Analysis of the Spin Exchange Interactions in the Three Phases of Vanadium Pyrophosphate, (VO)2P2O7, in Terms of Spin−Orbital Interaction Energy

Hj, Koo; Mh, Whangbo

doi:10.1021/ic000046t

Cited by 36 publications

(48 citation statements)

References 24 publications

(55 reference statements)

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“…However, QM calculations (B3LYP) have been reported for cluster models of VOPO. [10][11][12][13][14] Petit et al 13 confirmed that the interchain couplings are one order of magnitude smaller than the intrachain couplings, consistent with the experimental conclusions that the magnetic structure of VOPO can be described as a spin- 1 2 alternating AFM Heisenberg model. Their cluster models lead to J OPO = À144 K or À200 K and J O = À105 K.…”

Section: Introductionsupporting

confidence: 54%

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The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

Cheng

Nielsen

Tahir-Kheli

et al. 2011

Phys. Chem. Chem. Phys.

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We have studied the magnetic structure of the high symmetry vanadyl pyrophosphate ((VO) 2 P 2 O 7 , VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, J OPO = À156.8 K and J O = À68.6 K, and two weaker couplings appear along the c (between two layers) and b directions (between two chains in the same layer), which we calculate to be ferromagnetic, J layer = 19.2 K and J chain = 2.8 K. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that J OPO originates from a super-exchange interaction through the bridging -O-P-O-unit. In contrast, J O results from a direct overlap of 3d x 2 À y 2 orbitals on two vanadium atoms in the same V 2 O 8 motif, making it very sensitive to structural fluctuations. Based on the variations in V-O bond length as a function of strain along a, we found that the V-O bonds of V-(OPO) 2 -V are covalent and rigid, whereas the bonds of V-(O) 2 -V are fragile and dative. These distinctions suggest that compression along the a-axis would have a dramatic impact on J O , changing the magnetic structure and spin gap of VOPO. This result also suggests that assuming J O to be a constant over the range of 2-300 K whilst fitting couplings to the experimental magnetic susceptibility is an invalid method. Regarding its role as a catalyst, the bonding pattern suggests that O 2 can penetrate beyond the top layers of the VOPO surface, converting multiple V atoms from the +4 to +5 oxidation state, which seems crucial to explain the deep oxidation of n-butane to maleic anhydride.

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Section: Introductionsupporting

confidence: 54%

“…It is the overlap between the two O(2) on the same P (V-O(2)-P-O(2)-V) that is responsible for the superexchange coupling resulting in the AFM coupling. A similar description was proposed by Koo et al 10 based on reduced cluster models.…”

Section: This Journal Is C the Owner Societies 2011mentioning

confidence: 87%

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory

Cheng

Nielsen

Tahir-Kheli

et al. 2011

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…has been under discussion for more than ten years. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The crystal structure reveals patterns which are indicative either of a spin ladder system, or of an alternating dimer chain system. Thus, in the structure of the VPO compound 18 shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, a qualitative analysis of the exchange interactions in VPO has been reported. 16 However, it is based on the comparison of monoelectronic energy gaps obtained with the extended Hückel formalism and does not give access to the exchange parameters.…”

Section: Introductionmentioning

confidence: 99%

Magnetostructural correlations and spin model of(VO)2P2O<

et al. 2001

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We report a theoretical density functional analysis of the exchange interactions in (VO) 2 P 2 O 7 using molecular fragments. The calculations confirm that the magnetic structure must be decribed on the basis of linear dimer chains. The strongest exchange interaction is found through O-P-O bridges. The magnitude of the exchange parameters is governed not only by V-V distance but also by the whole structure along the superexchange pathway. The two chains present in the structure of (VO) 2 P 2 O 7 are magnetically inequivalent. For the monoclinic phase of (VO) 2 P 2 O 7 , important variations in the calculated parameters for dimers with identical bridges are observed within one chain. The magnetic structure of this chain should be described not by two but by three or even four coupling constants.

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“…The underlying exchange interactions can also be qualitatively described in terms of molecular orbitals. [41][42][43] In the HKUST-1 framework, a strong direct exchange interaction within a Cu(II)-Cu(II) motif is present, but the cupric pairs are too far apart (48 Å) to display any long-range magnetic order. Indeed, super-exchange with carboxylates tends to occur only within the same COO head.…”

mentioning

confidence: 99%