Spin Polarization Mechanism Research Articles

Two novel cyclic dimer M2L2 complexes constructed from 2-[(4-carboxyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3 oxide: Crystal structure and magnetic properties

Two novel complexes derived from 2-[(4-carboxyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (NITPBAH), [Mn(hfac)2(NITPBAH)]2 (1) and [Co(hfac)2(NITPBAH)]2 (2) (hfac=hexafluoroacetylacetonate), have been synthesized as well as characterized structurally and magnetically. The X-ray crystal structure analyses show that the structures of the two compounds are isomorphic and both consist of cyclic dimer units bridged by NITPBAH ligands, in which metal ion Mn(II) or Co(II) is coordinated by four oxygen atoms from two hfac ligands, one oxygen atom from nitronyl nitroxide and one oxygen atom from carboxyl group of another radical ligand. The magnetic studies show that the manganese(II) or cobalt(II) ion strong antiferromagnetically interacts with the directly coordinated nitroxide group. There exists a weak antiferromagnetic coupling between the metal ion and the nitroxide through phenyl ring and carboxyl group of the radical ligand, which is agreement with spin polarization mechanism.

Persistent optical nuclear spin narrowing in a singly charged InAs quantum dot

We review the investigation of the hole-assisted dynamical nuclear spin polarization mechanism in a singly charged InAs quantum dot. Using coherent dark state spectroscopy, we measure the locking of the Overhauser field to a value determined only by the laser frequencies. Importantly, we review data that the locking effect can suppress nuclear spin fluctuations. We determine the onset time of the nuclear spin narrowing effect and its persistence absent laser interactions by directly measuring the enhancement of the electron spin coherence. This nuclear field locking effect can be explained in terms of an anisotropic hyperfine coupling between the hole spin and the nuclear spins.

Scalar Relativistic Computations and Localized Orbital Analyses of Nuclear Hyperfine Coupling and Paramagnetic NMR Chemical Shifts.

A method is reported by which calculated hyperfine coupling constants (HFCCs) and paramagnetic NMR (pNMR) chemical shifts can be analyzed in a chemically intuitive way by decomposition into contributions from localized molecular orbitals (LMOs). A new module for density functional calculations with nonhybrid functionals, global hybrids, and range-separated hybrids, utilizing the two-component relativistic zeroth-order regular approximation (ZORA), has been implemented in the parallel open-source NWChem quantum chemistry package. Benchmark results are reported for a test set of few-atom molecules with light and heavy elements. Finite nucleus effects on (199)Hg HFCCs are shown to be on the order of -11 to -15%. A proof of concept for the LMO analysis is provided for the metal and fluorine HFCCs of TiF3 and NpF6. Calculated pNMR chemical shifts are reported for the 2-methylphenyl-t-butylnitroxide radical and for five cyclopentadienyl (Cp) sandwich complexes with 3d metals. Nickelocene and vanadocene carbon pNMR shifts are analyzed in detail, demonstrating that the large carbon pNMR shifts calculated as +1540 for Ni (exptl.: +1514) and -443 for V (exptl.: -510) are caused by different spin-polarization mechanisms. For Ni, Cp to Ni π back-donation dominates the result, whereas for vanadocene, V to Cp σ donation with relaxation of the carbon 1s shells can be identified as the dominant mechanism.

Self-assembly, metal binding ability, and magnetic properties of dinickel(ii) and dicobalt(ii) triple mesocates

Two metallacyclic complexes of general formula Na8[MII2L3]·xH2O [M = Ni (4) and Co (5) with x = 15 (4) and 17 (5)] have been self-assembled in aqueous solution from N,N′-1,3-phenylenebis(oxamic acid) (H4L) and M2+ ions in a ligand/metal molar ratio of 3 : 2 in the presence of NaOH acting as base. X-Ray structural analyses of 4 and 5 show triple-stranded, dinuclear anions of the meso-helicate-type (so-called mesocates) with C3h molecular symmetry. The two octahedral metal–tris(oxamate) moieties of opposite chiralities (Δ,Λ form) are connected by three m-phenylene spacers at intermetallic distances of 6.822(2) (4) and 6.868(2) A (5) to give a metallacryptand core. In the crystal lattice, the binding of these heterochiral dinickel(II) and dicobalt(II) triple mesocates to sodium(I) ions leads to oxamato-bridged heterobimetallic three-dimensional open-frameworks with a hexagonal diamond architecture having small pores of 17.566(4) (4) and 17.640(2) A (5) in diameter where the crystallization water molecules and the sodium(I) countercations are hosted. Variable temperature (2.0–300 K) magnetic susceptibility measurements reveal relatively anisotropic S = 2 NiII2 (4) and S = 3 CoII2 (5) ground states resulting from the moderate to weak intramolecular ferromagnetic coupling between the two high-spin NiII (SNi = 1) or CoII (SCo = 3/2) ions across the m-phenylenediamidate bridges [J = +3.6 (4) and +1.1 cm−1 (5); H = −JS1·S2]. A simple molecular orbital analysis of the electron exchange interaction identifies the π-type pathways of the meta-substituted phenylene spacers involving the dz2 and dx2−y2 pairs of magnetic orbitals of the two trigonally distorted octahedral high-spin MII ions (M = Ni and Co) as responsible for the overall ferromagnetic coupling observed in 4 and 5 in agreement with a spin polarization mechanism. The decrease of the overall ferromagnetic coupling from 4 to 5 is in turn explained by the additional antiferromagnetic exchange contribution involving the dxy pair of magnetic orbitals of the two trigonally distorted octahedral high-spin CoII ions across the σ-type pathway of the meta-substituted phenylene spacers.

Structure and Magnetism in Fe–Gd Based Dinuclear and Chain Systems. The Interplay of Weak Exchange Coupling and Zero Field Splitting Effects

The synthesis and characterization of two Fe-Gd systems based on bpca(-) (Hbpca = bis(2-pyridilcarbonyl)amine) as bridging ligand is presented, taking the systems as a case study for structure-property correlations. Compound 1, [Fe(LS)(II)(μ-bpca)(2)Gd(NO(3))(2)(H(2)O)]NO(3)·2CH(3)NO(2), is a zigzag polymer, incorporating the diamagnetic low spin Fe(LS)(II) ion. The magnetism of 1 is entirely determined by the weak zero field splitting (ZFS) effect on the Gd(III) ion. Compound 2 is a Fe(III)-Gd(III) dinuclear compound, [Fe(LS)(III)(bpca)(μ-bpca)Gd(NO(3))(4)]·4CH(3)NO(2)·CH(3)OH, its magnetism being interpreted as due to the antiferromagnetic coupling between the S(Fe) = ½ and S(Gd) = 7/2 spins, interplayed with the local ZFS on the lanthanide center. In both systems, the d-f assembly is determined by the bridging capabilities of the ambidentate bpca(-) ligand, which binds the d ion by a tridentate moiety with nitrogen donors and the f center by the diketonate side. We propose a spin delocalization and polarization mechanism that rationalizes the factors leading to the antiferromagnetic d-f coupling. Although conceived for compound 2, the scheme can be proposed as a general mechanism. The rationalization of the weak ZFS effects on Gd(III) by multiconfiguration and spin-orbit ab initio calculations allowed us to determine the details of the small but still significant anisotropy of Gd(III) ion in the coordination sites of compounds 1 and 2. The outlined methodologies and generalized conclusions shed new light on the field of gadolinium coordination magnetochemistry.

Chemical Control of Spin Propagation between Heterometallic Rings

We present a synthetic, structural, theoretical, and spectroscopic study of a family of heterometallic ring dimers which have the formula [{Cr(7)NiF(3)(Etglu)(O(2)CtBu)(15)}(2)(NLN)], in which Etglu is the pentadeprotonated form of the sugar N-ethyl-D-glucamine, and NLN is an aromatic bridging diimine ligand. By varying NLN we are able to adjust the strength of the interaction between rings with the aim of understanding how to tune our system to achieve weak magnetic communication between the spins, a prerequisite for quantum entanglement. Micro-SQUID and EPR data reveal that the magnetic coupling between rings is partly related to the through-bond distance between the spin centers, but also depends on spin-polarization mechanisms and torsion angles between aromatic rings. Density functional theory (DFT) calculations allow us to make predictions of how such chemically variable parameters could be used to tune very precisely the interaction in such systems. For possible applications in quantum information processing and molecular spintronics, such precise control is essential.

π−π Stacking and magnetic coupling mechanism on a mononuclear Cu(II) complex

A mononuclear copper(II) complex was synthesized and in the crystal there are three types of π−π stacking interactions among adjacent complexes. The fitting for the data of the variable-temperature magnetic susceptibilities reveals that there is a weak anti-ferromagnetic coupling among adjacent Cu(II) ions with Weiss constant θ = −2.99 K = −2.08 cm−1. Theoretical calculations reveal that two types of π−π stacking resulted in anti-ferromagnetic couplings with 2J = −12.40 cm−1 and 2J = −9.74 cm−1, respectively, and the third type of π−π stacking led to a weak ferromagnetic interaction with 2J = 4.28 cm−1. The theoretical calculations also indicate that the ferromagnetic coupling sign from the π−π stacking accords with McConnell I spin-polarization mechanism, whereas the anti-ferromagnetic coupling signs cannot be explained with McConnell I spin-polarization mechanism.

Very Long-Distance Magnetic Coupling in a Dicopper(II) Metallacyclophane with Extended π-Conjugated Diphenylethyne Bridges

Self-assembly of the rigid rodlike ligand N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and Cu(2+) ions affords a novel dinuclear copper(II) metallacyclophane (nBu(4)N)(4)[Cu(2)(dpeba)(2)]·4MeOH·2Et(2)O (1) featuring a very long intermetallic distance (r = 15.0 Å). Magnetic susceptibility measurements for 1 reveal a moderately weak but nonnegligible intramolecular antiferromagnetic coupling between the two metal centers across the double para-substituted diphenylethynediamidate bridge (J = -3.9 cm(-1); H = -JS(1)S(2), where S(1) = S(2) = S(Cu) = (1)/(2)). Density functional electronic structure calculations on 1 support the occurrence of a spin polarization mechanism.

Magnetic exchange coupling in imido bimetallic uranium(V) complexes. A relativistic DFT study

Abstract Magnetic exchange coupling between uranium U(V) ions, in the case of the two para- and meta-imido diuranium complexes, respectively [(C 5 H 5 ) 3 U] 2 (μ-1,4-N 2 C 6 H 4 ) and [(C 5 H 5 ) 3 U] 2 (μ-1,3-N 2 C 6 H 4 ) exhibiting the 5f 1 -5f 1 configuration, have been investigated using relativistic DFT calculations, combined with the broken symmetry (BS) approach. Using the B3LYP functional, the singlet BS state of the para complex has been found of lower energy than the high spin (HS) triplet one, in agreement with the observed antiferromagnetic character of the complex. On the contrary the BP86 functional fails to predict this magnetic property. The spin density distributions and MO analysis explain well the antiferromagnetic character of the para complex and clarify the failure of the BP86 functional. The effective participation of the 5f metal orbitals in bonding with the imido ligand plays a key role for electronic and magnetic communication between the two active U(V) 5f 1 electrons. The same technique led us to explain the ferromagnetic character of the meta isomer in agreement with experiment. For both isomers the spin polarization mechanism explains well their observed magnetic behaviour.

Magnetoresistance of nanocarbon materials based on carbon nanotubes

The results of experimental investigations of magnetoresistance in nanocarbon material (NCM) containing carbon nanotubes in magnetic field up to 5 T and at temperature up to 0.54 K are reported. The obtained experimental magnetoresistance curves of NCM are described satisfactorily within the framework of the shrinkage effect of wave function of localized state in a magnetic field along with the spin-polarization mechanism.

π–π Stacking, hydrogen bonding and anti-ferromagnetic coupling mechanism on a mononuclear Cu(II) complex

Weak anti-ferromagnetic coupling is observed in a mononuclear copper(II) complex, [Cu(Pid)(OSO3)(H2O)] · (H2O) (Pid = 2,2′-(1,10-phenanthrolin-2-ylimino)diethanol). The Cu(II) complex is a distorted square pyramid. Analysis of the crystal structure indicates that there are two types of magnetic coupling pathways, where one pathway involves π–π stacking between adjacent complexes and the second one involves the O–H ··· O hydrogen bonds between adjacent complexes. The variable-temperature magnetic susceptibilities show that there is a weak anti-ferromagnetic coupling between adjacent Cu(II) ions with Curie–Weiss constant θ = −13.71 K = −9.93 cm−1. Theoretical calculations reveal that the π–π stacking resulted in anti-ferromagnetic coupling with 2J = −6.30 cm−1, and the O–H ··· O hydrogen-bonding pathway led to a weaker anti-ferromagnetic interaction with 2J = −3.38 cm−1. The theoretical calculations also indicate that anti-ferromagnetic coupling sign from the π–π stacking accords with the McConnell I spin-polarization mechanism.

Phloroglucinol-bridged trinuclear complexes with three paramagnetic octahedral nickel(II) ions: Syntheses, crystal structures, and magnetic properties

Three new C3-symmetric tritopic ligands with a central phloroglucinol bridging unit have been synthesized and characterized. The ligands are accessible through Schiff-base condensation of 2,4,6-triformylphloroglucinol with 2-aminomethylpyridine (H3tfpg-ampy), N,N-bis(pyridin-2-ylmethyl)-ethylenediamine (H3tfpg-unspenp), and benzhydrazide (H6tfpg-bhy). These ligands differ in nature and number of the donor atoms within the resulting binding pockets. Based on these ligands the synthesis of the first trinuclear phloroglucinol-bridged nickel(II) complexes with three octahedrally coordinated nickel centers is reported. The ligands H3tfpg-ampy and H6tfpg-bhy, which provide tridentate binding pockets, react with nickel(II) perchlorate in the presence of bis(pyridin-2-ylethyl)-amine (bpea) as an additional tridentate capping ligand leading to the formation of the trinuclear complexes [Ni3(tfpg-ampy)(bpea)3](ClO4)3 and [Ni3(tfpg-bhy)(bpea)3](ClO4)3, respectively. Due to the pentadentate binding pocket in ligand H3tfpg-unspenp, no additional coligand is needed and a water molecule occupies the sixth coordination site at the nickel(II) ion resulting in the complex [Ni3(tfpg-unspenp)(H2O)3](ClO4)3. Temperature-dependent magnetic measurements reveal overall weak antiferromagnetic exchange interactions within the trinuclear complex together with a rather strong zero-field splitting (ZFS) for the nickel(II) ions. The observed isotropic coupling constants for the three complexes are in the range of 0.14<−J<0.37cm−1, whereas for the zero-field splitting parameter ∣D∣ values between 1.8 and 5.5cm−1 are found. This is indicative for competitive spin-polarization and superexchange mechanisms, with the latter prevailing the interaction between the nickel(II) ions through the meta-phenylene-linkage for the complexes reported.

Synthesis and characterization of trinuclear square-planar Ni II3 and Cu II3 complexes of an extended phloroglucinol ligand: Experimental evidence for the relative contributions of benzene-like and radialene-like resonance structures

The synthesis and characterization of the extended phloroglucinol ligand H 3felddien, its trinuclear Ni II complex [(felddien)Ni 3](BF 4) 3 and its trinuclear Cu II complex [(felddien)Cu 3](ClO 4) 3 is presented. Detailed NMR studies provide strong evidence that the ligand H 3felddien has to be described as the N-protonated tautomer and not as the O-protonated tautomer, with strong contribution of a radialene-like keto-enamine resonance structure resulting in a C s and a C 3h isomer. The trinucleating tris(tetradentate) ligand provides three donor sets comprised of a phenolate, an imine, and two tertiary amine donors. This donor set enables the synthesis of the diamagnetic square-planar coordinated Ni II complex [(felddien)Ni 3](BF 4) 3 which provides the opportunity to perform detailed NMR spectroscopic characterizations for the evaluation of the electronic structure of the central phloroglucinol unit. In conjunction with a single-crystal X-ray diffraction and a UV–vis absorption spectroscopic analysis, these data indicate that in the coordinated form, the benzene-like phenolate-imine and the radialene-like keto-enamine resonance structures have contributions to the overall resonance hybrid. The weakening of the central π system as a consequence of the contribution of the keto-enamine resonance structure explains the relative small ferromagnetic interactions in the trinuclear Cu II complex [(felddien)Cu 3](ClO 4) 3. This detailed analysis identifies the strong resonance with unsaturated groups in 2,4,6 position of phloroglucinol as the main source for the low ferromagnetic couplings by the spin-polarization mechanism in all our extended phloroglucinol ligands. A replacement of the unsaturated imine functions by saturated amine functions may be a synthetic opportunity to enhance the ferromagnetic interactions by the spin-polarization mechanism in this ligand system.

Theoretical Insights into the Magnetostructural Correlations in Mn3-Based Single-Molecule Magnets

Density functional theory (DFT) and the valence bond configuration interaction (VBCI) model have been applied to the oximato-based Mn(III)(3)O single-molecule magnets (SMMs), allowing one to correlate the Mn(III)-Mn(III) exchange coupling energy (J) with the bridging geometry in terms of two structural angles: the Mn-O-N-Mn torsion angle (γ) and the Mn(3) out-of-plane shift of O (angle δθ). Using DFT, a two-dimensional (γ, δθ) energy surface of J is derived and shown to yield essentially good agreement with the reported J values deduced from magnetic susceptibility data on trigonal oximato-bridged Mn(3) SMMs. VBCI is used to understand and analyze the DFT results. It is shown that the exchange coupling in these systems is governed by a spin-polarization mechanism inducing a pronounced and dominating ferromagnetic exchange via the oximato bridge as opposed to kinetic exchange, which favors a weaker and antiferromagnetic exchange via the bridging oxide. In the light of these results, a discussion of the exchange coupling in the Mn(6) family of the SMM with a record demagnetization barrier is given.

Hydrothermal Syntheses, Crystal Structures, and Magnetic Properties of a Series of Unique Three-Dimensional Lanthanide−Organic Coordination Frameworks with aN-Protonated 2,6-Dihydroxypyridine-4-Carboxylate Tecton

A series of novel three-dimensional (3-D) lanthanide−organic frameworks (LnOFs), with the general formula [Ln2(H-L)3(H2O)4]∞ (Ln = DyIII for 1, GdIII for 2, TbIII for 3, EuIII for 4, and HoIII for 5; H-L = N-protonated 2,6-dihydroxypyridine-4-carboxylate), have been synthesized under hydrothermal conditions. X-ray structural analysis reveals that complexes 1−5 are isostructural and show the unique 3-D coordination framework with a trinodal (3,4,5)-connected (4.62)(42.6)(42.84)(43.6.86)(42.65.83) net topology, in which the H-L ligands adopt different μ4- and μ3-bridging forms. Variable-temperature magnetic susceptibility studies reveal that complexes 1−3 and 5 show ferromagnetic behaviors. Notably, complex 1 (DyIII) is the first instance leading to ferromagnetic coupling for a lanthanide ion through a spin-polarization mechanism. The alternating current (ac) signal observed for 1 and 5 should originate from the long-range ferromagnetic ordering, or it could reflect the splitting of the J multiplet for DyII...

W-band transient EPR and photoinduced absorption on spin-labeled fullerene derivatives

We investigated by W-band (94 GHz) transient electron paramagnetic resonance (TREPR) and photoinduced absorption (PIA) spectroscopy two fullerene derivatives bearing a nitroxide radical unit. After pulsed laser photoexcitation of the molecules in liquid toluene solution, complex EPR spectra are recorded, with lines in absorption and emission. The intrinsic higher spectral and temporal resolution of the W-band frequency leads to the assignment of all the lines in the spectrum and the determination of the sign and the absolute value of the exchange coupling between the fullerene in its photoexcited triplet state (S(T) = 1) and the radical (S(R) = 1/2). The two compounds with different fullerene-nitroxide spacers show opposite-ferromagnetic and antiferromagnetic-exchange couplings. The time evolution of the spectra and the polarization of the lines are interpreted in terms of several possible spin polarization mechanisms. The EPR measurements are complemented with PIA experiments.

π–π Stacking and ferromagnetic coupling mechanism on a binuclear Cu(ii) complex

The ferromagnetic couplings were observed in an unpublished crystal that consists of binuclear copper(II) complexes, namely, [Cu(2)(μ(1,3)-SCN)(2)(PhenOH)(OCH(3))(2)(HOCH(3))(2)] (PhenOH = 2-hydroxy-1,10-phenanthroline), and in the binuclear complex Cu(ii) ion assumes a distorted octahedral geometry and thiocyanate anion functions as a μ(1,3)-SCN(-) equatorial-axial (EA) bridging ligand. The analysis for the crystal structure indicates that there are three types of magnetic coupling pathways, in which two pathways involve π-π stacking between the adjacent complexes and the third one is the μ(1,3)-SCN(-) bridged pathway. The fitting for the data of the variable-temperature magnetic susceptibilities shows that there is a ferromagnetic coupling between adjacent Cu(II) ions with J = 50.02 cm(-1). Theoretical calculations reveal that the two types of π-π stacking resulted in ferromagnetic couplings with J = 4.16 cm(-1) and J = 2.75 cm(-1), respectively, and the bridged thiocyanate anions pathway led to a weaker ferromagnetic interaction with J = 0.88 cm(-1). The theoretical calculations also indicate that the ferromagnetic coupling sign from the two types of π-π stacking does not accord with McConnell I spin-polarization mechanism. The analysis for the Wiberg bond indexes that originate from the π-π stacking atoms indicates that the Wiberg bond indexes are relevant to the associated magnetic coupling magnitude and the Wiberg bond index is one of the key factors that dominates the associated magnetic coupling magnitude.

Rational design of single-molecule magnets: a supramolecular approach

Since the discovery that Mn(12)OAc acts as a single-molecule magnet (SMM), an increasing number of transition metal complexes have been demonstrated to behave as SMMs. The signature of a SMM is a slow relaxation of the magnetization at low temperatures accompanied by a magnetic hysteresis. The origin of SMM behaviour is the existence of an appreciable thermal barrier U for spin-reversal called magnetic anisotropy barrier which is related to the combination of a large total spin ground state (S(t)) and an easy-axis magnetic anisotropy. The extensive research on Mn(12)OAc and other SMMs has established more prerequisites for a rational development of new SMMs besides the high-spin ground state and the magnetic anisotropy: the symmetry should be at least C(3) to minimize the quantum tunneling of the magnetization through the anisotropy barrier but lower than cubic to avoid the cancellation of the local anisotropies upon projection onto the spin ground state. Based on these prerequisites, we have designed the ligand triplesalen which combines the phloroglucinol bridging unit for high spin ground states by the spin-polarization mechanism with a salen-like ligand environment for single-site magnetic anisotropies by a strong tetragonal ligand field. The C(3) symmetric, trinuclear complexes of the triplesalen ligand (talen(t-Bu(2)))(6-) exhibit a strong ligand folding resulting in an overall bowl-shaped molecular structure. This ligand folding preorganizes the axial coordination sites of the metal salen subunits for the complementary binding of three facial nitrogen atoms of a hexacyanometallate unit. This leads to a high driving force for the formation of heptanuclear complexes [M(t)(6)M(c)](n+) by the assembly of three molecular building blocks. Attractive van der Waals interactions of the tert-butyl phenyl units of two triplesalen trinuclear building blocks increase the driving force. In this respect, we have been able to synthesize the isostructural series [Mn(III)(6)Cr(III)](3+), [Mn(III)(6)Fe(III)](3+), and [Mn(III)(6)Co(III)](3+) with [Mn(III)(6)Cr(III)](3+) being a SMM. A detailed analysis and comparison of the magnetic properties of the three heptanuclear complexes and the tetranuclear half-unit [Mn(III)(3)Cr(III)](3+) provides significant insight for further optimization of the SMM properties. The modular assembly of the heptanuclear complexes from three molecular building blocks allows the fine-tuning of the molecular and steric properties of each building block without losing the driving force for the formation of the heptanuclear complexes. This possibility of rational improvements of our isostructural series is the main advantage of our supramolecular approach.

Physical analysis of the through-ligand long-distance magnetic coupling: spin-polarization versus Anderson mechanism

The physical factors governing the magnetic coupling between two magnetic sites are analyzed and quantified as functions of the length of the bridging conjugated ligand. Using wave-function-theory based ab initio calculations, it has been possible to separate and calculate the various contributions to the magnetic coupling, i.e. the direct exchange, the spin polarization and the kinetic exchange. It is shown in model systems that while the Anderson mechanism brings the leading contribution for short-length ligands, the spin polarization dominates the through-long-ligand couplings. Since the spin polarization decreases more slowly than the kinetic exchange, highly spin polarizable bridging ligands would generate a good magneto-communication between interacting magnetic units.

π–π Stacking and magnetic coupling mechanism on a mono-nuclear Mn(II) complex

A novel magnetic coupling is observed in a unpublished crystal that consists of a mono-nuclear manganese(II) complex, namely, [Mn(DPP)(NCS) 2] (DPP = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline), in which neutral DPP molecule functions as tridentate chelated ligand. In the complex Mn(II) ion assumes a distorted trigonal bipyramidal geometry and in the crystal there is a π–π stacking interaction between the adjacent complexes, which involves pyridyl ring and the symmetry-related pyrazolyl ring and pyridyl ring. The fitting for the data of the variable-temperature magnetic susceptibilities with infinite uniform Mn(II) chain formula gave the magnetic coupling constant J = −0.11 cm −1, and theoretical calculations reveal that there exists a very weak anti-ferromagnetic coupling between the adjacent Mn(II) ions with J = −0.02 cm −1. The magnetic coupling sign is explained based on McConnell I spin-polarization mechanism with the analysis of the spin density population and the factors that dominate the magnetic coupling magnitude.