Neutral terphenyl-based halogen bond donors form two-point halogen bonding motifs with oxadiazoles in the solid state.

The syntheses and crystal structures of two novel trisamides, the ethyl- (2) and propyl-substituted (3) N,N′,N′′-trialkylbenzene-1,3,5-carboxamides, are reported. The compounds are prepared in good yields by aminolysis of the trimethyl-1,3,5-benzenecarboxylate and the respective primary amine. Compound 2 crystallizes in the P212121 space group with a complete molecule in the asymmetric unit and four molecules per unit cell, whereas 3 does it in the R3c space group with one-third of the molecule in the asymmetric unit and six molecules per unit cell. Their solid-state structures show that the NH···OC hydrogen bond plays the most important role in the supramolecular framework of both cases, despite considerable differences in crystal packing. Supramolecular sheets are formed in 2, whereas molecules of 3 are packed in a H-bonded primitive cubic [46] three-dimensional network. The main difference in the molecular conformation is the tilting of the carboxamide group with respect to the aryl, which in the case of 3 occurs in the same direction, leading to the formation of “solid-state” chiral molecules.

In our efforts to tune the structures of mixed-ligands malonate-containing coordination compounds, four copper(II) and two high-spin cobalt(II) complexes of formulas [Cu(mal)(H2O)(dpo)] n (1), [Cu2(mal)2(H2O)2(dpp)] n ·7nH2O (2), [Cu2(mal)2(H2O)2(bpe)] n ·2nH2O (3), {[Cu(mal)2(H2O)2][Cu(dien)]} n ·4nH2O (4) [Co2(mal)2(H2O)6(dpo)]·2H2O (5) and [Co(mal)(H2O)(phen)] n ·2nH2O (6) [H2mal = malonic acid, dpo =4,4′-bipyridine-N,N′-dioxide, dpp = 2,3-bis(pyridyl)pyrazine, bpe =1,2-bis(4-pyridyl)ethylene, dien = diethylenetriamine and phen = 1,10-phenanthroline] have been synthesized and structurally characterized by X-ray diffraction on single crystals. Complexes 1, 2, 4, and 6 are chain compounds, 5 is a dinuclear species, and 3 has a sheet-like structure. The malonate ligand in this family acts as either a blocking (1 and 5) or bridging ligand (2–6). The rod-like molecules dpo (1 and 5) and bpe (3) exhibit the bis-monodentate (1 and 3) and monodentate (5) coordination modes, whereas dpp (2), dien (4), and phen (6) act as bis-bidentate (2), tridentate (4), and bidentate (6) ligands. The neutral motifs of 1–6 are interlinked through hydrogen bonds and weak C–H···π and π–π type interactions affording supramolecular three-dimensional networks. Variable-temperature magnetic susceptibility measurements show the occurrence of weak ferro- (2, 3, 5, and 6) and antiferromagnetic (1 and 4) interactions, the exchange pathways being the carboxylate-malonate (3–6), oxo-carboxylate (2), bis-bidentate (dpp) (2) or hydrogen bonds (1). Remarkably, the equatorial-apical exchange pathway through the carboxylate bridge present in 4 provides the first case of the occurrence of an antiferromagnetic interaction in a malonate-containing copper(II) complex.

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Four potential tetradentate ligands of formulae 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)ethane (H(4)L(1), 1), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)propane (H(4)L(2), 2), 1,2-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)benzene (H(4)L(3), 3) and 1,8-bis-(3,5-di-tert-butyl-2-hydroxybenzamido)naphthalene (H(4)L(4), 4) have been prepared and the crystal structures of three of them (1, 3 and 4) determined by single crystal X-ray diffraction. The investigation of their complexing ability toward Co(II) afforded the compounds of formulae [Co(III)(L(3))Na(I)(H(2)O)(2)] (5), [Co(III)(L(n))Li(I)(H(2)O)2] with n = 1 (6), 2 (7) and 3 (8) and [Co(II)(L(4))Li(I)(2)] (9). Complexes 5-8 are square planar Co(III) species, as corroborated by the crystal structure of 5. In this compound, two amide-nitrogen and two phenolate-oxygen atoms of a fully deprotonated (L(3))(4-) anion build a slightly distorted square planar surrounding around the cobalt atom, the Co-N distances [1.858(3) and 1.861(3) A] being somewhat longer than the Co-O ones [1.798(3) and 1.801(3) A]. Magnetic and 1H NMR data at room temperature for 6-8 support the occurrence of an intermediate S = 1 low-lying state for the Co(III) center which is stabilized by the strong donating ability of the fully deprotonated bis-amidate ligands. In the case of the compound with the naphthalene derivative (9), the analytical and spectroscopic data suggest the occurrence of a low spin Co(II) complex. The weakening of the ligand field strength of the tetradentate bis-amidate ligand in the naphthalene derivative (5-6-5 ring-membered fused chelate) when compared to the situation in complexes 5-8 (5-5-5 ring-membered fused chelate) would account for this feature.