Structure, Single Crystal EPR Spectra, and Exchange Interactions in [Cu(l-proline)₂]₂·5H₂O and Cu(d,l-proline)₂·2H₂O

Abstract

A new copper(II) compound, [Cu(L-proline)(2)](2).5H(2)O (C(20)Cu(2)H(42)N(4)O(13)) (called compound I) was synthesized and crystallized, and its structure was solved using X-ray methods. It is monoclinic, space group P2(1), with a = 11.187(1) Å, b = 12.172(3) Å, c = 11.661(1) Å, beta = 114.96(1) degrees, and Z = 2. There are two chemically different copper molecules (labeled A and B), both with the copper atom in a N(2)O(2) square planar coordination. Molecule type A has one water molecule in an apical position. Molecule B has water molecules in each of the two apical positions. Single-crystal EPR measurements have been performed in I and also in Cu(D,L-proline)(2).2H(2)O (compound II). From the similar angular variations of the position of the single resonance observed in both compounds, we evaluated the molecular g tensors. Interpretation of the molecular g tensors resulted in d(x)()()2(-)(y)()()2 orbital ground states. From the angular variations of the line width we calculated the magnitude of the exchange interactions coupling neighbor copper ions in each compound. In I copper ions type A at 7.25 Å are arranged in chains coupled through axial-equatorial bonds. The exchange coupling within these chains is |J/k| = 118 mK. The coupling between copper ions type B is weaker. However, the interactions between copper ions type A and B generate a three-dimensional magnetic network. Our data in compound II indicate that a superexchange pathway containing a weak hydrogen bond C-H- - -O is the path for an exchange interaction with |J'/k| = 48 mK between coppers in neighbor layers at 9.75 Å.

X-Ray and EPR study on copper (II) complexes with an enamine ligand

“…The metal center lies on the same line with the apical O atoms, which makes an angle of 84.39 (1) 0 with the equatorial plane. These data show the main deviations from the octahedral geometry and are consistent with a Cu(II) complex with a strong Jahn-Teller distortion [16][17][18]. The resolved crystal structure is shown in Figure 3, while selected bond lengths and angles are listed in Table 2.…”

EPR measurements of weak exchange interactions coupling unpaired spins in model compounds

“…The exchange interactions produce a spin dynamics with a characteristic frequency oex that averages out the splitting of the lines. Cases where x > 1 allow simple implementations of the exchange narrowing process to evaluate exchange interactions [38,[43][44][45][46][47][48][49][50][51][52][53][54].…”

“…It is similar to what is obtained with the simpler Anderson theory (Eq. (8)) and has been used in several works to calculate exchange interactions from line width data [28,[38][39][40][42][43][44][45][46][47][48][49][50][51][52][53][54][55].…”

“…(9) on co02 allows the separation of contributions to the width arising from the exchange narrowing process from those arising from dipolar and other interactions that are frequency independent (see for example, refs. 28,[42][43][44][45][46][47][48][49]. The molecular g-tensors gA and g~ corresponding to individual metal sites can be evaluated under simple assumptions [56,57] from the crystal g-tensor obtained from the observed resonance positions and the value of CO~x is calculated by Eq.…”

Application of l-thiazolidine-4-carboxylic acid monolayer in electrochemical determination of copper(II)

“…In this paper, a novel self-assembly system based on RSR, L-thiazolidine-4-carboxylic acid (L-thioproline), was reported. Our findings demonstrated the electrodes modified with L-thioproline monolayer offered a very simple, reproducible and repeatable method for the determination of Cu 2+ , which preconcentrated Cu 2+ by the chelation through the amino acid moiety of thioproline [32]. Moreover, thioproline monolayer had long-term stability for repetitive analyses.…”