Effect of 3d heterometallic ions on the magnetic properties of azido-Cu(II) with isonicotinic acid coligands: A theoretical perspective

doi:10.1016/j.jmgm.2020.107562

Journal of Molecular Graphics and Modelling

Volume 97, June 2020, 107562

https://doi.org/10.1016/j.jmgm.2020.107562 Get rights and content

Highlights

•
The supposedly empty 4s/4p/4d orbitals of the M^II ions are found to play an important role in the mechanism of magnetic coupling and are probed using NBO analysis.
•
As the number of unpaired electrons on the M^II ions increases, the overlap integrals of the magnetic orbitals in the Cu^IIM^II model complexes increases accordingly, and the magnetic coupling constant gradually decreases.
•
More electrons occupied the empty 4d orbital as the highest energy increased, whereas the magnetic coupling constant declined gradually as the number of unpaired electrons in the complex system increased.

Abstract

Based on density functional theory and the broken-symmetry approach, the magnetic properties of an azido-Cu(II) complex with isonicotinic acid coligands were studied at the B1LYP/def2-TZVP level. According to the molecular magnetic orbitals and Mulliken spin population analysis, there are strong orbital interactions between the paramagnetic Cu^II/Ni^II ions and the bridging azide ligands and isonicotinic ions. The supposedly empty 4s/4p/4d orbitals of the M^II ions are found to play an important role in the mechanism of magnetic coupling and are probed using NBO analysis. As the number of unpaired electrons on the M^II ions increases, the number of electrons that occupy the empty 4d orbitals with the highest energy and overlap integrals of the magnetic orbitals in the Cu^IIM^II (M = Cu, Ni, Co, Fe, Mn) model complexes increases accordingly, and the magnetic coupling constant gradually decreases.

Graphical abstract

The magnetic coupling constant of 3d heterometallic azido-Cu(II) complexes with isonicotinic acid coligands were calculated. The supposedly empty 4s/4p/4d orbitals of the M^II ions are found to play an important role in the mechanism of magnetic coupling and are probed using NBO analysis. As the number of unpaired electrons on the M^II ions increases, the number of electrons that occupy the empty 4d orbitals with the highest energy and overlap integrals of the magnetic orbitals in the Cu^IIM^II (M = Cu, Ni, Co, Fe, Mn) model complexes increases accordingly, and the magnetic coupling constant gradually decreases.

Introduction

In molecular-based magnets, ligands and paramagnetic centre chains are connected as described by coordination chemistry. Molecular-based magnets have a small mass and density as well as good solubility and chemical regulation performances [[1], [2], [3], [4], [5], [6]]. Thus, they have attracted much attention because of their potential application value in high-density information storage, quantum computing, spin electronics and big data. The key to constructing molecular-based magnets with ideal magnetic properties is selecting high-performance bridging ligands [[7], [8], [9], [10], [11], [12], [13], [14], [15]]. The high-performance bridging ligands must possess good coordination ability and electron transmission capacity and maintain an appropriate distance between adjacent metal paramagnetic centres, thus realising the maximum overlap of molecular orbitals. To date, conjugated micromolecular bridging ligands of multiple types have been the most commonly researched ligands. Common micromolecular bridging ligands include nitrine (N₃⁻), thiocyanate (SCN⁻), oxalato (C₂O₄²⁻) and carboxylate (RCOO⁻) bridges [[16], [17], [18], [19], [20], [21], [22], [23], [24], [25]]. In some available micromolecular bridging ligands, the azide anion shows good coordination ability, a unique and diversified coordination mode and outstanding magnetic transmission ability. Therefore, the azide anion is commonly applied to construct molecular-based magnets, and the major coordination modes are shown in Fig. 1 [[12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27]].

Although N₃⁻ has rich bridging modes, pure metal azides are unstable and generally require a certain proportion of coligands to increase stability. The selection of coligands generally determines the structure and performance of metal azides. Because carboxylic ligands have rich coordination modes and good electron transmission capacity, they are introduced into the azide complex to improve stability and regulate the magnetic properties. A 3d-3d heterometallic complex is formed by introducing 3d heterometallic ions into an azido-Cu(II) complex system. The magnetic properties of the 3d-3d heterometallic complex can be adjusted by changing the spin centre to control the magnetic anisotropy of the system. Moreover, the role of specific spin centres in magnetic behaviour can be investigated to help explain the mechanisms of the magnetic exchange behaviour of spin centres connected by specific ligands, and new molecular-based magnetic materials can be obtained. In some heterospin systems, electrons can freely jump among different spin carriers and introduce new light, electricity and magnetic properties. Zhao and Gao et al. synthesised a series of 3d-3d heterometallic complexes containing azide and carboxylic acids [[28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41]]. Moreover, the magnetic properties of the complex can be adjusted by changing the type of metal ions, providing a new method for the regulation of the magnetic behaviours of molecular-based magnets and directional design synthesis. To examine the effects of 3d heterometallic ions on the magnetic properties of the azido-Cu(II) complex, 3d heterometallic azido-Cu(II) complexes with benzoate coligands and heterocycle carboxylic acid coligands ([Cu(4-aba)(N₃)]_n (4-aba = 4-azidobenzoic acid) [31] [Cu(4-tfmba)(N₃)(solvent)]_n (4-tfmba = 4-trifluoromethyl benzoic acid) [32] [Cu(3-fba)(N₃)(C₂H₅OH)]_n (3-fba = 3-fluorobenzoic acid) [33] [Cu(2,6-dfba)(N₃)(CH₃OH)]_n (2,6-Hdfba = 2,6-difluorobenzoic acid) [34] [(CuL)₂Mn(N₃)₂], (H₂L = N,N′-bis(salicylidene)-1,3-propanediamine) [35] [(Cu^IIL)₂Co^II(N₃)₂] (H₂L=N,Nˊ-bis(salicylidene)-1,3-propanediamine) [41] [Mn(salophen)(H₂O)]₂[Cu₂(N₃)₆]· 4H₂O [42] [Co₂(CuL)₄(l-N₃)₄]·2CH₃OH (H₂L = 2,3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclopentadeca-7,13-dien) [43] [CuNi(N₃)₂(isonic)₂]_∞ [40] and [CuCo(N₃)₂(isonic)₂]_∞ [40] and {[M(cyclam)][FeL(N₃)(m_1,5-N₃)]₂} (H₂L = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene) [44] were chosen to explore the relationship between the magnetic coupling constant of the paramagnetic centres of the Cu^IIM^II azide-Cu(II) series complexes and the M^II metal ions. By considering the effects of calculation conditions on the magnetic coupling constant between Cu^II and M^II paramagnetic centres, appropriate calculation conditions were chosen. Later, the Cu^II ions were fixed, and the M^II (M = Mn, Fe, Co, Ni, Cu) ions were changed to calculate the magnetic coupling constant (J) between paramagnetic centres. The relationship between the magnetic coupling constant and the heterometallic ion M^II was analysed using Mulliken spin density analysis and natural bond orbital analysis, enriching and perfecting the molecular magnetic contents. In the present study, the conclusions provide certain theoretical references for the controlled synthesis of new molecular-based magnets.

Section snippets

Computational method

The magnetic coupling constant between Cu^II and M^II paramagnetic centres can be described by the Heisenberg-Dirac-Van Vleck Hamiltonian: $\hat{H} = - 2 J {\hat{S}}_{M} \cdot {\hat{S}}_{C u}$ where J is isotropic in nature and S_M and S_Cu are the spins of the M^II ions (S_Mn = 5/2, S_Fe = 2, S_Co = 3/2, S_Ni = 1, S_Cu = 1/2) and Cu^II ion (S = 1/2). J is the magnetic coupling constant between the Cu^II and M^II paramagnetic centres, and ${\hat{S}}_{M}$ and ${\hat{S}}_{Cu}$ are the spin operators of M^II and Cu^II, respectively. The value and sign of J express the type

Magnetic coupling constant (J)

To assess the method for the chosen complex H₄[CuNi(N₃)₃(isonic)₅], we have chosen some generalised gradient approximation (GGA) functionals (XLYP [64], PW91 [[65], [66], [67], [68], [69]], BP86 [45,46], BLYP [70,71], PBE [72,73] and OLYP [74]) and some hybrid GGA functionals (B1LYP [75], B3LYP [45,46,76,77], B3LYP* [78], B3P86 [45,46,79], X3LYP [80], O3LYP [[81], [82], [83]], PBE0 [72,73,84] and B3PW91 [85]) with the def2-TZVP basis set (Table 1) [47,48]. The computed magnetic coupling

Effects of M^II ions on the magnetic properties of the azido-Cu(II) complexes

According to experimental studies [[31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44]] introducing heterometallic ions into an azido-Cu(II) complex system makes the magnetic interaction between the different paramagnetic centres different from that between identical paramagnetic centres. When ligands and ligand fields are similar, the magnetic coupling constant between paramagnetic centres is negatively related to the number of unpaired electrons in 3d

Summary and conclusions

In the present study, the magnetic properties of the Cu^IINi^II complex (H₄[Cu^IIM^II(N₃)₃(isonic)₅]) formed by azide and isonicotinic acid were examined at the B1LYP/def2-TZVP level using the DFT-BS method. The calculated magnetic coupling constant (J_calc) agreed well with the experimental value and accurately described the magnetic properties. According to the magnetic orbital analysis, Cu^II and Ni^II ions had strong orbital interactions with azide anions and isonicotinic anions. The main

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Guizhou Education Department Youth Science and Technology Talents Growth Project (Grant No. KY[2017]292), the Joint Foundation Project of Guizhou Province, Bijie City and Guizhou University of Engineering Science (Grant Nos. LH[2017]7013 and LH[2015]7588) and the National Undergraduate Innovative and Entrepreneurial Training Program (Grant No. 201810668003).

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The truncated version of the model complex was obtained by substituting the azide ions of 4-azobenzoic acid with hydrogen atoms. The geometry of the complex was optimized at the B3LYP/def2-TZVP level of theory [18,29–32]. To account for relativistic effects, we adopted the ZORA-def2-TZVPP basis set in subsequent single point determinations [33–35].
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Thus, we calculated the magnetic coupling constant at the B1LYP/def2-TZVPP level for the purpose of this study. The analysis of molecular magnetic orbitals aids in understanding the exchange between the paramagnetic centers [13–14,17,20]. For the anti-[Cu2(bpypz)2(DCNE)2] complex in the BS state, the molecular orbitals with localized Cu(1) and Cu(2) paramagnetic centers are called local magnetic orbitals (LMOs) (Fig. 2) [13].
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Thus, B3LYP was applied to analyse the magnetic properties of [Cu2(dpyam)2 (μ1,1-N3)2 (O2CCH3)2]. To investigate the effects of the basis set on the calculated results, Jcalc values of [Cu2(dpyam)2 (μ1,1-N3)2(O2CCH3)2] were calculated using the B3LYP method under five basis sets (SVP, TZV, TZVP, def2-SVP, def2-TZVP, def2-TZVPP, def2-QZVP and def2-QZVPP) [91–96]. The results are shown in Table 2 and Jcalc was in the range of 36.75–47.94 cm−1.
The magnetic properties of the azide copper complex [Cu₂(dpyam)₂(μ_1,1-N₃)₂(O₂CCH₃)₂] were studied using the density functional theory-broken symmetry methodology under different functional methods and basis sets. The magnetic coupling constant between paramagnetic centres was calculated as 36.75 cm⁻¹, which agreed with the experimental value of 31.9 cm⁻¹. Accordingly, the calculations at the B3LYP/def2-TZVP level could describe the magnetic properties of the azide copper complex accurately. To study thoroughly the effect of carboxylic acid auxiliary ligands in azido-Cu(II) systems, acetas were deleted from the auxiliary ligands(1) and replaced by H₂O-(2), HCOO-(3), CH₃COO-(4), C₂H₅COO-(5), and C₆H₅COO-(6), yielding six research models. With the increased electron donating effect on carboxylic acid substituents, the ferromagnetic interaction between the paramagnetic centres was enhanced, whereas the contribution of the antiferromagnetic interaction was reduced. The parameters $ρ_{HS}^{2} - ρ_{BS}^{2}, S_{ab}^{2}$ , and ${(ε_{1} - ε_{2})}^{2}$ can be extended to other binuclear complexes for the study of magneto-structural correlation.

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Effect of 3d heterometallic ions on the magnetic properties of azido-Cu(II) with isonicotinic acid coligands: A theoretical perspective

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Computational method

Magnetic coupling constant (J)

Effects of MII ions on the magnetic properties of the azido-Cu(II) complexes

Summary and conclusions

Declaration of competing interest

Acknowledgements

Coord. Chem. Rev.

Coord. Chem. Rev.

Coord. Chem. Rev.

Coord. Chem. Rev.

Coord. Chem. Rev.

Coord. Chem. Rev.

Coord. Chem. Rev.

Comput. Theor. Chem.

Polyhedron

Coord. Chem. Rev.

Inorg. Chem. Commun.

J. Mol. Struct.

J. Mol. Struct.: THEOCHEM

Chem. Phys.

Coord. Chem. Rev.

Chem. Phys. Lett.

J. Mol. Graph.

Chem. Phys. Lett.

Chem. Phys. Lett.

Reversible photoinduced magnetic properties in the heptanuclear complex [MoIV(CN)2(CNCuL)6]8+: a photomagnetic high-spin molecule

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Adv. Mater.

Magnetism: Molecules to Materials

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Coord. Chem. Rev.

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Acc. Chem. Res.

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Structure and magnetic properties of a novel two-dimensional thiocyanato-bridged heterometallic polymer {Cu(en)2[Ni(en)(SCN)3]2}n

J. Chem. Soc., Dalton Trans.

Synthesis, structural characterization, and Monte Carlo simulation of the magnetic properties of two new alternating mnii azide 2-D honeycombs. Study of the ferromagnetic ordered phase below 20 K

Inorg. Chem.

Composition dependence of magnetic relaxation for CoIIxNiII1−x chain-based compounds with mixed double azide-tetrazolate bridges

Dalton Trans.

The ligand field of the azido ligand: insights into bonding parameters and magnetic anisotropy in a Co(II)-azido complex

J. Am. Chem. Soc.

Structural and magnetic properties of three one-dimensional azido-bridged copper(II) and manganese(II) coordination polymers

Inorg. Chem.

A unique 3d alternating ferro- and antiferromagnetic manganese azide system with threefold interpenetrating (10,3) nets

Angew. Chem. Int. Ed.

Random mixed-metal Co1−xNix single-chain magnets with simultaneous azide, carboxylate and tetrazolate bridges

Dalton Trans.

Solvent-induced single-crystal-to-single-crystal transformation and tunable magnetic properties of 1D azido-Cu(II) chains with a carboxylate bridge

Dalton Trans.

Solvent coligands fine-tuned the structures and magnetic properties of triple-bridged 1D azido-copper(II) coordination polymers

New J. Chem.

Ferromagnetic ordering and slow magnetic relaxation observed in a triple-bridged azido-Cu(II) chain compound with mixed carboxylate/ethanol linkers

New J. Chem.

A substituent effect of phenylacetic acid coligand perturbed structures and magnetic properties observed in two triple-bridged azido-Cu(II) chain compounds with ferromagnetic ordering and slow magnetic relaxation

Dalton Trans.

Trinuclear heterometallic CuII-MnII complexes of a salen type Schiff base ligand: anion dependent variation of phenoxido bridging angles and magnetic coupling

Dalton Trans.

Structural and magnetic modulations of copper(II) azido complexes: unexpected in situ reactions of mono-N-donor pyridine-based co-ligands

Effects of M^II ions on the magnetic properties of the azido-Cu(II) complexes

Reversible photoinduced magnetic properties in the heptanuclear complex [Mo^IV(CN)₂(CNCuL)₆]⁸⁺: a photomagnetic high-spin molecule

Formate the analogue of azide: structural and magnetic properties of M(HCOO)₂(4,4‘-bpy)·nH₂O (M = Mn, Co, Ni; n = 0, 5)

Rational enantioselective design of chiral heterobimetallic single-chain magnets: synthesis, crystal structures and magnetic properties of oxamato-bridged M^IICu^II chains (M=Mn, Co)

Structure and magnetic properties of a novel two-dimensional thiocyanato-bridged heterometallic polymer {Cu(en)₂[Ni(en)(SCN)₃]₂}_n

Composition dependence of magnetic relaxation for Co^II_xNi^II_1−x chain-based compounds with mixed double azide-tetrazolate bridges

Random mixed-metal Co_1−xNi_x single-chain magnets with simultaneous azide, carboxylate and tetrazolate bridges

Trinuclear heterometallic Cu^II-Mn^II complexes of a salen type Schiff base ligand: anion dependent variation of phenoxido bridging angles and magnetic coupling