Crystal Structure and Characterization of Two Layered Copper(II) Coordination Polymers with Anions of 3-Phosphonopropionic Acid and (RS)-2-Phosphonobutyric Acid

Blue single crystals of Cu[μ3-O3P(CH2)2COOH]*2H2O (1) and Cu[(RS)-μ3-
O3PCH(C2H5)COOH]*3H2O (2) have been prepared in aqueous Cu2+-solutions (pH = 2.5–3.5) containing 3-
phosphonopropionic acid (1) and (RS)-2-phosphonobutyric acid (2), respectively. 1: Space group Pbca (no. 61)
with a = 812.5(2), b = 919.00(9), c = 2102.3(2) pm. Cu2+ is five-fold coordinated by three oxygen atoms
stemming from [O3P(CH2)2COOH]2– anions and two water molecules. The Cu-O bond lengths range from
194.0(3) to 231.8(4) pm. The connection between the [O3P(CH2)2COOH]2– anions and the Cu2+ cations yields a
polymeric structure with layers parallel to (001). The layers are linked by hydrogen bonds. 2: Space group Pbca
(no. 61) with a = 1007.17(14), b = 961.2(3), c = 2180.9(4) pm. The copper cations are surrounded by five
oxygen atoms in a square pyramidal fashion with Cu-O bonds between 193.6(4) and 236.9(4) pm. The
coordination between [O3PCH(C2H5)COOH]2- and Cu2+ results in infinite puckered layers parallel to (001). The
layers are not connected by any hydrogen bonds. Each layer contains both R and S isomers of the
[O3PCH(C2H5)COOH]2- dianion. Water molecules not bound to Cu2+ are intercalated between the layers.
UV/Vis spectra suggest three d-d transition bands at 743, 892, 1016 nm for 1 and four bands at 741, 838, 957
and 1151 nm for 2, respectively. Magnetic measurements suggest a weak antiferromagnetic coupling between
Cu2+ due to a super-superexchange interaction. Thermoanalytical investigations in air show that the compounds
are stable up to 95 °C (1) and 65 °C (2), respectively.