CaADC (1) and Mg(ADC)(H2O)2 (2) were synthesized by grinding Ca(CH3COO)2 and Mg(CH3COO)2·4H2O with acetylenedicarboxylic acid (H2ADC) in an agate mortar. After careful heating for two hours in an argon atmosphere at moderate temperatures, 50 °C and 70 °C, respectively, polycrystalline materials of good crystallinity were obtained. The crystal structures of 1 and 2 were solved and refined from X‐ray powder diffraction data. In the course of the structural refinement it turned out that 1 and 2 are isotypic to SrADC(I41/amd, Z = 4) and Mn(ADC)(H2O)2 (I2/a, Z = 4). In both compounds metal cations are connected by bridging ADC2– ligands to form a 3D coordination network. Thermoanalytical investigations show that CaADC decomposes above 50 °C, whereas for Mg(ADC)(H2O)2 a mass loss of approx. 33 % is observed above 150 °C. The loss of one water molecule as well as a decarboxylation is very likely. The remaining residue is amorphous to X‐rays.
Single crystals of 2 ϱ [Bi(ADC) 2/4 (ADC) 3/3 (H 2 O) 2 ]·2H 2 O (P1, Z = 2) and 3 ϱ [Bi(ADC) 2/4 (ADC) 3/3 (H 2 O) 3 ]·H 2 O (P1, Z = 2) were obtained by isothermal evaporation of aqueous solutions containing acetylenedicarboxylic acid (H 2 ADC) and Bi(NO 3 ) 3 ·5H 2 O. Their crystal * Prof. Dr. U. Ruschewitz
From a solution of [Zn(H2O)6](NO3)2 and acetylenedicarboxylic acid in deionized water, single crystals of zinc acetylenedicarboxylate dihydrate, {[Zn(C4O4)(H2O)2]}n, were obtained by slow evaporation of the solvent. The asymmetric unit consits of one zinc cation which is located on a centre of symmetry, half of an acetylenedicarboxylate anion, the anion lying on a twofold axis, and one water molecule in a general position. Thus, zinc is octahedrally coordinated by four O atoms of acetylenedicarboxylate anions and two water molecules in trans positions. These octahedra are connected by dicarboxylate ligands into a three‐dimensional network.
Single crystals of PbADC (1) and PbADC·H2O (2) formed at the phase boundary of an aqueous silica gel containing acetylenedicarboxylic acid (HOOC–C≡C–COOH, H2ADC) and an aqueous solution containing Pb(NO3)2. By choosing different concentrations of Pb(NO3)2, compounds 1 and 2 were obtained as phase pure products. Additionally, 1 was obtained by grinding Pb(CH3COO)2·3H2O with H2ADC resulting in a polycrystalline sample. The crystal structures of 1 (I41/amd, Z = 4; SrADC type structure) and 2 (P21/c, Z = 4, new structure type) were solved and refined from X‐ray single crystal data. Compound 1 exhibits a three‐dimensional framework structure: lead cations with a diamond‐like arrangement are interconnected by bridging ADC2– ligands. In 2 double‐layers are formed by lead cations, bridging ADC2– anions, and water molecules. These layers are held together by hydrogen bonds through water molecules and oxygen atoms of the ADC2– ligands. Suspending 1 for 24 h in water at ambient conditions leads to the formation of 2, which can be converted to 1 again by careful dehydration at approx. 400 K in vacuo. This reversible reaction can be structurally interpreted as a topochemical reaction, which transforms a 3D coordination network into a 2D network structure and vice versa, as both crystal structures show noticeable structural similarities.
$^{1}_{\infty}\rm [M^{II}(Py)_{2}(H_{2}O)_{n}(ADC)_{2/2}]$ with MII = Fe, Co, Ni (n = 2) and MII = Cu (n = 1): Four New Coordination Polymers with Acetylenedicarboxylate (ADC2−) as Bridging Ligand
By slow diffusion of pyridine (Py) into an aqueous solution of a respective metal salt and acetylenedicarboxylic acid (H2ADC) single crystals of new coordination polymers of composition $^{1}_{\infty}\rm [M^{II}(Py)_{2}(H_{2}O)_{n}(ADC)_{2/2}]$ (M = Fe, Co, Ni; C2/c, Z = 4) (1 – 3) and $^{1}_{\infty}\rm [Cu^{II}(Py)_{2}(H_{2}O)_{n}(ADC)_{2/2}]$ (P212121, Z = 4) (4) were obtained. In compounds 1 – 3 octahedral MIIO4N2 units are connected via acetylenedicarboxylate anions to form chain‐like polymers. In compound 4 square pyramidal CuIIO3N2 units are found, which are also connected to chains by acetylenedicarboxylates. Thermoanalytical investigations on 3 show an abrupt mass loss of approx. 40 % above 130 °C, which points to a release of both pyridine ligands (calc.: 43 %). Thereafter, the sample decomposes continuously, which is confirmed by XRPD measurements, as an amorphous residue is found. Magnetic susceptibility measurements of 1 – 3 display paramagnetic behaviour in the temperature range 2‐300 K. While μeff of 3 (d8 configuration) with orbital singlet ground state is nearly temperature‐independent, 1 (d6) and 2 (d7) exhibit complicated μeff−T behaviour on account of a ligand‐field ground state derived from the cubic states 5T2 and 4T1, respectively. On the basis of a tetragonal ligand‐field model excellent adaptations are obtained with reasonable ligand‐field parameters. Exchange interactions between the magnetic ions are detected in no case.
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