DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, 3351–3352 3351 Complexed bridging ligand, [M(bpca)2] (M 5 Mn(II) or Fe(II); Hbpca 5 bis(2-pyridylcarbonyl)amine), as a building block for linear trinuclear complexes Takashi Kajiwara and Tasuku Ito Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan. E-mail: ito@agnus.chem.tohoku.ac.jp Received 24th August 1998, Accepted 25th August 1998 The antiferromagnetically coupled trimanganese complex [MnII(bpca)2{MnII(hfac)2}2] (Hbpca 5 bis(2-pyridylcarbonyl) amine; Hhfac 5 hexafluoroacetylacetone) and its iron–manganese mixed metal derivative, [FeII(bpca)2- {MnII(hfac)2}2], were synthesized by the reaction of two equivalents of [Mn(hfac)2(H2O)2] with one equivalent of [M(bpca)2], the latter acting as a bridging complexedligand.The chemistry of multi-metal-centered complexes or metal complex assemblies with highly ordered solid state structures has attracted much attention.1 In such chemistry, “complexedligands” are known to be beneficial in the construction of multi-metal complexes and the control of their properties.Monomeric complexes containing the tridentate ligand bpca2 (Hbpca = bis(2-pyridylcarbonyl)amine), [M(bpca)2] (M = Mn(II),2 Fe(II),3 Ni(II),4 Cu(II),4 Zn(II) 4) and [M(bpca)2]X (M = Fe(III); X2 = NO3 2, ClO4 2),3 could be examples of this type of complexed ligand, although no example has been reported to our knowledge.They have four free C]] O groups which may act as two sets of bidentate donors, and, upon reaction with a metal ion M9, they may give a trinuclear complex of the type M9(m-bpca)M(m-bpca)M9. It has been reported that oximato and oxamido complexes can act as a complexed ligand to give di-,5 tri-,6 and tetra-nuclear complexes.7 One of the characteristics of the present system is that {M(bpca)2} has a delocalized p-system which might mediate M–M9 interactions in redox and magnetic behaviour in a diVerent way from oxamido complexes.Here we report two examples of trinuclear complexes containing bridging {M(bpca)2}. [Mn(bpca)2]?H2O2 or [Fe(bpca)2]?H2O3 was allowed to react with two equivalents of [Mn(hfac)2(H2O)2] in CHCl3 solution (Hhfac = hexafluoroacetylacetone). Slow evaporation aVorded almost quantitatively orange and black crystals of trinuclear complexes, [Mn(bpca)2{Mn(hfac)2}2] and [Fe(bpca)2{Mn- (hfac)2}2], respectively.† Fig. 1 shows the structure of [Mn(bpca)2{Mn(hfac)2}2].‡ As expected, a {Mn(bpca)2} unit binds two {Mn(hfac)2} units as a bridging bis-bidentate complexed-ligand. The central Mn ion, Mn1, is surrounded by four pyridyl nitrogens (N1, N3, N4 and N6) with Mn–N distances of 2.221(2)–2.262(2) Å and two amide nitrogens (N2 and N5) with distances of 2.196(2) and 2.203(2) Å. The latter are slightly longer than those in the parent monomeric [Mn(bpca)2] (2.179(7) and 2.169(7) Å).2 The C]] O distances (average 1.233 Å) are definitely longer than those in the monomer, which results in the low frequency shift of C]] O stretching (1670 cm21: an intense band at 1700 cm21 for the parent monomer2).These facts suggest that the minus charge of bpca2 is delocalized on the O–C–N–C–O moiety in the trinuclear complex, whereas it is located mainly on the amide nitrogen in [Mn(bpca)2]. Terminal Mn ions, Mn2 and Mn3, are coordinated by six oxygen atoms from two hfac anions and from a {Mn(bpca)2} unit with Mn–O distances of 2.113(3)– 2.190(2) Å.These two terminal Mn ions are in a chiral environment with the combination D, L. The three Mn ions are arranged in an almost linear fashion with separations of 5.6708(6) Å for Mn1 ? ? ? Mn2 and 5.6855(6) Å for Mn1 ? ? ? Mn3, respectively. The structure of [Fe(bpca)2{Mn(hfac)2}2] was isostructural to [Mn(bpca)2{Mn(hfac)2}2].§ Overall structural features including delocalization of the O–C–N–C–O moiety are very similar to each other.Fig. 1 An ORTEP8 drawing of [Mn(bpca)2{Mn(hfac)2}2] with thermal ellipsoids at 30% probability. Hydrogen atoms and fluorine atoms are omitted for clarity. Selected bond distances (Å): Mn(1)–N(1) 2.246(2), Mn(1)–N(2) 2.196(2), Mn(1)–N(3) 2.221(2), Mn(1)–N(4) 2.262(2), Mn(1)–N(5) 2.203(2), Mn(1)–N(6) 2.242(2), Mn(2)–O(1) 2.153(2), Mn(2)–O(2) 2.176(2), Mn(2)–O(5) 2.146(3), Mn(2)–O(6) 2.163(3), Mn(2)–O(7) 2.126(3), Mn(2)–O(8) 2.113(3), Mn(3)–O(3) 2.171(2), Mn(3)–O(4) 2.190(2), Mn(3)–O(9) 2.152(2), Mn(3)–O(10) 2.147(2), Mn(3)–O(11) 2.120(2), Mn(3)–O(12) 2.122(2), O(1)–C(6) 1.221(3), O(2)–C(7) 1.220(3), O(3)–C(19) 1.251(3), O(4)–C(18) 1.241(3), Mn(1) ? ? ? Mn(2) 5.6708(6), Mn(1) ? ? ? Mn(3) 5.6855(6).3352 J.Chem. Soc., Dalton Trans., 1998, 3351–3352 The temperature dependence of the magnetic susceptibility of the compounds was measured down to 2.0 K. Fig. 2 shows the magnetic susceptibility data for [Mn(bpca)2{Mn(hfac)2}2] in the form of cmT and cm vs.T plots. The cmT value at room temperature, 12.9 cm3 K mol21, is slightly smaller than the spin-only value of 13.1 cm3 K mol21 for the dilute three-spin system with a g value of 2.00. On lowering the temperature, the cmT value gradually decreases suggesting antiferromagnetic interaction between adjoining Mn(II) ions through the delocalized p-system. Magnetic data of the trimer was analyzed by the three-spin model with exchange coupling constant J [H = 22J(SMn1?SMn2 1 SMn1?SMn3)].9 The least squares calculation yielded the best fit parameters of g = 1.98(1) and J = 20.35(1) cm21.[Fe(bpca)2{Mn(hfac)2}2] containing low-spin Fe(II) gave a temperature independent cmT value of 8.52 cm3 K mol21 above 10.0 K. The weak magnetic interaction in [Mn(bpca)2{Mn- (hfac)2}2] may be related to the Mn–N distances of 2.196(2)– 2.262(2) Å, which are longer than the M–N separations of divalent late first row transition metal ions. In fact, [Mn- (bpca)2{Mn(hfac)2}2] shows no distinct MLCT (from Mn to bpca2) band in the absorption spectrum,¶ suggesting weak dp– pp interactions.This study shows that [M(bpca)2]n1 could be a potential building block for supramolecular compounds. In fact, similar trinuclear complexes [M(bpca)2{Mn(hfac)2}2] (M = Ni(II), Cu(II)) have been isolated via similar reactions, in which {M(bpca)2} is acting as a building block.10 Such studies are now in progress in our laboratories. Fig. 2 Plots of cmT (o) and cm (x) vs.T for [Mn(bpca)2{Mn(hfac)2}2]. Solid line corresponds to the theoretical curve for which parameters are given in the text. Acknowledgements This work was supported by Grant-in-Aid for Scientific Research on Priority Areas (No. 10149102) from the Ministry of Education, Science and Culture, Japan. Notes and references † Elemental analysis: 1, found: C, 36.37; 1.62; N, 5.85. Calc. for C44H18N6O12Mn3F24: C, 36.61; H, 1.26; N, 5.82%. 2, found: C, 36.59; H, 1.53; N, 5.77.Calc. for C44H18N6O12FeMn2F24: C, 36.59; H, 1.26; N, 5.82%. ‡ Crystal data: C44H18N6O12Mn3F24, M = 1443.44, orthorhombic, space group Pna21 (no. 33), a = 17.142(9), b = 20.552(3), c = 16.233(4) Å, U = 5718(3) Å3, Z = 4, Dc = 1.676 g cm23, F(000) = 2940.00, m(Mo- Ka) = 12.30 cm21, 3953 unique reflections (I > 2.0s(I)) collected at room temperature with Mo-Ka radiation (l = 0.71069 Å) up to 2q = 55.08 on a Rigaku AFC 7S diVractometer. Final R value is 0.058 for observed data.CCDC reference number 186/1132. See http:// www.rsc.org/suppdata/dt/1998/3351/ for crystallographic files in .cif format. § Crystal data: C44H18N6O12FeMn2F24, M = 1444.35, orthorhombic, space group Pna21 (no. 33), a = 16.701(6), b = 20.134(7), c = 16.353(5) Å, U = 5498(2) Å3, Z = 4, R = 0.052. ¶ Electronic spectrum in CHCl3 solution: lmax = 290 nm (e = 60500 dm3 mol21 cm21) and ca. 420 nm (shoulder, ca. 600 dm3 mol21 cm21). 1 For example, H. O. Stumpf, L.Ouahab, Y. Pei, D. Grandjean and O. Kahn, Science, 1993, 261, 447; S. L. Suib, Chem. Rev., 1993, 93, 803. 2 D. Marcos, J.-V. Folgado and D. Beltrán-Porter, Polyhedron, 1990, 9, 2699. 3 S. Wocadlo, W. Massa and J.-V. Folgado, Inorg. Chim. Acta, 1993, 207, 199. 4 D. Marcos, R. Martinez-Mañe, J.-V. Folgado, A. Beltrán-Porter, D. Beltrán-Porter and A. Fuertes, Inorg. Chim. Acta, 1989, 159, 11. 5 F. Birkelbach, M. Winter, U. Flörke, H.-J. Haupt, C. ButzlaV, M. Lengen, E. Bill, A. X. Trautwein, K. Weighardt and P. Chaudhuri, Inorg. Chem., 1994, 33, 3990; P. Basu, S. Pal and A. Chakravorty, J. Chem. Soc., Dalton Trans., 1991, 3217; A. Escuer, R. Vicente, J. Ribas, R. Costa and X. Solans, Inorg. Chem., 1992, 31, 2627. 6 For example, S. Chattopadhyay, P. Basu, S. Pal and A. Chakravorty, J. Chem. Soc., Dalton Trans., 1990, 3829; R. Costa, A. Garcia, R. Sanchez, J. Ribas, X. Solans and V. Rodriguez, Polyhedron, 1993, 12, 2697. 7 C. Krebs, M. Winter, T. Weyhermüller, E. Bill, K. Wieghardt and P. Chaudhuri, J. Chem. Soc., Chem. Commun., 1995, 1913; F. Corazza, E. Solari, C. Floriani, A. Chiesi-Villa and C. Guastini, J. Chem. Soc., Chem. Commun., 1986, 1562. 8 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 9 O. Kahn, Molecular Magnetism, VCH Publishers, Weinheim, 1993; S. Ménage, S. E. Vitols, P. Bergerat, E. Codjovi, O. Kahn, J.-J. Girerd, M. Guillot, X. Solans and T. Calvet, Inorg. Chem., 1991, 30, 2666. 10 T. Noguchi, T. Kajiwara and T. Ito, unpublished work. Communication 8/06618C