Variation of the ground spin state in homo- and hetero-octanuclear copper(ii) and nickel(ii) double-star complexes with a meso-helicate-type metallacryptand coreElectronic supplementary information (ESI) available: Preparation and general physical characterization data of the ligands H4mpba and H4Mempba and the complexes Na8[Ni2(mpba)3]·12H2O and Na8[Ni2(Mempba)3]·18H2O. Magnetic characterization data of Na8[Ni2(mpba)3]·12H2O and Na8[Ni2(Mempba)3]·18H2O (Fig. S1). Spin states and energies for 1–6(Tables S1–S3). CCDC reference number 758079for 3. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b926709c

Homo- and heterometallic octanuclear complexes of formula Na2{[Cu2(mpba)3][Cu(Me5dien)]6}(ClO4)6·12H2O (1), Na2{[Cu2(Mempba)3][Cu(Me5dien)]6}(ClO4)6·12H2O (2), Na2{[Ni2(mpba)3][Cu(Me5dien)]6}(ClO4)6·12H2O (3), Na2{[Ni2(Mempba)3][Cu(Me5dien)]6}(ClO4)6·9H2O (4), {[Ni2(mpba)3][Ni(dipn)(H2O)]6}(ClO4)4·12.5H2O (5), and {[Ni2(Mempba)3][Ni(dipn)(H2O)]6}(ClO4)4·12H2O (6) [mpba = 1,3-phenylenebis(oxamate), Mempba = 4-methyl-1,3-phenylenebis(oxamate), Me5dien = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine, and dipn = dipropylenetriamine] have been synthesized through the “complex-as-ligand/complex-as-metal” strategy. Single-crystal X-ray diffraction analyses of 1, 3, and 5show cationic MII2M′II6entities (M, M′ = Cu and Ni) with an overall double-star architecture, which is made up of two oxamato-bridged MIIM′II3star units connected through three meta-phenylenediamidate bridges between the two central metal atoms leading to a binuclear metallacryptand core of the meso-helicate-type. Dc magnetic susceptibility data for 1–6in the temperature range 2–300 K have been analyzed through a “dimer-of-tetramers” model [H= −J(S1A·S3A+ S1A·S4A+ S1A·S5A+ S2B·S6B+ S2B·S7B+ S2B·S8B) −J′S1A·S2B, with S1A= S2B= SMand S3A= S4A= S5A= S6B= S7B= S8B= SM′]. The moderate to strong antiferromagnetic coupling between the MIIand M′IIions through the oxamate bridge in 1–6(−JCu–Cu= 52.0–57.0 cm−1, −JNi–Cu= 39.1–44.7 cm−1, and −JNi–Ni= 26.3–26.6 cm−1) leads to a non-compensation of the ground spin state for the tetranuclear MIIM′II3star units [SA= SB= 3SM′−SM= 1 (1and 2), 1/2 (3and 4), and 2 (5and 6)]. Within the binuclear MII2meso-helicate cores of 1–4, a moderate to weak antiferromagnetic coupling between the MIIions (−J′Cu–Cu= 28.0–48.0 cm−1and −J′Ni–Ni= 0.16–0.97 cm−1) is mediated by the triple m-phenylenediamidate bridge to give a ground spin singlet (S= SA−SB= 0) state for the octanuclear MII2CuII6molecule. Instead, a weak ferromagnetic coupling between the NiIIions (J′Ni–Ni= 2.07–3.06 cm−1) operates in the binuclear NiII2meso-helicate core of 5and 6leading thus to a ground spin nonet (S= SA+ SB= 4) state for the octanuclear NiII8molecule. Dc magnetization data for 5reveal a small but non-negligible axial magnetic anisotropy (D= −0.23 cm−1) of the S= 4 NiII8ground state with an estimated value of the energy barrier for magnetization reversal of 3.7 cm−1(U= −DS2). Ac magnetic susceptibility data for 5show an unusual slow magnetic relaxation behaviour at low temperatures which is typical of “cluster glasses”. The temperature dependence of the relaxation time for 5has been interpreted on the basis of the Vogel–Fulcher law for weakly interacting clusters, with values of 2.5 K, 1.4 × 10−6s, and 4.0 cm−1for the intermolecular interaction parameter (T0), the pre-exponential factor (τ0), and the effective energy barrier (Ueff), respectively. [ABSTRACT FROM AUTHOR]