Centre for Theoretical Chemistry and Physics (CTCP), New Zealand Institute for Advanced Study (NZIAS), Massey University Albany, Private Bag 102904, North Shore MSC, Auckland, New Zealand.
Inorg Chem. 2010 Apr 5;49(7):3169-82. doi: 10.1021/ic901949a.
The nucleation of chromium dihalide clusters is investigated by studying clusters of the form Cr(n)X(2n) (n <or= 4, X = F, Cl, Br, and I) for different spin states and the corresponding low temperature solid-state modifications using density functional theory. Using both wave function based (coupled cluster) and density functional theory, we predict that in all cases the ground state of the CrX(2) monomer is a bent (5)B(2) state arising from a weakly Renner-Teller distorted (5)Pi(g) state of the linear CrX(2) unit. These quintet units can form antiferromagnetically coupled, two-dimensional chains with chromium being bridged by two halides and a nucleation growth pattern that resembles the structural motif found for the solid state. Deviations from this two-dimensional chain growth are only found for the trimers and tetramers of CrBr(2) and CrI(2), where a "triangular" three-dimensional geometry takes slight precedence over the planar ribbon motif. We find that each single CrX(2) unit adds an almost constant amount of energy between 45 and 50 kcal/mol to the cluster growth. This is in accordance with the calculated sublimation energies for the solid state which gave 58 kcal/mol for CrF(2), and between 41 and 46 kcal/mol for CrCl(2), CrBr(2), and CrI(2). The large deviation of the calculated from the experimental sublimation energy for CrF(2) is due to the high electronegativity of fluorine ligand, which substantially increases the ionic interactions, resulting in a much more tightly packed solid-state structure, which is not so well described by spin-broken density functional theory. In accordance with this, CrF(2) shows an unusually large bulk modulus (395 kbar) compared to the heavier halides CrCl(2) (82 kbar), CrBr(2) (40 kbar), and CrI(2) (18 kbar).
采用密度泛函理论研究了形式为 Cr(n)X(2n)（n <= 4，X = F、Cl、Br 和 I）的簇的成核，研究了不同自旋态和相应的低温固态修饰的铬二卤化物簇。我们使用基于波函数的（耦合簇）和密度泛函理论，预测在所有情况下，CrX(2)单体的基态是一个弯曲的（5）B(2)态，源自线性 CrX(2)单元的弱 Renner-Teller 扭曲（5）Pi(g)态。这些五重态单元可以形成反铁磁耦合的二维链，其中铬被两个卤化物桥接，成核生长模式类似于固态中发现的结构基序。这种二维链生长的偏离仅在 CrBr(2)和 CrI(2)的三聚体和四聚体中发现，其中“三角形”三维几何结构略微优先于平面带状基序。我们发现，每个单个的 CrX(2)单元为簇的生长增加了几乎恒定的能量，约为 45 到 50 kcal/mol。这与计算的固态升华能一致，其中 CrF(2)为 58 kcal/mol，CrCl(2)、CrBr(2)和 CrI(2)之间为 41 到 46 kcal/mol。计算值与 CrF(2)的实验升华能的大偏差是由于氟配体的高电负性，这大大增加了离子相互作用，导致更紧密堆积的固态结构，这不能被自旋破缺的密度泛函理论很好地描述。与此一致，CrF(2)表现出异常大的体弹模量（395 kbar），与较重的卤化物 CrCl(2)（82 kbar）、CrBr(2)（40 kbar）和 CrI(2)（18 kbar）相比。
