Coordination Algorithms Control Molecular Architecture: [Cu^I₄(L2)₄]⁴⁺ Grid Complex Versus [M^II₂(L2)₂X₄]^y+ Side‐By‐Side Complexes (M=Mn, Co, Ni, Zn; X=Solvent or Anion) and [Fe^II(L2)₃][Cl₃Fe^IIIOFe^IIICl₃]

Abstract

The synthesis and characterisation of a pyridazine-containing two-armed grid ligand L2 (prepared from one equivalent of 3,6-diformylpyridazine and two equivalents of p-anisidine) and the resulting transition metal (Zn, Cu, Ni, Co, Fe, Mn) complexes (1-9) are reported. Single-crystal X-ray structure determinations revealed that the copper(I) complex had self-assembled as a [2 x 2] grid, [Cu(I) (4)(L2)(4)][PF(6)](4).(CH(3)CN)(H(2)O)(CH(3)CH(2)OCH(2)CH(3))(0.25) (2.(CH(3)CN)(H(2)O)(CH(3)CH(2)OCH(2)CH(3))(0.25)), whereas the [Zn(2)(L2)(2)(CH(3)CN)(2)(H(2)O)(2)][ClO(4)](4).CH(3)CN (1.CH(3)CN), [Ni(II) (2)(L2)(2)(CH(3)CN)(4)][BF(4)](4).(CH(3)CH(2)OCH(2)CH(3))(0.25) (5 a.(CH(3)CH(2)OCH(2)CH(3))(0.25)) and [Co(II) (2)(L2)(2)(H(2)O)(2)(CH(3)CN)(2)][ClO(4)](4).(H(2)O)(CH(3)CN)(0.5) (6 a.(H(2)O)(CH(3)CN)(0.5)) complexes adopt a side-by-side architecture; iron(II) forms a monometallic cation binding three L2 ligands, [Fe(II)(L2)(3)][Fe(III)Cl(3)OCl(3)Fe(III)].CH(3)CN (7.CH(3)CN). A more soluble salt of the cation of 7, the diamagnetic complex [Fe(II)(L2)(3)][BF(4)](2).2 H(2)O (8), was prepared, as well as two derivatives of 2, [Cu(I) (2)(L2)(2)(NCS)(2)].H(2)O (3) and [Cu(I) (2)(L2)(NCS)(2)] (4). The manganese complex, [Mn(II) (2)(L2)(2)Cl(4)].3 H(2)O (9), was not structurally characterised, but is proposed to adopt a side-by-side architecture. Variable temperature magnetic susceptibility studies yielded small negative J values for the side-by-side complexes: J=-21.6 cm(-1) and g=2.17 for S=1 dinickel(II) complex [Ni(II) (2)(L2)(2)(H(2)O)(4)][BF(4)](4) (5 b) (fraction monomer 0.02); J=-7.6 cm(-1) and g=2.44 for S= 3/2 dicobalt(II) complex [Co(II) (2)(L2)(2)(H(2)O)(4)][ClO(4)](4) (6 b) (fraction monomer 0.02); J=-3.2 cm(-1) and g=1.95 for S= 5/2 dimanganese(II) complex 9 (fraction monomer 0.02). The double salt, mixed valent iron complex 7.H(2)O gave J=-75 cm(-1) and g=1.81 for the S= 5/2 diiron(III) anion (fraction monomer=0.025). These parameters are lower than normal for Fe(III)OFe(III) species because of fitting of superimposed monomer and dimer susceptibilities arising from trace impurities. The iron(II) centre in 7.H(2)O is low spin and hence diamagnetic, a fact confirmed by the preparation and characterisation of the simple diamagnetic iron(II) complex 8. Mössbauer measurements at 77 K confirmed that there are two iron sites in 7.H(2)O, a low-spin iron(II) site and a high-spin diiron(III) site. A full electrochemical investigation was undertaken for complexes 1, 2, 5 b, 6 b and 8 and this showed that multiple redox processes are a feature of all of them.

Synthesis and Some First‐Row Transition‐Metal Complexes of the 1,2,4‐Triazole‐Based Bis(terdentate) Ligands TsPMAT and PMAT

“…This was expected to lead to the formation of 4-amino-3,5-bis 17). However, TsPEAT (16) could not be isolated from these experiments and only unchanged sulfonamide 11 was recovered, almost quantitatively, when the reaction was carried out under identical conditions as for TsPMAT (14). In fact, no 1,2,4-triazole compound of any kind was present in the filtered reaction mixture, as evidenced by 13 C NMR analysis of the residue after evaporation.…”

“…Owing to the instability of dichloride 9, the usefulness of hydrochloride 8 was explored. Initially the acyclic ligands TsPMAT (14) and PMAT (15) were targeted (Scheme 4). After 24 h under reflux, we could not detect any product when the reaction of hydrochloride 8 with sulfonamide 10·0.5 H 2 O in the presence of potassium carbonate was carried out in acetonitrile.…”

“…This was attributed to the insolubility of hydrochloride 8 in this solvent. Carrying out the reaction at 60 8C in N,N-dimethylformamide, in which hydrochloride 8 is readily soluble, we obtained TsPMAT (14) as a colourless powder in 60 % yield after workup. Removal of the 4-toluenesulfonyl group was achieved by heating a solution of TsPMAT (14) in concentrated sulfuric acid at 100 8C for 8 h. Thus, PMAT (15) was isolated as a yellowish oil in virtually quantitative yield (Scheme 4).…”

“…A bis(terdentate) [46] and a mixed quadridentatequinquedentate ligand [47] based on 2,5-disubstituted 1,3,4-oxadiazoles have also recently been reported. Attempts to extend the approach used for the synthesis of TsPMAT (14) and PMAT (15) to the preparation of other acyclic and macrocyclic ligands are also described. Employing PMAT (15), we were recently able to identify, for the first time by means of single-crystal X-ray diffraction, that the half-spin-crossover species of the doubly 1,2,4-triazole-bridged complex [Fe II 2 (PMAT) 2 ](BF 4 ) 4 ·DMF (27·DMF) is composed of discrete dinuclear high-spin/low-spin units.…”

“…These results are in contrast to the recent results of Kaizaki and co-workers [50] who found a 1:1 mixture of high-spin/high-spin and low-spin/lowspin dinuclear units present at the half-spin-crossover plateau of the two-step transition in their pyrazolate-bridged system. Here, we detail the synthesis of complex 27·DMF and some analogous first-row transition-metal complexes of PMAT (15), as well as reporting the results of our initial investigation of the coordination chemistry of TsPMAT (14).…”