DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 31–41 31 Further attempts to rationalise the co-ordination chemistry of manganese with SchiV base ligands and supplementary carboxylate donors Michael Watkinson,a Matilde Fondo,b Manuel R. Bermejo,*b Antonio Sousa,*b Charles A. McAuliVe,*c Robin G. Pritchard,c Nongnuj Jaiboon,c Nadeem Aurangzeb c and Mohammed Naeemc a Department of Chemistry, Queen Mary and Westfield College, University of London, London, UK E1 4NS b Departamento de Química Inorgánica, Facultad de Química, Universidad de Santiago, 15706 Santiago de Compostela, Galicia, Spain.E-mail: qiansoal@usc.es c Department of Chemistry, University of Manchester Institute of Science and Technology (UMIST), Sackville Street, Manchester, UK M60 1QD Received 17th July 1998, Accepted 27th October 1998 Some manganese(III) complexes of SchiV base ligands with ancillary carboxylate donors have been found to exhibit structural diversity, although some patterns emerged.Thus, when the ligands 3CH3O-salen and 3CH3O-salpn [3CH3O-salen = dianion of N,N9-bis(3-methoxysalicylidene)ethane-1,2-diamine, 3CH3O-salpn = dianion of N,N9- bis(3-methoxysalicylidene)propane-1,3-diamine] are used in conjunction with carboxylates RCO2 2 (R = Me, Et, Prn or CH2Ph) unidentate carboxylate bonding occurs as in the crystallographically observed [Mn(3CH3O-salen)(O2CMe)- (H2O)]?2H2O 1, [Mn(3CH3O-salen)(O2CCH2Ph)(H2O)]?H2O 4, and [Mn(3CH3O-salpn)(O2CCH2Ph)(H2O)] 5.On the other hand, employing the more sterically encumbered carboxylates ButCO2 2 and PriCO2 2, bidentate chelating binding of the carboxylate occurs, as in [Mn(3CH3O-salpn)(O2CBut)] 2 and [Mn(3CH3O-salpn)(O2CPri)] 3. The reactivity of [Mn(salpn)(acac)] (acac = acetylacetonate) with Me3SiCl and aliphatic carboxylic acids, RCO2H (R = Me, Et, Prn, Bun, Pri or But), has also been investigated. A dimer species [{Mn(salpn)Cl}2]?CH3CN 6 was isolated from the reaction of Me3SiCl with [Mn(salpn)(acac)] while the carboxylic acids seem to lead to the isolation of monomers, such as [Mn(salpn)(O2CPri)] 7.This synthetic route has also been applied to the preparation of related complexes, in which the manganese(III) centre is not attainable with reliability via the aerobic oxidation of a manganese(II) precursor, although some rare examples have been obtained by the latter method, such as [Mn(5NO2-salen)(O2CMe)(H2O)], 8, [5NO2-salen = dianion of N,N9-bis(5-nitrosalicylidene)ethane-1,2-diamine]). Single crystals were grown from a dimethylformamide solution of the material of stoichiometry Mn(3Br,5NO2-salpn)(O2CMe)?H2O [3Br,5NO2- salpn = dianion of N,N9-bis(3-bromo-5-nitrosalicylidene)propane-1,3-diamine], isolated from this route and found to consist of the unexpected [{Mn(m-3Br,5NO2-salpn)(m-O)}2]?3DMF 9, apparently containing a manganese(IV) species, in spite of the electron withdrawing nature of the substituents on the aromatic rings of the ligand.Introduction Much of the recent interest in the co-ordination chemistry of manganese has been driven by the involvement of manganese in a number of biological systems.1–5 Owing to the strong experimental evidence associated with the presence of a multinuclear cluster of manganese ions within the Oxygen Evolving Complex (OEC) of Photosystem II, and the intrinsic interest in such compounds, inorganic chemists have been enticed into the area, resulting in the preparation of a great number of extremely elegant biomimetic compounds.6 Such complexes have not been limited to multinuclear cluster complexes, since enzymes such as manganese catalase, ribonucleotide reductase and the xylose isomerases involve two manganese ions which are thought to be associated in a dimer.Thus, great interest has also surrounded the preparation of dinuclear complexes 7 in addition to the higher nuclearity cluster compounds. Dinuclear units in which the manganese ions are linked by two or three ions that include O22 in a bis(m-oxo) bridge 8 or O22 together with two carboxylates, 9 alkoxides or a combination of alkoxide/phenoxide and carboxylate donors are widely observed and have been well characterised.10 Our recent investigations in this area have centred on the preparation of manganese complexes of tetradentate (N2O2 donor set) SchiV base ligands with ancillary carboxylate ligands to see whether diVerent structural behaviour in model complexes results through the variation of the carboxylate used, in order to model the aspartate and glutamate side chains of proteins.We have found that changing these carboxylate donors can have a profound eVect on the structural chemistry in the resultant complexes. When acetate was employed with the salpn ligand the polymeric complex [{Mn(salpn)(O2CMe)]2- (H2O)3}n] was isolated.11 Unlike the other rare examples of such polymeric compounds12 in which the ligands stack on top of one another, there was twist of 908 between adjacent ligands in the polymeric backbone.This results in the polymer having a dimeric, rather than the more usual monomeric, repeat unit. Consequently we extended our investigations to other linear chain carboxylates, butyrate (O2CPrn) and valerate (O2CBun), and found that a diverse range of structural chemistry was available.13 With butyrate and the salen ligand a dinuclear species was characterised, [Mn2(salen)2(O2CPrn)(H2O)(EtOH)]- [O2CPrn]; an apparent ‘snapshot’ of polymer formation (the non-co-ordinated carboxylate, when viewed in the crystal packing diagram, appears ideally positioned to bind to the manganese centres and hence allow polymer formation to occur) which, on the basis of cyclic voltammetry studies, maintains its structural integrity in acetonitrile solution.In complete32 J. Chem. Soc., Dalton Trans., 1999, 31–41 contrast, when the valerate counter ion was used the monomeric species [Mn(salpn)(O2CBun)] was isolated.We have since isolated other monomeric species, together with dimeric and polymeric species, by using other linear, branched chain and aromatic carboxylates. Interestingly, the polymeric species we have isolated can contain either monomeric or dimeric repeat units together with ligation of the carboxylate in the anti-anti or syn-anti mode.14 Despite the large number of species we have now structurally characterised, we have been unable, as yet, to establish any pattern in the structural chemistry obtained.We were therefore keen to rationalise this behaviour through the structural characterisation of additional compounds of this type and to establish whether we could prepare a specific structural motif to order. An obvious means of achieving this goal was by attempting to replace a ligand already co-ordinated to a manganese centre whilst maintaining the geometric integrity of that centre.An ideal candidate appeared to be the monomeric species [Mn(salpn)(acac)] 15 and herein we report our findings. Results and discussion Preparation of complexes of 3CH3O-salen and 3CH3O-salpn with auxiliary carboxylate ligands All of the complexes were prepared as previously reported 11–14 by the reaction of the ligand with a stoichiometric quantity of the appropriate manganese(II) carboxylate salt in ethanol under aerobic conditions, yielding complexes of stoichiometry MnL(O2CR) (see Table 1).All complexes show characteristic shifts in their infrared spectra to lower frequency of n(C]] N), cf. ‘free’ ligand values, upon co-ordination to manganese, which together with parent ion peaks in their FAB mass spectra corresponding to [MnL]1 and room temperature magnetic moments typical of such compounds 14 indicate complete coordination of the SchiV base ligand. Unfortunately little other information can be deduced without resorting to single crystal X-ray diVraction. In view of our previous interesting findings and our desire to rationalise the structural chemistry in these species further we sought crystals suitable for X-ray diVraction studies.Crystal structure of [Mn(3CH3O-salen)(O2CMe)(H2O)]? 2H2O 1 Previously we had proposed that complexes prepared by this method containing the 3CH3O-salen ligand and aliphatic carboxylate anions were isostructural.14 This was based on a comparison of a variety of behaviour, in particular the almost identical fragmentation patterns observed by FAB mass spectroscopy; such a phenomenon has not been observed by us in any other series of these compounds.The crystallographic characterisation of the monomeric species, 1, indicates that although the co-ordination mode of the carboxylate remains as the unusual unidentate mode when this ligand is used, a slight variation in structure is possible, Fig. 1. The structure is found to consist of a monomeric manganese(III) centre which is ligated in the xy plane by the tetradentate SchiV base ligand.The axial co-ordination sites of manganese are filled by a water molecule and a unidentate acetate ligand. This mode of co- N OH HO N R1 R2 R1 R2 (CH2) n H23CH3O-salen: n = 2, R1 = CH3O, R2 = H H23CH3O-salpn: n = 3, R1 = CH3O, R2 = H H25NO2-salpn: n = 3, R1 = H, R2 = NO2 H23Br,5NO2-salpn: n = 3, R1 = Br, R2 = NO2 ordination of the carboxylate anion was also observed in both of our previous examples of these materials, [{Mn(3CH3Osalen)( O2CEtn)}2] and [{Mn(3CH3O-salen)(O2CBun)}2],14 and this perhaps accounts for the unusual similarity in the fragmentation pattern observed in the FAB mass spectra of these complexes.Unlike the previous two structurally characterised complexes, in which the co-ordination sphere was completed by weak m-phenoxy interactions [cf. Mn–O(1*) = 2.559 and 2.771 Å in the propionate and valerate, respectively], the manganese co-ordination sphere in 1 is completed by a water molecule [Mn–O(1w) 2.334(4) Å].In all other respects the structures are identical and it is perhaps not surprising that we were previously unable to distinguish between these structural motifs. Such subtle diVerences in solid state structure are also observed in [Mn(salpn)Cl] (see below) and it seems possible that the monomeric versus dimeric structure is aVected by the solvent used for crystallisation. It is important to stress though that, with the exception of iPr and tBu (see below), the carboxylate is always co-ordinated in the unidentate mode when a methoxy group is ortho to the phenolic oxygen donor.All other bond lengths and angles are typical of such complexes. Crystal structures of [Mn(3CH3O-salpn)(O2CBut)] 2 and [Mn(3CH3O-salpn)(O2CPri)] 3 Both complexes 2 and 3 were found to exist as monomeric species in which the SchiV base ligand aVords cis sites at the manganese(III) centre for bidentate chelation of the carboxylate ligands.They consist (Fig. 2) of extremely distorted octahedral centres, typical in such complexes.13,14 The asymmetric nature of the Mn–Nimine and Mn–Ocarboxylate bond lengths is particularly striking, Mn–N(1) 2.150(5) and 2.150(13), Mn–N(2) 1.986(5) and 1.939(15), Mn–O(5) 2.329(5) and 2.372(12) Å; Mn–O(6) 2.071(4) and 2.026(13) Å for 2 and 3, respectively. The distortion in the octahedral centres is further exemplified by the following angles for 2 and 3, respectively: O(2)–Mn(1)–O(6) 155.5(2) and 154.8(5), O(2)–Mn(1)–N(1) 110.1(2) and 113.3(5), O(6)–Mn(1)–O(5) 58.7(2) and 58.5(5) and N(1)–Mn(1)–O(5) 153.1(2) and 150.1(5)8.Such co-ordination is very rare in these compounds with only one example of such a monomeric SchiV base complex in the Cambridge Crystallographic Database,13 whilst two further examples have also recently been reported by us.14 The presence of cis sites at the metal centre for chelation of the carboxylate results from the flexibility in the trimethylene backbone between the imine nitrogens of the SchiV base ligand; however, such ’flexing’ of the ligand backbone is not guaranteed.It is apparent that when sterically demanding carboxylates are employed, such as trimethylacetate and isobutyrate, monomers such as 2 and 3 will prevail, as only monomeric species have been observed with these carboxylates. It therefore seems reasonable to propose that with these sterically demanding carboxylates and a tetradentate N2O2 donor set SchiV base ligand with a trimethylene backbone a monomeric complex will result.Nevertheless, steric congestion cannot be the sole reason for the ligand to adopt the strained cis conformation, as we have also observed monomers with valerate (O2CBun) 13 and propionate (O2CEt)14 anions; the former is the exclusive product whilst a polymeric species, with trans sites ligated by an anti-anti bridging carboxylates, is also observed for the latter.Crystal structures of [Mn(3CH3O-salen)(O2CCH2Ph)(H2O)]? H2O 4 and [Mn(3CH3O-salpn)(O2CCH2Ph)(H2O)] 5 The structural characterisation of complex 4, Fig. 3(a), serves to substantiate further our proviso that only unidentate coordination of a carboxylate ligand should be observed with the 3CH3O-salen ligand. As in 1 the co-ordination sphere of the octahedral manganese centre consists of the tetradentate SchiV base ligand in the xy plane, with the axial sites filled with the unidentate carboxylate O(5) and a water molecule O(1w).AJ. Chem. Soc., Dalton Trans., 1999, 31–41 33 Table 1 Analytical and some selected data for the manganese(III) carboxylate complexes containing 3CH3O-salen and 3CH3O-salpn as ligands Analysis (%) a IR/cm21 Complex [Mn(3CH3O-salen)(O2CPh)]?H2O [Mn(3CH3O-salen)(O2CCH2Ph)]?2H2O [Mn(3CH3O-salpn)(O2CMe)] [Mn(3CH3O-salpn)(O2CEt)] [Mn(3CH3O-salpn)(O2CPrn)] [Mn(3CH3O-salpn)(O2CBun)] [Mn(3CH3O-salpn)(O2CPri)] [Mn(3CH3O-salpn)(O2CBut)] [Mn(3CH3O-salpn)(O2CPh)] [Mn(3CH3O-salpn)(O2CCH2Ph)] C 57.1 (57.7) 56.9 (56.5) 55.2 (55.5) 56.1 (56.4) 56.9 (57.3) 57.7 (58.1) 57.4 (57.3) 58.3 (58.1) 60.5 (60.5) 60.5 (61.1) H 4.2 (4.8) 5.0 (5.3) 4.8 (5.1) 5.2 (5.4) 5.1 (5.6) 6.0 (5.9) 5.6 (5.6) 6.3 (5.9) 4.8 (4.9) 4.8 (5.1) N 5.3 (5.4) 5.1 (5.1) 6.1 (6.2) 6.1 (6.0) 5.8 (5.8) 5.5 (5.6) 5.7 (5.8) 5.4 (5.6) 5.3 (5.4) 5.1 (5.3) Mn 11.8 (12.1) 11.6 (11.7) 10.9 (11.4) 11.6 (11.1) n(C]] N) 1625 1624 1616 1616 1616 1616 1617 1614 1613 1616 meff /mB 4.8 4.8 4.8 4.6 4.4 4.7 4.8 4.6 4.9 4.9 FABb m/z 381 381 395 395 395 395 395 395 395 395 Yield c (%) 95 82 86 86 71 68 76 94 78 78 a Found (calculated).b Peaks corresponding to [ML]1. c Based on manganese. further water molecule of crystallisation O(2w) is hydrogen bonded to O(6). The structural characterisation of 5, Fig. 3(b), as a related monomer was somewhat surprising. We have only structurally characterised one material containing this carboxylate, which was polymeric,14 where the carboxylate bridged planar manganese SchiV base centres are in the syn-anti mode.The reasons for this bridging mode lay in the steric demands associated with the carboxylate, and we therefore expected 5 to be either a monomeric complex as observed for 2 and 3, typical of sterically demanding carboxylates, or a polymeric complex as we have previously reported.14 The isolation of a monomeric species in which the carboxylate is unidentate appears to indicate that the governing factor when the carboxylate is of an intermediate steric nature is the ortho-methoxy group, and that provided tBu and iPr groups are avoided on the carboxylate the unidentate mode of binding will always prevail.Comparison of the bond lengths about the metal centres in complexes 1, 4 and 5 reveals some interesting structural diVerences between the three monomers. In all three structures the Mn–Ocarboxylate bond lengths are identical (within their e.s.d.s): Mn–O(5) 2.130(3), 1; Mn(1)–O(5) 2.135(10), 4; and Mn(1)– O(5) 2.139(7) Å, 5.Perhaps more interesting are the diVerences in bond lengths between the manganese ions and the donor atoms of the SchiV base ligands. For 1 and 4 these bond lengths are virtually identical when viewed within the extent of the data limits, with the exception of Mn–N(2) which shows a slight lengthening in 1. For 5 it is immediately obvious that all these bond lengths are longer than those observed for 1 and 4: Fig. 1 Molecular structure of [Mn(3CH3O-salen)(O2CMe)(H2O)]? 2H2O 1. Selected bond lengths (Å) and angles (8) with estimated standard deviations (e.s.d.s) in parentheses: Mn–O(1) 1.891(3), Mn–O(2) 1.885(3), Mn–N(1) 1.988(4), Mn–N(2) 1.986(4), Mn–O(5) 2.130(3) and Mn–O(1w) 2.334(4); O(1)–Mn–O(2) 95.36(13), O(1)–Mn–N(1) 91.0(2), O(1)–Mn–N(2) 171.6(2), O(1)–Mn–O(5) 96.96(14), O(1)–Mn–O(1w) 89.0(2), O(2)–Mn–N(1) 172.9(2), O(2)–Mn–N(2) 91.2(2), O(2)–Mn– O(5) 93.69(13), O(2)–Mn–O(1w) 90.6(2), O(5)–Mn–O(1w) 172.28(14), N(1)–Mn–N(2) 82.2(2), N(1)–Mn–O(5) 88.7(2), N(1)–Mn–O(1w) 86.3(2), N(2)–Mn–O(5) 87.8(2) and N(2)–Mn–O(1w) 85.7(2).Mn(1)–O(1) 1.912(6), Mn(1)–N(1) 2.026(8), Mn(1)–N(2) 2.050(9) Å for 5, cf. Mn–O(1) 1.891(3), Mn–N(1) 1.988(4), Mn– N(2) 1.986(4) for 1 and Mn–O(1) 1.880(9), Mn–N(1) 1.995(11) and Mn–N(2) 1.971(11) Å for 4. The lengthening observed in the Mn–Ophenolic bond lengths in 5 is not nearly as pronounced as the diVerences in the Mn–Nimine bond length, that of Mn(1)– N(2) being particularly marked.These diVerences must be accounted for by the change of ligand backbone bridges in 1 and 4. Preparation of monomeric manganese SchiV base complexes with chelating carboxylate ligands The reaction of Me3SiCl with [Mn(salpn)(acac)]. Our initial reasons for investigating the reactivity of [Mn(salpn)(acac)] with Me3SiCl were twofold. First, we wished to discover whether it was a straightforward procedure to replace the acetylacetonate ligand, and, secondly, to see whether such a reaction could lead to the formation of cluster compounds. This reagent has previously been employed as an abstractor of carboxylate ligands co-ordinated to metal centres 16 and has subsequently been employed in this manner to prepare manganese clusters.17 The reaction of [Mn(salpn)(acac)] with Me3SiCl in dry degassed acetonitrile resulted in the formation of a compound of stoichiometry Mn(salpn)Cl in 61% yield (see Table 2).The positive ion FAB mass spectrum of the complex shows a parent ion peak at m/z 335 which corresponds to a cation of the form [Mn(salpn)]1. No fragments involving chloride co-ordination were observed, indicating that if chloride is ligated to the metal centre in the solid state that this ligation is weak. The absence of bands in the infrared spectrum at 1635 and 1600 cm21, which we attribute to the acetylacetonate group of the starting material, together with a shift in the imine band from 1615 to 1623 cm21, indicate that complete displacement of acetylacetonate has occurred, apparently via a simple counter ion exchange.In the light of these data, and the only slightly lowered room temperature magnetic moment of 4.5 mB, relative to that expected for magnetically dilute d4 manganese(III), it is reasonable to propose the formation of a five-co-ordinate monomeric species as has previously been observed in related compounds.18 Crystals suitable for single crystal X-ray diVraction studies were mounted in an atmosphere of the mother-liquor (since decomposition occurs in the absence of solvent vapour).These were found to consist of the weakly m-phenoxy bridged dimeric species [{Mn(salpn)Cl}2]?CH3CN 6, shown in Fig. 4. The structure is essentially analogous to that found for the related [Mn(salen)Cl] 18b and other species 18a,c–e however due to the much shorter m-phenoxy bonds Mn(1)–O(1*) 2.487(4) Å (cf. 2.897 Å in a related monomer18c) and the roughly octahedral manganese(III) geometry, we thus prefer to present this structure as a dimer rather than a monomer. Indeed such a structure has been postulated by Pecoraro and co-workers,1934 J. Chem. Soc., Dalton Trans., 1999, 31–41 who suggested that the absence of solvent molecules capable of co-ordinating to the manganese(III) centre would lead to the formation of 6, rather than the monomeric octahedral species that have been reported.The remaining bond lengths and angles are unexceptional for such compounds. The characterisation of complex 6 clearly demonstrates that it is a simple procedure to replace the acetylacetonate ligand. Fig. 2 (a) Molecular structure of [Mn(3CH3O-salpn)(O2CBut)] 2. Selected bond lengths (Å) and angles (8) with e.s.d.s in parentheses: Mn(1)–O(1) 1.868(4), Mn(1)–O(2) 1.918(4), Mn(1)–N(1) 2.150(5), Mn(1)–N(2) 1.986(5), Mn(1)–O(5) 2.329(5) and Mn(1)–O(6) 2.071(4); O(1)–Mn(1)–O(2) 91.0(2), O(1)–Mn(1)–N(1) 87.9(2), O(1)–Mn(1)– N(2) 177.3(2), O(1)–Mn(1)–O(5) 94.0(2), O(1)–Mn(1)–O(6) 91.2(2), O(2)–Mn(1)–N(1) 110.1(2), O(2)–Mn(1)–N(2) 88.9(2), O(2)–Mn(1)– O(5) 96.8(2), O(2)–Mn(1)–O(6) 155.5(2), O(5)–Mn–O(6) 58.7(2), N(1)– Mn(1)–N(2) 89.6(2), N(1)–Mn(1)–O(5) 153.1(2), N(1)–Mn(1)–O(6) 94.4(2), N(2)–Mn(1)–O(5) 88.7(2) and N(2)–Mn–O(6) 90.0(2).(b) Molecular structure of [Mn(3CH3O-salpn)(O2CPri)], 3. Selected bond lengths (Å) and angles (8) with e.s.d.s in parentheses: Mn(1)–O(1) 1.867(12), Mn(1)–O(2) 1.875(11), Mn(1)–N(1) 2.150(13), Mn(1)–N(2) 1.939(15), Mn(1)–O(5) 2.372(12) and Mn(1)–O(6) 2.026(13); O(1)– Mn(1)–O(2) 90.0(5), O(1)–Mn(1)–N(1) 89.3(6), O(1)–Mn(1)–N(2) 179.0(6), O(1)–Mn(1)–O(5) 93.8(5), O(1)–Mn(1)–O(6) 92.5(5), O(2)– Mn(1)–N(1) 113.3(5), O(2)–Mn(1)–N(2) 89.0(6), O(2)–Mn(1)–O(5) 96.4(5), O(2)–Mn(1)–O(6) 154.8(5), O(5)–Mn–O(6) 58.5(5), N(1)– Mn(1)–N(2) 89.7(6), N(1)–Mn(1)–O(5) 150.1(5), N(1)–Mn(1)–O(6) 91.7(5), N(2)–Mn(1)–O(5) 87.3(5) and N(2)–Mn–O(6) 88.2(6).Of interest is the change of geometry at the metal centre in that the cis-chelated sites of the “pretemplated” complex do not remain. In 6 trans sites are open at the metal centre due to the Fig. 3 (a) Molecular structure of [Mn(3CH3O-salen)(O2CCH2Ph)- (H2O)]?H2O 4. Selected bond lengths (Å) and angles (8) with e.s.d.s in parentheses: Mn–O(1) 1.880(9), Mn–O(2) 1.887(9), Mn–N(1) 1.995(11), Mn–N(2) 1.971(11), Mn–O(5) 2.135(10) and Mn–O(1w) 2.353(9); O(1)–Mn–O(2) 93.5(4), O(1)–Mn–N(1) 172.5(5), O(1)–Mn–N(2) 92.0(4), O(1)–Mn–O(5) 98.7(4), O(1)–Mn–O(1w) 91.8(4), O(2)–Mn– N(1) 91.7(4), O(2)–Mn–N(2) 172.7(5), O(2)–Mn–O(5) 94.5(4), O(2)– Mn–O(1w) 87.9(4), O(5)–Mn–O(1w) 169.1(3), N(1)–Mn–N(2) 82.4(5), N(1)–Mn–O(5) 86.2(4), N(1)–Mn–O(1w) 83.0(4), N(2)–Mn–O(5) 89.5(4) and N(2)–Mn–O(1w) 87.1(4).(b) Molecular structure of [Mn(3CH3O-salpn)(O2CCH2Ph)(H2O)] 5. Selected bond lengths (Å) and angles (8) with e.s.d.s in parentheses: Mn(1)–O(1) 1.912(6), Mn(1)– O(2) 1.914(6), Mn(1)–N(1) 2.026(8), Mn(1)–N(2) 2.050(9), Mn(1)–O(5) 2.139(7) and Mn(1)–O(6) 2.316(6); O(1)–Mn(1)–O(2) 87.0(3), O(1)– Mn(1)–N(1) 89.7(3), O(1)–Mn(1)–N(2) 175.2(3), O(1)–Mn(1)–O(5) 94.3(3), O(1)–Mn(1)–O(6) 87.5(2), O(2)–Mn(1)–N(1) 173.9(3), O(2)– Mn(1)–N(2) 89.8(3), O(2)–Mn(1)–O(5) 100.4(3), O(2)–Mn(1)–O(6) 89.9(3), O(5)–Mn–O(6) 169.6(3), N(1)–Mn(1)–N(2) 93.1(3), N(1)– Mn(1)–O(5) 85.0(3), N(1)–Mn(1)–O(6) 84.7(3), N(2)–Mn(1)–O(5) 89.8(3) and N(2)–Mn–O(6) 88.9(3).J.Chem. Soc., Dalton Trans., 1999, 31–41 35 Table 2 Analytical and some selected data for the manganese complexes containing salpn, 5NO2-salpn and 3Br,5NO2-salpn as ligands Analysis (%) a IR/cm21 Complex [Mn(salpn)Cl] [Mn(salpn)(O2CMe)]?H2O [Mn(salpn)(O2CEt)] [Mn(salpn)(O2CPrn)] [Mn(salpn)(O2CBun)] [Mn(salpn)(O2CPri)] [Mn(salpn)(O2CBut)] Mn(5NO2-salpn)(H2O) Mn(3Br,5NO2-salpn) [Mn(5NO2-salpn)(O2CMe)]?H2O [Mn(5NO2-salpn)(O2CEt)] [Mn(5NO2-salpn)(O2CPrn)]?2H2O [Mn(5NO2-salpn)(O2CPri)] [Mn(5NO2-salpn)(O2CBut)] [Mn(3Br,5NO2-salpn)(O2CMe)]?2H2O [Mn(3Br,5NO2-salpn)(O2CEt)] [Mn(3Br,5NO2-salpn)(O2CPrn)]?H2O C 55.0 (55.1) 55.2 (55.3) 58.5 (58.8) 60.0 (59.7) 60.3 (60.6) 59.2 (59.7) 60.2 (60.6) 45.9 (46.0) 37.0 (36.8) 45.4 (45.4) 47.6 (48.2) 45.8 (46.0) 48.5 (49.2) 49.1 (50.2) 33.6 (33.6) 36.1 (36.6) 36.2 (36.6) H 4.5 (4.3) 5.0 (5.1) 5.2 (5.2) 5.4 (5.5) 5.8 (5.7) 5.5 (5.5) 5.5 (5.7) 3.6 (3.6) 2.6 (2.5) 3.8 (3.8) 3.8 (3.8) 3.9 (4.6) 3.9 (4.1) 4.2 (4.4) 2.6 (2.8) 2.6 (2.6) 2.6 (3.0) N 7.2 (7.6) 6.6 (6.8) 6.7 (6.9) 6.5 (6.6) 6.4 (6.4) 6.2 (6.6) 6.2 (6.4) 12.2 (12.6) 10.8 (10.1) 11.4 (11.2) 11.0 (11.2) 10.4 (10.2) 11.3 (10.9) 10.5 (10.6) 8.3 (8.3) 8.5 (8.5) 8.7 (8.1) Mn 14.3 (14.8) 13.8 (13.4) 13.0 (13.5) 13.1 (13.0) 12.9 (12.6) 13.1 (13.0) 12.8 (12.6) n(C]] N) 1623 1615 1614 1614 1616 1616 1614 1622 1598 1622 1622 1620 1623 1622 1620 1622 1626 meff/mB 4.5 4.8 4.8 4.8 4.5 4.5 4.7 4.8 4.7 4.9 4.9 5.0 5.0 4.7 4.8 FABb m/z 335 335 335 335 335 335 335 425 425 425 425 425 583 583 581 Yield c (%) 61 57 58 79 57 66 72 46 40 59 54 47 62 58 54 57 54 a Found (calculated). b Peaks corresponding to [ML]1.c Based on manganese. SchiV base ligand adopting an equatorial position. Larson and Pecoraro15 have previously employed [Mn(salpn)(acac)] in the preparation of the dinuclear manganese(IV) species [{Mn- (salpn)O}2] through peroxide oxidation of the manganese(III) species [Mn(salpn)(acac)] in acetonitrile.In this instance the cis sites at the manganese centre, occupied by the acetylacetonate ligand, were replaced directly by the bridging m-oxo groups in the manganese(IV) complex; this was attributed directly to the pretemplated nature of the manganese(III) species. Refined mechanistic interpretations of this reaction were made which invoked the initial process to be deprotonation of hydrogen peroxide by the acetylacetonate ligand and showed that both the bridging m-oxo groups originated from the same molecule of hydrogen peroxide.From these results it was therefore apparent that if we used the co-ordinated acetylacetonate as a base, and avoided high thermodynamic driving forces (e.g. the formation of Si–O bonds), we would be able directly to replace the acetylacetonate with carboxylate groups through the reaction of carboxylic acids with [Mn(salpn)(acac)] and produce manganese(III) complexes. The reaction of carboxylic acids with [Mn(salpn)(acac)].A series of straight- and branched-chain aliphatic carboxylic acids, RCO2H (R = Me, Et, Prn, Bun, Pri or But), were treated Fig. 4 Molecular structure of [{Mn(salpn)Cl}2]?CH3CN 6. Lattice acetonitrile is not depicted. Selected bond lengths (Å) and angles (8) with e.s.d.s: Mn(1)–Cl(1) 2.4521(18), Mn(1)–O(1) 1.919(4), Mn(1)– O(2) 1.868(4), Mn(1)–N(1) 2.026(5), Mn(1)–N(2) 2.039(5) and Mn(1)– O(1*) 2.487(4); O(1)–Mn(1)–Cl(1) 99.45(13), O(2)–Mn(1)–Cl(1) 96.78(14), N(1)–Mn(1)–Cl(1) 90.62(14), N(2)–Mn(1)–Cl(1) 91.92(15), O(1)–Mn(1)–O(2) 86.51(17), O(1)–Mn(1)–N(1) 87.16(18), O(1)– Mn(1)–N(2) 168.47(18), O(2)–Mn(1)–N(1) 170.96(19), O(2)–Mn(1)– N(2) 90.36(19) and N(1)–Mn(1)–N(2) 94.6(2).with [Mn(salpn)(acac)] in ethanol aVording a succession of compounds of stoichiometry [Mn(salpn)(O2CR)], see Table 2. All compounds exhibit magnetic properties typical of manganese( III) SchiV base compounds of this type 11,13,14 with most magnetic moments being close to the spin only value of 4.9 mB expected for magnetically dilute high spin d4 systems, indicating little or no antiferromagnetic interactions in the solid state.The positive ion FAB mass spectra of the compounds all show parent ion peaks relating to the fragment [Mn(salpn)]1 at m/z 335 and no other fragments relating to carboxylate (or acetylacetonate) co-ordination to a monomeric manganese species. This behaviour is consistent with the other monomeric manganese( III) SchiV base complexes reported herein and those that we have previously reported with bidentate and chelating carboxylates. 13,14 All compounds show a strong band between 1614 and 1616 cm21 in their infrared spectra attributable to n(C]] N). These values are comparable with those of the starting material; however, the complete absence of strong bands at 1635 and 1600 cm21 of the acetylacetonate species indicate that this anion has been replaced by a carboxylate anion.This is substantiated by the presence of bands between 1543 and 1548, 1466 and 1470 and 616 and 622 cm21 which can be assigned to nasym(OCO), nsym(OCO) and d(OCO), respectively. The diVerence between the asymmetric and symmetric stretching modes of the carboxylate of ca. 80 cm21 can be tentatively assigned to the presence of bidentate and chelating carboxylate groups.13,14 Electrochemistry of the complexes. The electrochemical behaviour of the complexes was investigated in dichloromethane solution using tetrabutylammonium hexafluorophosphate as a supporting electrolyte.All compounds formulated as [Mn(salpn)(O2CR)] show essentially identical behaviour which is typified by the voltammogram of [Mn(salpn)(O2CBun)], in Fig. 5(a). There are two diVerent redox processes occurring. The first process (O1/R1) corresponds to the quasi-reversible manganese(II/III) couple, E1/2 = 20.25 to 20.30 V (see Table 3 for electrochemical data) whilst the second redox process (O2/ R2) is assigned to the sequential oxidation of the species to the manganese(IV) state (Epa = 0.97 to 1.00 V).This second process does not show reversible electrochemistry. However, the reductive waves between 0.18 and 0.25 V can be associated with this oxidative process, as the reductive wave is absent when the electrode is rotated and also through alteration of the voltage window, since when a window up to 0.9 V is employed the reductive wave is not observed.It is interesting that cyclic voltammetry serves as a very sensitive test of the purity of these compounds. Despite the apparent purity of the compounds36 J. Chem. Soc., Dalton Trans., 1999, 31–41 Fig. 5 Cyclic voltammograms of (a) [Mn(salpn)(O2CBun)], (b) [Mn(salpn)(O2CBut)], (c) [Mn(salpn)(O2CMe)]2n(H2O)3n and (d) [{Mn(salpn)Cl}2] in dichloromethane. Calomel electrode all potentials are versus the saturated calomel electrode. Table 3 Electrochemical data for the complexes versus saturated calomel electrode Assigned couple (V) Compound [{Mn(salpn)Cl}2] [Mn(salpn)(O2CMe)]?H2O [Mn(salpn)(O2CEt)] [Mn(salpn)(O2CPrn)] [Mn(salpn)(O2CBun)] [Mn(salpn)(O2CPri)] [Mn(salpn)(O2CBut)] [{[Mn(salpn)(O2CMe)]2(H2O)3}n] MnII/III 0.0 20.19 20.19 20.17 20.19 20.18 20.21 20.18 MnIII/II 20.31 20.35 20.35 20.34 20.32 20.42 20.40 20.34 E1/2 20.16 20.27 20.27 20.25 20.26 20.30 20.30 20.26 MnIII/IV 1.21 0.98 0.98 1.00 0.97 1.00 0.97 1.00 MnIV/III 1.18 0.22 0.22 0.22 0.25 0.17 0.18 — E1/2 1.20 ——————— (viz.as judged by elemental analyses and infrared spectroscopy, see Table 2) cyclic voltammetry is able to detect the presence of starting material as this species shows a quasi-reversible couple at Epa 0.53 V and Epc 0.45 V. A typical example is given in Fig. 5(b) in which the starting material impurity (labelled SM) is clearly present, in spite of the apparent “purity” of the complex. In these cases further reaction with the appropriate acid until this wave is no longer observed indicates complete displacement of acetylacetonate has occurred.These voltammetric studies appear to suggest that similar solution species are present. However, as yet we are unable to predict the form these species take in solution, i.e. whether they exist as the desired monomers with cis chelated carboxylates or as ionised species of the form Mn(salpn)1. We have four reasons to suppose that the solution species are the desired cis chelated monomers.First, the subtle changes in the E1/2 values of the manganese(II/III) couples indicate that changing the carboxylate auxiliary ligand aVects, albeit slightly, the potential at which this process occurs. If the solution species was the cationic Mn(salpn)1 these values would be expected to be identical. Secondly, the cyclic voltammogram of the polymeric species [Mn(salpn)(O2CMe)]2n(H2O)3n whose structure we have previously reported,11 in which the manganese centre contains trans co-ordinated carboxylates, shows subtle diVerences electrochemically, Fig. 5(c). As for the species previously described a quasi-reversible manganese(II/III) couple is observed {Epa 20.18 V, Epc 20.34 V, E1/2 20.26 V, cf. 20.27 V for [Mn(salpn)- (O2CMe)]}. However, unlike the previous complexes no reversible process relating to the oxidative wave at Epa 1.0 V is observed. Thirdly, when the cyclic voltammogram of 6 was recorded diVerent behaviour was again observed, Fig. 5(d). Two quasi-reversible processes are observed which we assign to the manganese-(II/III) and -(III/IV) couples with E1/2 values of 20.16 and 1.20 V, respectively. Li and Pecoraro18c have previously reported that the only solution species observed for the structurally related [Mn(salen)Cl] 18b was the Mn(salen)1 cation. It seems reasonable to propose that in solution 6 will behave in a similar manner and that the diVerences between the voltammogram of 6 and those of the carboxylate complexes prepared are as a result of such ionisation.Finally dichloromethane solutions of the complexes formulated as [Mn(salpn)(O2CR)] show no conductivity. X-Ray studies. X-Ray powder diVraction studies of [Mn- (salpn)(O2CBun)] and [Mn(salpn)(O2CBut)] indicate that these species are monomeric with cis-chelated carboxylates in the solid state. This is based on the identical nature of the powder diVraction patterns with those of the crystallographically characterised monomers derived from our conventional reaction of the appropriate manganese(II) carboxylate salt with the SchiV base ligand.13,14 These powder diVraction patterns are shown in Fig. 6. Crystals suitable for single crystal X-ray dif-J. Chem. Soc., Dalton Trans., 1999, 31–41 37 fraction studies of [Mn(salpn)(O2CPri)] 7 were found to consist, as expected, of a monomeric manganese(III) SchiV base complex with a cis-chelated carboxylate ligand, Fig. 7. The distorted N2O4 octahedral co-ordination sphere of the manganese centre is essentially identical to those that we have previously characterised in other related monomers.13,14 The distortion of the manganese centre is as a result of the chelation of the carboxylate. These structures are all typified by asymmetric coordination of the carboxylate [in this case Mn(1)–O(3) 2.304(4) Fig. 6 Powder X-ray diVraction patterns of (a) [Mn(salpn)(O2CBun)] and (b) [Mn(salpn)(O2CBut)] prepared in this study compared with those of their crystallographically characterised monomers.13,14 Fig. 7 Molecular structure of [Mn(salpn)(O2CPri)] 7. Selected bond lengths (Å) and angles (8) with e.s.d.s: Mn(1)–O(1) 1.899(3), Mn(1)– O(2) 1.872(3), Mn(1)–O(3) 2.304(4), Mn(1)–O(4) 2.099(4), Mn(1)–N(1) 1.990(4) and Mn(1)–N(2) 2.128(4), O(1)–Mn(1)–O(2) 89.73(15), O(1)– Mn(1)–N(1) 89.59(15), O(2)–Mn(1)–N(1) 176.21(15), O(1)–Mn(1)– N(2) 112.59(15), O(2)–Mn(1)–N(2) 87.51(15), N(1)–Mn(1)–N(2) 89.31(16), O(3)–Mn(1)–N(2) 153.48(14), O(4)–Mn(1)–N(2) 94.28(14), O(1)–Mn(1)–O(3) 93.90(15), O(1)–Mn(1)–O(4) 153.03(15) and O(4)– Mn(1)–O(3) 59.21(13).and Mn(1)–O(4) 2.099(4) Å]. It is such co-ordination that we have attributed to the absence of fragments relating to the monomeric manganese species [Mn(salpn)(O2CR)]1 in the FAB mass spectra of the complexes. All other bond lengths and angles are unexceptional. Preparation of manganese(III) complexes of SchiV base ligands containing electron-withdrawing substituents with ancillary carboxylate donors In view of the apparent success of the reaction of carboxylic acids with [Mn(salpn)(acac)] for the preparation of complexes of the form [Mn(salpn)(O2CR)], we wondered whether this synthetic method might access a route to manganese(III) complexes of this stoichiometry with electron withdrawing substituents about the aromatic rings of the SchiV base ligands, e.g. 5NO2- salpn and 3Br,5NO2-salpn. Our desires for such a route were based on our experiences with the related salen ligands with these substituents 20,21 and the inconsistent nature of the products obtained under our standard aerobic reaction conditions. 11,13,14 We found that aerial oxidation under Boucher conditions 22 does not yield any manganese(III) complex with 3Br, 5NO2 substituents and that for 5NO2 substituents, although some manganese(III) species could be detected by cyclic voltammetry, the main product of the reaction was a manganese(II) species.Manganese(III) species could be isolated, however, by the chemical oxidation of the manganese(II) species using ferrocenium tetrachloroferrate(III).20 Furthermore, we have even found that it is possible to isolate manganese(II) species from the reduction of manganese(III) acetate in the presence of 3Br,5NO2-salen.21 Our attempts to isolate manganese( III) complexes with ancillary carboxylate ligands, as indicated, have been largely unsuccessful, manganese(II) complexes of stoichiometry Mn(L)?nH2O being isolated routinely.However, on one occasion, in the reaction of 5NO2-salpn with manganese(II) acetate tetrahydrate, we have been able to isolate a manganese(III) species from the reaction liquor after removal of the precipitated manganese(II) complex and slow evaporation yielding [Mn(5NO2-salpn)(O2CMe)(H2O)]. This is consistent with the isolation of [Mn(5NO2-salen)(O2CMe)(H2O)] 8, Fig. 8, using 5NO2-salen. The structure consists of an octahedrally co-ordinated manganese(III) centre, analogous with 1, 4 and 5, in which the xy plane of the manganese ion is coordinated by the SchiV base ligand and axial sites are filled by water and the acetate ligated in the unidentate mode.The Mn–Ophenolic bond lengths are identical with those observed in 1 and 4 indicating that the ortho-methoxy group and para-nitro group do not aVect this bond length in any way. The Mn–Nimine bonds are shorter than all of the other bonds in 4 and 5.The Mn–Ocarboxylate distance is the shortest of any of these Fig. 8 Molecular structure of [Mn(5NO2-salen)(O2CMe)(H2O)] 8. Selected bond lengths (Å) and angles (8) with e.s.d.s: Mn(1)–O(1) 1.882(4), Mn(1)–O(2) 1.890(4), Mn(1)–N(1) 1.977(4), Mn(1)–N(2) 1.970(4), Mn(1)–O(7) 2.347(5) and Mn(1)–O(8) 2.123(4); O(1)–Mn(1)– O(2) 91.67(14), O(1)–Mn(1)–N(2) 172.31(17), O(2)–Mn(1)–N(2) 92.81(16), O(1)–Mn(1)–N(1) 91.25(15), O(2)–Mn(1)–N(1) 173.09(17), N(2)–Mn(1)–N(1) 83.63(16), O(1)–Mn(1)–O(8) 92.86(15), O(2)– Mn(1)–O(8) 95.39(16), N(2)–Mn(1)–O(8) 92.93(17), N(1)–Mn(1)–O(8) 90.71(18), O(1)–Mn(1)–O(7) 92.17(17), O(2)–Mn(1)–O(7) 89.94(17), N(2)–Mn(1)–O(7) 81.68(18), N(1)–Mn(1)–O(7) 84.69(19), O(8)– Mn(1)–O(7) 173.26(16).38 J.Chem. Soc., Dalton Trans., 1999, 31–41 monomers, Mn–O(8) 2.123(4) Å, whilst the manganese–water distance is intermediate between 1 and 4 at 2.347(5) Å. In view of the success in the displacement of acetylacetonate with a carboxylate in [Mn(salpn)(acac)] we attempted to apply the same reaction to [Mn(5NO2-salpn)(acac)] and [Mn- (3Br,5NO2-salpn)(acac)] prepared by the same method as [Mn(salpn)(acac)] (see Experimental section).15 It appears that this does provide a satisfactory route to compounds of stoichiometry MnL(O2CR), but in much lower yields than the unsubstituted analogue, due to the precipitation of yellow materials of composition MnL(H2O)n, n = 0,2, in up to 50% yield.We have only been able to isolate crystals from one of these complexes, Mn(3Br,5NO2-salpn)(O2CMe)?2H2O. These were not the expected complex, but rather a di-m-oxo manganese(IV) species, [{Mn(m-3Br,5NO2-salpn)(m-O)}2]?5DMF, 9, Fig. 9, which is structurally analogous with a related dimer that we have previously reported.20 In the previous case the remarkable feature of the structure lay in the non-planar nature of the salen ligand. Although this twist is still inherent in 9 it is perhaps less surprising since there is much greater conformational freedom between the imino nitrogen atoms N1 and N2 in this ligand than in a salen-based ligand.The most surprising feature of the compound is the apparent attainment of the 14 oxidation state with this ligand. This assignment is based on the similarity between the bond lengths and angles in the central Mn–O2–Mn of 9 and other well characterised di-m-oxo-bridged manganese( IV) species.20 The Mn–O(3) bridging bonds of 1.797(4) Å and 1.809(5) Å, the Mn–O(3)–Mn9 angle of 98.7(2)8 and the Mn? ? ? Mn separation of 2.736(2) Å are all typical of such systems.Fig. 9 Molecular structure of [{Mn(m-3Br,5NO2-salpn)(m–O)}2]? 5DMF 9. Selected bond lengths (Å) and angles (8) with e.s.d.s: Mn(1)– Mn(1*) 2.736(2), Mn(1)–O(1) 1.933(5), Mn(1)–O(1*) 1.952(5), Mn(1)– O(3) 1.809(5), Mn(1)–O(3*) 1.797(4), Mn(1)–N(1) 1.997(6) and Mn(1)– N(1*) 1.993(6); O(1)–Mn(1)–O(1*) 93.1(2), O(1)–Mn(1)–O(3) 173.6(2), O(1)–Mn(1)–O(3*) 92.5(2), O(1)–Mn(1)–N(1) 88.4(2), O(1)– Mn(1)–N(1*) 87.5(2), O(1*)–Mn(1)–O(3) 93.2(2), O(1*)–Mn(1)–O(3*) 174.5(2), O(1*)–Mn(1)–N(1) 86.0(2), O(1*)–Mn(1)–N(1*) 87.1(2), O(3)–Mn(1)–O(3*) 81.3(2), O(3)–Mn(1)–N(1) 93.3(2), O(3)–Mn(1)– N(1*) 91.6(2), O(3*)–Mn(1)–N(1) 94.7(2), O(3*)–Mn(1)–N(1*) 92.7(2) and N(1)–Mn(1)–N(1*) 171.7(2). Conclusion The co-ordination chemistry of manganese(III) SchiV base complexes with ancillary carboxylate ligands is an area of tremendous variety.Although at times capricious, some obvious patterns are developing. When sterically restricting carboxylates 2O2CBut and 2O2CPri are employed with salpn based ligands monomers ensue, in which the carboxylate asymmetrically chelates cis sites at the metal centre as is observed in complexes 2, 3, 7 and previous studies.13,14 This behaviour appears to be independent of ligand substituents. When tetradentate SchiV base ligands with methoxy groups ortho to the phenolic donor atoms are used and sterically very demanding carboxylates are avoided the unique mode of co-ordination of the carboxylate is unidentate, 1, 4 and 5.Unlike our previous studies 14 in which the co-ordination spheres of the manganese centres were completed by weak m-phenoxy bridges to a second metal centre forming dimers, the complexes reported herein are all monomers in which water molecules complete the co-ordination sphere. The diVerences between these two structural motifs are relatively minor and of greatest significance is the unidentate binding mode of the carboxylate which appears to result exclusively for these systems.A similar binding mode is also observed in 8. It is apparent that we are able to prepare monomeric species of stoichiometry [Mn(salpn)(O2CR)] by the reaction of [Mn- (salpn)(acac)] with a variety of aliphatic carboxylic acids. This is substantiated by cyclic voltammetry and X-ray studies. X-Ray powder diVraction shows the products of these reactions with valeric and trimethylacetic acid to be the same as the monomers that we have crystallographically characterised from the reaction of the manganese(II) carboxylate salt and the SchiV base ligand.13,14 Single crystal studies of 7 further substantiate this view.This methodology is also a relatively satisfactory means of preparing complexes of manganese(III) with electron withdrawing substituents on the aromatic rings of the SchiV base ligands which normally prevent the aerial oxidation of manganese(II) salts.20 Although manganese(II) side products are also isolated a number of manganese(III) complexes have been isolated in fair yield.On one occasion we have been able to isolate from one of these products single crystals of a manganese(IV) di-m-oxo dimer in which the manganese centres are also bridged by two ligands, 9, a further remarkable example of oxidation of manganese to the 14 level with concomitant formation of di-m-oxo bridges upon recrystallisation from DMF.We believe these results develop the chemistry of these systems considerably. Clear and predictable patterns have developed, and we hope will continue to develop yet unpredictable and fascinating structures also persist within this niche. Experimental All experiments, except for the preparation of complex 6, were carried out in air. All reagents (Aldrich and Maybridge Chemicals) and solvents were used as received except acetonitrile (for the preparation of 6) and dichloromethane (for cyclic voltammetry) which were freshly distilled from CaH2 prior to use.Physical measurements Infrared spectra were recorded on a Bruker IFS66V spectrophotometer as KBr discs, FAB mass spectra on a Kratos MS-45 spectrometer with a FAB probe and a xenon reaction gas using a m-nitrobenzyl alcohol matrix. Room temperature magnetic moments were measured on a Faraday balance which was calibrated using HgCo(NCS)4.Elemental analyses were performed by the in-house services of the University of Santiago and UMIST. Cyclic voltammetry was performed with a Princeton Applied Research model 270 potentiostat and potential scan-J. Chem. Soc., Dalton Trans., 1999, 31–41 39 Table 4 Crystal data and details of refinement Formula M Crystal dimensions/mm Crystal system Space group a/Å b/Å c/Å b/8 V/Å3 Z Dc/g cm23 F(000) m/cm21 2qmax/8 Number of unique data Number of observed data a Number of variables Rb R9 c 1 C20H21MnN2O9 488.33 0.45 × 0.38 × 0.12 Monoclinic P21/c (no. 14) 12.053(2) 19.874(4) 9.312(2) 99.97(2) 2196.9 4 1.476 1008 6.55 50.10 2166 2166 382 0.0433 0.1186 2 C25H31Cl2MnN2O6 581.36 0.56 × 0.45 × 0.33 Monoclinic P21/n (no. 14) 13.034(3) 12.111(4) 18.446(5) 102.760(10) 2839.9 4 1.360 1208 6.93 45.00 3679 3679 325 0.0748 0.2098 3 C23H27MnN2O6 482.41 0.52 × 0.16 × 0.10 Monoclinic P21/c (no. 14) 9.692(2) 12.088(2) 20.027(4) 99.55(3) 2313.8 4 1.385 1008 6.11 44.84 1097 1097 134 0.1063 0.2957 4 C26H27MnN2O8 550.44 0.40 × 0.27 × 0.12 Monoclinic P21/c (no. 14) 9.927(2) 13.495(3) 18.761(4) 95.88(3) 2500.1 4 1.462 1160 5.82 44.90 888 888 184 0.0541 0.1385 5 C28H32MnN2O8 579.50 0.62 × 0.42 × 0.21 Monoclinic P21/c (no. 14) 10.440(6) 13.647(5) 19.300(11) 99.33(6) 2713 4 1.419 1212 5.40 45.02 3547 3544 343 0.0946 0.2518 6 C19H19ClMnN3O2 411.76 0.40 × 0.25 × 0.25 Monoclinic P21/n (no.14) 10.849(4) 12.409(5) 13.610(4) 95.54(3) 1823.6 4 1.500 848 8.89 50.00 3161 3161 236 0.0444 0.1057 7 C21H23MnN2O4 422.35 0.35 × 0.30 × 0.20 Orthorhombic Pbca (no.61) 17.844(4) 18.881(5) 12.337(3) 90.0 4156.5 8 1.350 1760 6.63 50.00 3643 3643 323 0.048 0.1226 8 C18H17MnN4O9 488.30 0.35 × 0.30 × 0.15 Monoclinic P21/c (no. 14) 14.014(2) 12.086(2) 13.370(2) 115.71(2) 2040.4 4 1.590 1000 7.07 50.00 3573 3573 357 0.0461 0.1096 9 C49H59Br4Mn2N13O19 1563.61 0.25 × 0.25 × 0.20 Monoclinic P21/n (no. 14) 12.592(2) 12.103(3) 20.266(2) 92.11(2) 3086.7(10) 2 1.682 1572 3.079 50.00 5398 5398 418 0.0430 0.0817 a I > 2.00s(I).b R = S Fo| 2 |Fc /S|Fo|. c R9 = [Sw(|Fo|2 2 |Fc|2)2/SwFo 2)]� �4 .40 J. Chem. Soc., Dalton Trans., 1999, 31–41 ning unit with the operating program ECHEM. The electrolytic cell consisted of a METROHM model 6.12404 carbon disc working electrode, a saturated calomel reference electrode and a platinum wire auxiliary electrode. Voltammograms were obtained of ca. 1 mM dichloromethane solutions of the complexes using 0.1 M Bu4NPF6 as a supporting electrolyte.Preparations SchiV base ligands. All ligands were prepared in virtually quantitative yields as previously reported and satisfactorily characterised by elemental analysis, 1H NMR, infrared and FAB mass spectroscopy.20 Compounds of stoichiometry [Mn(3CH3O-salen)(O2CR)] and [Mn(3CH3O-salpn)(O2CR)]. All comps were prepared by the same method as previously reported in high yields (based on manganese).11,13,14 They were characterised by elemental analysis, infrared, mass spectroscopy, room temperature magnetic moment measurement and FAB mass spectroscopy.[MnL(acac)] complexes. All complexes were prepared as previously reported 15 by the reaction of [Mn(acac)3] (Aldrich) with the appropriate ligand. The [MnL(acac)] were characterised satisfactorily. [Mn(salpn)Cl]. Acetonitrile (25 cm3) was freshly distilled from CaH2 and added to [Mn(salpn)(acac)] (0.5 g, 1.15 mmol) under nitrogen. Chlorotrimethylsilane (0.15 cm3, 1.15 mmol) was added to the solution which resulted in the immediate formation of an emerald green suspension which rapidly darkened to form a dark solid.The reaction was stirred for 5 min before cooling to 5 8C. The resultant microcrystalline precipitate formed was collected by filtration, washed copiously with diethyl ether and dried in vacuo. Monomeric complexes [Mn(salpn)(O2CR)], by the reaction of carboxylic acids with [Mn(salpn)(acac)]. All the monomeric manganese(III) complexes were prepared similarly, typified by that of [Mn(salpn)(O2CPri)].To an ethanolic solution (25 cm3) of [Mn(salpn)(acac)] (0.568 g, 1.3 mmol) was added isobutyric acid (1.27 g, 1.4 mmol). The solution was heated to reflux with stirring for 2 h then reduced in volume (ca. 4 cm3) and the complex precipitated in diethyl ether (100 cm3) from this solution. The green solid thus formed was collected by filtration, washed with diethyl ether (2 × 5 cm3) and dried in vacuo.Reaction of [Mn(5NO2salpn)(acac)] and [Mn(3Br,5NO2- salpn)(acac)] with carboxylic acids These reactions were performed in an analogous way to the reactions of carboxylic acids with [Mn(salpn)(acac)] with one modification. Prior to volume reduction the precipitated yellow material was removed by filtration. This material was washed with diethyl ether (20 cm3) and dried in vacuo yielding complexes of stoichiometry MnL(H2O)n (n = 0–2) in 35–50% yield. X-Ray diVraction studies Powder studies.X-Ray powder diVraction patterns were recorded using a Scintag XRD2000 powder diVractometer using Cu-Ka radiation of l = 1.5481 Å. Single crystal studies. Crystals suitable for X-ray studies were obtained in the following ways. Those of complexes 1 and 4 were obtained by slow evaporation of acetonitrile solutions of the complexes. Crystals of 2 and 3 were obtained by layering a concentrated dichloromethane solution of the complexes with n-hexane.Crystals of 5 were obtained by slow evaporation of an acetonitrile–ethanol solution of the complexes. Cooling of a saturated acetonitrile solution of the complex at 5 8C for 3 weeks produced crystals of it as its acetonitrile solvate, 6. Crystals of 7 and 8 were obtained by layering a concentrated ethanolic solution of the complex with n-hexane. Crystals of 9 were obtained from a DMF solution of [Mn(3Br,5NO2- salpn)(O2CMe)]?2H2O after several weeks. Crystal data and experimental conditions are listed in Table 4.All data were collected at ambient temperature with Mo-Ka radiation of l = 0.71069 Å on a Nicolet P3, 1 and 3, a Siemens P4, 2 and 5, CAD-4, 4, or Rigaku AFC6S diVractometer, 6–9. The intensities of three representative reflections declined by 14.4% for 7. A linear correction factor was applied to account for this. All data were corrected for Lorentz-polarisation eVects. The structures were solved by direct methods 24,25 and refined using full matrix least squares on F2.Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in idealised positions. All calculations were performed using the TEXSAN26 crystallographic package. CCDC reference number 186/1217. See http://www.rsc.org/suppdata/dt/1999/31/ for crystallographic files in .cif format. 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