$^{1}_{\infty}\rm [M^{II}(Py)_{2}(H_{2}O)_{n}(ADC)_{2/2}]$ mit M II = Fe, Co, Ni (n = 2) und M II = Cu (n = 1): Vier neue Koordinationspolymere mit dem Acetylendicarboxylat‐Dianion (ADC 2− ) als verbrückendem Liganden

Abstract $^{1}_{\infty}\rm [M^{II}(Py)_{2}(H_{2}O)_{n}(ADC)_{2/2}]$ with M II = Fe, Co, Ni (n = 2) and M II = Cu (n = 1): Four New Coordination Polymers with Acetylenedicarboxylate (ADC 2− ) as Bridging Ligand By slow diffusion of pyridine (Py) into an aqueous solution of a respective metal salt and acetylenedicarboxylic acid (H 2 ADC) 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 $^{1}_{\infty}\rm [Cu^{II}(Py)_{2}(H_{2}O)_{n}(ADC)_{2/2}]$ (P2 1 2 1 2 1 , Z = 4) ( 4 ) were obtained. In compounds 1 – 3 octahedral M II O 4 N 2 units are connected via acetylenedicarboxylate anions to form chain‐like polymers. In compound 4 square pyramidal Cu II O 3 N 2 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 μ eff of 3 (d 8 configuration) with orbital singlet ground state is nearly temperature‐independent, 1 (d 6 ) and 2 (d 7 ) exhibit complicated μ eff − T behaviour on account of a ligand‐field ground state derived from the cubic states 5 T 2 and 4 T 1 , 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.