Salen-type compounds of calcium and strontium

Salen complexes of the heavy alkaline-earth metals, calcium and strontium, were prepared by the reaction of various salen(t-Bu)H2 ligands with the metals in ethanol. Six new calcium and strontium compounds, [Ca(salen-(t-Bu))(HOEt)₂(thf)] (1), [Ca(salen(t-Bu))(HOEt)₂] (2), [Ca(salpen(t-Bu))(HOEt)₃] (3), [Ca(salophen(t-Bu))(HOEt)(thf)] (4), [Sr(salen(t-Bu))(HOEt)₃] (5), and [Sr(salophen(t-Bu))(HOEt)(thf)₂] (6), were formed in this way with the quatridentate Schiff-base ligands N,N′-bis(3,5-di-tert-butylsalicylidene)ethylenediamine (salen(t-Bu)H₂), N,N′-bis(3,5-di-tert-butyl-salicylidene)-1,3-propanediamine (salpen(t-Bu)H₂), and N,N′-o-phenylenebis(3,5-di-tert-butylsalicylideneimine (salophen-(t-Bu)H₂). Initially, ammonia solutions of the metals were combined with the salen(t-Bu)H₂ ligands, and in the reaction of strontium with salen(t-Bu)H₂, the unusual tetrametallic cluster [{OC₆H₂(t-Bu)₂ CHN(CH₂)₂NH₂}Sr (μ₃-salean(t-Bu)H₂)Sr (μ₃-OH)]₂ (7) was produced (salean(t-Bu)H₄ = N,N′-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-ethylenediamine). In this compound, the imine bonds of the salen(t-Bu)H₂ ligand were reduced to form the known ligands salean(t-Bu)H₄ and (HO)C₆H₂(t-Bu)₂CHN (CH₂)₂NH₂. Compounds 1, 5, 6, and 7 were structurally characterized by single-crystal X-ray diffraction. Crystal data for 1 (C₄₄H₇₄CaN₂O₆): triclinic space group P1̄, a = 8.3730(10) Å, b = 14.8010(10) Å, c = 18.756(2) Å, α = 72.551(10)°, β = 81.795(10)°, γ = 78.031 (10)°, Z = 2. Crystal data for 5 (C₃₈H₆₄SrN₂O₅): monoclinic space group P2₁/c, a = 23.634(3) Å, b = 8.4660(10) Å, c = 24.451(3) Å, β = 101.138(10)°, Z = 4. Crystal data for 6 (C₄₆H₆₇N₂O₅Sr): orthorhombic space group P2₁2₁2₁, a = 10.5590(2) Å, b = 16.2070(3) Å, c = 26.7620(6) Å, Z = 4. Crystal data for 7 (C₉₈H₁₅₆N₈O₈Sr₄): triclinic space group P1, a = 14.667(1) Å, b = 15.670(1) Å, c = 18.594(2) Å, α = 92.26(1)°, β = 111.84(1)°, γ = 117.12(1)°, Z = 4.