  We report measurements of the physical properties and electronic structure of
the hexagonal compounds Yb2Ni12Pn7 (Pn = P, As) by measuring the electrical
resistivity, magnetization, specific heat and partial fluorescence yield x-ray
absorption spectroscopy (PFY-XAS). These demonstrate a crossover upon reducing
the unit cell volume, from an intermediate valence state in Yb2Ni12As7 to a
heavy-fermion paramagnetic state in Yb2Ni12P7, where the Yb is nearly
trivalent. Application of pressure to Yb2Ni12P7 suppresses T_FL, the
temperature below which Fermi liquid behavior is recovered, suggesting the
presence of a quantum critical point (QCP) under pressure. However, while there
is little change in the Yb valence of Yb2Ni12P7 up to 30 GPa, there is a strong
increase for Yb2Ni12As7 under pressure, before a near constant value is
reached. These results indicate that any magnetic QCP in this system is well
separated from strong valence fluctuations. The pressure dependence of the
valence and lattice parameters of Yb2Ni12As7 are compared and at 1 GPa, there
is an anomaly in the unit cell volume as well as a change in the slope of the
Yb valence, indicating a correlation between structural and electronic changes.
