist of the ligand between successive rigid pyridinedi-imine units. Each manganese@) is seven-co-ordinate, bonded to three alkoxide oxygen donors, three nitrogen atoms from a pyridine- di-imine unit, and one perchlorate oxygen. The geometry about each metal centre is approximately pentagonal bipyramidal, although the Mn-OC10, distances are rather long [2.610(2) and 2.728(2) A] so that the anions may be better described as Figure 4.The manganese co-ordination spheres of structure (3) in the same orientation as Figure 3 semi-co-ordinated, occupying the otherwise vacant site above each manganese. There are also two unco-ordinated water molecules for each macrocyclic unit in the lattice. A crystal- lographic two-fold axis passes through the centres of the cubane faces defined by Mn(l), 0(2), Mn(l'), O(2') and Mn(2), 0(1), Mn(2'), O( 1'). There is also an approximate, non-crystallo- graphic S4 axis coincident with the C2. Within the cubane core, angles about manganese are all acute (78-82"), while those about oxygen are obtuse (96-102"); this would be expected in view of their respective co-ordination geometries. A few man- ganese(1) cubane structures with formulae [Mn,(CO), 2X4] (X = F, OH, or OR, where R = alkyl) ' 2 g 1 have been reported previously but to our knowledge, complex (2) is the first example in either the Mn" oxidation state or in the absence of carbonyl ligands.The thiocyanate complex (3) has a dimeric structure with two (2 + 2) macrocyclic units linked together as shown in Figure 3;J. CHEM. SOC. DALTON TRANS. 1987 2 0 0 0 0 - 1 5 0 0 0 - - 10000- 2559 [Ba(HZL)(CL04)1+ [Ba(HL)I+ / (671) (571) \ the co-ordination sphere is shown in Figure 4. The two halves of the structure are crystallographically independent and show considerable geometrical differences. As for (2), each man- ganese(r1) ion is seven-co-ordinate and has approximate pentagonal-bipyramidal geometry. In every case the donors in the pentagonal plane are the three nitrogen atoms of a pyridine- di-imine unit and two alkoxide donors, all from the same macrocycle.Each manganese has the nitrogen atom of an N- bridged thiocyanate group as one axial ligand; Mn(1) and Mn(2) are both bonded to N(80), while Mn(3) and Mn(4) are bridged by N( 50). The co-ordination spheres about Mn( 1) and Mn(3) are completed by the nitrogen donors of terminally bonded thiocyanates "(70) and N(60) respectively]. For Mn(2) and Mn(4) the seventh donor is an alkoxide oxygen atom 5 000- from the adjacent macrocycle and it is these two interactions [Mn(2)-O(4) and Mn(4)-0(2)] which hold the dimer together. Consequently, the alkoxides 0(1) and O(3) are doubly bridging but O(2) and O(4) are triply bridging. The atoms O( 1) and O(3) are linked via a hydrogen bond; this was indicated by the O(1)-0(3) distance of 2.42(1) A and is required for the stoicheiometry; the hydrogen atom was located from difference Fourier maps.The macrocycles themselves are non-planar, each is folded to accommodate the bridging thiocyanate groups by reducing the metal-metal distances to 3.135(5) A for both Mn(1)-Mn(2) and Mn(3)-Mn(4). The extent of the folding is indicated by the angles between the least-squares planes of the donors in the pentagonal plane for each pair of manganese atoms. The angle (*I [Mn2 (L) - H+]+ 300 0 2000 1000 ! 70000 0 - 5 0 0 0 0 A - 75 0 1000 1250 1500 3 0 0 0 0 10000 5 00 [ Mn4(LI2- 3H+l+ (1 0 8 2 ) 500 7 50 1000 1250 M a s s ( m / e ) Figure 5. Positive-ion 2s2Cf p.d.m.s. traces showing the assignments of the main peaks.(a) An unrecrystallised sample of the barium complex (l), (6) the products from transmetallation of (1) with Mn(C1O4),-6H,O, (c) the Mn,(L) component of the transmetallation reaction, ( d ) a recrystallised sample of complex (3)2560 J. CHEM. SOC. DALTON TRANS. 1987 between the mean planes of Mn( l), N( l), N(2), N(6), O( l), 0(2), and Mn(2), N(3), N(4), N(5), 0(1), O(2) is 104.6' and that between Mn(3), N(7), N(8), N(12), 0(3), 0(4), and Mn(4), N(9), N( lo), N( 1 l), 0(3), 0(4), is 108.6'. An unusual feature of the structure is the presence of four distinctly different bonding geometries for thiocyanate, in addition to the unco-ordinated counter ion. One of the two terminal thiocyanate groups is bonded in approximately linear fashion [Mn(3)-N(60)-C(61) 173(1)"], whereas the other is distinctly bent [Mn(l)-N(70)-C(71) 128(1)']. A similar effect is observed for the two bridging thiocyanates; N(80)-C(81)-S(82) is inclined at 33(1)" to the Mn(l), Mn(2), N(80) plane but N(50)-C(51)-S(52) makes an angle of only 7(1)" with the Mn(3), Mn(4), N(50) plane.In addition, the Mn-N-C angles show wide variation; 139(1) and 119(1)" for Mn(1)- and Mn(2)-N(80)-C(8 1) respectively compared with 133( 1) and 145(1)" for Mn(3)- and Mn(4)-N(50)-C(51). There are no striking inter- or intra-molecular interactions to account for these differences; the environments of the two terminal thio- cyanates and of the two bridging groups, while not identical, show no major differences. The individual geometries can be ascribed to a number of weak interactions and to crystal- packing effects.For example, S(72) is ca. 3.8 A from six macrocyclic ring atoms, 3 8, from the same asymmetric unit [N(6), C(23), C(36)], and 3 8, from an adjacent unit [C(15), C(16), and C(46)]. Any straightening of the N(70)-C(71)-S(72) angle is prevented by this network of interactions. There are six previous structurally characterised examples of N-bridging thiocyanate ligands.14-'* In most cases the bridging NCS is associated with an i.r. band in the region below 2 OOO cm-'. The i.r.spectrum (in Nujol) of (3) shows four peaks due to the C-N stretch of the thiocyanates at ca. 2 085, 2 065, 2 045, and 2025 cm-' and the envelope is broadened on the low-energy side, but there is no distinct signal below 2 000 cm-'. Formation of the (4 + 4) Macrocycle H,L'.-On first iso- lating the (4 + 4) macrocycle H,L' it was not clear at which stage in the template and transmetallation reactions the larger ring had been formed.The first possibility is that it formed as a minor product in the barium template reaction and crystallised out preferentially in the subsequent manganese transmetallation step. A plausible driving force for this reaction is the expected preference of Ba2+ for alcohol donors rather than the softer imine nitrogens. The presence of a mixture of H2L and H,L' ligands in the barium product would not necessarily be detected by the normal methods of characterisation as the differences between a mononuclear H2L complex and the binuclear H,L' equivalent might not be very obvious.Microanalytical results would be identical, i.r. and n.m.r. spectra would be very similar, and recrystallisation would tend to remove the minor com- ponent. The major difference between the two complexes would be their masses, so the obvious way of detecting any H,L' component is mass spectroscopy. The technique of californium- 252 plasma desorption mass spectroscopy '' (252Cf p.d.m.s.) was chosen since it enables spectra to be obtained without excessive fragmentation of the complexes. Figure 5 shows the 252Cf p.d.m.s. traces of the complexes. The spectrum of the unrecrystallised barium complex [Figure 5(a)] is quite simple and the major peaks can readily be assigned. There is no indication of any signal at twice the mass of the assigned peaks to suggest a Ba,(H,L') species and the absence of an extensive fragmentation pattern makes it unlikely that a (4 + 4) complex was present but disintegrated in the instru- ment.The minor peaks at 807 and 907 a.m.u. are likely to be addition complexes of the assigned species with BaClO,. The spectrum of the Mn" transmetallation product [Figure 5(b)] shows signals in two well defined regions. Those centred at ca. 1 400 a.m.u. are due to the Mn,(L') complex (2) while signals + \ - H20 w 42 (111) (V) Scheme. in the region ca. 540 a.m.u. correspond to various Mn2(L) fragments. Most of the peaks in the lower mass region appear to be due to fragmentation of (2); by comparison with spectrum (c) only the signals at 642 and 541 a.m.u. arise from the presence of a Mn,(L) complex in the transmetallation mixture (see Ex- perimental section).The spectrum of the thiocyanate complex [Figure 5(d)] shows extensive fragmentation, consistent with a dimer held together by metal-ligand bonds. The peak ratios indicate that the signals around 1 200 a.m.u. correspond to the parent ion. It is significant that, in spite of the expected facile cleavage of the dimer, the spectrum of (3) gives clear indication of the presence of the parent ion. This supports the conclusion that the barium complex contains no (4 + 4) component and hence that the (4 + 4) macrocycle in (2) must be formed during the trans- metallation reaction with manganese and not in the initial template process. Comparison of the structures of (2) and (3) (Figures 1 and 3) suggests a possible route for the formation of the (4 + 4) macrocyclic product H4L' (Scheme).In (3) the two bimetallic macrocyclic units are held together by axial co-ordination of an alkoxide from one macrocycle to a manganese centre in theJ. CHEM. SOC. DALTON TRANS. 1987 2561 second unit. In this complex only two such 'intermolecular' bonds are formed because the strongly co-ordinated thio- cyanate ligands occupy the equivalent axial site on the second manganese centre in each (2 + 2) macrocycle. If the terminal thiocyanate groups were not present, four Mn-alkoxide bonds could be formed between two binuclear macrocyclic units in a cofacial orientation (I). The resulting system has the cubane-like core found in (2) but still retains two discrete (2 + 2) ligands. Structure (I) might be expected to show reasonable stability since it is held together by four metal-ligand bonds.The next step is hydrolysis of an imine bond from one macrocycle to form (11). The terminal amine group is then free to rotate (about the saturated C-C bond) and can add at an imine group on the second macrocycle by nucleophilic attack at the carbon atom, (111). One of the C-N single bonds then breaks, either reforming (11), or leaving a new 'intermolecular' imine link and releasing another free amine which undergoes a Schiff-base condensation with the free carbonyl to form the product (V). Similar attack by nucleophilic amine groups on co- ordinated imino ligands has been implicated in the mechanism of transamination reactions in related systems.20 An alternative route involves the hydrolysis of two imine groups, one in each macrocycle, (IV).Each free amine then attacks the carbonyl of the adjacent ligand to give the product (V). This seems a less likely process since it involves simultaneous hydrolysis of two imine groups in the correct spatial orientation. The resulting complex (V) has the structure and conformation observed for the (4 + 4) complex (2). In effect, the (4 + 4) macrocycle is formed by a template reaction where the templating moiety is the Mn,(alkoxide), cluster. The cubane core itself forms as a result of the requirement of Mn" for a good donor in the axial position. This pseudo-cubane core then holds the ligands in an orientation favouring the formation of the (4 + 4) macrocycle, normally the role of a single metal ion in a template reaction.Imine bonds are frequently observed to be susceptible to hydrolysis when not co-ordinated to a metal ion but are generally thought to be relatively stable once co- ordinated. Indeed, this is the reasoning behind the use of the transmetallation reaction to prepare complexes which are inaccessible by other methods; where, for example the metal ion is an ineffective template and the free ligand is unstable.20 The observed rearrangement of the (2 + 2) macrocycle during the transmetallation reaction with manganese shows that the macrocycle structures in general, and the imine bonds in particular, are quite labile. Formation of a macrocyclic product, however, depends on the presence of a templating moiety since in the absence of any metal ion the only products isolated are poorly characterised viscous oils, probably of oligomeric or polymeric composition.The fact that bi- and tetra-nuclear products can be isolated from labile transmetallation mixtures implies that these are the most stable products (at least in the kinetic sense). If this is the case, it follows that the same products should be accessible by direct template synthesis. Accordingly we have attempted to prepare the complexes using manganese@) as template. Reac- tion of 2,6-diacetylpyridine with 1,3-diamino-2-hydroxypro- pane in the presence of Mn2+ yielded a product with mass spectrum, i.r. spectrum, and analysis identical to those obtained from the transmetallation reaction. Addition of NCS - to the template mixture also resulted in the formation of (3).However, the yield of a second, insoluble, carbonyl-containing component was increased with respect to the transmetallation route. The probable explanation of this effect is that the thiocyanate ions, by co-ordinating to some of the metal sites, reduce the number of sites available for amine or carbonyl co-ordination. Hence the efficiency of the templating ion is reduced and the insoluble product precipitates before ring closure can occur. A similar carbonyl-containing complex can be isolated if the reaction is carried out using strontium as template., Similar direct preparations have been attempted with other transition metals. Iron(I1) has proved an effective template for the formation of bimetallic complexes of L2-' but copper(r1) and iron(II1) have not been successful in our hands.This may be a function of the size of the metal ions since the two effective ions, manganese(I1) and iron(II), have rather similar radii. Bioinorganic Model Studies.-Both (2) and (3) are of interest as models for the photosynthetic water-splitting system. Recent work in this area suggests that the protein complex may contain four manganese centres in a mixed valence Mn"'-Mn'" cluster., Accordingly we are attempting to purify bulk samples of (2) and (3) and to investigate the electrochemical, e.s.r., and magnetic properties of these complexes and their derivatives. Preliminary magnetic susceptibility data suggest that the manganese centres in these complexes interact with each other only weakly,' this is in accord with the properties of the biological system.2 Experimental Preparation of Complexes.-[Ba(H2 L)(H,O),][ClO,] ,.2,6- Diacetylpyridine (0.025 mol) and barium perchlorate (0.01 5 mol) were dissolved in methanol (200 cm3) and heated to reflux. 1,3-Diamino-2-hydroxypropane (0.025 mol) in methanol (20 cm3) was added and the refluxing continued for 2.5 h. The white product crystallised on cooling and was filtered off; a second crop was obtained by evaporation of the filtrate under reduced pressure. Yield: 75% (Found: C, 35.7; H, 4.2; N, 10.3. Calc. for C,,H3,BaCl,N6012: C, 35.7; H, 4.2; N, 10.4%). 13C N.m.r. in (CD,),SO: 6 165.62 (C1), 123.91 (C2), 139.69 (C'), 154.98 (C6), 16.01 (C7), 57.42 (C'), and 68.60 p.p.m. (C'). [ Mn,( L')(ClO,),] -2H20. (a) By transmetallation.[ Ba( H L)- (H20),][C104] , (2 mmol) was suspended in refluxing methanol (100 cm3) and a solution of Mn(C1O,),-6H2O (4.2 mmol) in methanol (20 cm3) was added. Refluxing was con- tinued overnight and a yellow product separated on cooling. This was collected and a further crop obtained by evaporation of the filtrate under reduced pressure. Yield: 35%. The reaction can also be carried out in ethanol. (b) By template. 2,6-Diacetylpyridine (6 mmol) and mangan- ese(I1) perchlorate (6 mmol) were dissolved in methanol (100 cm3) and heated to reflux. 1,3-Diamin0-2-hydroxypropane (6 mmol) dissolved in cold methanol (40 cm3) was added slowly to the refluxing mixture, and refluxing continued overnight. The solution was cooled, reduced in volume by evaporation under reduced pressure, and .the yellow product collected.Yield: 30%. The products obtained from both routes were indistinguishable; they were recrystallised from acetonitrile by vapour diffusion of diethyl ether (Found: C, 37.8, H, 3.8; N, 11.2. Calc. for C,,H60C1,Mn,N,,02,: C, 37.9; H, 4.0; N, 11.1%). 252Cf p.d.m.s. data indicated that this product contained both (2) and an equivalent complex of the (2 + 2) ligand. Both compounds can be dissolved in acetonitrile but the solubility of the (2 + 2) complex appears to be lower than that of (2). Hence, by repeated washing with acetonitrile a sample of the (2 + 2) complex was collected and its mass spectrum recorded [Figure 5(c)]. This complex has not been further characterised as attempts at recrystallisation always yielded (2) as the only crystals large enough for X-ray analysis along with yellow powders, presumed to contain the (2 + 2) portion.[ClO,], (1.2 mmol) was suspended in refluxing methanol (100 cm3). Mn(C10,)2-6H20 (2.5 mmol) in methanol (30 cm3) was added, quickly followed by NaNCS (10 mmol) in methanol (50 cm3). Refluxing was continued overnight and the yellow product collected by filtration of the cooled solution. The [Mn,( HL)(L)(NCS),]NCS-2H20. CWH, L)(H20)21 -2562 J. CHEM. SOC. DALTON TRANS. 1987 product was recrystallised from acetonitrile-ethanol(5 : 1) con- taining NaNCS. A small amount of yellow material insoluble in acetonitrile can be separated before recrystallisaton but reforms in the dissolved sample and is difficult to remove completely 45.0 H, 4.3; N, 16.8%).(Found: c , 44.8; H, 4.2; N, 16.3. Calc. C53H61Mn4N1706Ss: c , Cry s t allography .-Crys tal data for [ M n4( L' )( Cl 04)4] 2H20.C4,H6,C14Mn4N 2022, orange, crystal dimensions 0.75 x 0.25 x 0.25 mm, monoclinic, a = 20.209(10), b = space group C2/c, 2 = 4, F(0oO) = 5926.4. Using 1.8" 8-28 scans with variable scan rates (4-29" min-l), 6 806 unique reflections were collected in the range 3 < 28 < 55". 5 547 Reflections, for which I > 30 (I) were used for the structural analysis. Crystal data for [Mn,(HL)(L)(NCS),]NCS. C5,H5,Mn4- N,@,&, yellow, crystal dimensions 0.35 x 0.19 x 0.15 mm, monoclinic, a = 44.193(10), b = 13.082(4), c = 22.621(4) A, p = 105.73(2)", U = 12 588(5) pi3, space group C2/c, 2 = 8, F(OO0) = 5 646.63. 2" o-scans with variable scan rates (3-29" min-') were used to collect 8 144 unique reflections in the range 3 > 28 > 45" and of these 3 435 having I > 30(I) were used in the subsequent calculations.Data for both crystals were collected at - 140 "C on a Nicolet R3m four-circle diffractometer using graphite-monochromated Mo-K, radiation. The cell parameters were determined by least- squares refinement of 25 accurately centred reflections (28 > 23"). Crystal stability was monitored by recording three check reflections every 100 reflections, no significant variations were observed. The data sets were corrected for Lorentz- polarisation effects and empirical absorption corrections were applied based on yr-scan data. Both structures were solved by direct methods using the program SOLV 22 and refined by blocked-cascade least-squares techniques.The refinement of (2) converged with R = 0.043 and R' = 0.062. All non-hydrogen atoms were refined aniso- tropically; hydrogen atoms were inserted at calculated positions using a riding model with thermal parameters equal to 1.2 U of their carrier atoms. For (3) the refinement converged with R = 0.074 and R' = 0.094. The manganese, oxygen, and sulphur atoms were refined anisotropically, the remaining non-hydrogen atoms were refined isotropically and, as for (2) all the hydrogen atoms except the hydroxy hydrogen H(l) were inserted at calculated positions. H( 1) was located from a difference map, inserted at that position and not further refined. The function minimised in the refinement was Cw(lFoI - where w = [02(Fo) + gFO2]-' and g = 0.0075 and 0.0013 for (2) and (3) respectively.The final difference maps showed no significant features. All programs used for data collection and structure solution are contained in the SHELXTL (version 4.0) package.22 14.241(3), c = 20.596(9) A, p = 91.07(4)", U = 5 924(4) A3, 252Cf P.D.M.S.-Samples were dissolved in a suitable solvent (CH3CN or CH,OH-H,O) and applied to the aluminised surface of a thin (10 micron) mylar film. The solvent was evaporated and the sample placed in the 252Cf p.d.m.s. instrument and raised to a potential of 10 kV. A 257Cf source (15 pC) was placed behind the sample foil and an acceleration grid (at ground potential) positioned 2-3 mm in front of the sample. 2s2Cf fission particles passed through the foil and ionised the sample on the front surface.The ions were accelerated by the 10 kV potential and travelled 42 cm to a detector. When a fission event occurred a clock was started in the instrument and the times of flight for the sample ions were determined from their arrival at the stop detector. Times were integrated for a period of 6-18 h and the spectra were calibrated from the time of flight of the inherent sodium and hydrogen ions. Infrared Spectra.-These were recorded as KBr discs or Nujol mulls on a Pye Unicam SP3-300 infrared spectro- photometer. Acknowledgements We thank the New Zealand University Grants Committee for the funds to purchase instruments used in this work. We are also grateful to Professor S. M. Nelson for all his advice and interest.References 1 K. Sauer, Ace. Chem. Res., 1980, 13, 249 and refs. therein. 2 G. C. Dismukes, Photochem. Photobiol., 1986,43,99 and refs. there- in. 3 See, for example, J. A. Kirby, A. S. Robertson, J. P. Smith, A. C. Thompson, S. R. Cooper, and M. P. Klein, J. Am. Chem. SOC., 1981, 103, 5529; F. M. Ashmawy, C. A. McAuliffe, R. V. Parish, and J. Tames. J. Chem. SOC., Dalton Trans., 1985, 1391; P. S. Pavacik, J. C. Huffman, and G. Christou, J. Chem. SOC., Chem. Commun., 1986,43. 4 Govindjee, T. Wydrzynski, and S. B. Marks, in 'Bioenergetics of Membranes,' ed. L. Packer, Elsevier-North Holland, Amsterdam, 1977, p. 305. 5 G. C. Dismukes and Y. Siderer, Proc. Nat. Acad. Sci. U.S.A., 1981,78, 274; J. C. de Paula, W. F. Beck, and G. W. Brudvig, J. Am. Chem. Soc., 1986, 108, 4002.6 K. Wieghardt, U. Bossek, and W. Gebert, Angew. Chem., Int. Ed. Engl., 1983, 22, 328. 7 V. McKee and J. Smith, J. Chem. SOC., Chem. Commun., 1983, 1465. 8 N. A. Bailey, D. E. Fenton, R. Moody, C. 0. Rodriguez de Barbarin, I. N. Sciambarella, J. M. Latour, D. Limosin, and V. McKee, J. Chem. Soc., Dalton Trans., 1987, 2519. 9 S. Brooker, K. Faulalo, and V. McKee, unpublished work. 10 V. McKee and W. B. Shepard, J. Chem. SOC., Chem. Commun., 1985, 158. 11 C. 0. Rodriguez de Barbarin, Ph.D. Thesis, University of Sheffield, 1984. 12 E. Horn, M. R. Snow, and P. C. Zeleny, Aust. J. Chem., 1980, 33, 1659. 13 M. Heberhold, G. Suss, J. Ellerman, and H. Gabelein, Chem. Ber., 1978, 11, 2931. 14 F. A. Cotton, A. Davison, W. H. Ilsley, and H. S. Trop, Inorg.Chem., 1979, 18, 2719. 15 L. R. Groeneveld, G. Vos, G. C. Verschoor, and J. Reedijk, J. Chem. SOC., Chem. Commun., 1982, 620; G. A. van Albada, R. A. G. de Graaff, J. G. Haasnoot, and J. Reedijk, Inorg. Chem., 1984,23, 1404. 16 P. A. Harding, K. Henrick, L. F. Lindoy, M. McPartlin, and P. A. Tasker, J. Chem. Soc., Chem. Commun., 1983, 1300. 17 M. G. B. Drew, F. S. Esho, and S. M. Nelson, Znorg. Chim. Acta, 1983, 76, L269; M. G. B. Drew, F. S. Esho, A. Lavery, and S. M. Nelson, J. Chem. SOC., Dalton Trans., 1984, 545. 18 B. Murphy, J. Nelson, S. M. Nelson, M. G. B. Drew, and P. Yates, J. Chem. SOC., Dafron Trans., 1987, 123; J. Nelson, personal com- munication. 19 B. Sundqvist and R. D. Macfarlane, Mass Spec. Rev., 1985, 4, 421. 20 S. M. Nelson, Pure Appl. Chem., 1980,52, 2461.21 H. Adams,N. A. Bailey, D. E. Fenton, R. J. Good, R. Moody,andC. 0. 22 G. M. Sheldrick, SHELXTL User Manual, Revision 4, Nicolet XRD Rodriguez de Barbarin, J. Chem. SOC., Dalton Trans., in the press. Corporation, Madison, Wisconsin, 1984. Received 29th December 1986; Paper 612479 J. CHEM. SOC. DALTON TRANS. 1987 2555 In memory of S. M. Nelson Formation of a (4 + 4) Schiff-base Macrocyclic Ligand by a Template Rearrangement. Crystal and Molecular Structures of Two Tetranuclear Manganese@) Complexes t Sally Brooker, Vickie McKee," and William B. Shepard Chemistry Department, University of Canterbury, Christchurch, New Zealand Lewis K. Pannell Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, MD 20892, U.S.A.Two tetranuclear manganese( it) complexes (2) and (3) have been obtained by Schiff-base condensation of 1,3-diamino-2- hydroxypropane and 2,6-diacetylpyridine in the presence of Ba2+, followed by transmetallation using Mn2+. The complexes have been characterised by analytical, spectroscopic, 252Cf plasma desorption mass spectroscopic, and single-crystal X-ray diffraction methods. Complex (2) contains a 40-membered macrocycle formed by a ( 4 + 4) Schiff-base condensation of four molecules of 1,3-diamino-2- hydroxypropane with four molecules of 2,6- diacetylpyridine. The macrocycle is wrapped around a cubane-like Mn,(alkoxide), core. Complex (3) is dimeric. The asymmetric unit contains two binuclear, 20-membered macrocycles each formed by a (2 + 2) Schiff-base condensation reaction.This complex contains five geometrically distinct thiocyanate groups. Routes for the formation of (3) are discussed and the possible significance of the compounds as models for the photosynthetic water-splitting system is noted. There is much current interest in the nature of the manganese cofactor of photosystem I1 which is thought to be the active site for the photosynthetic water-splitting For some time it has been accepted that the natural system must involve at least two magnetically coupled manganese centres probably bridged by oxygen donors.' The properties of many binuclear synthetic systems have been investigated as models for the photosynthetic site.3 A tetranuclear cluster has also been proposed to account for the properties of the various inter- mediates (S-states, oxidation levels) in the water-splitting cycle: particularly their complex e.s.r. chara~teristics.~,~ As yet, however, few tetranuclear model compounds involving oxidation states 11, 111, or IV have been characterised.6 Consequently, low molecular weight model systems involving either bi- or poly-nuclear manganese complexes are potentially of great value in contributing to the understanding of the photosynthetic process.The (2 + 2) macrocyclic ligand H,L was chosen for an investigation of the general properties of binuclear manganese systems having endogenous oxygen bridging. It is large enough, and has enough donor atoms, to bind two transition-metal ions and hold them close together. The macrocycle has six imine- type nitrogen donors and two pendant alcohol groups which have the potential to deprotonate and form alkoxide bridges.Bridging is not enforced however, as the ligand has sufficient flexibility for the alcohol groups to twist away from the central cavity. This flexibility means that the ligand can, to some extent, adjust to suit the stereochemical preferences of the co- ordinating metal ions. The ligand H,L can be prepared in good yield by a template reaction involving condensation of two molecules of 2,6-di- acetylpyridine with two molecules of 1,3-diamino-2-hydroxy- ~~~ t Supplementary data available (No. SUP 56675, 7 pp.): mass spectra and assignments. See Instructions for Authors, J. Chem. SOC., Dalton Trans., 1987, Issue 1, pp. xvii-xx. Non-S.I unit employed: 1 a.m.u = 1.6602 x lP2' kg.7 0 2 1 3<N N OH N I H ~ L '2556 J. CHEM. SOC. DALTON TRANS. 1987 Table 1. Atomic co-ordinates ( x lo4) for [Mn4(L’)(C10,),J~2H,0 (2) and [Mn,(HL)(L)(NCS),]NCS (3) X 5 850(1) 4 946( 1) 6 509( 1) 6 6 0 3 1) 5 475(1) 4 499( 1) 4 296(1) 5 743( 1) 6 486( 1) 6 878(2) 7 296(2) 7 330(2) 6 929( 1) 6 972(1) 7 462(2) 6 632( 1) 6 249( 1) 6 018(1) 5 236( 1) 5 451(2) 4 688(1) 4 407(2) 3 920(2) 1 605(1) 1 545(1) 825( 1) 1600(2) 1206(2) 1124(2) 1952(3) 2 122(4) 2 466(4) 2 232(4) 2 254(4) 2 532(4) 2 036(3) 2 005(4) 1852(3) 2 091(4) 1955(3) 2 060(4) 2 330(4) 1 946(4) 2 014(4) 1917(4) 1 748(4) 1 681(4) 1768(3) 1513(3) 1498(4) 1409(3) 1271(4) 1 104(4) 1 113(4) 1592(3) 1490(4) 790(3) 789(4) 694(4) 1 Oll(1) 1 100(2) 1 900(4) 2 399(4) 1434(3) 1391 Y 3 837(1) 2 242(1) 4 924(2) 3 127(2) 796(2) 1153(2) 2 945(2) 5 275(2) 5 824(2) 6 509(2) 6 241(2) 5 310(2) 4 655(2) 3 614(2) 3 232(3) 2 108(2) 1738(2) 736(2) 65(2) -929(2) 256(2) -440(2) - 167(2) 259(2) 2 628(2) 3 219(2) 1 894(2) 1361(8) 1405(8) 1606(7) 3 289(8) - 7 14( 10) - 1 023(12) -1 586(13) -1 796(14) - 1 505(13) - 961( 12) - 620( 12) - 941( 15) -58(10) 367( 13) 1 395(12) 2 207( 12) 3 069(10) 3 970( 13) 4 348(14) 4 629(13) 5 656( 15) 6 114(15) 5 559(13) 4 556(12) 4 097(10) 3 815(11) 4 058( 15) 2 161(12) 1 404(12) 298( 12) 3 005(9) - 76( 10) - 677( 1 1) - 1 052(13) 4 143(10) 5 157(13) 5 796(15) 1495 z 2 462(1) 1 663(1) 1995(1) 1 806(1) 1 776(1) 973(1) 884( 1) 2 967( 1) 2 188(1) 1 906(1) 1410(2) 1 225(1) 1537(1) 1439(1) 967(2) 1816(1) 2 400( 1) 2 263( 1) 1 500(1) 1622(2) 1009(2) 612(2) 162(2) 1 295(1) 1 184(1) 476( 1) 539(4) 1268(4) - 202(4) 530(4) 1956(6) 2 491(7) 2 919(8) 2 813(8) 2 274(7) 1838(7) 1232(7) 1031(9) 925(6) 312(7) 256(7) 534(8) 791(5) 862(7) 620(8) 1282(7) 1417(8) 1882(8) 2 211(8) 2 038(7) 1 587(6) 2 361(7) 3 006(8) 2 062(5) 2 316(7) 1810(7) 2 079(7) 2 128(5) 2 556(7) 3 076(7) -518(1) -1 372(6) -1 328(7) -1 855(8) 186 X 3 745(2) 4 050( 1) 3 945(1) 3 485(2) 4 296(1) 4 882(1) 4 732(1) 6 022(1) 5 927(2) 5 690(1) 2 481(1) 5 002( 1) 2 122( 1) 2 100(1) 2 598(1) 3 108(1) 5 768(1) 5 702( 1) 5 908( 1) 5 159(1) 6 299(1) 7 766(2) 618(5) 619(4) 680(4) 5 13(4) 1013(4) 712(3) 898(4) 529(4) 473(4) 359(4) 6(4) 47(4) 704(4) 799(3) 753(4) 157(4) 410(3) 255(3) 323(4) 585(3) 85(4) 674(3) 1028(4) 969(3) 1 086(4) 889(4) 891(5) 498(3) 246(4) 1467(3) 1692(3) - 102( 1) 2 018(1) 1354(3) 1 247(4) 1091(1) 1 llO(4) 868(4) 524(1) 1922(3) 2 019(3) 2 146(1) Y 768(2) 1424(2) 2 462(2) 2 869(3) 3 967(2) 4 342(2) 5 335(2) 6 003(2) 6 990(2) 2 317(1) 3 750(1) 3 966( 1) 3 597(2) 3 812(2) 4 957(2) 3 480(2) 2 905(1) 2 463(2) 3 889(2) 2 785(2) 2 465(2) 347(4) 5 289(17) 4 250(16) 3 680(13) 2 534(14) 2 165(10) 1959(16) 1124(11) 765(11) 280(10) - 138(12) - 296( 12) - 1 423(13) -239(14) 252( 13) 402( 14) 1465(14) 1258(10) 1863(12) 2 969(12) 3 175(10) 3 725( 15) 4 169(12) 4 200( 12) 4 890( 10) 5 102(12) 5 558(13) 6 672( 15) 2 738(10) 2 988(13) 3 326(5) 3 409(11) 3 477( 12) 3 538(4) -1 172(11) - 1 800(15) - 2 682(4) - 1 388(14) - 1 386(15) - 1 441(4) 1 627(10) I532(12) 1385(4) Z 1 10( 1) 520(1) 483(1) -21(2) 865(1) 1 275( 1) 1 502(1) 2 737(1) 2 973(2) 2 518(1) 1 825(1) 1758(1) 2 335(1) 1 678(1) 1811(1) 590( 1) 1 202(1) -38(1) 39U) - 407( 1) - 378(1) 3 17(2) - 2 428( 10) - 2 457( 10) - 1 922(8) -1 889(8) -1 351(6) - 2 440(9) -1 201(7) -631(7) - 308(7) 87(6) 297(7) 212(8) 998(7) 1330(8) 1355(8) 732(6) 1056(7) 1012(7) 888(5) 1086(9) 738(7) 748(7) 389(6) 700(7) - 272(5) - 674(8) - 589(9) - 408(6) - 657(7) - 999(4) - 676(6) - 822(7) - 1 043(2) 91 l(6) 1 170(8) 1514(3) -1 389(7) -1 721(8) - 2 200(3) 1898(5) 2 425(7) 3 175(2)J.CHEM. SOC. DALTON TRANS. 1987 2557 Table 2. Selected bond lengths (A) and angles (”) for [Mn,(L’)- Mn( 1)-N( I ) Mn( 1)-N(6) Mn( 1 )-O( 2) Mn( 1)-O( 14’) Mn(2)-N(4) Mn(2)-0( 1) Mn(2)-0( 1’) N( 1)-Mn( 1)-N(2) N(2)-Mn( 1)-N(6) N(2)-Mn( 1)-O( 1) N(1 1 N(6)-Mn( 1)-0(2) N(1)-Mn( 1)-O(2’) N(6)-Mn( 1)-O(2’) O(2)-Mn( 1)-O(2’) N(2)-Mn( 1)-O( 14’) O( 1 )-Mn( 1 )-O( 14’) 0(2’)-Mn( 1)-O( 14‘) N(3)-Mn(2)-N(5) N(3)-Mn(2)-0( 1) N(5)-Mn(2)-0(1) N(4)-Mn(2)-0(2) O(1 )-Mn(2)-0(2) N(4)-Mn(2)-0( 1 ’) O( 1 )-Mn(2)-0( 1 ’) Mn( 1 )-O( 1 )-M n( 2) Mn( 1)-O( 1 )-Mn(2‘) Mn(l)-0(2)-Mn(l’) - 2.267(2) 2.309(2) 2.142(2) 2.6 1 O(2) 2.279(2) 2.297( 2) 2.143(2) 69.4( 1) 136.6( 1) 72.3( 1) 1O4.4( 1) 104.3(1) 139.8(1) 71.4(1) 77.7( 1) 73.3( 1) 84.0( 1) 103.3(1) 135.6( 1) 70.9( 1 ) 151.3(1) 1 4 1 4 1) 78.8( 1) 106.7( 1) 77.q 1) 95.7( 1) 1 0 0 3 1) 101.9(1) Mn( 1)-N(2) Mn(l)-O( 1) Mn( 1)-O(2’) Mn(2)-N(3) Mn(2)-N(5) Mn(2)-O(2) Mn(2)-O(21) 2.291(2) 2.19 3( 2) 2.287(2) 2.328(2) 2.286(2) 2.177(2) 2.728(2) 69.3( 1) 141.7( 1) 146.8( 1) 98.q 1) 81.9( 1) 150.7( 1) 78.4( 1) 84.4( 1) 89.8( 1) 165.3(1) 68.7( 1) 69.1(1) 139.2(1) 146.6( 1) 72.7( 1) 1O4.3(1) 100.6(1) 82.0( 1) 102.0( 1) 100.9( 1) 96.6( 1) * Atoms marked ’ are related by a two-fold rotation axis to those given in Table 1.They have co-ordinates 1 -x, y, 4-2. propane in the presence of Ba2+.’ The resulting complex, [Ba( H2L)(H20),] [ClO,] (l), undergoes facile transmetalla- tion reactions in which the barium ion can be replaced by two transition-metal ions; this reaction is generally accompanied by deprotonation of one or both of the alcohol groups. We have previously reported the structure and properties of a binuclear, singly-bridged copper(I1) complex of the monodeprotonated ligand HL-.’v8 A number of binuclear complexes of iron(m) with L2- have also been prepared; these contain seven-co- ordinate iron bridged by both alkoxide groups.’ In this paper we report the preparation and structures of two tetranuclear manganese(I1) complexes derived from H,L.One of these is a dimer, [Mn,(HL)(L)(NCS),]NCS (3) while the second is a complex of the larger macrocycle H,L’, with stoicheiometry [Mn,(L’)(C10,),]~2H20 (2). The structure of the latter complex has been communicated previously,” the ligand has the same connectivity as H2L but the ring has been expanded to twice the size. The mechanism by which the (4 + 4) macrocycle H,L’ is formed, and the potential of the complexes as models for the photosynthetic system are discussed. Results and Discussion Synthesis ofthe Complexes.-The (2 + 2) macrocycle H,L was synthesised as the barium(I1) complex [Ba(H,L)(H,O),]- [CIO,], (1) in ca.75% yield uiu a Ba2+ ion template reaction from 2,6-diacetylpyridine and 1,3-diamino-2-hydroxypropane. The identity of this complex was established from i.r.7 13C n.m.r., and mass spectral data; an X-ray structural determination has also been carried out.’ When methanol or ethanol solutions of (1) were treated with an excess of Mn(C104)2.6H,07 the single Ba2+ ion of the precursor could be replaced by manganese(r1) ions yielding the perchlorate complex. Addition of excess NaNCS to the refluxing solution gave the corresponding Table 3. Selected bond lengths (A) and angles (”) for CMn,(HL)(L)(NCS),INCS (3) Mn( 1)-O( 1) Mn(l)-N( 1) Mn( 1)-N(6) Mn(1 jN(80) M n( 2)-O( 2) M n (2)-N (3) Mn(2)-N(5) Mn(3)-O(3) M n (3)-N (7) Mn(3)-N(12) Mn(3)-N(60) Mn(4)-O(3) Mn(4)-N(9) Mn(4)-N(ll) O( 1 )-Mn( 1)-0(2) O(2)-Mn( 1)-N( 1) 0(2)-Mn(l)-N(2) OU)-Mn(l)-N(6) N( 1 FMn( 1 b”6) 0 ( 1 )-Mn( 1 )-N(70) N( 1)-Mn( 1)-N(70) N(6)-Mn( 1)-N(70) O(2)-Mn( 1)-N(80) N(2)-Mn( 1)-N(80) N( 70)-M n( 1 )-N (80) O(ltMn(2)-0(4) O(1 )-Mn(2W(3) 0(4)-Mn(2)-N(3) 0(2)-Mn(2)-N4) N(3)-Mn(2)-N(4) 0(2)-Mn(2)-N(5) N(3)-Mn(2)-”5) O(l)-Mn(2)-N(80) 0(4)-Mn(2)-N(80) N(4)-Mn( 2)-N(80) 0(3)-Mn(3)-0(4) 0(4)-Mn(3)-N(7) 0(4)-Mn(3)-N(8) 0(3)-Mn(3)-N( 12) N(7)-Mn( 3)-N( 12) 0(3)-Mn(3)-N(50) N(7)-Mn( 3)-N( 50) N( 12)-Mn(3)-N(50) 0(4)-Mn(3)-N(60) N(8 )-Mn(3)-N(60) N( 50)-Mn( 3)-N( 60) 0(2tMn(4F0(4) 0(2tMn(4)-N(9) 0(4)-Mn(4)-“9) 0(3)-Mn(4)-N( 10) N(9)-Mn(4)-N(10) 0(3)-Mn(4)-N( 1 1) N(9)-Mn(4)-N( 1 1) 0(2)-Mn(4)-N(50) 0(4)-Mn(4)-N( 50) N( 1 O)-Mn(4)-N( 50) Mn( 1)-O( 1)-Mn(2) Mn( 1)-0(2)-Mn(4) Mn( 1 )-0(2)-Mn(2) Mn(2)-0(2)-Mn(4) 2.244( 11) 2.241(12) 2.264( 14) 2.461( 12) 2.247( 10) 2.304(14) 2.288( 13) 2.242( 10) 2.277( 13) 2.289( 13) 2.163( 15) 2.238(11) 2.304( 13) 2.322( 14) 73.0(4) 140.6(4) 143.6(4) 146.0(4) 69.7(5) 110.1(4) 87.7( 5 ) 8 5.3 ( 5 ) 81.7(4) 86.0(4) 168.7(4) 94.1(3) 72.8(4) 104.5(4) 1 44.3 ( 5 ) 68.6(5) 75.0(4) 134.8(4) 81.8(4) 167.6(4) 92.7(4) 14 1.7(4) 142.4(4) 148.3( 4) 69.5(5) 79.0(4) 9 1.4(4) 94.9(5) 74.7(4) 102.4(4) 97.2(5) 170.9( 5 ) 83.2(3) 94.8(4) 146.9(5) 139.0(4) 69.3(5) 142.6(4) 1 3 8.5( 5) 166.2(4) 83.3(4) 92.1(4) 87.8(4) 128.6(4) 86.8(3) 96.1(4) Mn( 1)-0(2) Mn( 1)-N(2) Mn( 1)-N(70) Mn(2)-0( 1) M n( 2)-0 (4) M n(2)-N(4) Mn(2)-N(80) Mn( 3)-0(4) Mn( 3)-N(8) Mn(3)-N( 50) Mn(4)-0( 2) Mn(4)-O(4) Mn(4)-N( 10) Mn(4)-N( 50) O( 1)-Mn( 1)-N( 1) O(1)-Mn( 1)-N(2) N( 1)-Mn( 1)-N(2) O(2)-Mn( 1)-N(6) N(2)-Mn( 1)-N(6) 0(2)-Mn(l)-N(70) N(2)-Mn( 1 )-N(70) O( 1 )-Mn( 1)-N(80) N( 1 )-Mn( 1 )-N(80) N(6)-Mn( 1)-N(80) O( 1 kMn(2)-0(2) 0(2)-Mn(2)-0(4) 0(2)-Mn(a-N(3) 0(1)-MnWN(4) 0(4FMn(a-N(4) O(1 )-Mn(a-N(5) 0(4)-Mn(2)-N(5) N(4kMn(2)-N(5) 0(2)-Mn(2)-N(80) N(3)-Mn(2)-N(80) N( 5)-Mn(2)-N(80) O( 3)-Mn(3)-N( 7) 0(3)-Mn(3)-N(8) N(7)-Mn( 3)-N( 8) 0(4)-Mn(3)-N( 12) N(8)-Mn(3)-N( 12) 0(4)-Mn(3)-N( 50) N(8)-Mn( 3)-N( 50) 0(3)-Mn(3)-N(60) N(7)-Mn(3)-N(60) N(12)-Mn(3)-N(60) 0(2)-Mn(4)-0( 3) 0(3)-Mn(4)-0(4) 0(2)-Mn(4)-N( 10) 0(4)-Mn(4)-N( 10) 0(2)-Mn(4)-N( 1 1) 0(4)-Mn(4)-N( 1 1) N( 10)-Mn(4)-N( 1 1) 0(3)-Mn(4)-N(50) N(9)-Mn(4)-N( 50) N(l 1)-Mn(4)-N(50) Mn( 3)-O( 3)-Mn(4) Mn(2)-0(4)-Mn(4) M n( 3)-0(4)-Mn(4) 0(3tMn(4)-N(9) Mn(2)-0(4)-Mn(3) 2.3 14( 10) 2.323( 15) 2.242( 14) 2.277(11) 2.229(9) 2.251 (13) 2.388(12) 2.300( 10) 2.333( 13) 2.44 1 ( 14) 2.251(10) 2.237( 14) 2.4 1 O( 12) 138.3(4) 71.3(4) 70.0(5) 73.9(4) 139.6(4) 1 O4.0(4) 94.5(5) 80.8(4) 8 1.9(4) 87.0(4) 73.7(4) 82.9( 3) 146.0(4) 14 1.3( 5) 97.7(4) 145.0(4) 97.2(4) 69.5(5) 84.8(4) 8 5.5 (4) 80.2(4) 14 1.0(4) 72.2(4) 68.8(5) 73.6(4) 136.8(4) 8 1.6(4) 75.2(5) 94.1 ( 5 ) 90.3 ( 5 ) 94.0(5) 94.1(3) 75.7(4) 71.5(4) 100.5(4) 143.7(5) 102.5(4) 73.3(4) 70.6(5) 79.8(4) 94.9(4) 76.3(4) 88.8(4) 95.4(4) 125.8(5) 87.1 (3) 2.21 l(8) thiocyanate complex.The macrocyclic products all showed a band at ca. 1 620 cm-’ in their i.r. spectra attributed to the imine bonds.The disappearance of the carbonyl signal at ca. 1700 cm-’ was taken as an indication of the formation of a closed macrocyclic ring rather than an open chain system. Description of the Structures.-Crystals of [Mn,(L’)(ClO,),]* 2H,O (2) and [Mn,(HL)(L)(NCS),]NCS (3) were obtained2558 J. CHEM. SOC. DALTON TRANS. 1987 Figure 1. The structure of complex (2). Dotted lines represent the long Mn-OClO, bonds Figure 3. The structure of complex (3); the ionic thiocyanate has been omitted. The dotted line represents the hydrogen bond Figure 2. The cubane core of complex (2) in the same orientation as Figure 1 from acetonitrile solution and their X-ray crystal structures have been determined. Atomic co-ordinates are listed in Table 1 and selected bond lengths and angles are given in Tables 2 and 3.The structure of (2) contains the (4 + 4) ligand co-ordinated to four manganese centres and utilising all 16 potential donor atoms (Figure 1). The alcohol groups have been deprotonated and each one bridges three manganese centres, forming a central cubane-type structure with stoicheiometry Mn,(alkoxide), (Figure 2). Alternatively, this structure may be viewed as two interpenetrating tetrahedra [Mn, and (alkoxide),] but the Mn- Mn separations [3.33( 1)-3.45( 1) A] suggest that there are no metal-metal bonds. The macrocycle is able to wrap itself around this cluster by virtue of the flexible propane links which permit a 90" twist of the ligand between successive rigid pyridinedi-imine units. Each manganese@) is seven-co-ordinate, bonded to three alkoxide oxygen donors, three nitrogen atoms from a pyridine- di-imine unit, and one perchlorate oxygen.The geometry about each metal centre is approximately pentagonal bipyramidal, although the Mn-OC10, distances are rather long [2.610(2) and 2.728(2) A] so that the anions may be better described as Figure 4. The manganese co-ordination spheres of structure (3) in the same orientation as Figure 3 semi-co-ordinated, occupying the otherwise vacant site above each manganese. There are also two unco-ordinated water molecules for each macrocyclic unit in the lattice. A crystal- lographic two-fold axis passes through the centres of the cubane faces defined by Mn(l), 0(2), Mn(l'), O(2') and Mn(2), 0(1), Mn(2'), O( 1'). There is also an approximate, non-crystallo- graphic S4 axis coincident with the C2.Within the cubane core, angles about manganese are all acute (78-82"), while those about oxygen are obtuse (96-102"); this would be expected in view of their respective co-ordination geometries. A few man- ganese(1) cubane structures with formulae [Mn,(CO), 2X4] (X = F, OH, or OR, where R = alkyl) ' 2 g 1 have been reported previously but to our knowledge, complex (2) is the first example in either the Mn" oxidation state or in the absence of carbonyl ligands. The thiocyanate complex (3) has a dimeric structure with two (2 + 2) macrocyclic units linked together as shown in Figure 3;J. CHEM. SOC. DALTON TRANS. 1987 2 0 0 0 0 - 1 5 0 0 0 - - 10000- 2559 [Ba(HZL)(CL04)1+ [Ba(HL)I+ / (671) (571) \ the co-ordination sphere is shown in Figure 4.The two halves of the structure are crystallographically independent and show considerable geometrical differences. As for (2), each man- ganese(r1) ion is seven-co-ordinate and has approximate pentagonal-bipyramidal geometry. In every case the donors in the pentagonal plane are the three nitrogen atoms of a pyridine- di-imine unit and two alkoxide donors, all from the same macrocycle. Each manganese has the nitrogen atom of an N- bridged thiocyanate group as one axial ligand; Mn(1) and Mn(2) are both bonded to N(80), while Mn(3) and Mn(4) are bridged by N( 50). The co-ordination spheres about Mn( 1) and Mn(3) are completed by the nitrogen donors of terminally bonded thiocyanates "(70) and N(60) respectively]. For Mn(2) and Mn(4) the seventh donor is an alkoxide oxygen atom 5 000- from the adjacent macrocycle and it is these two interactions [Mn(2)-O(4) and Mn(4)-0(2)] which hold the dimer together.Consequently, the alkoxides 0(1) and O(3) are doubly bridging but O(2) and O(4) are triply bridging. The atoms O( 1) and O(3) are linked via a hydrogen bond; this was indicated by the O(1)-0(3) distance of 2.42(1) A and is required for the stoicheiometry; the hydrogen atom was located from difference Fourier maps. The macrocycles themselves are non-planar, each is folded to accommodate the bridging thiocyanate groups by reducing the metal-metal distances to 3.135(5) A for both Mn(1)-Mn(2) and Mn(3)-Mn(4). The extent of the folding is indicated by the angles between the least-squares planes of the donors in the pentagonal plane for each pair of manganese atoms.The angle (*I [Mn2 (L) - H+]+ 300 0 2000 1000 ! 70000 0 - 5 0 0 0 0 A - 75 0 1000 1250 1500 3 0 0 0 0 10000 5 00 [ Mn4(LI2- 3H+l+ (1 0 8 2 ) 500 7 50 1000 1250 M a s s ( m / e ) Figure 5. Positive-ion 2s2Cf p.d.m.s. traces showing the assignments of the main peaks. (a) An unrecrystallised sample of the barium complex (l), (6) the products from transmetallation of (1) with Mn(C1O4),-6H,O, (c) the Mn,(L) component of the transmetallation reaction, ( d ) a recrystallised sample of complex (3)2560 J. CHEM. SOC. DALTON TRANS. 1987 between the mean planes of Mn( l), N( l), N(2), N(6), O( l), 0(2), and Mn(2), N(3), N(4), N(5), 0(1), O(2) is 104.6' and that between Mn(3), N(7), N(8), N(12), 0(3), 0(4), and Mn(4), N(9), N( lo), N( 1 l), 0(3), 0(4), is 108.6'.An unusual feature of the structure is the presence of four distinctly different bonding geometries for thiocyanate, in addition to the unco-ordinated counter ion. One of the two terminal thiocyanate groups is bonded in approximately linear fashion [Mn(3)-N(60)-C(61) 173(1)"], whereas the other is distinctly bent [Mn(l)-N(70)-C(71) 128(1)']. A similar effect is observed for the two bridging thiocyanates; N(80)-C(81)-S(82) is inclined at 33(1)" to the Mn(l), Mn(2), N(80) plane but N(50)-C(51)-S(52) makes an angle of only 7(1)" with the Mn(3), Mn(4), N(50) plane. In addition, the Mn-N-C angles show wide variation; 139(1) and 119(1)" for Mn(1)- and Mn(2)-N(80)-C(8 1) respectively compared with 133( 1) and 145(1)" for Mn(3)- and Mn(4)-N(50)-C(51).There are no striking inter- or intra-molecular interactions to account for these differences; the environments of the two terminal thio- cyanates and of the two bridging groups, while not identical, show no major differences. The individual geometries can be ascribed to a number of weak interactions and to crystal- packing effects. For example, S(72) is ca. 3.8 A from six macrocyclic ring atoms, 3 8, from the same asymmetric unit [N(6), C(23), C(36)], and 3 8, from an adjacent unit [C(15), C(16), and C(46)]. Any straightening of the N(70)-C(71)-S(72) angle is prevented by this network of interactions. There are six previous structurally characterised examples of N-bridging thiocyanate ligands.14-'* In most cases the bridging NCS is associated with an i.r.band in the region below 2 OOO cm-'. The i.r.spectrum (in Nujol) of (3) shows four peaks due to the C-N stretch of the thiocyanates at ca. 2 085, 2 065, 2 045, and 2025 cm-' and the envelope is broadened on the low-energy side, but there is no distinct signal below 2 000 cm-'. Formation of the (4 + 4) Macrocycle H,L'.-On first iso- lating the (4 + 4) macrocycle H,L' it was not clear at which stage in the template and transmetallation reactions the larger ring had been formed. The first possibility is that it formed as a minor product in the barium template reaction and crystallised out preferentially in the subsequent manganese transmetallation step. A plausible driving force for this reaction is the expected preference of Ba2+ for alcohol donors rather than the softer imine nitrogens. The presence of a mixture of H2L and H,L' ligands in the barium product would not necessarily be detected by the normal methods of characterisation as the differences between a mononuclear H2L complex and the binuclear H,L' equivalent might not be very obvious.Microanalytical results would be identical, i.r. and n.m.r. spectra would be very similar, and recrystallisation would tend to remove the minor com- ponent. The major difference between the two complexes would be their masses, so the obvious way of detecting any H,L' component is mass spectroscopy. The technique of californium- 252 plasma desorption mass spectroscopy '' (252Cf p.d.m.s.) was chosen since it enables spectra to be obtained without excessive fragmentation of the complexes.Figure 5 shows the 252Cf p.d.m.s. traces of the complexes. The spectrum of the unrecrystallised barium complex [Figure 5(a)] is quite simple and the major peaks can readily be assigned. There is no indication of any signal at twice the mass of the assigned peaks to suggest a Ba,(H,L') species and the absence of an extensive fragmentation pattern makes it unlikely that a (4 + 4) complex was present but disintegrated in the instru- ment. The minor peaks at 807 and 907 a.m.u. are likely to be addition complexes of the assigned species with BaClO,. The spectrum of the Mn" transmetallation product [Figure 5(b)] shows signals in two well defined regions. Those centred at ca. 1 400 a.m.u. are due to the Mn,(L') complex (2) while signals + \ - H20 w 42 (111) (V) Scheme.in the region ca. 540 a.m.u. correspond to various Mn2(L) fragments. Most of the peaks in the lower mass region appear to be due to fragmentation of (2); by comparison with spectrum (c) only the signals at 642 and 541 a.m.u. arise from the presence of a Mn,(L) complex in the transmetallation mixture (see Ex- perimental section). The spectrum of the thiocyanate complex [Figure 5(d)] shows extensive fragmentation, consistent with a dimer held together by metal-ligand bonds. The peak ratios indicate that the signals around 1 200 a.m.u. correspond to the parent ion. It is significant that, in spite of the expected facile cleavage of the dimer, the spectrum of (3) gives clear indication of the presence of the parent ion. This supports the conclusion that the barium complex contains no (4 + 4) component and hence that the (4 + 4) macrocycle in (2) must be formed during the trans- metallation reaction with manganese and not in the initial template process.Comparison of the structures of (2) and (3) (Figures 1 and 3) suggests a possible route for the formation of the (4 + 4) macrocyclic product H4L' (Scheme). In (3) the two bimetallic macrocyclic units are held together by axial co-ordination of an alkoxide from one macrocycle to a manganese centre in theJ. CHEM. SOC. DALTON TRANS. 1987 2561 second unit. In this complex only two such 'intermolecular' bonds are formed because the strongly co-ordinated thio- cyanate ligands occupy the equivalent axial site on the second manganese centre in each (2 + 2) macrocycle.If the terminal thiocyanate groups were not present, four Mn-alkoxide bonds could be formed between two binuclear macrocyclic units in a cofacial orientation (I). The resulting system has the cubane-like core found in (2) but still retains two discrete (2 + 2) ligands. Structure (I) might be expected to show reasonable stability since it is held together by four metal-ligand bonds. The next step is hydrolysis of an imine bond from one macrocycle to form (11). The terminal amine group is then free to rotate (about the saturated C-C bond) and can add at an imine group on the second macrocycle by nucleophilic attack at the carbon atom, (111). One of the C-N single bonds then breaks, either reforming (11), or leaving a new 'intermolecular' imine link and releasing another free amine which undergoes a Schiff-base condensation with the free carbonyl to form the product (V).Similar attack by nucleophilic amine groups on co- ordinated imino ligands has been implicated in the mechanism of transamination reactions in related systems.20 An alternative route involves the hydrolysis of two imine groups, one in each macrocycle, (IV). Each free amine then attacks the carbonyl of the adjacent ligand to give the product (V). This seems a less likely process since it involves simultaneous hydrolysis of two imine groups in the correct spatial orientation. The resulting complex (V) has the structure and conformation observed for the (4 + 4) complex (2). In effect, the (4 + 4) macrocycle is formed by a template reaction where the templating moiety is the Mn,(alkoxide), cluster.The cubane core itself forms as a result of the requirement of Mn" for a good donor in the axial position. This pseudo-cubane core then holds the ligands in an orientation favouring the formation of the (4 + 4) macrocycle, normally the role of a single metal ion in a template reaction. Imine bonds are frequently observed to be susceptible to hydrolysis when not co-ordinated to a metal ion but are generally thought to be relatively stable once co- ordinated. Indeed, this is the reasoning behind the use of the transmetallation reaction to prepare complexes which are inaccessible by other methods; where, for example the metal ion is an ineffective template and the free ligand is unstable.20 The observed rearrangement of the (2 + 2) macrocycle during the transmetallation reaction with manganese shows that the macrocycle structures in general, and the imine bonds in particular, are quite labile.Formation of a macrocyclic product, however, depends on the presence of a templating moiety since in the absence of any metal ion the only products isolated are poorly characterised viscous oils, probably of oligomeric or polymeric composition. The fact that bi- and tetra-nuclear products can be isolated from labile transmetallation mixtures implies that these are the most stable products (at least in the kinetic sense). If this is the case, it follows that the same products should be accessible by direct template synthesis. Accordingly we have attempted to prepare the complexes using manganese@) as template. Reac- tion of 2,6-diacetylpyridine with 1,3-diamino-2-hydroxypro- pane in the presence of Mn2+ yielded a product with mass spectrum, i.r.spectrum, and analysis identical to those obtained from the transmetallation reaction. Addition of NCS - to the template mixture also resulted in the formation of (3). However, the yield of a second, insoluble, carbonyl-containing component was increased with respect to the transmetallation route. The probable explanation of this effect is that the thiocyanate ions, by co-ordinating to some of the metal sites, reduce the number of sites available for amine or carbonyl co-ordination. Hence the efficiency of the templating ion is reduced and the insoluble product precipitates before ring closure can occur.A similar carbonyl-containing complex can be isolated if the reaction is carried out using strontium as template., Similar direct preparations have been attempted with other transition metals. Iron(I1) has proved an effective template for the formation of bimetallic complexes of L2-' but copper(r1) and iron(II1) have not been successful in our hands. This may be a function of the size of the metal ions since the two effective ions, manganese(I1) and iron(II), have rather similar radii. Bioinorganic Model Studies.-Both (2) and (3) are of interest as models for the photosynthetic water-splitting system. Recent work in this area suggests that the protein complex may contain four manganese centres in a mixed valence Mn"'-Mn'" cluster., Accordingly we are attempting to purify bulk samples of (2) and (3) and to investigate the electrochemical, e.s.r., and magnetic properties of these complexes and their derivatives.Preliminary magnetic susceptibility data suggest that the manganese centres in these complexes interact with each other only weakly,' this is in accord with the properties of the biological system.2 Experimental Preparation of Complexes.-[Ba(H2 L)(H,O),][ClO,] ,. 2,6- Diacetylpyridine (0.025 mol) and barium perchlorate (0.01 5 mol) were dissolved in methanol (200 cm3) and heated to reflux. 1,3-Diamino-2-hydroxypropane (0.025 mol) in methanol (20 cm3) was added and the refluxing continued for 2.5 h. The white product crystallised on cooling and was filtered off; a second crop was obtained by evaporation of the filtrate under reduced pressure.Yield: 75% (Found: C, 35.7; H, 4.2; N, 10.3. Calc. for C,,H3,BaCl,N6012: C, 35.7; H, 4.2; N, 10.4%). 13C N.m.r. in (CD,),SO: 6 165.62 (C1), 123.91 (C2), 139.69 (C'), 154.98 (C6), 16.01 (C7), 57.42 (C'), and 68.60 p.p.m. (C'). [ Mn,( L')(ClO,),] -2H20. (a) By transmetallation. [ Ba( H L)- (H20),][C104] , (2 mmol) was suspended in refluxing methanol (100 cm3) and a solution of Mn(C1O,),-6H2O (4.2 mmol) in methanol (20 cm3) was added. Refluxing was con- tinued overnight and a yellow product separated on cooling. This was collected and a further crop obtained by evaporation of the filtrate under reduced pressure. Yield: 35%. The reaction can also be carried out in ethanol. (b) By template. 2,6-Diacetylpyridine (6 mmol) and mangan- ese(I1) perchlorate (6 mmol) were dissolved in methanol (100 cm3) and heated to reflux.1,3-Diamin0-2-hydroxypropane (6 mmol) dissolved in cold methanol (40 cm3) was added slowly to the refluxing mixture, and refluxing continued overnight. The solution was cooled, reduced in volume by evaporation under reduced pressure, and .the yellow product collected. Yield: 30%. The products obtained from both routes were indistinguishable; they were recrystallised from acetonitrile by vapour diffusion of diethyl ether (Found: C, 37.8, H, 3.8; N, 11.2. Calc. for C,,H60C1,Mn,N,,02,: C, 37.9; H, 4.0; N, 11.1%). 252Cf p.d.m.s. data indicated that this product contained both (2) and an equivalent complex of the (2 + 2) ligand. Both compounds can be dissolved in acetonitrile but the solubility of the (2 + 2) complex appears to be lower than that of (2).Hence, by repeated washing with acetonitrile a sample of the (2 + 2) complex was collected and its mass spectrum recorded [Figure 5(c)]. This complex has not been further characterised as attempts at recrystallisation always yielded (2) as the only crystals large enough for X-ray analysis along with yellow powders, presumed to contain the (2 + 2) portion. [ClO,], (1.2 mmol) was suspended in refluxing methanol (100 cm3). Mn(C10,)2-6H20 (2.5 mmol) in methanol (30 cm3) was added, quickly followed by NaNCS (10 mmol) in methanol (50 cm3). Refluxing was continued overnight and the yellow product collected by filtration of the cooled solution. The [Mn,( HL)(L)(NCS),]NCS-2H20. CWH, L)(H20)21 -2562 J.CHEM. SOC. DALTON TRANS. 1987 product was recrystallised from acetonitrile-ethanol(5 : 1) con- taining NaNCS. A small amount of yellow material insoluble in acetonitrile can be separated before recrystallisaton but reforms in the dissolved sample and is difficult to remove completely 45.0 H, 4.3; N, 16.8%). (Found: c , 44.8; H, 4.2; N, 16.3. Calc. C53H61Mn4N1706Ss: c , Cry s t allography .-Crys tal data for [ M n4( L' )( Cl 04)4] 2H20.C4,H6,C14Mn4N 2022, orange, crystal dimensions 0.75 x 0.25 x 0.25 mm, monoclinic, a = 20.209(10), b = space group C2/c, 2 = 4, F(0oO) = 5926.4. Using 1.8" 8-28 scans with variable scan rates (4-29" min-l), 6 806 unique reflections were collected in the range 3 < 28 < 55". 5 547 Reflections, for which I > 30 (I) were used for the structural analysis.Crystal data for [Mn,(HL)(L)(NCS),]NCS. C5,H5,Mn4- N,@,&, yellow, crystal dimensions 0.35 x 0.19 x 0.15 mm, monoclinic, a = 44.193(10), b = 13.082(4), c = 22.621(4) A, p = 105.73(2)", U = 12 588(5) pi3, space group C2/c, 2 = 8, F(OO0) = 5 646.63. 2" o-scans with variable scan rates (3-29" min-') were used to collect 8 144 unique reflections in the range 3 > 28 > 45" and of these 3 435 having I > 30(I) were used in the subsequent calculations. Data for both crystals were collected at - 140 "C on a Nicolet R3m four-circle diffractometer using graphite-monochromated Mo-K, radiation. The cell parameters were determined by least- squares refinement of 25 accurately centred reflections (28 > 23"). Crystal stability was monitored by recording three check reflections every 100 reflections, no significant variations were observed.The data sets were corrected for Lorentz- polarisation effects and empirical absorption corrections were applied based on yr-scan data. Both structures were solved by direct methods using the program SOLV 22 and refined by blocked-cascade least-squares techniques. The refinement of (2) converged with R = 0.043 and R' = 0.062. All non-hydrogen atoms were refined aniso- tropically; hydrogen atoms were inserted at calculated positions using a riding model with thermal parameters equal to 1.2 U of their carrier atoms. For (3) the refinement converged with R = 0.074 and R' = 0.094. The manganese, oxygen, and sulphur atoms were refined anisotropically, the remaining non-hydrogen atoms were refined isotropically and, as for (2) all the hydrogen atoms except the hydroxy hydrogen H(l) were inserted at calculated positions. H( 1) was located from a difference map, inserted at that position and not further refined.The function minimised in the refinement was Cw(lFoI - where w = [02(Fo) + gFO2]-' and g = 0.0075 and 0.0013 for (2) and (3) respectively. The final difference maps showed no significant features. All programs used for data collection and structure solution are contained in the SHELXTL (version 4.0) package.22 14.241(3), c = 20.596(9) A, p = 91.07(4)", U = 5 924(4) A3, 252Cf P.D.M.S.-Samples were dissolved in a suitable solvent (CH3CN or CH,OH-H,O) and applied to the aluminised surface of a thin (10 micron) mylar film.The solvent was evaporated and the sample placed in the 252Cf p.d.m.s. instrument and raised to a potential of 10 kV. A 257Cf source (15 pC) was placed behind the sample foil and an acceleration grid (at ground potential) positioned 2-3 mm in front of the sample. 2s2Cf fission particles passed through the foil and ionised the sample on the front surface. The ions were accelerated by the 10 kV potential and travelled 42 cm to a detector. When a fission event occurred a clock was started in the instrument and the times of flight for the sample ions were determined from their arrival at the stop detector. Times were integrated for a period of 6-18 h and the spectra were calibrated from the time of flight of the inherent sodium and hydrogen ions. Infrared Spectra.-These were recorded as KBr discs or Nujol mulls on a Pye Unicam SP3-300 infrared spectro- photometer. Acknowledgements We thank the New Zealand University Grants Committee for the funds to purchase instruments used in this work. We are also grateful to Professor S. M. Nelson for all his advice and interest. References 1 K. Sauer, Ace. Chem. Res., 1980, 13, 249 and refs. therein. 2 G. C. Dismukes, Photochem. Photobiol., 1986,43,99 and refs. there- in. 3 See, for example, J. A. Kirby, A. S. Robertson, J. P. Smith, A. C. Thompson, S. R. Cooper, and M. P. Klein, J. Am. Chem. SOC., 1981, 103, 5529; F. M. Ashmawy, C. A. McAuliffe, R. V. Parish, and J. Tames. J. Chem. SOC., Dalton Trans., 1985, 1391; P. S. Pavacik, J. C. Huffman, and G. Christou, J. Chem. SOC., Chem. Commun., 1986,43. 4 Govindjee, T. Wydrzynski, and S. B. Marks, in 'Bioenergetics of Membranes,' ed. L. Packer, Elsevier-North Holland, Amsterdam, 1977, p. 305. 5 G. C. Dismukes and Y. Siderer, Proc. Nat. Acad. Sci. U.S.A., 1981,78, 274; J. C. de Paula, W. F. Beck, and G. W. Brudvig, J. Am. Chem. Soc., 1986, 108, 4002. 6 K. Wieghardt, U. Bossek, and W. Gebert, Angew. Chem., Int. Ed. Engl., 1983, 22, 328. 7 V. McKee and J. Smith, J. Chem. SOC., Chem. Commun., 1983, 1465. 8 N. A. Bailey, D. E. Fenton, R. Moody, C. 0. Rodriguez de Barbarin, I. N. Sciambarella, J. M. Latour, D. Limosin, and V. McKee, J. Chem. Soc., Dalton Trans., 1987, 2519. 9 S. Brooker, K. Faulalo, and V. McKee, unpublished work. 10 V. McKee and W. B. Shepard, J. Chem. SOC., Chem. Commun., 1985, 158. 11 C. 0. Rodriguez de Barbarin, Ph.D. Thesis, University of Sheffield, 1984. 12 E. Horn, M. R. Snow, and P. C. Zeleny, Aust. J. Chem., 1980, 33, 1659. 13 M. Heberhold, G. Suss, J. Ellerman, and H. Gabelein, Chem. Ber., 1978, 11, 2931. 14 F. A. Cotton, A. Davison, W. H. Ilsley, and H. S. Trop, Inorg. Chem., 1979, 18, 2719. 15 L. R. Groeneveld, G. Vos, G. C. Verschoor, and J. Reedijk, J. Chem. SOC., Chem. Commun., 1982, 620; G. A. van Albada, R. A. G. de Graaff, J. G. Haasnoot, and J. Reedijk, Inorg. Chem., 1984,23, 1404. 16 P. A. Harding, K. Henrick, L. F. Lindoy, M. McPartlin, and P. A. Tasker, J. Chem. Soc., Chem. Commun., 1983, 1300. 17 M. G. B. Drew, F. S. Esho, and S. M. Nelson, Znorg. Chim. Acta, 1983, 76, L269; M. G. B. Drew, F. S. Esho, A. Lavery, and S. M. Nelson, J. Chem. SOC., Dalton Trans., 1984, 545. 18 B. Murphy, J. Nelson, S. M. Nelson, M. G. B. Drew, and P. Yates, J. Chem. SOC., Dafron Trans., 1987, 123; J. Nelson, personal com- munication. 19 B. Sundqvist and R. D. Macfarlane, Mass Spec. Rev., 1985, 4, 421. 20 S. M. Nelson, Pure Appl. Chem., 1980,52, 2461. 21 H. Adams,N. A. Bailey, D. E. Fenton, R. J. Good, R. Moody,andC. 0. 22 G. M. Sheldrick, SHELXTL User Manual, Revision 4, Nicolet XRD Rodriguez de Barbarin, J. Chem. SOC., Dalton Trans., in the press. Corporation, Madison, Wisconsin, 1984. Received 29th December 1986; Paper 612479

ISSN:1477-9226    

DOI:10.1039/DT9870002555

出版商:RSC    

年代:1987

数据来源: RSC